BRD4 Bromodomain Inhibitors Promote Human Herpes Simplex Virus Replication And Its Mechanism Study

Human herpes simplex virus(HSV)are enveloped double-strand DNA viruses that belongs to Herpesviridae family,which share significant similarity in DNA sequences and genome structures.HSV-1 infection is the main cause of herpes infections on the mouth and lips,including cold sores and fever blisters.HSV-2 is a major pathogen of sexually transmitted diseases(STD),which infects epithelial cells on or around genitals causing genital lesions and neonatal infections.HSV can set up primary lytic infection and latent infection in different host cells.The lytic infection begins with viral entry into a host through broken skin or mucous membranes and then undergoes productive infection.Following the lytic infection at the site of inoculation,the virus gains access to sensory nerve termini and be transported via retrograde axonal transport to the sensory neurons and establishes latency,where it remains in a transcriptionally silenced state.The latent virus can be periodically activated by a range of stresses for recurrent infection at or near the site of primary infection,and this is the main cause of HSV recurrent infection.During HSV infection,the HSV genome is rapidly incorporated into nucleosomes bearing histone modifications that resemble characteristics of heterochromatic structures.Some studies have found that histone modifications have an important role in HSV lytic and latent infections.For example,chemicals that inhibit histone deacetylase activity are reported to enhance viral replication.Inhibition of the histone demethylase LSD1 blocks virus lytic replication and reactivation from latency.These results showed the important role of epigenetic regulation in affecting HSV infection.Whether other factors of epigenetic regulation have a role in HS V infection is not well studied.In this study,we took an approach by screening a chemical library of epigenetic regulation to identify factors affecting HSV infection,and further investigate their mechanisms of epigenetic regulation on HSV infection.We discovered several structurally different BET bromodomain inhibitors,including PFI-1,JQ1,and I-BET-762 with enhancement effect on HSV infection.We identified bromodomain-containing protein 4(BRD4)as a critical player in HSV infection.Using JQ1 as a probe,we found that JQ1,a defined BD1 inhibitor,acts through BRD4 protein since knockdown of BRD4 expression ablated JQ1 effect on HSV infection.BRD4 regulates HSV replication through complex formation involving CDK9 and RNAP ?;whereas,JQ1 promotes HSV-1 infection by allocating the complex to HSV gene promoters.Therefore,suppression of BRD4 expression or inhibition of CDK9 activity impeded HSV infection.Our data support a model that JQ1 enhances HSV infection by switching BRD4 to transcription regulation of viral gene expression from chromatin targeting since transient expression of BRD4 BD1(aa 1-196),BD1/2(aa 1-640)or C-terminal(aa 197-1362)domain had similar effect to that by JQ1 treatment.In addition to the identification that BRD4 is a modulator for JQ1 action on HSV infection,this study demonstrates BRD4 has an essential role in HSV infection.In summary,we combined multiple approaches including virology,cell biology,and chemical biology to identify epigenetic factors affecting HSV infection and demonstrate the host factor BRD4 plays an important role in regulating viral gene transcription of HSV during lytic infection.And this work provides a novel strategy in better understanding and studying the complex mechanism of virus-host interaction.