Co-Detection of miR-21 and TNF- mRNA in Budding Cancer Cells in Colorectal Cancer

MicroRNA-21 (miR-21) is upregulated in many cancers including colon cancers and is a prognostic indicator of recurrence and poor prognosis. In colon cancers, miR-21 is highly expressed in stromal fibroblastic cells and more weakly in a subset of cancer cells, particularly budding cancer cells. Exploration of the expression of inflammatory markers in colon cancers revealed tumor necrosis factor alpha (TNF-) mRNA expression at the invasive front of colon cancers. Surprisingly, a majority of the TNF- mRNA expressing cells were found to be cancer cells and not inflammatory cells. Because miR-21 is positively involved in cell survival and TNF- promotes necrosis, we found it interesting to analyze the presence of miR-21 in areas of TNF- mRNA expression at the invasive front of colon cancers. For this purpose, we developed an automated procedure for the co-staining of miR-21, TNF- mRNA and the cancer cell marker cytokeratin based on analysis of frozen colon cancer tissue samples (n = 4) with evident cancer cell budding. In all four cases, TNF- mRNA was seen in a small subset of cancer cells at the invasive front. Evaluation of miR-21 and TNF- mRNA expression was performed on digital slides obtained by confocal slide scanning microscopy. Both co-expression and lack of co-expression with miR-21 in the budding cancer cells was noted, suggesting non-correlated expression. miR-21 was more often seen in cancer cells than TNF- mRNA. In conclusion, we report that miR-21 is not linked to expression of the pro-inflammatory cytokine TNF- mRNA, but that miR-21 and TNF- both take part in the cancer expansion at the invasive front of colon cancers. We hypothesize that miR-21 may protect both fibroblasts and cancer cells from cell death directed by TNF- paracrine and autocrine activity.