A mutation in a CD44 variant of inflammatory cells enhances the mitogenic interaction of FGF with its receptor
Shlomo Nedvetzki, Itshak Golan, Nathalie Assayag, Erez Gonen, Dan Caspi, Micha Gladnikoff, Avner Yayon, David Naor
Shlomo Nedvetzki, Itshak Golan, Nathalie Assayag, Erez Gonen, Dan Caspi, Micha Gladnikoff, Avner Yayon, David Naor
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Article Autoimmunity

A mutation in a CD44 variant of inflammatory cells enhances the mitogenic interaction of FGF with its receptor

Abstract

Synovial fluid cells from joints of rheumatoid arthritis (RA) patients express a novel variant of CD44 (designated CD44vRA), encoding an extra trinucleotide (CAG) transcribed from intronic sequences flanking a variant exon. The CD44vRA mutant was detected in 23 out of 30 RA patients. CD44-negative Namalwa cells transfected with CD44vRA cDNA or with CD44v3-v10 (CD44vRA wild type) cDNA bound FGF-2 to an equal extent via their associated heparan sulfate chains. However, Namalwa cells, immobilizing FGF-2 via their cell surface CD44vRA, bound substantially more soluble FGF receptor-1 (FGFR-1) than did Namalwa cells immobilizing the same amount of FGF-2 via their cell surface CD44v3-v10. The former cells stimulated the proliferation of BaF-32 cells, bearing FGFR-1, more efficiently than did the latter cells. Finally, isolated primary synovial fluid cells from RA patients expressing CD44vRA bound more soluble FGFR-1 to their cell surface–associated FGF-2 than did corresponding synovial cells expressing CD44v3-v10 or synovial cells from osteoarthritis patients. The binding of soluble FGFR-1 to RA synovial cells could be specifically reduced by their preincubation with Ab’s against the v3 exon product of CD44. Hence, FGF-2 attached to the heparan sulfate moiety expressed by the novel CD44 variant of RA synovium cells exhibits an augmented ability to stimulate FGFR-1–mediated activities. A similar mechanism may foster the destructive inflammatory cascade not only in RA, but also in other autoimmune diseases.

Authors

Shlomo Nedvetzki, Itshak Golan, Nathalie Assayag, Erez Gonen, Dan Caspi, Micha Gladnikoff, Avner Yayon, David Naor

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Synovial fluid cells from RA patients bind soluble FGFR-1. (a) CD44 expr...
Synovial fluid cells from RA patients bind soluble FGFR-1. (a) CD44 expression on synovial fluid cells from RA and OA patients. Cells collected from the joints of an RA or an OA patient were analyzed by flow cytometry using anti–pan CD44 mAb (F-10-44-2), anti-CD44v3 mAb, or anti-CD44v6 mAb. The first histogram in each panel shows staining with second Ab alone. Similar flow-cytometric histograms were recorded in 11 samples of RA patients and 6 of OA patients. (b) Enhanced binding of soluble FGFR-1 to synovial fluid cells of RA patients. Cells from the joints of 11 RA and 6 OA patients were incubated with soluble FGFR-1 conjugated to AP, in the presence (not shown) or absence (b) of FGF-2. The interaction of the FGFR-1 with the FGF-2, bound to the joint cells, was detected using an AP substrate at OD 405. Similar results were observed in the presence of FGF-2 (not shown). Insets: Binding of anti–FGF-2 Ab to joint cells of RA and OA patients to assess the endogenous FGF-2 inclusion in these cells. The first histogram in each inset shows staining with second Ab only (goat anti-rabbit Fab’-FITC). Equal levels of endogenous FGF-2 in RA and OA cells were observed in samples of 11 RA and 6 OA patients. (c) Enhanced binding of soluble FGFR-1 is dependent on CD44vRA expression on RA synovial fluid cells. The binding of FGFR-1 to three patient samples (RA12, RA13, and RA14) of RA synovial fluid cells expressing CD44vRA, one patient sample (RA15) of RA synovial fluid cells expressing CD44v3-v10, and two samples of primary human keratinocytes (Ker-1 and Ker-2) expressing CD44v3-v10 were analyzed as indicated in b. Note that the keratinocytes were loaded with FGF-2 because, unlike synovial fluid cells, they do not contain the endogenous growth factor. Statistical analysis of the principal groups is shown.