PHOSPHORYLATION OF THE CAMP RESPONSE ELEMENT-BINDING PROTEIN AND ACTIVATION OF TRANSCRIPTION BY ALPHA(1) ADRENERGIC-RECEPTORS

Activation of alpha(1) adrenergic receptors not only stimulates smooth muscle contraction but also modifies gene expression. We wondered if alpha(1) adrenergic receptors could activate transcription of genes re gulated by the cAMP response element-binding protein (CREB). Using Rat 1 cells stably transfected with each of the three cloned human alpha(1 ) adrenergic receptor subtypes, norepinephrine strongly stimulated CRE B phosphorylation in alpha(1A) and alpha(1B) but more weakly in alpha( 1D)-transfected cells, Norepinephrine increased the activity of a soma tostatin cAMP-regulated enhancer-chloramphenicol acetyltransferase rep orter in these cells, alpha(1) adrenergic receptors are known to activ ate protein kinase C (PKC) and increase [Ca2+](i). Nonetheless, neithe r GF109203X a PKC inhibitor, nor BAPTA-AM, a calcium chelator, blocked phosphorylation of CREB induced by norepinephrine, In addition, alpha (1) adrenergic receptor-induced CREB phosphorylation was not mediated via the mitogen-activated protein kinase pathway because norepinephrin e did not stimulate mitogen-activated protein kinase activity in these cells. Activation of alpha(1) adrenergic receptors increased cAMP acc umulation in these cells. Norepinephrine-induced cAMP-regulated enhanc er-chloramphenicol acetyltransferase activity was inhibited either by expression of the PKA inhibitory peptide or a dominant negative PKA re gulatory subunit mutant. These results demonstrate that alpha(1) adren ergic receptors activate the transcription factor CREB by a PKA-depend ent pathway.