Decreased miR122 in hepatocellular carcinoma leads to chemoresistance with increased arginine

// Takahiro Kishikawa 1 , Motoyuki Otsuka 1, 2 , Poh Seng Tan 3, 4 , Motoko Ohno 1 , Xiaochen Sun 3 , Takeshi Yoshikawa 1 , Chikako Shibata 1 , Akemi Takata 1 , Kentaro Kojima 1 , Kenji Takehana 5 , Maki Ohishi 6 , Sana Ota 6 , Tomoyuki Noyama 1 , Yuji Kondo 1 , Masaya Sato 1 , Tomoyoshi Soga 5 , Yujin Hoshida 3 , Kazuhiko Koike 1 1 Department of Gastroenterology, Graduate School of Medicine, The University of Tokyo, Tokyo 113–8655, Japan 2 Japan Science and Technology Agency, PRESTO, Kawaguchi, Saitama 332–0012, Japan 3 Liver Cancer Program, Tisch Cancer Institute, Division of Liver Diseases, Department of Medicine, Icahn School of Medicine at Mount Sinai, NY 10029, USA 4 Division of Gastroenterology and Hepatology, University Medicine Cluster, National University Health System, 119228, Singapore 5 Pharmacology Research Laboratory, Research Institute, Ajinomoto Pharmaceutical Co., Ltd., Kawasaki, Kanagawa 210–8681, Japan 6 Institute for Advanced Biosciences, Keio University, Tsuruoka, Yamagata 997–0052, Japan Correspondence to: Motoyuki Otsuka, e-mail: otsukamo-tky@umin.ac.jp Keywords: HCC, miR122, SLC7A1, nitric oxide, arginine Received: January 26, 2015 Accepted: January 28, 2015 Published: March 21, 2015 ABSTRACT Reduced expression of microRNA122 (miR122), a liver-specific microRNA, is frequent in hepatocellular carcinoma (HCC). However, its biological significances remain poorly understood. Because deregulated amino acid levels in cancers can affect their biological behavior, we determined the amino acid levels in miR122-silenced mouse liver tissues, in which intracellular arginine levels were significantly increased. The increased intracellular arginine levels were through upregulation of the solute carrier family 7 (SLC7A1), a transporter of arginine and a direct target of miR122. Arginine is the substrate for nitric oxide (NO) synthetase, and intracellular NO levels were increased in miR122-silenced HCC cells, with increased resistance to sorafenib, a multikinase inhibitor. Conversely, maintenance of the miR122-silenced HCC cells in arginine-depleted culture media, as well as overexpression of miR122 in miR122-low-expressing HCC cells, reversed these effects and rendered the cells more sensitive to sorafenib. Using a reporter knock-in construct, chemical compounds were screened, and Wee1 kinase inhibitor was identified as upregulators of miR122 transcription, which increased the sensitivity of the cells to sorafenib. These results provide an insight into sorafenib resistance in miR122-low HCC, and suggest that arginine depletion or a combination of sorafenib with the identified compound may provide promising approaches to managing this HCC subset.