Amino Acid Availability Controls TRB3 Transcription in Liver through the GCN2/eIF2α/ATF4 Pathway

Abstract

In mammals, plasma amino acid concentrations are markedly affected by dietary or pathological conditions. It has been well established that amino acids are involved in the control of gene expression. Up to now, all the information concerning the molecular mechanisms involved in the regulation of gene transcription by amino acid availability has been obtained in cultured cell lines. The present study aims to investigate the mechanisms involved in transcriptional activation of the TRB3 gene following amino acid limitation in mice liver. The results show that TRB3 is up-regulated in the liver of mice fed a leucine-deficient diet and that this induction is quickly reversible. Using transient transfection and chromatin immunoprecipitation approaches in hepatoma cells, we report the characterization of a functional Amino Acid Response Element (AARE) in the TRB3 promoter and the binding of ATF4, ATF2 and C/EBPβ to this AARE sequence. We also provide evidence that only the binding of ATF4 to the AARE plays a crucial role in the amino acid-regulated transcription of TRB3. In mouse liver, we demonstrate that the GCN2/eIF2α/ATF4 pathway is essential for the induction of the TRB3 gene transcription in response to a leucine-deficient diet. Therefore, this work establishes for the first time that the molecular mechanisms involved in the regulation of gene transcription by amino acid availability are functional in mouse liver.

Liver-specific Gene Inactivation of the Transcription Factor ATF4 Alleviates Alcoholic Liver Steatosis in Mice

“…TRB3, a known direct target of ATF4 (25,29,30), is induced by ethanol treatment in cells (33,42) and livers, as shown in our current study. However, the role of TRB3 in alcoholic liver steatosis has not been studied previously.…”

“…Furthermore, ATF4 regulates AMPK activity via Tribbles homolog 3 (TRB3), a direct target of ATF4 (25), which could bind directly to AMPK and suppress its phosphorylation. Taken together, our results identify the ATF4-TRB3-AMPK axis as a novel pathway responsible for ethanol-induced liver steatosis.…”

ATF4-dependent Regulation of the JMJD3 Gene during Amino Acid Deprivation Can Be Rescued in Atf4-deficient Cells by Inhibition of Deacetylation

“…Following activation of the AAR, increased acetylation of both H3 and H4, in parallel with a rapid increase in ATF4 binding, has been observed at the ASNS and ATF3 proximal promoters (35,39). Carraro et al observed that AARinduction led to an increase in H2B, H3, and H4 acetylation levels at the TRB3 CARE site (59). The sodium-dependent neutral amino acid transporter 2 (SNAT2) gene has an intronic CARE enhancer (60).…”

Elevated cJUN expression and an ATF/CRE site within the ATF3 promoter contribute to activation of ATF3 transcription by the amino acid response

“…Amino acid deficiency triggers a series of signal transduction pathways collectively referred to as the amino acid response (AAR). A number of genes critical to the AAR have been identified (6,21), but the mechanistic details of their transcriptional control are not fully understood. The general control nonderepressible 2 (GCN2) kinase acts as an sensor for amino acid levels by binding uncharged transfer tRNA, which leads to phosphorylation of the alpha subunit of the translation initiation factor eIF2 and increased translation of the activating transcription factor 4 (ATF4).…”