We have created fusion proteins between Fas and the ligand-binding domain of the estrogen or retinoic acid receptor. Murine fibrosarcoma L929 cells and human cervical carcinoma HeLa cells expressing the fusion proteins demonstrated apoptotic phenotypes in a tightly estrogen- or retinoic acid-dependent manner in vitro. Moreover, the fusion protein-expressing L929 cells transplanted into nude mice were also killed through apoptosis after injection of an estrogen agonist. This represents a novel system, “cell targeting,” that can eliminate cells not only in vitro but also in vivo through the activation of a natural suicide machinery, i.e., apoptosis, by currently used hormones. This system implies wide applications not only in developmental biology and neurobiology but also in medicine, especially for cancer gene therapy.
This work was supported in part by research grants from the Ministry of Education, Science, Sports and Culture of Japan.