Small GTP Binding Proteins in Gastrointestinal Mucosa

顶端转运体和酶向肠上皮细胞刷状缘的运输对于肠上皮细胞的建立至关重要。 从肠腔正常吸收液体、营养和电解质。同样，建立正常的 细胞间紧密连接和粘附连接处的蛋白质纲要决定了上皮细胞的完整性， 屏障功能顶端运输或连接完整性的异常导致肠道病变 包括腹泻、便秘和肠屏障功能障碍。过去十年的调查 确定Rab 11 a和Rab 8a依赖性膜再循环系统的组分调节 顶端膜和连接蛋白的运输需要维持适当的顶端极性。 肌球蛋白Vb（MYO 5 B）功能丧失导致严重腹泻，原因是继发于 在微绒毛包涵体新生儿中观察到Rab 11 a和Rab 8a依赖性顶端运输缺陷 疾病（MVID）。与此同时，Rab 11 a相互作用蛋白Rab 11-FIP 1和Rab 11-FIP 2， 连接结构和功能，部分通过其磷酸化的关键极性相关激酶 MARK2/Par1b.所有这些研究都使人们认识到，顶端极性的协调调节 和顶端再循环系统的组分的运输是肠上皮细胞生理学的核心， 病理生理学我们假设，通过回收系统的各个方面提供的途径， 特定货物运输至顶膜和细胞间连接的特异性。顶端 再循环系统是破坏根尖细胞的病理生理学干预的关键目标 膜运输到刷状缘和功能性连接完整性的建立。分析这个 假设，我们将追求两个具体目标：首先，我们将确定顶端元素的作用， 在运输离子转运蛋白和酶到肠上皮细胞顶端刷状缘的再循环系统中。这些 研究将检查内源性肠上皮细胞顶端蛋白在人类肠上皮细胞中的命运 在渗透膜上的二维单层培养物上分化。第二，我们将研究 Rab 11-FIP 1B及其被MARK 2/Par 1b磷酸化在肠上皮细胞调控中的作用 连接功能这些研究将使我们更好地了解Rab 11-FIP 1B的磷酸化是如何发生的。 管制前往和维持路口的交通。 影响：这些研究将确定根尖再循环系统的组成部分， 贩运特定的灌木丛边界和过境货物。心尖部多径路的定义 货物贩运到灌木边境和路口将提供洞察如何破坏特定的途径， 可能会改变生理和如何病理生理损失的贩运可以恢复通过改道 蛋白质的替代路线顶端膜。

Trafficking of apical transporters and enzymes to the enterocyte brush border is critical for the establishment of normal fluid, nutrient and electrolyte absorption from the gut lumen. Similarly, establishment of the normal compendium of proteins at the intercellular tight and adherens junctions determines the integrity of epithelial barrier function. Aberrations in either apical trafficking or junctional integrity lead to enteric pathologies including diarrhea, constipation and intestinal barrier dysfunction. Investigations over the past decade have established that components of the Rab11a and Rab8a-dependent membrane recycling systems regulate trafficking of apical membrane and junctional proteins required for the maintenance of proper apical polarity. Loss of functional Myosin Vb (MYO5B) leads to severe diarrhea due to loss of apical transporters secondary to deficits in Rab11a and Rab8a-dependent apical trafficking as observed in neonates with Microvillus Inclusion Disease (MVID). At the same time, the Rab11a-interacting proteins, Rab11-FIP1 and Rab11-FIP2, regulate junctional structure and function, in part through their phosphorylation by the critical polarity-related kinase MARK2/Par1b. All of these studies have led to the recognition that the coordinated regulation of apical polarity and trafficking by components of the apical recycling system lies at the heart of enterocyte physiology and pathophysiology. We have hypothesized that pathways through aspects of the recycling system provide for specificity of trafficking of particular cargoes to the apical membrane and the intercellular junctions. The apical recycling system represents a critical target for intervention in pathophysiologies that undermine apical membrane trafficking to the brush border and establishment of functional junctional integrity. To analyze this hypothesis, we will pursue two specific aims: First, we will determine the roles of elements of the apical recycling system in trafficking of ion transporters and enzymes to the enterocyte apical brush border. These studies will examine the fates of endogenous enterocyte apical proteins in human intestinal enteroids differentiated on two-dimensional monolayer cultures on permeable membranes. Second, we will examine the role of Rab11-FIP1B and its phosphorylation by MARK2/Par1b in the regulation of intestinal enterocyte junctional function. These studies will allow a greater understanding of how phosphorylation of Rab11-FIP1B regulates trafficking to and maintenance of junctions. Impact: These studies will identify components of the apical recycling system that may regulate apical trafficking of particular brush border and junctional cargoes. Definition of the multiple pathways for apical cargo trafficking to the brush border and junctions will provide insights into how disruption of specific pathways may alter physiology and how pathophysiological loss of trafficking may be restored through rerouting of proteins to alternative routes to the apical membrane.!