Demonstration of an insulin‐insensitive storage pool of glucose transporters in rat hepatocytes and HepG2 cells

Abstract

The subcellular distribution of glucose transporters in rat hepatocytes and HepG2 cells was studied in the absence and in the presence of insulin. Glucose transporters were quantitated by measuring glucose-sensitive cytochalasin B binding and by protein immunoblotting using isoform-specific antibodies. Plasma membrane contamination into subcellular fractions was assessed by measuring distribution of 5'-nucleotidase and cell surface carbohydrate label. In hepatocytes, GLUT-2 occurred in a low-density microsomal (LDM) fraction at a significant concentration, and as much as 15% of cellular GLUT-2 was found intracellularly that cannot be accounted for by plasma membrane contamination. In HepG2 cells which express GLUT-1 and GLUT-2, the two isoforms showed distinct subcellular distribution patterns: GLUT-2 was highly concentrated in LDM while very little GLUT-1 was found in this fraction, indicating that a large portion of GLUT-2 occurs in intracellular organelles. Insulin treatment did not change the subcellular distribution patterns of glucose transporters in both cell types. Our results suggest that rat hepatocytes and HepG2 cells possess an intracellular storage pool for GLUT-2, but lack the insulin-responsive glucose transporter translocation mechanism.

Modulation of cellular glucose metabolism in human HepG2 cells by combinations of structurally related flavonoids

“…The model chosen for the in vitro experiments is well established and very well characterized for glucose and energy metabolic properties. HepG2 cells have been shown to possess an intracellular storage pool for GLUT2, but lack the insulin‐responsive glucose transporter translocation mechanism . The fact that we could still evidence a small insulin driven increase in glucose transport (22%) in the HepG2 cells may be explained by the fact that GLUT1 can also undergo some insulin‐dependent trafficking to the cell surface, a twofold compared to a 20‐fold increase with GLUT4 .…”

Oestrogen improves glucose metabolism and insulin signal transduction in HepG2 cells

“…33 Perhaps this is the reason why high insulin does not change glucose transport in HepG2 cells or why glucose transport may not serve as an index of insulin resistance in hepatocytes. 34 However, glucose transport does serve as an index of insulin resistance in skeletal muscle cells. The results show that the expression of insulin signalling molecules, namely IR and IRS-2, is decreased by long-term stimulation of HepG2 cells with a high concentration of insulin, which proves that insulin resistance is induced in HepG2 cells.…”

“…The increased glucose transport is due to increased expression of GLUT-1 and GLUT-2 by oestradiol in HepG2 cells. 34,38 The actions of insulin are mediated by insulin signalling proteins and the expression of IRS-1 and IRS-2 has been demonstrated to be regulated by the oestrogen receptor. 39 The present data show that various concentrations of oestradiol (1, 10 and 100 nmol/L) increase both mRNA and protein levels of IRS-1 and IRS-2, but exhibit no effect on the expression of IR compared with control cells.…”

Prolonged insulin treatment sensitizes apoptosis pathways in pancreatic β cells

“…The various nonpancreatic β cell lines so far studied are not classical insulin target cells; therefore, we performed additional experiments on a liver cell line (human liver carcinoma cells HepG2) that is considered a common insulin target and is used in numerous studies on IR signaling (Hah et al 1992, Fawcett et al 2001, Patel et al 2004, Biswas et al 2007). HepG2 cells were treated with insulin (100 nM) or a cytokine mixture alone or in combination for 24 h (as done for MIN6 cells) and measurements of caspase activity and cell reducing power were then made.…”