Background & aims: PTEN (phosphatase and tensin homologue deleted from chromosome 10) is a dual-specificity phosphatase implicated in embryonic development, intestinal cell proliferation and differentiation, and tumor suppression. The transcription factor Cdx-2 is critical in intestinal development and homeostasis, and its expression is altered in colorectal cancers. However, the regulation of the Cdx-2 gene has not been entirely elucidated. Here, we hypothesize that Cdx-2 may be a target of PTEN signaling in the intestine.
Methods: The expression patterns for Cdx-2 and PTEN along wild-type mouse colon, as well as in colon tumors occurring in Pten(+/-) mice, were examined. The effect of PTEN or phosphatidylinositol 3-kinase inhibition and tumor necrosis factor alpha on Cdx-2 messenger RNA and protein expression, Cdx-2 DNA binding activity, and the promoter activity of the Cdx-2 gene was analyzed in human colon cancer cell lines.
Results: Cdx-2 expression correlates with PTEN along the length of the murine colon and in colonic polyps that develop in Pten(+/-) mice. In colon cancer cells, PTEN stimulates Cdx-2 protein expression and the transcriptional activity of the Cdx-2 promoter. Phosphatidylinositol 3-kinase inhibition by wortmannin or by a dominant-negative phosphatidylinositol 3-kinase mimics the Cdx-2 stimulation by PTEN. Inversely, cell treatment by tumor necrosis factor alpha decreases Cdx-2 expression. Phosphatidylinositol 3-kinase inhibition by PTEN or wortmannin has an inverse effect compared with tumor necrosis factor alpha on the balance between the p50 and p65 subunits of nuclear factor kappaB. p65 inhibits the activity of the Cdx-2 promoter, whereas p50 prevents p65 action.
Conclusions: Our results suggest that the intestinal Cdx-2 homeobox gene is a target of PTEN/phosphatidylinositol 3-kinase signaling and tumor necrosis factor alpha signaling via nuclear factor kappaB-dependent pathways.