A NOVEL LIPID-ANCHORED A-KINASE ANCHORING PROTEIN FACILITATES CAMP-RESPONSIVE MEMBRANE EVENTS

Compartmentalization of protein kinases with substrates is a mechanism that may promote specificity of intracellular phosphorylation events. We have cloned a low-molecular weight A-kinase Anchoring Protein, cal led AKAP18, which targets the cAMP-dependent protein kinase (PKA) to t he plasma membrane, and permits functional coupling to the L-type calc ium channel. Membrane anchoring is mediated by the first 10 amino acid s of AKAP18, and involves residues Gly1, Cys4 and Cys5 which are lipid -modified through myristoylation and dual palmitoylation, respectively . Transient transfection of AKAP18 into HEK-293 cells expressing the c ardiac L-type Ca2+ channel promoted a 34 +/- 9% increase in cAMP-respo nsive Ca2+ currents. In contrast, a targeting-deficient mutant of AKAP 18 had no effect on Ca2+ currents in response to the application of a cAMP analog. Further studies demonstrate that AKAP18 facilitates GLP-1 -mediated insulin secretion in a pancreatic beta cell line (RINm5F), s uggesting that membrane anchoring of the kinase participates in physio logically relevant cAMP-responsive events that may involve ion channel activation.