Study On Interactions Of Human Cytomegalovirus UL70and UL35Proteins With Cellular Factors

Human cytomegalovirus (HCMV) is a member of the herpesvirus family, and persists as a subclinical, lifelong infection in the normal human host. But HCMV causes significant morbidity and mortality in immuno-compromised individuals such as AIDS patients and organ transplant recipients, and also the leading viral cause of congenital abnormalities and mental retardation in newborns. Reaction from latency often results in serious diseases. To better understand the mechanism of HCMV lytic infection, the interactions between viral proteins and host proteins have been studied in order to elucidate how these cellular factors regulate the critical processes during lytic infection, including viral replication and the transcription initiation of MIEP.(1) Little is known about how UL70is imported in the nuclear compartment where viral DNA replication occurs. It has not been reported whether any host proteins facilitate the nuclear import of UL70by interacting with these proteins. Our results provide the first direct evidence that UL70specifically interacts with human protein DNAJB6, which is expressed as two isoforms, DNAJB6a and DNAJB6b, as a result of alternative splicing. These two proteins are differ at the less conserved C-terminal region in which a NLS is present in the longer DNAJB6a, a protein predominantly localized in the nuclei, but is absent in the shorter DNAJB6b, a protein primarily localized in the cytoplasm. DNAJB6a facilitates the nuclear import of UL70, while DNAJB6b enhances the cytoplasmic accumulation of UL70. And then the level of viral DNA synthesis and progeny production are positively related to UL70proteins in the nucleus. Therefore, these results suggest that the relative expression levels of DNAJB6isoforms may play a key role in regulating the cellular localization of UL70, leading to modulation of HCMV DNA synthesis and lytic infection.(2) The mechanism that HCMV UL35protein activates MIEP transcription is still unknown. We carry out a yeast two-hybrid screen and identify the interaction between UL35and IFI35, one of the interferon-induced proteins. Then the interaction and their binding domains are confirmed by co-immunoprecipitation analysis, and these two proteins are co-localized in human cells. The UL35-dependent transcription of MIEP is activated by up-regulated IFI35, but its activity is not changed by down-regulated IFI35. Similarly, the expression of downstream genes and viral DNA synthesis are also increased in cells in which IFI35are up-regulated. What’s more, the promoters of immunological factors are activated by UL35and IFI35together. These results further confirm that cellular factors are required for UL35-dependent transcription initiation of MIEP, and immune factors may participate to prompt the process.