title: Ecto-F1-ATPase and MHC-class I close association on cell membranes.
abstract: Subunits of the mitochondrial ATP synthase complex are expressed on the surface of tumors, bind the TCR of human Vgamma9/Vdelta2 lymphocytes and promote their cytotoxicity. Present experiments show that detection of the complex (called ecto-F1-ATPase) at the cell surface by immunofluorescence correlates with low MHC-class I antigen expression. Strikingly, the alpha and beta chains of ecto-F1-ATPase are detected in membrane protein precipitates from immunofluorescence-negative cells, suggesting that ATPase epitopes are masked. Removal of beta2-microglobulin by mild acid treatment so that most surface MHC-I molecules become free heavy chains reveals F1-ATPase epitopes on MHC-I+ cell lines. Ecto-F1-ATPase is detected by immunofluorescence on primary fibroblasts which express moderate levels of MHC-I antigens. Up-regulation of MHC-I on these cells following IFN-gamma and/or TNF-alpha treatment induces a dose-dependent disappearance of F1-ATPase epitopes. Finally, biotinylated F1-ATPase cell surface components co-immunoprecipitate with MHC-I molecules confirming the association of both complexes on Raji cells. Confocal microscopy analysis of MHC-I and ecto-F1-ATPase beta chain expression on HepG2 cells shows a co-localization of both complexes in punctate membrane domains. This demonstrates that the TCR target F1-ATPase is in close contact with MHC-I antigens which are known to control Vgamma9/Vdelta2 T cell activity through binding to natural killer inhibitory receptors.
authors.affiliation: INSERM, U563, Toulouse, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Vantourout
authors.forename: Laurent O
authors.initials: LO
authors.lastname: Martinez
authors.forename: Aurélie
authors.initials: A
authors.lastname: Fabre
authors.forename: Xavier
authors.initials: X
authors.lastname: Collet
authors.forename: Eric
authors.initials: E
authors.lastname: Champagne
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology*; D016207:Cytokines / Q000494:pharmacology; D000939:Epitopes / Q000378:metabolism; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018613:Microscopy, Confocal; D011485:Protein Binding / Q000187:drug effects; D006180:Proton-Translocating ATPases / Q000378:metabolism*
chemical_list: D016207:Cytokines; D000939:Epitopes; D015395:Histocompatibility Antigens Class I; D000251:Adenosine Triphosphatases; C027201:ectoATPase; D006180:Proton-Translocating ATPases