Announcements

• Correction: same assay for pluripotency can be used for adult stem cells as for ES cells.

• Wednesday, April 25: cell biology of cancer, pp. 762-770, 775-789

• Friday, April 27, 9 AM: optional review session• Monday, April 30, 8 AM: final exam

– 139 points; 90 points from days 34-43; 49 points cumulative (days 1-43).

Positions of Presidential contenders on ES cell research

• From Nature, 19 April, 2007• New policy could easily be put into law by

executive order.• Republicans:

– Brownback: opposes– Giuliani: won’t say– Romney: supported as governor of MA; now opposes– McCain: supports

• Democrats:– Clinton, Obama, Edwards support

Day 43 Outline/Objectives

A. Cell biology of cancer1. Features of cancer cells2. Stages of tumor progression3. Oncogenes and tumor

suppressor genes

B. SOS

After reading the text, attending lecture, and reviewing lecture notes, you should be able to:

• Discuss the two features of cancer cells: (1) unregulated cell proliferation and (2) ability to spread.

• Compare an contrast the properties of transformed versus non-transformed cells.

• Compare and contrast the properties of oncogenes and tumor suppressor genes, giving examples of each.

Cancer cells defined by

1. Ability to proliferate uncontrollably• Causes tumor formation• Angiogenesis feeds the tumor• Cancer cells increase secretion of angiogenesis

activators and decrease angiogenesis inhibitors

2. Ability to spread through the body.• Invasion: cancer cells migrate into surrounding

tissues, blood vessels• Metastasis: cancer cells spread through circulatory

system to establish secondary tumors.

Normal versus tumor growth in skin

• Cancer cells don’t necessarily divide faster than normal cells.

• Normal: Rates of cell division and differentiation balanced.

• Tumor: Balance of cell division and cell differentiation favors cell division.

Normal and transformed cell properties

Normal cells• Regulated growth

– Dependent on GF’s– Subject to cycle cycle control

• Anchorage-dependent• Contact inhibited (density-

dependent)• Subject to apoptosis• Flattened cells, normal

nuclei, normal chromosome number

Transformed (cancer) cells• Uncontrolled growth

– Independent of GF’s– Don’t obey checkpoints

• Anchorage-independent• Loss of contact inhibition >

pile up in culture• Escape apoptosis

pathways• Rounded cells, large nuclei,

abnormal chromosome number

Stages in Process of Metastasis

1. ↓ E-cadherin, ↑ motility, ↑ proteases, which digest basal lamina.

2. In blood most cancer cells die but some that survive and reproduce well are selected.

3. Metastases form at preferential sites, based on

a. origin and blood flow pattarns• Most organs > lungs• Stomach, colon > liver

b. Molecular interactions• E.g. prostate cancer cells

respond to growth factors secreted by bone cells

Tumor Progression:Evolution at the Cellular Level

Benign tumor (polyp in epithelial cells) is confined

by basal lamina; then additional mutation occurs.

Malignant tumor (carcinoma in epithelial cells) grows very fast, becomes invasive, and metastasizes.

Causes of Cancer1. Inherited or spontaneous gene mutations2. Chemicals (carcinogens) → mutations in DNA

– Either directly or after activation in liver– E.g. chemicals in tobacco smoke

3. Ionizing and ultraviolet radiation → mutations in DNA– Ionizing radiation removes electrons, generating reactive ions

that cause DNA damage– UV radiation causes pyrimidine dimer formation in DNA

4. Viruses and other infectious agents → tissue damage or introduction of cancer-causing genes (oncogenes)– Less common– Epstein-Barr virus > Burkitt’s lymphoma– Hepatitis B and C viruses > liver cancer– Human papillomavirus > cervical cancer

Oncogenes and Tumor Suppressors

Proto-oncogene• Normal gene (c-onc)

involved in cell proliferation.

• Gain-of-function, dominant mutation creates an oncogene (onc), which causes cancer.

• 1 mutant copy (heterozygous condition) is sufficient to cause cancer.

Tumor Suppressor• Gene which normally acts

to suppress cell proliferation.

• Loss-of-function, recessive mutation in tumor suppressor gene causes cancer.

• 2 mutant copies are necessary to cause cancer.

Discovery of oncogenes:Transforming retroviruses and src

• Discovered by Harold Varmus and M. Bishop, 1975-76 (Nobel Prize, 1989).

• A transforming retrovirus:– cancer-causing single-stranded RNA virus– Uses reverse transcriptase enzyme to make ssDNA,

then dsDNA, which integrates into host DNA.– Note: not all retroviruses are TRV’s, most oncogenes

not caused by TRV’s.

• Varmus and Bishop studied Rous Sarcoma Virus (RSV) in chickens, which carried gene called src:

Southern Blots Probed with viral src Gene Revealed Cellular Origin of OncogenesInfected chicken #1 Infected chicken #2 Uninfected chicken

DNA DNA DNA (Negative Control)

c-srcProto-oncogeneSURPRISE!

v-src

Origin of Transforming Retroviruses

Capsid protein Reverse Transcriptase Envelope Protein

Mutation creates oncogene

Cancers Usually Result from a Series of Mutations in a Single Cell

• Development of colon cancer:

oncogene Tumor suppressorsoncogene

SOS II InstructionsBIO 324, ID hertz1pl, CRN 22008085,

A. Please use only a pencil and erase thoroughly if you change a response.

B. The Course Designator Number for this class is BIO 324.C. The CMU Faculty ID for this class is hertz1pl. Please enter this

alpha/numeric code in the section titled “CMU Faculty User ID.”D. The Course Reference Number for this class is 22008085. Enter this

5-digit number in the section titled “Course Reference Number.”E. Please mark the appropriate response to the remaining questions. If

you do not have an opinion with regard to any question, please leave the response to the question blank. When finished, return the completed survey to the front of the class.

F. You may express your personal reactions to this class on the accompanying “Individual Opinions” sheet that is provided for this purpose. Please include the section number in the space provided.

G. Please answer the following additional questions:9. The instructor has stimulated my thinking.10. I have needed to work hard to achieve success in this course.