Schwaninger M, Blume R, Oetjen E, Lux G, Knepel W
Department of Biochemical Pharmacology, University of Göttingen, Germany.
J Biol Chem. 1993 Nov 5;268(31):23111-5.
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.
环磷酸腺苷反应元件（CRE）及其同源转录因子CREB可介导基因转录的诱导，以响应膜去极化和钙内流。在本研究中，通过转染报告基因融合体，在胰岛细胞系中研究了环孢素A（CsA）和FK506对去极化诱导的胰高血糖素基因转录的影响。CsA和FK506抑制去极化诱导的胰高血糖素基因转录，FK506比CsA更有效。CsA/FK506反应性由胰高血糖素CRE介导，也由促性腺激素和生长抑素基因中特征明确的CRE介导。雷帕霉素拮抗FK506的抑制作用，但不拮抗CsA的抑制作用，提示FK506和CsA可能通过与不同的细胞内亲免素形成复合物而发挥作用。已知受药物-亲免素复合物抑制的钙调神经磷酸酶的过表达使胰岛细胞对CsA和FK506的抑制作用更具抗性。这些结果证明了CsA和FK506对CRE介导的、钙诱导的转录的抑制作用，并提示膜去极化依赖钙调神经磷酸酶的磷酸酶活性来激活CREB/CRE介导的基因转录。对CRE介导的基因转录的干扰代表了CsA/FK506作用的一种新机制，这可能是这些强效免疫抑制药物的药理作用和毒性表现的基础。
