We have quantitated the relative contributions of the constitutively active α4β1 and α4β7 integrins and the domains embodying their cognate binding sites in mediating human B-cell lymphoma adhesion and chemotaxis on fibronectin. By cooperating, the central cell-binding and IIICS carboxyterminal domains were entirely responsible for the adhesion activity displayed by fibronectin, and their relative contribution to this process was estimated to be 30% versus 70%. Assessment of the leukocyte-substrate binding strength (ie, dynes/cell) indicated a 10-fold higher avidity of the cell- IIICS domain interaction. The two integrins interchangeably recognized both domains, but differed quantitatively in their participation in the adhesive event, as well as in domain preference. The use of 3Fn (according to the nomenclature proposed by Bork and Koonin [Curr Opin Struct Biol 6:366, 1996] for the type III fibronectin modules) module-specific antibodies and recombinant polypeptides showed that α4 integrins recognized both the RGD sequence (3Fn10) and an apparently novel synergistic site located within the 3Fn8 module; even in this case, the integrins displayed a distinct binding site preference. Interleukin-1β (IL-1β)/IL-2-induced chemotaxis also involved cooperative function of the central cell-binding and IIICS domains, but the mechanisms regulating this phenomenon differed markedly from those controlling cell adhesion. First, the relative contribution of the individual domains was comparable, but neither of the individual domains promoted migration to the extent observed on intact fibronectin. Secondly, α4β1 and α4β7 integrins were both involved in the domain-binding necessary for initiation of migration, but the relative contribution of each receptor in the chemotactic process was less disparate than for initial cell adhesion. Thirdly, the mode by which chemotactic B-lymphoma movement was supported by the central cell-binding domain differed from that sustaining cell adhesion in that it involved independent recognition of either the 3Fn8 or the 3Fn9 module, which acted in synergy with the 3Fn10 module. Our data provide novel evidence concerning the relative importance of the constitutively active α4β1 and α4β7 integrins for the interaction of B-cell lymphoma cells with fibronectin, and they emphasize a multiple and diverse recognition of sites responsible for either anchorage or locomotion of tumor leukocytes on this matrix molecule.
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