Inhibition of GSK‐3 activates CREB transcriptional targets during induction of cardiomyocyte hypertrophy

Abstract

Glycogen synthase kinase 3 (GSK‐3) is strongly anti‐hypertrophic in heart, but is inhibited by growth factors and hypertrophic stimuli. Despite its known role as a central regulator of cardiac hypertrophy, the full transcription network downstream of GSK‐3 is poorly understood. We used a systems‐level approach to delineate the transcription program downstream of GSK‐3 in neonatal rat ventricular myocytes upon the induction of hypertrophy. We first identified a set of phenylephrine (PE) induced genes, and found that 14 of the PE‐induced genes were up‐regulated by direct inhibition of GSK‐3 alone. Computational analysis revealed that CREB binding sites were statistically over‐represented for the GSK‐3 regulated genes. CREB binds to the upstream sequences of 8 of the 12 genes tested by chromatin immunoprecipitation. Upon inhibition of GSK‐3, CBP was recruited to 6 of the eight genes that had CREB present. Direct inhibition of GSK‐3 also resulted in the phosphorylation of CREB on Ser 133, suggesting a role for GSK‐3 in CREB activation. Inhibition of GSK‐3 alone induced hypertrophy marker genes at 24 hours, but did not result in an increase in protein synthesis by 48 hours. Thus, inhibiting GSK‐3 alone is sufficient to induce a partial phenotype by inducing late gene changes characteristic of hypertrophy, but not to the full hypertrophic phenotype. Supported by American Heart Association Grant 0835284N (J.W.T.).