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RagD regulates amino acid mediated-casein synthesis and cell proliferation via mTOR signalling in cow mammary epithelial cells

Published online by Cambridge University Press:  22 May 2018

Ying Mu ,
Dongmei Zheng ,
Cong Wang ,
Wei Yu  and
Xiaonan Zhang
Ying Mu*
Affiliation:
Food Science College of Northeast Agricultural University, Harbin, Heilongjiang, 150030, China
Dongmei Zheng
Affiliation:
Food Science College of Northeast Agricultural University, Harbin, Heilongjiang, 150030, China
Cong Wang
Affiliation:
Food Science College of Northeast Agricultural University, Harbin, Heilongjiang, 150030, China
Wei Yu
Affiliation:
Food Science College of Northeast Agricultural University, Harbin, Heilongjiang, 150030, China
Xiaonan Zhang
Affiliation:
Food Science College of Northeast Agricultural University, Harbin, Heilongjiang, 150030, China
*
*For correspondence; e-mail: [email protected]
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Abstract

This research paper addresses the hypothesis that RagD is a key signalling factor that regulates amino acid (AA) mediated-casein synthesis and cell proliferation in cow mammary epithelial cells (CMECs). The expression of RagD was analysed at different times during pregnancy and lactation in bovine mammary tissue from dairy cows. We showed that expression of RagD at lactation period was higher (P < 0·05) than that at pregnancy period. When CMECs were treated with methionine (Met) or lysine (Lys), expression of RagD, β-casein (CSN2), mTOR and p-mTOR, and cell proliferation were increased. Further, when CMECs were treated to overexpress RagD, expression of CSN2, mTOR and p-mTOR, and cell proliferation were up-regulated. Furthermore, the increase in expression of CSN2, mTOR and p-mTOR, and cell proliferation in response to Met or Lys supply was inhibited by inhibiting RagD, and those effects were reversed in the overexpression model. When CMECs were treated with RagD overexpression together with mTOR inhibition or conversely with RagD inhibition together with mTOR overexpression, results showed that the increase in expression of CSN2 and cell proliferation in response to RagD overexpression was prevented by inhibiting mTOR, and those effects were reversed by overexpressing mTOR. The interaction of RagD with subunit proteins of mTORC1 was analysed, and the result showed that RagD interacted with Raptor. CMECs were treated with Raptor inhibition, and the result showed that the increase in expression of mTOR and p-mTOR in response to RagD overexpression was inhibited by inhibiting Raptor.

In conclusion, our study showed that RagD is an important activation factor of mTORC1 in CMECs, activating AA-mediated casein synthesis and cell proliferation, potentially acting via Raptor.

Keywords

RagDcasein synthesiscell proliferationmTOR signallingcow mammary epithelial cells
Type
Research Article
Information
Journal of Dairy Research , Volume 85 , Issue 2 , May 2018 , pp. 204 - 211
Copyright
Copyright © Hannah Dairy Research Foundation 2018 

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