title: Activating transcription factor 4 mediates up-regulation of alanine aminotransferase 2 gene expression under metabolic stress.
abstract: Alanine aminotransferase (ALT) provides a molecular link between carbohydrate and amino acid metabolism. In humans, two ALT isoforms have been characterized: ALT1, cytosolic, and ALT2, mitochondrial. To gain insight into the transcriptional regulation of the ALT2 gene, we cloned and characterized the human ALT2 promoter. 5'-deletion analysis of ALT2 promoter in transiently transfected HepG2 cells and site-directed mutagenesis allowed us to identify ATF4 as a new factor involved in the transcriptional regulation of ALT2 expression. Quantitative RT-PCR assays showed that the metabolic stressors histidinol and tunicamycin increased ATF4 levels and up-regulated ALT2 in HepG2 and Huh7 cells. Consistently, knock-down of ATF4 decreased ALT2 mRNA levels in HepG2 and Huh-7 cells. Moreover, ATF4 silencing prevented the activating effect of histidinol and tunicamycin on ATF4 and ALT2 expression. Our findings point to ALT2 as an enzyme involved in the metabolic adaptation of the cell to stress.
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Facultat de Farmàcia, Universitat de Barcelona, Joan XXIII s/n, 08028 Barcelona, Spain.
authors.forename: María C
authors.initials: MC
authors.lastname: Salgado
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Facultat de Farmàcia, Universitat de Barcelona, Joan XXIII s/n, 08028 Barcelona, Spain.
authors.forename: Isidoro
authors.initials: I
authors.lastname: Metón
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Facultat de Farmàcia, Universitat de Barcelona, Joan XXIII s/n, 08028 Barcelona, Spain.
authors.forename: Ida G
authors.initials: IG
authors.lastname: Anemaet
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Facultat de Farmàcia, Universitat de Barcelona, Joan XXIII s/n, 08028 Barcelona, Spain. Electronic address: baanantevazquez@ub.edu.
authors.forename: Isabel V
authors.initials: IV
authors.lastname: Baanante
mesh_terms: D051701:Activating Transcription Factor 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000410:Alanine Transaminase / Q000378:metabolism*; D000596:Amino Acids / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D050260:Carbohydrate Metabolism / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D056945:Hep G2 Cells; D006641:Histidinol / Q000494:pharmacology; D006801:Humans; D008928:Mitochondria / Q000235:genetics; D011401:Promoter Regions, Genetic; D013312:Stress, Physiological / Q000235:genetics*
chemical_list: C497109:ATF4 protein, human; D000596:Amino Acids; D051701:Activating Transcription Factor 4; D006641:Histidinol; D000410:Alanine Transaminase
keywords: Activating transcription factor 4; Alanine aminotransferase 1; Alanine aminotransferase 2; Amino acid deprivation; ER stress; Gene knock-down