AKAP12 and AKAP5 form higher-order hetero-oligomers

Affinity chromatography using immobilized AKAPs as "bait" demonstrates unequivocally that AKAP5 and AKAP12 do form minimally hetero-dimers. Steric-exclusion chromatography of AKAP5 and AKAP12 mixtures revealed the existence of very large, supermolecular complexes containing both AKAPs. Docking of AKAP5 to AKAP12 was increased 4-fold by beta-adrenergic agonist stimulation. Overexpression of AKAP12 was found to potentiate AKAP5-mediated Erk1/2 activation in response to stimulation with beta-adrenergic agonist.AKAP5 and AKAP12 are capable of forming hetero-oligomeric supermolecular complexes that influence AKAP locale and function.Scaffold proteins have emerged as essential elements of cell signaling, providing docking sites at which protein kinases, phosphoprotein phosphatases, G-protein-linked receptors/ion channels can interact. An important subset of scaffold molecules possesses a docking site for the regulatory subunits (i.e., RI/RII) of cyclic AMP-dependent protein kinase A (PKA, A-kinase), termed A-kinase-anchoring proteins (AKAP) intimately involved in cellular signaling [1-4]. AKAPs dock PKA, acting as well as molecular "tool boxes" reflecting multivalency and the ability to dock other signaling proteins, including a full range of protein kinases (e.g., PKA, protein kinase C [5-8], and the tyrosine kinases [9]), phosphoprotein phosphatases (e.g., protein phosphatase 2B (PP2B) [5,10], cyclic AMP phosphodiesterases (e.g., PDE4) [11-14], adaptor molecules [11,13,15,16], ion channels [17-20], and members of the superfamily of G protein-coupled receptors (GPCR) [21-23]. AKAP5 and AKAP12, for example, associates with the prototypic GPCR, the β2-adrenergic receptor [23]. To what extent these AKAPs associate with other members of the GPCR superfamily is not known. The AKAPs that do dock GPCRs have been one of the major foci of AKAP research [23-26].In 2003 we first reported the oligomerization of AKAPs [27], noting that AKAP12 oligomers were SDS-resistant and could on