Abstract 1045: Differentiated tumor cells secrete stem cell factor (SCF) to promote maintenance of cancer stem cells and induce EMT in colorectal tumors

Abstract

Abstract Colorectal tumors are hierarchically organized in which cancer stem cells (CSCs) are at the top of the hierarchy and give rise to non-tumorigenic differentiated tumor cells (DTC). The maintenance of normal intestinal stem cells requires ‘niche’ signals that are provided, at least in the small intestine, by neighboring differentiated Paneth cells. CSC maintenance may also depend on niche signals although little is known about the nature of such signals and their potential source. For the present study we tested the hypothesis that DTCs could provide CSC-maintaining signals. We used CSC-enriched colonosphere cultures that were established from human colorectal tumors and CSC-derived stably differentiated offspring that was derived from them. We found that DTCs established from multiple colorectal tumors greatly increased the clone-forming capacity of CSCs. This effect was reproduced by DTC-conditioned medium, suggesting the involvement of a secreted factor. By using a cytokine array we identified stem cell factor (SCF) as a major DTC-secreted factor. While SCF was mainly produced by DTCs, its receptor, c-Kit, was mainly expressed by CSCs. Indeed, recombinant SCF enhanced clone-forming capacity to a similar extent as DTC-conditioned medium. Furthermore, basal and DTC-stimulated clone-forming capacity was strongly reduced in the presence of an SCF-neutralizing antibody or in the presence of the cKit inhibitors Imatinib or ISCK03. qPCR and western blot analysis showed that inhibition of cKit caused a strong reduction in the expression of stem cell genes, including LGR5, CD133, OLMF4 and SOX2. Furthermore, DTCs induce the E-to N-cadherin switch in CSCs and to a strong increase in the expression of EMT markers such as vimentin, ZEB1, ZEB2, SNAIL1 and fibronectin. cKIT inhibitors prevented EMT. Our results identify a critical role for non-tumorigenic DTCs in the support of colorectal CSCs. DTCs induce EMT and EMT-associated stem cell characteristics at least in part via paracrine SCF-cKit signaling. We conclude that cKit inhibitors that are widely used in the clinic to treat gastrointestinal stromal tumors (GIST) and acute myeloid leukemia (AML), may have therapeutic value in the treatment of (a subgroup of) colorectal tumors. Citation Format: Szabolcs Fatrai, Susanne J. van Schelven, Inne H.M. Borel Rinkes, Onno Kranenburg. Differentiated tumor cells secrete stem cell factor (SCF) to promote maintenance of cancer stem cells and induce EMT in colorectal tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1045. doi:10.1158/1538-7445.AM2014-1045