1. Genetics Of Cancer Regulation of cell proliferation and cancer
Oncogenes and Tumor Suppressor Genes identified by turmorigenic viruses
Oncogenes identified by DNA transfection experiments
Tumor suppressor genes revealed by hereditary cancers
Multiple mutations are required for cancer cell formation

2. Terminology Cancer – abnormal, rapidly growing, cells
Malignant cancer – Named by tissue of origin: Sarcomas – bone, muscle, connective tissue; Carcinomas – epithelial tissue; Leukemia – blood; Lymphoma – lymphatic
Two Types of mutations that contribute to cancer cell phenotype:
Oncogenes – gain of function in genes that promote cell proliferation
positive regulators of proliferation
cell cycle genes
differentiation genes
negative regulator of apoptosis (cell death)
Tumor suppressor genes – loss of function in genes that inhibit cell proliferation
negative regulators of proliferation (cell cycle, differentiation)
activators of apoptosis
regulators of genomic integrity
DNA Repair genes
cell cycle checkpoints
Cancer can be sporadic (no family history) or hereditary (inherited pre-disposition)

3. Positive-acting signaling pathways controlling cell proliferation

4. Negative-acting signaling pathways controlling cell proliferation

5. Mutations in signaling pathways increasing cell proliferation

6. Regulation of Cell Proliferation: Cell Cycle Control
Cdk4/Cyclin D
Cdk4/Cyclin D
Cell Proliferation
Signals
Most non-proliferating cells are in G0
At end of mitosis, cells enter either G0 in the absence of cell proliferation signals
G0 is similar to G1 in proliferating cells except that genes required for S phase are not expressed
Regulation is at the level of regulation of transcription
The decision to divide or not is made here for most mammalian cells
Regulation of G0 to G1 and G1 to S altered in many cancers
Cdk4/Cyclin D, Rb and E2F are key regulators of G0 to G1 to S and are mutated in many cancers
Positive-acting regulators: Cdk4/Cyclin D, E2F, Cdk2/Cyclin A
Negative-acting regulators: Rb, inhibitors of Cdk4/Cyclin D
Cdk2/Cyclin A
DNA polymerases
Etc…

7. Regulation of Cell Proliferation: Proliferation Signaling Pathways
Similar to figure
15-13 in text
Positive-acting regulators: SH2 proteins Receptor Tyrosine Kianse (Sev), SH2/SH3 adaptor (Drk), GNRP (aka GEF) SOS, Ras
Negative-acting regulators: Ras GAP
Activation of MAP Kinases
Transcription of Genes that
Promote Cell Proliferation

8. Regulation of Cell Proliferation: Cell Cycle Checkpoint Pathways
Cdk4
Cyclin D
Negative-acting regulators of cell proliferation: p53, p21

9. Regulation of Cell Proliferation: Apoptosis Signalling Pathways
Activation
Of Apoptosis
Bcl-2
Inhibition
Of Apoptosis
Positive-acting regulators of apoptosis: Fas Ligand, Fas Receptor, Apaf, Caspase proteases
Negative-acting regulator of apoptosis: Cell Survival Receptor, Bcl-2
Apoptosis

13. Discovery of Oncogenes and Proto-oncogenes in animal RNA tumor viruses
Formation of RNA
Tumor Viruses:
WT RNA virus
Integrate into
host genome
Pick up part
of host proto-
oncogene
RNA tumor virus
with oncogene
V-erbB: constitutively active because of loss of regulatory domains
Other functions intact (signaling)
Positive-acting pathway for survival and proliferation
Contributes to loss of control of cell proliferation
Proto-oncogene to oncogene: gain of function mutation
- hypermorph or neomorph

14. Retroviral Oncogenes and Tumors
Rous sarcoma virus
- First oncogene…
Mechanisms of gain of function mutations include:
Loss of regulatory domains
Other mutations in coding sequence
Increase in copy number
Increase in transcription levels
not a kinase…

15. Identification of Human Oncogenes by DNA Transfection Experiments
Tumor Cell DNA + Rodent Fibroblasts
ID transformed cells by colony = loss of
contact inhibition = transformed phenotype
Rodent colony DNA + Rodent Fibroblasts
After several passages, screen transformed
Rodent colony DNA with Human Alu DNA
Human DNA contains oncogene
N-ras discovered by this procedure

16. Ras and the Ras Oncogene
Mutation in coding sequence causing gain of function: constitutively active Ras
Constitutively activated pathway promoting cell survival and proliferation

17. Discovery of Oncogenes by Translocations
Philadelphia Chromosome – t(9;22)(q34;q11)
Chronic myelogenous leukemia (CML)
First defined translocation associated with cancer
Protein fusion ; BCR::ABL (break point cluster gene::ABL protein kinase)
Other leukemias caused by translocation that fuse strong promoters to regulatory genes:
Fusion to bcl-2 – anti-apoptosis… (next slide)
Fusion to cyclin D1 – positive cell cycle regulator
Abl kinase is now constitutively active, promoting cell survival and proliferation

18. Discovery of Oncogenes by Translocations
B-cell lymphomas
Gene Fusion: Antibody gene enhancer fused to bcl-2 promoter and transcribed region

19. Discover of Tumor Suppressor by Hereditary forms of Cancer
Autosomal dominant mutation
Mapped to Rb locus, gene cloned and studied – this is why we know about regulation of G1 to S in mammals
Dominant due to Loss of Heterozygocity:
Recessive at the level of the cell – heterozygotes are wild type
Dominant at the level of the organism
Wild type allele is lost by one of several mechanisms (two slides ahead)
Highly Penetrant (almost 100%) with obvious familial basis

20. Retinoblastoma also occurs sporadically
Requires two mutations
Less frequent
Note: mechanism for tumor promotion by some DNA tumor viruses involved inactivation of Rb:
DNA Tumor Viruses Transforming Genes (transformation = loss of growth control)
Human papilloma virus (HPV) E7 protein = transforming gene
E7 binds and inactivates pRB
Some associated with cervical cancer
Risk of tumor promotion in HPV virus types correlates with strength of E7 binding to pRB binding

21. Mechanisms for LOH ND = nondisjunction
NDR = nondisj + reduplication of remaining chromosome
REC = recombination
Other = point mutations, deletions, gene conversions (both Rb alleles identical)

22. Multiple mutations are required for conversion of normal cell to cancer cell
Development of cancer from colon polyps involves a series of
Mutations
Inheritance of Mutations in APC gene increase risk of colon cancer
Common sequence of mutations:
LOH for APC: mutation of RAS; LOH for p53; others; malignancy
Familial Adenomatous polyposis or Adenomatous Polyposis Coli
Hundreds of polyps in colon by young adulthood (as opposed to HNPCC)
Linked to cytological defect at 5q = APC gene
APC gene codes for 300kD beta-catenin, which is involved in cell to cell contact
LOH for APC is associated with development of malignant tumors from benign polyps
APC, p53 = tumor suppressor genes
HNPCC = hereditary non polyposis colon cancer
Inherited mutation in DNA mismatch repair genes
Promotes mutation that lead to colon cancer, other cancers…