GSK3B and cardiac hypertrophy: Phosphorylative activation of the transcription factor cAMP response element binding (CREB) protein at serine 133, a major event in the propagation of cAMP-PKA signaling to the nucleus, was not affected by NR4A2 overexpression, nor was the inhibitory phosphorylation of glycogen synthase kinase-3β (GSK-3β) at serine 9, a potent inhibitory mechanism of cardiac hypertrophy (Fig. 4, A and B).