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Abstract
Background: Hepatitis A virus (HAV) infection is a major public health problem worldwide. The infection does not induce any visible cytopathic effects or interfere with macromolecular synthesis in host cells. However, the hepatitis B and C viruses have recently been reported to activate intracellular signals. To clarify the effects of HAV infection on intracellular signalling, we examined the influence of 9 FLAG- tagged HAV proteins (VP2, VP3, VP1-2A, 2B, 2C, 3A, 3BC, 3C and 3D) on signal transduction pathways. Methods: Viral protein expression vectors were co-transfected into HeLa cells with reporter Plasmids controlled by a synthetic promoter containing direct repeats of the cyclic AMP response element (CRE), serum response factor (SRF), activator protein 1 (AP-1), nuclear factor kB (NF-kB) or serum response element (SRE). Cells were harvested 42 h after transfection and luciferase assays were performed. Viral protein activation twice that of the control was defined as significant. Results: VP3 induced an SRE-associated signal 2.2 ± 0.3 times higher than that of control. VP3 did not activate CRE-, SRF-, AP-I- or NF-kB- associated signalling. The other HAV proteins tested also failed to induce these pathways. Conclusions: HAV interacts with the host signalling mechanism, and HAV VP3, different from HBX and hepatitis C core protein, may activate only SRE-associated intracellular signalling, a pathway associated with cell proliferation and differentiation.