Steroid regulation of epithelial sodium channels (ENaC) in mammary epithelial cells

The epithelial sodium channel (ENaC) is important in lactating mammary cells for regulating the Na + content of milk, while in cancerous mammary cells ENaC may play a role in oncogenesis. The goal of this study is to determine how steroids and/or the serum‐and glucocorticoid induced kinase (SGK1), affect ENaC expression in mammary epithelial cells (MEC). Using real‐time PCR we determined ENaC (α, β, γ ) mRNA induction in response to steroid hormones in 3 MEC lines. Under basal conditions, mouse HC11 MEC expressed α and γ ENaC mRNA; these levels were 10‐fold and 2‐fold lower than those in cortical collecting duct cells. In HC11, dexamethasone (dex) (1μM, 24h) induced ENaC mRNA levels 3‐fold and γ ENaC mRNA levels 12‐fold (βENaC was too low for detection). Next we determined the effects of changes in SGK1 expression/activity on ENaC mRNA levels. We previously reported that in CCD cells SGK1 upregulates α and βENaC mRNA levels. In contrast, in HC11 cells, SGK1 most significantly increased γ ENaC mRNA as compared to cells expressing dominant negative SGK1. This suggests that the regulation of ENaC mRNA levels by SGK1 is cell specific. We also tested the effect of dex in two human MEC lines. In MCF10A, dex induced all three subunits: α(5‐fold), β(18‐fold), and γ (15‐fold). In the cancerous T47D, both the β and γ subunit were induced by dex (2‐ and 10‐fold), while surprisingly αENaC was unchanged. In summary, these data reveal that MEC express ENaC subunits, which are regulated by steroid hormones in a subunit and cell‐specific manner. ENaC gene expression in the cancerous MEC is regulated differently than in non‐cancerous MEC.