title: Maintenance of Epstein-Barr Virus Latent Status by a Novel Mechanism, Latent Membrane Protein 1-Induced Interleukin-32, via the Protein Kinase Cδ Pathway.
abstract: Epstein-Barr virus (EBV), an oncogenic herpesvirus, has the potential to immortalize primary B cells into lymphoblastoid cell lines (LCLs) in vitro. During immortalization, several EBV products induce cytokines or chemokines, and most of these are required for the proliferation of LCLs. Interleukin-32 (IL-32), a recently discovered proinflammatory cytokine, is upregulated after EBV infection, and this upregulation is detectable in all LCLs tested. EBV latent membrane protein 1 (LMP1) is responsible for inducing IL-32 expression at the mRNA and protein levels. Mechanistically, we showed that this LMP1 induction is provided by the p65 subunit of NF-κB, which binds to and activates the IL-32 promoter. Furthermore, the short hairpin RNA (shRNA)-mediated depletion of endogenous LMP1 and p65 in LCLs suppressed IL-32 expression, further suggesting that LMP1 is the key factor that stimulates IL-32 in LCLs via the NF-κB p65 pathway. Functionally, knockdown of IL-32 in LCLs elicits viral reactivation and affects cytokine expression, but it has no impact on cell proliferation and apoptosis. Of note, we reveal the mechanism whereby IL-32 is involved in the maintenance of EBV viral latency by inactivation of Zta promoter activity. This atypical cytoplasmic IL-32 hijacks the Zta activator protein kinase Cδ (PKCδ) and inhibits its translocation from the cytoplasm to the nucleus, where PKCδ binds to the Zta promoter and activates lytic cycle progression. These novel findings reveal that IL-32 is involved in the maintenance of EBV latency in LCLs. This finding may provide new information to explain how EBV maintains latency, in addition to viral chromatin structure and epigenetic modification.
  
  
  OBJECTIVE
  EBV persists in two states, latency and lytic replication, which is a unique characteristic of human infections. So far, little is known about how herpesviruses maintain latency in particular tissues or cell types. EBV is an excellent model to study this question because more than 90% of people are latently infected. EBV can immortalize primary B cells into lymphoblastoid cell lines in vitro. Expression of IL-32, a novel atypical cytoplasmic proinflammatory cytokine, increased after infection. The expression of IL-32 was controlled by LMP1. In investigating the regulatory mechanism, we demonstrated that the p65 subunit of NF-κB is required for this upregulation. Of note, the important biological activity of IL-32 was to trap protein kinase Cδ in the cytoplasm and prevent it from binding to the Zta promoter, which is the key event for EBV reaction. So, the expression of LMP1-induced IL-32 plays a role in the maintenance of EBV latency.
authors: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Kun-Yi
authors: KY
authors: Lai
authors: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Ya-Ching
authors: YC
authors: Chou
authors: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Jiun-Han
authors: JH
authors: Lin
authors: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Yi
authors: Y
authors: Liu
authors: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Kai-Min
authors: KM
authors: Lin
authors: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Shin-Lian
authors: SL
authors: Doong
authors: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Mei-Ru
authors: MR
authors: Chen
authors: Department of Otolaryngology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors: Te-Huei
authors: TH
authors: Yeh
authors: Research Center for Emerging Viral Infections, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan Graduate Institute of Medical Biotechnology, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan suejane.lin@mail.cgu.edu.tw chtsai@ntu.edu.tw.
authors: Sue-Jane
authors: SJ
authors: Lin
authors: Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan suejane.lin@mail.cgu.edu.tw chtsai@ntu.edu.tw.
authors: Ching-Hwa
authors: CH
authors: Tsai
mesh_terms: D001402:B-Lymphocytes / Q000821:virology; D002478:Cells, Cultured; D006564:Herpesviridae; D004854:Herpesvirus 4, Human / Q000502:physiology*; D054884:Host-Pathogen Interactions; D006801:Humans; D007378:Interleukins / Q000096:biosynthesis*; D051745:Protein Kinase C-delta / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000378:metabolism; D014763:Viral Matrix Proteins / Q000378:metabolism*; D017735:Virus Latency
chemical_list: C037662:EBV-associated membrane antigen, Epstein-Barr virus; C496971:IL32 protein, human; D007378:Interleukins; D051996:Transcription Factor RelA; D014763:Viral Matrix Proteins; D051745:Protein Kinase C-delta