Abstract
Interleukin‐1β (IL‐1β) mediates destruction of matrix collagens in diverse inflammatory diseases including arthritis, periodontitis, and pulmonary fibrosis by activating fibroblasts, cells that interact with matrix proteins through integrin‐based adhesions. In vitro, IL‐1β signaling is modulated by focal adhesions, supramolecular protein complexes that are enriched with tyrosine kinases and phosphatases. We assessed the importance of tyrosine phosphatases in regulating cell–matrix interactions and IL‐1β signaling. In human gingival fibroblasts plated on fibronectin, IL‐1β enhanced the maturation of focal adhesions as defined by morphology and enrichment with paxillin and α‐actinin. IL‐1β also induced activation of ERK and recruitment of phospho‐ERK to focal complexes/adhesions. Treatment with the potent tyrosine phosphatase inhibitor pervanadate, in the absence of IL‐1β, recapitulated many of these responses indicating the importance of tyrosine phosphatases. Immunoblotting of collagen bead‐associated complexes revealed that the tyrosine phosphatase, SHP‐2, was also enriched in focal complexes/adhesions. Depletion of SHP‐2 by siRNA or by homologous recombination markedly altered IL‐1β‐induced ERK activation and maturation of focal adhesions. IL‐1β‐induced tyrosine phosphorylation of SHP‐2 on residue Y542 promoted focal adhesion maturation. Association of Gab1 with SHP‐2 in focal adhesions correlated temporally with activation of ERK and was abrogated in cells expressing mutant (Y542F) SHP‐2. We conclude that IL‐1β mediated maturation of focal adhesions is dependent on tyrosine phosphorylation of SHP‐2 at Y542, leading to recruitment of Gab1, a process that may influence the downstream activation of ERK. J. Cell. Physiol. 207: 132–143, 2006. © 2005 Wiley‐Liss, Inc.