Responsiveness to transforming growth factor-beta (TGF-beta)-mediated growth inhibition is a function of membrane-bound TGF-beta type II receptor in human breast cancer cells.

Abstract

Transforming growth factor-beta (TGF-beta) is a potent inhibitor of growth and proliferation of breast epithelial cells, and loss of sensitivity to its effects has been associated with malignant transformation and tumorigenesis. The biological effects of TGF-beta are mediated by the TGF-beta receptor complex, a multimer composed of TGF-beta receptor type I (TbetaR-I) and TGF-beta receptor type II (TbetaR-II) subunits. Evidence suggests that loss of expression of Tbeta3R-II is implicated in the loss of sensitivity of tumorigenic breast cell lines to TGF-beta-mediated growth inhibition. A panel of human breast cell lines, including the immortalized MCF-10F and tumorigenic MCF-7, ZR75-1, BT474, T47-D, MDA-MB231, BT20, and SKBR-3 cell lines, was characterized for responsiveness to TGF-beta-induced G1 growth arrest. Only the nontumorigenic MCF-10F and the tumorigenic MDA-MB231 cell lines demonstrated a significant inhibitory response to TGF-beta1 and a significant binding of 125I-labeled TGF-beta ligand. While expression of TbetaR-I mRNA was similar across the panel of cell lines, TbetaR-II mRNA expression was decreased significantly in all seven tumorigenic cell lines in comparison with the nontumorigenic MCF- 10F cell line. When total cellular protein was fractionated by centrifugation, TbetaR-I protein was observed in both the cytosolic and membrane fractions at similar levels in all cell lines; however, TbetaR-II protein was present in the cytosolic fraction in all cell lines, but was observed in the membrane fraction of only the TGF-beta-responsive MCF-10F and MDA-MB231 cells. Thus, lack of membrane-bound TbetaR-II protein appears to be an important determinant of resistance to TGF-beta-mediated growth inhibition in this group of breast cell lines.