HEPATOCELLULAR EXPRESSION OF GLUCOSE-6-PHOSPHATASE IS UNALTERED DURING HEPATIC REGENERATION

Gluconeogenesis and glycogenolysis are essential hepatic functions req uired for glucose homeostasis. During the initial phase of hepatic reg eneration, the immediate-early genes (IEG) are rapidly expressed, and the IEG RL-1 encodes for glucose-6-phosphatase (G-6-Pase). G-6-Pase is a microsomal enzyme essential for gluconeogenesis and glycogenolysis. This study employs a partial-hepatectomy model to examine the express ion and activity of G-6-Pase. After partial hepatectomy, rat hepatic G -6-Pase gene expression is transcriptionally regulated, and mRNA level s are increased approximate to 30-fold. However, in contrast to this r apid gene induction, microsomal enzyme activity is unchanged after par tial hepatectomy Western blotting demonstrates that microsomal G-6-Pas e protein expression is also unchanged after partial hepatectomy, and similar results are also noted in whole liver homogenate. Thus, despit e marked induction in gene expression of the IEG G-6-Pase after partia l hepatectomy, protein expression and enzyme activity remain unchanged . These data indicate that, although this hepatocyte IEG is transcript ionally regulated, the physiologically important level of regulation i s posttranscriptional. This highlights the importance of correlating g ene expression of IEG with protein expression and physiological functi on.