The regulatory role of UDP-glucose in glycogen biogenesis was investigated in fibroblasts containing a point mutation in the UDP-glucose pyrophosphorylase gene and, consequently, chronically low UDP-glucose levels (Qc). Comparisons were made with cells having the intact gene and restored UDP-glucose levels (G3). Glycogen was always very low in Qc cells. [14C]Glucose incorporation into glycogen was decreased and unaffected by insulin in Qc cells, whereas insulin stimulated glucose incorporation by 50% in G3 cells. Glycogen synthase (GS) activity measured in vitro was virtually absent and the amount of enzyme in Qc cells was decreased by about 50%. The difference in GS activity between cells persisted even when G3 cells were devoid of glycogen. Incubation of G3 cell extracts with either exogenous UDP-glucose or glycogen resulted in increases in GS activity. Incubation of Qc cell extracts with exogenous UDP-glucose had no effect on GS activity; however, incubation with glycogen fully restored enzyme activity. Incubation of G3 cell extracts with radioactive UDP-glucose resulted in substantial binding of ligand to immunoprecipitated GS, whereas no binding was detected in Qc immunoprecipitates. Incubation of Qc cell extracts with exogenous glycogen fully restored UDP-glucose binding in the immunoprecipitate. These data suggest that chronically low UDP-glucose levels in cells result in inactivation of GS, owing to loss of the ability of GS to bind UDP-glucose.
A point mutation in the UDP-glucose pyrophosphorylase gene results in decreases of UDP-glucose and inactivation of glycogen synthase
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Juan-Carlos HIGUITA, Alberto ALAPE-GIRÓN, Monica THELESTAM, Abram KATZ; A point mutation in the UDP-glucose pyrophosphorylase gene results in decreases of UDP-glucose and inactivation of glycogen synthase. Biochem J 15 March 2003; 370 (3): 995–1001. doi: https://doi.org/10.1042/bj20021320
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