Calcineurin regulates cyclin D1 accumulation in growth-stimulated fibroblasts.
Calcium (Ca(2+)) and calmodulin (CaM) are required for progression of mammalian cells from quiescence into S phase. In multiple cell types, cyclosporin A causes a G(1) cell cycle arrest, implicating the serine/threonine phosphatase calcineurin as one Ca(2+)/CaM-dependent enzyme required for G(1) transit. Here, we show, in diploid human fibroblasts, that cyclosporin A arrested cells in G(1) before cyclin D/cdk4 complex activation and retinoblastoma hyperphosphorylation. This arrest occurred in early G(1) with low levels of cyclin D1 protein. Because cyclin D1 mRNA was induced normally in the cyclosporin A-treated cells, we analyzed the half-life of cyclin D1 in the presence of cyclosporin A and found no difference from control cells. However, cyclosporin A treatment dramatically reduced cyclin D1 protein synthesis. Although these pharmacological experiments suggested that calcineurin regulates cyclin D1 synthesis, we evaluated the effects of overexpression of activated calcineurin on cyclin D1 synthesis. In contrast to the reduction of cyclin D1 with cyclosporin A, ectopic expression of calcium/calmodulin-independent calcineurin promoted synthesis of cyclin D1 during G(1) progression. Therefore, calcineurin is a Ca(2+)/CaM-dependent target that regulates cyclin D1 accumulation in G(1).
Kahl
Christina R
CR
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Means
Anthony R
AR
D015152:Blotting, Northern; D001973:Bromodeoxyuridine / Q000494:pharmacology; D042846:CDC2-CDC28 Kinases / Q000378:metabolism; D019703:Calcineurin / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002453:Cell Cycle; D002455:Cell Division; D002460:Cell Line; D004396:Coloring Agents / Q000494:pharmacology; D056741:Cyclin D; D019938:Cyclin D1 / Q000096:biosynthesis* / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D016213:Cyclins / Q000378:metabolism; D016572:Cyclosporine / Q000378:metabolism / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism*; D016193:G1 Phase; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism; D016196:S Phase; D013997:Time Factors
D002147:Calmodulin; D004396:Coloring Agents; D056741:Cyclin D; D016213:Cyclins; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D019938:Cyclin D1; D016572:Cyclosporine; D004247:DNA; D005982:Glutathione Transferase; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D019703:Calcineurin; D001973:Bromodeoxyuridine; D002118:Calcium