Interferon regulatory factor 7 is induced by Epstein-Barr virus latent membrane protein 1.
Infection by Epstein-Barr virus (EBV) generates several types of latency with different profiles of gene expression but with expression of Epstein-Barr nuclear antigen 1 (EBNA-1) in common. The BamHI Q promoter (Qp) is used for the transcription of EBNA-1 mRNA in type I latency, which is an EBV infection state exemplified by Burkitt's lymphoma (BL). However, Qp is inactive in type III latency, and other promoters (C/Wp) are used for transcription of EBNA-1, which raises the question of how usage of these promoters is governed. Interferon (IFN) regulatory factor 7 (IRF-7) was identified first as a negative regulator of Qp. Expression of IRF-7 is associated with EBV type III latency, where Qp is inactive, but not with type I latency, raising the possibility that a viral gene product(s) expressed in type III latency might induce IRF-7 and repress Qp. Here, detailed analysis of the expression of IRF-7 revealed that it is associated with the expression of EBV latent membrane protein 1 (LMP-1) and that LMP-1 stimulates the expression of IRF-7 in type III latency in which Qp is inactive. In contrast, LMP-1 is not expressed in type I latency cells in which Qp is active. LMP-1 represses the constitutive activity of Qp reporter constructs. Mutational analysis of Qp reporter constructs revealed that the Qp IFN-stimulated response element (ISRE) is essential for the repression by LMP-1. Furthermore, LMP-1 reduced EBNA-1 mRNA derived from Qp only in type I cells in which IRF-7 could be induced. Finally, IFN-alpha, but not IFN-gamma, repressed endogenous Qp activity, which is consistent with the ability of IFN-alpha to induce IRF-7. Thus, IRF-7 may mediate repression of Qp by LMP-1. The induction of IRF-7 by LMP-1 may be relevant to the silencing of Qp in EBV type III latency.
Zhang
L
L
Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7295, USA. luzhang@med.unc.edu
Pagano
J S
JS
D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019309:Epstein-Barr Virus Nuclear Antigens / Q000235:genetics / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D017930:Genes, Reporter; D004854:Herpesvirus 4, Human / Q000235:genetics / Q000502:physiology*; D006801:Humans; D050839:Interferon Regulatory Factor-7; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D014763:Viral Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D017735:Virus Latency / Q000235:genetics*
D004268:DNA-Binding Proteins; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D019309:Epstein-Barr Virus Nuclear Antigens; C494234:IRF7 protein, human; D050839:Interferon Regulatory Factor-7; D012333:RNA, Messenger; D014763:Viral Matrix Proteins