Article

Kaposi's sarcoma-associated herpesvirus K-bZIP represses gene transcription via SUMO modification.

Department of Biological Chemistry, University of California--Davis (UC Davis), School of Medicine, Sacramento, 95817, USA.
Journal of Virology (Impact Factor: 4.65). 09/2005; 79(15):9912-25. DOI: 10.1128/JVI.79.15.9912-9925.2005
Source: PubMed

ABSTRACT Kaposi's sarcoma-associated herpesvirus (KSHV) is a human gammaherpesvirus implicated in AIDS-related neoplasms. Previously, we demonstrated that the early lytic gene product K-bZIP is a transcriptional repressor that affects a subset of viral gene transcriptions mediated by the viral transactivator K-Rta (Y. Izumiya et al. J. Virol. 77:1441-1451, 2003). Sumoylation has emerged as an important posttranslational modification that affects the location and function of cellular and viral proteins and also plays a significant role in transcriptional repression along with Ubc9, the E2 SUMO conjugation enzyme. Here, we provide evidence that K-bZIP is sumoylated at the lysine 158 residue and associates with Ubc9 both in a cell-free system and in virus-infected BCBL-1 cells. Reporter assays showed that the expression of SUMO-specific protease 1 attenuated the transcriptional repression activity of K-bZIP. The expression of a K-bZIPK158R mutant, which was no longer sumoylated, exhibited the reduced transcriptional repression activity. This indicates that sumoylation plays an important part in the transcriptional repression activity of K-bZIP. Finally, chromatin immunoprecipitation experiments demonstrated that K-bZIP interacts with and recruits Ubc9 to specific KSHV promoters. Thus, our data indicate that K-bZIP is a SUMO adaptor, which recruits Ubc9 to specific viral target promoters, thereby exerting its transcriptional repression activity.

Full-text

Available from: Hsing-Jien Kung, Nov 28, 2014
1 Follower
 · 
94 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Kaposi's sarcoma-associated herpesvirus (KSHV) primarily persists as a latent episome in infected cells. During latent infection, only a limited number of viral genes are expressed that help to maintain the viral episome and prevent lytic reactivation. The latent KSHV genome persists as a highly ordered chromatin structure with bivalent chromatin marks at the promoter-regulatory region of the major immediate-early gene promoter. Various stimuli can induce chromatin modifications to an active euchromatic epigenetic mark, leading to the expression of genes required for the transition from the latent to the lytic phase of KSHV life cycle. Enhanced replication and transcription activator (RTA) gene expression triggers a cascade of events, resulting in the modulation of various cellular pathways to support viral DNA synthesis. RTA also binds to the origin of lytic DNA replication to recruit viral, as well as cellular, proteins for the initiation of the lytic DNA replication of KSHV. In this review we will discuss some of the pivotal genetic and epigenetic factors that control KSHV reactivation from the transcriptionally restricted latent program.
    Viruses 01/2015; 7(1):116-153. DOI:10.3390/v7010116 · 3.28 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The retinoblastoma protein (pRb/p105) tumor suppressor plays a pivotal role in cell cycle regulation by blockage of the G1-to-S phase transition. pRb tumor suppressor activity is governed by a variety of post-translation modifications, most notably, phosphorylation by cyclin dependent kinase (Cdk) complexes. Here, we report a novel regulation of pRb through Protein Arginine Methyltransferase 4 (PRMT4)-mediated arginine methylation that parallels phosphorylation. PRMT4 specifically methylates pRb at the pRb C-terminal domain (pRb C(term)) on Arginine (R) residues R775, R787, and R798 in vitro and R787 in vivo. Arginine methylation is important for efficient pRb C(term) phosphorylation manifested by the reduced phosphorylation of methylation impaired pRb (R3K) mutant. Methyl mimetic pRb (R3F) disrupts E2F-1/DP1-pRb complex formation in cells as well as in an isolated system. Lastly, studies using Gal4-E2F-1 reporter system show that pRb (R3F) expression reduces the ability of pRb to repress E2F-1 transcription activation while pRb (R3K) expression further represses E2F-1 transcription activation compared to cells expressing wild-type pRb. Together, our results suggest that arginine methylation negatively regulates pRb tumor suppressor function during cell cycle control in part by serving as a better substrate for Cdk complex phosphorylation and disrupting E2F-1 interaction.
    Molecular and Cellular Biology 10/2014; 35(1). DOI:10.1128/MCB.00945-14 · 5.04 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Kaposi's sarcoma-associated herpesvirus (KSHV/human herpesvirus 8) is a γ-herpesvirus linked to Kaposi's sarcoma (KS) and two lymphoproliferative disorders, primary effusion lymphoma (PEL or body-cavity B-lymphoma [BCBL]) and a subset of Multicentric Castleman's Disease. During lytic growth, pervasive viral transcription generating a variety of transcripts with uncertain protein-coding potential has been described on a genome-wide scale in β- and γ-herpesviruses. One class of such RNAs is called long non-coding RNAs (lncRNAs). KSHV encodes a viral lncRNA known as polyadenylated nuclear RNA (PAN RNA), a copious early gene product. PAN RNA has been implicated in KSHV gene expression, replication, and immune modulation. PAN RNA expression is required for optimal expression of the entire KSHV lytic gene expression program. Latent KSHV episomes are coated with viral latency-associated nuclear antigen (LANA). LANA rapidly dissociates from episomes during reactivation. Here we review recent studies suggesting that PAN RNA may function as a viral lncRNA, including a role in the facilitation of LANA-episomal dissociation during lytic replication.
    Viruses 11/2014; 6(11):4165-4177. DOI:10.3390/v6114165 · 3.28 Impact Factor