Regulation of transforming growth factor-β type II receptor expression in human breast cancer MCF-7 cells by vitamin D₃ and its analogues

In view of the tumor suppressor role of the transforming growth factor- β (TGFβ) type II receptor (RII), the identification and characterization of agents that can induce the expression of this receptor are of potential importance to the development of chemoprevention approaches as well as treatment of cancer. To date, the identification of exogenous agents that control RII expression has been rare. We demonstrated that proliferation of MCF-7 early passage cells (MCF-7 E), which express RII and are sensitive to TGFβ growth inhibition activity, was significantly inhibited by vitamin D₃ and its analogue EB1089. In contrast, proliferation of MCF-7 late passage cells (MCF-7 L), which have lost cell surface RII and are resistant to TGFβ, was not affected by these two compounds. TGFβ-neutralizing antibody was able to block the inhibitory effect on MCF-7 cells by these compounds, indicating that treatment induced autocrine-negative TGFβ activity. An RNase protection assay showed approximately a 3-fold induction of the RII mRNA, while a receptor cross-linking assay revealed a 3-4-fold induction of the RII protein. In contrast, there was no change in either RII mRNA or protein in the MCF-7 cells.