Translational control mechanisms and cell signalling in calicivirus protein synthesis

• Main Author: Abdul Wahab, Azimah
• Published: University of Surrey 2012
• Subjects: 579.25
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580680

Caliciviruses cause importarit diseases of humans and animals; noroviruses are responsible for outbreaks of gastroenteritis in man, and feline calicivirus (FCV) causes an upper respiratory tract infection in cats. Since 2003, murine norovirus (MNV) has been used as a model for norovirus infection since human noroviruses are unable to replicate in tissue culture. Caliciviruses have a positive-sense RNA genome of about 7 to 8 kb, with a viral protein, VPg, covalently linked to the 5' end of the RNA. The VPg acts as a novel proteinaceous 'cap substitute' and interacts with the cap-binding protein, eIF4E. To further analyse the requirement of translation initiation factors for calicivirus translation, I have investigated the effect of FCV and MNV infection on eIF4E and its regulator, 4E-BPl. I found that FCV and MNV infection have different effects on the phosphorylation status of eIF4E and its regulator, 4E-BPl. For both viruses, eIF4E is phosphorylated and 4E-BPl is dephosphorylated during the course of infection. This would be expected to inhibit host cell protein synthesis. This has led me to investigate the signalling pathways involved in mediating these effects. Using specific inhibitors I have shown that phosphorylation of eIF4E during FCV and MNV infection occurs through activation of the MEKlMAPK pathway, while 4E-BPl phosphorylation occurs through PI3KJmTOR activation. When I use specific inhibitors are used to block either the p38 or MEK pathways, replication of MNV is inhibited. However, FCV replication is only inhibited by MEK inhibition. In addition, eIF4E phosphorylation is prevented by blocking p38 but not MEK. This suggests that the changes in eIF4E phosphorylation may not affect the interaction between eIF4E and VPg or be important for Fev and MNV replication. These, changes may therefore only be involved in host-cell. shut-off. In contrast, inhibition of the mTOR pathway significantly inhibited both FeV and MNV replication, suggesting that the phosphorylation status of 4E-BPl during infection is important for virus replication. I hypothesise that the change in phosphorylation status of 4E-BPl may lead to the inhibition of eIF4F complex formation and therefore calicivirus translation; this may affect the switch from translation to replication of the viral RNA. I propose that the mTOR pathway could be a target for antiviral therapy. I have also further investigated the exact requirements for components of the eIF4F cap-binding complex for translation initiation on FeV and MNV mRNA. I have shown that a small-molecule inhibitor of the eIF4E-eIF4G interaction has a greater inhibitory effect on FeV than MNV replication, demonstrating a requirement by FeV for eIF4E and an intact eIF4G for viral RNA translation.