The Regulation of Parathyroid Hormone Secretionand Synthesis

Rajiv Kumar* and James R. Thompson†

*Division of Nephrology and Hypertension, Department of Internal Medicine, Biochemistry and Molecular Biology,and †Department of Physiology, Biophysics and Bioengineering, Mayo Clinic College of Medicine, Mayo Clinic,Rochester, Minnesota

The central role of the parathyroidglands in regulating Ca2� homeostasisby modulating bone metabolism, thesynthesis of 1�,25-dihydroxyvitaminD (1�,25(OH)2D) in proximal tubules,and the reabsorption of Ca2� in thedistal nephron is widely appreciated bythe readers of this journal.1–5 Second-ary hyperparathyroidism (2°HPT) fre-quently occurs in the setting of chronickidney disease (CKD), of end-stage re-nal disease (ESRD), or after renal trans-plantation,6–12 and uncontrolled 2°HPTin CKD and ESRD associates with an in-

creased incidence of fractures and mor-tality.13–16

The pathogenesis of 2°HPT in CKD iscomplex. Phosphate retention, hyperphos-phatemia, low serum Ca2� (sCa2�), elevatedlevels of parathyroid hormone (PTH),1�,25(OH)2D deficiency, intestinal Ca2�

malabsorption, the reduction of vitamin Dreceptors (VDR) and calcium-sensing recep-tors (CaSR) in the parathyroid glands, andaltered mRNA-binding protein activitiesmodulatingPTH transcriptsplayarole inthedevelopment of 2°HPT.17–30 Parathyroid hy-perplasia is often present as well.31,32 On the

basis of these observations regardingpathogenesis, therapy for 2°HPT in thecontext of CKD and ESRD includes thecontrol of serum phosphate concentra-tions, the administration of Ca2� andvitamin D analogs, and the administra-tion of calcimimetics.33,34,16,35,36

Nevertheless, 2°HPT remains a signifi-cant clinical problem and additional meth-ods for the treatment of this condition wouldbe helpful, especially in refractory situations,where other measures have failed or are onlypartiallyeffective.Knowledgeabout themec-hanisms by which parathyroid hormone se-cretion and synthesis occur is therefore ofvalue in designing new approaches to thetreatment of this condition. Here we brieflyreview the mechanisms that modulate PTHrelease and secretion and identify abnormal-ities that are present in progressive renal dis-ease.

PTH RELEASE AND SYNTHESISDETERMINE SERUM PTHCONCENTRATIONS

Serum PTH concentrations are depen-dent upon the release of PTH stored in

Published online ahead of print. Publication dateavailable at www.jasn.org.

Correspondence: Dr. Rajiv Kumar, Division of Ne-phrology and Hypertension, Departments of Medi-cine, Biochemistry and Molecular Biology, MayoClinic and Foundation, 200 1st Street SW, Roches-ter, MN 55905. Phone: 507-284-0020; Fax: 507-538-9536; E-mail: rkumar@mayo.edu

Copyright © 2011 by the American Society ofNephrology

ABSTRACTSecondary hyperparathyroidism classically appears during the course of chronic renalfailure and sometimes after renal transplantation. Understanding the mechanisms bywhich parathyroid hormone (PTH) synthesis and secretion are normally regulated isimportant in devising methods to regulate overactivity and hyperplasia of the para-thyroid gland after the onset of renal insufficiency. Rapid regulation of PTH secretionin response to variations in serum calcium is mediated by G-protein coupled, calcium-sensing receptors on parathyroid cells, whereas alterations in the stability of mRNA-encoding PTH by mRNA-binding proteins occur in response to prolonged changes inserum calcium. Independent of changes in intestinal calcium absorption and serumcalcium, 1�,25-dihydroxyvitamin D also represses the transcription of PTH by associ-ating with the vitamin D receptor, which heterodimerizes with retinoic acid X receptorsto bind vitamin D-response elements within the PTH gene. 1�,25-Dihydroxyvitamin Dadditionally regulates the expression of calcium-sensing receptors to indirectly alterPTH secretion. In 2°HPT seen in renal failure, reduced concentrations of calcium-sensing and vitamin D receptors, and altered mRNA-binding protein activities withinthe parathyroid cell, increase PTH secretion in addition to the more widely recognizedchanges in serum calcium, phosphorus, and 1�,25-dihydroxyvitamin D. The treatmentof secondary hyperparathyroidism by correction of serum calcium and phosphorusconcentrations and the administration of vitamin D analogs and calcimimetic agentsmay be augmented in the future by agents that alter the stability of mRNA-encodingPTH.

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secretory granules within the parathy-roid gland and by the synthesis of newPTH.1,37 sCa2�, phosphorus, and vita-min D metabolites play a role in regulat-ing PTH release and synthesis.1,3,28,38 – 41

RapidPTHreleasefromsecretorygranulesinhypocalcemic states is modulated by thebinding of Ca2� to CaSRs on chief cells,whereas long-term replenishment of PTHstores is dependent on new PTH synthesisthat is controlled by the availability ofmRNA-encoding PTH for ribosomal trans-lation into prepro-PTH.2,42,43,27,44–49 Hy-pocalcemia also retards the rate of degrada-tion of PTH within the parathyroid gland,thus making more PTH available for re-lease,50,51 and increases cell division in theparathyroid gland possibly through the ac-tion of the CaSR.1,42,45,52 Phosphorus addi-tionally alters PTH synthesis, although theprecise mechanisms by which changes inphosphate concentrations are detectedor sensed by the parathyroid gland areunknown.28 1�,25-DihydroxyvitaminD (1�,25(OH)2D) alters the transcrip-tion of PTH and may have an indirecteffect on PTH release by increasing theexpression of CaSR.38 – 41,45,53–56

ROLE OF THE CASR INMEDIATING PTH RELEASE

Changes in concentrations of sCa2� aresensed by chief cells through a cell-sur-face, seven-transmembrane, G protein–coupled receptor, the CaSR,42,57–59 andreceptor activity results in rapid alter-ations in PTH secretion.37 After the in-duction of abrupt and sustained hy-pocalcemia, plasma concentrations ofPTH increase within 1 minute, peak at 4to 10 minutes, and thereafter declinegradually to approximately 60% of themaximum at 60 minutes, despite ongo-ing and constant hypocalcemia. Abruptrestoration of normocalcemia from thehypocalcemic state causes levels of PTHto decrease with an apparent half-life ofapproximately 3 minutes. In addition toits role in the parathyroid gland, theCaSR plays an important role in regulat-ing Ca2� reabsorption in the thick as-cending limb of the loop of Henle.60 – 62

The vital role of the CaSR in Ca2� ho-

meostasis is demonstrated by the bio-logic consequences of inactivating oractivating mutations of the receptor.Inactivating mutations of the CaSR resultin familial benign hypercalcemia or neona-tal severe hyperparathyroidism, whereasactivating mutations result in autosomaldominant hypocalcemia.62,63,53,64–68

The CaSR has a large extracellular do-main of approximately 600 amino acids,a seven-pass transmembrane domain,and an intracellular carboxyl-terminaldomain that has several phosphorylationsites.69 The receptor binds Ca2� in its ex-tracellular domain, most likely as a dimerin the so-called “Venus flytrap” configu-ration (Figure 1, A through C).70 –73 Ourmodel of the human CaSR shown in Fig-ure 1 was obtained using multiple se-quence alignments and initial coordinatemodels and two separate algorithms.74–77

The best model resulted from using theextracellular domain of the glutamatereceptor (Protein Data Bank code

1ewk)78 as the template for main chainatoms. The atomic coordinates withinthe model were inspected and manuallycorrected for steric clashes, for alterna-tive residue rotamer choices that im-prove hydrogen bonding, and for Ram-achandran and other conformationaloutliers. The CaSR dimer from D23 toI528 displays perfect twofold symmetrysimilar to that of the glutamate receptorbound with both glutamate and gadolin-ium ions.79 The putative Ca2�-bindingsites were included in our CaSR modelbased on the presence of Gd2� atomiccoordinates within other glutamate re-ceptor structures (PDBs 1ewk and 1isr).In the glutamate receptor, the Gd2� lo-cation occurs at an acidic patch, includ-ing the ligating residues E238, D215, andE224 with one standout residue R220.The acidic residues of equivalent posi-tions in CaSR are conserved, although anarginine residue is not conserved. There-fore, it is likely that the Ca2�-binding po-

Figure 1. A hypothetical dimeric model of residues D23 (blue) to I528 (red) of the humancalcium sensing receptor extracellular domain (CaSR ECD). (A) Both monomers contain-ing just the Venus flytrap region of the CaSR ECD are shown in a closed and presumablyactive conformation as was reported for the extracellular domain of the glutamatereceptor with glutamate bound. The two yellow spheres (yellow arrows) indicate putativeCa2�-binding sites, found at the nexus of where both lobes of a monomer meet. Mostresidues forming this cation-binding site are not conserved in glutamate receptor. Theadditional cyan spheres within the topmost lobes of the dimer designate possibleMg2�-binding sites (green spheres indicated by green arrows) brought over from gluta-mate receptor coordinates. These Mg2� sites are completely conserved in CaSR. Thedimer interface of the portion of CaSR shown is completely formed from interactionsbetween these two upper lobes. There are no intermolecular disulfide bridges linking thedimer together within this portion of the ECD of CaSR, although two intramoleculardisulfides exist. (B) A model of the apo-CaSR dimer is portrayed. Again, the color rampsfrom blue to red from D23 to I528. The Mg2� sites are present, although there is noexperimental basis for this premise. Of note is the significant opening and expansionof the cavities between the upper and lower lobes of each monomer, the areasindicated by the two yellow ovals. (C) The upper lobes of the CaSR atomic coordi-nates shown above in (A) (with Ca2� bound, now made gray in color) are superim-posed on the apo-form model for the CaSR dimer drawn in rainbow as in (B). The redarrows point to a large displacement in the orientation and position of the carboxy-terminal end of the structure near where the CaSR cysteine-rich domains (not shown)might be found. Significant conformational changes within parts of the CaSR ECDconnecting with the transmembrane domains probably occur on Ca binding.

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sition in the glutamate receptor and theCaSR are similar.

When Ca2� binds to the CaSR, it elic-its a conformational change within theextracellular domain of the receptor(compare Figure 1B with Figure 1C).These changes are possibly transmittedthrough the seven-pass transmembranedomain to allow interactions of the intra-cellular domains of the receptor withheterotrimeric G protein subunits, Gqa

and Gia. In addition to Ca2�, the CaSRbinds several metals, amino acids, antibi-otics, and organic compounds that mod-ulate its activity (Figure 2).80 – 85 Formodeling of phenylalanine and neomy-cin, coordinates were docked into ourmodel of CaSR manually, maximizingthe number of hydrogen bonds whileminimizing the number of steric clashes.

Agents such as L-amino acids with ar-omatic side chains exert allosteric effectson the CaSR and sensitize it to the effectsof agonists such as Ca2�.80,81,86 – 89 These

substances (“calcimimetic” agents) po-tentiate the CaSR to subthreshold con-centrations of Ca2�. Several syntheticCaSR modulators have been developedfor the treatment of hyperparathyroid-ism. NPS-R-467 and NPS-R-568 (phe-nylalkylamines) are examples of alloste-ric activators of the CaSR. Cinacalcet(Sensipar) is an example of a calcimi-metic phenylalkylamine used to reducePTH secretion that is now increasinglyused in the treatment of 2°HPT in renaldisease and in primary hyperparathy-roidism.90 –92 Other compounds, knownas “calcilytic” agents, block the CaSR andallow the release of increased amounts ofPTH from the parathyroid gland for anygiven sCa2� concentration.83,93–95 Theseagents, when administered intermit-tently, could be useful for the treatmentof osteoporosis.83,93–95

When extracellular Ca2� binds to theCaSR, it elicits conformational changeswithin the receptor. The heterotrimericG protein subunits, Gqa and Gia, are re-cruited to the receptor and alter theamounts or activity of several intracellu-lar mediators including Ca2�, cAMP,and phospholipases within the chief cell(Figure 3).42,59,70 Intracellular Ca2� is al-tered as a result of activation of phospho-lipase C (PLC) by the Gq� subunit of theheterotrimeric G proteins. This results inthe PLC-mediated hydrolysis of phos-phatidylinositol-4,5,-bisphosphate andthe resultant formation of inositol 1,4,5-trisphosphate and diacylglycerol. 1,4,5-Trisphosphate mobilizes intracellularCa2� stores by binding to its cognate re-ceptor. The CaSR also interacts with Gi�

to inhibit adenylate cyclase activity thatreduces intracellular cyclic AMP.42 In ad-dition, activation of PLA2 results in theproduction of arachidonic acid and acti-vation of phophatidylinositol 4-kinasewhich replenishes phosphatidylinositol-4,5,-bisphosphate.42,59,70 These changeswithin chief cells rapidly enhance the re-lease of preformed PTH from the para-thyroid gland.

In addition to controlling PTH re-lease and modulating Ca2� flux in thekidney, the CaSR also plays a role in thecontrol of cellular differentiation, cellu-lar growth, and apoptosis.96 CaSRs acti-

vate signaling pathways that regulate cel-lular growth through MAPKs, ERKs, andJNK kinases.96 –100 The binding of CaSRsto intracellular scaffolding proteins suchas filamin A is important in mediatingthis effect.97,101–108 The CaSR interactswith filamin A to create a scaffold neces-sary for the organization of Gq�, Rhoguanine nucleotide exchange factor, andRho signaling pathways.55 The affinity ofthe CaSR for filamin A is greater in thepresence of Ca2�.104 Filamin A protectsthe CaSR from degradation,104 and si-lencing filamin A expression with siR-NAs inhibits CaSR signaling.101 CaSRactivation increases the activity of a se-rum-response element by increasing themembrane localization of the Rho pro-tein.55

Transcription of the CaSR is not in-fluenced by Ca2� concentrations but isaltered in vivo by 1�,25(OH)2D in theparathyroid gland, in the kidney, andin thyroid C cells.24,55,54,56 Vitamin Dresponse elements have been identifiedin the two promoter regions (P1 andP2), 380 and 160 bp upstream of thetranscription start sites of the CaSRgene, respectively.55 These vitamin Dresponse elements are atypical hexam-eric repeats that are separated by threenucleotides. In CKD, CaSR amountsare reduced in the parathyroid gland,most likely as a result of hyperplasiaand perhaps as a result of reduced serum1�,25(OH)2Dconcentrations.109–112 The re-ductions in CaSR concentrations in theparathyroid gland attenuate the respon-siveness of the gland to sCa2� and contrib-ute to 2°HPT.

THE REGULATION OF PTHSYNTHESIS

As noted earlier, replenishment of PTHstores after the release of preformed PTH isdependent on the synthesis of new prepro-PTH by ribosomes.1,2,43 This is dependent,in turn, upon the availability of mRNA-encoding PTH. As we discuss in the sec-tions that follow, changes in mRNA con-centrations are the result of changes inPTH gene transcription or mRNA stability.

Figure 2. Models of bound phenylala-nine and neomycin molecules within thecavities of the CaSR dimer. (A) Above thepredicted Ca2�-binding sites shown byyellow spheres are phenylalanine mole-cules shown in a conformation that stacksits side-chain ring against a tryptophan res-idue that is unique to CaSR, whereas re-maining atoms occupy the same locationsas found for the glutamate moleculesbound to glutamate receptor. (B) Two neo-mycin molecules may also be dockedwithin a third buried location as shown inthe bottom-most image.

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Transcriptional Regulation ofmRNA-Encoding PTHThe rate of transcription of the PTH geneis repressed by 1�,25(OH)2D.38,39,41,45

1�,25(OH)2D binds to the VDR receptorand the liganded VDR, in association withthe retinoic acid X receptor (RXR), bindsto a vitamin D response element within thepromoter region of the PTH gene.113 Struc-turally,thisresponseelementresemblesthosefound in other genes that are upregulated by1�,25(OH)2D. Reduced 1�,25(OH)2D con-centrations in CKD or ESRD, as well as re-duced VDR concentrations within the para-thyroid gland, contribute to 2°HPT.23

Role of RNA-Binding Proteins inthe Regulation of mRNA-EncodingPTH by Changing mRNA StabilityWhen sCa2� concentrations decrease,levels of mRNA-encoding PTH increasewithin the parathyroid gland.46,47 Sur-prisingly, changes in mRNA synthesis inresponse to decreases in sCa2� are notdue to changes in PTH gene transcrip-tion.28,27,44,48,49 Rather, levels of bovineand murine mRNA-encoding pth areregulated by proteins that bind elements

within the 3�-untranslated region thatinfluence mRNA stability.28,27,44,48,49

By way of background, after tran-scription, nascent RNA undergoes 5�-methyl capping, splicing, cleavage, andpolyadenylation in the nucleus (Figure4A).114 –117 After export from the nu-cleus, mRNA transcripts interact withRNA-binding proteins that influenceRNA half-life and stability within the cell(Figure 4A).95,118 –120 RNA-binding pro-teins interact with sequence-specific ele-ments, adenine- and uridine-rich ele-ments (AREs), that are usually presentwithin the 3�-untranslated regions (3�-UTRs) of RNA and regulate the rate atwhich mRNAs are translated or de-graded in cells.121,114,122–124 The fate ofan mRNA species containing an AREbound to ARE-binding proteins ispartly dependent upon the relativeamounts of different bound stabilizingor destabilizing ARE-binding proteins.AREs have a variable structure: Class I AREscontain several copies of the AUUUAmotif dispersed within U-rich regions; ClassII AREs possess at least two overlappingUUAUUUA(U/A)nonamers;ClassIIIAREs

are less well-defined and generally do notcontain an AUUUA sequence.125,114,122

As shown in Figure 4A, RNAs targetedfor degradation undergo deadenylation,decapping, and degradation in a largemultiprotein complex, the exosome, orin cytoplasmic compartments known asGW bodies or processing bodies (P-bod-ies).126 –128 A 63-nucleotide ARE in the3�-UTR of murine mRNA-encodingPTH, comprised of a core 26-nucleotideminimal binding sequence and adjacentflanking regions, regulates mRNA stabilityin response to changes in Ca2� and phos-phate concentrations.28,44,129 The ARE inthe 3�-UTR of mRNA-encoding PTHbinds two proteins, AU-rich element–binding protein 1 (AUF1) and K-ho-mology splicing regulatory protein(KSRP).27,29 AUF1 increases mRNA half-life, whereas KSRP has the opposite ef-fect.27,29 Both proteins are regulated bychanges in sCa2� and phosphate and arealtered in CKD.27,30,130

The Bioactivity of KSRP Is Alteredby Other Intracellular EnzymesPeptidyl-prolyl cis-trans isomerase, NIMA-interacting-1 (Pin1), a peptidyl-prolyl iso-merase,altersKSRPphosphorylationandthebinding of KSRP to the AREs in mRNA-en-coding PTH. Pin1 binds to KSRP and pre-vents the phosphorylation of KSRP at serineresidue181.NonphosphorylatedKSRPisac-tiveandenhancesdegradationofmRNA-en-coding PTH (Figure 4B). Pin1 specificallybinds serine/threonine–protein motifs andcatalyzes the cis-trans isomerization of pep-tide bonds, thereby changing the activity ofproteins. Pin1 interacts with AUF1 andstabilizes mRNA-encoding GMCSF andTGFB.131,132 Interestingly, Pin1 epitopesand Pin1 enzymatic activity are detectable inrat parathyroid glands and parathyroid ex-tracts.30 In heterologous cell systems, inhibi-tion of Pin1 activity, or knockdown of Pin1expression, increases mRNA-encoding PTHby inhibiting degradation, whereas overex-pression of Pin1 reduces mRNA-encodingPTH by accelerating its decay. Pin1 null micehave increased levels of PTH in the parathy-roid gland and circulating serum PTH con-centrations without changes in sCa2� andphosphate levels.

Induction of 2°HPT by feeding rats

Extra-cellular

Intra-cellular

Cellmembrane

Ca2+

GqaActivationof PLA2

AAGqaGqi

Activationof MAPK

Activationof PLC

Inhibitionof AC

Activationof PKC

ERK 1/2Mobilization ofintra-cellular Ca

Formation ofDAG

MEKFormation ofIns(1,4,5)P3

PtdIns(4,5)P2

DecreasedcAMP

Figure 3. Pathways by which the CaSR homodimer signals in cells after binding of Ca2�

to the extracellular domains (red line) of the CaSR molecules in the homodimeric pair.Through the association of the CaSR with the i-type heterotrimeric G protein, Gi�,adenylate cyclase (AC) activity is inhibited and cyclic AMP (cAMP) concentrations de-crease. Association of the CaSR with the Gq� subunit of q-type heterotrimeric G proteinresults in the activation of PLC that increases inositol (1,4,5)P3 and diacylglycerol (DAG)with attendant downstream effects such as an increase in intracellular calcium that ismobilized from intracellular stores, and the activation of PKC. MAPK and PLA2 areactivated by Gq�-dependent pathways with increases in MEK and ERK and an increase inarachidonic acid formation.

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a low Ca2� diet or by inducing CKDwith adenine reduces Pin1 activity inthe parathyroid gland.30 Reduced Pin1activity correlates with increased levelsof mRNA-encoding PTH in the PTglands of rats fed a low Ca diet or ratswith renal failure. As a result of low

Pin1 activity, less nonphosphorylatedKSRP is available to bind to the ARE inthe 3�-UTR of mRNA-encodingPTH.30 The reduction in Pin1 activityreduces the ratio of the ARE-BPs,KSRP, and AUF1. AUF1 activity pre-dominates, and the half-life and stabil-

ity of mRNA-encoding PTH is in-creased because of unopposed AUF1activity. Increased amounts of mRNAallow more PTH to be synthesized inribosomes and hyperparathyroidismresults. It is not known what triggersthe reduction in Pin1 activity in the

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Degradation

Translation

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Cytoplasm

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Transcription

5' methyl capping

Splicing

Cleavage

Polyadenylation

Stabilization

Export

E1 E2 E3 E4

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P

P

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Figure 4. (A) Cellular processing of mRNA. Nascent mRNA comprised of exons (E1 through E4) and intervening sequences (IVS)is processed in the nucleus by 5�-methyl capping, splicing, cleavage, and polyadenylation. In the cytoplasm, AU-rich element–binding proteins (ARE-BPs, blue box and red oval) bind to AREs within the 3�-region of RNA and stabilize or destabilize mRNA.Stabilized mRNA undergoes translation in ribosomes, whereas destabilized mRNA undergoes deadenylation, decapping, anddegradation in exosomes or P-bodies. (Adapted from reference 130 with permission from the American Society for ClinicalInvestigation.) (B) Processing of mRNA-encoding PTH. Murine mRNA-encoding PTH is bound by ARE-BPs, which either stabilizeor destabilize the mRNA. The ratio of activities of stabilizing/destabilizing ARE-binding proteins bound to mRNA-encoding PTHdetermines the half-life of the mRNA. KSRP is a mRNA-destabilizing ARE-BP for mRNA-encoding PTH that is active in itsdephosphorylated state. The peptidyl-prolyl isomerase Pin1 is responsible for the dephosphorylation of KSRP. In CKD, Pin1activity is reduced, and as a result less dephosphorylated (active) KSRP is available. Consequently, a stabilizing ARE-BP, AUF1, isactive and mRNA-encoding PTH is degraded to a lesser extent, resulting in higher intracellular mRNA levels, more PTH synthesis,and secondary hyperparathyroidism. Abbreviation: P, phosphate. (Adapted from reference 130 with permission from the AmericanSociety for Clinical Investigation.)

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parathyroids in CKD and Ca2� defi-ciency.

CONCLUSIONS

Thus, in CKD and ESRD, multiple ab-normalities contribute to the develop-ment of 2°HPT by enhancing the rateof PTH release and synthesis (Figure 5).These factors include a reduction innumber of CaSRs in the parathyroidgland, and a reduction in the number ofVDRs, which influence the transcriptionof CaSR and PTH. In addition, there arechanges in the amounts of mRNA-encoding PTH binding proteins, spe-cifically those that increase mRNA deg-radation and that favor an increase inlevels of mRNA-encoding PTH withinthe chief cell. Modulators of CaSR andVDR already are available and are inwidespread use for the treatment of2°HPT in CKD and ESRD. The devel-opment of parathyroid gland specificmodulators of ARE-binding proteinsmight result in drugs that are effective

for the control of secondary hyper-parathyroidism and parathyroid hy-perplasia. Such drugs might be used inconjunction with vitamin D analogsand calcimimetic agents for the treat-ment of 2°HPT.

DisclosuresDr. Kumar’s laboratory is supported by NIHgrants DK76829 and DK77669, and grantsfrom Genzyme (GRIP) and Abbott.

DISCLOSURESNone.

REFERENCES

1. Habener JF, Rosenblatt M, Potts JT Jr.:Parathyroid hormone: Biochemical aspectsof biosynthesis, secretion, action, and me-tabolism. Physiol Rev 64: 985–1053, 1984

2. Potts JT: Parathyroid hormone: Past andpresent. J Endocrinol 187: 311–325, 2005

3. Kumar R: Metabolism of 1,25-dihydroxyvi-tamin D3. Physiol Rev 64: 478–504, 1984

4. DeLuca HF, Schnoes HK: Vitamin D: Recent

advances. Annu Rev Biochem 52: 411–439,1983

5. Gesek FA, Friedman PA: On the mecha-nism of parathyroid hormone stimulation ofcalcium uptake by mouse distal convolutedtubule cells. J Clin Invest 90: 749–758,1992

6. Isakova T, Gutierrez O, Shah A, Castaldo L,Holmes J, Lee H, Wolf M: Postprandialmineral metabolism and secondary hyper-parathyroidism in early CKD. J Am SocNephrol 19: 615–623, 2008

7. Moranne O, Froissart M, Rossert J, GauciC, Boffa JJ, Haymann JP, M’Rad MB, Jac-quot C, Houillier P, Stengel B, FouquerayB: Timing of onset of CKD-related meta-bolic complications. J Am Soc Nephrol 20:164–171, 2009

8. Potts JT, Reita RE, Deftos LJ, Kaye MB,Richardson JA, Buckle RM, Aurbach GD:Secondary hyperparathyroidism in chronicrenal disease. Arch Intern Med 124: 408–412, 1969

9. Johnson WJ, Goldsmith RS, Arnaud CD:Prevention and treatment of progressivesecondary hyperparathyroidism in ad-vanced renal failure. Med Clin North Am56: 961–975, 1972

10. Kumar R: Renal osteodystrophy: A complexdisorder. J Lab Clin Med 93: 895–898,1979

11. Bricker NS, Slatopolsky E, Reiss E, AvioliLV: Caclium, phosphorus, and bone in re-nal disease and transplantation. Arch InternMed 123: 543–553, 1969

12. Reiss E, Canterbury JM, Kanter A: Circulat-ing parathyroid hormone concentration inchronic renal insufficiency. Arch Intern Med124: 417–422, 1969

13. Danese MD, Kim J, Doan QV, Dylan M,Griffiths R, Chertow GM: PTH and the risksfor hip, vertebral, and pelvic fracturesamong patients on dialysis. Am J KidneyDis 47: 149–156, 2006

14. Jadoul M, Albert JM, Akiba T, Akizawa T,Arab L, Bragg-Gresham JL, Mason N, PrutzKG, Young EW, Pisoni RL: Incidence andrisk factors for hip or other bone fracturesamong hemodialysis patients in the Dialy-sis Outcomes and Practice Patterns Study.Kidney Int 70: 1358–1366, 2006

15. Rudser KD, de Boer IH, Dooley A, Young B,Kestenbaum B: Fracture risk after parathy-roidectomy among chronic hemodialysis pa-tients. J Am Soc Nephrol 18: 2401–2407,2007

16. Block GA, Klassen PS, Lazarus JM, OfsthunN, Lowrie EG, Chertow GM: Mineral me-tabolism, mortality, and morbidity in main-tenance hemodialysis. J Am Soc Nephrol15: 2208–2218, 2004

17. Slatopolsky E, Bricker NS: The role of phos-phorus restriction in the prevention of sec-ondary hyperparathyroidism in chronic re-nal disease. Kidney Int 4: 141–145, 1973

18. Slatopolsky E, Caglar S, Gradowska L, Can-

Parathyroid chief cell

CaSR; reduced amountsin PTG in CRF/ESRD

Cell membrane

Systemic factors–Reduced SCa–Increased SPi–Reduced 1α, 25(OH)2D

Nucleus

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RXR VDRIncreased expressionin CRF/ESRD(reduced repression)

Reduced expressionin CRF/ESRD

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Figure 5. Alterations within the parathyroid gland that favor the development of 2°HPTin the context of CRF and ESRD.

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terbury J, Reiss E, Bricker NS: On the pre-vention of secondary hyperparathyroidismin experimental chronic renal disease using“proportional reduction” of dietary phos-phorus intake. Kidney Int 2: 147–151, 1972

19. Slatopolsky E, Caglar S, Pennell JP, Tag-gart DD, Canterbury JM, Reiss E, BrickerNS: On the pathogenesis of hyperparathy-roidism in chronic experimental renal insuf-ficiency in the dog. J Clin Invest 50: 492–499, 1971

20. Slatopolsky E, Gradowska L, KashemsantC, Keltner R, Manley C, Bricker NS: Thecontrol of phosphate excretion in uremia.J Clin Invest 45: 672–677, 1966

21. McCarthy JT, Kumar R: Behavior of the vi-tamin D endocrine system in the develop-ment of renal osteodystrophy. SeminNephrol 6: 21–30, 1986

22. McCarthy JT, Kumar R: Renal osteodystro-phy. Endocrinol Metab Clin North Am 19:65–93, 1990

23. Brown AJ, Dusso A, Lopez-Hilker S, Lewis-Finch J, Grooms P, Slatopolsky E: 1,25-(OH)2D receptors are decreased in para-thyroid glands from chronically uremicdogs. Kidney Int 35: 19–23, 1989

24. Brown AJ, Zhong M, Finch J, Ritter C, Mc-Cracken R, Morrissey J, Slatopolsky E: Ratcalcium-sensing receptor is regulated byvitamin D but not by calcium. Am J Physiol270: F454–F460, 1996

25. Ritter CS, Finch JL, Slatopolsky EA, BrownAJ: Parathyroid hyperplasia in uremic ratsprecedes down-regulation of the calciumreceptor. Kidney Int 60: 1737–1744, 2001

26. Ritter CS, Martin DR, Lu Y, Slatopolsky E,Brown AJ: Reversal of secondary hyper-parathyroidism by phosphate restriction re-stores parathyroid calcium-sensing recep-tor expression and function. J Bone MinerRes 17: 2206–2213, 2002

27. Naveh-Many T, Bell O, Silver J, Kilav R: Cisand trans acting factors in the regulation ofparathyroid hormone (PTH) mRNA stabilityby calcium and phosphate. FEBS Lett 529:60–64, 2002

28. Naveh-Many T, Sela-Brown A, Silver J:Protein-RNA interactions in the regula-tion of PTH gene expression by calciumand phosphate. Nephrol Dial Transplant14: 811– 813, 1999

29. Nechama M, Ben-Dov IZ, Briata P, GherziR, Naveh-Many T: The mRNA decay pro-moting factor K-homology splicing regula-tor protein post-transcriptionally deter-mines parathyroid hormone mRNA levels.Faseb J 22: 3458–3468, 2008

30. Nechama M, Uchida T, Mor Yosef-Levi I,Silver J, Naveh-Many T: The peptidyl-prolylisomerase Pin1 determines parathyroidhormone mRNA levels and stability in ratmodels of secondary hyperparathyroidism.J Clin Invest 119: 3102–3114, 2009

31. Dusso AS, Arcidiacono MV, Sato T, Al-varez-Hernandez D, Yang J, Gonzalez-Su-

arez I, Tominaga Y, Slatopolsky E: Molecu-lar basis of parathyroid hyperplasia. J RenNutr 17: 45–47, 2007

32. Dusso AS, Sato T, Arcidiacono MV, Alvarez-Hernandez D, Yang J, Gonzalez-Suarez I, To-minaga Y, Slatopolsky E: Pathogenic mecha-nisms for parathyroid hyperplasia. Kidney IntSuppl S8–S11, 2006

33. Locatelli F, Cannata-Andia JB, Drueke TB,Horl WH, Fouque D, Heimburger O, Ritz E:Management of disturbances of calciumand phosphate metabolism in chronic renalinsufficiency, with emphasis on the controlof hyperphosphataemia. Nephrol DialTransplant 17: 723–731, 2002

34. Moe SM, Drueke TB: Management of sec-ondary hyperparathyroidism: The impor-tance and the challenge of controllingparathyroid hormone levels without elevat-ing calcium, phosphorus, and calcium-phosphorus product. Am J Nephrol 23:369–379, 2003

35. Block GA, Martin KJ, de Francisco AL,Turner SA, Avram MM, Suranyi MG, HerczG, Cunningham J, Abu-Alfa AK, Messa P,Coyne DW, Locatelli F, Cohen RM, Evene-poel P, Moe SM, Fournier A, Braun J, Mc-Cary LC, Zani VJ, Olson KA, Drueke TB,Goodman WG: Cinacalcet for secondaryhyperparathyroidism in patients receivinghemodialysis. N Engl J Med 350: 1516–1525, 2004

36. Shoben AB, Rudser KD, de Boer IH, YoungB, Kestenbaum B: Association of oral cal-citriol with improved survival in nondia-lyzed CKD. J Am Soc Nephrol 19: 1613–1619, 2008

37. Fox J, Heath H 3rd: The “calcium clamp”:Effect of constant hypocalcemia on para-thyroid hormone secretion. Am J Physiol240: E649–E655, 1981

38. Cantley LK, Russell J, Lettieri D, SherwoodLM: 1,25-Dihydroxyvitamin D3 suppressesparathyroid hormone secretion from bo-vine parathyroid cells in tissue culture. En-docrinology 117: 2114–2119, 1985

39. Russell J, Lettieri D, Sherwood LM: Sup-pression by 1,25(OH)2D3 of transcriptionof the pre-proparathyroid hormone gene.Endocrinology 119: 2864–2866, 1986

40. Silver J, Naveh-Many T, Mayer H, Schmel-zer HJ, Popovtzer MM: Regulation by vita-min D metabolites of parathyroid hormonegene transcription in vivo in the rat. J ClinInvest 78: 1296–1301, 1986

41. Silver J, Russell J, Sherwood LM: Regula-tion by vitamin D metabolites of messen-ger ribonucleic acid for preproparathyroidhormone in isolated bovine parathyroidcells. Proc Natl Acad Sci U S A 82: 4270–4273, 1985

42. Hofer AM, Brown EM: Extracellular calciumsensing and signalling. Nat Rev Mol CellBiol 4: 530–538, 2003

43. Potts JT, Gardella TJ: Progress, paradox,and potential: Parathyroid hormone re-

search over five decades. Ann N Y Acad Sci1117: 196–208, 2007

44. Moallem E, Kilav R, Silver J, Naveh-Many T:RNA-Protein binding and post-transcrip-tional regulation of parathyroid hormonegene expression by calcium and phos-phate. J Biol Chem 273: 5253–5259, 1998

45. Russell J, Bar A, Sherwood LM, Hurwitz S:Interaction between calcium and 1,25-di-hydroxyvitamin D3 in the regulation ofpreproparathyroid hormone and vitaminD receptor messenger ribonucleic acid inavian parathyroids. Endocrinology 132:2639 –2644, 1993

46. Naveh-Many T, Friedlaender MM, MayerH, Silver J: Calcium regulates parathyroidhormone messenger ribonucleic acid(mRNA), but not calcitonin mRNA in vivo inthe rat. Dominant role of 1,25-dihydroxyvi-tamin D. Endocrinology 125: 275–280,1989

47. Naveh-Many T, Silver J: Regulation of para-thyroid hormone gene expression by hy-pocalcemia, hypercalcemia, and vitamin Din the rat. J Clin Invest 86: 1313–1319,1990

48. Hawa NS, O’Riordan JL, Farrow SM: Post-transcriptional regulation of bovine para-thyroid hormone synthesis. J Mol Endocri-nol 10: 43–49, 1993

49. Vadher S, Hawa NS, O’Riordan JL, FarrowSM: Translational regulation of parathyroidhormone gene expression and RNA: Pro-tein interactions. J Bone Miner Res 11:746–753, 1996

50. Habener JF, Kemper B, Potts JT Jr.: Calci-um-dependent intracellular degradation ofparathyroid hormone: A possible mecha-nism for the regulation of hormone stores.Endocrinology 97: 431–441, 1975

51. Morrissey JJ, Cohn DV: Secretion and deg-radation of parathormone as a function ofintracellular maturation of hormone pools.Modulation by calcium and dibutyryl cyclicAMP. J Cell Biol 83: 521–528, 1979

52. Roth SI, Raisz LG: Effect of calcium concen-tration on the ultrastructure of rat parathy-roid in organ culture. Lab Invest 13: 331–345, 1964

53. Bai M, Quinn S, Trivedi S, Kifor O, PearceSH, Pollak MR, Krapcho K, Hebert SC,Brown EM: Expression and characterizationof inactivating and activating mutations inthe human Ca2�o-sensing receptor. J BiolChem 271: 19537–19545, 1996

54. Rogers KV, Dunn CK, Conklin RL, HadfieldS, Petty BA, Brown EM, Hebert SC, Nem-eth EF, Fox J: Calcium receptor messengerribonucleic acid levels in the parathyroidglands and kidney of vitamin D-deficientrats are not regulated by plasma calcium or1,25-dihydroxyvitamin D3. Endocrinology136: 499–504, 1995

55. Canaff L, Hendy GN: Human calcium-sensing receptor gene. Vitamin D re-sponse elements in promoters P1 and P2

BRIEF REVIEW www.jasn.org

222 Journal of the American Society of Nephrology J Am Soc Nephrol 22: 216–224, 2011

confer transcriptional responsiveness to1,25-dihydroxyvitamin D. J Biol Chem277: 30337–30350, 2002

56. Yao JJ, Bai S, Karnauskas AJ, BushinskyDA, Favus MJ: Regulation of renal calciumreceptor gene expression by 1,25-dihy-droxyvitamin D3 in genetic hypercalciuricstone-forming rats. J Am Soc Nephrol 16:1300–1308, 2005

57. Brown EM, Gamba G, Riccardi D, LombardiM, Butters R, Kifor O, Sun A, Hediger MA,Lytton J, Hebert SC: Cloning and charac-terization of an extracellular Ca(2�)-sens-ing receptor from bovine parathyroid. Na-ture 366: 575–580, 1993

58. Brown EM, Hebert SC: Calcium-receptor-regulated parathyroid and renal function.Bone 20: 303–309, 1997

59. Brown EM, MacLeod RJ: Extracellular cal-cium sensing and extracellular calcium sig-naling. Physiol Rev 81: 239–297, 2001

60. Brown EM, Pollak M, Hebert SC: Molecularmechanisms underlying the sensing of ex-tracellular Ca2� by parathyroid and kidneycells. Eur J Endocrinol 132: 523–531, 1995

61. Brown EM, Pollak M, Hebert SC: The extra-cellular calcium-sensing receptor: Its role inhealth and disease. Annu Rev Med 49: 15–29, 1998

62. Brown EM, Pollak M, Riccardi D, HebertSC: Cloning and characterization of an ex-tracellular Ca(2�)-sensing receptor fromparathyroid and kidney: New insights intothe physiology and pathophysiology of cal-cium metabolism. Nephrol Dial Transplant9: 1703–1706, 1994

63. Schwarz P, Larsen NE, Lonborg Friis IM,Lillquist K, Brown EM, Gammeltoft S: Familialhypocalciuric hypercalcemia and neonatalsevere hyperparathyroidism associated withmutations in the human Ca2�-sensing re-ceptor gene in three Danish families. ScandJ Clin Lab Invest 60: 221–227, 2000

64. Pollak MR, Brown EM, Chou YH, HebertSC, Marx SJ, Steinmann B, Levi T, SeidmanCE, Seidman JG: Mutations in the humanCa(2�)-sensing receptor gene cause famil-ial hypocalciuric hypercalcemia and neona-tal severe hyperparathyroidism. Cell 75:1297–1303, 1993

65. Brown EM, Pollak M, Hebert SC: Sensing ofextracellular Ca2� by parathyroid and kid-ney cells: Cloning and characterization ofan extracellular Ca(2�)-sensing receptor.Am J Kidney Dis 25: 506–513, 1995

66. Hebert SC: Bartter syndrome. Curr OpinNephrol Hypertens 12: 527–532, 2003

67. Brown EM: Mutations in the calcium-sens-ing receptor and their clinical implications.Horm Res 48: 199–208, 1997

68. Chattopadhyay N, Mithal A, Brown EM:The calcium-sensing receptor: A windowinto the physiology and pathophysiologyof mineral ion metabolism. Endocr Rev 17:289–307, 1996

69. Bai M, Trivedi S, Brown EM: Dimerization

of the extracellular calcium-sensing re-ceptor (CaR) on the cell surface of CaR-transfected HEK293 cells. J Biol Chem273: 23605–23610, 1998

70. Bai M, Trivedi S, Kifor O, Quinn SJ, BrownEM: Intermolecular interactions betweendimeric calcium-sensing receptor mono-mers are important for its normal function.Proc Natl Acad Sci U S A 96: 2834–2839,1999

71. Fan GF, Ray K, Zhao XM, Goldsmith PK,Spiegel AM: Mutational analysis of the cys-teines in the extracellular domain of thehuman Ca2� receptor: Effects on cell sur-face expression, dimerization and signaltransduction. FEBS Lett 436: 353–356,1998

72. Ward DT, Brown EM, Harris HW: Disulfidebonds in the extracellular calcium-polyva-lent cation-sensing receptor correlate withdimer formation and its response to diva-lent cations in vitro. J Biol Chem 273:14476–14483, 1998

73. Zhang Z, Sun S, Quinn SJ, Brown EM, BaiM: The extracellular calcium-sensing recep-tor dimerizes through multiple types of in-termolecular interactions. J Biol Chem 276:5316–5322, 2001

74. Guex N, Peitsch MC: SWISS-MODEL andthe Swiss-PdbViewer: An environment forcomparative protein modeling. Electro-phoresis 18: 2714–2723, 1997

75. Kelley LA, MacCallum RM, Sternberg MJ:Enhanced genome annotation using struc-tural profiles in the program 3D-PSSM. JMol Biol 299: 499–520, 2000

76. Kopp J, Schwede T: The SWISS-MODELRepository of annotated three-dimen-sional protein structure homology mod-els. Nucleic Acids Res 32: D230 –D234,2004

77. Schwede T, Kopp J, Guex N, Peitsch MC:SWISS-MODEL: An automated protein ho-mology-modeling server. Nucleic AcidsRes 31: 3381–3385, 2003

78. Kunishima N, Shimada Y, Tsuji Y, Sato T,Yamamoto M, Kumasaka T, Nakanishi S,Jingami H, Morikawa K: Structural basis ofglutamate recognition by a dimericmetabotropic glutamate receptor. Nature407: 971–977, 2000

79. Tsuchiya D, Kunishima N, Kamiya N,Jingami H, Morikawa K: Structural views ofthe ligand-binding cores of a metabotropicglutamate receptor complexed with an an-tagonist and both glutamate and Gd3�.Proc Natl Acad Sci U S A 99: 2660–2665,2002

80. Nemeth EF, Bennett SA: Tricking the para-thyroid gland with novel calcimimeticagents. Nephrol Dial Transplant 13: 1923–1925, 1998

81. Nemeth EF: Calcimimetic and calcilyticdrugs: Just for parathyroid cells? Cell Cal-cium 35: 283–289, 2004

82. Nemeth EF: Pharmacological regulation of

parathyroid hormone secretion. Curr PharmDes 8: 2077–2087, 2002

83. Mun HC, Franks AH, Culverston E, KrapchoK, Nemeth EF, Conigrave AD: The VenusFly Trap domain of the extracellular Ca2�-sensing receptor is required for L-aminoacid sensing. J Biol Chem 279: 51739–51744, 2004

84. Brown EM, Butters R, Katz C, Kifor O: Neo-mycin mimics the effects of high extracel-lular calcium concentrations on parathyroidfunction in dispersed bovine parathyroidcells. Endocrinology 128: 3047–3054, 1991

85. Brown EM, Vassilev PM, Quinn S, HebertSC: G-protein-coupled, extracellular Ca(2�)-sensing receptor: A versatile regulator of di-verse cellular functions. Vitam Horm 55:1–71, 1999

86. Fox J, Lowe SH, Conklin RL, Petty BA, Nem-eth EF: Calcimimetic compound NPS R-568stimulates calcitonin secretion but selectivelytargets parathyroid gland Ca(2�) receptor inrats. J Pharmacol Exp Ther 290: 480–486,1999

87. Nemeth EF, Delmar EG, Heaton WL, MillerMA, Lambert LD, Conklin RL, Gowen M,Gleason JG, Bhatnagar PK, Fox J: Calcilyticcompounds: Potent and selective Ca2� re-ceptor antagonists that stimulate secretionof parathyroid hormone. J Pharmacol ExpTher 299: 323–331, 2001

88. Nemeth EF, Fox J: Calcimimetic com-pounds: A direct approach to controllingplasma levels of parathyroid hormone inhyperparathyroidism. Trends EndocrinolMetab 10: 66 –71, 1999

89. Nemeth EF, Steffey ME, Hammerland LG,Hung BC, Van Wagenen BC, DelMar EG,Balandrin MF: Calcimimetics with potentand selective activity on the parathyroidcalcium receptor. Proc Natl Acad Sci U S A95: 4040–4045, 1998

90. Block GA, Zeig S, Sugihara J, Chertow GM,Chi EM, Turner SA, Bushinsky DA: Com-bined therapy with cinacalcet and lowdoses of vitamin D sterols in patients withmoderate to severe secondary hyperpara-thyroidism. Nephrol Dial Transplant 23:2311–2318, 2008

91. Silverberg SJ, Bilezikian JP: The diagnosisand management of asymptomatic primaryhyperparathyroidism. Nat Clin Pract Endo-crinol Metab 2: 494–503, 2006

92. Valle C, Rodriguez M, Santamaria R, Alma-den Y, Rodriguez ME, Canadillas S, Martin-Malo A, Aljama P: Cinacalcet reduces theset point of the PTH-calcium curve. J AmSoc Nephrol 19: 2430–2436, 2008

93. Gowen M, Stroup GB, Dodds RA, JamesIE, Votta BJ, Smith BR, Bhatnagar PK, LagoAM, Callahan JF, DelMar EG, Miller MA,Nemeth EF, Fox J: Antagonizing the para-thyroid calcium receptor stimulates para-thyroid hormone secretion and bone for-mation in osteopenic rats. J Clin Invest 105:1595–1604, 2000

BRIEF REVIEWwww.jasn.org

J Am Soc Nephrol 22: 216–224, 2011 PTH Secretion and Synthesis 223

94. Rubin MR, Bilezikian JP: New anabolic ther-apies in osteoporosis. Endocrinol MetabClin North Am 32: 285–307, 2003

95. Hieronymus H, Silver PA: A systems view ofmRNP biology. Genes Dev 18: 2845–2860,2004

96. Tfelt-Hansen J, Chattopadhyay N, Yano S,Kanuparthi D, Rooney P, Schwarz P, BrownEM: Calcium-sensing receptor induces pro-liferation through p38 mitogen-activatedprotein kinase and phosphatidylinositol3-kinase but not extracellularly regulatedkinase in a model of humoral hypercalce-mia of malignancy. Endocrinology 145:1211–1217, 2004

97. Hjalm G, MacLeod RJ, Kifor O, Chatto-padhyay N, Brown EM: Filamin-A binds tothe carboxyl-terminal tail of the calcium-sensing receptor, an interaction that partic-ipates in CaR-mediated activation of mito-gen-activated protein kinase. J Biol Chem276: 34880–34887, 2001

98. Arthur JM, Lawrence MS, Payne CR, RaneMJ, McLeish KR: The calcium-sensing re-ceptor stimulates JNK in MDCK cells. Bio-chem Biophys Res Commun 275: 538–541,2000

99. Hobson SA, Wright J, Lee F, McNeil SE,Bilderback T, Rodland KD: Activation of theMAP kinase cascade by exogenous calci-um-sensing receptor. Mol Cell Endocrinol200: 189–198, 2003

100. Ye CP, Yano S, Tfelt-Hansen J, MacLeodRJ, Ren X, Terwilliger E, Brown EM, Chat-topadhyay N: Regulation of a Ca2�-acti-vated K� channel by calcium-sensingreceptor involves p38 MAP kinase. J Neu-rosci Res 75: 491– 498, 2004

101. Huang C, Wu Z, Hujer KM, Miller RT: Si-lencing of filamin A gene expression inhib-its Ca2�-sensing receptor signaling. FEBSLett 580: 1795–1800, 2006

102. Davies SL, Gibbons CE, Vizard T, Ward DT:Ca2�-sensing receptor induces Rho ki-nase-mediated actin stress fiber assemblyand altered cell morphology, but not inresponse to aromatic amino acids. Am JPhysiol Cell Physiol 290: C1543–C1551,2006

103. Rey O, Young SH, Yuan J, Slice L, Rozen-gurt E: Amino acid-stimulated Ca2� oscil-lations produced by the Ca2�-sensing re-ceptor are mediated by a phospholipaseC/inositol 1,4,5-trisphosphate-independentpathway that requires G12, Rho, filamin-A,and the actin cytoskeleton. J Biol Chem280: 22875–22882, 2005

104. Zhang M, Breitwieser GE: High affinity inter-action with filamin A protects against calci-um-sensing receptor degradation. J BiolChem 280: 11140–11146, 2005

105. Loretz CA, Pollina C, Hyodo S, Takei Y,Chang W, Shoback D: cDNA cloning andfunctional expression of a Ca2�-sensingreceptor with truncated C-terminal tailfrom the Mozambique tilapia (Oreochro-

mis mossambicus). J Biol Chem 279:53288 –53297, 2004

106. Ward DT: Calcium receptor-mediated in-tracellular signalling. Cell Calcium 35:217–228, 2004

107. Carfi A, Gong H, Lou H, Willis SH, CohenGH, Eisenberg RJ, Wiley DC: Crystalliza-tion and preliminary diffraction studies ofthe ectodomain of the envelope glycop-rotein D from herpes simplex virus 1alone and in complex with the ectodo-main of the human receptor HveA. ActaCrystallogr D Biol Crystallogr 58: 836 –838, 2002

108. Awata H, Huang C, Handlogten ME, MillerRT: Interaction of the calcium-sensing re-ceptor and filamin, a potential scaffoldingprotein. J Biol Chem 276: 34871–34879,2001

109. Brown AJ, Ritter CS, Finch JL, SlatopolskyEA: Decreased calcium-sensing receptorexpression in hyperplastic parathyroidglands of uremic rats: Role of dietaryphosphate. Kidney Int 55: 1284 –1292,1999

110. Martin-Salvago M, Villar-Rodriguez JL,Palma-Alvarez A, Beato-Moreno A, Galera-Davidson H: Decreased expression of cal-cium receptor in parathyroid tissue in pa-tients with hyperparathyroidism secondaryto chronic renal failure. Endocr Pathol 14:61–70, 2003

111. Mathias RS, Nguyen HT, Zhang MY, PortaleAA: Reduced expression of the renal calci-um-sensing receptor in rats with experi-mental chronic renal insufficiency. J AmSoc Nephrol 9: 2067–2074, 1998

112. Yano S, Sugimoto T, Tsukamoto T, Chi-hara K, Kobayashi A, Kitazawa S, MaedaS, Kitazawa R: Association of decreasedcalcium-sensing receptor expression withproliferation of parathyroid cells in sec-ondary hyperparathyroidism. Kidney Int58: 1980 –1986, 2000

113. Demay MB, Kiernan MS, DeLuca HF, Kro-nenberg HM: Sequences in the human para-thyroid hormone gene that bind the 1,25-dihydroxyvitamin D3 receptor and mediatetranscriptional repression in response to1,25-dihydroxyvitamin D3. Proc Natl AcadSci U S A 89: 8097–8101, 1992

114. McKee AE, Silver PA: Systems perspectiveson mRNA processing. Cell Res 17: 581–590, 2007

115. Bentley DL: Rules of engagement: Co-tran-scriptional recruitment of pre-mRNA pro-cessing factors. Curr Opin Cell Biol 17:251–256, 2005

116. Blencowe BJ: Alternative splicing: New in-sights from global analyses. Cell 126: 37–47, 2006

117. Kornblihtt AR, de la Mata M, Fededa JP,Munoz MJ, Nogues G: Multiple links be-tween transcription and splicing. RNA 10:1489–1498, 2004

118. Moore MJ: From birth to death: The com-

plex lives of eukaryotic mRNAs. Science309: 1514–1518, 2005

119. Sanchez-Diaz P, Penalva LO: Post-tran-scription meets post-genomic: The saga ofRNA binding proteins in a new era. RNABiol 3: 101–109, 2006

120. Singh R, Valcarcel J: Building specificitywith nonspecific RNA-binding proteins.Nat Struct Mol Biol 12: 645– 653, 2005

121. Barreau C, Paillard L, Osborne HB: AU-richelements and associated factors: Are thereunifying principles? Nucleic Acids Res 33:7138–7150, 2005

122. Misquitta CM, Chen T, Grover AK: Controlof protein expression through mRNA sta-bility in calcium signalling. Cell Calcium 40:329–346, 2006

123. Schiavi SC, Belasco JG, Greenberg ME:Regulation of proto-oncogene mRNAstability. Biochim Biophys Acta 1114: 95–106, 1992

124. Schiavi SC, Wellington CL, Shyu AB, ChenCY, Greenberg ME, Belasco JG: Multipleelements in the c-fos protein-coding re-gion facilitate mRNA deadenylation anddecay by a mechanism coupled to transla-tion. J Biol Chem 269: 3441–3448, 1994

125. Chen CY, Shyu AB: AU-rich elements: char-acterization and importance in mRNA degra-dation. Trends Biochem Sci 20: 465–470,1995

126. Lebreton A, Tomecki R, Dziembowski A,Seraphin B: Endonucleolytic RNA cleavageby a eukaryotic exosome. Nature 456: 993–996, 2008

127. McPheeters DS, Cremona N, Sunder S,Chen HM, Averbeck N, Leatherwood J,Wise JA: A complex gene regulatory mech-anism that operates at the nexus of multi-ple RNA processing decisions. Nat StructMol Biol 16: 255–264, 2009

128. Schilders G, Pruijn GJ: Biochemical stud-ies of the mammalian exosome with in-tact cells. Methods Enzymol 448: 211–226, 2008

129. Kilav R, Bell O, Le SY, Silver J, Naveh-ManyT: The parathyroid hormone mRNA 3�-un-translated region AU-rich element is an un-structured functional element. J Biol Chem279: 2109–2116, 2004

130. Kumar R: Pin1 regulates parathyroid hor-mone mRNA stability. J Clin Invest 119:2887–2891, 2009

131. Shen ZJ, Esnault S, Malter JS: The pepti-dyl-prolyl isomerase Pin1 regulates thestability of granulocyte-macrophage col-ony-stimulating factor mRNA in activatedeosinophils. Nat Immunol 6: 1280 –1287,2005

132. Shen ZJ, Esnault S, Rosenthal LA, SzakalyRJ, Sorkness RL, Westmark PR, Sandor M,Malter JS: Pin1 regulates TGF-beta1 pro-duction by activated human and murineeosinophils and contributes to allergiclung fibrosis. J Clin Invest 118: 479 – 490,2008

BRIEF REVIEW www.jasn.org

224 Journal of the American Society of Nephrology J Am Soc Nephrol 22: 216–224, 2011