Phosphorylation of the cAMP Response Element-binding Protein and Activation of Transcription by α1 Adrenergic Receptors

Abstract Activation of α1 adrenergic receptors not only stimulates smooth muscle contraction but also modifies gene expression. We wondered if α1 adrenergic receptors could activate transcription of genes regulated by the cAMP response element-binding protein (CREB). Using Rat1 cells stably transfected with each of the three cloned human α1adrenergic receptor subtypes, norepinephrine strongly stimulated CREB phosphorylation in α1A and α1B but more weakly in α1D-transfected cells. Norepinephrine increased the activity of a somatostatin cAMP-regulated enhancer-chloramphenicol acetyltransferase reporter in these cells. α1 adrenergic receptors are known to activate protein kinase C (PKC) and increase [Ca2+ ]i. Nonetheless, neither GF109203X, a PKC inhibitor, nor BAPTA-AM, a calcium chelator, blocked phosphorylation of CREB induced by norepinephrine. In addition, α1adrenergic receptor-induced CREB phosphorylation was not mediated via the mitogen-activated protein kinase pathway because norepinephrine did not stimulate mitogen-activated protein kinase activity in these cells. Activation of α1 adrenergic receptors increased cAMP accumulation in these cells. Norepinephrine-induced cAMP-regulated enhancer-chloramphenicol acetyltransferase activity was inhibited either by expression of the PKA inhibitory peptide or a dominant negative PKA regulatory subunit mutant. These results demonstrate that α1 adrenergic receptors activate the transcription factor CREB by a PKA-dependent pathway.