Fractalkine is a novel chemoattractant for rheumatoid arthritis fibroblast-like synoviocyte signaling through MAP kinases and Akt.
OBJECTIVE
Fibroblast-like synoviocytes (FLS) are a major constituent of the hyperplastic synovial pannus that aggressively invades cartilage and bone during the course of rheumatoid arthritis (RA). Fractalkine (FKN/CX(3)CL1) expression is up-regulated in RA synovium and RA synovial fluid. While RA FLS express the FKN receptor, CX(3)CR1, the pathophysiologic relevance of FKN stimulation of RA FLS is not understood. This study was undertaken to better characterize the relationship between FKN and the RA FLS that both produce it and express its receptor.


METHODS
RA FLS were subjected to chemotaxis and proliferation assays, Western blotting, enzyme-linked immunosorbent assays, and filamentous actin staining to characterize the relationship between FKN and RA FLS.


RESULTS
FKN secretion by RA FLS was regulated mainly by tumor necrosis factor alpha. Stimulation of RA FLS with FKN led to significant cytoskeletal rearrangement but no proliferation. Chemotaxis assays revealed that FKN was a novel chemoattractant for RA FLS. Stimulation of RA FLS with FKN resulted in activation of MAP kinases and Akt. JNK, ERK-1/2, and Akt (at both Ser-473 and Thr-308) were each up-regulated in a time-dependent manner. Inhibition of ERK-1/2-mediated signaling, but not JNK or Akt, significantly repressed FKN-induced RA FLS migration.


CONCLUSIONS
These findings indicate a novel role of FKN in regulating RA FLS cytoskeletal structure and migration. FKN specifically induces RA FLS phosphorylation of the MAP kinases JNK and ERK-1/2, as well as full activation of Akt.
Midwestern University, Downers Grove, Illinois.
Michael V
MV
Volin
Nha
N
Huynh
Karolina
K
Klosowska
Kyle K
KK
Chong
James M
JM
Woods
D008841:Actin Cytoskeleton / Q000378:metabolism; D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D015153:Blotting, Western; D002478:Cells, Cultured; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C / Q000378:metabolism* / Q000494:pharmacology; D002630:Chemotactic Factors / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism* / Q000494:pharmacology; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011994:Recombinant Proteins; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology
C515538:CX3CL1 protein, human; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; D002630:Chemotactic Factors; D008565:Membrane Proteins; D011994:Recombinant Proteins; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases