The Akt-glycogen synthase kinase 3β pathway regulates transcription of atrial natriuretic factor induced by β-adrenergic receptor stimulation in cardiac myocytes

We examined the mechanism of atrial natriuretic factor (ANF) transcription by isoproterenol (ISO), an agonist for the beta-adrenergic receptor (beta AR), in cardiac myocytes. ISO only modestly activated members of the mitogen-activated protein kinase family. ISO-induced ANF transcription was not affected by inhibition of mitogen-activated protein kinases, whereas it was significantly inhibited by KN93, an inhibitor of Ca2+/calmodulin-dependent kinase (CaM kinase II). Production of 3'-phosphorylated phosphatidylinositides (3 phosphoinositides) was also required for ISO-induced ANF transcription. ISO caused phosphorylation (Ser-473) and activation of Akt through CaM kinase II- and 3 phosphoinositides-dependent mechanisms. Constitutively active Akt increased myocyte surface area, total protein content, and ANF expression, whereas dominant negative Akt blocked ISO-stimulated ANF transcription. ISO caused Ser-9 phosphorylation and decreased activities of GSK3 beta. Overexpression of GSK3 beta inhibited ANF transcription, which was reversed by ISO. ISO failed to reverse the inhibitory effect of GSK3 beta(S9A), an Akt-insensitive mutant. Kinase-inactive GSK3 beta increased ANF transcription. Cyclosporin A partially inhibited ISO-stimulated ANF transcription, indicating that calcineurin only partially mediates ANF transcription. These results suggest that both CaM kinase II and 3 phosphoinositides mediate beta AR-induced Akt activation and ANF transcription in cardiac myocytes. Furthermore, beta AR-stimulated ANF transcription is predominantly mediated by activation of Akt and subsequent phosphorylation/inhibition of GSK3 beta.