Spatial restriction of PDK1 activation cascades by anchoring to mAKAPα

The muscle A-kinase anchoring protein (mAKAP) tethers cAMP-dependent enzymes to perinuclear membranes of cardiornyocytes. We now demonstrate that two alternatively spliced forms of mAKAP are expressed: mAKAP alpha and mAKAP beta. The longer form, mAKAP alpha, is preferentially expressed in the brain. mAKAP beta is a shorter form of the anchoring protein that lacks the first 244 amino acids and is preferentially expressed in the heart. The unique amino terminus of mAKAP alpha can spatially restrict the activity of 3-phosphoinositide-dependent kinase-1 (PDK1). Biochemical and genetic analyses demonstrate that simultaneous recruitment of PDK1 and ERK onto mAKAP alpha facilitates activation and release of the downstream target p90RSK. The assembly of tissue-specific signaling complexes provides an efficient mechanism to integrate and relay lipid-mediated and mitogenic activated signals to the nucleus.