REQUIREMENT FOR THE SYNERGY SITE FOR CELL-ADHESION TO FIBRONECTIN DEPENDS ON THE ACTIVATION STATE OF INTEGRIN ALPHA-5-BETA-1

We investigated the influence of the activation state of integrin alph a 5 beta 1 on its dependence on the PHSRN synergy site for binding to RGD in fibronectin. K562 and MV3 cells lacked alpha v beta 3 expressio n and adhered to fibronectin through alpha 5 beta 1. Mel57 cells adher ed through alpha v beta 3 and alpha 5 beta 1. A recombinant fibronecti n polypeptide, containing five type III repeats from the central cell binding domain 3Fn6-10, and a mutated polypeptide lacking the synergy site were equally effective in promoting Mel57 adhesion. For K562 and MV3, the mutated polypeptide was not or poorly active compared to the control polypeptide. Expression of alpha v beta 3 in MV3 induced stron g adhesion to the mutated polypeptide. TS2/16 stimulatory beta 1-integ rin antibodies or Mn2+ induced alpha 5 beta 1-mediated adhesion of K56 2 and MV3 to GRGDSP. In the presence of TS2/16 or Mn2+, alpha 5 beta 1 -mediated MV3 adhesion to the mutated polypeptide was equally strong a s adhesion to the control polypeptide. Mn2+ or TS2/16 induced weak K56 2 binding to the mutated polypeptide, and in the presence of a combina tion of phorbol 12-myristate 13-acetate. Mn2+, and TS2/16, alpha 5 bet a 1-mediated K562 adhesion to the mutated and control polypeptide was equally strong. Our findings demonstrate that requirement for the PHSR N synergy site for alpha 5 beta 1-mediated adhesion to RGD in fibronec tin depends on the activation state of the integrin.