Regulation of PKA binding to AKAPs in the heart - Alterations in human heart failure

Background - cAMP-dependent protein kinase (PKA) regulates a broad range of cellular responses in the cardiac myocyte. Downstream regulation of the PK A pathway is mediated by a class of scaffolding proteins called A-kinase an choring proteins (AKAPs), which sequester PKA to specific subcellular locat ions through binding to its regulatory subunit (R). However, the effect of RU: autophosphorylation on AKAP binding and the degree of RII autophosphory lation in failing and nonfailing human hearts remains unknown. Methods and Results-We investigated AKAP-RII binding by overlay analysis an d surface plasmon resonance spectroscopy and measured RII autophosphorylati on in human hearts by backphosphorylation. Binding of Ht31 peptide (represe nting the RII-binding region of AKAPs) to cardiac RII was increased approxi mate to 145% (P<0.01) for autophosphorylated Ra: relative to unphosphorylat ed control. By surface plasmon resonance, RII autophosphorylation significa ntly increased binding affinity to Ht31 by approximate to 200% (P<0.01). Ba seline PKA-dependent phosphorylation of RII was significantly decreased app roximate to 30% (P<0.05) in human hearts with dilated cardiomyopathy compar ed with nonfailing controls. Conclusions-These results suggest that AKAP binding of PKA in the heart is regulated by RII autophosphorylation. Therefore AKAP targeting of PKA may b e reduced; in patients with end-stage heart failure; This mechanism may be responsible for the decreased cAMP-dependent phosphorylation of proteins in dilated cardiomyopathy that we and others have previously observed.