Synergistic growth stimulation of mouse fibroblasts by tumor-derived adhesion factor with insulin-like growth factors and insulin.

Tumor-derived adhesion factor (TAF) has been purified as a major secretory protein with cell-adhesion activity from culture medium conditioned by human bladder carcinoma cells (K. Akaogi et al., Biochem. Biophys. Res. Commun., 198: 1046-1053, 1994). TAF is closely related or identical to a putative protein encoded by the mac25 gene (M. Murphy et al., Cell Growth & Differ., 4: 715-722, 1993) and prostacyclin-stimulating factor (T. Yamauchi et al., Biochem. J., 303: 591-598, 1994). TAF has a characteristic cysteine cluster in its NH2-terminal sequence, which is conserved in the NH2 termini of insulin-like growth factor-binding proteins. In the present study, we examined the interaction of TAF with insulin-like growth factors (IGFs) and insulin. Although in a ligand blotting assay TAF bound neither IGFs nor insulin, immunoprecipitation assay showed weak interaction of TAF with IGF-I, IGF-II, and insulin. TAF by itself stimulated the growth of BALB/c3T3 cells on the usual plastic substrates and significantly enhanced IGF- or insulin-mediated cell growth. Moreover, marked potentiation of the mitogenic activities of IGFs and insulin by TAF was found in the culture on type IV collagen substrates. The synergistic growth stimulation was completely blocked by heparin. These results suggest that TAF may regulate the growth of fibroblastic cells in collaboration with IGFs and insulin.