Glucose increases hepatic lipase expression in HepG2 liver cells through upregulation of upstream stimulatory factors 1 and 2

Abstract

Aims/hypothesis Elevated hepatic lipase (HL, also known as LIPC) expression is a key factor in the development of the atherogenic lipid profile in type 2 diabetes and insulin resistance. Recently, genetic screens revealed a possible association of type 2 diabetes and familial combined hyperlipidaemia with the USF1 gene. Therefore, we investigated the role of upstream stimulatory factors (USFs) in the regulation of HL. Methods Levels of USF1, USF2 and HL were measured in HepG2 cells cultured in normal-or high-glucose medium (4.5 and 22.5 mmol/l, respectively) and in livers of streptozotocin-treated rats.Results Nuclear extracts of cells cultured in high glucose contained 2.5±0.5-fold more USF1 and 1.4±0.2-fold more USF2 protein than cells cultured in normal glucose (mean± SD, n=3). This coincided with higher DNA binding of nuclear proteins to the USF consensus DNA binding site. Secretion of HL (2.9±0.5-fold), abundance of HL mRNA (1.5±0.2-fold) and HL (-685/+13) promoter activity (1.8± 0.3-fold) increased in parallel. In chromatin immunoprecipitation assays, the proximal HL promoter region was immunoprecipitated with anti-USF1 and anti-USF2 antibodies. Co-transfection with USF1 or USF2 cDNA stimulated HL promoter activity 6-to 16-fold. USF and glucose responsiveness were significantly reduced by removal of the −310E-box from the HL promoter. Silencing of the USF1 gene by RNA interference reduced glucose responsiveness of the HL (−685/+13) promoter region by 50%. The hyperglycaemia in streptozotocin-treated rats was associated with similar increases in USF abundance in rat liver nuclei, but not with increased binding of USF to the rat Hl promoter region. Conclusions/interpretation Glucose increases HL expression in HepG2 cells via elevation of USF1 and USF2. This mechanism may contribute to the development of the dyslipidaemia that is typical of type 2 diabetes.

Hepatocyte Growth Factor Family Negatively Regulates Hepatic Gluconeogenesis via Induction of Orphan Nuclear Receptor Small Heterodimer Partner in Primary Hepatocytes

“…Similar induction of shp mRNA and protein level was observed in HepG2 cells (data not shown). Previous reports have demonstrated that USF-1 increased glycolysis via activation of key glycolytic enzyme genes, L-PK and GK gene promoters (1,14,16). As a positive control, Ad USF-1 treatment was shown to induce l-pk and gk mRNA expression significantly in primary hepatocytes (Fig.…”

“…USF-1 protein level is found to be increased in feeding (28) and high glucose conditions (14), correlated to the decrease in hepatic gluconeogenesis under these conditions. Therefore, the induction of SHP gene expression by USF-1 in primary hepatocytes, as demonstrated in this study, may provide a plausible link connecting the decrease of PEPCK and Glc-6-Pase gene expression by SHP to USF-1 expression pattern.…”

“…Therefore, the induction of SHP gene expression by USF-1 in primary hepatocytes, as demonstrated in this study, may provide a plausible link connecting the decrease of PEPCK and Glc-6-Pase gene expression by SHP to USF-1 expression pattern. Previous studies linking USF-1 to hepatic glucose metabolism demonstrated regulation of key glycolytic enzyme gene expression, GK and L-PK, by USF-1 by binding to the respective gene promoters (1,14,16). However, no information was available regarding any direct link between USF-1 and regulation of hepatic gluconeogenesis.…”

“…Upstream stimulatory factor (USF)-1 is a transcription factor regulating several genes involved in glucose and lipid metabolism (1,14). USF-1 binds as a homodimer or heterodimerizes with its highly homologous USF-2 to E-box motifs (CANNTG) of target gene promoters (15).…”

Apoptotic events induced by high glucose in human hepatoma HepG2 cells involve endoplasmic reticulum stress and MAPK’s activation

“…Chronic hyperglycemia is capable of exerting adverse effects on hepatic cells, i.e., metabolic disorders of glucose, lipid, and energy, breakdown of redox equilibrium, and dysregulation of several cellular processes, which can also lead to hepatic insulin resistance [28,29]. In the present study, the HepG2 cell line has been used as an in vitro model system aiming to investigate the effects of prolonged elevated glucose.…”