Background

Both self-renewal of intestinal epithelial tissue and human colorectal cancer (CRC) cells are promoted by Wnt/b-catenin signalling(1). Here, we aim to determine the mechanisms through which these signals affect cancer cell reprogramming via regulating the stem-cell-associated gene, NANOG(2).

Method

Immunohistochemistry for NANOG using a human colorectal cancer tissue array and murine intestinal sections showed nuclear NANOG protein in discrete subpopulations of cancer cells. Using both mouse and human NANOG-proximal promoter reporter assays, cell lines derived from different stages of tumorigenesis also exhibited a high degree of NANOG heterogeneity and stem-cell like properties in vitro which are modulated by Wnt/b-catenin signalling.

Results

CRCs express NANOG from both NANOG1 and NANOGP8 loci. Unlike in embryonic stem (ES) cells, the absence of SOX2 and/or OCT4-response elements caused no repression of NANOG-promoter activity in CRC, whilst b-catenin/TCF4 and JUN signals synergize to induce NANOG-promoter activity. Mutation in the octamer M1 element reduces NANOG-promoter activity, making NANOG unresponsive to b-catenin/TCF4 and c-Jun. NANOG-expressing cells revealed high levels of stem-cell associated Wnt-target genes. Furthermore, single CRCs expressing endogenous or elevated levels of NANOG formed spheroidal embryoid bodies (EMB). These results support a model whereby a b-catenin/TCF4:c-Jun complex controls a subpopulation of CRCs driving self-renewal and proliferation via the NANOG1 promoter.

Conclusion

Increased Wnt-signalling and stem-cell-associated signals drive a subpopulation of NANOG-tumour-specific cells to subsequently adopt a cancer stem cell phenotype.