Characterization of transforming growth factor-b receptors in the human endometrium

Transforming growth factor-$ beta$ (TGF-$ beta$) is a multifunctional polypeptide growth factor which is believed to play an important role in the growth and differentiation of uterine cells. Although the expression of TGF-$ beta$ in the uterus has been previously described, the receptors for TGF-$ beta$ in this tissue have not been characterized. In the present study, the cell surface receptors for TGF-$ beta$ were characterized on cultures of stromal cells prepared from human endometrial biopsies, and on a human endometrial epithelial cell line (RL95-2) using affinity labeling techniques. On stromal cells, five TGF-$ beta$ binding proteins were identified. Analysis of the sensitivity of these proteins to dithiothreitol and phosphatidylinositol-specific phospholipase C, together with results from immunoprecipitations with anti-TGF-$ beta$ receptor antibodies, confirmed that three of these binding proteins correspond to the cloned type I, II, and III TGF-$ beta$ receptors. The other two binding proteins exhibited characteristics of isoform-specific glycosyl-phosphatidylinositol-anchored TGF-$ beta$ binding proteins. On RL95-2 cells, three TGF-$ beta$ binding proteins, corresponding to the type I, II and III TGF-$ beta$ receptors, were identified. The number of receptors on endometrial cells and their relative affinity for TGF-$ beta$ was estimated by Scatchard analysis. These receptors are responsive to physiological concentrations of TGF-$ beta$ as demonstrated by the effect of TGF-$ beta$ on DNA synthesis in these cells. Accordingly, they have the potential to respond to TGF-$ beta$ expressed in the endometrium in an autocrine and/or paracrine manner