Pope Jillian L, Ahmad Rizwan, Bhat Ajaz A, Washington Mary K, Singh Amar B, Dhawan Punita
Department of Veterans Affairs, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
Mol Cancer. 2014 Jul 6;13:167. doi: 10.1186/1476-4598-13-167.
The tight junction protein Claudin-1, a claudin family member, has been implicated in several gastro-intestinal pathologies including inflammatory bowel disease (IBD) and colorectal cancer (CRC). In this regard, we have demonstrated that claudin-1 expression in colon cancer cells potentiates their tumorigenic ability while in vivo expression of claudin-1 in the intestinal epithelial cells (IECs) promotes Notch-activation, inhibits goblet cell differentiation and renders susceptibility to mucosal inflammation. Notably, a key role of inflammation in colon cancer progression is being appreciated. Therefore, we examined whether inflammation plays an important role in claudin-1-dependent upregulation of colon carcinogenesis.
APCmin mice were crossed with Villin-claudin-1 transgenic mice to generate APC-Cldn1 mice. H&E stained colon tissues were assessed for tumor number, size and histological grade. Additionally, microarray and qPCR analyses of colonic tumors were performed to assess molecular changes due to claudin-1 expression. APC-Cldn1 and APCmin controls were assessed for colonic permeability via rectal administration of FITC-dextran, and bacterial translocation via qPCR analysis of 16S rDNA.
Claudin-1 overexpression in APCmin mice significantly increased (~4-fold) colonic tumor growth and size, and decreased survival. Furthermore, transcriptome analysis supported upregulated proliferation, and increased Wnt and Notch-signaling in APC-Cldn1 mice. APC-Cldn1 mice also demonstrated inhibition of mucosal defense genes while expression of pro-inflammatory genes was sharply upregulated, especially the IL-23/IL-17 signaling. We predict that increased Notch/Wnt-signaling underlie the early onset of adenoma formation in APC-Cldn1 mice. An increase in mucosal permeability due to the adenomas and the inherent barrier defect in these mice further facilitate bacterial translocation into the mucosa to induce inflammation, which in turn promote the tumorigenesis.
Taken together, these results confirm the role of claudin-1 as a promoter of colon tumorigenesis and further identify the role of the dysregulated antigen-tumor interaction and inflammation in claudin-1-dependent upregulation of colon tumorigenesis.
紧密连接蛋白Claudin-1是claudin家族成员，与多种胃肠道疾病有关，包括炎症性肠病（IBD）和结直肠癌（CRC）。在这方面，我们已经证明，结肠癌细胞中Claudin-1的表达增强了它们的致瘤能力，而肠道上皮细胞（IECs）中Claudin-1的体内表达促进Notch激活，抑制杯状细胞分化，并使机体易患粘膜炎症。值得注意的是，炎症在结肠癌进展中的关键作用正在得到认可。因此，我们研究了炎症在Claudin-1依赖性结肠癌发生上调中是否起重要作用。
将APCmin小鼠与Villin-Claudin-1转基因小鼠杂交，以产生APC-Cldn1小鼠。对苏木精和伊红（H&E）染色的结肠组织进行肿瘤数量、大小和组织学分级评估。此外，对结肠肿瘤进行微阵列和定量聚合酶链反应（qPCR）分析，以评估由于Claudin-1表达引起的分子变化。通过直肠给予异硫氰酸荧光素（FITC）-葡聚糖评估APC-Cldn1和APCmin对照的结肠通透性，并通过对16S核糖体DNA（rDNA）的qPCR分析评估细菌易位。
APCmin小鼠中Claudin-1的过表达显著增加了结肠肿瘤的生长和大小（约4倍），并降低了生存率。此外，转录组分析支持APC-Cldn1小鼠中增殖上调以及Wnt和Notch信号增加。APC-Cldn1小鼠还表现出粘膜防御基因的抑制，而促炎基因的表达急剧上调，尤其是白细胞介素（IL）-23/IL-17信号。我们预测，Notch/Wnt信号增加是APC-Cldn1小鼠腺瘤形成早发的基础。腺瘤导致的粘膜通透性增加以及这些小鼠固有的屏障缺陷进一步促进细菌易位进入粘膜以诱导炎症，进而促进肿瘤发生。
综上所述，这些结果证实了Claudin-1作为结肠肿瘤发生促进因子的作用，并进一步确定了失调的抗原-肿瘤相互作用和炎症在Claudin-1依赖性结肠肿瘤发生上调中的作用。
