Study on transcription factors involved in papillomavirus DNA replication

Abstract

Mammalian DNA viruses often utilize components of the host cellular DNA replication machinery to carry out replication of their genomes. Thus, these viruses can be used as tools for characterizing factors involved in cellular DNA replication. To identify cellular factors that participate in viral DNA replication, we performed a two-hybrid assay in the yeast Saccharomyces cerevisiae with El protein as bait. Using this assay, we isolated Inil/hSNF55, a component of SWI/SNF complex, which facilitates transcription by altering the structure of chromatin6. In vitro binding and immunoprecipitation assays confirmed that El interacts directly with Inil/hSNF5. Transient DNA replication assays revealed that HPV DNA replication is stimulated in a dose-dependent manner by the addition of lnil/hSNF5 and that Inil/hSNF5 antisense RNA blocks HPV DNA replication. Amino acid substitutions at residues conserved among the various El proteins abolished El-Ini1lhSNF5 interaction and reduced HPV DNA replication in vivo. These data suggest that InillhSNF5 is required for efficient replication of papillomavirus DNA and thereby imply the involvement of Inil/hSNF5 (either alone or in the SWI-SNF complex) in mammalian DNA replication. The SWI/SNF complex facilitates transcription by altering the structure of chromatin. Inil/hSNF5, a component of hSWI/SNF complex, has been involved in modulation of chromatin structure. Inil/hSNF5 binds DNA nonspecifically and regulates DNA replication through protein-protein interactions with viral replicator El. Using GST pulldown assay and two-hybrid assay in yeast and mammal, we found that E2 also could bind to hSNF5 with El and E2 per se associated with hSNF5. We also showed that E2 proteins from low-risk and high-risk group of human papillomaviruses bind to hSNF5 in vitro. Detailed analysis of E2 binding domain for hSNF5 demonstrated that E2 binds to the conserved region III of hSNF5 distinct to El binding region. Overexpression of Inil/hSNF5 modulat...