Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL) Induces Rheumatoid Arthritis Synovial Fibroblast Proliferation through Mitogen-activated Protein Kinases and Phosphatidylinositol 3-Kinase/Akt

Abstract

A hallmark of rheumatoid arthritis (RA) is the pseudo-tumoral expansion of fibroblast-like synoviocytes (FLSs), and the RA FLS has therefore been proposed as a therapeutic target. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been described as a pro-apoptotic factor on RA FLSs and, therefore, suggested as a potential drug. Here we report that exposure to TRAIL-induced apoptosis in a portion (up to 30%) of RA FLSs within the first 24 h. In the cells that survived, TRAIL induced RA FLS proliferation in a dose-dependent manner, with maximal proliferation observed at 0.25 nm. This was blocked by a neutralizing anti-TRAIL antibody. RA FLSs were found to express constitutively TRAIL receptors 1 and 2 (TRAIL-R1 and TRAIL-R2) on the cell surface. TRAIL-R2 appears to be the main mediator of TRAIL-induced stimulation, as RA FLS proliferation induced by an agonistic anti-TRAIL-R2 antibody was comparable with that induced by TRAIL. TRAIL activated the mitogen-activated protein kinases ERK and p38, as well as the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway with kinetics similar to those of TNF-α. Moreover, TRAIL-induced RA FLS proliferation was inhibited by the protein kinase inhibitors PD98059, SB203580, and LY294002, confirming the involvement of the ERK, p38, and PI3 kinase/Akt signaling pathways. This dual functionality of TRAIL in stimulating apoptosis and proliferation has important implications for its use in the treatment of RA. A hallmark of rheumatoid arthritis (RA) is the pseudo-tumoral expansion of fibroblast-like synoviocytes (FLSs), and the RA FLS has therefore been proposed as a therapeutic target. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been described as a pro-apoptotic factor on RA FLSs and, therefore, suggested as a potential drug. Here we report that exposure to TRAIL-induced apoptosis in a portion (up to 30%) of RA FLSs within the first 24 h. In the cells that survived, TRAIL induced RA FLS proliferation in a dose-dependent manner, with maximal proliferation observed at 0.25 nm. This was blocked by a neutralizing anti-TRAIL antibody. RA FLSs were found to express constitutively TRAIL receptors 1 and 2 (TRAIL-R1 and TRAIL-R2) on the cell surface. TRAIL-R2 appears to be the main mediator of TRAIL-induced stimulation, as RA FLS proliferation induced by an agonistic anti-TRAIL-R2 antibody was comparable with that induced by TRAIL. TRAIL activated the mitogen-activated protein kinases ERK and p38, as well as the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway with kinetics similar to those of TNF-α. Moreover, TRAIL-induced RA FLS proliferation was inhibited by the protein kinase inhibitors PD98059, SB203580, and LY294002, confirming the involvement of the ERK, p38, and PI3 kinase/Akt signaling pathways. This dual functionality of TRAIL in stimulating apoptosis and proliferation has important implications for its use in the treatment of RA. Rheumatoid arthritis (RA) 1The abbreviations used are: RA, rheumatoid arthritis; ERK, extracellular signal-regulated kinase; FCS, fetal calf serum; FLS, fibroblast-like synoviocyte; IL, interleukin; MAP, mitogen-activated protein; PBS, phosphate-buffered saline; PI3, phosphatidylinositol 3; RT, reverse transcription; TNF, tumor necrosis factor; TRAIL, TNF-related apoptosis-inducing ligand. is an autoimmune disease characterized by chronic inflammation of joints leading to progressive and irreversible joint destruction. The aggressive front of synovial tissue, called pannus, invades and destroys local articular structure. The pannus is characterized by a synovial hyperplasia that is mainly composed of fibroblast-like synoviocytes (FLSs) combined with a massive infiltration of lymphocytes and macrophages. Both increased proliferation and/or insufficient apoptosis might contribute to the expansion of RA FLSs, and several reports suggest inducing apoptosis of RA FLSs as a therapeutic approach. Intraarticular expression of proinflammatory cytokines, in particular tumor necrosis factor (TNF)-α and IL-1β, plays a crucial role in the pathogenesis of RA (1Pope R.M. Nat. Rev. Immunol. 2002; 2: 527-535Crossref PubMed Scopus (329) Google Scholar). An anti-inflammatory role has been suggested for the TNF family member TRAIL (TNF-related apoptosis-inducing ligand) following the observations that the blockade of TRAIL in mice exacerbated autoimmune arthritis and that intraarticular TRAIL gene transfer relieved the symptoms (2Song K. Chen Y. Goke R. Wilmen A. Seidel C. Goke A. Hilliard B. J. Exp. Med. 2000; 191: 1095-1104Crossref PubMed Scopus (322) Google Scholar). In addition, one report described an increased sensitivity of TRAIL-deficient mice to collagen-induced arthritis (3Lamhamedi-Cherradi S.E. Zheng S.J. Maguschak K.A. Peschon J. Chen Y.H. Nat. Immunol. 2003; 4: 255-260Crossref PubMed Scopus (297) Google Scholar). TRAIL can interact with five different receptors, namely two agonistic receptors called DR4/TRAIL-R1 and DR5/TRAIL-R2 (hereafter referred to as TRAIL-R1 and -R2, respectively), two membrane-anchored decoy receptors designated DcR1/TRAIL-R3 and DcR2/TRAIL-R4 (hereafter referred to as TRAIL-R3, and -R4, respectively), and a soluble decoy receptor known as osteoprotegerin (OPG) (4Baetu T.M. Hiscott J. Cytokine Growth Factor Rev. 2002; 13: 199-207Crossref PubMed Scopus (92) Google Scholar). The physiological relevance of OPG as a receptor for TRAIL is unclear, because the affinity for this ligand at physiological temperatures has been described to be very low (5Truneh A. Sharma S. Silverman C. Khandekar S. Reddy M.P. Deen K.C. McLaughlin M.M. Srinivasula S.M. Livi G.P. Marshall L.A. Alnemri E.S. Williams W.V. Doyle M.L. J. Biol. Chem. 2000; 275: 23319-23325Abstract Full Text Full Text PDF PubMed Scopus (223) Google Scholar). Notably, the affinities of TRAIL-R3 and -R4 for TRAIL at physiological temperatures are ∼50–100-fold lower than those between TRAIL and its cognate receptors TRAIL-R1 and -R2 (5Truneh A. Sharma S. Silverman C. Khandekar S. Reddy M.P. Deen K.C. McLaughlin M.M. Srinivasula S.M. Livi G.P. Marshall L.A. Alnemri E.S. Williams W.V. Doyle M.L. J. Biol. Chem. 2000; 275: 23319-23325Abstract Full Text Full Text PDF PubMed Scopus (223) Google Scholar). The receptors TRAIL-R1 and -R2 contain a cytoplasmic death domain and can induce apoptosis through the activation of caspases upon ligation with a TRAIL ligand (reviewed in Ref. 6Wang S. El-Deiry W.S. Oncogene. 2003; 22: 8628-8633Crossref PubMed Scopus (702) Google Scholar). Nevertheless, the binding of TRAIL to these TRAIL receptors can also activate the transcription factor NFκB, which is known to control cell proliferation (7Schneider P. Thome M. Burns K. Bodmer J.L. Hofmann K. Kataoka T. Holler N. Tschopp J. Immunity. 1997; 7: 831-836Abstract Full Text Full Text PDF PubMed Scopus (599) Google Scholar). Indeed, although TRAIL is known to induce apoptosis in tumor cells (reviewed in Ref. 6Wang S. El-Deiry W.S. Oncogene. 2003; 22: 8628-8633Crossref PubMed Scopus (702) Google Scholar), TRAIL has also been shown to promote endothelial cell proliferation (8Secchiero P. Gonelli A. Carnevale E. Milani D. Pandolfi A. Zella D. Zauli G. Circulation. 2003; 107: 2250-2256Crossref PubMed Scopus (259) Google Scholar). Thus, depending on the cellular system, TRAIL is capable of initiating apoptosis or cell survival. The effect of TRAIL on the RA FLS appears to be controversial. Ichikawa et al. described TRAIL-R1 and -R2 expression on primary isolated FLSs from RA patients and reported that an agonistic anti-TRAIL-R2 antibody, as well as cross-linked TRAIL, induces apoptosis on these FLS (9Ichikawa K. Liu W. Fleck M. Zhang H. Zhao L. Ohtsuka T. Wang Z. Liu D. Mountz J.D. Ohtsuki M. Koopman W.J. Kimberly R. Zhou T. J. Immunol. 2003; 171: 1061-1069Crossref PubMed Scopus (94) Google Scholar). Similar observations have been reported by analyzing synovial fluid fibroblasts of RA patients (10Miranda-Carus M.E. Balsa A. Benito-Miguel M. De Ayala C.P. Martin-Mola E. Arthritis Rheum. 2004; 50: 2786-2793Crossref PubMed Scopus (39) Google Scholar). The conclusion that TRAIL induces apoptosis of the RA FLS was challenged previously by Perlman et al., who detected neither the expression of TRAIL-R1 and -R2 nor TRAIL susceptibility on primary isolated FLSs from RA patients (11Perlman H. Nguyen N. Liu H. Eslick J. Esser S. Walsh K. Moore T.L. Pope R.M. Arthritis Rheum. 2003; 48: 3096-3101Crossref PubMed Scopus (28) Google Scholar). Here we report for the first time that TRAIL can induce RA FLS proliferation in vitro through MAP kinases and PI3 kinase/Akt activation. Reagents—Recombinant human TNF-α was purchased from R&D Systems (Lille, France). Recombinant human IL-1β and recombinant human TRAIL were obtained from PeproTech (Rocky Hill, NJ). Polyclonal goat anti-TRAIL-R1, anti-TRAIL-R2, anti-TRAIL-R4, and mouse anti-TRAIL antibodies were purchased from R&D Systems. Control MOPC2.1 IgG was obtained from Sigma. Anti-phospho-ERK1/2 and anti-phospho-p38 (Thr(P)-180/Tyr(P)-182) were obtained from Upstate Biotechnology and BD Biosciences, respectively. The monoclonal mouse anti-phospho-Akt (Ser-473) antibody was obtained from Cell Signaling Technology (Beverly, MA). The rabbit polyclonal anti-NFκB p65 antibody was purchased from Santa Cruz Biotechnology (Santa Cruz, CA), fluorescein isothiocyanate-conjugated secondary antibodies were obtained from Jackson ImmunoResearch (West Grove, Pennsylvania), and peroxidase-conjugated secondary antibodies were purchased from Sigma. Preparation of Fibroblast-like Synoviocytes of Rheumatoid Arthritis Patients—Fibroblasts were isolated from synovium samples obtained from patients meeting the American College of Rheumatology criteria for RA (revised 1987) who had undergone surgery for synovectomy or total joint replacement surgery (12Arnett F.C. Edworthy S.M. Bloch D.A. McShane D.J. Fries J.F. Cooper N.S. Healey L.A. Kaplan S.R. Liang M.H. Luthra H.S. Medsger Jr., T.A. Mitchell D.M. Neustadt D.H. Pinals R.S. Schaller J.G. Sharp J.T. Wilder R.L. Hunder G.G. Arthritis Rheum. 1988; 31: 315-324Crossref PubMed Scopus (18640) Google Scholar). Fresh synovial tissues were minced and digested in a solution of dispase (Roche Applied Science), collagenase (Sigma), and DNase (Calbiochem). Synovial fibroblasts were cultured in RPMI 1640 supplemented with 10% fetal calf serum (FCS), 2 mm glutamine, 100 UI/ml penicillin, and 100 μg/ml streptomycin. The cells were used at passage 4–10, at which time they were a homogeneous population of fibroblasts. Upon reaching confluence, the cells were passaged by brief trypsinization as described previously (13Koch A.E. Polverini P.J. Leibovich S.J. Arthritis Rheum. 1986; 29: 471-479Crossref PubMed Scopus (107) Google Scholar). For enzyme-linked immunosorbent assay, Western blot, and reverse transcription (RT)-PCR experiments, RA FLSs were seeded in 6-well plates at 2 × 105 cells/well or in 6 cm-dishes at 4 × 105 cells. Fetal calf serum content of the media was progressively decreased from 10 to 1% with final starvation for 12 h in RPMI and 1% FCS. Cells were stimulated with TNF-α (2 nm), IL-1β (1 nm), or TRAIL (at indicated concentrations). Flow Cytometric Analysis—RA FLSs were harvested with Versene (Invitrogen) according to the and in supplemented with serum and to one cells were for on in with of goat antibody, anti-TRAIL-R2 antibody, antibody, or mouse anti-TRAIL antibody. a cells were with an control antibody. Cells were in cell and for on with the fluorescein antibody. cells were by and was Cell was by through the of FLSs were seeded in plates at a of 1 × 10 4 Cells were cultured in RPMI with a of and and for 24 h with RPMI and 1% FCS. FLS were stimulated with of TRAIL or media for h. was in (1 was h the of the FLSs were a of and a was a For a assay, TRAIL at was with anti-TRAIL or MOPC2.1 IgG and to cells. For with protein kinases FLSs were for an with the inhibitors the and cultured with or TRAIL Similar were obtained cells serum or cells. of were stimulated with TRAIL at for indicated time and apoptosis was binding and the of The × 105 cells of RA FLS were and at × in binding × 105 RA FLSs were with of at 10 μg/ml for at Upon the of cells were and was isolated the was by with was obtained by of of total with at as the and the was according to the was for expression of human TRAIL the and a The used were 1 at for by at for for and for The were on a 1% from 100 to for TRAIL and from to for was on were and was to a of and a reverse of a Western cells were and the was on Cells were with and with mm 100 mm 1 mm 1 mm mm 2 mm 1% 10% and Cells were harvested with a cell For experiments, cell were and at × for were of protein were by or and was as described previously K. P. A.E. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus (107) Google Scholar). were a of and were and were were as to of the of NFκB, RA FLSs were seeded at 2 cells/well in Cells were stimulated with TRAIL at or with at 1 for with PBS, and in with for Cells were with and for 10 binding was with goat serum in Cells were with the rabbit polyclonal anti-NFκB p65 antibody (Santa Cruz at μg/ml or an control for at goat antibody was used at μg/ml for at were with and the of was a are as the S.E. were with a of were TRAIL of RA FLS, of the effect of TRAIL on RA FLS, cells were for with TRAIL. The first 24 h of with TRAIL in apoptosis of of the cells as by This to from cells C. H. C. J. Immunol. PubMed Scopus Google Scholar). shown in the of cells was observed upon 4 h of TRAIL time the cells from the the cell of RA FLS was also in an of because a of is of cell death C. H. C. J. Immunol. PubMed Scopus Google Scholar). 24 h of of RA FLSs were Similar were obtained for RA FLSs from different patients cell in cells the h of TRAIL proliferation of RA FLS was by in were observed for of the of TRAIL with a proliferation for 0.25 nm. TRAIL induced a in RA FLS proliferation similar to that induced by the proinflammatory IL-1β of TRAIL and IL-1β the effect of these two on RA FLS cells of fibroblast-like synoviocytes from rheumatoid arthritis TRAIL induces RA FLS proliferation in a dose-dependent RA FLSs were stimulated for h with the indicated of TRAIL, and proliferation was effect of TRAIL combined with IL-1β on RA FLS Cells were stimulated for h with IL-1β (1 nm), TRAIL nm), or the two was as described for A. the anti-TRAIL antibody TRAIL-induced RA FLS TRAIL was with anti-TRAIL antibody or the control antibody MOPC2.1 IgG (1 the proliferation of RA FLS h upon treatment and are as the of the of from the of stimulated to the of from the of from the indicated of patients were and shown as S.E. RA of the of TRAIL-induced we the effect of a neutralizing anti-TRAIL antibody. This to an of RA FLS the control antibody had effect with the anti-TRAIL antibody or the control antibody proliferation RA FLSs TRAIL and TRAIL-R1 and -R2 the expression of TRAIL and its receptors in RA the of TRAIL expression by TNF-α and IL-1β by and cells The TRAIL protein be detected in soluble in media or on the RA FLS cell This might be to the sensitivity of the antibodies or a low The expression of different TRAIL receptors on RA FLS was by TRAIL-R1 and -R2 on RA FLSs were constitutively was of the receptors was RA FLSs were with IL-1β, or TRAIL TRAIL-induced of RA FLS with an agonistic anti-TRAIL-R2 antibody induced an in RA FLS proliferation in with cells This to the maximal observed upon the of recombinant TRAIL that TRAIL-R2 TRAIL-induced proliferation to a TRAIL the p38, and the in TRAIL-induced cell we the effect of TRAIL on signaling that control cell those the MAP kinases and and PI3 kinase/Akt C.P. L. C. Oncogene. 2003; 22: PubMed Scopus Google Scholar). RA FLSs were with TRAIL and by Western of MAP kinase was induced by TRAIL and to although with a lower in with that of TNF-α A and with TRAIL also induced activation of the of and in a manner, with activation between and 10 and and The kinetics and of ERK and were comparable with those induced by in the RA and RA FLSs were as described in the to activation following TRAIL an antibody for The transcription factor plays a role in cell and can be activated by MAP kinases and W.S. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Arthritis Rheum. PubMed Scopus Google Scholar). Upon from the to the which can be S. Immunol. Full Text Full Text PDF PubMed Scopus Google Scholar). therefore of be detected in the RA FLS following TRAIL was in the in RA FLSs IL-1β induced its In of was upon exposure to TRAIL A and Western these observations was in the upon TNF-α Thus, the exposure of RA FLS to TRAIL the kinases and and PI3 the transcription factor p38, and ERK Control RA FLS that MAP kinases and PI3 kinase/Akt a role in TRAIL-induced we used the inhibitors and RA FLSs were with the inhibitors at different or with for 1 h and stimulated with TRAIL. these cell was K. P. A.E. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus (107) Google Scholar). was by ERK and TRAIL-induced proliferation in a dose-dependent the PI3 kinase blocked the proliferation induced by TRAIL, the crucial role by this pathway The TRAIL has for because appears to tumor cells K. Y. Peschon H. Immunity. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). Fibroblast-like synoviocytes a crucial role in the of rheumatoid as these cells are in inflammation and joint destruction. The pseudo-tumoral proliferation of RA FLS is to be the for the of the RA synovium and can be by in vitro because RA FLS cells in RA FLSs leading to the effect of TRAIL on RA FLS survival. of RA FLSs with TRAIL induced apoptosis within the first 24 h in of the cells as detected by and decreased TRAIL induced RA FLS proliferation in a dose-dependent at h. This was inhibited by neutralizing anti-TRAIL confirming that cell proliferation is induced by this Moreover, combined with TRAIL and IL-1β had an effect on RA FLS two of are to TRAIL in the pathogenesis of RA The increased of TRAIL detected in RA FLS with proinflammatory for a of TRAIL from synovial cells is also suggest that TRAIL has two different on RA FLS, namely an of apoptosis that is by an increased proliferation of the observations from those in the collagen-induced mouse of arthritis that an role for TRAIL by the proliferation of synovial cells (2Song K. Chen Y. Goke R. Wilmen A. Seidel C. Goke A. Hilliard B. J. Exp. Med. 2000; 191: 1095-1104Crossref PubMed Scopus (322) Google S.E. Zheng S.J. Maguschak K.A. Peschon J. Chen Y.H. Nat. Immunol. 2003; 4: 255-260Crossref PubMed Scopus (297) Google Scholar). This the different between RA in the joints of patients and the mouse one membrane-anchored TRAIL receptor and two soluble decoy receptors have been in the mouse P. D. A. B. A. D. M. S. Hofmann K. H. Tschopp J. Zheng J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar), in the of TRAIL signaling between and The TRAIL from its to induce apoptosis S.R. K. P.J. W.S. C.P. C. Immunity. Full Text PDF PubMed Scopus Google Scholar). depending on the cellular system, TRAIL can different that also and For TRAIL has been shown to promote cell and proliferation on endothelial and cells (8Secchiero P. Gonelli A. Carnevale E. Milani D. Pandolfi A. Zella D. Zauli G. Circulation. 2003; 107: 2250-2256Crossref PubMed Scopus (259) Google P. C. E. Milani D. G. S. Zauli G. 2004; PubMed Scopus Google and to and P. E. M. S. R. A. Zauli G. 2004; PubMed Scopus Google P. Gonelli A. P. E. L. C. Milani D. Zauli G. 2002; PubMed Scopus Google Scholar). Here we for the first time that TRAIL is to induce proliferation of RA A the effect of TRAIL on RA FLSs for to 24 and reported the of apoptosis (9Ichikawa K. Liu W. Fleck M. Zhang H. Zhao L. Ohtsuka T. Wang Z. Liu D. Mountz J.D. Ohtsuki M. Koopman W.J. Kimberly R. Zhou T. J. Immunol. 2003; 171: 1061-1069Crossref PubMed Scopus (94) Google Scholar). of apoptosis were induced by TRAIL on the different RA FLS in which a portion of cells (9Ichikawa K. Liu W. Fleck M. Zhang H. Zhao L. Ohtsuka T. Wang Z. Liu D. Mountz J.D. Ohtsuki M. Koopman W.J. Kimberly R. Zhou T. J. Immunol. 2003; 171: 1061-1069Crossref PubMed Scopus (94) Google Scholar). RA FLSs express TRAIL-R2 and were to an agonistic anti-TRAIL-R2 antibody, TRAIL-R2 as the receptor TRAIL-induced apoptosis (9Ichikawa K. Liu W. Fleck M. Zhang H. Zhao L. Ohtsuka T. Wang Z. Liu D. Mountz J.D. Ohtsuki M. Koopman W.J. Kimberly R. Zhou T. J. Immunol. 2003; 171: 1061-1069Crossref PubMed Scopus (94) Google Scholar). In with these et al. (10Miranda-Carus M.E. Balsa A. Benito-Miguel M. De Ayala C.P. Martin-Mola E. Arthritis Rheum. 2004; 50: 2786-2793Crossref PubMed Scopus (39) Google fibroblasts of RA synovial fluid samples and found that of express cells apoptosis in vitro with an agonistic TRAIL-R2 antibody (10Miranda-Carus M.E. Balsa A. Benito-Miguel M. De Ayala C.P. Martin-Mola E. Arthritis Rheum. 2004; 50: 2786-2793Crossref PubMed Scopus (39) Google Scholar). these reports suggested the of TRAIL-R2 on RA FLSs as a potential Perlman et al. the conclusion because they the expression of TRAIL-R1 or TRAIL-R2 or the susceptibility to TRAIL in RA FLSs (11Perlman H. Nguyen N. Liu H. Eslick J. Esser S. Walsh K. Moore T.L. Pope R.M. Arthritis Rheum. 2003; 48: 3096-3101Crossref PubMed Scopus (28) Google Scholar). A for these observations might be the use of different to and/or RA fibroblasts. The described suggest two of of RA fibroblasts by TRAIL. TRAIL induced in a of RA FLSs that was by an of proliferation in the cells. This effect appears to be mainly by because an agonistic TRAIL-R2 antibody induced proliferation of RA FLS in a similar as that of recombinant TRAIL. that TRAIL can promote proliferation as well as as has been for of the TNF family G. Immunol. 2000; PubMed Scopus Google Scholar). For cells the activation apoptosis at of cell activation P.J. S. A. 2000; PubMed Scopus Google Scholar). that TRAIL cell proliferation by activation of the MAP kinases and and the kinase this was et al. reported that TRAIL and in RA FLSs, these cells from apoptosis T. A. M. Y. H. S. K. N. K. M. K. H. K. T. S. K. 2003; PubMed Scopus Google Scholar). The and PI3 kinase/Akt have been reported to activate NFκB, and, in cell TRAIL has been reported to activate ligation of TRAIL-R1 H. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). activation of in RA FLSs by TRAIL. Notably, very similar observations were in a different cellular (8Secchiero P. Gonelli A. Carnevale E. Milani D. Pandolfi A. Zella D. Zauli G. Circulation. 2003; 107: 2250-2256Crossref PubMed Scopus (259) Google TRAIL the proliferation of primary human endothelial cells by the and the pathways. suggest that TRAIL cell through an The of MAP kinases RA FLS proliferation and the of PI3 kinase confirming that are for RA FLS have been proposed to control the sensitivity of RA FLSs expression of apoptosis as and J. P. C. B. S. Arthritis Rheum. 2002; PubMed Scopus Google G. B. M. M. J.L. Arthritis Rheum. 2004; 50: PubMed Scopus Google and the of MAP and PI3 kinases Arthritis Rheum. PubMed Scopus Google Wang Y. J.F. Liang Liu D. P. Mountz J.D. Arthritis Rheum. PubMed Scopus Google Scholar). kinases have been shown to be activated by as IL-1β, and which are at in the joints of arthritis patients W.S. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Wang Y. J.F. Liang Liu D. P. Mountz J.D. Arthritis Rheum. PubMed Scopus Google A.E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The that TRAIL contribute to by inducing and In with this RA FLS proliferation is by the combined of IL-1β and TRAIL. is for TRAIL and of the human cell with TRAIL in within by progressive of the cells the P. Gonelli A. P. E. L. C. Milani D. Zauli G. 2002; PubMed Scopus Google Scholar). The of TRAIL to induce death and in one cell might therefore be a of the effect of TRAIL observed on RA FLS the proposed to use TRAIL for RA the suggest is a potential to joint in RA. for for with cell and for of the and and for synovial