Subproteomic analysis of the cellular proteins associated with the 3' untranslated region of the hepatitis C virus genome in human liver cells

Role of DEAD box 1 in retinoblastoma and neuroblastoma

Analysis of hereditary and nonhereditary retinoblastoma led to the formulation of the two-hit hypothesis of cancer in the early 1970s. The two-hit hypothesis was validated in the 1980s when both copies of the RB1 gene were shown to be mutated in hereditary and nonhereditary retinoblastoma. However, consistent genetic abnormalities other than RB1 mutations suggest that additional events may be required for the formation of these malignant tumors. For example, MYCN amplification has long been known to occur in both retinoblastoma and neuroblastoma tumors and is strongly associated with poor prognosis in neuroblastoma. The DEAD box gene, DEAD box 1 (DDX1), is often coamplified with MYCN in both these childhood tumors. Here, we examine possible roles for DDX1 overexpression in retinoblastoma and neuroblastoma.

DDX1 promotes proliferation of the JC virus through transactivation of its promoter

Recently, we demonstrated that the DEAD box protein 1 (DDX1), an RNA helicase, and the cleavage stimulation factor (CstF) form a complex that binds to the JC virus transcriptional control region (JCV-TCR). Here, we examined the function of DDX1, which is expressed at much higher levels in the JCV-susceptible cell line IMR-32 than in non-susceptible cell lines. DDX1 had no effect on the replication efficiency of JCV, but overexpression of DDX1 significantly increased transactivation of the JCV promoter. Furthermore, DDX1 enhanced the expression of JCV proteins in JCV infected cells, and knockdown of DDX1 using small interfering (si) RNA suppressed the expression of JCV proteins. Our results clearly demonstrate that DDX1 regulates proliferation of JCV in vitro through transcriptional activation.

DDX3 DEAD-box RNA helicase is required for hepatitis C virus RNA replication

DDX3, a DEAD-box RNA helicase, binds to the hepatitis C virus (HCV) core protein. However, the role(s) of DDX3 in HCV replication is still not understood. Here we demonstrate that the accumulation of both genome-length HCV RNA (HCV-O, genotype 1b) and its replicon RNA were significantly suppressed in HuH-7-derived cells expressing short hairpin RNA targeted to DDX3 by lentivirus vector transduction. As well, RNA replication of JFH1 (genotype 2a) and release of the core into the culture supernatants were suppressed in DDX3 knockdown cells after inoculation of the cell culture-generated HCVcc. Thus, DDX3 is required for HCV RNA replication.

Subproteomic study of hepatitis C virus replicon reveals Ras-GTPase-activating protein binding protein 1 as potential HCV RC component

Hepatitis C virus (HCV) RNA synthesis takes place on a detergent resistant membrane (DRM) structure. To identify potential cellular proteins related to HCV replication complexes (RC), we purified DRMs from HCV subgenomic replicon cells and its parental Huh7 cells. The proteins of DRM fractions were separated by two-dimensional gel electrophoresis and identified by mass spectrometry. Comparing with parental Huh7 cells, 60 proteins were up-regulated while 14 proteins were down-regulated in HCV replicon cells. Ras-GTPase-activating protein binding protein 1 (G3BP1), one of the elevated proteins, was found to be associated with HCV NS5B and knockdown of G3BP1 by siRNA in HCV replicon cells significantly reduced HCV replication, which may indicate it a potential component of HCV RC. These results suggest that HCV viral gene and proteins may regulate the presence of host cellular proteins in DRM, ensure appropriate concentrations of replication components, and hence control the rates or efficiencies of HCV replication.