title: Kaposi's sarcoma-associated herpesvirus K-Rta exhibits SUMO-targeting ubiquitin ligase (STUbL) like activity and is essential for viral reactivation.
abstract: The small ubiquitin-like modifier (SUMO) is a protein that regulates a wide variety of cellular processes by covalent attachment of SUMO moieties to a diverse array of target proteins. Sumoylation also plays an important role in the replication of many viruses. Previously, we showed that Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a SUMO-ligase, K-bZIP, which catalyzes sumoylation of host and viral proteins. We report here that this virus also encodes a gene that functions as a SUMO-targeting ubiquitin-ligase (STUbL) which preferentially targets sumoylated proteins for degradation. K-Rta, the major transcriptional factor which turns on the entire lytic cycle, was recently found to have ubiquitin ligase activity toward a selected set of substrates. We show in this study that K-Rta contains multiple SIMs (SUMO interacting motif) and binds SUMOs with higher affinity toward SUMO-multimers. Like RNF4, the prototypic cellular STUbL, K-Rta degrades SUMO-2/3 and SUMO-2/3 modified proteins, including promyelocytic leukemia (PML) and K-bZIP. PML-NBs (nuclear bodies) or ND-10 are storage warehouses for sumoylated proteins, which negatively regulate herpesvirus infection, as part of the intrinsic immune response. Herpesviruses have evolved different ways to degrade or disperse PML bodies, and KSHV utilizes K-Rta to inhibit PML-NBs formation. This process depends on K-Rta's ability to bind SUMO, as a K-Rta SIM mutant does not effectively degrade PML. Mutations in the K-Rta Ring finger-like domain or SIM significantly inhibited K-Rta transactivation activity in reporter assays and in the course of viral reactivation. Finally, KSHV with a mutation in the Ring finger-like domain or SIM of K-Rta replicates poorly in culture, indicating that reducing SUMO-conjugates in host cells is important for viral replication. To our knowledge, this is the first virus which encodes both a SUMO ligase and a SUMO-targeting ubiquitin ligase that together may generate unique gene regulatory programs.
authors.affiliation: Department of Dermatology, University of California Davis School of Medicine, UC Davis Comprehensive Cancer Center, Sacramento, California, United States of America. yizumiya@ucdavis.edu
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Izumiya
authors.forename: Keisuke
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Kevin Y
authors.initials: KY
authors.lastname: Kim
authors.forename: Mamata
authors.initials: M
authors.lastname: Pochampalli
authors.forename: Chie
authors.initials: C
authors.lastname: Izumiya
authors.forename: Bogdan
authors.initials: B
authors.lastname: Shevchenko
authors.forename: Don-Hong
authors.initials: DH
authors.lastname: Wang
authors.forename: Steve B
authors.initials: SB
authors.lastname: Huerta
authors.forename: Anthony
authors.initials: A
authors.lastname: Martinez
authors.forename: Mel
authors.initials: M
authors.lastname: Campbell
authors.forename: Hsing-Jien
authors.initials: HJ
authors.lastname: Kung
mesh_terms: D020816:Amino Acid Motifs; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006566:Herpesviridae Infections / Q000201:enzymology / Q000235:genetics; D019288:Herpesvirus 8, Human / Q000502:physiology*; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D000071156:Promyelocytic Leukemia Protein; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D025841:Small Ubiquitin-Related Modifier Proteins / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D014779:Virus Replication / Q000502:physiology*
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D017874:Immediate-Early Proteins; C118265:K8 protein, Human herpesvirus 8; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D012097:Repressor Proteins; C417604:Rta protein, Human herpesvirus 8; C117909:SUMO2 protein, human; C492189:SUMO3 protein, human; D025841:Small Ubiquitin-Related Modifier Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D014452:Ubiquitins; D014764:Viral Proteins; C070576:PML protein, human; D044767:Ubiquitin-Protein Ligases