Abstract 3345: Targeting the YAP1/COX2/SOX2 signaling axis eliminates cancer stem cells in urothelial carcinoma
Authors: Oki Akira , Hoque Mohammad 
Published: July 2016

Urothelial cancer stem cells (CSCs) contribute to tumor maintenance and resistance to therapy and accumulated evidence suggest that chronic carcinogen exposure induce “stemness”. Therapeutic targeting of CSCs could improve treatment response and prolong patient survival. Here we used our recently published in vitro chronic arsenic (As) exposed models to characterize the property of urothelial CSCs due to arsenic exposure. We hypothesized that urothelial stem cells have a survival selection advantage during carcinogen exposure such as As, and it facilitates their malignant transformation and in acquiring selective phenotypes similar to CSC.

Arsenic-exposed cells displayed more aggressive phenotype than arsenic unexposed cells in a time dependent manner as determined by MTT, invasion, and wound healing assay. In gene set enrichment analysis of expression array of chronic arsenic exposed and unexposed cells; EGFR, COX2 and YAP1 were top-ranked oncogenic signature based on enrichment score in As-exposed cells. Further analysis indicated that several known basal cell markers such as KRT5, KRT6A, and KRT6C etc were overexpressed in As exposed cells in comparison with As unexposed cells. Because the presence of urothelial CSCs in basal-type provides a biological explanation for their aggressive behaviors, we assessed the influence of As on generating CSC phenotypes. As exposure was associated with overabundance of potential CSCs characterized by sphere formation, self-renewal capacity, redifferentiation, and chemotherapy resistance. To explore global association of As exposure and CSC generation, we used the Human Stem Cell RT2 Profiler™ PCR Array and found that SOX2 has been gradually overexpressed in line with acquired spheroid formation and self-renewal capacities. SOX2 is frequently overexpressed in numerous urothelial carcinoma (UC) cell lines as well as in arsenic-exposed cells, especially in the spheroid cells. Stable silencing of SOX2 reduces in vitro CSCs properties with reduce expression of CSCs associated molecules such as NANOG,OCT4 etc and also in vivo tumorigenicity. COX2 and YAP1 are also frequently overexpressed in UC cell lines, and inhibition of COX2 or YAP1 reduced SOX2 expression. Interestingly, the inhibition of COX2 and YAP1 expression inversely induced YAP1 and COX2 expression, respectively. Combination treatment with COX2 and YAP1 inhibitors reduced SOX2 expression and suppressed spheroid formation significantly than either inhibitor alone. In xenograft model, the combination treatment suppressed the tumor growth rate, but not either inhibitor alone. In conclusion, chronic As exposure induces CSCs with SOX2 overexpression, one of the most important CSC factor for UC. COX2 and YAP1 coordinately regulate SOX2 expression, and mutually compensate for the reduction of expression of SOX2 to maintain CSCs. Thus targeting the COX2/YAP/SOX2 signaling axis eliminates urothelial CSCs.

Citation Format: Akira Oki, Mohammad Hoque. Targeting the YAP1/COX2/SOX2 signaling axis eliminates cancer stem cells in urothelial carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3345.