STARVATION AND REFEEDING REGULATE GLYCOGEN-SYNTHASE GENE-EXPRESSION IN RAT-LIVER AT THE POSTTRANSCRIPTIONAL LEVEL

Starvation and refeeding affect glycogen metabolism. The effects of st arvation and refeeding on the level of glycogen synthase (GS) gene exp ression were examined in rat liver, Depletion of hepatic glycogen stor es by 72 h of starvation (7% of control) was supercompensated by 24 h of refeeding a standard laboratory diet (247% of control), Upon furthe r refeeding, glycogen concentration gradually returned to control leve ls after 120 h, After 72 h of starvation, GS activity and immunoreacti ve protein in the liver were, 60-64% lower than in control rats with f ree access to food. After 72 h of refeeding, GS activity and immunorea ctive protein returned to control values. No significant differences i n GS mRNA levels were found between fed, starved and refed rats, as de termined by Northern blot analysis and PCR quantification, indicating that the long-term regulation of GS gene expression in starvation and refeeding occurs via a posttranscriptional mechanism. The amount of GS mRNA associated with polyribosomes was 90% lower in starved than in f ed rats. These data indicate that the efficiency of GS mRNA translatio n, rather than its abundance, decreases during starvation.