title: Only in the presence of immunophilins can cyclosporin and FK506 disrupt in vivo binding of calcineurin A to its autoinhibitory domain yet strengthen interaction between calcineurin A and B subunits.
abstract: The two immunosuppressants cyclosporin A (CsA) and FK506 exert their major therapeutic effect by inhibiting T-cell activation. It is believed that the drugs first bind to their cellular receptors, known as immunophilins, and then target the protein phosphatase calcineurin for inhibition. The catalytic activity of calcineurin is regulated by its autoinhibitory domain (AID) and by the calcium-binding proteins calcineurin B (CnB) and calmodulin. We have used the yeast two-hybrid system to show that AID, CnB and calmodulin can only bind to a truncated catalytic subunit of yeast calcineurin (i.e.,CnA1 delta), devoid of AID, but not to full-length CnA1. Both CsA and FK506 cause disruption of the CnA1 delta-AID interaction, whereas their presence permits CnA1 delta to bind more strongly to CnB. In contrast, the binding of CnA1 delta to calmodulin is unaffected by the immunosuppressants. Significantly, in the absence of its cognate cytosolic receptor, neither CsA nor FK506 inhibits or stimulates the CnA1 delta-AID, CnA1 delta-CnB interactions. These in vivo observations not only provide supportive evidence for the mechanism by which drug-receptor complexes could modulate calcineurin activity but also unveil the possibility of identifying novel immunophilin-independent calcineurin inhibitors which may disturb the association of CnA1 delta to AID.
mesh_terms: D001483:Base Sequence; D019703:Calcineurin; D002147:Calmodulin / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology*; D016572:Cyclosporine / Q000494:pharmacology*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism*; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae; D013601:T-Lymphocytes / Q000276:immunology; D022021:Tacrolimus Binding Proteins
chemical_list: D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D007166:Immunosuppressive Agents; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; D005576:Colforsin; D016572:Cyclosporine; D003577:Cytochrome P-450 Enzyme System; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D022021:Tacrolimus Binding Proteins