TGFβ responsive tyrosine phosphatase promotes rheumatoid synovial fibroblast invasiveness.
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.
Division of Cellular Biology, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.
Stephanie M
SM
Stanford
Division of Cellular Biology, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.
German R
GR
Aleman Muench
Division of Rheumatology, Allergy and Immunology, UCSD School of Medicine, La Jolla, California, USA.
Beatrix
B
Bartok
Division of Cellular Biology, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA Inflammatory and Infectious Disease Center, Sanford-Burnham Institute for Medical Research, La Jolla, California, USA.
Cristiano
C
Sacchetti
Microscopy Core, The Scripps Research Institute, La Jolla, California, USA.
William B
WB
Kiosses
Division of Cellular Biology, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.
Jay
J
Sharma
Division of Cellular Biology, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.
Michael F
MF
Maestre
Inflammatory and Infectious Disease Center, Sanford-Burnham Institute for Medical Research, La Jolla, California, USA Department of Experimental Medicine and Surgery, University of Rome Tor Vergata, Rome, Italy.
Massimo
M
Bottini
Inflammatory and Infectious Disease Center, Sanford-Burnham Institute for Medical Research, La Jolla, California, USA.
Tomas
T
Mustelin
Division of Rheumatology, Allergy and Immunology, UCSD School of Medicine, La Jolla, California, USA.
David L
DL
Boyle
Division of Rheumatology, Allergy and Immunology, UCSD School of Medicine, La Jolla, California, USA.
Gary S
GS
Firestein
Division of Cellular Biology, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.
Nunzio
N
Bottini
D000818:Animals; D001172:Arthritis, Rheumatoid / Q000378:metabolism / Q000473:pathology*; D002465:Cell Movement / Q000235:genetics / Q000502:physiology; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology* / Q000502:physiology / Q000637:transplantation; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D055785:Gene Knockdown Techniques; D064593:Heterografts; D006801:Humans; D008819:Mice, Nude; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2 / Q000235:genetics / Q000502:physiology*; D013583:Synovial Membrane / Q000378:metabolism / Q000473:pathology* / Q000637:transplantation; D053773:Transforming Growth Factor beta1 / Q000502:physiology*; D015854:Up-Regulation
D012333:RNA, Messenger; D053773:Transforming Growth Factor beta1; C489852:PTPRK protein, human; D017027:Protein Tyrosine Phosphatases; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2
Fibroblasts; Inflammation; Rheumatoid Arthritis