Contraction of collagen matrices mediated by alpha 2 beta 1A and alpha v beta 3 integrins

The beta 1-null fibroblastic cell line GD25 and its derivatives were studie d to gain an understanding of the roles of pi and beta 3 integrins in the i nitial (1-hour) contraction of collagen gels. Stable transfectants of CD25 cells expressing the beta 1A splice variant of beta 1 (beta 1A-GD25) did no t express alpha 2 beta 1A and did not adhere to collagen. After transfectio n of alpha 2 into beta 1A-GD25 cells, the alpha 2 beta 1A-GD25 transfectant s contracted collagen gels in the presence of serum, whereas beta 1A-GD25 c ells did not. The GD25 parental cells, however, also contracted collagen ge ls. Collagen gel contraction by GD25 cells was blocked by antibodies to alp ha v beta 3 or a RGD-containing peptide, indicating that alpha v beta 3 is the integrin responsible for mediation of contraction by GD25 cells. Collag en gel contraction by alpha 2 beta 1A-GD25 cells was not inhibited by antib odies to avp3 or RGD-containing peptide, but was inhibited by anti-alpha 2 antibody. Flow cytometry demonstrated negligible expression of avp3 by beta 1A-GD25 and alpha 2 beta 1A-GD25 cells when compared to GD25 cells. Platel et derived growth factor (PDGF) and sphingosine-1-phosphate (S1P) enabled g el contraction by alpha 2 beta 1A-GD25 and GD25 cells, respectively, in the absence of serum. PDGF-stimulated contraction by alpha 2 beta 1A-GD25 cell s was attenuated in the presence of inhibitors of phosphatidylinositol-3-ki nase whereas such inhibitors had no effect on S1P-stimulated contraction by GD25 cells. These experiments using the beta 1-null GD25 cells and beta 1A and alpha 2 beta 1A transfectants demonstrate that alpha 2 beta 1A and alp ha v beta 3 independently mediate collagen gel contraction and are regulate d by different serum factors and signaling pathways.