Adhesion mediated by fibronectin's alternatively spliced EDb (EIIIB) and its neighboring type III repeats

Adhesion functions of cellular fibronectin's (FN) alternatively spliced EDb (EIIIB) domain, as well as its neighboring type III repeats III7 and III8, were investigated with several cultured murine and human cell types. Minigene constructs encoding various permutations of these repeats and expressed in bacteria were used as shown previously in function studies of EDa and its neighboring repeats (P.Xia and L. A. Culp Exp. Cell Res. 213, 253-265, 1994). When substrata of recombinant proteins were incubated with several fibroblastic or neuronal derivative cell lines, cell attachment responses varied widely in a cell-type-specific manner. Balb/c 3T3 cells were shown to adhere to recombinant protein substrata in dose-dependent and EDTA-sensitive manners. Responses also varied with which repeat combinations were being tested, from excellent (Balb/c 3T3, src-3T3), to intermediate (Platt cells), to poor (LZEJ, VA-13, and F11), with EDb plus-containing proteins generally giving better adhesion than EDb minus proteins. On select recombinant proteins, cells showed limited cytoplasmic spreading (3T3 and src-3T3) or neurite extension (Platt and F11), while other cell lines (VA-13 and LZEJ) did not show any morphological changes beyond attachment. Again, EDb plus-containing recombinants were more effective at inducing these morphological changes than the neighboring repeats. These results demonstrate that the EDb domain of cellular FNs and its neighboring type III homology repeats contain important adhesion-promoting sequences, which may be regulated by cells through alternative splicing of FN's primary transcript.