Characterisation of the interaction of infectious bronchitis virus with cyclin Dl

• Main Author: Harrison, Sally M.
• Published: University of Leeds 2007
• Subjects: 616.2
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485777

The cell cycle describes the growth and division of cells and is split into five distinct phases, GO, Gl, S, G2 and M. Each stage of the cell cycle is controlled by both positive and negative regulatory molecules, including cyclins, their partner molecules the cyclin dependent kinases (CDKs) and cyclin dependent kinase inhibitors (CDKIs). The relationship between the cell cycle and virus infection is well characterised for DNA and retroviruses, but less so with RNA viruses. This study 'investigated the relationship between the coronavirus infectious bronchitis viI1}s (mV), (a major pathogen of chickens causing severe economic losses to poultry' producing countries) and the G1 phase cell cycle regulatory molecule cyclin D1. Cyclin D1 has been shown to be reduced in mv-infected cells with an arrest ofinfected cells in the G2 phase of the cell cycle. This study shows that the reduction of cyclin D I is post transcriptional and independent of the cell cycle stage at the 'time of infection. siRNA analysis was also used to investigate' whether the reduction' of cyclin D1 was essential for virus replication. The mechanism of cyclin D1 nuclear export and degradation in mv-infected cells was determined by the use of MG132, which inhibits the cellular proteasome, LiCI, an inhibitor of glycogen synthase three beta (GSK 3~) and leptomycin B (LMB), which inhibits chromosome region maintenance-l (CRM-l) mediated nuclear export. Confocal microscopy and Western blot analysis indicated that LiCI, LMB and MG132 stabilised cyclin D1 levels in mvinfected cells, although a population of cyclin 'D I appeared to be reduced independently of GSK 3~, potentially by a virus mediated mechanism. These studies 'also lead to LiCI possibly being a novel inhibitor ofmv in cell culture. , The virus protein(s) responsible for inducing the phenotypic G2 phase arrest and reduction of cyclin Dr in mY-infected cells was also investigated, using the mv nucleocapsid (N) and accessory protein 5a as candidates. Neither of these proteins however appeared to induce the G2 phentoype, although the mv 5aprotein did appear to reduce cyclin D1. Over expression studies showed that mv 5a induced some cell cycle perturbations, which were then confirmed by the use of reverse genetics in which 'the 5a ORF had been knocked out. Thisleads.to t?e hypothesis that the induction of the G2 phenotype could be regulated by multiple virus proteins.