title: Hepatic ALT isoenzymes are elevated in gluconeogenic conditions including diabetes and suppressed by insulin at the protein level.
abstract: BACKGROUND
  Alanine transaminase (ALT) plays an important role in gluconeogenesis by converting alanine into pyruvate for glucose production. Early studies have shown that ALT activities are upregulated in gluconeogenic conditions and may be implicated in the development of diabetes. ALT consists of two isoforms, ALT1 and ALT2, with distinctive subcellular and tissue distributions. Whether and how they are regulated are largely unknown.
  
  
  METHODS
  By using Western blotting analysis, we measured hepatic ALT isoforms at the protein level in obese and diabetic animals and in Fao hepatoma cells treated with dexamethasone and insulin. In addition, we measured glucose output in Fao cells over-expressing ALT1 and ALT2.
  
  
  RESULTS
  Both ALT isoforms in the liver were increased in diabetic Goto-Kakizaki rats and during fasting. However, in ob/ob mice, only ALT2, but not ALT1, protein levels were elevated, and the increase of ALT2 was correlated with that of ALT activity. We further demonstrated that, in vitro, both ALT1 and ALT2 were induced by glucocorticoid dexamethasone, but suppressed by insulin in Fao cells. Finally, we showed that the over-expression of ALT1 and ALT2 in Fao cells directly increased glucose output.
  
  
  CONCLUSIONS
  We have shown the similarity and difference in the regulation of ALT isoforms in gluconeogenic conditions at the protein level, supporting that ALT isoenzymes play an important role in glucose metabolism and may be implicated the development of insulin resistance and diabetes.
authors: Department of Gastrointestinal Surgery, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China.|Division of Endocrinology, Diabetes and Nutrition, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA.
authors: Kun
authors: K
authors: Qian
authors: Division of Endocrinology, Diabetes and Nutrition, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA.|Department of Endocrinology and Metabolism Disease, Kunshan Hospital of Jiangsu University, Jiangsu, China.
authors: Shao
authors: S
authors: Zhong
authors: Division of Endocrinology, Diabetes and Nutrition, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA.
authors: Keming
authors: K
authors: Xie
authors: Division of Endocrinology, Diabetes and Nutrition, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA.
authors: Daozhan
authors: D
authors: Yu
authors: Division of Endocrinology, Diabetes and Nutrition, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA.
authors: Rongze
authors: R
authors: Yang
authors: Division of Endocrinology, Diabetes and Nutrition, Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA.|VA Research Service, Geriatric Research, Education and Clinical Center, Baltimore Veterans Administration Medical Center, Baltimore, USA.
authors: Da-Wei
authors: DW
authors: Gong
mesh_terms: D000410:Alanine Transaminase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology* / Q000378:metabolism; D004790:Enzyme Induction / Q000187:drug effects; D004794:Enzyme Repression / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology; D005943:Gluconeogenesis / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009765:Obesity / Q000201:enzymology* / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D005938:Glucocorticoids; D007004:Hypoglycemic Agents; D007328:Insulin; D007527:Isoenzymes; D011994:Recombinant Proteins; D003907:Dexamethasone; D000410:Alanine Transaminase
keywords: ALT isoenzymes; diabetes; gluconeogenesis; regulation