Abstract
Recombinant wild-type rabbit osteopontin (rOP) and the protein with an aspartate-to-glutamate transposition induced by a point mutation in the rabbit OP cDNA within the Gly-Arg-Gly-Asp-Ser (GRGDS) sequence were expressed in Escherichia coli and purified to homogeneity. P388D1 cells bound rOP in a saturable manner. rOP induced adhesion and haptotaxis of P388D1 cells, whereas mutated rabbit OP (rOPmut) did not. Anti-rOP IgG F(ab')2 and synthetic GRGDS peptide inhibited rOP-mediated adhesion and haptotaxis of P388D1 cells. Fibronectin (FN)-mediated adhesion of P388D1 cells was markedly inhibited in the presence of fluid-phase rOP. Adhesion of P388D1 cells to rOP was significantly inhibited by anti-[alpha-subunits of VLA4 (alpha 4) and VLA5 (alpha 5)] monoclonal antibodies (mAbs), but not by anti-[alpha-subunit of vitronectin (VN) receptor (alpha V) or Mac-1 (alpha M)] mAb. Adhesion of P388D1 cells to FN and VN was significantly inhibited by anti-alpha V mAb but not anti-alpha 4, -alpha 5 or -alpha M mAb. Haptotaxis of P388D1 cells to rOP was significantly inhibited by anti-alpha V mAb, but not by anti-alpha 4, -alpha 5 and alpha M mAbs, whereas that to FN showed no inhibition with all three mAbs. Haptotaxis of P388D1 cells to VN was significantly inhibited by anti-alpha 5 and -alpha V mAbs but not by anti-alpha 4 and -alpha M mAbs. Similar features of inhibition of adhesion and haptotaxis of P388D1 cells to human OP were observed by mAbs. rOP had no chemotactic effect on P388D1 cells. Significant polymorphonuclear leucocyte migration was observed 3-12 h after intradermal injection of rOP into rabbits.