Transforming growth factor (TGF)-β is a potent regulator of many cell functions and a growth inhibitor for mammary epithelial cells. We now know of three highly homologous members of the human TGF-β gene family. We have studied the expression of TGF-β1, -β2, and -β3 mRNA in four human breast cancer cell lines. Using the RNase protection assay, we have detected mRNA expression of TGF-β1, -β2, and -β3 by T-47D cells, TGF-β1 and -β3 by ZR-75-1 cells, and TGF-β1 by MCF-7 cells. Treatment of these estrogen receptor-positive cells with 10 nm estradiol for 48 h resulted in decreased mRNA levels of TGF-β2 and -β3 but did not affect mRNA levels of TGF-β1. Expression of TGF-β1 and -β2 mRNA by an estrogen receptor-negative cell line, MDA-MB-231, was not changed by estradiol treatment. Treatment of cells with the antiestrogen tamoxifen (1 µm) did not significantly alter mRNA levels for any of the three TGF-β species. We have further determined that estradiol treatment of T-47D was associated with diminished secretion of TGF-β into the medium. Both TGF-β1 and -β2 inhibited the proliferation of MCF-7 cells, and neither protein affected the growth of T-47D cells. TGF-β1 was at least 10-fold more potent than TGF-β2 at inhibiting the growth of MCF-7 cells.

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