αvβ1 is a receptor for vitronectin and fibrinogen, and acts with α5β1 to mediate spreading on fibronectin

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Abstract
We have shown previously that VUP was the only line out of ten human melanoma lines that failed to express the vit-ronectin receptor αvβ3, but instead expressed αvβ1. Levels of αvβ1 expression were low on parental VUP cells so that iterative sorting by FACS, using an anti-αv antibody (13C2), was utilised to derive sublines with 8-to 10-fold higher amounts of cell surface αvβ1. There was little dif-ference between low (V−) and high (V+) αvβ1-expressing sublines with regard to adherence to collagen type I, collagen type IV or laminin substrata. However, adherence to vitronectin and fibrinogen correlated closely with αvβ1 expression (35-42% adhesion for V(+) lines versus 6-8% adhesion for V− lines on vitronectin, for example). Utilising a high αvβ1-expressing subline (V+B2) we have shown that binding to vitronectin and fibrinogen was inhibited specif-ically by function-blocking antibodies to αv (17E6 and 14D9) and β1 (A11B2). V(+) sublines spread more compared with V(−) sublines on both vitronectin and fibronectin. However, neither α5-nor αv-blocking anti-bodies had any effect on attachment or spreading of V+B2 on fibronectin whereas the combination of α5 (PID6)-and αv(17E6)-blocking antibodies abrogated binding to fibronectin almost completely. This is the first report of an αvβ1 integrin able to recognise vitronectin and fibrinogen, and also cooperate with α5β1 to mediate attachment to and spreading on fibronectin.

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