The ubiquitin specific protease, called USP7 or HAUSP, contributes to several nuclear processes by binding and, in some cases, removing ubiquitin from specific target proteins resulting in their stabilization. USP7 targets include several proteins in the p53 pathway (p53, Mdm2, MdmX). We have discovered that EBNA1 forms a stable complex with USP7 in human cells which prevents the USP7-p53 interaction, resulting in destabilization of p53 and decreased p53 function in response to DNA damage. Through biochemical and structural approaches, we have defined the mechanism of the USP7 interaction with EBNA1, p53, Mdm2 and MdmX, showing that they bind the same binding pocket in the USP7 N-terminal TRAF domain. In addition, we found that USP7 acts in concert with EBNA1 to disrupt PML nuclear bodies and that USP7 itself can negatively regulate PML nuclear bodies through its protein interaction domains. The mechanism of this function is being explored. We also identified cellular GMP synthetase (GMPS) as a USP7 binding partner. We showed that GMPS stimulates the ability of USP7 to cleave monoubiqutin from histone H2B and that the USP7-GMPS complex is recruited by EBNA1 to the oriP FR element, where it affects H2B ubiquitylation. In this way, USP7 also affects chromatin structure. Recently we characterized an interaction of USP7 with a DNA replication protein (MCM-BP) that we previously discovered as an interactor of the MCM replicative helicase complex. In keeping with this interaction, we showed that USP7 has a role in DNA replication that involves unloading the MCM complex at the end of S phase. Further studies are necessary to determine the precise mechanism of action. Finally, we have recently used proteomics approaches to identify several novel cellular interactions of USP7 and are currently studying the mechanisms and significance of these interactions.
Publications:

Georges, A., Coyaud, E., Marcon, E. Greenblatt, J., Raught, B. and Frappier, L. 2019 USP7 Regulates Cytokinesis through FBXO38 and KIF20B Scientific Reports. 9(1):2724.

Georges, A., Marcon, E. Greenblatt, J. and Frappier, L. 2018 Identification and Characterization of USP7 Targets in Cancer Cells. Scientific Reports. 8(1):15833.

Pfoh, R., Lacdao, I.,Georges, A., Capar, A., Zheng, H., Frappier, L., and Saridakis, V. 2015 Crystal structure of the USP7-ICP0 complex reveals a novel mechanism used by viral and cellular proteins to target USP7. PLoS Pathogens. 11(6): e1004950.

Jagannathan, M., Nguyen, T., Gallo, D., Luthra, N., Brown, G. and Frappier, L. 2014 A Role for USP7 in DNA Replication. Mol. Cell. Biol. 34, 132-145.

Sarkari, F, Wang, X., Nguyen, T and Frappier, L. 2011 The Herpesvirus Associated Ubiquitin Specific Protease, USP7, as a Negative Regulator of the PML Proteins and PML Nuclear Bodies. PLoS One, 6(1): e16598. doi:10.1371/journal.pone.0016598. PMID: 21305000

Sarkari, F., , Sheng, Y. and Frappier, L. 2010 USP7/HAUSP Promotes the Sequence-Specific DNA Binding Activity of p53. PLoS One. 5(9): e13040. doi:10.1371/journal.pone.0013040. PMID: 20885946

Sarkari, F., La Delfa, A., Arrowsmith, C.H., Frappier, L., Sheng, Y. and Saradakis, V. 2010 Further Insight into Substrate Recognition by USP7/HAUSP: Crystal Structures and Biochemical Analysis of the HdmX and Hdm 2 Interaction with USP7/HAUSP. J. Mol. Biol. 402, 825-837. PMID: 20713061

Sivachandran, N., Cao, J.Y. and Frappier, L. 2010 Epstein-Barr Nuclear Antigen 1 Hijacks the Host Kinase CK2 to Disrupt PML Nuclear Bodies. J. Virol. 84(21) 11113-11123. PMID: 20719947

Sarkari, F., Sanchez-Alcaraz, T., Wang, S., Holowaty, M.N., Sheng, Y. and Frappier, L. 2009 EBNA1-mediated Recruitment of a Histone H2B Deubiquitylating complex to the Epstein-Barr virus Latent Origin of DNA Replication. PLoS Pathogens, 5(10):e1000624. PMID: 19834552

Sivachandran, N., Sarkari, F. and Frappier, L. 2008 Epstein-Barr Nuclear Antigen 1 Contributes to Nasopharyngeal Carcinoma through disruption of PML Nuclear Bodies. PLoS Pathogens, 4(10): e1000170. doi:10.1371/journal.ppat.1000170.

Sheng, Y., Saridakis, V., Sarkari, F., Duan, S., Wu, T., Arrowsmith, C.H. and Frappier, L. 2006 Molecular recognition of p53 and Mdm2 by USP7/HAUSP. Nature Structural and Molecular Biology. 13, 285-291

Saridakis, V., Sheng, Y., Sarkari, F., Holowaty, M.N., Shire, K., Nguyen, T., Zhang, R.G., Liao, J., Lee, W., Edwards, A.M., Arrowsmith, C.H. and Frappier, L. 2005 Structure of the p53-binding domain of HAUSP/USP7 bound to Epstein-Barr Nuclear Antigen 1: Implications for EBV-mediate immortalization. Mol. Cell 18, 25-36.

Holowaty, M.N., Sheng, Y., Nguyen, T., Arrowsmith, C. and Frappier, L. 2003. Protein interaction domains of the ubiquitin specific protease, USP7/HAUSP. J. Biol. Chem. 278, 47753-47761.

Holowaty, M.N., Zeghouf, M., Wu, H., Tellam, J., Athanasopoulos, V., Greenblatt, J. and Frappier, L. 2003. Protein profiling with Epstein-Barr nuclear antigen 1 reveals an interaction with the herpesvirus associated ubiquitin specific protease, HAUSP/USP7. J.Biol. Chem., 29987-29994.