Regulation of integrin function by CD47 ligands -: Differential effects on αvβ3 and α4β1 integrin-mediated adhesion

We examined the regulation of alpha(4)beta(1) integrin function in melanoma cells and T cells by ligands of CD47. A CD47 antibody (B6H12) that inhibited alpha(v)beta(3)-mediated adhesion of melanoma cells induced by CD47-binding peptides from thrombospondin-1 directly stimulated alpha(4)beta(1)-mediated adhesion of the same cells to vascular cell adhesion molecule-1 and N-terminal regions of thrombospondin-1 or thrombospondin-2. B6H12 also stimulated alpha(4)beta(1)- as well as alpha(2)beta(1)- and alpha(5)beta(1)-mediated adhesion of CD47-expressing T cells but not of CD47-deficient T cells. alpha(4)beta(1) and CD47 co-purified as a detergent-stable complex on a CD47 antibody affinity column. CD47-binding peptides based on C-terminal sequences of thrombospondin-1 also, specifically enhanced adhesion of melanoma cells and T cells to alpha(4)beta(1) ligands. Unexpectedly, activation of alpha(4)beta(1) function by the thrombospondin-1 CD47-hinding peptides also occurred in CD47-deficient T cells. CD47-independent activation of alpha(4)beta(1), required the Val-Val-Met (VVM) motif of the peptides and was sensitive to inhibition by pertussis toxin. These results indicate that activation of alpha(4)beta(1), by the CD47 antibody B6H12 and by VVM peptides occurs by different mechanisms. The antibody directly activates a CD47-alpha(4)beta(1) complex, whereas VVM peptides may target an unidentified G(i)-linked receptor that regulates alpha(4)beta(1).