Steroid sulfatase activity and expression in mammary myoepithelial cells

Purpose: This investigation examined mRNA expression and enzymatic activity of steroid sulfatase (STS) in human mammary myoepithelial cells (MMECs) and MCF-7 cells and assessed the effects of 17-β estradiol on the activity of STS. Methods: The mRNA level of STS in MMECs was determined by RT-PCR analysis using specific primers for STS. STS enzymatic activity prior to and after treatment with 17-β estradiol was determined by measuring ³H-metabolites formed after exposure to [³H]estrone 3-sulfate (E1S) and [³H]dehydroepiandrosterone-sulfate (DHEA-S). Results: Our data demonstrate the presence of STS in the MMECs. Based on RT-PCR analysis, MMECs had slightly lower levels of STS compared to MCF-7 cells. However, sulfatase activity was about 120 times greater in the MMECs than the MCF-7 cells (E1S V_max=2640nmol/(mg DNAh) compared to 20.9nmol/(mg DNAh)). Exposure to 17-β estradiol was associated with 70% reduction in E1S sulfatase activity in the MCF-7 cells and 9% increase in the MMECs after 6 days. Discussion: Our studies indicate for the first time the presence of STS in MMECs. This is suggestive of a previously undetermined role for MMECs in converting precursor hormones into active steroid hormones within mammary tissue. In addition, differential response of the MMECs and the MCF-7 cells to estrogen demonstrates differences in hormone metabolism between these two cell types, perhaps related to the absence of estrogen receptors in the MMECs and their presence in the MCF-7 cells. The MMECs may have an important role in hormonal regulation within mammary tissue.