The mechanism by which the calcium influx signal, triggered by membrane depolarization, is transduced to the nucleus to activate c-fos proto-oncogene transcription has been characterized. A calcium response element (CaRE) that is indistinguishable from a CAMP response element (CRE) mediates transcriptional inducibility by depolarization. Its cognate transcription factor CREB is the target for both calcium and CAMP signals. CREB is rapidly phosphorylated in response to depolarization or cAMP, at a site known to be important for the transcriptional activating function of this protein. The convergent effects of calcium and CAMP on CREB activation are mediated by distinct protein kinase signaling pathways. CREB and its binding site, the Ca/CRE, can thus function as a regulatory element that integrates both calcium and cAMP signals in the control of gene expression.
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