Regulation of expression of the intestinal oligopeptide transporter (Pept-1) in health and disease

The abundance of the oligopeptide transporter (Pept-1) in the brush-border membrane of the intestinal epithelium is the central mechanism for regulation of transport of products of protein digestion (dipeptides and tripeptides) and peptidomimetic drugs (for example, beta-lactam antibiotics). Within the past few years, there has been substantial progress in identifying the factors controlling this regulation and the mechanisms of their actions. The purpose of this report is to review this progress. The studies of individual substrates and hormones in a human intestinal cell line (Caco-2) have shown that dipeptides, certain amino acids, insulin, and leptin increase and epidermal growth factor and triiodothyronine decrease the membrane population of Pept-1. In the case of dipeptides, epidermal growth factor, and thyroid hormone, there are parallel changes in the gene expression brought about by alteration of transcription and/or stability of Pept-1 mRNA. In contrast, the treatment with insulin and leptin does not induce any alteration in the Pept-1 gene expression, and the mechanism of increased protein expression appears to be increased trafficking from a preformed cytoplasmic pool to the apical membrane. In vivo studies in rats have shown modulation of protein and gene expressions of the intestinal oligopeptide transporter during the day and during development and in nutritional and metabolic alterations, such as high-protein diet, fasting, and diabetes. Patients with intestinal diseases, such as ulcerative colitis, Crohn's disease, and short-bowel syndrome, may have induction of the Pept-1 expression in their colon. Finally, pharmacological studies have shown that the expression of Pept-1 can be upregulated by agents such as 5 fluorouracil and downregulated by agents such as cyclosporine. In conclusion, the above studies have produced a wealth of new information on regulation of a key transporter in the intestine. This information may have useful applications in nutritional and pharmacological treatments, for example, in diabetic patients needing enteral nutrition or in ulcerative colitis patients needing the suppression of the intestinal inflammation.