NUTRITIONAL REGULATION OF THE GUANYLIN/STA RECEPTOR

鸟苷酸环化酶C（GC-C）是一种受体酶，是主要的 肠上皮细胞刷状缘表面的环GMP。 GC-C具有细胞外配体结合结构域。配体结合激活 一个细胞内酶结构域，最终导致打开 囊性纤维化跨膜调节因子（CFTR）氯离子通道。GC-C可以 结合两个不同的配体。它可以结合STa肠毒素产生的 大肠杆菌和其他消化道细菌。这些毒素是 婴儿和旅行者腹泻的原因。它还可以绑定 新发现的肠肽鸟苷素，由 肠嗜铬（EC）细胞。鸟苷素类似于 利钠肽（即，心房钠尿肽（ANP）在其 受体-产物关系、受体结构和 鸟苷酸环化酶由于鸟苷素和ST具有相同的受体， STa毒素引起的大量腹泻可能是由于 GC-C的不受调节的激活。 刷状缘表面环GMP的产生与 氯化物分泌增加和吸收减少，与 与STa毒素相关的分泌性腹泻。然而，GC的作用- C在正常肠道生理中的作用尚不清楚。很少有人知道 GC-C及其天然配体鸟苷素的生物学。然而，鸟苷酸-STa 受体效应系统可以调节肠电解质平衡或水 损失，视为肠对应的大脑和心房 利钠肽系统此外，合成或活化 鸟苷素和GC-C可能受肠道对饮食的反应控制， 因素，如拉伸，渗透，或激素刺激。 这项研究的长期目标是了解鸟苷素- 受体相互作用及其机制的细胞信号转导， 生物化学和分子方法。了解结构和 该受体系统的功能可能有助于设计新的抗- 胃肠药物、疫苗或肠道调节剂。由于大鼠 肠道对STa的反应在治疗过程中会增强十倍之多， 饥饿和因为STa相关的分泌性腹泻在 饥饿的人，我们将重点放在这个受体系统在禁食 大鼠 这项建议的具体目标如下： GC-C和GN在不同肠道的饮食和昼夜调节 网站. (2)为了确定GC-C突然下降的分子基础- 肠上皮细胞刷状缘表面的调节， 再喂养禁食的大鼠。(3)确定GC-C的定位和移动 在其合成、组装和运输到刷状边缘期间， 在与STa毒素结合后

Guanylyl cyclase C (GC-C) is a receptor-enzyme that is the major source of cyclic GMP at the brush border surface of the intestinal epithelial cell. GC-C has an extracellular ligand binding domain. Ligand binding activates an intracellular enzyme domain, ultimately leading to the opening of the cystic fibrosis transmembrane regulator (CFTR) chloride channels. GC-C can bind two different ligands. It can bind the STa enterotoxins produced by Escherichia coli and other diarrhetic bacteria. These toxins are a major cause of infant and travelers diarrhea world-wide. It can also bind the newly discovered intestinal peptide, guanylin, which is produced by enterochromaffin (EC) cells. Guanylin resembles the circulating natriuretic peptides (i.e., atrial natriuretic peptide -- ANP) in its precursor-product relationship, receptor structure, and activation of guanylate cyclase. Because guanylin and ST have the same receptor, the profuse diarrhea caused by the STa toxin is probably due to the unregulated activation of GC-C. Production of cyclic GMP at the brush border surface is associated with increased chloride secretion and decreased absorption, consistent with the secretory diarrhea associated with the STa toxin. However, the role of GC- C in normal intestinal physiology is unclear. Very little is known about the biology of GC-C and its natural ligand, guanylin. Yet the guanylin-STa receptor effector system may regulate enteric electrolyte balance or water loss, seeing as an intestinal counterpart to the brain and atrial natriuretic peptide systems. Further, the synthesis or activation of guanylin and GC-C may be controlled by the intestinal response to dietary factors, such as stretch, osmotic, or hormonal stimuli. The long term goal of the proposed research is to understand the guanylin- receptor interaction and its mechanisms of cell signaling using both biochemical and molecular approaches. Understanding the structure and function of this receptor system may contribute to the design of new anti- diarrheal drugs, vaccines or intestinal modulators. Because the rat intestinal response to STa is heightened by as much as ten-fold during starvation and because STa-associated secretory diarrhea is exacerbated in famished individuals, we will focus on this receptor system in the fasted rat. The specific aims of this proposal are as follows: (l) To determine the dietary and circadian regulation of GC-C and GN at different intestinal sites. (2) To determine the molecular basis for the abrupt GC-C down- regulation from the enterocyte brush border surface that occurs when fasted rats are refed. (3) To define the localization and movement of GC-C during its synthesis, assembly, and transport to the brush border and after its binding to the STa toxin.