benign vs malignant
benign: cells that're undergiong uncontrolled proliferation but that doesn't manifest in disease
malignant: cells with unlimited cell renewal and result in what is generally considered to be cancer
cells w/ a finite lifespan, finite ability to grow, that are directly removed from the organism
cells with unlimited life span, capable of growing indefinitely
immortalized cells that've gained some (lab-measurable) properties, including anchorage-independency or failure to stop growing upon contact w/ other cells - properties make it resemble a cancer cell
transformed cells that have ability to form a tumor
determine this by doing an assay for tumor formation
properties of cancer cells?
1) epithelial to mesenchymal morphology
2) altered metabolism
3) unlimited cell renewal; are immortal
4) anchorage independent
5) proliferate even when in contact w/ other cells
6) grow independent of growth factors
7) changes in ploidy
morphology of cancer cells?
changes from normal epithelial to mesenchymal, spindle-shaped, fibroblast cell type
appears refractile in light microscope due to cytoskeletal changes including actin depolymerization
how is cancer cell metabolism altered?
they rely on glycolysis for their ATP production, whereas normal cells use TCA cycle for ATP
why do cancer cells rely on an inefficient form of ATP production for their energy?
1) cancer cells grow in hypoxic environment; get their oxygen from glycolysis; have intrinsic property of enhanced glycolytic rate
2) use TCA cycle components to make amino acids, ntds, fatty acids that cancer cells need to make more of themselves
what is cancer cells' potential?
thus considered immortalized
how do normal vs cancer cells proliferate?
normal epithelial or mesenchymal cells require anchorage to proliferate; cancer cells are anchorage independent for growth b/c do not need to activate the ERK pathway, upregulate Cyclin D, in order to proliferate
what is "contact inhibition" re: normal vs. cancer cells?
epithelial cells are restrained in their growth when they come into contact with another cell
cancer cells lose contact inhibition; so they proliferate even when they are touching adjacent cells
growth factors' importance to normal vs. cancer cells?
growth factors trigger the ERK pathway, lead to Cyclin D upregulation. normal cells need this for transcriptional upregulation of Cyclin D to enter cell cycle, divide
cancer cells grow in a manner independent of growth factors b/c can upreglate ERK pathway independent of Cyclin D
how does retinoblastoma circumvent growth factors for its growth?
Rb normally prevents cell cycle progression by binding to E2F, preventing turning on of E2F target genes
In retinoblastoma, a cell that mutates/loses Rb has an unrestrained E2F; so can do transcription absent of signaling
what is cancer cell re: ploidy?
aneuploid, could be gain or loss of genetic material due to deletions, gene amplification, chromosomal translocation
have something other than 4N
what is metastasis?
cancer cells acquire ability to recruit blood vessels or cause angiogenesis in order to grow as a tumor
to enter bloodstream, travel to distant sites within organism, tumor cells become invasive
this ability to seed at distant sites is metastasis
what did fibroblasts growing in culture show?
1) senescence: they were seen to have a finite life span, to stop proliferating after a certain period of time when they had depleted pRb and p53, and this was an M1 event, senescence
2) lacking telomerase: fibroblasts continued to proliferate after M1 until an M2 event or crisis, due to no telomerase expression, so stopped growing
restoration of telomerase expression allowed them to continue to grow indefinitely
what is the appearance of senescent cells?
how are they visualizable?
huge, flat, "fried egg" look
they express an acidic form of Beta-galactosidase that's detectable at a low pH by using a colorimetric assay in which senescent cells stain blue
bottom image is senescent fibroblast cells, top is normal fibroblasts
what is the definition of senescence, vs. quiescence?
senescence: irreversible cell cycle arrest
whereas quiescence: reversible cell cycle arrest
what causes replicative senescence?
what is the basis of senescence re: telomere shortening?
telomeres protect chroosomes from being viewed by the cell as DNA damage, by forming a t-loop at the end of the chromosome
with each round of replication, telomeres shorten, some DNA repeats are lost; eventually, becomes so short, cannot form a T loop
when telomeres shorten so much they cannot form t-loop, cell perceives DNA damage, activates p53 pathway -> senescence
when does p53 pathway get activated? what if it was lost?
p53 activated when telomeres shorten enough that they cannot form t-loops
cell perceives these as DNA damage, activates p53 pathway, which causes senescence
if p53 is deleted, cells continue to proliferate and telomeres continue to shorten; eventually, chromosomes lose coding regions, undergoes a crisis
what causes premature senescence?
prolonged DNA damage or other forms of stress
cells can undergo senescence by activation of p53 by means other than telomere shortening
stresses such as sustianed DNA damage that cannot be repaired, or activation of specific oncogene pathways, trigger p53-dependent senescence
how can a cell exit a crisis re: telomeres?
how do cancer cells do telomere maintenance?
1) telomerase expression is re-activated; in most cells
2) ALT cells, a telomerase-independent method, do homologous recombination of telomeric DNA; in 10-20% of cells
how is ALT dependence shown experimentally?
ALT cell is proven if can show that a cell can exit a crisis even with a telomerase inhibitor added to culture, i.e. TERT