title: HLA class I antibody-mediated endothelial cell proliferation via the mTOR pathway.
abstract: Anti-HLA Abs have been shown to contribute to the process of transplant vasculopathy by binding to HLA class I molecules expressed by the endothelial and smooth muscle cells of the graft and transducing intracellular signals that elicit cell proliferation. The aim of this study was to determine the role of mammalian target of rapamycin (mTOR) in HLA class I-induced endothelial cell proliferation and to explore in depth the relationship between mTOR complexes and their downstream targets following ligation of HLA class I molecules by anti-HLA Abs. We used small interfering RNA technology to abrogate mTOR, rapamycin-insensitive companion of mTOR (rictor), or regulatory associated protein of mTOR (raptor) to study the function of these gene products to activate proteins involved in MHC class I-induced cell proliferation and survival. Knockdown of mTOR inhibited class I-mediated phosphorylation of proteins downstream of mTOR complex 1 and mTOR complex 2. Furthermore, knockdown of mTOR, rictor, or raptor blocked HLA class I-induced endothelial cell proliferation. Long-term pretreatment with the mTOR inhibitor rapamycin significantly blocked both mTOR-raptor and mTOR-rictor complex formation. Interestingly, rapamycin also blocked class I-induced Akt phosphorylation at Ser(473) and Bcl-2 expression. These results support the role of anti-HLA Abs in the process of transplant vasculopathy and suggest that exposure of the graft endothelium to anti-HLA Abs may promote proliferation through the mTOR pathway.
authors.affiliation: Department of Pathology and Laboratory Medicine, David Geffen School of Medicine and Molecular Biology Institute, University of California-Los Angeles, 1000 Veteran Avenue, Los Angeles, CA 90095, USA.
authors.forename: Peter T
authors.initials: PT
authors.lastname: Jindra
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Jin
authors.forename: Enquire
authors.initials: E
authors.lastname: Rozengurt
authors.forename: Elaine F
authors.initials: EF
authors.lastname: Reed
mesh_terms: D049109:Cell Proliferation; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D006680:HLA Antigens / Q000276:immunology*; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D006801:Humans; D007518:Isoantibodies / Q000502:physiology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D011494:Protein Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011506:Proteins; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000502:physiology
chemical_list: D006680:HLA Antigens; D015395:Histocompatibility Antigens Class I; D007518:Isoantibodies; D046912:Multiprotein Complexes; D011506:Proteins; D034741:RNA, Small Interfering; D014157:Transcription Factors; D011494:Protein Kinases; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases