Inserm, Unité 682, Strasbourg, France.
Oncogene. 2013 Aug 8;32(32):3782-8. doi: 10.1038/onc.2012.401. Epub 2012 Sep 17.
The gut-specific homeotic transcription factor Cdx2 is a crucial regulator of intestinal development and homeostasis, which is downregulated in colorectal cancers (CRC) and exhibits a tumor suppressor function in the colon. We have previously established that several endodermal transcription factors, including HNF4α and GATA6, are involved in Cdx2 regulation in the normal gut. Here we have studied the role of HNF4α in the mechanism of deregulation of Cdx2 in colon cancers. Crossing Apc(Δ14/+) mice prone to spontaneous intestinal tumor development with pCdx2-9LacZ transgenic mice containing the LacZ reporter under the control of the 9.3-kb Cdx2 promoter showed that this promoter segment contains sequences recapitulating the decrease of Cdx2 expression in intestinal cancers. Immunohistochemistry revealed that HNF4α, unlike GATA6, exhibited a similar decrease to Cdx2 in genetic (Apc(min/+) and Apc(Δ14/+)) and chemically induced (Azoxymethane (AOM) treatment) models of intestinal tumors in mice. HNF4α and Cdx2 also exhibited a comparable deregulated pattern in human CRC. Correlated patterns were observed between HNF4α and Cdx2 in several experimental models of human colon cancer cell lines: xenografts in nude mice, wound healing and glucose starvation. Furthermore, Cdx2 decreased by knocking down HNF4α in human colon cancer cells using siRNA and in the colon of mice conditionally knocked out for the Hnf4α gene in the adult intestine (Hnf4α(f/f);VilCre(ERT2) mice). Finally, the conditionally knocked out mice Hnf4α(f/f);VilCre(ERT2) treated with the carcinogen AOM developed colorectal tumors earlier than wild-type mice, as previously reported for mice with a reduced Cdx2 expression. In conclusion, this study provides evidence that the downregulation of HNF4α is an important determinant of the reduced expression of the Cdx2 tumor suppressor gene in intestinal cancers. Consistently, similar to Cdx2, HNF4α exerts a tumor suppressor function in the colon in that its loss of function facilitates tumor progression.
肠道特异性同源盒转录因子 Cdx2 是肠道发育和稳态的关键调节因子，在结直肠癌（CRC）中下调，并在结肠中表现出肿瘤抑制功能。我们之前已经确定，包括 HNF4α 和 GATA6 在内的几种内胚层转录因子参与了正常肠道中 Cdx2 的调节。在这里，我们研究了 HNF4α 在结肠癌中 Cdx2 失调机制中的作用。将易发生自发性肠道肿瘤发展的 Apc(Δ14/+) 小鼠与含有 Cdx2 启动子控制下的 LacZ 报告基因的 pCdx2-9LacZ 转基因小鼠杂交，该启动子片段包含复制肠道癌中 Cdx2 表达减少的序列。免疫组织化学显示，与 GATA6 不同，HNF4α 在遗传（Apc(min/+) 和 Apc(Δ14/+)）和化学诱导（氧化偶氮甲烷（AOM）处理）的小鼠肠道肿瘤模型中与 Cdx2 表现出相似的减少。HNF4α 和 Cdx2 在人类 CRC 中也表现出类似的失调模式。在几种人类结肠癌细胞系的实验模型中观察到 HNF4α 和 Cdx2 之间存在相关模式：裸鼠异种移植、伤口愈合和葡萄糖饥饿。此外，通过 siRNA 敲低人结肠癌细胞中的 HNF4α 以及在成年肠道中条件性敲除 Hnf4α 基因的小鼠（Hnf4α(f/f);VilCre(ERT2) 小鼠）中，Cdx2 减少。最后，用致癌剂 AOM 处理的条件性敲除 Hnf4α(f/f);VilCre(ERT2) 小鼠比野生型小鼠更早地发展出结直肠肿瘤，正如先前报道的 Cdx2 表达降低的小鼠一样。总之，这项研究提供了证据表明，HNF4α 的下调是肠道癌中 Cdx2 肿瘤抑制基因表达降低的重要决定因素。与 Cdx2 相似，HNF4α 在结肠中发挥肿瘤抑制功能，因为其功能丧失促进了肿瘤的进展。
