Regulation Of Human Herpesvirus 8 Gene Expression By Interferon Regulatory Factor 7

Human herpesvirus 8 (HHV-8) is the etiologic agent of Kaposi's sarcoma,the mostcommon neoplasm in untreated HIV-1 infected individuals,and several B celldisorders.These malignancies are more prevalent and invasive in immunosuppressedpopulation,such as HIV-1 positive individuals and transplant patients.With thealarming increase in the number of HIV-1 patients,it is likely that KSHV-associatedmalignancies will become a serious problem in their disease progresses.KSHVinfection goes through lytic and latent phases,and the switch from latency to lyricreplication is governed by viral replication and transcription activator (RTA).RTA cantransactivate various genes either by direct binding to the promoters or by interactingwith cellular or viral co-factors.The type-I interferon (IFN-alpha/beta) response iscritical to immunity against viruses.All elements of IFN responses,whether thesystemic production of IFN in innate immunity or the local action of IFN fromplasmacytoid dendritic cells in adaptive immunity,are under the control of interferonregulatory factor 7 (IRF-7).It has been reported that RTA is sufficient to activate theviral early gene open reading frame 57 (ORF57).And the cellular IRF-7 negativelyregulates this process by competing with RTA for binding to the RTA responseelement in the ORF57 promoter to down-regulate RTA-induced gene expression.Butwhether IRF-7 could modulate the other genes expression of HHV-8 is still not wellunderstood.In this study,polyclonal antibody against RTA,ORF57,IRF-7 and GST weregenerated and evaluated.When human embryonic kidney cells 293T were co-transfected with IRF-7 and RTA expression plasmids,as well as ORF57 promoterderived luciferase reporter,the RTA transactivation on the ORF57 promoter wasrepressed,and the repression was detected in a dose-dependent manner.So do thePAN promoter.The 293T cells were co-transfected with wild type or lysine residuesmutant of IRF-7,RTA expression plasmid,and ORF57 or PAN promoter derivedluciferase reporter.Compared with wild type IRF-7,some lysine residues mutant ofIRF-7 could not negative regulate the activation of RTA.However,the changes are not in the same trend.293T Cells were also co-transfected with RTA and IRF-7expression plasmids.The result showed that RTA could down-regulate theaccumulation of IRF-7.These results prove that IRF-7can down-regulate RTA-induced gene expression,suchas ORF57 and PAN.Some lysine residues mutant of IRF-7 can affect the function ofIRF-7.These results are valuable for further studying the mechanism and treatment ofHHV-8 associate diseases.