Analysis of the ubiquitin-modified proteome identifies novel host factors in Kaposi's sarcoma herpesvirus lytic reactivation.

Unlabelled: Kaposi's sarcoma herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma and is associated with primary effusion lymphoma (PEL), multicentric Castleman's disease, and two inflammatory diseases. KSHV-associated cancers are primarily associated with genes expressed during latency, while other pathologies are associated with lytic gene expression. The major lytic switch of the virus, Replication and Transcription Activator (RTA), interacts with cellular machinery to co-opt the host ubiquitin proteasome system to evade the immune response as well as activate the program of lytic replication.

Kaposi's sarcoma herpesvirus viral FLICE inhibitory protein modulates A20 deubiquitinase activity.

KSHV viral FLICE inhibitory protein (vFLIP) is a potent activator of NF-κB signalling and an inhibitor of apoptosis and autophagy. Inhibition of vFLIP function and NF-κB signalling promotes lytic reactivation. Here we provide evidence for a novel function of vFLIP through inhibition of the deubiquitinating (DUB) activity of the negative regulator, A20.

Gold nanoparticles loaded with cullin-5 DNA increase sensitivity to 17-AAG in cullin-5 deficient breast cancer cells.

HSP90 inhibitors have the potential to treat many types of cancer due to the dependence of tumor cells on HSP90 for cell growth and proliferation. The Cullin-5 (Cul5) E3 ubiquitin ligase is required for HSP90 inhibitors to induce client protein degradation and subsequent cell death. Cul5 is expressed at low levels in breast cancer cells compared to patient matched controls.

The Itch ubiquitin ligase is required for KSHV RTA induced vFLIP degradation.

Expression of Kaposi's sarcoma herpesvirus vFLIP, a potent activator of NFkB signaling, promotes latency. Inhibition of NFkB signaling promotes lytic reactivation. We previously reported that lytic inducer, RTA, inhibits vFLIP induced NFkB signaling by inducing the degradation of vFLIP via the proteasome.

Coxsackievirus A16 infection induces neural cell and non-neural cell apoptosis in vitro.

Coxsackievirus A16 (CA16) is one of the main causative pathogens of hand, foot and mouth disease (HFMD). Viral replication typically results in host cell apoptosis. Although CA16 infection has been reported to induce apoptosis in the human rhabdomyosarcoma (RD) cell line, it remains unclear whether CA16 induces apoptosis in diverse cell types, especially neural cells which have important clinical significance.

KSHV RTA abolishes NFκB responsive gene expression during lytic reactivation by targeting vFLIP for degradation via the proteasome.

Kaposi's sarcoma herpesvirus (KSHV) is a gamma-2 herpesvirus present in all cases of Kaposi's sarcoma, primary effusion lymphoma (PEL), and some cases of multicentric Castleman's disease. Viral FLICE inhibitory protein (vFLIP) is a latently expressed gene that has been shown to be essential for survival of latently infected PEL cells by activating the NFκB pathway. Inhibitors of either vFLIP expression or the NFĸB pathway result in enhanced lytic reactivation and apoptosis.

Regulation of Hsp90 client proteins by a Cullin5-RING E3 ubiquitin ligase.

We report a link between Cullin5 (Cul5) E3 ubiquitin ligase and the heat shock protein 90 (Hsp90) chaperone complex. Hsp90 participates in the folding of its client proteins into their functional conformation. Many Hsp90 clients have been reported to be aberrantly expressed in a number of cancers.

E1B 55k-independent dissociation of the DNA ligase IV/XRCC4 complex by E4 34k during adenovirus infection.

The ligase IV/XRCC4 complex plays a central role in DNA double-strand break repair by non-homologous end joining (NHEJ). During adenovirus infection, NHEJ is inhibited by viral proteins E4 34k and E1B 55k, which redirect the Cul5/Rbx1/Elongin BC ubiquitin E3 ligase to polyubiquitinate and promote degradation of ligase IV. In cells infected with E1B 55k-deficient adenovirus, ligase IV could not be found in XRCC4-containing complexes and was observed in a novel ligase IV/E4 34k/Cul5/Elongin BC complex.

Structural insight into the human immunodeficiency virus Vif SOCS box and its role in human E3 ubiquitin ligase assembly.

Human immunodeficiency virus (HIV) virion infectivity factor (Vif) causes the proteasome-mediated destruction of human antiviral protein APOBEC3G by tethering it to a cellular E3 ubiquitin ligase composed of ElonginB, ElonginC, Cullin5, and Rbx2. It has been proposed that HIV Vif hijacks the E3 ligase through two regions within its C-terminal domain: a BC box region that interacts with ElonginC and a novel zinc finger motif that interacts with Cullin5. We have determined the crystal structure of the HIV Vif BC box in complex with human ElonginB and ElonginC.

Characterization of a novel Cullin5 binding domain in HIV-1 Vif.

Human immunodeficiency virus tyoe 1 (HIV-1) Vif counteracts host restriction cytidine deaminase (APOBEC3G) A3G by co-opting the cellular ubiquitin-proteasome machinery. Vif utilizes a viral-specific BC-box to recruit ElonginB-ElonginC and a novel zinc-binding HCCH motif to recruit Cullin5 (Cul5) to form an E3 ubiquitin ligase targeting A3G for polyubiquitination and subsequently proteasomal degradation. To determine the structural requirements in HIV-1 Vif HCCH motif for Cul5 binding and Vif function, we investigated the arrangement of the His and Cys residues, the role of the spacing between them, and the requirement for the conserved residues.

DDB1 and Cul4A are required for human immunodeficiency virus type 1 Vpr-induced G2 arrest.

Vpr-mediated induction of G2 cell cycle arrest has been postulated to be important for human immunodeficiency virus type 1 (HIV-1) replication, but the precise role of Vpr in this cell cycle arrest is unclear. In the present study, we have shown that HIV-1 Vpr interacts with damaged DNA binding protein 1 (DDB1) but not its partner DDB2. The interaction of Vpr with DDB1 was inhibited when DCAF1 (VprBP) expression was reduced by short interfering RNA (siRNA) treatment.

Adenovirus E4orf6 assembles with Cullin5-ElonginB-ElonginC E3 ubiquitin ligase through an HIV/SIV Vif-like BC-box to regulate p53.

The adenovirus protein E4orf6 targets p53 for polyubiquitination and proteasomal degradation and is known to form a complex with the Cul5-ElonginB-ElonginC E3 ubiquitin ligase. However, whether Cul5 is directly responsible for the E4orf6-mediated degradation of p53 remains unclear. By using a dominant-negative mutant of Cul5 and silencing Cul5 expression through RNA interference, we have now demonstrated that E4orf6-mediated p53 degradation requires Cul5.

Zinc chelation inhibits HIV Vif activity and liberates antiviral function of the cytidine deaminase APOBEC3G.

APOBEC3 proteins are cellular antiviral proteins that are targeted for proteasomal degradation by primate lentiviral Vif proteins. Vif acts as a substrate receptor for the Cullin5 (Cul5) E3 ubiquitin ligase, specifically interacting with Cul5 through a novel H-(x5)-C-(x17-18)-C-(x3-5)-H zinc binding motif. Using the membrane-permeable zinc chelator, N,N,N',N'-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN), we demonstrated a requirement for zinc for Vif function in vivo.

Lentiviral Vif: viral hijacker of the ubiquitin-proteasome system.

Since the beginning of time, microorganisms have been devising ways to bypass detection and destruction by our immune system. Therefore, it is no surprise that along with the identification of the cellular antiviral protein APOBEC3G (A3G) has come the recognition of the viral solution to this assault. Here, we review the research that led up to the identification of A3G and the mechanism that the human immunodeficiency virus protein Vif developed to evade A3G's antiviral activities.

Assembly of HIV-1 Vif-Cul5 E3 ubiquitin ligase through a novel zinc-binding domain-stabilized hydrophobic interface in Vif.

APOBEC3G (A3G) and related cytidine deaminases are potent inhibitors of retroviruses. HIV-1 Vif hijacks the cellular Cul5-E3 ubiquitin ligase to degrade APOBEC3 proteins and render them ineffective against these viruses. Here, we report that HIV-1 Vif is a novel zinc-binding protein containing an H-x(5)-C-x(17-18)-C-x(3-5)-H motif that is distinct from other recognized classes of zinc fingers.

Primate lentiviral virion infectivity factors are substrate receptors that assemble with cullin 5-E3 ligase through a HCCH motif to suppress APOBEC3G.

Cullin-Ring E3 ubiquitin ligases target substrates for ubiquitin-dependent, proteasome-mediated degradation and regulate critical cellular processes. These cullins assemble with cellular substrate receptor proteins through specific adaptor molecules. F-box- and BC-box-containing receptors use Skp1, ElonginB, and ElonginC as adaptors to recruit Cul1/Cul7 and Cul2/Cul5, respectively.

Selective assembly of HIV-1 Vif-Cul5-ElonginB-ElonginC E3 ubiquitin ligase complex through a novel SOCS box and upstream cysteines.

APOBEC3G, which induces hypermutations in newly synthesized viral DNA, is suppressed by HIV-1 Vif, acting through Cul5-ElonginB-ElonginC E3 ubiquitin ligase. We have now characterized a novel SOCS box in HIV-1 Vif that mediates its interaction with ElonginC. In this SOCS box, alanine replaces the consensus cysteine in the previously identified SOCS box.