Abstract
Amino acids (AA) are one of the key nutrients that regulate cell proliferation and casein synthesis in cow mammary epithelial cells (CMEC), but the mechanism of this regulation is not yet clear. In this study, the effect of SESN2 on AA-mediated cell proliferation and casein synthesis in CMEC was assessed. After 12 h of AA starvation, CMECs were cultured in the absence of all AA (AA−), in the presences of only essential AA (EAA+), or of all AA (AA+). Cell proliferation, casein expression, and activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway were increased; but SESN2 expression was decreased in response to increased EAA or AA supply. Overexpressing or inhibiting SESN2 demonstrated that cell proliferation, casein expression, and activation of the mTORC1 pathway were all controlled by SESN2 expression. Furthermore, the increase in cell proliferation, casein expression, and activation of the mTORC1 pathway in response to AA supply was inhibited by overexpressing SESN2, and those effects were reversed by inhibiting SESN2. These results indicate that SESN2 is an important inhibitor of mTORC1 in CMEC blocking AA-mediated cell proliferation and casein synthesis.
Highlights
Proliferation of cow mammary epithelial cells (CMEC) and casein synthesis by those cells are regulated by hormones, nutrients and environmental stress[1,2,3,4,5]
The main signaling pathway that mediates Amino acids (AA)-induced cell proliferation and protein synthesis is the mammalian target of rapamycin complex 1 pathway8,9. mTORC1 is the main regulatory factor in the pathway, and it is composed of mTOR, G protein β subunit-like protein (GβL), regulatory associated protein of mammalian target of rapamycin (Raptor), proline-rich Akt substrate of 40 kDa (PRAS40), and Deptor[10]
We investigated the function of SESN2 in the process of cell proliferation and casein synthesis associated with AA-mediated stimulation of the mTORC1 pathway in CMEC
Summary
Proliferation of cow mammary epithelial cells (CMEC) and casein synthesis by those cells are regulated by hormones (e.g. prolactin, insulin and glucocorticoids), nutrients (e.g. glucose and amino acids) and environmental stress (e.g. heat stress)[1,2,3,4,5]. Amino acids (AA) are the most important as they are the building blocks of protein synthesis and the regulators of cell proliferation and casein synthesis in mammalian epithelial cells[6,7]. The main signaling pathway that mediates AA-induced cell proliferation and protein synthesis is the mammalian target of rapamycin complex 1 (mTORC1) pathway. Kimball et al reported that sestrins/sestrin[2] negatively regulated the amino-acid-sensing pathway upstream of mTORC1 by interacting with GTPase-activating proteins toward Rags 2 (GATOR2)[26]. We investigated the function of SESN2 in the process of cell proliferation and casein synthesis associated with AA-mediated stimulation of the mTORC1 pathway in CMEC. We hypothesized that SESN2 mediated AA responses through inhibition of mTORC1 activation
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