Molecular characterization of a cDNA that encodes six isoforms of a novel murine A kinase anchor protein.

We have cloned cDNA that encodes six novel A kinase anchor proteins (collectively named AKAP-KL). AKAP-KL diversity is generated by alternative mRNA splicing and utilization of two translation initiation codons. AKAP-KL polypeptides are evident in lung, kidney, and cerebellum, but are absent from many tissues. Different isoforms predominate in different tissues. Thus, AKAP-KL expression is differentially regulated in vivo. All AKAP-KL isoforms contain a 20-residue domain that avidly binds (Kd approximately 10 nM) regulatory subunits (RII) of protein kinase AII and is highly homologous with the RII tethering site in neuronal AKAP75. The distribution of AKAP-KL is strikingly asymmetric (polarized) in situ. Anchor protein accumulates near the inner, apical surface of highly polarized epithelium in tubules of nephrons. Both RII and AKAP-KL are enriched at an intracellular site that lies just below the plasma membrane of alveolar epithelial cells in lung. AKAP-KL interacts with and modulates the structure of the actin cytoskeleton in transfected cells. We also demonstrate that the tethering domain of AKAP-KL avidly ligates RII subunits in intact cells. AKAP-KL may be involved in (a) establishing polarity in signaling systems and (b) physically and functionally integrating PKAII isoforms with downstream effectors to capture, amplify, and precisely focus diffuse, trans-cellular signals carried by cAMP.