5 research outputs found
Internal translation initiation stimulates expression of the ARF/core+1 open reading frame of HCV genotype 1b
The hepatitis C virus possesses an alternative open reading frame overlapping the Core gene, whose products are referred to as Core+1 or alternative reading frame (ARF) or F protein(s). Extensive studies on genotype HCV-1 a demonstrated that ribosomal frameshifting supports the synthesis of core+1 protein, when ten consecutive As are present within core codons 9-11 whereas, in the absence of this motif, expression of the core+1 ORF is mediated mainly by internal translation initiation. However, in HCV-1b, no Core+1 isoforms produced by internal translation initiation have been described. Using constructs which contain the Core/Core+1(342-770) region from previously described HCV-1b clinical isolates from liver biopsies, we provide evidence for the synthesis of Core+1 proteins by internal translation initiation in transiently transfected mammalian cells using nuclear or cytoplasmic expression systems. Site directed mutagenesis analyses revealed that (a) the synthesis of Core+1 proteins is independent from the polyprotein expression, as we observed an increase of Core+1 protein expression from constructs lacking the polyprotein translation initiator, (b) the main Core+1 product is expressed from AUG(85), similarly to the Core+1/S protein of HCV-1 a, (c) synthesis of Core+1 isoforms is also mediated from GUG(58) or under certain conditions GUG(26) internal codons, albeit at lower efficiency. Finally, comparable to HCV-1 a Core+1 proteins, the HCV-1 b Core+1 products are negatively regulated by core expression and the proteaosomal pathway. The expression of Core+1 ORF from HCV-1b clinical isolates and the preservation of translation initiation mechanism that stimulates its expression encourage investigating the role of these proteins in HCV pathogenesis. (c) 2010 Published by Elsevier B.V
Hepatitis C Virus core+1/ARF Protein Modulates the Cyclin D1/pRb Pathway and Promotes Carcinogenesis
High levels of HCV core+1 antibodies in HCV patients with hepatocellular carcinoma
The core region of the hepatitis C virus (HCV) genome possesses an
overlapping ORF that has been shown to encode a protein, known as the
alternate reading frame protein (ARFP), F or core+1. The biological role
of this protein remains elusive, as it appears to be non-essential for
virus replication. However, a number of independent studies have shown
that the ARFP/F/core+1 protein elicits humoral and cellular immune
responses in HCV-infected individuals and interacts with important
cellular proteins. To assess the significance of the core+1 humoral
response in HCV-infected patients, we examined the prevalence of
anti-core+1 antibodies in sera from patients with hepatocellular
carcinoma (HCC) in comparison with chronically HCV-infected individuals
without HCC. We produced two HCV core+1 histidine-tagged recombinant
proteins for genotypes la (aa 11-160) and 1b (aa 11-144), as well as a
non-tagged highly purified recombinant core+1/S protein (aa 85-144) of
HCV-1b. Using an in-house ELISA, we tested the prevalence of core+1
antibodies in 45 patients with HCC in comparison with 47 chronically
HCV-infected patients without HCC and 77 negative-control sera. More
than 50% of the serum samples from HCC patients reacted with all core+1
antigens, whereas <26% of the sera from the non-HCC HCV-infected
individuals tested positive. No core+1-specific reactivity was detected
in any of the control samples. In conclusion, the high occurrence of
anti-core+1 antibodies in the serum of HCC patients suggests a role for
the ARFP/F/core+1 protein in the pathogenesis of HCC