CONCERTED ACTION OF TENASCIN-C DOMAINS IN CELL-ADHESION, ANTIADHESIONAND PROMOTION OF NEURITE OUTGROWTH

We used a new approach to identify domains of chicken tenascin-C requi red for interaction with cells. Instead of expressing the parts of int erest, we deleted them from an otherwise intact tenascin-C molecule an d scored for the concomitant change in activity. As a starting point f or all mutant constructs we expressed the smallest naturally occurring tenascin-C splice variant in vertebrate cells. The tenascin-C mutants had either deletions of all EGF-like repeats, all fibronectin type II I repeats or of the fibrinogen globe. In double mutants the fibronecti n type III repeats were deleted together with either the EGF-like repe ats or the fibrinogen globe, respectively. All tenascin-C variants ass embled correctly to hexameric molecules of the expected molecular char acteristics. Intact tenascin-C and the mutant missing the fibrinogen g lobe did not promote adhesion of chick embryo fibroblasts, whereas bot h, the hexamers containing solely the fibrinogen globe or the EGF-like repeats were adhesive substrates and even supported cell spreading. W hen tenascin-C was added to the medium of fibroblasts plated on fibron ectin-coated wells, cell adhesion was blocked by intact tenascin-C, bu t not by mutants missing the fibrinogen globe. In neurite outgrowth as says using dorsal root ganglia, processes formed on all substrates exc ept on the mutant missing only the fibrinogen globe, where the ganglia failed to adhere. The mutants missing the fibronectin type III repeat s allowed more rapid neurite outgrowth than all other tenascin-C varia nts and the mutant consisting essentially of oligomerized EGF-like rep eats was as active a substrate for neurite outgrowth as laminin. From the combined data, it is concluded that the activities of intact tenas cin-C cannot be mimicked by investigating domain by domain, but the co ncerted action of several domains leads to the diverse cellular respon ses.