title: GSK3β regulates milk synthesis in and proliferation of dairy cow mammary epithelial cells via the mTOR/S6K1 signaling pathway.
abstract: Glycogen synthase kinase 3 (GSK3) is a serine/threonine kinase, whose activity is inhibited by AKT phosphorylation. This inhibitory phosphorylation of GSK3β can in turn play a regulatory role through phosphorylation of several proteins (such as mTOR, elF2B) to promote protein synthesis. mTOR is a key regulator in protein synthesis and cell proliferation, and recent studies have shown that both GSK3β and mTORC1 can regulate SREBP1 to promote fat synthesis. Thus far, however, the cross talk between GSK3β and the mTOR pathway in the regulation of milk synthesis and associated cell proliferation is not well understood. In this study the interrelationship between GSK3β and the mTOR/S6K1 signaling pathway leading to milk synthesis and proliferation of dairy cow mammary epithelial cells (DCMECs) was analyzed using techniques including GSK3β overexpression by transfection, GSK3β inhibition, mTOR inhibition and methionine stimulation. The analyses revealed that GSK3β represses the mTOR/S6K1 pathway leading to milk synthesis and cell proliferation of DCMECs, whereas GSK3β phosphorylation enhances this pathway. Conversely, the activated mTOR/S6K1 signaling pathway downregulates GSK3β expression but enhances GSK3β phosphorylation to increase milk synthesis and cell proliferation, whereas inhibition of mTOR leads to upregulation of GSK3β and repression of GSK3β phosphorylation, which in turn decreases milk synthesis, and cell proliferation. These ﬁndings indicate that GSK3β and phosphorylated GSK3β regulate milk synthesis and proliferation of DCMECs via the mTOR/S6K1 signaling pathway. These findings provide new insight into the mechanisms of milk synthesis.
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. zx291765746@163.com.
authors.forename: Xia
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. erjinzhi@126.com.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhao
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. siyu19880329@163.com.
authors.forename: Yu
authors.initials: Y
authors.lastname: Si
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. hyllw335474663@163.com.
authors.forename: Yuling
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. yuguiyan@126.com.
authors.forename: Cuiping
authors.initials: C
authors.lastname: Yu
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. luochaochao839505@163.com.
authors.forename: Chaochao
authors.initials: C
authors.lastname: Luo
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. nazhang1981@126.com.
authors.forename: Na
authors.initials: N
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. qingzhangli2004@163.com.
authors.forename: Qingzhang
authors.initials: Q
authors.lastname: Li
authors.affiliation: Key Laboratory of Dairy Science of Ministry of Education, Northeast Agricultural University, Harbin 150030, China. gaoxj5390@sina.com.
authors.forename: Xuejun
authors.initials: X
authors.lastname: Gao
mesh_terms: D000818:Animals; D002417:Cattle; D049109:Cell Proliferation; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology*; D005260:Female; D038362:Glycogen Synthase Kinase 3 / Q000502:physiology*; D007774:Lactation; D018021:Lithium Chloride / Q000494:pharmacology; D008321:Mammary Glands, Animal / Q000166:cytology*; D008715:Methionine / Q000494:pharmacology; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D008715:Methionine; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride; D020123:Sirolimus