期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：31
页码：11443-11448
DOI：10.1073/pnas.1412099111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The sodium-coupled neutral amino acid transporter 2 (SNAT2) translocates small neutral amino acids into the mammary gland to promote cell proliferation during gestation. It is known that SNAT2 expression increases during pregnancy, and in vitro studies indicate that this transporter is induced by 17{beta}-estradiol. In this study, we elucidated the mechanism by which 17{beta}-estradiol regulates the transcription of SNAT2. In silico analysis revealed the presence of a potential estrogen response element (ERE) in the SNAT2 promoter. Reporter assays showed an increase in SNAT2 promoter activity when cotransfected with estrogen receptor alpha (ER-) after 17{beta}-estradiol stimulation. Deletion of the ERE reduced estradiol-induced promoter activity by 63%. Additionally, EMSAs and supershift assays showed that ER- binds to the SNAT2 ERE and that this binding competes with the interaction of ER- with its consensus ERE. An in vivo ChIP assay demonstrated that the binding of ER- to the SNAT2 promoter gradually increased in the mammary gland during gestation and that maximal binding occurred at the highest 17{beta}-estradiol serum concentration. Liquid chromatography-elevated energy mass spectrometry and Western blot analysis revealed that the SNAT2 ER--ERE complex contained poly(ADP-ribose) polymerase 1, Lupus Ku autoantigen protein p70, and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) proteins and that the silencing of each of these proteins nearly abolished 17{beta}-estradiol-stimulated SNAT2 promoter activity. Nuclear levels of GAPDH increased progressively during gestation in the mammary gland, and GAPDH binding was nucleotide-specific for the SNAT2 ERE. Thus, this study provides new insights into how the mammary epithelium adapts to control amino acid uptake through the transcriptional regulation of the SNAT2 transporter via 17{beta}-estradiol.
