RT Journal Article
SR Electronic
T1 Hepatic mTORC1 signaling activates ATF4 as part of its metabolic response to feeding and insulin
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2021.05.02.442369
DO 10.1101/2021.05.02.442369
A1 Vanessa Byles
A1 Yann Cormerais
A1 Krystle Kalafut
A1 Victor Barrera
A1 James E. Hughes Hallett
A1 Shannan Ho Sui
A1 John M. Asara
A1 Christopher M. Adams
A1 Gerta Hoxhaj
A1 Issam Ben-Sahra
A1 Brendan D. Manning
YR 2021
UL http://biorxiv.org/content/early/2021/05/03/2021.05.02.442369.abstract
AB Objective The mechanistic target of rapamycin complex 1 (mTORC1) is dynamically regulated by fasting and feeding cycles in the liver to promote protein and lipid synthesis while suppressing autophagy. However, beyond these functions, the metabolic response of the liver to feeding and insulin signaling orchestrated by mTORC1 remains poorly defined. Here, we determine whether ATF4, a stress responsive transcription factor recently found to be independently regulated by mTORC1 signaling in proliferating cells, is responsive to hepatic mTORC1 signaling to alter hepatocyte metabolism.Methods ATF4 protein levels and expression of canonical gene targets were analyzed in the liver following fasting and physiological feeding in the presence or absence of the mTORC1 inhibitor rapamycin. Primary hepatocytes from wild-type or liver-specific Atf4 knockout (LAtf4KO) mice were used to characterize the effects of insulin-stimulated mTORC1-ATF4 function on hepatocyte gene expression and metabolism. Both unbiased steady-state metabolomics and stable-isotope tracing methods were employed to define mTORC1 and ATF4-dependent metabolic changes. RNA-sequencing was used to determine global changes in feeding-induced transcripts in the livers of wild-type versus LAtf4KO mice.Results We demonstrate that ATF4 and its metabolic gene targets are stimulated by mTORC1 signaling in the liver in response to feeding and in a hepatocyte-intrinsic manner by insulin. While we demonstrate that de novo purine and pyrimidine synthesis is stimulated by insulin through mTORC1 signaling in primary hepatocytes, this regulation was independent of ATF4. Metabolomics and metabolite tracing studies revealed that insulin-mTORC1-ATF4 signaling stimulates pathways of non-essential amino acid synthesis in primary hepatocytes, including those of alanine, aspartate, methionine, and cysteine, but not serine.Conclusion The results demonstrate that ATF4 is a novel metabolic effector of mTORC1 in liver, extending the molecular consequences of feeding and insulin-induced mTORC1 signaling in this key metabolic tissue to the control of amino acid metabolism.Competing Interest StatementBDM is a shareholder and scientific advisory board member of Navitor Pharmaceuticals. CMA is a shareholder, director and officer of Emmyon, Inc. All other authors declare no competing financial interests.