Lipoprotein lipase (LPL) plays a major role in the hydrolysis of triglycerides (TG) from circulating TG-rich lipoproteins. The role of LPL in the liver has been controversial but recent studies in mice with liver LPL overexpression or deficiency have revealed important new roles of the enzyme in glucose and lipid metabolism. The objective of this study was to identify regulatory elements and factors that control the transcription of the human LPL gene in hepatocytes. Deletion analysis of the human LPL promoter revealed that the proximal region which harbors a binding site for the forkhead box transcription factor FOXA2/HNF-3β at position -47/-40 is important for its hepatic cell activity. Silencing of FOXA2 in HepG2 cells reduced the LPL mRNA and protein levels. Direct binding of FOXA2 to the novel binding site was established in vitro and ex vivo. Mutagenesis of the FOXA2 site reduced the basal activity and abolished the FOXA2-mediated transactivation of the LPL promoter. Ιnsulin decreased LPL mRNA levels in HepG2 cells and this was associated with phosphorylation of AKT and nuclear export of FOXA2. In summary, the data of the present study combined with previous findings on the role of FOXA2 in HDL metabolism and gluconeogenesis, suggest that FOXA2 is a key regulator of lipid and glucose homeostasis in the adult liver. Understanding the mechanisms by which FOXA2 exerts its functions in hepatocytes may open the way to novel therapeutic strategies for patients with metabolic diseases such as dyslipidemia, diabetes and the metabolic syndrome.
Keywords: FOXA2; HNF-3β; Insulin; Lipoprotein lipase; Lipoproteins; Liver; Promoter; Transcriptional activation; Triglycerides.
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