DIFFERENTIAL METABOLIC EFFECTS OF ADENOVIRUS-MEDIATED GLUCOKINASE ANDHEXOKINASE-I OVEREXPRESSION IN RAT PRIMARY HEPATOCYTES

The first step of glucose metabolism is the phosphorylation of glucose , catalyzed by the hexokinase family of enzymes. To address the metabo lic impact of increasing glucose phosphorylation capacity in liver, ra t primary hepatocytes were treated with recombinant adenoviruses conta ining the cDNAs encoding either rat Liver glucokinase (AdCMV-GKL) or r at hexokinase I (Ad-CMV-HKI). Maximal glucose phosphorylation in Ad-CM V-GKL- and AdCMV-HKI-treated hepatocytes was increased 7.1 +/- 1.2- an d 6.3 +/- 0.8-fold, respectively, over hepatocytes treated with an ade novirus expressing beta-galactosidase. Glucose usage (measured with 3 and 20 mM 2-[H-3]glucose and 5-[H-3]glucose) was significantly increas ed in AdCMV-GKL-treated cells preincubated in 1 or 25 mM glucose. Trea tment of hepatocytes with Ad-CMV-HKI also caused enhanced glucose util ization, but the increases were smaller and were less apparent in cell s preincubated in high (25 mM) glucose. AdCMV-GKL-treated hepatocytes incubated for 48 h in the presence of variable glucose concentrations had glycogen levels that were maximally 15.0 +/- 0.6-fold greater than levels in corresponding control cells. AdCMV-HKI-treated hepatocytes incubated under similar conditions had unchanged glycogen levels relat ive to controls. In AdCMV-GKL-treated cells, lactate output was increa sed to a maximum of 3.0 +/- 0.4-fold (at 25 mM glucose), glucose oxida tion was increased 3.5 +/- 0.3-fold, and triglyceride production was u nchanged relative to untreated cells. Among these three parameters, on ly lactate production was increased in AdCMV-HKI-treated cells, and th en only at low glucose concentrations. We conclude that overexpression of glucokinase has potent effects on glucose storage and utilization in hepatocytes and that these effects are not matched by overexpressio n of hexokinase I.