Hepatitis C virus (HCV) infection leading to chronic hepatitis is a major factor in the causation of liver cirrhosis, hepatocellular carcinoma, and liver failure. This process may involve the interplay of various host cell factors, as well as the interaction of these factors with viral RNA and proteins. We report a novel strategy using a sequencespecific biotinylated peptide nucleic acid ( The hepatitis C virus, a blood-borne pathogen that causes chronic hepatitis, is the primary reason for liver transplantation in the United States. HCV 1 preferentially replicates in liver tissue without any direct cytopathic effect and thus is able to maintain long term, persistent infection. More than 50% of HCV-infected patients do not respond to treatment; instead, the majority of patients develop chronic hepatitis C, which leads to progressive liver fibrosis, cirrhosis, end-stage liver disease, and hepatocellular carcinoma. The hepatitis C virus is a positive single-stranded RNA virus of a 9.6-kb genome. After its entry into cells, the (ϩ) strand RNA first serves as a messenger RNA for the translation of viral proteins. Newly synthesized HCV replicase (NS5B) then copies the (ϩ) strand RNA genome into the (Ϫ) strand RNA, which serves as a template for the production of the viral genome. The conserved 5Ј-and 3Ј-nontranslated (5ЈNTR and 3ЈNTR) regions of the HCV genome have multiple regulatory elements that are essential for replication of HCV and translation of viral proteins. Although the 5ЈNTR of HCV contains the internal ribosomal entry site, which is required for capindependent translation of (ϩ) strand HCV RNA (1-4), it is also the 3Ј region of the (Ϫ) strand RNA, which functions as the initiation site for replication of the (ϩ) strand HCV RNA genome. The 3Ј regions of both (Ϫ) and (ϩ) strand HCV RNAs are highly structured and serve as the initiation sites for viral replication (5). Various cellular proteins have been shown to interact with 5ЈNTR of HCV RNA; these include La autoantigen (6) nuclear factors NF90, NF110, NF45, and RNA helicase A (7), as well as the polypyrimidine tract-binding protein (8 -10). Recently, we affinity-captured different cellular proteins interacting with HCV 3ЈNTR and identified them by LC/MS/ MS; some of these proteins were found to be essential for HCV replication as confirmed by siRNA (11).Another recent study using sequence-specific gene silencing of the RNAi screen has identified 26 human genes encoding proteins that physically interact with HCV RNA or protein and modulate HCV replication (12). A more direct approach would be to capture the replicating HCV RNA genome in situ under physiological conditions and then identify all the cellular From the §Department of Biochemistry and Molecular Biology and Centre for the Study of Emerging and Re-emerging Pathogens,

Persistent hepatitis C virus (HCV) infection leads to chronic hepatitis C (CHC), which often progresses to liver cirrhosis (LC) and hepatocellular carcinoma (HCC). The molecular mechanisms that establish CHC and cause its subsequent development into LC and HCC are poorly understood. We have identified a cytoplasmic double-stranded RNA binding protein, Stau1, which is crucial for HCV replication. In this study, Stau1 specifically interacted with the variable-stem-loop region in the 3′ NTR and domain IIId of the HCV-IRES in the 5′ NTR, and promoted HCV replication and translation. Stau1 coimmunoprecipitates HCV NS5B and a cell factor, protein kinase R (PKR), which is critical for interferon-induced cellular antiviral and antiproliferative responses. Like Stau1, PKR displayed binding specificity to domain IIId of HCV-IRES. Stau1 binds to PKR and strongly inhibits PKR-autophosphorylation. We demonstrated that the transport of HCV RNA on the polysomes is Stau1-dependent, being mainly localized in the monosome fractions when Stau1 is downregulated and exclusively localized in the polysomes when Stau1 is overexpressed. Our findings suggest that HCV may appropriate Stau1 to its advantage to prevent PKR-mediated inhibition of eIF2α, which is required for the synthesis of HCV proteins for translocation of viral RNA genome to the polysomes for efficient translation and replication.

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis C (CHC), liver cirrhosis, and hepatocellular carcinoma (HCC).Immunohistochemistry of archived HCC tumors showed abundant FBP1 expression in HCC tumors with the CHC background. Oncomine data analysis of normal versus HCC tumors with the CHC background indicated a 4-fold increase in FBP1 expression with a concomitant 2.5-fold decrease in the expression of p53. We found that FBP1 promotes HCV replication by inhibiting p53 and regulating BCCIP and TCTP, which are positive and negative regulators of p53, respectively. The severe inhibition of HCV replication in FBP1-knockdown Huh7.5 cells was restored to a normal level by downregulation of either p53 or BCCIP. Although p53 in Huh7.5 cells is transcriptionally inactive as a result of Y220C mutation, we found that the activation and DNA binding ability of Y220C p53 were strongly suppressed by FBP1 but significantly activated upon knockdown of FBP1. Transient expression of FBP1 in FBP1 knockdown cells fully restored the control phenotype in which the DNA binding ability of p53 was strongly suppressed. Using electrophoretic mobility shift assay (EMSA) and isothermal titration calorimetry (ITC), we found no significant difference in in vitro target DNA binding affinity of recombinant wild-type p53 and its Y220C mutant p53. However, in the presence of recombinant FBP1, the DNA binding ability of p53 is strongly inhibited. We confirmed that FBP1 downregulates BCCIP, p21, and p53 and upregulates TCTP under radiation-induced stress. Since FBP1 is overexpressed in most HCC tumors with an HCV background, it may have a role in promoting persistent virus infection and tumorigenesis. IMPORTANCEIt is our novel finding that FUSE binding protein 1 (FBP1) strongly inhibits the function of tumor suppressor p53 and is an essential host cell factor required for HCV replication. Oncomine data analysis of a large number of samples has revealed that overexpression of FBP1 in most HCC tumors with chronic hepatitis C is significantly linked with the decreased expression level of p53. The most significant finding is that FBP1 not only physically interacts with p53 and interferes with its binding to the target DNA but also functions as a negative regulator of p53 under cellular stress. FBP1 is barely detectable in normal differentiated cells; its overexpression in HCC tumors with the CHC background suggests that FBP1 has an important role in promoting HCV infection and HCC tumors by suppressing p53. H epatitis C virus (HCV) infection is a leading cause of chronic liver diseases. More than a decade after the identification of HCV as the major causative agent of non-A, non-B hepatitis (1), molecular strategies for complete eradication of HCV infection are actively pursued. HCV is the major cause of chronic liver disease. According to new findings from the U.S. Centers for Disease Control and Prevention (CDC), the number of individuals in the U.S. living with chronic hepatitis C virus infection is about 2.7 million (2). Globa...

Crk is the prototypical member of a class of Src homology 2 (SH2) and Src homology 3 (SH3) domain-containing adaptor proteins that positively regulate cell motility via the activation of Rac1 and, in certain tumor types such as GBM, can promote cell invasion and metastasis by mechanisms that are not well understood. Here we demonstrate that Crk, via its phosphorylation at Tyr251, promotes invasive behavior of tumor cells, is a prominent feature in GBM, and correlating with aggressive glioma grade IV staging and overall poor survival outcomes. At the molecular level, Tyr251 phosphorylation of Crk is negatively regulated by Abi1, which competes for Crk binding to Abl and attenuates Abl transactivation. Together, these results show that Crk and Abi1 have reciprocal biological effects and act as a molecular rheostat to control Abl activation and cell invasion. Finally, these data suggest that Crk Tyr251 phosphorylation regulate invasive cell phenotypes and may serve as a biomarker for aggressive GBM.

BackgroundFUSE binding protein1 (FBP1) is a transactivator of transcription of human c-myc proto-oncogene and expressed mainly in undifferentiated cells. It is also present in differentiated normal cells albeit with very low background. FBP1 is abundantly expressed in the majority of hepatocellular carcinoma tumors and has been implicated in tumor development. Although it down-regulates the expression of proapoptotic p21 protein, it is not known whether FBP1 also interacts and antagonizes the function of tumor suppressor protein p53.MethodsWestern blotting was carried out to detect the expression level of FBP1, p21 and p53, and also p53 regulatory factors, BCCIP and TCTP; real-time quantitative PCR was done to determine the fold change in mRNA levels of target proteins; immunoprecipitation was carried out to determine the interaction of FBP1 with p53, BCCIP and TCTP. Cells stably knockdown for either FBP1; p53 or BCCIP were examined for p53 reporter activity under normal and radiation-induced stress.ResultsFBP1 physically interacted with p53, impairing its transcription activity and reducing p53-mediated sensitivity to cellular stress. Knockdown of FBP1 expression activated p53-mediated response to cellular stress while transient expression of FBP1 in FBP-knockdown cells restored the inhibition of p53 activity. FBP1 not only interacted with both BCCIP and TCTP, which, respectively, function as positive and negative regulators of p53, but also regulated their expression under cellular stress. In FBP knockdown cells, TCTP expression was down-regulated under radiation-induced stress whereas expression of BCCIP and p21 were significantly up-regulated suggesting FBP1 as a potential regulator of these proteins. We hypothesize that the FBP1-mediated suppression of p53 activity may occur via preventing the interaction of p53 with BCCIP as well as by FBP1-mediated regulation of p53 regulatory proteins, TCTP and BCCIP. Since FBP1 suppresses p53 activity and is overexpressed in most HCC tumors, it may have a possible role in tumorigenesis.ConclusionFBP1 physically interacts with p53, functions as a regulator of p53-regulatory proteins (TCTP and BCCIP), and suppresses p53 transactivation activity under radiation-induced cellular stress. Since it is abundantly expressed in most HCC tumors, it may have implication in tumorigenesis and thus may be a possible target for drug development.