Human heart failure is accompanied by altered protein kinase A subunit expression and post-translational state

beta-Adrenergic receptor blockade reduces total mortality and all-cause hospitalizations in patients with heart failure (HF). Nonetheless, beta-blockade does not halt disease progression, suggesting that cAMP-dependent protein kinase (PICA) signaling downstream of p-adrenergic receptor activation may persist through unique post-translational states. In this study, human myocardial tissue was used to examine the state of PICA subunits. As expected, total myosin binding protein-C phosphorylation and Ser23/24 troponin I phosphorylation significantly decreased in HF. Examination of PICA subunits demonstrated no change in type II regulatory (RII alpha) or catalytic (C alpha) subunit expression, although site specific RII alpha (Ser96) and C alpha (Thr197) phosphorylation were increased in HF. Further, the expression of type I regulatory subunit (RI) was increased in HF. Isoelectric focusing of Rice demonstrated up to three variants, consistent with reports that Ser77 and Ser83 are in vivo phosphorylation sites. Western blots with site-specific monoclonal antibodies showed increased Ser83 phosphorylation in HF. 8-fluo-cAMP binding by wild type and phosphomimic Ser77 and Ser83 mutant RI alpha proteins demonstrated reduced Kd for the double mutant as compared to WT RI alpha. Therefore, failing myocardium displays altered expression and post-translational modification of PICA subunits that may impact downstream signaling. (C) 2013 Elsevier Inc. All rights reserved.