Moll R, Zimbelmann R, Goldschmidt M D, Keith M, Laufer J, Kasper M, Koch P J, Franke W W
Division of Cell Biology, German Cancer Research Center, Heidelberg.
Differentiation. 1993 Jun;53(2):75-93. doi: 10.1111/j.1432-0436.1993.tb00648.x.
The differentiation of the predominant cell types of the mucosal epithelium of the mammalian gastrointestinal tract is characterized by increasing amounts of an intermediate-sized filament (IF) protein designated cytokeratin (CK) 20 which is a major cellular protein of mature enterocytes and goblet cells. Here we report the isolation of the human gene encoding CK 20, its complete nucleotide sequence and the amino acid sequence deduced therefrom that identifies this polypeptide (mol. wt. 48553) as a member of the type I-CK subfamily. Remarkable, however, is the comparably great sequence divergence of CK 20 from all other known type I-CKs, with only 58% identical amino acids in the conserved alpha-helical 'rod' domain of CK 20 and, e.g. CK 14. Using riboprobes corresponding to exon 6 of the gene in Northern blot and ribonuclease protection assays, we show that the approximately 1.75 kb mRNA encoding CK 20 is specifically produced in cells of the intestinal and gastric mucosa, including tumors and cell lines derived therefrom. The appearance of CK 20-positive cells in human embryonic and fetal development and in adult tissues has been studied using immunohistochemistry with CK 20-specific antibodies. CK 20 synthesis has first been recognized at embryonic week 8 in individual 'converted' simple epithelial cells of the developing intestinal mucosa. In later fetal stages, CK 20 synthesis extends over most goblet cells and a variable number of villus enterocytes. The distribution of CK 20-positive cells in the developing gastric and intestinal mucosa is similar to--but not identical with--the pattern in the adult intestine in which all enterocytes and goblet cells as well as certain 'low-differentiated' columnar cells contain CK 20, whereas the neuroendocrine ('enterochromaffin') and Paneth cells are negative. In gastrointestinal carcinomas similarly examined, CK 20 has been detected in almost all cases (50/52) of colorectal adenocarcinomas, including all grades of differentiation and malignancy and also metastatic tumors, whereas CK 20 immunostaining in gastric carcinomas has been found less consistent and more heterogeneous. The possible biological meaning of the specific expression of the CK 20 gene in certain cells of the gastrointestinal tract and carcinomas derived therefrom and the regulatory mechanisms involved in the integration of the protein in the IF cytoskeleton are discussed.
哺乳动物胃肠道黏膜上皮的主要细胞类型分化的特征是，一种中等大小的丝状（IF）蛋白——细胞角蛋白（CK）20的含量不断增加，CK 20是成熟肠上皮细胞和杯状细胞的主要细胞蛋白。在此，我们报告了编码CK 20的人类基因的分离、其完整核苷酸序列以及由此推导的氨基酸序列，该序列确定此多肽（分子量48553）为I型CK亚家族的成员。然而，值得注意的是，CK 20与所有其他已知I型CK的序列差异相当大，在CK 20和例如CK 14的保守α螺旋“杆”结构域中，只有58%的氨基酸相同。在Northern印迹和核糖核酸酶保护试验中，使用与该基因外显子6对应的核糖探针，我们发现编码CK 20的约1.75 kb mRNA在肠和胃黏膜细胞中特异性产生，包括肿瘤及其衍生的细胞系。使用CK 20特异性抗体进行免疫组织化学研究了人类胚胎和胎儿发育以及成人组织中CK 20阳性细胞的出现情况。在胚胎第8周时，首次在发育中的肠黏膜单个“转化”的简单上皮细胞中识别到CK 20的合成。在胎儿后期，CK 20的合成扩展到大多数杯状细胞和数量不等的绒毛肠上皮细胞。发育中的胃和肠黏膜中CK 20阳性细胞的分布与成人肠道中的模式相似，但不完全相同，在成人肠道中，所有肠上皮细胞和杯状细胞以及某些“低分化”柱状细胞都含有CK 20，而神经内分泌（“肠嗜铬”）细胞和潘氏细胞为阴性。在同样检查的胃肠道癌中，几乎所有（50/52）结直肠腺癌病例中都检测到了CK 20，包括所有分化程度和恶性程度以及转移性肿瘤，而在胃癌中，CK 20免疫染色的结果不太一致且更具异质性。本文讨论了CK 20基因在胃肠道某些细胞及其衍生癌中的特异性表达的可能生物学意义，以及该蛋白整合到IF细胞骨架中的调控机制。
