SESN2 negatively regulates cell proliferation and casein synthesis by inhibition the amino acid-mediated mTORC1 pathway in cow mammary epithelial cells

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.

Seryl-tRNA synthetase-mediated essential amino acids regulate β-casein synthesis via cell proliferation and mammalian target of rapamycin (mTOR) signaling pathway in bovine mammary epithelial cells

“…In the current study, the stimulating effects of EAA and SARS led to enhanced cell viability or cell proliferation (MKI67)/cell cycle progression (CCND1) and lower cell cycle arrest (SFN) in BMEC. The overall results confirm earlier findings that EAA sufficiency (Luo et al, 2018) and LARS (Wang et al, 2014) promote cell viability, cell cycle, and β-casein production in BMEC. In summary, SARS may help EAA accelerate cell cycle progression of BMEC, which could further promote mammary cell population expansion and increase milk production.…”

“…The markedly enhanced (decreased) expression of SARS and β-casein and the increase (decrease) of EAA re-stimulation (re-deprivation) time suggest that EAA affected the protein abundance of SARS and β-casein in similar patterns and that these effects were timedependent. As Luo et al (2018) reported, when BMEC were first treated with AA deprivation and then resupplied with AA or EAA for the same durations as in this study, the protein abundance of mTOR at the lysosomal outer surface of BMEC (indication of mTOR activation) was gradually enhanced along with the increase of AA or EAA treatment time, which reached the maximum at 6 h of AA/EAA treatment. Therefore, the activation of the mTOR system may be altered along with different treatment time of EAA deficiency and EAA sufficiency.…”

“…Therefore, it is essential to evaluate whether SARS could affect EAA-stimulated β-casein production by regulating mammary cell population. Compared with the EAA-deprivation and SARS knockdown (si-SARS) groups, the higher mammary cell viability within the EAA-supplement and WT groups was in line with EAA-stimulated mammary cell viability (Luo et al, 2018) and LARS-promoted cell proliferation in BMEC (Wang et al, 2014). Overall, EAA and SARS had similar stimulating effects on cell viability for BMEC, and the subsequent enhanced cell viability Figure 4.…”

“…In ruminants, AA could promote mammary cell proliferation and milk protein synthesis primarily through their regulation of the mTORC1 pathway (Bruhat et al, 2009;Appuhamy et al, 2012;Arriola Apelo et al, 2014;Rezaei et al, 2016;Luo et al, 2018). Although the critical role of the mTOR system in EAA regulating milk protein synthesis in human and rodents is well characterized, a greater understanding of the process in ruminants is needed.…”

“…Of those dietary nutrients understood to influence milk protein synthesis, the EAA are among the most important because they provide the substrates for protein synthesis and act as regulators of casein synthesis in the bovine mammary gland tissues (Appuhamy et al, 2011;Li et al, 2017). Importantly, several studies have demonstrated that EAA stimulate cell proliferation of bovine mammary epithelial cells (BMEC; Theodorou et al, 2011;Luo et al, 2018). By measuring mammary epithelial cell DNA, Capuco et al (2001) found that during lactation, the number of mammary epithelial cells within the mammary glands gradually decreases, largely accounting for the decline in milk production with advancing lactation.…”