The mTORC1/4EBP1/PPARγ Axis Mediates Insulin-Induced Lipogenesis by Regulating Lipogenic Gene Expression in Bovine Mammary Epithelial Cells.
4EBP1 is a chief downstream factor of mTORC1, and PPARγ is a key lipogenesis-related transcription factor. mTORC1 and PPARγ are associated with lipid metabolism. However, it is unknown which effector protein connects mTORC1 and PPARγ. This study investigated the interaction between 4EBP1 with PPARγ as part of the underlying mechanism by which insulin-induced lipid synthesis and secretion are regulated by mTORC1 in primary bovine mammary epithelial cells (pBMECs). Rapamycin, a specific inhibitor of mTORC1, downregulated 4EBP1 phosphorylation and the expression of PPARγ and the following lipogenic genes: lipin 1, DGAT1, ACC, and FAS. Rapamycin also decreased the levels of intracellular triacylglycerol (TAG); 10 types of fatty acid; and the accumulation of TAG, palmitic acid (PA), and stearic acid (SA) in the cell culture medium. Inactivation of mTORC1 by shRaptor or shRheb attenuated the synthesis and secretion of TAG and PA. In contrast, activation of mTORC1 by Rheb overexpression promoted 4EBP1 phosphorylation and PPARγ expression and upregulated the mRNA and protein levels of lipin 1, DGAT1, ACC, and FAS, whereas the levels of intracellular and extracellular TAG, PA, and SA also rose. Further, 4EBP1 interacted directly with PPARγ. Inactivation of mTORC1 by shRaptor prevented the nuclear location of PPARγ. These results demonstrate that mTORC1 regulates lipid synthesis and secretion by inducing the expression of lipin 1, DGAT1, ACC, and FAS, which is likely mediated by the 4EBP1/PPARγ axis. This finding constitutes a novel mechanism by which lipid synthesis and secretion are regulated in pBMECs.
['Guo|Zhixin|Z|', 'Cheng|Xiaoou|X|', 'Feng|Xue|X|', 'Zhao|Keyu|K|', 'Zhang|Meng|M|', 'Yao|Ruiyuan|R|', 'Chen|Yuhao|Y|', 'Wang|Yanfeng|Y|', 'Hao|Huifang|H|', 'Wang|Zhigang|Z|http://orcid.org/0000-0002-6818-2205']
D000818:Animals D019755:Carbon-Carbon Lyases D002417:Cattle D051048:Diacylglycerol O-Acyltransferase D004847:Epithelial Cells D039642:Eukaryotic Initiation Factors D005260:Female D005786:Gene Expression Regulation D007328:Insulin D050155:Lipogenesis D008321:Mammary Glands, Animal D000076222:Mechanistic Target of Rapamycin Complex 1 D047495:PPAR gamma D014280:Triglycerides
PPARγ lipogenesis bovine mammary epithelial cells 4EBP1 mTORC1 insulin