Summary

Human cancer cell lines A431 and MCF7, which do not produce tenascin (TN) in vitro, were found to produce TN when injected into nude mice or co-cultured with the embryonic mesenchyme. The TN expression in the developing A431 solid tumor was demonstrated by immunohistochemistry and by in situ hybridization. Human TN was detected in culture media by western blot analysis using human specific monoclonal antibody (RCB-1). During tumorigenesis, in the early stage, mouse TN was actively induced and deposited in the peri- and intertumor spaces surrounding the developing tumor. Two days later, TN derived from human epithelial cancer cells was induced and mainly deposited in the intertumor basement membrane. After this stage, tumor cells were actively producing TN. On the other hand, TN induction in non TN-producing cells, such as A431 and MCF7 cell lines, was also observed in vitro. Although cell lines such as NIH-3T3, phi 2, STO, 2H6, 3E5 and CMT315, had no effect on the TN induction, primary cultured embryonic mesenchyme effectively stimulated the TN expression in the cancer cell lines. This mesenchymal effect decreased with age and was entirely lost postnatally. Furthermore, conditioned media from these embryonic mesenchymes could reproduce the same effects on TN induction as observed in the co-culture study. In conclusion, these findings suggest that TN induction in epithelial cancer cells may depend on interactions with the surrounding environment, that these interactions may be mediated by a soluble factor(s) derived from the surrounding mesenchyme and that the TN induction observed in the tumorigenesis may reflect histogenesis during the embryonic period.