PDE4 and mAKAP? are nodal organizers of ?2-ARs nuclear PKA signalling in cardiac myocytes.

ABSTRACT: Aims:?1- and ?2-adrenergic receptors (?-ARs) produce different acute contractile effects on the heart partly because they impact on different cytosolic pools of cAMP-dependent protein kinase (PKA). They also exert different effects on gene expression but the underlying mechanisms remain unknown. The aim of this study was to understand the mechanisms by which ?1- and ?2-ARs regulate nuclear PKA activity in cardiomyocytes. Methods and results:We used cytoplasmic and nuclear targeted biosensors to examine cAMP signals and PKA activity in adult rat ventricular myocytes upon selective ?1- or ?2-ARs stimulation. Both ?1- and ?2-AR stimulation increased cAMP and activated PKA in the cytoplasm. Although the two receptors also increased cAMP in the nucleus, only ?1-ARs increased nuclear PKA activity and up-regulated the PKA target gene and pro-apoptotic factor, inducible cAMP early repressor (ICER). Inhibition of phosphodiesterase (PDE)4, but not Gi, PDE3, GRK2 nor caveolae disruption disclosed nuclear PKA activation and ICER induction by ?2-ARs. Both nuclear and cytoplasmic PKI prevented nuclear PKA activation and ICER induction by ?1-ARs, indicating that PKA activation outside the nucleus is required for subsequent nuclear PKA activation and ICER mRNA expression. Cytoplasmic PKI also blocked ICER induction by ?2-AR stimulation (with concomitant PDE4 inhibition). However, in this case nuclear PKI decreased ICER up-regulation by only 30%, indicating that other mechanisms are involved. Down-regulation of mAKAP? partially inhibited nuclear PKA activation upon ?1-AR stimulation, and drastically decreased nuclear PKA activation upon ?2-AR stimulation in the presence of PDE4 inhibition. Conclusions:?1- and ?2-ARs differentially regulate nuclear PKA activity and ICER expression in cardiomyocytes. PDE4 insulates a mAKAP?-targeted PKA pool at the nuclear envelope that prevents nuclear PKA activation upon ?2-AR stimulation.

SUBMITTER: Bedioune I 

PROVIDER: S-EPMC6106106 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature