Kaposi's Sarcoma-associated Herpesvirus (KSHV) Encodes a SUMO E3 ligase That Is SIM-dependent and SUMO-2/3-specific

Abstract

Sumoylation has emerged as a major post-translational modification of cellular proteins, affecting a variety of cellular processes. Viruses have exploited the sumoylation pathway to advance their own replication by evolving several ways to perturb the host sumoylation apparatus. However, there has been no report of virally encoded enzymes directly involved in catalyzing the sumoylation reaction. Here, we report that the K-bZIP protein encoded by Kaposi's sarcoma-associated herpesvirus (KSHV) is a SUMO E3 ligase with specificity toward SUMO2/3. K-bZIP is a nuclear factor that functions to modulate viral gene expression and to prolong the G1 phase, allowing viral transcription and translation to proceed at the early stage of infection. In addition to functioning as a transcriptional factor, we show that K-bZIP carries a SIM (SUMO-interacting motif), which specifically binds to SUMO-2/3 but not SUMO-1. K-bZIP catalyzes its own SUMO modification as well as that of its interacting partners such as the cellular tumor suppressor proteins p53 and Rb, both in vitro and in vivo. This reaction depends on an intact SIM. Sumoylation of p53 leads to its activation and K-bZIP is recruited to several p53 target chromatin sites in a SIM-dependent manner. In addition to the identification of a viral SUMO-2/3 E3 ligase, our results provide additional insights into the mechanisms whereby K-bZIP induces cell cycle arrest.Increasing evidence indicates that sumoylation, i.e. posttranslational modification of proteins by the small ubiquitinlike modifier (SUMO) 2 plays a central role in cellular signal transduction. Like phosphorylation, sumoylation is rapid and reversible. In a manner similar to the binding of phosphorylated tyrosine by signal molecules carrying Src homology 2 (SH2) and phosphotyrosine binding (PTB) domains, sumoylated proteins are specifically engaged by proteins with a SUMO-interacting motif (SIM). Modulation of sumoylation has a profound effect on protein-protein interactions and the propagation of cellular signals. Viruses have evolved different mechanisms to exploit the host sumoylation pathway to create a cellular environment that is favorable for viral replication by modulating the functions of viral and cellular proteins (reviewed in Ref. 1). Many viral proteins are themselves sumoylated, and this post-translational modification affects specific functions of these targets. For DNA tumor viruses, the immediate-early and early gene products, which include transcriptional factors, are often sumoylated. Examples include immediate-early 1 (IE 1) and immediate-early 2 (IE 2) proteins of cytomegalovirus (CMV) (2, 3), E1 and E2 of human papillomavirus (HPV) (4, 5), BZLF1 of Epstein-Barr virus (EBV) (6), and K-bZIP of Kaposi's sarcomaassociated herpesvirus (KSHV) (7). Some viral proteins indirectly modulate the sumoylation status of specific cellular proteins. For example, the HPV E7 protein and adenovirus E1A protein block sumoylation of the cellular tumor suppressor Rb (8). Additionally, the KSHV viral protein kinase ...

The Latency-Associated Nuclear Antigen of Kaposi's Sarcoma-Associated Herpesvirus Inhibits Expression of SUMO/Sentrin-Specific Peptidase 6 To Facilitate Establishment of Latency

“…Viruses can counteract or enhance the host's sumoylation to evade the immune response and antagonize apoptosis, while some viruses exploit the host's sumoylation machinery to sumoylate the viral components which are necessary to perform viral functions (48). It has been reported that KSHV modulates the SUMO pathway through RTA/ORF50, K-bZIP/K8, and vPK/ORF36 during lytic replication as well as LANA/ORF73 and viral IRF3 (IRF3)/K10.5/LANA-2 during latency (27,35,(49)(50)(51)(52)(53)(54)(55)(56). Our results showed that LANA bound directly to the SENP6 promoter and repressed its activity, inhibiting SENP6 expression at both the RNA and protein levels.…”

Covalent modification by SUMO is required for efficient disruption of PML oncogenic domains by Kaposi's sarcoma-associated herpesvirus latent protein LANA2

“…Here, we demonstrate that LANA2 is sumoylated and that this SUMO-LANA2 covalent interaction, as we demonstrated previously for non-covalent SUMO binding to LANA2, is required for efficient disruption of PODs by LANA2. Recently, it has also been demonstrated that the KbZIP protein encoded by KSHV is a SUMO E3 ligase that catalyses its own sumoylation, as well as that of its interacting partners, in a SIM-dependent manner (Chang et al, 2010). It is tempting to speculate about a possible interplay between these two viral proteins in achieving efficient viral replication.…”

Influenza A Virus Multiplication and the Cellular SUMOylation System

“…Subsequently, it was shown that K-bZIP contains a SUMO2/3-specific SUMO Interacting Motif (SIM) that allows K-bZIP to enhance its own SUMOylation and that of other cellular proteins known to interact with it, including the tumor suppressor proteins p53 and pRB [153]. In consequence, it has been postulated that K-bZIP acts as a viral encoded SUMO ligase that helps ensure the maintenance of the proper cellular environment needed for viral multiplication by triggering the SUMOylation and subsequent activation of p53, which in turn triggers cell cycle arrest in G1 [153].…”