The Bcl-2 family comprises a group of structurally related proteins that play a fundamental role in the regulation of the intrinsic pathway of apoptosis by controlling mitochondrial membrane permeability and the release of the pro-apoptotic factor, Cytochrome c. Bcl-2 family proteins are grouped into three classes: those that inhibit apoptosis (Bcl-2, Bcl-xL , Bcl-w, Mcl-1, Bcl-10, and Bcl-2 related protein A1); those that promote apoptosis (BAK, Bax, Bcl-rambo, Bcl-xS , and BOK/Mtd); and the pro-apoptotic BH3 domain only proteins that bind and regulate the anti-apoptotic Bcl-2 proteins (Bad, BID, Bik/Nbk, BIM, BLK, Bmf, Hrk/DP5). Bcl-2 and Bcl-xL inhibit apoptosis by binding to the pro-apoptotic Bax and BAK proteins. When cytoplasmic levels of free Bad protein increase in apoptotic cells, Bcl-2 and Bcl-xL bind to Bad and release Bax and BAK. Bax and BAK, or processed forms of these protein, can then insert into the mitochondrial membrane and cause the release of Cytochrome c. Cleavage of BID as a result of Caspase-8 or Caspase-10 activation also promotes Bax/BAK-mediated release of Cytochrome c. The activity of specific Bcl-2 family proteins can be assessed by monitoring their ability to promote or inhibit Cytochrome c release.
Assay Protocols for Bcl-2 Family Proteins