Appearance of a cytosolic protein that stimulates glyceraldehyde-3-phosphate dehydrogenase activity during initiation of renal epithelial cell growth

Abstract

Rats fed a K-deficient diet exhibit accelerated kidney growth and enhanced activity of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (G3PD; D-glyceraldehyde-3-phosphate:NAD+ oxidoreductase, EC 1.2.1.12). Cultures of renal epithelial cells (BSC-1 line) served as a model for this phenomenon because a reduction in the medium K concentration from 5.4 to 3.2 mM resulted in augmented growth and increased G3PD activity. Mixing the soluble supernatant fraction from cells grown in low-K medium (3.2 mM) with that from cells grown in control medium indicated that the cytosol of low-K cells contained a positive modifier of G3PD activity. Appearance of modifier activity that occurred within 1 hr after exposure of cells to low-K medium was blocked by cycloheximide but not by actinomycin D. Modifier activity was also observed in mouse fibroblasts stimulated by low-K medium and in proliferating renal medullary tissue from rats fed a K-deficient diet. A single protein that contained G3PD-stimulating activity was isolated from the soluble supernatant of BSC-1 cells exposed to low-K medium. This protein was not detectable in control cells. The material yielded a single band on NaDodSO4/polyacrylamide gel electrophoresis with an apparent Mr of 62,000. These results suggest that a new protein with the capacity to stimulate G3PD activity appears in the cytosol during the initiation of cell growth.