Abstract 2327: Oncogenic K-Ras and H-Ras differentially regulate cancer stem cell-like properties via repression of non-canonical Wnt signaling.
Authors: Wang Man-Tzu , Galeas Jacqueline , Ritchie Cayde , McCormick Frank 
Published: August 2014

Cancer stem cells (CSCs) can cause cancer treatment failures and tumor recurrence due to their stem cell-like properties, such as the unlimited self-renewal, tumorigenicity, and chemo-resistance. Ras is the most common oncogene in human cancers, but its roles in stem cell-like properties have not been convincingly demonstrated. With a high degree of sequence homology as well as common sets of downstream effectors and upstream affecters, the three isoforms of Ras, N-, H- and K-Ras, have long been assumed to be functionally redundant. However, knockout of K-Ras, not N- or H-Ras, in mice leads to embryonic lethality, suggesting a non-redundant role of K-Ras in embryonic development. Herein, we report that oncogenic K-Ras, differentially from H-Ras, causes CSC-like properties in transformed mouse fibroblast and pancreatic cancer cells. When compared to the NIH3T3 cells with H-RasV12, the cells transformed with K-RasV12 demonstrated significantly enhanced sphere forming efficiency, elevated resistance toward cisplatin, and heightened sensitivity to the CSC inhibitor, salinomycin, while the RasGTPase, p-Erk and p-Akt activities are comparable. In the comparison with H-RasV12 transformed cells, K-RasV12 transformed NIH3T3 cells possessed significantly increased tumor initiating frequency in limited cell transplantation and in vivo serial transplantation assays. Through stem cell signaling-related genes focusing PCRarray, we further identified Frizzled 8 (Fzd8), a Wnt receptor and potential activator of non-canonical Wnt/Ca2+ signaling, was significantly down-regulated in K-RasV12 transformed NIH3T3 cells when compared to normal cells or H-RasV12- transformed cells. In clinical human pancreatic tissues, Fzd8 was dramatically reduced in malignant specimens, whereas normal tissue showed high expressions of Fzd8. Knockdown of K-Ras in pancreatic cancer cells led to significant increases in Fzd8 at RNA and protein levels, suggesting oncogenic K-Ras repress the expression of Fzd8. TOPFlash assay revealed that K-RasV12 transformed NIH3T3 had dramatically enhanced canonical beta-catenin activity when compared to normal or H-RasV12- transformed cells. Human pancreatic cancer cells with K-Ras knocked down showed significantly reduced canonical beta-catenin activity. In a syngenic mouse model, over-expression of Fzd8 in oncogenic K-Ras driven mouse pancreatic cancer cells delayed the orthotropic tumor formation, and further decreased peritoneal metastatic spreads. Our data collectively suggest that oncogenic K-Ras regulates the stem cell-like properties of cancer cells, differentially from oncogenic H-Ras, through repression of Fzd8-mediated non-canonical Wnt/Ca2+ signaling. Restoration of Fzd8 suppressed oncogenic K-Ras induced pancreatic tumorigenesis, providing an alternative way to target this “undruggable” oncogene.

Citation Format: Man-Tzu Wang, Jacqueline Galeas, Cayde Ritchie, Frank McCormick. Oncogenic K-Ras and H-Ras differentially regulate cancer stem cell-like properties via repression of non-canonical Wnt signaling. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2327. doi:10.1158/1538-7445.AM2013-2327