MOLECULAR BIOLOGY OF NEOPLASIA I & II

Question 1

List the phenotypic hallmarks of cancer.

Answer 1

• Dysregulation of cell proliferation by constitutive activation of growth-stimulatory pathways
o CML & Philadelphia chromosome
• T(9,22) fuses proto-oncogene c-able with bcr
• Enhanced tyrosine kinases active & abnormal cellular localization
• Gleevec: Inhibitor molecule
• Limitless replicative potential
o Cells in culture have a finite replicative potential
• Senescence can be circumvented by disabling pRb & p53
o Telomeres
• Sign of number or replication
• Telomerase
• Upregulated in neoplasia
• Telomerase only resent in germ cells and stem cells
• Yet many tumors have stable telomeres
• Angiogenesis
o See below
• Invasion
o See below
• Metatstasis
o See below

Question 2

List the three classes of genes involved in cancer

Answer 2

• Growth promotes
• Growth suppressors
• Caretakes
o DNA repair enzymes

Further differentiation
•	Oncogene & proto-oncogenes
•	Tumor suppressor genes
•	Pro or anti-apoptotic proteins
•	Immortalization of gene

Question 3

Describe the types of proteins encoded by oncogenes and their mechanisms of action

Answer 3

• Signal transduction molecules
o Non-receptor protein-tyrosine kinases
o Cytoplasmic serine\threonin kinases
o GTP-binding proteins
• Ras is the
• Inactive ras bind GDP, and can the replace GDP with GTP
• Activate MAP kinase
• Ras has a GTPase
• GTPase inactive so get chronic signaling
• 1 of 2 changes in 3 amino acids

Question 4

Describe how tumor suppressor genes exert their functions, and how loss of heterozygosity relates to a defect in tumor suppressor function.

Answer 4

• Insensitivity to growth inhibitory signals
o Tumor suppressor genes: Inhibit cell proliferation
o Deletion of genetic material common in solid tumors
• Loss of hetrozygocity (see only 1 band instead of 2
• Non-disjunction
• Nondystjunction and duplication
• Mototoc recombination
• Gene coversion
o Two hit hypothesis
• Heredity Rb developed in families most often
• Born with one good copy but acquire mutations on normal cells
o Tumor Suppressor Genes
• Cell cycle checkpoints
• Rb inhibits G1/S restriction point
• Cyclin-Dependent Kinase Inhibitors
o CDKIp16INK4a induce G1 cell cycle arrest by inhibiting CDK4 & 6
• P53 (see below)
• Viral oncogenes
oTransforming sequences not derived from cellular gene
o Proteins that complex with and inactivate TSGs
o HPV
• Caretaker Genes
o DNA repair genes
o BRCA1, 2 or P or HNPCC

Question 5

Describe how the proteins Rb and p53 function to regulate cell proliferation.

Answer 5

• Rb phosphorylation allows cell cycle to pass through G1 to S check point
• P53 (Dominate Negative Mutations)
o Cell cycle arrest & apoptosis in response in DNA damage
o P53 activation triggered by DNA damage stress
o P21 upregulated and blocks cells cycle
o Time for damage to be resolved
o If DNA damage cannot be repaired = apoptosis (Bax protein)
o Responsible for resistance to chemotherapy
• Evasion of apoptosis
o Two pathways for apoptosis
• Intrinsic (Mitochondrial Pathway)
• P53 activate BAX
• Bax binds outer membrane of mitochondria
• Release of cytochrome C
• BCL2 anti-apotpotic
o Overexpression commonly seen in lymyphoma
• Extrinsic (dearth receptor initiated pathway)
• Cytotoxic T. lymphocytes

Question 6

Describe mechanisms by which tumor cells evade apoptosis.

Answer 6

• Independence of apoptosis
• Dysregulation of apoptosis
• Resistance to hypoxia, XRT & chemotherapy
• Anchorage independence
• BCL2 is anti-apoptotic in independent pathway
o Upregulated in follicular lymphomas
• Telomeres
o Sign of number or replication
o Telomerase
• Upregulated in neoplasia
• Telomerase only resent in germ cells and stem cells
• Yet many tumors have stable telomeres

Question 7

Explain senescence and immortalization and the mechanisms by which tumor cells avoid “crisis”.

Answer 7

• Senescence: Stop replication after a finite number of replications
• Immortalization: Evasion of senescence by disabling pRb and p53

Question 8

Explain the role of angiogenesis in tumor formation.

Answer 8

• Growth over 1 mm tumor must have its own blood supply
• Ratio of VEGF to anti-angiogenetic agents
• Angiogenesis Inhibitors can inhibit tumor growth
o Angiostatin
o Endostatin

Question 9

Define the steps that lead to tumor metastasis.

Answer 9

•	Loss of cell-cell cohesion (cadherins)
   o	Can signal increase proliferation
•	Loss of cell-extracellular matrix attachments (Integrins)
•	Matrix degradation
•	Matrix metalloproteinase
•	Collagenase
•	Cell motility
•	Vascular Extraversion
•	Metastasis is angiogenesis dependent
•	Proliferation in new foreign environment
•	Drug targets
     o	Anti-adhesive Agents
     o	MMPs inhibitors
     o	Ant-motility

Question 10

Discuss the stages and molecular evolution of cancer involved in the development of neoplasia.

Answer 10

• Monoclonality & Clonal Evolution
o Development of cancer requires many mutations
o Begini tissue surrounding malignant tissue lacks all but 1 mutation found in tumor tissue
o Chromothripsis: Sudden massive changes without stepwise development (5% of tumors)
o Epigenetic changes (mythelation)

Discard
•	Tumor invade immune recognition
•	Genetic instability
•	Weinberg Hypothesis
      o	Generate many building blocks that support growth
      o	Grow so rapidly
      o	Use anaerobic glycolysis