The immunosuppressive drugs cyclosporin A and tacrolimus inhibit membrane depolarization‐induced CREB transcriptional activity at the coactivator level

1 Cyclosporin A and tacrolimus are clinically important immunosuppressive drugs directly targeting the transcription factor nuclear factor of activated T cells (NFAT). Through inhibition of calcineurin phosphatase activity they block the dephosphorylation and thus activation of NFAT. Cyclosporin A and tacrolimus also inhibit other calcineurin‐dependent transcription factors including the ubiquitously expressed cAMP response element‐binding protein (CREB). Membrane depolarization by phosphorylating CREB on Ser119 leads to the recruitment of its coactivator CREB‐binding protein (CBP) that stimulates initiation of transcription. 2 It was unknown at what step in CREB‐mediated transcription cyclosporin A and tacrolimus interfere. 3 In transient transfection experiments, using GAL4‐CREB fusion proteins and a pancreatic islet β‐cell line, cyclosporin A inhibited depolarization‐induced activation of CREB proteins which carried various deletions or mutations throughout their sequence providing no evidence for the existence of a distinct CREB domain conferring cyclosporin A sensitivity. In a mammalian two‐hybrid assay, cyclosporin A did not inhibit Ser119‐dependent interaction of CREB with its coactivator CBP. 4 Using GAL4‐CBP fusion proteins, cyclosporin A inhibited depolarization‐induced CBP activity, with cyclosporin A‐sensitive domains mapped to both the N‐ (aa 1–451) and C‐terminal (aa 2040–2305) ends of CBP. The depolarization‐induced transcriptional activity of the CBP C‐terminus was enhanced by overexpression of calcineurin and was inhibited by cyclosporin A and tacrolimus in a concentration‐dependent manner with IC50 values (10 and 1 nM, respectively) consistent with their known IC50 values for inhibition of calcineurin. 5 These data suggest that, in contrast to NFAT, cyclosporin A and tacrolimus inhibit CREB transcriptional activity at the coactivator level. British Journal of Pharmacology (2005) 144, 982–993. doi:10.1038/sj.bjp.0706127