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The hepatitis C virus NS5A protein interacts with β-catenin and stimulates its transcriptional activity in a PI3K-dependent fashion

University of Leeds

¹ E-mail: m.harris{at}leeds.ac.uk

Hepatitis C virus (HCV) infection is increasingly associated with the development of hepatocellular carcinoma (HCC). HCV is not thought to be directly oncogenic but, by modulating a range of cellular functions, may predispose patients to the development of liver tumours. However, the molecular mechanisms by which HCV infection might contribute to HCC remain to be characterised. In this regard, we previously showed that the HCV NS5A protein bound to the p85 regulatory subunit of phosphoinositide-3 kinase (PI3K), thereby stimulating the activity of the p110 catalytic subunit of the enzyme. One of the downstream consequences of this was the stabilisation of the proto-oncogene, β-catenin, with a concomitant stimulation of its transcriptional activity. Here, we further analyse the mechanism by which NS5A mediates activation of β-catenin. Although our previous data were consistent with a role for the PI3K downstream effector kinases, Akt and GSK-3β, in NS5A-mediated activation of β-catenin, we demonstrate here that it is in fact independent of either of these kinases. Truncation analysis revealed that both the N- and C-termini of NS5A are required for full activation of β-catenin. Furthermore, we demonstrate that NS5A, either alone or in complex with p85, is able to bind directly to β-catenin, again both N- and C-termini contribute to this interaction. We propose that NS5A activates β-catenin via a novel mechanism that involves a direct interaction between the two proteins and is augmented by PI3K activity. This may contribute to the association between chronic HCV infection and the development of HCC.

Received 22 July 2009; accepted 16 October 2009.