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Effects of insulin on the expression of liver-specific genes are part of the adaptive mechanisms aimed at maintaining energy homeostasis in mammals. When the diet is rich in carbohydrates, secreted insulin stimulates the expression of genes for enzymes involved in glucose utilization (glucokinase, L-type pyruvate kinase and lipogenic enzymes) and inhibits genes for enzymes involved in glucose production (phosphenolpyruvate carboxykinase). The mechanisms by which insulin controls the expression of these genes have been poorly understood. Recently, the transcription factor sterol-regulatory-element-binding protein 1c has been proposed as a key mediator of insulin transcriptional effects. Here we review the evidence that has led to this proposal and the consequences for our understanding of insulin effects in physiological or pathological conditions.

In a screen for sterol regulatory element-binding protein (SREBP)-1c target genes in the liver, we identified long chain fatty acyl-CoA synthetase 5 (ACS-5). Hepatic ACS-5 mRNA is poorly expressed during fasting and diabetes and strongly induced by carbohydrate refeeding and insulin treatment. In cultured hepatocytes, insulin and a high glucose concentration induce ACS-5 mRNA. Adenoviral overexpression of a nuclear form of SREBP-1c in liver of diabetic mice or in cultured hepatocytes mimics the effect of insulin to induce ACS-5. By contrast, a dominant negative form of SREBP-1c abolishes the effect of insulin on ACS-5 expression. The dietary and SREBP-1c-mediated insulin regulation of ACS-5 expression indicate that ACS-5 is involved in the anabolic fate of fatty acids.