INHIBITION OF CAMP-RESPONSIVE ELEMENT-MEDIATED GENE-TRANSCRIPTION BY CYCLOSPORINE-A AND FK506 AFTER MEMBRANE DEPOLARIZATION

The cAMP-responsive element (CRE) and its cognate transcription factor CREB can mediate induction of gene transcription in response to membrane depolarization and calcium influx. In this study, the effect of cyclosporin A (CsA) and FK506 on depolarization-induced glucagon gene transcription was investigated in a pancreatic islet cell line by transfection of reporter fusion genes. CsA and FK506 inhibited depolarization-induced glucagon gene transcription, FK506 being more potent than CsA. CsA/FK506 responsiveness was mediated by the glucagon CRE and also by well characterized CREs of the choriogonadotropin and somatostatin genes. Rapamycin antagonized the inhibitory effect of FK506 but not CsA, suggesting that FK506 and CsA may act through complex formation with distinct intracellular immunophilins. Overexpression of calcineurin, which is known to be inhibited by drug-immunophilin complexes, rendered pancreatic islet cells more resistant to the inhibitory effects of CsA and FK506. These results demonstrate an inhibition by CsA and FK506 of CRE-mediated, calcium-induced transcription and suggest that membrane depolarization relies on calcineurin phosphatase activity for activation of CREB/CRE-mediated gene transcription. The interference with CRE-mediated gene transcription represents a novel mechanism of CsA/FK506 action, which may underlie pharmacological effects and toxic manifestations of these potent immunosuppressive drugs.