Involvement of αvβ5 integrin–mediated activation of latent transforming growth factor β1 in autocrine transforming growth factor β signaling in systemic sclerosis fibroblasts

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Abstract
Objective To confirm the involvement of αvβ5 in the self‐activation system in systemic sclerosis (SSc) fibroblasts. Methods Levels of αvβ5 expression were analyzed by immunoprecipitation. The promoter activity of the human α2(I) collagen gene was determined by transient transfection assay. Phosphorylation levels and DNA binding ability of Smad3 were investigated by immunoprecipitation and DNA affinity precipitation, respectively. The localization of active transforming growth factor β (TGFβ) was determined by coculture assay using TMLC cells (mink lung epithelial reporter cells that stably express a portion of the plasminogen activator inhibitor 1 promoter). The morphologic features of cells were determined by immunofluorescence analysis. Results Levels of αvβ5 expression were significantly elevated in SSc fibroblasts compared with normal fibroblasts. Treatment with anti‐αvβ5 antibody or β5 antisense oligonucleotide significantly reduced human α2(I) collagen gene promoter activity in SSc fibroblasts. In SSc fibroblasts pretreated with TGFβ1 antisense oligonucleotide, the exogenous latent TGFβ1 stimulation significantly increased human α2(I) collagen gene promoter activity; this effect was significantly reduced in the presence of anti‐αvβ5 antibody. Phosphorylation levels and DNA binding ability of Smad3 in SSc fibroblasts were significantly reduced by treatment with β5 antisense oligonucleotide. The luciferase activity of TMLC cells cocultured with SSc fibroblasts was significantly elevated compared with that of TMLC cells cocultured with normal fibroblasts and was significantly reduced in the presence of anti‐αvβ5 antibody. Anti‐αvβ5 antibody reversed the myofibroblastic features of SSc fibroblasts. Conclusion Up‐regulated expression of αvβ5 contributes to the establishment of autocrine TGFβ signaling in SSc fibroblasts through activation of endogenous latent TGFβ1.