Expression of functional alpha 4 beta 1 integrin by human dermal fibroblasts.

Fibroblasts interact with the extracellular matrix through cell-surface receptors belonging to the integrin family. In this report, we present evidence that cultured normal human fibroblasts express the integrin alpha 4 beta 1 and that this receptor facilitates fibroblast attachment to fibronectin. Fluorescence-activated cell sorter analysis and immunoprecipitation with monoclonal antibodies demonstrated that normal dermal fibroblasts express the alpha 4-subunit on the cell surface, primarily in association with the beta 1-subunit. Cell-attachment assays demonstrated that normal human fibroblasts can attach to the 40-kDa fibronectin fragment containing the type III connecting segment domain recognized by alpha 4 beta 1. Adhesion to this fragment was inhibited by anti-alpha 4 antibody. Furthermore, our results indicate that alpha 4 beta 1 collaborates with another fibronectin receptor, alpha 5 beta 1, during fibroblast attachment to full-length fibronectin. The region of fibronectin recognized by alpha 5 beta 1 contains the amino acid sequence arg-gly-asp (RGD). A short synthetic RGD peptide, or the 120-kDa fibronectin fragment containing the RGD sequence, only partially inhibited attachment to full-length fibronectin, suggesting that fibroblasts utilize more than the RGD recognition sequence for binding to fibronectin. Accordingly, RGD peptide combined with anti-alpha 4 antibody produced more potent inhibition of cell attachment than either reagent alone. These observations show for the first time that functional alpha 4 beta 1 fibronectin receptor is not restricted to lymphoid cells and transformed cells.