Abstract 179: Regulation of stromal miR-125b on normal colonic epithelial cell renewal and its putative role in tumorigenesis
Authors: Yan Helen H N , Lau Jackie K Y , Chan Annie S Y , Tsui Wai Yin , Chan Tsun Leung , Leung Suet Yi 
Published: August 2015

MicroRNAs (miRNAs) are small non-coding RNAs which exert their effects by post-transcriptionally silencing target mRNAs. Deregulation of miRNA expression is a frequent event in tumorigenesis. MiR-125b is a highly conserved miRNA among various species and is composed of three homologs: hsa-miR-125a, hsa-miR-125b-1 and hsa-miR-125-2. The tumorigenic roles of miR-125b have been studied in various cancers including prostate, colon, glioma etc, and studies have demonstrated that it can act as a tumor suppressor or an oncogene depending on the cellular context. It was characterized as an oncogene in prostate cancer and glioma through down-regulation of pro-apoptotic regulators BAK1 and Bcl-2 modifying factor (BMF), respectively. In colon cancer, a recent clinico-pathological study showed that high expression of miR-125b was associated with tumor invasion and poor prognosis. However, the localization of miR125b in normal colon and tumors is currently unknown. Therefore, we aimed to address the precise expression and the functional role of miR-125b in normal colon, which may provide insight on its potential oncogenic effects during carcinogenesis.

We performed gene expression analysis of miR-125b in normal colon tissues from 16 pairs of colon top versus basal crypts and 4 pairs of crypts versus stroma by real-time RT-PCR. Colon top and basal crypts were microdissected from frozen sections, whereas pure normal crypts and stromal fractions were isolated from freshly resected human colon specimens. We found that miR-125b was significantly enriched in the basal crypts (p&lt;0.001) and the stromal compartment (p = 0.027). Functionally, knockdown of miR-125b by a specific miRCURY antisense oligonucleotide was able to dose dependently inhibit the growth of a normal colon myofibroblast cell line, CCD18, and significantly increase the mRNA level of several key Hedgehog signaling components, including PTCH (p&lt;0.001), SMO (p&lt;0.001), GLI1 (p&lt;0.001) and its downstream target BMP4 (p = 0.017). Finally, we observed a drastic decrease in both the number and size of normal colon organoids when they were co-cultured with myofibroblasts transfected with miR-125b antisense oligonucleotide, as compared with negative control. Our results suggest that expression of miR-125b in the colonic stromal basal crypt compartment functions to inhibit Hedgehog signaling, leading to paracrine enhancement of colon crypt proliferation and stem cell renewal. Thus, given the well-known importance of hedgehog signaling in colon cancer, our findings suggest that dysregulated miR-125b

expression may contribute to carcinogenesis through disruption of this pathway.

Note: This abstract was not presented at the meeting.

Citation Format: Helen H N Yan, Jackie K Y Lau, Annie S Y Chan, Wai Yin Tsui, Tsun Leung Chan, Suet Yi Leung. Regulation of stromal miR-125b on normal colonic epithelial cell renewal and its putative role in tumorigenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 179. doi:10.1158/1538-7445.AM2015-179