title: Cyclosporin-A inhibits ERK phosphorylation in B cells by modulating the binding of Raf protein to Bcl2.
abstract: Extracellular signal-related kinase (ERK) signaling is regulated by sequential phosphorylation of upstream kinases including Raf. We report herein that ERK phosphorylation is inhibited by a short incubation with Cyclosporin-A (CsA) in anti-IgM activated Daudi B cells. As Bcl2, through its BH4 domain, was previously shown to bind both Calcineurin (Can) and Raf proteins, we hypothesized that CsA inhibited Can binding to Bcl2 allowing the latter to bind more Raf at the mitochondria thereby diverting it from activating the ERK cascade. In support of this less Bcl2 coprecipitated with Can heterodimer in total lysates of cells treated with CsA as compared to controls. In parallel, Raf1 was augmented in both the mitochondrial fractions of cells treated with CsA and in Bcl2 immunoprecipitates under CsA. Finally, introduction of a Bcl2 BH4 domain into Daudi cells augmented ERK phosphorylation in unstimulated cells and this augmentation was unsensitive to CsA. We therefore suggest that CsA indirectly inhibited ERK activation through sequestration of Raf1, at the mitochondria.
authors.affiliation: INSERM unite 131, IFR13, 32 Rue des Carnets 92140 Clamart, Université Paris XI, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Gary-Gouy
authors.forename: Alexander
authors.initials: A
authors.lastname: Sainz-Perez
authors.forename: Georges
authors.initials: G
authors.lastname: Bismuth
authors.forename: Ataollah
authors.initials: A
authors.lastname: Ghadiri
authors.forename: Brian A
authors.initials: BA
authors.lastname: Perrino
authors.forename: Ali
authors.initials: A
authors.lastname: Dalloul
mesh_terms: D001402:B-Lymphocytes / Q000187:drug effects* / Q000201:enzymology; D019703:Calcineurin / Q000187:drug effects / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology*; D019281:Dimerization; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects* / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000187:drug effects* / Q000378:metabolism
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2; D016572:Cyclosporine; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D019703:Calcineurin