title: Down-regulation of MHC II in mesenchymal stem cells at high IFN-gamma can be partly explained by cytoplasmic retention of CIITA.
abstract: Mesenchymal stem cells (MSCs) are located in postnatal bone marrow, show plasticity, are linked to various bone marrow disorders, exhibit phagocytosis, exert Ag-presenting properties (APC), and are immune suppressive. Unlike professional APCs, MSCs respond bimodally to IFN-gamma in MHC-II expression, with expression at 10 U/ml and baseline, and down-regulation at 100 U/ml. The effects at high IFN-gamma could not be explained by down-regulation of its receptor, IFN-gammaRI. In this study, we report on the mechanisms by which IFN-gamma regulates MHC-II expression in MSCs. Gel shift assay and Western blot analyses showed dose-dependent increases in activated STAT-1, indicating responsiveness by IFN-gammaRI. Western blots showed decreased intracellular MHC-II, which could not be explained by decreased transcription of the master regulator CIITA, based on RT-PCR and in situ immunofluorescence. Reporter gene assays with PIII and PIV CIITA promoters indicate constitutive expression of PIII in MSCs and a switch to PIV by IFN-gamma, indicating the presence of factors for effect promoter responses. We explained decreased MHC-II at the level of transcription because CIITA protein was observed in the cytosol and not in nuclei at high IFN-gamma level. The proline/serine/threonine region of CIITA showed significant decrease in phosphorylation at high IFN-gamma levels. An understanding of the bimodal effects could provide insights on bone marrow homeostasis, which could be extrapolated to MSC dysfunction in hematological disorders.
authors.affiliation: Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey, 185 South Orange Avenue, Newark, NJ 07103, USA.
authors.forename: Katherine C
authors.initials: KC
authors.lastname: Tang
authors.forename: Katarzyna A
authors.initials: KA
authors.lastname: Trzaska
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Smirnov
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Kotenko
authors.forename: Stephan K
authors.initials: SK
authors.lastname: Schwander
authors.forename: Jerrold J
authors.initials: JJ
authors.lastname: Ellner
authors.forename: Pranela
authors.initials: P
authors.lastname: Rameshwar
mesh_terms: D002478:Cells, Cultured; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism*; D015536:Down-Regulation; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism* / Q000494:pharmacology; D059630:Mesenchymal Stem Cells / Q000187:drug effects / Q000276:immunology*; D009687:Nuclear Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D017471:Receptors, Interferon / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism; D015534:Trans-Activators / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D000096743:Interferon gamma Receptor
chemical_list: D000949:Histocompatibility Antigens Class II; D007371:Interferon-gamma; D009687:Nuclear Proteins; D017471:Receptors, Interferon; D050794:STAT1 Transcription Factor; D015534:Trans-Activators; D000096743:Interferon gamma Receptor; C083728:MHC class II transactivator protein