Contribution of DNA Replication to the FAM111A-Mediated Simian Virus 40 Host Range Phenotype

Host range (HR) mutants of simian virus 40 (SV40) containing mutations in the C terminus of large T antigen fail to replicate efficiently or form plaques in restrictive cell types. HR mutant viruses exhibit impairments at several stages of the viral life cycle, including early and late gene and protein expression, DNA replication, and virion assembly, although the underlying mechanism for these defects is unknown. Host protein FAM111A, whose depletion rescues early and late gene expression and plaque formation for SV40 HR viruses, has been shown to play a role in cellular DNA replication. SV40 viral DNA replication occurs in the nucleus of infected cells in viral replication centers where viral proteins and cellular replication factors localize. Here, we examined the role of viral replication center formation and DNA replication in the FAM111A-mediated HR phenotype. We found that SV40 HR virus rarely formed viral replication centers in restrictive cells, a phenotype that could be rescued by FAM111A depletion. Furthermore, while FAM111A localized to nucleoli in uninfected cells in a cell cycle-dependent manner, FAM111A relocalized to viral replication centers after infection with SV40 wild-type or HR viruses. We also found that inhibition of viral DNA replication through aphidicolin treatment or through the use of replication-defective SV40 mutants diminished the effects of FAM111A depletion on viral gene expression. These results indicate that FAM111A restricts SV40 HR viral replication center formation and that viral DNA replication contributes to the FAM111A-mediated effect on early gene expression.IMPORTANCE SV40 has served as a powerful tool for understanding fundamental viral and cellular processes; however, despite extensive study, the SV40 HR mutant phenotype remains poorly understood. Mutations in the C terminus of large T antigen that disrupt binding to the host protein FAM111A render SV40 HR viruses unable to replicate in restrictive cell types. Our work reveals a defect of HR mutant viruses in the formation of viral replication centers that can be rescued by depletion of FAM111A. Furthermore, inhibition of viral DNA replication reduces the effects of FAM111A restriction on viral gene expression. Additionally, FAM111A is a poorly characterized cellular protein whose mutation leads to two severe human syndromes, Kenny-Caffey syndrome and osteocraniostenosis. Our findings regarding the role of FAM111A in restricting viral replication and its localization to nucleoli and viral replication centers provide further insight into FAM111A function that could help reveal the underlying disease-associated mechanisms.