The protein disulfide isomerase AGR2 is essential for the production of intestinal mucus

Protein disulfide isomerases (PDIs) aid protein folding and assembly by catalyzing formation and shuffling of cysteine disulfide bonds in the endoplasmic reticulum (ER). Many members of the PDI family are expressed in mammals but the roles of specific PDIs in vivo are poorly understood. A recent homology-based search for additional PDI family members identified anterior gradient homolog 2 (AGR2), a protein originally presumed to be secreted by intestinal epithelial cells, but the function of AGR2 has been obscure. Here we show that AGR2 is expressed in the ER of secretory cells and is essential for in vivo production of intestinal mucin, a large cysteine-rich glycoprotein that forms the protective mucus gel lining the intestine. A cysteine residue within the AGR2 thioredoxin-like domain forms mixed disulfide bonds with MUC2, consistent with a direct role for AGR2 in mucin processing. Despite a complete absence of intestinal mucin, mice lacking AGR2 appeared healthy but were highly susceptible to dextran sodium sulfate-induced experimental colitis, indicating a critical role for AGR2 in protection from environmental insults. We conclude that AGR2 is a unique member of the PDI family that has a specialized and non-redundant role in intestinal mucus production. Keywords: small intestine and colon gene expression profiles for Agr2-/- and littermate control mice DNA miocroarrays were used to analyze small intenstine and colon mRNA expression of AGR2 KO and littermate control mice. The experiment incorporated a 1 color design and used Agilent arrays that contained roughly 44,00 60mer probes that provide complete coverage of the mouse genome. 12 arrays were hybridized and represent 8 small intestine samples ( 4 each KO and WT) and 4 colon samples (2 each KO and WT)蛋白质二硫键异构酶（Protein disulfide isomerases, PDIs）可催化内质网（endoplasmic reticulum, ER）内半胱氨酸二硫键的形成与重排，协助蛋白质的折叠与组装。哺乳动物体内表达多种PDI家族成员，但特定PDI在活体中的生理功能仍未得到充分阐释。近期一项通过同源性搜索筛选PDI家族新成员的研究发现了前部梯度同源蛋白2（anterior gradient homolog 2, AGR2）——该蛋白最初被认为由肠上皮细胞分泌，但其自身的功能长期以来一直模糊不明。本研究证实，AGR2表达于分泌细胞的内质网中，且对肠黏蛋白的活体合成不可或缺；肠黏蛋白是一种富含半胱氨酸的大型糖蛋白，可形成覆盖肠道黏膜的保护性黏液凝胶。AGR2硫氧还蛋白样结构域内的一个半胱氨酸残基可与MUC2形成混合二硫键，这表明AGR2在黏蛋白的加工成熟过程中发挥直接作用。尽管AGR2敲除小鼠完全无法产生肠黏蛋白，但它们外观健康，却对葡聚糖硫酸钠诱导的实验性结肠炎高度易感，这提示AGR2在抵御肠道环境损伤中发挥关键作用。综上，本研究认为AGR2是PDI家族的独特成员，在肠道黏液生成过程中具有专门化且不可替代的生理功能。关键词：Agr2-/-小鼠及同窝对照小鼠的小肠与结肠基因表达谱 本研究采用DNA微阵列技术，分析AGR2敲除（AGR2 KO）小鼠与同窝野生型（WT）小鼠的小肠及结肠mRNA表达水平。实验采用单通道杂交设计，所用安捷伦（Agilent）芯片包含约44000条60聚体探针，可完整覆盖小鼠基因组。本次实验共完成12张芯片的杂交，样本涵盖8份小肠组织样本（敲除组与野生型组各4份）及4份结肠组织样本（敲除组与野生型组各2份）。