Regulation of the levels of three transforming growth factor β mRNAs by estrogen and their effects on the proliferation of human breast cancer cells

Transforming growth factor (TGF) β is a potent regulator of cell proliferation and may play a role in breast cancer cell growth. We have evaluated the regulation of TGFβ1, TGFβ2, and TGFβ3 mRNAs by 17β-estradiol (E₂) and 4-hydroxytamoxifen (MOH) in estrogen receptor-positive (ER(+)) MCF-7 and estrogen receptor-negative (ER(-)) MDA-MB-231 human breast cancer cells. We also determined the effect of TGFβ1, TGFβ2, and TGFβ3 on the proliferation of these cells. Cells were deprived of estrogen before the addition of hormones, and mRNA was measured by Northern blot analysis. We found that MCF-7 cells expressed mRNAs of all three TGFβ species. Treatment of MCF-7 cells with 10^-10 M E₂ for 7 days resulted in a dramatic decrease in the TGFβ2 and TGFβ3 mRNA levels, but not in the TGFβ1 mRNA level. MOH was found to block these effects. In addition, the regulation of TGFβ2 and β3 gene expression occurs at both transcriptional and post-transcriptional levels. There is an inverse correlation between E₂-induced growth and levels of TGFβ2 and TGFβ3 mRNA. In contrast to MCF-7 cells, MDA-MB-231 cells expressed TGFβ1 and TGFβ2 mRNAs but TGFβ3 mRNA was not detected, and the TGFβ1 and TGFβ2 mRNAs were not regulated by estrogens or antiestrogens. TGFβ3 gene is present in MDA-MB-231 cells and based on the enzymes used, no restriction fragment length polymorphism (RFLP) was observed in the TGFβ3 gene between the MCF-7 and MDA-MB-231 cells. The addition of TGFβ1, TGFβ2, or TGFβ3 inhibited the growth of MDA-MB-231 but not the late passage of MCF-7 cells. Interestingly, the growth of early passage of MCF-7 cells was inhibited by the addition of TGFβ1, TGFβ2, or TGFβ3. In summary, E₂ can regulate the expression of different members of the TGFβ family; however, these may not be directly involved in the E₂-stimulated proliferation in the late passage of MCF-7 human breast cancer cells. It is possible that paracrine mechanism in regulating cell replication of ER(-) cells is more important for the function of TGFβ in ER(+) MCF-7 cells in response to E₂.