Inhibitor of Apoptosis is

Ref Robbins 9/e p55; Robbins 7/e p29 Conversely, if cells are exposed to growth factors and other survival signals, they synthesize anti-apoptotic members of the Bcl-2 family, the two main ones of which are Bcl-2 itself and Bcl-xL. These proteins antagonize Bax and Bak, and thus limit the escape of the mitochondrial pro-apoptotic proteins. Cells deprived of growth factors not only activate the pro-apoptotic Bax and Bak but also show reduced levels of Bcl-2 and Bcl-xL, thus fuher tilting the balance toward death. The mitochondrial pathway seems to be the pathway that is responsible for apoptosis in most situa- tions, as we discuss later.