Mallo G V, Rechreche H, Frigerio J M, Rocha D, Zweibaum A, Lacasa M, Jordan B R, Dusetti N J, Dagorn J C, Iovanna J L
U.315 INSERM, Marseille, France.
Int J Cancer. 1997 Feb 20;74(1):35-44. doi: 10.1002/(sici)1097-0215(19970220)74:1<35::aid-ijc7>3.0.co;2-1.
Defining the molecular mechanisms involved in cancer formation and progression is still a major challenge in colorectal-cancer research. Our strategy was to characterize genes whose expression is altered during colorectal carcinogenesis. To this end, the phenotype of a colorectal tumour was previously established by partial sequencing of a large number of its transcripts and the genes of interest were selected by differential screening on high-density filters with mRNA of colorectal cancer and normal adjacent mucosa. Fifty-one clones were found over-expressed and 23 were underexpressed in the colorectal-cancer tissues of the 5 analyzed patients. Among the latter, clones 6G2 and 32D6 were found of particular interest, since they had significant homology with several homeodomain-containing genes. The highest degree of similarity was with the murine Cdx1 for 6G2, and with the murine Cdx2 and hamster Cdx3 for 32D6. Using a RT-PCR approach, complete sequence of both types of homeobox-containing cDNA was obtained. The amino-acid sequence of the human Cdx1 is 85% identical to the mouse protein, and human Cdx2 has 94% identity with the mouse Cdx2 and hamster Cdx3. Tissue-distribution analysis of Cdx1 and Cdx2 mRNA showed that both transcripts were specifically expressed in small intestine, in colon and rectum. Twelve tissue samples from colorectal adenocarcinomas and the corresponding normal mucosa were analyzed by Northern blot. Expression of the 2 types of mRNA was either reduced or absent in 10 of them. Several colon-cancer cell lines were also analyzed. Cdx2 mRNA was absent from LS174T cells and Cdx1 mRNA was absent in PF11, TC7 and SW480 cells; none was detected in HT29 cells. It was concluded that decrease in human Cdx1 and/or Cdx2 expression is associated with colorectal tumorigenesis.
确定参与癌症形成和进展的分子机制仍是结直肠癌研究中的一项重大挑战。我们的策略是对那些在结直肠癌发生过程中表达发生改变的基因进行特征描述。为此，此前通过对大量转录本进行部分测序确定了结直肠肿瘤的表型，并通过用结直肠癌和正常相邻黏膜的mRNA在高密度滤膜上进行差异筛选来选择感兴趣的基因。在5例分析患者的结直肠癌组织中，发现51个克隆过度表达，23个克隆表达不足。在后者中，克隆6G2和32D6特别令人感兴趣，因为它们与几个含同源结构域的基因有显著同源性。6G2与小鼠Cdx1的相似性最高，32D6与小鼠Cdx2和仓鼠Cdx3的相似性最高。使用逆转录聚合酶链反应（RT-PCR）方法，获得了两种含同源异型框cDNA的完整序列。人Cdx1的氨基酸序列与小鼠蛋白的同一性为85%，人Cdx2与小鼠Cdx2和仓鼠Cdx3的同一性为94%。Cdx1和Cdx2 mRNA的组织分布分析表明，这两种转录本在小肠、结肠和直肠中特异性表达。通过Northern印迹法分析了12份来自结直肠腺癌和相应正常黏膜的组织样本。其中10份样本中这两种mRNA的表达降低或缺失。还分析了几种结肠癌细胞系。LS174T细胞中不存在Cdx2 mRNA，PF11、TC7和SW480细胞中不存在Cdx1 mRNA；HT29细胞中均未检测到。得出的结论是，人Cdx1和/或Cdx2表达的降低与结直肠癌的发生有关。
