f13 Bio314 Chap 2

BIO 314 Cancer Biology

• Welcome!• Syllabus• -schedule, textbook, etc• Chapter 2: The Nature of Cancer

GENERAL INFORMATION: BIO 314 section 01 SESSIONS: Tues & Thurs, 1:00 – 2:20 in Javits 100Course director and instructor:

Susan Erster PhDDept of Biochemistry and Cell BiologyLife Sciences Bldg, Rm 316632-8562

[email protected] Office hours: TBA

Course teaching assistants: UGTA’s & grad TA’s will post office hours, contact info on

Blackboard

mailto:[email protected]

• COURSE MATERIALS: • “The Biology of Cancer”, R.A. Weinberg, Garland Science, 2006 or

2007 (2 different printings of first (and only) edition.)

• Robert A. Weinberg, PhD• Member, Whitehead Institute

Professor of Biology, MIThttp://wi.mit.edu/research/faculty/weinberg.html

• A Founding Member of Whitehead Institute, Robert A. Weinberg is a pioneer in cancer research most widely known for his discoveries of the first human oncogene—a gene that causes normal cells to form tumors—and the first tumor suppressor gene. His lab now primarily focuses on two areas: the interactions between epithelial and stromal cells (the two major types of cells found in mammalian tissue) that produce carcinomas and the processes by which cancer cells invade and metastasize.

• Dr. Weinberg is the author or editor of five books and more than 325 articles. His three most recent books, intended for a lay audience, are "One Renegade Cell", "Racing to the Beginning of the Road: The Search for the Origin of Cancer" and "Genes and the Biology of Cancer," co-authored with Dr. Harold E. Varmus, former Director of the National Institutes of Health.

http://wi.mit.edu/research/faculty/weinberg.html

• EXAMS AND GRADES:• There will be 4 midterm exams. 1, 2 and 3 will be given

during class time, the 4th will be given during our scheduled final exam time. There is no cumulative final exam in this course

• Midterm 1: Thu Sep 26th

• Midterm 2: Tue Oct 22rd

• Midterm 3: Thu Nov 14th

• Midterm 4: Mon Dec 16th 5:30-8:00 PM

• The lowest of the 4 midterm grades will be dropped. Your course grade will be determined by the average of your 3 highest midterms. If you miss an exam, that will count as your dropped grade. No makeup exams will be offered.

The Biology of CancerFirst Edition

Chapter 2:The Nature of Cancer

Copyright © Garland Science 2007

Robert A. Weinberg

The Nature of Cancer• Normal differentiated cells are carefully programmed to

participate in the construction of all tissue types required for survival

• Differentiated cells are “plastic”; they still contain the entire genome for directions, and most have the ability to grow and divide (essential to replace damaged, worn out cells)

• Risk: cell may inadvertently “reactivate” a gene expression program, or genes themselves may have been altered by mutation.

2.1 Tumors arise from normal tissues

– Cell theory– Tumors are composed of cells, and are derived from the

tissue in which they are discovered

• Tumors arise from cells that have lost the ability to assemble and create tissue of normal form and function– Tumors are classified by their tissue of origin, and by their

degree of aggressive growth

Figure 2.2a The Biology of Cancer (© Garland Science 2007)

Tumors metastasize: spread to anatomical sites distant from where disease began (primary site)

Normal mouse lung melanoma metastases after injection

Figure 2.2b The Biology of Cancer (© Garland Science 2007)

colon carcinoma metastases

Liver (brown-bile pigments)

Benign (non-invasive)Malignant (invasive, metastatic)

90% of cancer deaths are attributed to metastases

2.2 Tumors arise from many specialized cell types throughout the body

• Most (90%) human tumors are of epithelial origin (carcinomas)

• What is an epithelium, and how does it contribute to tissue formation?

• Epithelia: (sheet-like lining; secretion, protection, absorption, permeability)

• Basement membrane: (its not really a membrane; a better title is basal lamina): specialized ECM meshwork (collagens, laminins, proteoglycans)

• Stroma: connective tissue provides bulk, support, mobility.

Table 2.1 The Biology of Cancer (© Garland Science 2007)

Most cancers and cancer deaths result from cancers that originate in epithelial cells. These cancers are called carcinomasEpithelial cells derive from all three germ layers (ectoderm, mesoderm, and endoderm)Some epithelial cells are protective, like skin, others have complex functions such assecretion (hormones, milk, tears) absorption (gut) reception (light, sound), barrier between 2 compartmentsEpithelial cells are to a multicellular organism what the plasma membrane is to a single-celled organism

Protective epitheliaSecretive epithelia

Figure 20-18 Essential Cell Biology (© Garland Science 2010)

Squamous: flattened surface is ideal for passive transport. (if stratified, protective)Cuboidal: specialized junctions for communication, secretionColumnar: tallest; often have structural and/or functional polarity (secretion, absorption, ion transport, enzyme activity, receptivity, communication)

Epithelial Cells


Epithelial cells are polarized with free apical side and basal side, which is typically attached to connective tissue through specialized ECM (extra cellular matrix) called basal lamina. An example of polarization is the absorptive cells in gut epithelium, which import food molecules from the lumen on apical side, and export food molecules to underlying tissue on basal side.

Figure 20-23a, b Essential Cell Biology (© Garland Science 2010)

Epithelial cell junctions: tight junctions seal cells together, prevent leakage, formed by proteins called claudins and occludins

Tight Junctions


Adherens junctions and desmosomes bind epithelial cells to one another. Both adherens junctions and desmosomes require Transmembrane proteins called cadherins.

Adherens Junctions and Desmosomes


Adherens junction: cadherins are attached by linker molecules to the actin microfilaments of the cytoskeleton

Figure 20-27b Essential Cell Biology (© Garland Science 2010)

At the desmosome, cadherins connect to intermediate filaments such as keratins.This gives the epithelia strength, seen in exposed epithelia such as skin.


Hemi-desmosomes anchor keratin filaments of epithelial cell to the basal lamina.

Hemi-desmosomes

2.2 Tumors arise from many specialized cell types throughout the body

• Most (90%) human tumors are of epithelial origin (carcinomas)• What is an epithelium, and how does it contribute to tissue

formation?• Epithelia: (sheet-like lining; secretion, protection, absorption,

permeability)• Basement membrane: (its not really a membrane; a better title is

basal lamina): specialized ECM meshwork (collagens, laminins, proteoglycans) secreted by epithelial cells. Adheres to and organizes epithelial layer. Interacts with epithelial cell surface receptors.

• Stroma: Connective tissue includes tendons, bone, and cartilage, • gives strength, binds cells together, flexibility, and mobility.


In connective tissue (stroma), tensile strength comes from a family of fibrous proteins called collagens. The cells that produce collagen and live in connective tissue are called fibroblasts.


Cells organize the collagen they secrete. Collagen fibers can be oriented crosswise (here) or parallel (previous slide)

Space fillers in matrix are proteoglycans, extracellular proteins linked to negatively charged polysaccharides known as glycosaminoglycans

Figure 20-14c Essential Cell Biology (© Garland Science 2010)

The cells don’t attach directly to collagen, they attach to fibronectin, which attaches to cells and also to collagen.

Integrin attaches to fibronectin and also to cytoskeleton (next slide)

Integrins undergo conformational changes that allow them to transmit mechanical and chemical signals (signal transduction), important in proliferation, adhesion, migration, etc.

EXTRACELLULAR FLUID

Fibronectin

Micro-filaments

CYTOPLASM

Plasmamembrane

The extracellular matrix (ECM)

2.4 Cancers seem to develop progressively

• Gradations between fully normal and clearly malignant• These are cells that are evolving (ie selection) towards

more aggressive and invasive phenotypes

From L. J. Kleinsmith, Principles of Cancer Biology. Copyright (c) 2006 Pearson Benjamin Cummings.

Four major types of new tissue growth


epithelial

Stroma (mesenchymal):connective tissue cells ie fibroblasts, adipocytes, withincollagen matrix

Histology: fixation, dehydration, paraffin embed, sectioning, dewaxing, H+E staining (H = blue, DNA, E = pink, protein)

Normal

Figure 2.12a The Biology of Cancer (© Garland Science 2007)

Hyperplastic: normal in appearance but increased number


Hyperplastic: mammary gland ductal epithelium invades lumen, but not basement membrane or stroma

• Dysplastic: transition between benign and pre-malignant• Cells are now cytologically abnormal, specifically, less

differentiated and more proliferative


invasive ductalcarcinoma

Neoplastic (Invasive = malignant =carcinoma)

Figure 2.17 The Biology of Cancer (© Garland Science 2007)

2.5 Tumors are monoclonal growths

All the cells in the tumor derive from a single “deranged” cell


All of the cancer cells descend from the progenitor cell in which the translocation occurred

Translocation: yellow represents a portion of a non-homologous chromosome

Tumors are monoclonal

But…cancers develop over decades, and cancer cells areinherently genetically unstable, so although observationssuch as these support the monoclonal origin of tumors,they are not rigorous proof.

2.6 Cancers occur with different frequencies in different human populations

• Over a human lifetime, ~1016 cells are formed.• Each has the potential to give rise to a tumor, should disaster

strike.• Of the ~100 types of cancers, some occur with comparable

frequencies (incidence) in various human populations, while the frequencies of other cancers vary widely.

• Obvious factors contributing to variable cancer incidence are genetics and environment• Genetics: variable frequency of cancer susceptibility alleles in

different populations• Environment: air and water, lifestyle (diet, occupation, habits, etc)


2.7 The risks of cancers are often increased by lifestyle: Studies of cancer rates in migrant populations minimize genetic component

Japan

Observe differencebetween green andyellow

Early evidence of connections between lifestyle/exposure and certain cancers:

• 1760’s: tobacco and nasal cancer• Early 1800’s: miners and lung cancer• abstinence (convents) and breast cancer • 1940’s-1950’s: cigarette smoke, asbestos and lung cancer

2.8 Specific chemical agents can induce cancer

In 1915, Yamagiwa induced cancers in rabbits ears by repeatedly “painting” them with carcinogens derived from coal tars

Provided experimental systemsfor research


Carcinogenic (in lab mice) hydrocarbons found in coal tar, result from incomplete combustion of organic compounds.


Almost ¾ of cancers in US have lifestyle component; only 1-2% have occupational component.


Dose-response relationship between cigarette smoking and lung cancer


Correlation between meat consumption and colon cancer


Estimate of cancer deaths attributed to different environmental causes

2.9 Exploring the mutagen-carcinogen connection• The Ames test is used to detect potential carcinogenic properties of all new

compounds including drugs, biocides (pesticides, etc)• The easiest mutation to detect is one that changes the growth properties of

cells (ie bacteria)• Many mutations have been identified in the his operon of the bacteria

Salmonella. • The his operon encodes gene products required for the biosynthesis of the

amino acid histidine. The test strain are his mutants. His mutants cannot synthesize histidine. They cannot grow on minimal media, they can only grow in media that is supplemented with histidine.

• When these strains are exposed to mutagens, additional mutations occur that re-activate the his operon, allowing for growth in the absence of histidine. Simply put, if a compound is mutagenic, exposure will lead to more bacterial growth on minimal media.

Mortelmans, K., and Zeiger, E. (2000) Mutation Research vol 455, p29-60 on blackboard

More sophisticated tests take into account the fact that potential carcinogens are “processed” by various metabolic pathways, so the compound that our cells are exposed to may be different from the one we ingested/inhaled/absorbed. Sometimes these are referred to as pro-carcinogens and true (or ultimate) carcinogens

So, before exposing the test compound to bacteria, it is “activated” by exposure to mammalian extracts (mostly liver, which is the main detoxifying organ).

For example, oxidative activating systems will turn aromatic amines or polycyclic aromatic hydrocarbons into more electrophilic forms, which will attack DNA.

Reductive systems mimic the reducing activity of anaerobic intestinal microbes, these will reduce azo (R-N=N-R)compounds (frequent in dyes) to amines.


The Ames test (1975): Mutagens = carcinogens

“pro-carcinogensvs. ultimate carcinogens”


Mutagenicity in bacteria correlates with tumorigenicity in lab mice


Plants have developed toxins to avoid predation by animals and insects.Many of these are potentially mutagenic. BUT…Metabolic conversions in GI tract and then in liver?Metabolic pathways in different cell types?Concentrated in cells or quickly excreted?

Classifying carcinogens:

International Agency for Research on Cancer (IARC)Registry of known and suspected human carcinogens based on epidemiology and short-term tests (such as Ames test).

National Toxicology Program (NTP)Long term cancer studies, on animals, of known hazardous chemicals with high human exposure.

The classes of carcinogens and their mechanism of action will also be discussed later in the semester.

Epidemiology:Descriptive epidemiology: health records and cause of death to determine incidence and mortalityAnalytical epidemiology: to determine relative risk associated with a given factor (ie exposure to some carcinogen)*Retrospective (case-control); individuals with and without cancer are compared*Prospective (cohort); follow healthy, well-defined population for years, look for factors that correlate with outcome ($, contact)Bias and confounding factors: selection bias (in choosing a good control group) recall bias (cancer patients are more likely to recall past events that may have contributed) confounding factors (red meat vs fat content? OC vs behavior? Positive outlook vs favorable prognosis?)Meta-analysis: Combines data from multiple studies.

adapted from “Cancer Biology” 2006

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