Inhibition of Glutamine Synthetase Decreases Proliferation of Cultured Rat Intestinal Epithelial Cells

Manuscript received 4 May 1998. Initial reviews completed 9 June 1998. Revision accepted 1 October 1998.

Department of Pediatrics, Division of Neonatology, and ^* Department of Anatomy and Cell Biology, University of Florida, College of Medicine, Gainesville, FL 32610

The importance of glutamine synthetase (GS) for cell proliferation was examined in rat intestinal crypt cells (IEC-6) by inhibiting its activity with 10 mmol/L methionine sulfoximine (MS) at varying extracellular glutamine (Q) concentrations. In uninhibited cultures, cell number, protein, and DNA accumulation and synthesis showed a dependence on extracellular Q over a concentration range of 0.06 to 1.06 mmol/L, with apparent half-maximal responses of 0.46 mmol/L extracellular Q. In contrast, proliferation of GS-inhibited cultures required 1.06 mmol/L extracellular Q, with an apparent half-maximal response of 2 mmol/L. MS inhibited GS activity >97% in extracts of washed cells and appeared to be specific because its effects on proliferation were overcome by 4.06 mmol/L Q and were reversible. The increased dependence of IEC-6 cells on extracellular Q when GS was inhibited suggests that Q derived from GS (GS-Q) contributes importantly to cell proliferation at physiologic levels of extracellular Q (0.6 mmol/L). The unexpectedly high concentration of extracellular Q required to rescue maximal proliferation during GS-inhibition, relative to a reported K_m for Q-transport into the cell, indicates that intracellular Q derived from the extracellular medium (exo-Q) is inefficiently utilized. In a previous study, we found that GS-protein and mRNA are concentrated in the proliferative crypt region of the small intestine in vivo, and predicted that GS activity is important for crypt cell proliferation. Here, we show that enzyme activity is important for cell proliferation at physiologic concentrations of Q in this cell culture model. Finally, we speculate that exo-Q and GS-Q are utilized differently in the cell.

The Journal of Nutrition Vol. 129 No. 1 January 1999, pp. 57-62
Copyright ©1999 by the American Society for Nutritional Sciences

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