THE C-FOS CAMP-RESPONSE ELEMENT - REGULATION OF GENE-EXPRESSION BY A BETA-2-ADRENERGIC AGONIST, SERUM AND DNA METHYLATION

The transcription control region of the Proto-oncogene c-fos contains multiple cis-acting elements to which specific trans-acting factors bi nd. One such well-studied binding motif in the c-fos promoter is the m ajor cyclic AMP response element (CRE) TGACGT located at -62/-57. In t his study we investigated the role of this element in gene regulation by beta2-adrenergic/adenylate cyclase signalling and DNA methylation. By transient gene expression assays we were able to show that the c-fo s regulatory sequences spanning nucleotides -361 to +13 could mediate gene expression by the beta2-adrenergic agonist isoproterenol and the phosphodiesterase inhibitor theophylline. For isoproterenol however, a stimulating effect was observed in serum-starved cells, while an inhi bitory effect was measured in cells supplemented with serum. The gene regulation by the cAMP elevating agents could be due, at least partial ly, to the major CRE since this isolated motif mediated gene expressio n by these drugs. Distinct protein-DNA complexes were obtained with nu clear extracts prepared from cells exposed to isoproterenol or/and the ophylline under different serum conditions. We further show that DNA m ethylation of this CRE may also be involved in gene regulation as meth ylation of the CRE motif strongly reduced the binding of nuclear prote ins.