Phosphorylation and inactivation of BAD by mitochondria-anchored protein kinase A

Signaling pathways between cell surface receptors and the BCL-2 family of p roteins regulate cell death. Survival factors induce the phosphorylation an d inactivation of BAD, a proapoptotic member. Purification of BAD kinase(s) identified membrane-based cAMP-dependent protein kinase (PKA) as a BAD Ser -112 (S112) site-specific kinase. PKA-specific inhibitors blocked the IL-3- induced phosphorylation on S112 of endogenous BAD as well as mitochondria-b ased BAD S112 kinase activity. A blocking peptide that disrupts type II PKA holoenzyme association with A-kinase-anchoring proteins (AKAPs) also inhib ited BAD phosphorylation and eliminated the BAD S112 kinase activity at mit ochondria. Thus, the anchoring of PKA to mitochondria represents a focused subcellular kinase/substrate interaction that inactivates BAD at its target organelle in response to a survival factor.