title: Hepatitis C virus inhibitor synergism suggests multistep interactions between heat-shock protein 90 and hepatitis C virus replication.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: 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.
authors.forename: Naoko
authors.initials: N
authors.lastname: Kubota
authors.affiliation: 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.
authors.forename: Masataka
authors.initials: M
authors.lastname: Nomoto
authors.affiliation: 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.
authors.forename: Gi-Wook
authors.initials: GW
authors.lastname: Hwang
authors.affiliation: 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.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Watanabe
authors.affiliation: 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.
authors.forename: Michinori
authors.initials: M
authors.lastname: Kohara
authors.affiliation: 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.
authors.forename: Takaji
authors.initials: T
authors.lastname: Wakita
authors.affiliation: 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.
authors.forename: Akira
authors.initials: A
authors.lastname: Naganuma
authors.affiliation: 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.
authors.forename: Shusuke
authors.initials: S
authors.lastname: Kuge
keywords: Cell culture-derived hepatitis C virus; Heat-shock protein 90 inhibitors; Hepatitis C virus; Hepatitis C virus RNA replication; Inhibition of hepatitis C virus release