Precursors of ribose 5-phosphate suppress expression of glucose-regulated proteins in LLC-PK1 cells

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Abstract
Withdrawal of glucose from the medium bathing mammalian cells in culture results in cessation of growth and induces the synthesis of two stress proteins (Mr approximately 94-100 kDa and 78-80 kDa) that have been termed glucose-regulated proteins (GRPs). In LLC-PK1 cells, proteins of the same molecular weights, assayed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography, are fully induced by 24 h in glucose-free medium. The GRPs from LLC-PK1 cells cross-react with antibodies to GRPs of nonpolar cells, confirming their identification. Since glucose is not essential for energy production in cultured cells, but is essential for ribose 5-phosphate and nucleotide biosynthesis (Wice et al. J. Biol. Chem. 256: 7812-7819, 1981), we tested the effect of several precursors of ribose 5-phosphate on the induction of GRPs. The addition of 25 mM fructose or galactose to glucose-free medium suppressed the induction of GRPs. The pyrimidine ribonucleosides uridine and cytidine also suppressed GRP synthesis, ribose and the purine ribonucleosides guanosine and adenosine suppressed partially. The results, coupled with indirect evidence in the literature, lead to the suggestion that cell ribose 5-phosphate or a related metabolite regulates the expression of GRPs.

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