Boyd Cary, Náray-Fejes-Tóth Anikó
Department of Physiology, Dartmouth Medical School, Borwell Building 744W, 1 Medical Center Drive, Lebanon, New Hampshire 03756, USA.
Endocrinology. 2007 Aug;148(8):3958-67. doi: 10.1210/en.2006-1741. Epub 2007 May 17.
The epithelial sodium channel (ENaC) is a key mediator of sodium transport in epithelia; however, little is known about ENaC expression in mammary epithelia. Using real-time PCR, we demonstrated the expression of the ENaC subunit mRNAs in mouse and human mammary cell lines and in vivo mouse mammary tissue. We determined the effects of glucocorticoids, progesterone, and prolactin on ENaC expression in four mammary cell lines. Dexamethasone induced all detectable ENaC subunits in noncancerous cell lines, HC11 and MCF10A. Interestingly, in cancerous cell lines (T-47D and MCF-7), both beta- and gamma- but not alphaENaC mRNAs were induced by dexamethasone. Progesterone induced ENaC mRNA only in T-47D cells, and prolactin had no effects. gammaENaC was rapidly induced by steroids, whereas induction of alpha- and betaENaC was slower; moreover, the induction of the beta-subunit required de novo protein synthesis. Dexamethasone treatment did not affect ENaC mRNA stability. Western blot analysis revealed immunoreactive bands corresponding to different forms of alpha-, beta-, and gammaENaC; dexamethasone significantly increased the intensity of alphaENaC (85 kDa) and betaENaC (90 kDa). We also showed an in vivo reduction in alphaENaC levels in the mammary tissue of lactating mice as compared with controls, whereas beta- and gammaENaC mRNA levels were significantly increased. Furthermore, dexamethasone in vivo significantly increased alpha-, beta-, and gammaENaC mRNA expression. Our data indicate that both mouse and human mammary cells express all ENaC subunits, and they are regulated by steroid hormones in a temporal and cell-specific manner both in culture and in vivo.
上皮钠通道（ENaC）是上皮细胞中钠转运的关键介质；然而，关于ENaC在乳腺上皮中的表达情况却知之甚少。我们运用实时定量PCR技术，证实了ENaC亚基mRNA在小鼠和人类乳腺细胞系以及小鼠体内乳腺组织中的表达。我们确定了糖皮质激素、孕酮和催乳素对四种乳腺细胞系中ENaC表达的影响。地塞米松可诱导非癌细胞系HC11和MCF10A中所有可检测到的ENaC亚基。有趣的是，在癌细胞系（T-47D和MCF-7）中，地塞米松仅诱导β-和γ-而非α-ENaC mRNA的表达。孕酮仅在T-47D细胞中诱导ENaC mRNA的表达，而催乳素则无此作用。γ-ENaC可被类固醇迅速诱导，而α-和β-ENaC的诱导则较为缓慢；此外，β-亚基的诱导需要从头合成蛋白质。地塞米松处理并未影响ENaC mRNA的稳定性。蛋白质印迹分析显示出与不同形式的α-、β-和γ-ENaC相对应的免疫反应条带；地塞米松显著增加了α-ENaC（85 kDa）和β-ENaC（90 kDa）的条带强度。我们还发现，与对照组相比，哺乳期小鼠乳腺组织中α-ENaC水平在体内有所降低，而β-和γ-ENaC mRNA水平则显著升高。此外，体内给予地塞米松可显著增加α-、β-和γ-ENaC mRNA的表达。我们的数据表明，小鼠和人类乳腺细胞均表达所有ENaC亚基，并且它们在培养和体内均受到类固醇激素的时间和细胞特异性调控。
