MULTIPLE INTEGRINS MEDIATE CELL ATTACHMENT TO CYTOTACTIN TENASCIN

To identify potential cell surface receptors for chicken cytotactin (C T), we have characterized the ability of recombinant fusion proteins s panning the proximal fibronectin (FN) type III repeats of the molecule to support attachment of glioma and carcinoma cell lines. The third F N type III repeat, which contains the RGD tripeptide, supported cell a ttachment and cell spreading; however, mutation of RGD to RAD did not result in significant loss of either activity. In addition, the same r epeat of mouse CT, which contains a natural mutant, RVD, also supporte d cell attachment and spreading, although at a lower level; both activ ities were increased by mutation of the RVD sequence to RGD. Studies u tilizing RGD-containing peptides and well-characterized antibodies to integrins indicated that cell attachment to the third FN type III repe at was mediated by at least two different integrin receptors of the av subtype. Additional cellular receptors may also be involved in cell a ttachment to CT. For example, an antibody to the beta1 subfamily of in tegrins partially inhibited binding of cells to intact CT but did not inhibit cell binding to the third FN type III repeat. These findings s uggest that the RGD site in CT is able to mediate cell attachment to i ntegrins and thus is not a cryptic adhesion site. They also open the p ossibility that the functions of CT in processes such as counteradhesi on, cell migration, cell proliferation, and cell differentiation may b e mediated in part by interaction with multiple integrins.