title: Kaposi sarcoma-associated herpes virus (KSHV) G protein-coupled receptor (vGPCR) activates the ORF50 lytic switch promoter: a potential positive feedback loop for sustained ORF50 gene expression.
abstract: KSHV vGPCR, a lytic cycle associated protein, induces several signaling pathways leading to the activation of various transcription factors and consequently the expression of cellular and viral genes. Though the role of vGPCR in KSHV tumorigenicity has been well studied, its function related to the viral life cycle is poorly understood. Reduction in vGPCR by RNA interference also resulted in the reduction in KSHV lytic switch ORF50 gene and protein expression. Induction of vGPCR by doxycycline in BC3.14 cells also resulted in more KSHV production. When this was explored, induction of the ORF50 promoter by vGPCR expression was observed. Further examination of the molecular mechanisms by which vGPCR regulates the ORF50 promoter, using various ORF50 promoter constructs, revealed that induction of ORF50 promoter by vGPCR did not involve AP1 but was dependent on Sp1 and Sp3 transcription factors. vGPCR signaling led to an increase in Sp1 and Sp3 DNA binding activity and a decrease in histone deacetylase (HDAC) activity. These activities were pertussis toxin independent, did not involve Rho and Rac-GTPases and involved the heterotrimeric G protein subunits Galpha12 and Galphaq. Studies using pharmacologic inhibitors and dominant-negative proteins identified phospholipase C, the novel protein kinase C (novel PKC) family and protein kinase D (PKD) as part of the signaling initiated by vGPCR leading to ORF50 promoter activation. Taken together, this study suggests a role for vGPCR in the sustained expression of ORF50 which could lead to a continued activation of lytic cycle genes and ultimately to successful viral progeny formation.
authors.affiliation: H. M. Bligh Cancer Research Laboratories, Department of Microbiology and Immunology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA.
authors.forename: Virginie
authors.initials: V
authors.lastname: Bottero
authors.forename: Neelam
authors.initials: N
authors.lastname: Sharma-Walia
authors.forename: Nagaraj
authors.initials: N
authors.lastname: Kerur
authors.forename: Arun George
authors.initials: AG
authors.lastname: Paul
authors.forename: Sathish
authors.initials: S
authors.lastname: Sadagopan
authors.forename: Mark
authors.initials: M
authors.lastname: Cannon
authors.forename: Bala
authors.initials: B
authors.lastname: Chandran
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D004318:Doxycycline / Q000494:pharmacology; D025461:Feedback, Physiological; D015870:Gene Expression / Q000187:drug effects; D005814:Genes, Viral; D019288:Herpesvirus 8, Human / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics* / Q000502:physiology*; D008954:Models, Biological; D009154:Mutation; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism; D019707:Receptors, Chemokine / Q000235:genetics* / Q000502:physiology*; D015398:Signal Transduction; D016329:Sp1 Transcription Factor / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics* / Q000502:physiology*; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: C115448:G protein-coupled receptor, Human herpesvirus 8; D017874:Immediate-Early Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D012367:RNA, Viral; D019707:Receptors, Chemokine; C417604:Rta protein, Human herpesvirus 8; D016329:Sp1 Transcription Factor; D015534:Trans-Activators; D020741:rho GTP-Binding Proteins; D004318:Doxycycline