molecular biology of neoplasia II - lecture notes - julia

Question 1

review: what are the different mechansism by which a cell can undergo apoptosis?

Answer 1

• death receptor pathway
• fasL, TNF, TRAIL => activation of death receptors
• activates FADD
• activates caspase-8
• activates caspase-3
• apoptosis
• stress pathway
• bcl2 is inactivated and so stops inactivating Bax
• bax activates cyt c/apaf1 and omi/diablo
• ctyc/apaf-1 activate caspase 9
• omi/diablo inhibit IAP, which normally inhibits caspase 9 and casease 3,7
• caspase 9 activates caspase 3,7
• apoptosis

Question 2

what are some possible triggers of the stress pathway of apoptosis?

Answer 2

• chemo
• XRT
• hypoxia
• genetic damage
• GF or cytokine withdrawl
• loss of cohesion/adhesion

Question 3

what are modulators of the stress apoptosis pathway?

Answer 3

• Bcl-2/Bax family

Question 4

what is bcl-2? how is it involved in cancer?

Answer 4

• modulator of the stress pathway of apoptosis
• mitochondiral membrane protein that blocks apoptosis
• in follicular lymphomas, have a t(14;18) chromosomal translocation => abnormally high levels of bcl-2 protein => lack of normal apoptosis in response to abnormal cells

Question 5

how do normal and cancer cells differ in terms of senescence and immortalization?

Answer 5

• normal cells in culture have finite replicative potential
• senescence = after a certain number of replications, cells stop growing
• if a cell has disabled pRb and p53, senescence will be circumvented => cells continue replicating until enter crisis = massive cell death, karyotypic disarray, end-to-end fusion of chromsomes
• sometimes get variant cell that doesn’t go into crisis and can multiply without limit = immortialization

Question 6

how is telomerase involved in neoplasia?

Answer 6

• not present in most normal cells (except germ cells and stem cells)
• levels higher in malignant than benign neoplasms though some malignant neoplasms lack detectable telomerase activity (may be alternate methods of telomere stabilization or lengthening)

Question 7

what are the steps of new vessel growth into an new area?

Answer 7

1. perivascular detatchment and vessel dilation
2. onset of angiogenic sprouting
3. continuous sprouting - new vessel formation and maturation, recruitment of perivascular cells
4. tumor vasculature is established

these vessels probably won’t appear perfectly normal because growth not that well regulated - perfectly functional though

Question 8

what controls angiogenesis?

Answer 8

• dependent on local ratio of angiogenic inducers (VEGF) to anti-angiogenic agents
• normally ratio is low - no vascular proliferation
• but angiogenic switch can occur and angiogenesis will occur

Question 9

what can cause an angiogenic switch? (5)

Answer 9

• physiologic circumstances
• wound healing
• normal development
• physiologic hyperplasia
• pathologic conditions
• tumorigenesis
• subclone develops ability to stimulate angiogenesis due to clonal progression

Question 10

what are factors that increase angiogenesis (inhibitors)?

Answer 10

• thrombospondin-1
• statins
• angiostatin
• endostatin
• canstatin
• turnstatin

Question 11

what things activate angiogenesis?

Answer 11

• vegfs
• fgfs
• pdgfb
• egf
• lpa

Question 12

how can angiogenesis be targeted in therapies for tumors?

Answer 12

• give with low dose standard cytotoxic therapy
• targets vascular endothelial cells
• regressed to dormant microscopic lesions with endostatin treatment even though tumor cells were proliferating but get high rate of apoptosis of tumor cells
• apparently these haven’t panned out in clinic though for “various reasons”…

Question 13

how many tumor cells metastasize?

Answer 13

• millions of tumor cells are shed into the circulation daily
• but only 1 in 10,000 survive to initiate a metastatic focus

Question 14

what are the steps in establishment of a metastatic focus? what must the tumor cells be able to do?

Answer 14

1. decreased cellular cohesion (dyscoheision - due to change in cadherins)
2. matrix degradation by release of MMPs, TIMPs
3. changes in cell-matrix attachments (changes in integrins)
4. cells must be able to break through the basement membrane and get through the vascular endothelium
5. must be able to evade the immune system, platelets, etc
6. must be able to adhere to the vessel wall
7. must be able to get out of the vessel (extravascation)
8. angiogenesis
9. proliferation

Question 15

what do cadherins do? how do they mediate cell-cell cohesion?

Answer 15

• mediate homotypic cell-cell interactions at adherens junctions
• complexed with cytoskeleton via catenins
• involved in signaling pathway that regulates cell proliferation, apoptosis, differentiation, and cell motility
• loss correlates with increased invasiveness and metastatic potential

Question 16

what do integrins do and how must they change for metastasis?

Answer 16

• transmembrane receptors for basement membrane components and other ECM molecules
• focal adhesion kinase pathways regulate apoptosis, proliferation, and cell motility
• tumor cells have integrin switching = altered integrin expression patterns =>
• decreases adhesion to the basement membrane
• increased adhesion to the ECM
• increased migration over the ECM

Question 17

what are some examples of proteins that integrins detect?

Answer 17

• collagens
• laminin
• tenascin
• fibronectin
• vitronectin

Question 18

what proteins are involved in matrix degradation? what is different in cancer tissue?

Answer 18

• proteolytic enzymes: matrix metalloproteinases (MMPs) and collagenases
• these destroy the local basement membrane and ECM to allow tumor cells to invade
• expression of tissue inhibitors of metalloproteinases (TIMPs) is down regulated in cancer

Question 19

what factors direct migration of tumor cells?

Answer 19

• autocrine and paracrine factors:
• growth factors (IGFs, FGFs, TGF-beta) - all stimulate tumor cell motility
• hepatocyte growth factor = ligand for c-met protooncogene
• cytokines (interleukin-8, histamine)
• extracellular matrix factors
• intact ECM molecules (vitronectin, fibronectin, laminin, type I collagen)
• fragments of ECM molecules released from the matrix by MMPs

Question 20

how can antiadhesive agents be targeted as a therapy for cancer?

Answer 20

• peptidomimetrics and monoclonal antibodies targeted at integrins
• antagonists of alphavbeta3 (vitaxin) induce vascular cell apoptosis and inhibit angiogenesis by blocking endothelial cell matrix interactions

Question 21

how can matrix metalloprteinase inhibitors be used theraputically in treatment of neoplasm?

Answer 21

• blocks degradation of matrix
• blocks action of proteases and growth factors
• have been found to have anti-invasive properties in vitro and anti-angiogenic properties in vivo

Question 22

how are anti-motility agents being used theraputically to treat neoplasm?

Answer 22

• taxanes block microtubule cycling
• inhibitor of ca influx is used (carboxyamido-triazole)

Question 23

what are typical genetic steps toward colon cancer development?

Answer 23

certain genes have a high probability of mutating at each definable stage of colon cancer progression

1. starts with loss of APC gene on chromosome 5 => small benign polyp
2. oncogenic mutation of ras gene on chromosme 12 => large benign polyp
3. loss of p53 on chromosome 17 and loss of a gene on chromosme 18 (possible DCC) => cancer

Question 24

what would be the genetic profile of the tissue surrounding a tumor?

Answer 24

• benign tissue around the malignant tissue frequently contains many of the same set of mutations found in the tumor but lacks at least one mutation that is found in the tumor tissue