Functional characterization of antiadhesion molecules.

Cytotactin, cytotactin binding (CTB) proteoglycan, and several other extracellular matrix (ECM) proteins and proteoglycans are described as antiadhesion molecules because they inhibit cell spreading and attachment to normally permissive ECM proteins. For cytotactin and CTB proteoglycan, this effect appears to be due to the binding of these proteins to their cell-surface receptors, which initiates a transmembrane signal that inhibits cell spreading. In contrast, the binding of fibronectin or laminin to its cell-surface receptors promotes cell spreading. Cell behavior may be regulated in a variety of systems by the interplay between these two opposing signals. For example, eosinophils on laminin spreading, form numerous foci containing filamentous actin, and remain viable in culture. In contrast, eosinophils on a mixture of laminin and cytotactin do not spread or form foci containing filamentous actin and the maintenance of viability is inhibited. In another system designed to model the immune surveillance of tumors, monocytes migrate in response to tumor necrosis factor through a gel comprised of a mixture of basement membrane proteins (Matrigel). Migration is blocked if the gel is coated with cytotactin. This result is of particular significance because cytotactin is expressed at high levels in the stroma of adult breast tissue surrounding tumors but only at low levels in normal breast tissue. These observations suggest that inflammation and the immune surveillance of tumors are among the processes regulated by cytotactin.