Higuchi Toshio, Orita Takuya, Nakanishi Setsuko, Katsuya Ken, Watanabe Hirotaka, Yamasaki Yoshiki, Waga Iwao, Nanayama Toyomichi, Yamamoto Yoshihisa, Munger William, Sun Hong-Wei, Falk Ronald J, Jennette J Charles, Alcorta David A, Li Huiping, Yamamoto Tadashi, Saito Yutaka, Nakamura Motonao
Central Pharmaceutical Research Institute, Pharmaceutical Frontier Research Laboratories, Japan Tobacco Inc., Yokohama, Kanagawa 236-0004, Japan.
J Biol Chem. 2004 Jan 16;279(3):1968-79. doi: 10.1074/jbc.M304558200. Epub 2003 Oct 17.
Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis in the world. Here, we identify a cDNA encoding a novel mucin protein, shown previously to be up-regulated in IgAN patients, from a human kidney cDNA library. This protein contains a mucin tandem repeat of 19 amino acids consisting of many threonine, serine, and proline residues and likely to be extensively O-glycosylated; thus, this gene was classified in the mucin family and named MUC20. The human MUC20 gene contains at least four exons and is localized close to MUC4 on chromosome 3q29. We found variations in repeat numbers in the mucin tandem domain, suggesting polymorphism of this region. Northern blot and reverse transcription-PCR analyses revealed that human MUC20 mRNA was expressed most highly in kidney and moderately in placenta, colon, lung, prostate, and liver. Immunohistochemical analysis of human kidney revealed that MUC20 protein was localized in the proximal tubules. Immunoblotting analysis of MUC20 proteins produced in Madin-Darby canine kidney and HEK293 cells indicated the localization of MUC20 protein in a membrane fraction and extensive posttranslational modification. Immunoelectron microscopy of MUC20-producing Madin-Darby canine kidney cells demonstrated that MUC20 protein was localized on the plasma membrane. Expression of MUC20 mRNA in a human kidney cell line was up-regulated by tumor necrosis factor-alpha, phorbol 12-myristate 13-acetate, or lipopolysaccharide. Two species of MUC20 mRNA (hMUC20-L and hMUC20-S), resulting from alternative transcription, were identified in human tissue, whereas only one variant was observed in mouse tissues. Mouse MUC20 mRNA was expressed in the epithelial cells of proximal tubules, and the expression increased dramatically with the progression of lupus nephritis in the kidney of MRL/MpJ-lpr/lpr mice. Moreover, the expression of mouse MUC20 was augmented in renal tissues acutely injured by cisplatin or unilateral ureteral obstruction. These characteristics suggest that the production of MUC20 is correlated with development and progression of IgAN and other renal injuries.
免疫球蛋白A肾病（IgAN）是全球最常见的原发性肾小球肾炎。在此，我们从人肾cDNA文库中鉴定出一个编码新型粘蛋白的cDNA，该蛋白先前在IgAN患者中被证明上调。该蛋白包含一个由19个氨基酸组成的粘蛋白串联重复序列，其中包含许多苏氨酸、丝氨酸和脯氨酸残基，可能被广泛O-糖基化；因此，该基因被归类于粘蛋白家族并命名为MUC20。人MUC20基因至少包含四个外显子，定位于3号染色体q29上靠近MUC4的位置。我们发现粘蛋白串联结构域中的重复序列数量存在变异，表明该区域存在多态性。Northern印迹和逆转录PCR分析显示，人MUC20 mRNA在肾脏中表达最高，在胎盘、结肠、肺、前列腺和肝脏中中度表达。人肾组织的免疫组织化学分析显示，MUC20蛋白定位于近端小管。对在Madin-Darby犬肾细胞和HEK293细胞中产生的MUC20蛋白进行免疫印迹分析表明，MUC20蛋白定位于膜组分中且存在广泛的翻译后修饰。对产生MUC20的Madin-Darby犬肾细胞进行免疫电子显微镜检查表明，MUC20蛋白定位于质膜上。人肾细胞系中MUC20 mRNA的表达受肿瘤坏死因子-α、佛波酯12-肉豆蔻酸酯13-乙酸酯或脂多糖上调。在人体组织中鉴定出两种由选择性转录产生的MUC20 mRNA（hMUC20-L和hMUC20-S），而在小鼠组织中仅观察到一种变体。小鼠MUC20 mRNA在近端小管的上皮细胞中表达，并且在MRL/MpJ-lpr/lpr小鼠肾脏中随着狼疮性肾炎的进展表达显著增加。此外，在顺铂或单侧输尿管梗阻急性损伤的肾组织中，小鼠MUC20的表达增强。这些特征表明，MUC20的产生与IgAN和其他肾损伤的发生发展相关。
