The muscle A-kinase anchoring protein (mAKAP) tethers cAMP-dependent enzymes to perinuclear membranes of cardiomyocytes. We now demonstrate that two alternatively spliced forms of mAKAP are expressed: mAKAPα and mAKAPβ. The longer form, mAKAPα, is preferentially expressed in the brain. mAKAPβ 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 mAKAPα 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 mAKAPα 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.