GASTROINTESTINAL ENDOCRINOLOGY

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The long-term goal of this program is to provide useful new information on the mechanisms by which gastrointestinal hormones (GIH) and calcium- regulatory peptides influence body function. We will study gene expression, synthesis, storage, release, transport and mechanisms of action on target cells, hormone-hormone interrelationships, the target cell responses, and gene expression as regulated by these agents. The project by Dr. Thompson will study the role (both cause and effect) that GIH play in the aging of the gut. We plan to define some of the mechanisms involved in age-related changes in growth, secretion and gene expression of the GI tract. We will examine the role of GI hormones in regulating apoptosis in gut mucosa. We plan to study the effects of chronic caloric restriction as an anti-aging strategy. The project by Dr. Greeley will examine the role of chromogranin A (CGA) and the mechanisms by which CGA is processed to pancreastatin in enteroendocrine cells. We will study the regulation of CGA homeostasis and co-resident peptides. We will examine the role of prohormone convertases, and determine whether CGA co-resides with gastrin peptides and parathyroid hormone-related peptide (PTHrP) in pancreatic, colon, ovarian and liver cancer cells and whether CGA and co-resident peptides exhibit properties of regulated secretion. The project by Dr. Townsend will examine the effects of bombesin (BBS) on gene expression and release of the peptide, neurotensin. We will examine specific receptor and signal transduction pathways by which BBS affects peptide gene expression, peptide release and growth release and growth of GI cells. We will determine whether specific receptors and receptor-linked signal transduction pathways are different for each of these functions. We will examine both cells that express BBS receptors as well as human cells transfected with GRP or neuromedin B receptors and receptor mutants to dissect these pathways. We have found that the same GIH may either stimulate or inhibit growth of cancer cells. These studies will allow us to determine precisely the cell-specific mechanisms by which GIH affect growth of human cancer cells. The project by Dr. Cooper will examine the hypothesis that calcium-regulatory peptides, specifically PTHrP, play important regulatory roles in the gut. We will identify the mechanisms by which PTHrP regulates growth and differentiation of epithelial cells. We will determine whether PTHrP is an autocrine/paracrine regulatory agent and examine the effects of PTHrP on apoptosis in gut cells, and the role of PTHrP in regenerating liver. We will examine intracellular mechanisms by which vasoactive intestinal peptide (VIP) and PTHrP both stimulate cyclic AMP and ornithine decarboxylase mRNA activity and yet have opposite effects on growth of human colon cancer cells. Since the last competitive review we have demonstrated the productivity of our collaborating efforts by our publications: many publications relate to more than one project. With the support of this grant, our studies have evolved from whole animals to cellular, subcellular and molecular mechanisms of actions of GI hormones in order to meet the long-term objectives of our program.