Exam 3
CH10 – IMMORTALITY
• Senescence (= cell no longer proliferating = protection against cancer)
Transformation – overexpression of oncogene or Large T Ag or loss of tumor suppressor can cause
transformation
Immortalization – (in addition to gaining oncogene/losing tumor suppressor cells no longer lose
telomeres through re-expression of hTER) caused by loss of telomere making cells go into crisis but
before hTERT is express so cell does not die instead it can still divide indefinitely
To cause cancer, cells must escape senescence
- What’s the replicative capacity of human cells? → culture in vitro and determine how
many cell doublings by serial passaging until they become senescent
→ Pre-senescent fibroblasts: vigorous growth, cytoplasm not expanded
→ Senescent fibroblasts: cease proliferating. Cytoplasms with “fried egg” appearance/spread out,
flatten out
- AGE: Loss of proliferative capacity with Age mean population doubling gets lower)
Aging skin: ability to regenerate declines with age (keratinocyte layer things and ridge architecture is
lost (young tissue has deeper ridges, where stem cells are located)
- Embryonic stem cells and cancer cells, both divide indefinitely (“immortal”)
- 2 Theories of how cells keep track of divisions:
1. Measurement of cumulative stress (too much O2, ROS, nutrient depravations, heat/chemical stress,
etc)
2. Measurement telomere shortening
- MARKERS OF SENESCENCE:
p21, p16, p53 → increase with population doubling (may impose the senescent state as they inhibit
cell cycle progression by inhibiting cyclin kinases/CDKs)
Overexpression of p16 demonstrated that induced senescence of young cells when overexpressed.
SV40 Large T Ag requires both the p53 and Rb binding domains (to inhibit them) to transform cells
(state of unregulated growth/loss of senescence)
- SENESCENCE CAN PROMOTE CANCER
SASP (Senescence-associated secretory phenotype) → cells entering senscense early secreted
pro-inflammatory cytokines (SASPs) that may promote cancer
Senolytic drugs that kill senescent cells are being studied as anticancer therapy.
• Telomeric shortening and crisis
Telomere loss leads normal cells to senescence but transformed cells escape this (by for ex)
expressions of Large T Ag) and keep dividing until massive DNA damage occurs due to loss of
telomeres→ cell undergo crisis → either apoptose or become immortalized
- TRF (telomeric restriction fragments) assay to determine telomere length (add digestive
enzyme that digest al genomic DNA except telomeres and then run a gel to see telomere
length)
, - Telomeres made of 6 bp repeats (TTAGGG) & 3’ overhang
• Chromosomal breakage-fusion-bridge cycles
- CRISIS = CHROMOSOMAL END-TO-END FUSION OR BREAKAGE-FUSION-BRIDGE
CYCLES
•
•Mechanisms of telomere shortening → DNA replication occurs 5’→3’ and RNA primers
are required. The leading strand (5’→3’) replicates fully while the lagging strand (3’-->5’) gets
shorter after every replication (bc of last RNA primer not being replicated)
• Telomerase and immortalization
Telomerase (hTERT catalytic subunit*, hTR RNA subunit and 5 other subunits) extends
telomeres in 6 nt increments (expressed in embryos and stems cells and lost during
differentiation, but re-expressed in immortalized cells)
experiment: HEK cells treated with hTERT-expressing virus = cells maintain telomere length
*only component of the enzyme that requires re-expression
CH11 – MULTISTEP TUMORGENESIS
• Tumors form over a lifespan
- Cancer incidence rises with age (seems to decrease after 75 yr)
- 3 decade delay from the start of cigarette smoking
• “Genetic biographies” of cancer
CH10 – IMMORTALITY
• Senescence (= cell no longer proliferating = protection against cancer)
Transformation – overexpression of oncogene or Large T Ag or loss of tumor suppressor can cause
transformation
Immortalization – (in addition to gaining oncogene/losing tumor suppressor cells no longer lose
telomeres through re-expression of hTER) caused by loss of telomere making cells go into crisis but
before hTERT is express so cell does not die instead it can still divide indefinitely
To cause cancer, cells must escape senescence
- What’s the replicative capacity of human cells? → culture in vitro and determine how
many cell doublings by serial passaging until they become senescent
→ Pre-senescent fibroblasts: vigorous growth, cytoplasm not expanded
→ Senescent fibroblasts: cease proliferating. Cytoplasms with “fried egg” appearance/spread out,
flatten out
- AGE: Loss of proliferative capacity with Age mean population doubling gets lower)
Aging skin: ability to regenerate declines with age (keratinocyte layer things and ridge architecture is
lost (young tissue has deeper ridges, where stem cells are located)
- Embryonic stem cells and cancer cells, both divide indefinitely (“immortal”)
- 2 Theories of how cells keep track of divisions:
1. Measurement of cumulative stress (too much O2, ROS, nutrient depravations, heat/chemical stress,
etc)
2. Measurement telomere shortening
- MARKERS OF SENESCENCE:
p21, p16, p53 → increase with population doubling (may impose the senescent state as they inhibit
cell cycle progression by inhibiting cyclin kinases/CDKs)
Overexpression of p16 demonstrated that induced senescence of young cells when overexpressed.
SV40 Large T Ag requires both the p53 and Rb binding domains (to inhibit them) to transform cells
(state of unregulated growth/loss of senescence)
- SENESCENCE CAN PROMOTE CANCER
SASP (Senescence-associated secretory phenotype) → cells entering senscense early secreted
pro-inflammatory cytokines (SASPs) that may promote cancer
Senolytic drugs that kill senescent cells are being studied as anticancer therapy.
• Telomeric shortening and crisis
Telomere loss leads normal cells to senescence but transformed cells escape this (by for ex)
expressions of Large T Ag) and keep dividing until massive DNA damage occurs due to loss of
telomeres→ cell undergo crisis → either apoptose or become immortalized
- TRF (telomeric restriction fragments) assay to determine telomere length (add digestive
enzyme that digest al genomic DNA except telomeres and then run a gel to see telomere
length)
, - Telomeres made of 6 bp repeats (TTAGGG) & 3’ overhang
• Chromosomal breakage-fusion-bridge cycles
- CRISIS = CHROMOSOMAL END-TO-END FUSION OR BREAKAGE-FUSION-BRIDGE
CYCLES
•
•Mechanisms of telomere shortening → DNA replication occurs 5’→3’ and RNA primers
are required. The leading strand (5’→3’) replicates fully while the lagging strand (3’-->5’) gets
shorter after every replication (bc of last RNA primer not being replicated)
• Telomerase and immortalization
Telomerase (hTERT catalytic subunit*, hTR RNA subunit and 5 other subunits) extends
telomeres in 6 nt increments (expressed in embryos and stems cells and lost during
differentiation, but re-expressed in immortalized cells)
experiment: HEK cells treated with hTERT-expressing virus = cells maintain telomere length
*only component of the enzyme that requires re-expression
CH11 – MULTISTEP TUMORGENESIS
• Tumors form over a lifespan
- Cancer incidence rises with age (seems to decrease after 75 yr)
- 3 decade delay from the start of cigarette smoking
• “Genetic biographies” of cancer
