Abstract
The transcription factor cAMP response element-binding protein (CREB) promotes target DNA transcription in response to cellular stimulation in brain neurons. Phosphorylation of CREB is regulated by a variety of extracellular and intracellular signals. In this study, protein kinase C (PKC)-regulated CREB phosphorylation was investigated in cultured rat striatal neurons. We found that PKC activation with phorbol 12-myristate 13-acetate (PMA) produced a rapid and transient phosphorylation of CREB. The increase in CREB phosphorylation was dose-dependent and prevented by the two PKC selective inhibitors (chelerythrine and Gö6983). Interestingly, the PMA-induced CREB phosphorylation was also blocked by a calcium/calmodulin-dependent protein kinase inhibitor KN93 and the two mitogen-activated protein kinase (MAPK) kinase inhibitors PD98059 and U0126, but not by a p38 MAPK inhibitor SB203580. PMA activation of PKC markedly increased phosphorylation of MAPK/extracellular signal-regulated kinase 1/2. The protein kinase A (PKA) inhibitor H89 at a dose that completely blocked the PKA activator (8-br-cAMP)-induced CREB phosphorylation partially blocked the PMA-stimulated CREB phosphorylation. Furthermore, blockade of NMDA and AMPA glutamate receptors and L-type voltage-operated Ca(2+) channels did not alter the ability of PMA to induce CREB phosphorylation. These results demonstrate that PKC is among the protein kinases that can positively modulate CREB phosphorylation in striatal neurons, and the PKC signals to CREB activation are mediated via signaling mechanisms involving multiple downstream protein kinases.