ACTIVATING TRANSCRIPTION FACTOR-III STIMULATES 3',5'-CYCLIC ADENOSINEMONOPHOSPHATE-DEPENDENT GENE-EXPRESSION

Activating transcription factor-3 (ATF-3) is one member of a large fam ily of leucine zipper transcription factors which bind to promoters re sponsive to cAMP and phorbol ester at the related cAMP (CRE) and phorb ol eater response elements. We report here that ATF-3 is coexpressed w ith the neuropeptide precursor proenkephalin in human neuroblastoma SK -N-MC cells. Cotransfection experiments indicate that activation of pr oenkephalin gene expression by ATF-3 is dependent upon both the cataly tic subunit of the cAMP-dependent protein kinase and the CRE-2 element . The CRE-2 element is essential for second messenger-inducible expres sion and is known to bind AP-1-like transcription factors. ATF-3 expre ssed in;bacteria or from rabbit reticulocyte lysates binds to the proe nkephalin CRE-2 element as a homodimer and as a heterodimer with Jun-D , another activator of proenkephalin transcription. ATF-3 stimulates b inding of Jun-D to the proenkephalin CRE-2 element and acts synergisti cally with Jun-D to induce proenkephalin gene expression. Sequential i mmunoprecipations of ATF-3 from SK-N-MC cells expressing proenkephalin indicate that ATF-3 is complexed with Jun-D in vivo and that both pro teins are highly phosphorylated. Together, our results;suggest that AT F-3 may play an important role in the regulation of gene expression by cAMP-dependent intracellular signaling pathways.