1. Oncogenes 2. Tumor suppressor genes3. Invasion and metastasis4. Cancer stem cells5. Tumor microenvironment

Jimin Shao (邵吉民）

shaojimin@zju.edu.cn

Cancer pathogenesis

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Histopathological, genetic and epigenetic alterations of the human colon during cancer development

1. Oncogene(1) Oncogene: a gene that when mutated or expressed at abnormally-high levels contributes to

converting a normal cell into a cancer cell.

Cellular oncogene (c-onc)：• proto-oncogene：in normal physiologic version• oncogene：altered in cancer Viral oncogene （v-onc）

Identification of oncogene abnormalities for• Understanding of mechanisms• molecular diagnosis and monitoring• potential targets for therapies.

(2) Functions of proto-oncogenesProto-oncogenes at all levels of the various signal transduction cascades that control cell

growth, proliferation, and differentiation:• extracellular proteins: growth factors• membrane proteins: cell surface receptors• cellular proteins: relay signals • proteins in nucleus: transcription Factors, etc

(3) Mechanisms of Proto-oncogene Activation

Gene amplification, e.g. myc, CCND1 Point mutation, e.g. ras, Chromosomal rearrangement or translocation

-- transactivation of proto-onc-- fusion genes, e.g. abl-bcr

Viral insertion activation, e.g. c-Myc

Translocation

Ras• Locates on chromosome 11, codes for a protein with GTPase activity• relays signals by acting as a switch: when receptors on the cell surface are stimulated, Ras

is switched on and transduces signals that tell the cell to grow. If the cell-surface receptor is not stimulated, Ras is not activated and so the pathway that results in cell growth is not initiated.

• mutated in about 30% of cancers so that it is permanently switched on, telling the cell to grow regardless of whether receptors on the cell surface are activated or not.

Ras relays signals from the cell surface receptors to the nucleus

Ras relays signals by acting as a switch

The biology of cancer (2nd edition), RA Weinberg, 2013

2. Tumor suppressor genes(1) TSGs: genes that sustain loss-of function mutations in the development of cancer

(2) Mechanism for the inactivation of TSGs

1. Mutation: point mutation or frameshift mutation, p532. Deletion: LOH or homozygous deletion, Rb3. Viral oncoprotein inactivation: p53, Rb4. Promoter hypermethylation, histone modification changes: p16

RB: Cell Cycle Controller (G1/S transition)

Rb inactivation by viral oncoprotein

P53: Function as gatekeeper

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Inactivation of p53 in cancer •LOH on 17p13 in a number of tumors•Point mutation on exon 5-8 “hot-spot” (Dominant negative mutation)•MDM2 negative regulation• viral-oncogene products inactivation

3. Invasion and Metastasis(1)The multistep process of invasion and metastasis of cancer cells: Growth at primary site and angiogenesis local invasion intravasation into nearby blood and lymphatic vessels transport through the lymphatic and hematogenous systems extravasation into the parenchyma of distant tissues formation of micrometastases (small nodules of cancer cells), and colonization (the growth of

micrometastatic lesions into macroscopic tumors).

Up to 70% of patients with invasive cancer have overt or occult metastases at diagnosis. Invasion and metastasis are responsible for 90% of cancer-associated mortality Acquisition of the invasive and metastatic phenotype could be an early event in cancer progression. Millions of tumor cells are shed daily into the circulation. Less than 0.01% of circulating tumor cells

successfully initiate a metastatic focus. Circulating tumor cells can be detected in patients who do not develop overt metastatic disease.

(2) Mechanisms of cancer cell invation and metastasis

1) Loss of cell-to cell cohesive forces: Decreased cellular adhesion 2) Secretion of ECM-degrading enzymes: Degradation of ECM3) Active Locomotion and machinary: Abnormal or increased cellular motility 4) Metastatic Colonization5) Tumor angiogenesis6) Metastasis-related genes7) EMT8) Cancer Stem Cell

1) Loss of cell-to cell cohesive forces:

Cell adhesion molecules (CAMs）: the membrane proteins that mediate selective adhesion between cells, and between cells and extracellular matrix (ECM).

•E-cadherin: --Downregulation and occasional mutational inactivation of E-cadherin are frequently

observed in carcinoma cells.--Loss of cell-cell adhesion，Increased cell motility

•Integrins：--heterodimer receptors (alfa-beta subunits)--ligands: ECM components, collagens (I,IV), laminin (LN), fibronectin (FN), etc.

•Immunoglobin superfamily：VCAM-1, ICAM-1, CEA, DCC, etc

• Selectins• CD44 variants

Attachments of epithelial cells to their neighbors and the basement membrane. cancer cells develop alterations in their shape as well as in their attachment to other cells

and to the ECM.

2) Secretion of ECM-degrading enzymes Matrix Metalloproteinases (MMPs)：～20 Tissue inhibitors of metalloproteinases (TIMPs)： ～4

Plasminogen Activators (PAs) : urokinase-type (uPA), tissue-type PA (tPA) PA inhibitors (PAIs): ～3

3) Active locomotion and machinery E- cadherin Growth factors and receptors, ECM components (laminin, LN, etc） Autocrine motility factor (AMF), Autotaxin (ATX), Signaling, Protein Kinases, Cytoskeletal proteins RTK/CK/GPCR/CAM---Receptors---Rho GTPases ---signalling---cell mobility.

•Small G proteins of the Rho family (small Ras-like GTPases) control cellular processes such as adhesion, cell shape, and cell motility. •They are activated by cytoplasmic signal-transducing pathways and control the assembly of the actin cytoskeleton.•the motile behavior can be induced by a variety of growth factors (e.g. hepatocyte growth factor (HGF) produced by a variety of stromal cell types, many types of epithelial cells express Met, the receptor for HGF; EGF is able to induce motility of breast cancer cells).

ECM ---Integrins---FAK (focal adhesion kinase) ---signalling---cell mobility•The cellular machinery that responds to motogenic signals and operates as the engine of motility •continuous restructuring of the actin cytoskeleton in different parts of a cell, •the making and breaking of attachments between the migrating cell and the extracellular matrix.

26Locomotion of cells on solid substrates. Lamellipodia and filopodia

5) Inducing Angiogenesis

The development of the vasculature during embryogenesis involves the birth of new endothelial cells and their assembly into tubes (vasculogenesis) in addition to the sprouting (angiogenesis) of new vessels from existing ones.

Tumor-associated angiogenesis: during tumor progression, an ‘‘angiogenic switch’’ is almost always activated and remains on, causing normally quiescent vasculature to continually sprout new vessels that help sustain expanding neoplastic growths.

The blood vessels produced within tumors are typically aberrant: tumor neovasculature is marked by precocious capillary sprouting, convoluted and excessive vessel branching, distorted and enlarged vessels, erratic blood flow, microhemorrhaging, leakiness, and abnormal levels of endothelial cell proliferation and apoptosis.

The angiogenic switch is governed by angiogenic regulators (either induce or oppose angiogenesis), such as VEGF-A and TSP-1, that bind to cell surface receptors displayed by vascular endothelial cells.

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Anti-angiogenesis for cancer treatment

Metastasis-suppressor genes:

6) Metastasis-related genes Metastasis-enhancing genes: It seems likely that deregulated versions of some oncogenes are the primary forces driving many

of the steps of invasion and metastasis. Many of these genes encode growth factors, growth factor receptors, signal-transducing proteins,

or promote epithelial cancer cells’ EMT.

[J Clin Invest. 2009;119(6):1420-8. doi: 10.1172/JCI39104]

7) Epithelial-mesenchymal transition (EMT) EMT is normally used by cells early in embryogenesis and during wound healing.

I型EMT（上皮细胞-间质细胞转换）:胚胎发育;

发育异常，畸形（先天性瓣膜性心脏病）

II型EMT（上皮细胞-成纤维细胞转换）:创伤修复，瘢痕形成;

不愈合，过度愈合（纤维化性疾病）

III型EMT （肿瘤上皮-间质细胞转换）: 肿瘤侵袭转移;耐药，凋亡抵抗;干细胞样特征

EMT biomarkers

EMT Signaling Pathways

J. P. Thiery, H. Acloque, R. Y. Huang, M. A. Nieto, Cell 139, 871 (2009)

Z. Yu, Y. Li, H. Fan, Z. Liu, R. G. Pestell, Front Genet 3, 191 (2012)

4. Cancer stem cells(1) CSCs are tumor cells that have the principal properties: CSCs are rare tumor-initiating cells, seed new tumors (upon implantation in immunodeficient mice). self-renew as well as spawn more differentiated derivatives; these descendant cells form the great bulk

of many tumors. expression in CSC markers (also expressed by the normal stem cells in the tissue-of-origin). share transcriptional profiles with certain normal tissue stem cell populations. CSCs are metastatic cancer cells more resistant to various commonly used chemotherapeutic treatments, which help to explain the almost-

inevitable disease recurrence following apparently successful treatments. Their plasticity and dormancy correlates with their therapeutic resistance.

Cancer Cell Metastasis Cascade

(2) The origins of CSCs within a solid tumor have not been clarified and indeed may vary from one tumor type to another: Intrinsic CSCs and Induced CSCS.(3) the phenotypic plasticity operating within tumors may produce bidirectional interconversion between CSCs and non-CSCs.

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思考题1. 癌基因的概念、激活机制，举例说明癌基因激活与肿瘤发生发展的关系。

2. 抑癌基因的概念、失活机制，举例说明抑癌基因失活与肿瘤发生发展的关系。

3. 简述肿瘤侵袭和转移的基本过程、调控机制。

4. 肿瘤EMT的概念。

5. 肿瘤干细胞的概念。