The survival factor binds to a cell-surface receptor protein, thereby activating various intracellular signalling pathways. Some of these pathways lead to the activation of protein kinases that phosphorylate the Bad protein. Bad promotes apoptosis by binding to and inactivating apoptosis-inhibitor proteins such as Bcl-2. Once phosphorylated, Bad releases its bound Bcl-2 protein, which can now act to inhibit apoptosis. Thus, the survival factor suppresses apoptosis by keeping Bad phosphorylated and out of action.