Final answer:
Bcl-xL and other Bcl-2 family members are anti-apoptotic proteins that are up-regulated in cancer cells and allow them to resist cellular death. So the correct answer is Option D.
Step-by-step explanation:
The anti-apoptotic protein that is commonly up-regulated in cancer cells, allowing them to resist cellular death, is known as Bcl-xL and other Bcl-2 family members. These proteins are able to bind to apoptotic signaling molecules, preventing the apoptotic cascades from being initiated. For instance, Bcl-xL functions to inhibit the pro-apoptotic effects of molecules like Bax and Bak, which are critical for the release of cytochrome C from the mitochondria, an event that leads to apoptosis. If these events do not occur due to upregulation of anti-apoptotic proteins, cells can evade death and proliferate uncontrollably which is one of the hallmarks of cancer. This observation is buttressed by the finding that many tumor cells exhibit mutations in the p53 protein, which plays a critical role in the regulation of the cell cycle and can initiate apoptosis when DNA damage cannot be repaired.