title: Expression and Functions of Immediate Early Response Gene X-1 (IEX-1) in Rheumatoid Arthritis Synovial Fibroblasts.
abstract: In rheumatoid arthritis (RA), synovial fibroblasts (RA-SFs) accumulate in affected joints, where they play roles in inflammation and joint destruction. RA-SFs exhibit tumor-like proliferation and are resistant to apoptosis. Although RA-SF activation is well described, negative regulators of RA-SF activation are unknown. We previously reported that histone deacetylase (HDAC) inhibitors facilitate apoptosis in RA-SFs. Here we found that RA-SFs treated with the HDAC inhibitor Trichostatin A (TSA) exhibited an upregulation of the immediate early response gene X-1 (IEX-1). IEX-1 has roles in apoptosis sensitivity, cell-cycle progression, and proliferation, and is reported to be involved in immune responses, inflammation, and tumorigenesis, and to have anti-arthritic properties. To investigate IEX-1's role in RA-SFs, we used in vitro-cultured synovial fibroblasts from RA and osteoarthritis (OA) patients. We confirmed that TSA upregulated the IEX-1 protein and mRNA expressions in RA-SFs by western blotting and quantitative RT-PCR. Inhibiting HDAC1, 2, and 3 (but not 6 or 8) also upregulated IEX-1. The IEX-1 mRNA levels were higher in RA-SFs than in OA-SFs, and were further upregulated in RA-SFs by the pro-inflammatory cytokines TNFα and IL-1β. The staining of surgical specimens showed that IEX-1 was present in the pannus from affected RA joints. Si-RNA-mediated IEX-1 knockdown upregulated the lipopolysaccharide (LPS)-induced expression of TNFα and various chemokine mRNAs, indicating that IEX-1 downregulates TNFα and chemokines. Furthermore, apoptosis analysis showed that IEX-1 knockdown protected RA-SFs from apoptosis induced by TSA or by an anti-Fas mAb, indicating that IEX-1 is pro-apoptotic in RA-SFs. Collectively, our results showed that IEX-1 is induced by TNFα and IL-1β in RA-SFs, in which it suppresses TNFα and chemokine production and induces apoptosis; thus, IEX-1 negatively regulates RA-SF activation. Further investigation of IEX1's functions in RA-SFs may lead to new therapeutic approaches for RA.
authors.affiliation: Department of Rheumatology and Clinical Immunology, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Morinobu
authors.affiliation: Department of Rheumatology and Clinical Immunology, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Shino
authors.initials: S
authors.lastname: Tanaka
authors.affiliation: Department of Rheumatology and Clinical Immunology, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Nishimura
authors.affiliation: Department of Rheumatology and Clinical Immunology, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Soshi
authors.initials: S
authors.lastname: Takahashi
authors.affiliation: Department of Rheumatology and Clinical Immunology, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Goichi
authors.initials: G
authors.lastname: Kageyama
authors.affiliation: The Orthopedic Surgery, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Miura
authors.affiliation: The Orthopedic Surgery, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kurosaka
authors.affiliation: Department of Rheumatology and Clinical Immunology, Kobe University Graduate School of Medicine, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.|Clinical Laboratory, Kobe University Hospital, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Saegusa
authors.affiliation: Clinical Laboratory, Kobe University Hospital, 7-5-2 Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan.|The Center for Rheumatic Diseases, Shinko Hospital, 1-4-47 Wakinohama-cho, Chuo-ku, Kobe, 651-0072, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Kumagai
mesh_terms: D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics* / Q000378:metabolism*; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002478:Cells, Cultured; D018925:Chemokines / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D013583:Synovial Membrane / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D051017:Apoptosis Regulatory Proteins; D018925:Chemokines; D006877:Hydroxamic Acids; C099815:IER3 protein, human; D008565:Membrane Proteins; C439524:TNF protein, human; D014409:Tumor Necrosis Factor-alpha; C012589:trichostatin A