title: Ras guanine nucleotide-releasing protein 4 is aberrantly expressed in the fibroblast-like synoviocytes of patients with rheumatoid arthritis and controls their proliferation.
abstract: OBJECTIVE
  Ras guanine nucleotide-releasing protein 4 (RasGRP-4) is a calcium-regulated guanine nucleotide exchange factor and diacylglycerol/phorbol ester receptor not normally expressed in fibroblasts. While RasGRP-4-null mice are resistant to arthritis induced by anti-glucose-6-phosphate isomerase autoantibodies, the relevance of these findings to humans is unknown. We undertook this study to evaluate the importance of RasGRP-4 in the pathogenesis of human and rat arthritis.
  
  
  METHODS
  Synovial tissue from patients with rheumatoid arthritis (RA) and osteoarthritis (OA) were evaluated immunohistochemically for the presence of RasGRP-4 protein. Fibroblast-like synoviocytes (FLS) were isolated from synovial samples, and expression of RasGRP-4 was evaluated by real-time quantitative reverse transcription-polymerase chain reaction analyses. The proliferation potency of FLS was evaluated by exposing the cells to a RasGRP-4-specific small interfering RNA (siRNA). Finally, the ability of RasGRP-4-specific siRNAs to hinder type II collagen-induced arthritis in rats was evaluated to confirm the importance of the signaling protein in the disease.
  
  
  RESULTS
  Unexpectedly, RasGRP-4 protein was detected in the synovial hyperplastic lining, where proliferating FLS preferentially reside. FLS isolated from tissues obtained from a subpopulation of RA patients expressed much more RasGRP-4 than did FLS from examined OA patients. Moreover, the level of RasGRP-4 transcript was correlated with the FLS proliferation rate. The ability of cultured FLS to divide was diminished when they were treated with RasGRP-4-specific siRNAs. The intraarticular injection of RasGRP-4-specific siRNAs also dampened experimental arthritis in rats.
  
  
  CONCLUSIONS
  RasGRP-4 is aberrantly expressed in FLS and helps regulate their growth. This intracellular signaling protein is therefore a candidate target for dampening proliferative synovitis and joint destruction.
authors.affiliation: Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Michihito
authors.initials: M
authors.lastname: Kono
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Yasuda
authors.forename: Richard L
authors.initials: RL
authors.lastname: Stevens
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Koide
authors.forename: Takashi
authors.initials: T
authors.lastname: Kurita
authors.forename: Yuka
authors.initials: Y
authors.lastname: Shimizu
authors.forename: Yusaku
authors.initials: Y
authors.lastname: Kanetsuka
authors.forename: Kenji
authors.initials: K
authors.lastname: Oku
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Bohgaki
authors.forename: Olga
authors.initials: O
authors.lastname: Amengual
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Horita
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Shimizu
authors.forename: Tokifumi
authors.initials: T
authors.lastname: Majima
authors.forename: Takao
authors.initials: T
authors.lastname: Koike
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Atsumi
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001169:Arthritis, Experimental / Q000378:metabolism / Q000473:pathology; D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005260:Female; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D011917:Rats, Inbred Lew; D013583:Synovial Membrane / Q000378:metabolism* / Q000473:pathology; D013997:Time Factors; D020663:ras Guanine Nucleotide Exchange Factors / Q000378:metabolism*
chemical_list: C462507:RASGRP4 protein, human; D034741:RNA, Small Interfering; D020663:ras Guanine Nucleotide Exchange Factors