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 (K(d) ~ 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.