CELL-ADHESIVE RESPONSES TO TENASCIN-C SPLICE VARIANTS INVOLVE FORMATION OF FASCIN MICROSPIKES

Tenascin-C is an adhesion-modulating matrix glycoprotein that has mult iple effects on cell behavior. Tenascin-C transcripts are expressed in motile cells and at sites of tissue modeling during development, and alternative splicing generates variants that encode different numbers of fibronectin type III repeats. We have examined the in vivo expressi on and cell adhesive properties of two full-length recombinant tenasci n-C proteins: TN-190, which contains the eight constant fibronectin ty pe III repeats, and TN-ADC, which contains the additional AD2, AD1, an d C repeats. In situ hybridization with probes specific for the AD2, A D1, and C repeats shows that these splice variants are expressed at si tes of active tissue modeling and fibronectin expression in the develo ping avian feather bud and sternum. Transcripts incorporating the AD2, AD1, and C repeats are present in embryonic day 10 wing bud but not i n embryonic day 10 lung. By using a panel of nine cell lines in attach ment assays, we have found that C2C12, G8, and S27 myoblastic cells un dergo concentration-dependent adhesion to both variants, organize acti n microspikes that contain the actin-bundling protein fascin, and do n ot assemble focal contacts. On a molar basis, TN-ADC is more active th an TN-190 in promoting cell attachment and irregular cell spreading. T he addition of either TN-190 or TN-ADC in solution to C2C12, COS-7, or MG-63 cells adherent on fibronectin decreases cell attachment and res ults in decreased organization of actin microfilament bundles, with fo rmation of cortical membrane ruffles and retention of residual points of substratum contact that contain filamentous actin and fascin. These data establish a biochemical similarity in the processes of cell adhe sion to tenascin-C and thrombospondin-1, also an ''antiadhesive'' matr ix component, and also demonstrate that both the adhesive and adhesion -modulating properties of tenascin-C involve similar biochemical event s in the cortical cytoskeleton. In addition to these generic propertie s, TN-ADC is less active in adhesion modulation than TN-190. The coord inated expression of different tenascin-C transcripts during developme nt may, therefore, provide appropriate microenvironments for regulated changes in cell shape, adhesion, and movement.