Phosphorylation-dependent Association of PDE3A1 with SERCA2 and its Regulation of SERCA2 Activity in Human Myocardium

PDE3 regulates cAMP‐mediated signaling in the heart. Studies in mice showed that PDE3A is associated with SERCA2, PLB and AKAP18 in a signaling complex in the SR that regulates inotropic responses. Immunohistochemical studies demonstrate that PDE3A is co‐localized in Z‐bands of human cardiomyocytes with desmin, SERCA2, PLB and AKAP18. In SR fractions, cAMP or rPKAc increased PLB phosphorylation and SERCA2 activity; this was potentiated specifically by PDE3 inhibition. During S6 chromatography of solubilized SR membranes, PDE3 activity was recovered in high‐ and low‐molecular‐weight (HMW, LMW) peaks. HMW peaks contained PDE3A1 and PDE3A2, while LMW contained PDE3A1, PDE3A2 and PDE3A3; PDE3A1 was the principal PKA‐phosphorylated isoform. Phosphorylation by rPKAc increased cAMP‐hydrolytic activity, shifted PDE3A from LMW to HMW peaks and increased the co‐IP of PDE3A with SERCA2 and AKAP18. Phosphorylation of rPDE3A by rPKAc increased co‐IP of rSERCA2 and rAKAP18. S292/S293, a site unique to PDE3A1, was identified by alanine substitutions as the principal site regulating this interaction. Phosphorylation of PDE3A1 at this site thus promotes its incorporation into SERCA2/AKAP18 signalosomes, where it regulates contractility by modulating phosphorylation‐dependent protein‐protein interactions, PLB phosphorylation and SERCA2 activity. Agents capable of blocking this interaction and increasing myocardial contractility may constitute a novel therapeutic approach for heart failure.