Objectives: CD44 has recently been identified as one of the cell surface markers associated with cancer stem cells (CSCs) in several types of tumor. We have reported the functional role of CD44 variant isoform in the maintenance of low reactive oxygen species (ROS) levels in gastrointestinal cancer cells. While, microRNA (miRNA) is involved in the pathogenesis of many cancers and the networks of miRNA regulate CSCs properties. However, the mechanism underlying the miRNA in the regulation of CSC marker is mostly unrevealed. Methods and Results: To investigate the mechanism in the regulation of CD44, we performed 384 miRNA quantitative RT-PCR array analysis in six human gastrointestinal cancer cell lines that differ in CD44 expression status. We found 59 miRNAs which are suppressed in CD44 high expressing cancer cells, and further investigated the predicted 33miRNAs which interact directly with CD44 3’UTR using the online miRNA target database. As a result in these analyses, we identified 2 miRNA candidates, which could regulate CD44 expression in gastrointestinal cancer. In this study, we especially focused on miR-328 and examined the functional relevance of miR-328 implicated in CD44 regulation. We found that gastrointestinal cancer cells transfected with miR-328 mimic decreased CD44 expression and led to inhibition of cancer cell growth and impairing chemo- and ROS- resistance. Furthermore, we investigated the mechanism underlying the regulation of miR-328 by using human macrophage and gastrointestinal cancer cell lines. We found that co-culture with tumor-associated-macrophages (TAMs) triggers the CD44 expression through suppression of miR-328 in gastrointestinal cancer cells and promote stem-like property that possess sphere-forming ability. Finally, we showed that TAMs are closely related with both CD44 over-expression and miR-328 under-expression in human gastric cancer tissue. Conclusions: These findings reveal that TAMs in tumor microenvironment contribute CD44 expression via miR-328 suppression, resulting in tumor progression through enhancing ROS defense.

Citation Format: Takatsugu Ishimoto, Masayuki Watanabe, Nobuyuki Ozaki, Masaaki Iwatsuki, Yoshifumi Baba, Naoya Yoshida, Hideo Baba. Tumor-associated-macrophage induces CD44 expression through microRNAs suppression promotes cancer progression and chemoresistance. [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 5334. doi:10.1158/1538-7445.AM2013-5334