UbE2E1/UBCH6 Is a Critical E2 for the PRC1-catalyzed Ubiquitination of H2A at Lys-119.

UbE2E1/UbcH6 is an E2 ubiquitin-conjugating enzyme that is regulated by USP7. We identified UbE2E1 as a novel component of Polycomb repressive complex 1 (PRC1), the E3 ligase complex responsible for histone H2A ubiquitination and gene silencing. We demonstrate that UbE2E1 is critical for the monoubiquitination of H2A at residue Lys-119 (uH2AK119) through its association with the PRC1 complex.

The Role of Support Services in Promoting Social Inclusion for the Disadvantaged Urban-dwelling Elderly.

Background: Disadvantaged older adults living in non-family situations in Toronto are more likely than older adults living in family situations to have less economic security, less social support, and less choice in housing. Older adults who live in poverty and are precariously housed are more likely to be chronically ill, to live with multiple illnesses, to have poor nutrition, high stress and loneliness, all of which are strongly associated with the determinant of health social exclusion. The aim of this study is to: 1) evaluate the level of social disadvantage and exclusion experienced by low-income older adults 65 years of age and older living alone or in non-family situations; 2) assess the level of dependency on government and community services (support services) to maintain a reasonable standard of living (minimize effects of social exclusion); and 3) identify consequences of social exclusion not addressed by current available services.

Ubiquitin-specific protease 7 is a regulator of ubiquitin-conjugating enzyme UbE2E1.

Ubiquitin-specific protease 7 (USP7) is a deubiquitinating enzyme found in all eukaryotes that catalyzes the removal of ubiquitin from specific target proteins. Here, we report that UbE2E1, an E2 ubiquitin conjugation enzyme with a unique N-terminal extension, is a novel USP7-interacting protein. USP7 forms a complex with UbE2E1 in vitro and in vivo through the ASTS USP7 binding motif within its N-terminal extension in an identical manner with other known USP7 binding proteins.

The herpesvirus associated ubiquitin specific protease, USP7, is a negative regulator of PML proteins and PML nuclear bodies.

The PML tumor suppressor is the founding component of the multiprotein nuclear structures known as PML nuclear bodies (PML-NBs), which control several cellular functions including apoptosis and antiviral effects. The ubiquitin specific protease USP7 (also called HAUSP) is known to associate with PML-NBs and to be a tight binding partner of two herpesvirus proteins that disrupt PML NBs. Here we investigated whether USP7 itself regulates PML-NBs.

USP7/HAUSP promotes the sequence-specific DNA binding activity of p53.

The p53 tumor suppressor invokes cellular responses to stressful stimuli by coordinating distinct gene expression programs. This function relies heavily on the ability of p53 to function as a transcription factor by binding promoters of target genes in a sequence specific manner. The DNA binding activity of the core domain of p53 is subject to regulation via post-translational modifications of the C-terminal region.

Further insight into substrate recognition by USP7: structural and biochemical analysis of the HdmX and Hdm2 interactions with USP7.

Ubiquitin-specific protease 7 (USP7) catalyzes the deubiquitination of several substrate proteins including p53 and Hdm2. We have previously shown that USP7, and more specifically its amino-terminal domain (USP7-NTD), interacts with distinct regions on p53 and Hdm2 containing P/AxxS motifs. The ability of USP7 to also deubiquitinate and control the turnover of HdmX was recently demonstrated.

EBNA1-mediated recruitment of a histone H2B deubiquitylating complex to the Epstein-Barr virus latent origin of DNA replication.

The EBNA1 protein of Epstein-Barr virus (EBV) plays essential roles in enabling the replication and persistence of EBV genomes in latently infected cells and activating EBV latent gene expression, in all cases by binding to specific recognition sites in the latent origin of replication, oriP. Here we show that EBNA1 binding to its recognition sites in vitro is greatly stimulated by binding to the cellular deubiquitylating enzyme, USP7, and that USP7 can form a ternary complex with DNA-bound EBNA1. Consistent with the in vitro effects, the assembly of EBNA1 on oriP elements in human cells was decreased by USP7 silencing, whereas assembly of an EBNA1 mutant defective in USP7 binding was unaffected.

Epstein-Barr nuclear antigen 1 contributes to nasopharyngeal carcinoma through disruption of PML nuclear bodies.

Latent Epstein-Barr virus (EBV) infection is strongly associated with several cancers, including nasopharyngeal carcinoma (NPC), a tumor that is endemic in several parts of the world. We have investigated the molecular basis for how EBV latent infection promotes the development of NPC. We show that the viral EBNA1 protein, previously known to be required to maintain the EBV episomes, also causes the disruption of the cellular PML (promyelocytic leukemia) nuclear bodies (or ND10s).

Molecular recognition of p53 and MDM2 by USP7/HAUSP.

The ubiquitin-specific protease, USP7, has key roles in the p53 pathway whereby it stabilizes both p53 and MDM2. We show that the N-terminal domain of USP7 binds two closely spaced 4-residue sites in both p53 and MDM2, falling between p53 residues 359-367 and MDM2 residues 147-159. Cocrystal structures with USP7 were determined for both p53 peptides and for one MDM2 peptide.

Structure of the p53 binding domain of HAUSP/USP7 bound to Epstein-Barr nuclear antigen 1 implications for EBV-mediated immortalization.

USP7/HAUSP is a key regulator of p53 and Mdm2 and is targeted by the Epstein-Barr nuclear antigen 1 (EBNA1) protein of Epstein-Barr virus (EBV). We have determined the crystal structure of the p53 binding domain of USP7 alone and bound to an EBNA1 peptide. This domain is an eight-stranded beta sandwich similar to the TRAF-C domains of TNF-receptor associated factors, although the mode of peptide binding differs significantly from previously observed TRAF-peptide interactions in the sequence (DPGEGPS) and the conformation of the bound peptide.