The main objectives of this proposal are to elucidate and define the molecular, biochemical and physiological mechanisms involved in the digestion and absorption of dietary proteins, peptides and amino acids in the mammalian small intestine. Towards this goal, our studies will focus on the peptidases and peptide transporters associated with the brush-border membrane of small intestinal enterocytes. These enzymes/transporters play an important role in the final phases of protein digestion and also serve as markers of normal cell differentiation and malignant transformation. Therefore, a detailed study of these proteins is vitally important from a nutritional point of view and will enhance our knowledge of the basic physiological, biochemical and molecular processes that operate in the small intestine. These types of studies will lead to a better understanding of the biochemical and physiological alterations that are responsible for various gastrointestinal diseases. The gene promoter of one of these enzymes, DPPIV, will be characterized and mapped in detail. The 5'-flanking sequence of DPPIV possesses promoter activity. Therefore, elements responsible for cell type-specific regulation of DPPIV will be analyzed. This will include DNase footprinting, deletional analysis and use of transgenic mice. Strains of mice that express the DPPIV/hGH transgene have been produced and expression of the transgene will be analyzed in different tissues. Novel transcription factors that are involved in the regulation of DPPIV will be identified, cloned and sequenced. Areas of the DPPIV gene promoter responsible for its dietary regulation will be localized. Using rats as an animal model the effect of diet and small bowel adaption following surgical resection on the regulation and expression of intestinal ACE and DPPIV will be examined. These studies will involve the time course of dietary induction, measurement of mRNA levels and the effect of diet on gene transcription. Cellular changes in the expression of ACE and DPPIV along the crypt-villus axis during intestinal adaptation will be monitored by in situ hybridization and immunohistochemistry.
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