title: Synergism between the calmodulin-binding and autoinhibitory domains on calcineurin is essential for the induction of their phosphatase activity.
abstract: Elevation of the intracellular calcium concentration is necessary for cell growth and the activation of several lymphokine genes. The immunosuppressive drugs cyclosporin A and FK506 profoundly inhibit the calcium-dependent signaling pathway in T lymphocytes by interfering with the activity of the calcium/calmodulin (CaM)-dependent serine/threonine phosphatase, calcineurin (CN). Little is known, however, about how activation of CN enzyme activity or interaction with its substrate, nuclear factor of activated T cell (NF-AT), is regulated. We show here that the binding of CaM to CN may affect the conformation of CN at both the CaM-binding and the autoinhibitory (AI) domains and that this is critical for activation of CN to dephosphorylate NF-AT. Dissociation of the AI domain from the enzyme active site on CN leads to expose a binding site for NF-AT at the N terminus of CN and allows the CN binding to NF-AT. Since the cytoplasmic form of NF-AT can interact with CN mutants lacking enzyme activity, the interaction of the two molecules is independent of CN enzyme activity and occurs prior to the dephosphorylation of NF-AT. Dephosphorylation converts NF-AT from the cytoplasmic to the nuclear form by exposing the DNA-binding domain on NF-AT, and the nuclear form of NF-AT brings CN together into the nuclei. We therefore propose that the activation of CN by the CaM binding independently regulates the interaction with NF-AT and the dephosphorylation of NF-AT.
authors.affiliation: Division of Immunobiology, Research Institute for Biological Sciences, Science University of Tokyo, 2669 Yamazaki, Noda City, Chiba 278-0022, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tokoyoda
authors.forename: Y
authors.initials: Y
authors.lastname: Takemoto
authors.forename: T
authors.initials: T
authors.lastname: Nakayama
authors.forename: T
authors.initials: T
authors.lastname: Arai
authors.forename: M
authors.initials: M
authors.lastname: Kubo
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites; D019703:Calcineurin / Q000235:genetics / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D051379:Mice; D016297:Mutagenesis, Site-Directed; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D002147:Calmodulin; D004268:DNA-Binding Proteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D014157:Transcription Factors; D019703:Calcineurin; D010744:Phosphoric Monoester Hydrolases