Basic Study
Copyright ©The Author(s) 2016. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Hepatol. Feb 18, 2016; 8(5): 282-290
Published online Feb 18, 2016. doi: 10.4254/wjh.v8.i5.282
Hepatitis C virus inhibitor synergism suggests multistep interactions between heat-shock protein 90 and hepatitis C virus replication
Naoko Kubota, Masataka Nomoto, Gi-Wook Hwang, Toshihiko Watanabe, Michinori Kohara, Takaji Wakita, Akira Naganuma, Shusuke Kuge
Naoko Kubota, Masataka Nomoto, Gi-Wook Hwang, Akira Naganuma, Shusuke Kuge, Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Miyagi 980-8578, Japan
Toshihiko Watanabe, Shusuke Kuge, Department of Microbiology, Tohoku Pharmaceutical University, Miyagi 981-8558, Japan
Michinori Kohara, Department of Microbiology and Cell Biology, Tokyo Metropolitan Institute of Medical Science, Tokyo 156-0057, Japan
Takaji Wakita, Department of Virology II, National Institute of Infectious Diseases, Tokyo 162-8640, Japan
Author contributions: Kubota N, Nomoto M and Watanabe T performed the experiments; Hwang GW, Kohara M, Naganuma A and Kuge S designed the research study; Wakita T provided the JFH1/HCVcc system; Kuge S wrote the report; all of the authors critically read and commented on the article.
Institutional review board statement: No Ethics Committee approval was required.
Informed consent statement: No Ethics Committee approval was required.
Conflict-of-interest statement: All of the authors have no conflict of interest to declare in relationship to this article.
Data sharing statement: No additional data are available.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Shusuke Kuge, Professor, Department of Microbiology, Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan. skuge@tohoku-pharm.ac.jp
Telephone: +81-22-7270129 Fax: +81-22-7270129
Received: September 29, 2015
Peer-review started: October 1, 2015
First decision: November 4, 2015
Revised: December 3, 2015
Accepted: January 16, 2016
Article in press: January 19, 2016
Published online: February 18, 2016
Processing time: 139 Days and 16.5 Hours
Abstract

AIM: To address the effect of heat-shock protein 90 (HSP90) inhibitors on the release of the hepatitis C virus (HCV), a cell culture-derived HCV (JFH1/HCVcc) from Huh-7 cells was examined.

METHODS: We quantified both the intracellular and extracellular (culture medium) levels of the components (RNA and core) of JFH-1/HCVcc. The intracellular HCV RNA and core levels were determined after the JFH1/HCVcc-infected Huh-7 cells were treated with radicicol for 36 h. The extracellular HCV RNA and core protein levels were determined from the medium of the last 24 h of radicicol treatment. To determine the possible role of the HSP90 inhibitor in HCV release, we examined the effect of a combined application of low doses of the HSP90 inhibitor radicicol and the RNA replication inhibitors cyclosporin A (CsA) or interferon. Finally, we statistically examined the combined effect of radicicol and CsA using the combination index (CI) and graphical representation proposed by Chou and Talalay.

RESULTS: We found that the HSP90 inhibitors had greater inhibitory effects on the HCV RNA and core protein levels measured in the medium than inside the cells. This inhibitory effect was observed in the presence of a low level of a known RNA replication inhibitor (CsA or interferon-α). Treating the cells with a combination of radicicol and cyclosporin A for 24 h resulted in significant synergy (CI < 1) that affected the release of both the viral RNA and the core protein.

CONCLUSION: In addition to having an inhibitory effect on RNA replication, HSP90 inhibitors may interfere with an HCV replication step that occurs after the synthesis of viral RNA, such as assembly and release.

Keywords: Hepatitis C virus; Inhibition of hepatitis C virus release; Cell culture-derived hepatitis C virus; Heat-shock protein 90 inhibitors; Hepatitis C virus RNA replication

Core tip: Hepatitis C virus (HCV) is a major causative agent of hepatocellular carcinoma. Several non-structural proteins of HCV physically and functionally interact with heat-shock protein 90 (HSP90). Although HSP90 inhibitors, which inhibit the chaperone function of HSP90, have been shown to inhibit HCV replication by several groups, a recent report using a reporter system for HCV RNA replication (replicon) suggests that the effect is nonspecific. Thus, the inhibitory mechanism of HSP90 inhibitors remains controversial. Here, we address the effect of HSP90 inhibitors on the release of JFH1/cell culture-derived HCV from Huh-7 cells, and suggested that, HSP90 inhibitors may also interfere with an HCV replication step that occurs after the synthesis of viral RNA, such as assembly and release.