The intrinsic pathway is tightly regulated by the balance between pro-apoptotic and anti-apoptotic members of the Bcl-2 family. Anti-apoptotic proteins such as Bcl-2 and Bcl-xL oppose the action of Bax and Bak, preventing the release of cytochrome c. The tumor suppressor protein p53 also plays a significant role in the regulation of the intrinsic pathway by modulating the expression of Bcl-2 family proteins in response to cellular stress.
