Glycogen Synthase Kinase-3β Plays a Pro-Apoptotic Role in β-Adrenergic Receptor-Stimulated Apoptosis in Adult Rat Ventricular Myocytes: Role of β1 Integrins

β-adrenergic receptor (β-AR) stimulation induces apoptosis in adult rat ventricular myocytes (ARVM). β1 integrin signaling plays a protective role in β-AR-stimulated apoptosis. Glycogen synthase kinase-3β (GSK-3β), a multifunctional serine/threonine kinase, negatively regulates cardiac hypertrophy. Here we show that β-AR stimulation (isoproterenol; 15 min) increases tyr216 phosphorylation and GSK-3β activity. Inclusion of LiCl, inhibitor of GSK-3β, in the reaction mix or expression of catalytically inactive GSK-3β (KM-GSK) inhibited β-AR-stimulated GSK-3β activity. Inhibition of tyrosine kinase using genistein or chelation of intracellular Ca2+ using BAPTA-AM inhibited β-AR-stimulated increases in tyr216 phosphorylation and GSK-3β activity. Inhibition of GSK-3β using pharmacological inhibitors or infection with KM-GSK decreased β-AR-stimulated cytosolic cytochrome C release and apoptosis. Expression of β1 integrins increased ser9 phosphorylation and inhibited β-AR-stimulated increase in GSK-3β activity. Wortmannin, inhibitor of PI3-kinase, reversed the effects of β1 integrins on GSK-3β activity and apoptosis. Purified active matrix metalloproteinase-2 (MMP-2), shown to interfere with β1 integrin signaling, increased GSK-3β activity, while inhibition of MMP-2 inhibited β-AR-stimulated increases in GSK-3β activity. β-AR stimulation induced nuclear accumulation of GSK-3β. β-AR stimulation (3 h) increased the expression of transcription factor Gadd153 (growth arrest- and DNA damage-inducible gene 153). These data suggest that β-AR stimulation increases GSK-3β activity. Activation of GSK-3β plays a pro-apoptotic role in β-AR-stimulated apoptosis via the involvement of mitochondrial death pathway. β1 integrins inactivate GSK-3β and play an anti-apoptotic role via the involvement of PI3-kinase pathway. The apoptotic effects of GSK-3β may be mediated, at least in part, via its nuclear localization and induction of pro-apoptotic genes, such as Gadd153.