title: ORF45-Mediated Prolonged c-Fos Accumulation Accelerates Viral Transcription during the Late Stage of Lytic Replication of Kaposi's Sarcoma-Associated Herpesvirus.
abstract: Kaposi's sarcoma-associated herpesvirus (KSHV) encodes multiple viral proteins that activate extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase (MAPK) cascades. One of these viral proteins, ORF45, mediates sustained ERK-p90 ribosomal S6 kinase (RSK) activation during KSHV lytic replication and facilitates viral translation through the phosphorylation of a eukaryotic translation initiation factor, eIF4B. The importance of ERK-RSK activation for KSHV viral transcription has been shown; however, which transcription factor senses the sustained MAPK signaling and leads to viral transcription remains poorly understood. Here we show that the presence of ORF45 leads to the prolonged accumulation of c-Fos during the late stage of KSHV lytic replication through ERK-RSK-dependent phosphorylation and stabilization and that the depletion of c-Fos disrupts viral lytic transcription. Genome-wide screening revealed that c-Fos directly binds to multiple viral gene promoters and enhances viral transcription. Mutation of the ERK-RSK phosphorylation sites of c-Fos restrains KSHV lytic gene expression and virion production. These results indicate that the prolonged accumulation of c-Fos promotes the progression of viral transcription from early to late stages and accelerates viral lytic replication upon sustained ORF45-ERK-RSK activation during the KSHV lytic life cycle.
  
  
  OBJECTIVE
  During KSHV lytic replication, transient activation and sustained activation of ERK-RSK induce viral immediate early (IE) transcription and late transcription, respectively. Studies have revealed that ERK-RSK activates several transcription factors involved in IE gene expression, including Ets, AP-1, CREB, and C/EBP, which lead to the transient ERK-RSK activation-dependent IE transcription. Whereas c-Fos acts as a sensor of sustained ERK-RSK activation, ORF45-ERK-RSK signaling mediates c-Fos phosphorylation and accumulation during late KSHV lytic replication, consequently promoting viral transcription through the direct binding of c-Fos to multiple KSHV promoters. This finding indicates that c-Fos mediates distinct viral transcriptional progression following sustained ERK-RSK signaling during the KSHV lytic life cycle.
authors.affiliation: Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China Key Laboratory of Tropical Disease Control (Sun Yat-Sen University), Ministry of Education, Guangzhou, China.
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Li
authors.affiliation: Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China.
authors.forename: Shumin
authors.initials: S
authors.lastname: Du
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida, USA.
authors.forename: Denis
authors.initials: D
authors.lastname: Avey
authors.affiliation: Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida, USA.
authors.forename: Fanxiu
authors.identifier: http://orcid.org/0000-0002-4189-7008
authors.initials: F
authors.lastname: Zhu
authors.affiliation: Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, China Key Laboratory of Tropical Disease Control (Sun Yat-Sen University), Ministry of Education, Guangzhou, China kuangersh@mail.sysu.edu.cn.
authors.forename: Ersheng
authors.initials: E
authors.lastname: Kuang
mesh_terms: D002460:Cell Line; D004279:DNA, Viral / Q000378:metabolism; D019288:Herpesvirus 8, Human / Q000502:physiology*; D054884:Host-Pathogen Interactions; D006801:Humans; D017874:Immediate-Early Proteins; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D014158:Transcription, Genetic; D014779:Virus Replication
chemical_list: D004279:DNA, Viral; D017874:Immediate-Early Proteins; C456286:ORF45 protein, Kaposi's sarcoma-associated herpesvirus; D016760:Proto-Oncogene Proteins c-fos