Regulation of the tumor suppressor homeogene Cdx2 by HNF4α in intestinal cancer.

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.

Increasing the oxygen load by treatment with myo-inositol trispyrophosphate reduces growth of colon cancer and modulates the intestine homeobox gene Cdx2.

Preventing tumor neovascularisation is one of the strategies recently developed to limit the dissemination of cancer cells and apparition of metastases. Although these approaches could improve the existing treatments, a number of unexpected negative effects have been reported, mainly linked to the hypoxic condition and the subsequent induction of the pro-oncogenic hypoxia inducible factor(s) resulting from cancer cells' oxygen starvation. Here, we checked in vivo on colon cancer cells an alternative approach. It is based on treatment with myo-inositol trispyrophosphate (ITPP), a molecule that leads to increased oxygenation of tumors. We provide evidence that ITPP increases the survival of mice in a model of carcinomatosis of human colon cancer cells implanted into the peritoneal cavity. ITPP also reduced the growth of subcutaneous colon cancer cells xenografted in nu/nu mice. In the subcutaneous tumors, ITPP stimulated the expression of the homeobox gene Cdx2 that is crucial for intestinal differentiation and that also has an anti-tumoral function. On this basis, human colon cancer cells were cultured in vitro in hypoxic conditions. Hypoxia was shown to decrease the level of Cdx2 protein, mRNA and the activity of the Cdx2 promoter. This decline was unrelated to the activation of HIF1α and HIF2α by hypoxia. However, it resulted from the activation of a phosphatidylinositol 3-kinases-like mitogen-activated protein kinase pathway, as assessed by the fact that LY294002 and U0126 restored high Cdx2 expression in hypoxia. Corroborating these results, U0126 recapitulated the increase of Cdx2 triggered by ITPP in subcutaneous colon tumor xenografts. The present study provides evidence that a chemical compound that increases oxygen pressure can antagonize the hypoxic setting and reduce the growth of human colon tumors implanted in nu/nu mice.