inal answer:
Cancer cells may not stop dividing when growth factor is depleted due to mutation in apoptosis signaling, loss of receptor for apoptosis-inducing ligand, or overexpression of a growth factor pathway.
Step-by-step explanation:
Cancer cells do not stop dividing when growth factor is depleted due to a variety of hypotheses:
- Mutation in apoptosis signaling: Cells may have a mutation that prevents the initiation of apoptosis signaling, which is the natural process of programmed cell death. Without apoptosis, the cells continue to divide unchecked.
- Loss of receptor for apoptosis-inducing ligand: Another hypothesis is that the cells have lost expression of the receptor for the apoptosis-inducing ligand, rendering them insensitive to signals that would normally trigger cell death.
- Overexpression of a growth factor pathway: It is also possible that the cells overexpress a growth factor pathway that inhibits apoptosis. This pathway could override the usual cell cycle checkpoints and allow the cells to keep dividing.
Some hypotheses about why cancer cells do not stop dividing when growth factor is depleted include inherited genetic abnormalities that disrupt the function of the cell cycle's 'stop' and 'go' signals, environmental factors that cause DNA damage, and the dysfunction of apoptotic mechanisms. Mutations in genes like p53 can prevent cells from arresting the cell cycle, leading to uncontrolled division. Furthermore, cancer cells can lack proper intercellular communication, due to deficiencies in gap junctions and adherence molecules like cadherens and integrins, which allow them to ignore normal growth-constraining signals from their environment and neighboring cells.
These hypotheses highlight the complex nature of cancer cell behavior and the multiple mechanisms that may contribute to their uncontrolled division.