Characterisation of cyclin D1 down‐regulation in coronavirus infected cells

The positive strand RNA coronavirus, infectious bronchitis virus (IBV), induces a G2/M phase arrest and reduction in the G1 and G1/S phase transition regulator cyclin D1. Quantitative real‐time RT‐PCR and Western blot analysis demonstrated that cyclin D1 was reduced post‐transcriptionally within infected cells independently of the cell‐cycle stage at the time of infection. Confocal microscopy revealed that cyclin D1 decreased in IBV‐infected cells as infection progressed and inhibition studies indicated that a population of cyclin D1 could be targeted for degradation by a virus mediated pathway. In contrast to the SARS‐coronavirus, IBV nucleocapsid protein did not interact with cyclin D1.