Impaired hyperphosphorylation of rotavirus NSP5 in cells depleted of casein kinase 1α is associated with the formation of viroplasms with altered morphology and a moderate decrease in virus replication

Abstract

The rotavirus (RV) non-structural protein 5, NSP5, is encoded by the smallest of the 11 genomic segments and localizes in 'viroplasms', cytoplasmic inclusion bodies in which viral RNA replication and packaging take place. NSP5 is essential for the replicative cycle of the virus because, in its absence, viroplasms are not formed and viral RNA replication and transcription do not occur. NSP5 is produced early in infection and undergoes a complex hyperphosphorylation process, leading to the formation of proteins differing in electrophoretic mobility. The role of hyperphosphorylation of NSP5 in the replicative cycle of rotavirus is unknown. Previous in vitro studies have suggested that the cellular kinase CK1 α is responsible for the NSP5 hyperphosphorylation process. Here it is shown, by means of specific RNA interference, that in vivo, CK1 α is the enzyme that initiates phosphorylation of NSP5. Lack of NSP5 hyperphosphorylation affected neither its interaction with the virus VP1 and NSP2