TGFβ responsive tyrosine phosphatase promotes rheumatoid synovial fibroblast invasiveness

Abstract

Objective In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) that line joint synovial membranes aggressively invade the extracellular matrix, destroying cartilage and bone. As signal transduction in FLS is mediated through multiple pathways involving protein tyrosine phosphorylation, we sought to identify protein tyrosine phosphatases (PTPs) regulating the invasiveness of RA FLS. We describe that the transmembrane receptor PTPκ (RPTPκ), encoded by the transforming growth factor (TGF) β-target gene, PTPRK, promotes RA FLS invasiveness. Methods Gene expression was quantified by quantitative PCR. PTP knockdown was achieved using antisense oligonucleotides. FLS invasion and migration were assessed in transwell or spot assays. FLS spreading was assessed by immunofluorescence microscopy. Activation of signalling pathways was analysed by Western blotting of FLS lysates using phosphospecific antibodies. In vivo FLS invasiveness was assessed by intradermal implantation of FLS into nude mice. The RPTPκ substrate was identified by pull-down assays. Results PTPRK expression was higher in FLS from patients with RA versus patients with osteoarthritis, resulting from increased TGFB1 expression in RA FLS. RPTPκ knockdown impaired RA FLS spreading, migration, invasiveness and responsiveness to platelet-derived growth factor, tumour necrosis factor and interleukin 1 stimulation. Furthermore, RPTPκ deficiency impaired the in vivo invasiveness of RA FLS. Molecular analysis revealed that RPTPκ promoted RA FLS migration by dephosphorylation of the inhibitory residue Y527 of SRC. Conclusions By regulating phosphorylation of SRC, RPTPκ promotes the pathogenic action of RA FLS, mediating cross-activation of growth factor and inflammatory cytokine signalling by TGFβ in RA FLS.

Receptor Protein Tyrosine Phosphatase α–Mediated Enhancement of Rheumatoid Synovial Fibroblast Signaling and Promotion of Arthritis in Mice

“…Phospho–FAK‐Y 397 was unaffected by TNF and IL‐1β stimulation, and its phosphorylation was reduced by RPTPα knockdown (Figure C). As FAK promotes the activation of MAPKs and is critical for JNK activation in RA FLS , we examined whether RPTPα knockdown affected TNF‐ and IL‐1β–induced activation of the JNK and p38 MAPKs. We found that RPTPα knockdown impaired TNF‐ and IL‐1β–stimulated phosphorylation of the activation motif of JNK‐T 183 /Y 185 as well as p38‐T 180 /Y 182 (Figures B and C and data not shown).…”

Long noncoding RNA LERFS negatively regulates rheumatoid synovial aggression and proliferation

“…Determination of migration of FLSs in vivo. We adopted a recently reported in vivo assay to examine whether overexpression of LERFS inhibits the in vivo migration of RA FLSs (58,59). Eight-week-old male BALB/c athymic nude mice were obtained from the Guangdong Medical Laboratory Animal Center (Guangzhou, China).…”

Smad-dependent mechanisms of inflammatory bone destruction

“…Moreover, inhibition of the TGF-β1 type I receptor kinase has a preventive effect on the development of arthritis in mice [50] and TGF-β1 induces the expression of transmembrane receptor protein tyrosine phosphatase κ (RPTPκ), which seems to be involved in cytoskeletal reorganisation, migration and invasiveness of RA synovial fibroblasts, promoting fibroblast migration through dephosphorylation of the tyrosine-protein kinase v-src avian sarcoma viral oncogene homolog (SRC) [51]. …”