Abstract. decoy receptor 3 (dcr3), a member of the tumour necrosis factor receptor (tnfr) superfamily, lacks the transmembrane domain of conventional tnfrs in order to be a secreted protein. dcr3 competitively binds and inhibits members of the tnf family, including fas ligand (fasl), liGHt and tl1a. We previously reported that tnfα-induced dcr3 overexpression in rheumatoid synovial fibroblasts (ra-flS) protects the cells from fas-induced apoptosis and that dcr3 induces Vla-4 expression in tHP-1 macrophages to inhibit cycloheximide-induced apoptosis. meanwhile, recent studies have suggested that dcr3 acting as a ligand directly induces the differentiation of macrophages to osteoclasts. therefore, in the present study, we analyzed the direct effects of dcr3 as a ligand in ra-flS. the experiments showed that dcr3 binds to tl1a expressed in ra-flS resulting in the negative regulation of cell proliferation induced by inflammatory cytokines. DcR3-TL1A signalling may be involved in the pathogenesis of rheumatoid arthritis (ra).
IntroductionRheumatoid arthritis (RA) is an inflammatory joint disease characterized by hyperplasia of the synovial tissue and formation of pannus, which grow invasively into the cartilage, causing cartilage and bone destruction. analyses of hyperplastic synovial tissues of patients with ra have revealed a number of features of transformed long-living cells, such as the presence of somatic mutations, expression of oncogenes, and resistance to apoptosis (1-3).We recently reported that the decoy receptor 3 (dcr3)/ TR6/M68/TNFRSF6b is expressed in rheumatoid fibroblastlike synoviocytes (ra-flS), and that dcr3 expression induced in ra-flS by tnfα protected the cells from fas-induced apoptosis (4). dcr3, a member of the tumour necrosis factor receptor (tnfr) superfamily, lacks the transmembrane domain of conventional tnfrs to be a secreted protein (5). dcr3 is typically overexpressed in tumour cells, including lung and colon cancers (5), gliomas, gastrointestinal tract tumours (6) and virus-associated leukaemia (7). in addition, dcr3 is expressed in some normal tissues, including the colon, stomach, spleen, lymph nodes, spinal cord, pancreas and lungs (5,6). However, dcr3 is not expressed in human fibroblast NIH3T3 cells (8). DcR3 has three ligands, i.e., the fas ligand (fasl), liGHt and tl1a, all members of the tnf superfamily (9). Overexpression of DcR3 may benefit tumours by helping them to avoid the cytotoxic and regulatory effects of fasl (5), liGHt (10) and tl1a (11). We suggest that dcr3 is one of the key molecules that regulate the proliferation of ra-flS (4). recent studies have suggested that dcr3 directly induces osteoclast formation from monocytes (12), and that dcr3 triggers enhanced adhesion of monocytes via reverse signalling (13). However, it remains unclear whether dcr3 directly affects ra-flS proliferation. further, the molecules interacting with dcr3 for reverse signalling remain unknown. meanwhile, it has been reported that the dcr3 ligand proteins, fasl, liGHt and tl1a, are all e...