In response to transforming growth factor β1 (TGFβ) stimulation, fibroblasts modify their integrin repertoire and adhesive capabilities to certain extracellular matrix proteins. Although TGFβ has been shown to increase the expression of specific αv integrins, the mechanisms underlying this are unknown. In this study we demonstrate that TGFβ1 increased both β3 integrin subunit mRNA and protein levels as well as surface expression of αvβ3 in human lung fibroblasts. TGFβ1-induced αvβ3 expression was strongly adhesion-dependent and associated with increased focal adhesion kinase and c-Src kinase phosphorylation. Inhibition of β3 integrin activation by the Arg-Gly-Asp tripeptide motif-specific disintegrin echistatin or αvβ3 blocking antibody prevented the increase in β3 but not β5 integrin expression. In addition, echistatin inhibited TGFβ1-induced p38 MAPK but not Smad3 activation. Furthermore, inhibition of the Src family kinases, but not focal adhesion kinase, completely abrogated TGFβ1-induced expression of αvβ3 and p38 MAPK phosphorylation but not β5 integrin expression and Smad3 activation. The TGFβ1-induced αvβ3 expression was blocked by pharmacologic and genetic inhibition of p38 MAPK-but not Smad2/3-, Sp1-, ERK-, phosphatidylinositol 3-kinase, and NF-κB-dependent pathways. Our results demonstrate that TGFβ1 induces αvβ3 integrin expression via a β3 integrin-, c-Src-, and p38 MAPK-dependent pathway. These data identify a novel mechanism for TGFβ1 signaling in human lung fibroblasts by which they may contribute to normal and pathological wound healing. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.