Soluble Collagen VI Induces Tyrosine Phosphorylation of Paxillin and Focal Adhesion Kinase and Activates the MAP Kinase Erk2 in Fibroblasts

Signals from the extracellular matrix can modulate cellular differentiation and gene expression. We have shown previously that in contrast to other extracellular matrix molecules pepsin-solubilized collagen VI (CVI) can stimulate DNA synthesis of various mesenchymal cell types, apparently independent of integrin-mediated signal transduction. In order to further elucidate collagen VI-induced signaling events, we exposed mouse 3T3 fibroblasts and human HT1080 fibrosarcoma cells to soluble CVI. CVI induced tyrosine phosphorylation of proteins that associate with focal adhesions, such as paxillin, focal adhesion kinase (FAK), and p130CAS. Furthermore, it activated the mitogen-activated protein kinase, erk2. Kinetic analysis showed that these phosphorylations were transient, reaching a maximum after 5 min for transformed HT1080 cells and 30 min for 3T3 fibroblasts. These effects were partly inhibited by a beta1-integrin function blocking antibody and by single chains of CVI. Our results indicate that soluble fragments of native collagen VI, a ubiquitous component of the interstitial extracellular matrix, can mediate stimulation of DNA synthesis via tyrosine phosphorylation of paxillin, FAK, p130CAS, and erk2 in the absence of classical growth factors. Thus, CVI may serve as a matrix-derived sensor that allows for rapid reconstitution of a tissue defect by activating nearby mesenchymal cells.