Contraction of collagen matrices mediated by α2β1A and αvβ3 integrins

The β1-null fibroblastic cell line GD25 and its derivatives were studied to gain an understanding of the roles of β1 and β3 integrins in the initial (1-hour) contraction of collagen gels. Stable transfectants of GD25 cells expressing the β1A splice variant of β1 (β1A-GD25) did not express α2β1A and did not adhere to collagen. After transfection of α2 into β1A-GD25 cells, the α2β1A-GD25 transfectants contracted collagen gels in the presence of serum, whereas β1A-GD25 cells did not. The GD25 parental cells, however, also contracted collagen gels. Collagen gel contraction by GD25 cells was blocked by antibodies to αvβ3 or RGD-containing peptide, indicating that αvβ3 is the integrin responsible for mediation of contraction by GD25 cells. Collagen gel contraction by α2β1A-GD25 cells was not inhibited by antibodies to αvβ3 or RGD-containing peptide, but was inhibited by anti-α2 antibody. Flow cytometry demonstrated negligible expression of αvβ3 by β1A-GD25 and α2β1A-GD25 cells when compared to GD25 cells. Platelet derived growth factor (PDGF) and sphingosine-1-phosphate (S1P) enabled gel contraction by α2β1A-GD25 and GD25 cells, respectively, in the absence of serum. PDGF-stimulated contraction by α2β1A-GD25 cells was attenuated in the presence of inhibitors of phosphatidylinositol-3-kinase whereas such inhibitors had no effect on S1P-stimulated contraction by GD25 cells. These experiments using the β1-null GD25 cells and β1A and α2β1A transfectants demonstrate that α2β1A and αvβ3 independently mediate collagen gel contraction and are regulated by different serum factors and signaling pathways.