If damage to the cell cannot be repaired, the tumor suppressor protein p53 can induce apoptosis through the intrinsic apoptosis pathway. In this pathway, p53 can upregulate the expression of pro-apoptotic proteins of the Bcl-2 family, such as Bax and Puma, which induce the release of cytochrome c from the mitochondria and activate caspase enzymes leading to apoptosis. The extrinsic apoptosis pathway, on the other hand, is initiated by the binding of extracellular death ligands to death receptors on the cell surface, which activate caspases through the recruitment of adaptor proteins. However, p53 does not directly activate the extrinsic apoptosis pathway, and its role in this pathway is still a subject of research.