Effects of altering CpG dinucleotide composition in small DNA viruses

Le résumé fourni par la source

CpG dinucleotides are underrepresented in mammalian genomes and in many viruses infecting them. Previous studies have shown that increasing CpG frequencies in various RNA viruses and retroviruses reduces replicative fitness but the effects of this compositional modification are unknown in DNA viruses. To investigate this, the effects of increasing CpG frequencies were determined in the parvovirus minute virus of mice (MVM) at various stages of the viral life cycle and a system was set up for the murine polyoma virus (MPyV). Part of the VP gene (24.4 % of the viral genome) of MVM was replaced by synonymously coded inserts with a CpG-high sequence and several other compositional mutations. Infection time courses and TCID50s were performed to test replicative fitness. Genome copy numbers and viral RNA levels were measured via RT-qPCR. Immunofluorescence, western blots and in vitro translation were used to visualise and measure protein production and distribution. Knockout cell lines were used to find antiviral mechanisms involved. Compared to the wild type and scrambled virus, CpG-high viruses showed impaired growth curves in vitro. Immunofluorescence assays showed that the CpG-high viruses could establish infection and protein production in fewer cells. RT-qPCR revealed that viral mRNA levels were reduced in the CpG-high mutant, a phenotype that partially reverted in ZC3HAV1 (ZAP) knockout cells. Increasing CpGs in MVM led to reduced mRNA levels, which impacted all aspects of the viral life cycle, leading to fewer productively infected cells and reduced viral progeny numbers though there might be further restriction later in the replication cycle. This is thought to be due at least in part to selective recognition of CpGs in RNA by ZAP.

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