Glutamine regulates the expression of proteins with a potential health-promoting effect in human intestinal Caco-2 cells

Glutamine is an essential amino acid for the enterocytes with respect to maintaining the gut mucosal integrity and function. This study was conducted to explore a molecular basis for the beneficial effects of glutamine on intestinal cells by searching for glutamine-dependent changes in the proteome. Caco-2 cells were exposed to different concentrations of L-glutamine with or without L-methionine sulfoximine, an inhibitor of the glutamine synthetase activity. 2-DE combined with MALDI-TOF-MS was used to identify proteins whose expression is changed by glutamine. To assess the relative protein synthesis rate, incorporation of L-[2H5]glutamine into individual proteins was monitored. The expression levels of 14 proteins changed significantly with the glutamine availability. Examples of differentially expressed proteins with potential health-promoting effects on the intestine are plasma retinol-binding protein, ornithine aminotransferase, apolipoprotein A-I, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase, and acyl-CoA synthetase 5. Expression of these proteins was not changed by arginine deprivation. The differential change in the expression levels of the proteins was not correlated with their rate of synthesis, excluding an effect of glutamine depletion on general protein synthesis. Together, this study shows a gene-specific effect of glutamine on intestinal cells.