The integrin specificity of human recombinant osteopontin

The ability of full-length human recombinant osteopontin (OPN) to support the adhesion of various α V integrin-expressing cell lines was determined in order to characterize its integrin selectivity. The identity of this protein was assessed by cDNA sequence and mass spectroscopic analysis, and confirmed as full-length OPN. Neither the human embryonic kidney 293 cell line, which expresses the α Vβ 1 integrin, nor the human colonic adenocarcinoma HT-29 cell line, which expresses the α Vβ 5 integrin, were able to adhere to OPN; both of these cell lines are deficient in the β 3 subunit. In contrast, an α Vβ 3 integrin-expressing cell line, SK-MEL-24, was able to adhere to OPN in an arginine-glycine-aspartic acid dependent manner. In addition, this OPN-mediated cellular adhesion was completely blocked with an anti-α Vβ 3 integrin antibody (LM609), confirming that only the α Vβ 3 integrin mediated this cellular adhesion. These data demonstrate that, at least among the α V integrins, only the α Vβ 3 is able to support cellular adhesion to osteopontin. This finding may have implications for the design of therapeutics targeting OPN–integrin interactions.