Retinoic acid affects the EGF-R signaling pathway during differentiation induction of human endometrial adenocarcinoma cells

We have shown that moderately differentiated endometrial adenocarcinoma (RL95-2) cells differentiate in response to retinoic acid treatment, illustrated by their reorganization of actin filaments and cell enlargement (Carter et al., Anticancer Res. 16, 17-24, 1996). Tyrphostin, an inhibitor of epidermal growth factor receptor (EGF-R)-associated protein tyrosine kinases, caused a dramatic reorganization of actin filaments in RL95-2 cells, similar to retinoic-acid-treated cells (Carter and Bellido, J. Cell. Physiol. 178, 320-332, 1999). We evaluated the possibility that the differentiating effects of retinoids are due to retinoic-acid-induced decreases in phosphorylation of EGF-R and changes in downstream effector proteins. Retinoic acid caused a decrease in tyrosine phosphorylation of EGF-R. Retinoic acid treatment induced a dramatic actin filament reorganization and cell enlargement. Treatment with EGF reversed this effect, because cells treated with retinoic acid followed by EGF only possessed disrupted actin aggregates and appeared small, thus resembling medium controls. Retinoic acid induced a relocalization and decrease in the amount of Shc protein. another actin-binding protein which is an adaptor protein for EGF-R signaling. In addition, retinoic acid induced a relocalization of gelsolin from the plasma membrane to the cytoplasm. Retinoic acid decreased cell detachment in detachment assays; one-half as many retinoic-acid-treated cells detached as in controls. These results are consistent with the idea that retinoic acid induces differentiation of RL95-2 cells by interfering with the EGF-R signaling pathway. (C) 2000 Academic Press.