Final answer:
The p53 protein promotes tumor formation by inhibiting apoptosis when mutated, is a pivotal component of the cellular system that prevents uncontrolled cell division, and its mutation is linked with many human cancers.
Step-by-step explanation:
The protein that promotes tumor formation by inhibiting apoptosis and is a member of a larger family of about 20 proteins is the p53 protein. This protein serves a vital role in maintaining cellular integrity by regulating the cell cycle and promoting apoptosis when DNA damage is detected. Mutations in the tumor suppressor gene that codes for p53, known as TP53 in humans, are associated with a significant number of human cancers. The presence of mutated p53 can lead to a lack of proper cellular regulation, allowing for uncontrolled cell proliferation, which is a hallmark of cancer. The p53 protein, along with other proteins like Rb and p21, operates as part of a complex network of tumor suppressors that act as a checkpoint system to prevent the propagation of damaged cells and ensure proper cellular function.