Su2003 Nrip2, a Novel Regulator of the Non-Canonical Wnt Pathway, Promotes the Self-Renewal of Colorectal Cancer Initiating Cells

Abstract

As normal tissues contain normal tissue stem cells (NSCs), tumors are thought to contain tumor stem cells (TSCs) which perform self-renewal and generate their progenies. TSC can be a therapeutic target; however, cancer therapies targeting TSCs are limited, because most of the TSC markers are shared by NSCs. Therefore, it is important to identify TSC-specific markers. Previously, we reported that doublecortin-like kinase 1 (Dclk1)-positive epithelial cells do not produce any progenies in the normal small intestine but supply progeny tumor cells in the tumors of Apc mice. Selective ablation of Dclk1-positive TSCs collapses the intestinal tumors of Apc mice. Therefore, Dclk1 appears to be a specific marker of TSCs in the mouse intestinal tumors. In the present study, we performed microarray analysis in order to investigate the characteristics of Dclk1-positive TSCs in the tumors of Apc mice. Dclk1-positive tumor cells had higher expression levels of cyclooxygenase 1 (Cox1), leukotriene C4 synthase (Ltc4s), and arachidonate 5-lipoxygenase activating protein (Alox5ap) than Dclk1-negative cells in the tumors of Apc mice, suggesting that Dclk1positive cells in the tumors of Apc mice had higher expression levels of the genes which were related to prostaglandin and leukotriene metabolism. As well, microarray analysis revealed that gustducin alpha and gamma subunits, transient receptor potential cation channel, subfamily M, member 5 (TRPM5), and phospholipase C beta 2 were more highly expressed in Dclk1-positive tumor cells. Thus, Dclk1-positive tumor cells seemed to possess the characteristic of Tuft cells. Furthermore, Dclk1-positive tumor cells had higher expression level of Ras-related C3 botulinum toxin substrate 2 (Rac2) than Dclk1-negative tumor cells in Apc mouse intestine. In order to elucidate the role of Rac2 in Dclk1-positive TSCs, we generated tumor spheroids from Apc mouse tumors, and administrated EHT1864, Rac inhibitor to the spheroids. Following 5-day treatment with EHT1864, the growth of the tumor spheroids was significantly suppressed. Importantly, on day1, EHT1864 treatment significantly reduced the proportion of Dclk1-positive cells in the tumor spheroids. These results suggested that Rac2 played some roles for the maintenance of the intestinal tumor spheroids. In conclusion, this study may provide new insights into the maintenance mechanisms of Dclk1-positive TSC in the intestinal tumors, and give us hints to develop novel therapeutic strategies targeting TSCs against colorectal cancers.