Abstract 488: Epigenetic regulation of colorectal cancer stem cells by the miR-221/QKI5 axis
Authors: Mukohyama Junko , Shimono Yohei , Dalerba Piero , Isobe Taichi , Hu Qingjiang , Sahoo Debashis , Shibuya Naoki , Minami Hironobu , Mimori Koshi , Kakeji Yoshihiro , Suzuki Akira 
Published: August 2018

Abstract
Colorectal cancer stem cells (CSCs) have extensive abilities to initiate tumor formation, and are responsible for the progression and metastasis of colorectal cancers. MicroRNAs (miRNAs) are non-coding RNAs of 18-24 nucleotides that post-transcriptionally regulate expression of multiple genes by targeting their 3'untranslated regions (UTRs). miRNAs regulate various biological processes, and function as important regulators of CSC properties.
miR-221 is one of the oncogenic miRNAs frequently upregulated in human cancers including colorectal cancer. Previous studies have shown that miR-221 enhances proliferation, migration, and invasion of cancer cells. However, the role of miR-221 in human colorectal CSCs is not fully elucidated. In this study, we analyzed the colorectal CSCs directly isolated from the surgical specimens of colorectal cancer patients to explore the role of miR-221 in CSCs.
Expression profile of 754 miRNAs in the CD44+/EpCAM+ CSC and non-tumorigenic cancer cell (NTC) populations was analyzed by multiplex semi-quantitative PCR. Prognostic impact of miR-221 expression in CSCs was analyzed using the TCGA database. Target genes of miR-221 were validated by luciferase reporter assays and Western blot experiments. The roles of miR-221 and its target gene QKI-5 in colorectal CSCs were evaluated by organoid and xenotransplantation assays.
Comparison of the expression levels of 754 miRNAs in the CSCs and NTCs resulted in the identification of 10 miRNAs upregulated or downregulated in CSCs compared to NTCs. Among them, miR-221 was most highly expressed in CSCs and its expression level was very low in NTCs and human normal colon epithelial cells of human colorectal cancer specimens (n=6, p&lt;0.05). The estimated 5-year overall survival rate for miR-221high patients (n=177) was significantly lower than miR-221low ones (n=116) in TCGA dataset (54.6% vs. 73.6%; p&lt;0.001). The TNM stages at diagnosis were not significantly associated with the expression level of miR-221. In a multivariate analysis, miR-221 expression were significantly associated with overall survival (p=0.009). miR-221 targeted an RNA binding protein (RBP) QKI-5 and suppressed its expression. Knockdown of miR-221 in human colorectal cancer patient-derived xenograft cells suppressed the organoid formation in vitro in a QKI-5-suppression-dependent manner, and tumor formation initiated by colorectal CSCs in vivo (n=6, p=0.015 ).
Our results suggest that the miR-221/QKI5 axis plays important roles in the regulation of CSC properties in human colorectal cancers. Because miR-221 was preferentially and highly upregulated in human colorectal CSCs, but not in normal stem/progenitor cells, it is possible that miR-221 will be a biomarker that reflects amount and/or activity of CSCs in colorectal cancers and an attractive target to selectively attach colorectal CSCs by avoiding damages on their normal counterparts.
Citation Format: Junko Mukohyama, Yohei Shimono, Piero Dalerba, Taichi Isobe, Qingjiang Hu, Debashis Sahoo, Naoki Shibuya, Hironobu Minami, Koshi Mimori, Yoshihiro Kakeji, Akira Suzuki. Epigenetic regulation of colorectal cancer stem cells by the miR-221/QKI5 axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 488.