Reciprocal Activities between Herpes Simplex Virus Type 1 Regulatory Protein ICP0, a Ubiquitin E3 Ligase, and Ubiquitin-Specific Protease USP7

Abstract

Herpes simplex virus type 1 (HSV-1) regulatory protein ICP0 stimulates lytic infection and the reactivation of quiescent viral genomes. These roles of ICP0 require its RING finger E3 ubiquitin ligase domain, which induces the degradation of several cellular proteins, including components of promyelocytic leukemia nuclear bodies and centromeres. ICP0 also interacts very strongly with the cellular ubiquitin-specific protease USP7 (also known as HAUSP). We have shown previously that ICP0 induces its own ubiquitination and degradation in a RING finger-dependent manner, and that its interaction with USP7 regulates this process. In the course of these studies we found and report here that ICP0 also targets USP7 for ubiquitination and proteasomedependent degradation. The reciprocal activities of the two proteins reveal an intriguing situation that poses the question of the balance of the two processes during productive HSV-1 infection. Based on a thorough analysis of the properties of an HSV-1 mutant virus that expresses forms of ICP0 that are unable to bind to USP7, we conclude that USP7-mediated stabilization of ICP0 is dominant over ICP0-induced degradation of USP7 during productive HSV-1 infection. We propose that the biological significance of the ICP0-USP7 interaction may be most pronounced in natural infection situations, in which limited amounts of ICP0 are expressed.An important biological and clinical aspect of herpes simplex virus type 1 (HSV-1) is its ability to establish a latent state in neuronal cell nuclei following an initial epithelial infection (for general reviews, see references 31 and 32). Periodically the latent virus will reactivate and cause an episode of lytic replication at the site of the original epithelial infection. While in most cases this is not serious, in immunocompromised patients the infections can become severe and even life-threatening. Since latent virus is accessible to neither the immune system of the host nor current antiviral treatments, an understanding of the molecular mechanisms that govern the establishment, maintenance, and particularly the reactivation of latent genomes is important for the future development of effective therapies.ICP0 is a member of the immediate-early class of HSV-1 gene products, and it is required for the efficient initiation of viral lytic infection and reactivation of latent virus in animal models. ICP0 also stimulates reactivation of quiescent viral genomes in cultured cells (for reviews, see references 12, 13, 19, and 31). A major biochemical function of ICP0 is its E3 ubiquitin ligase activity, conferred by a RING finger domain near its N terminus (4,20). This activity leads to the proteasome-dependent degradation of several cellular proteins during infection. These include the promyelocytic leukemia protein PML and small ubiquitin-like modifier (SUMO)-modified forms of Sp100 (both of which are major components of nuclear substructures known as ND10 or PML nuclear bodies) (3,7,15,28,29), centromere proteins CENP-C and CENP-A (14, 24), and the ...

HSV ICP0 recruits USP7 to modulate TLR-mediated innate response

“…USP7, which appeared as a nuclear protein in the absence of ICP0 (Figure 4Aiii) translocated to a perinuclear compartment when coexpressed with wt-ICP0 (Figure 4Av). In agreement with previous studies showing that USP7 undergoes proteasomal degradation by ICP0, 37 we detected reduced levels of USP7 in cells coexpressing wt-ICP0 (Figure 4Av). ICP0-NLS-MUT failed to alter USP7 localization.…”

During its nuclear phase the multifunctional regulatory protein ICP0 undergoes proteolytic cleavage characteristic of polyproteins

“…In subsequent studies on the role of ubiqiuitin-specific protease 7, the same laboratory showed for the most part narrow strips containing full-length ICP0 only (14,15). They concluded that the protease blocks degradation of ICP0 by proteasome dependent pathway, presumably the proteasome-dependent pathway reported here.…”

USP7 and Daxx regulate mitosis progression and taxane sensitivity by affecting stability of Aurora-A kinase

“…21,25,26 To further understand the mechanism of Daxx-based mitosis progression and taxane resistance, we employed proteomic approach to isolate the Daxx mitotic complex and characterize Daxx-interacting proteins. Here we report that ubiquitin (Ub)-specific processing protease-7 (USP7), 27 a deubiquitylating enzyme, is a Daxx-interacting protein in mitosis. USP7 interacts with and stabilizes the mitotic checkpoint protein E3 Ub ligase CHFR (checkpoint with forkhead and Ring-finger), 28 but USP7 direct involvement in mitotic regulation has not yet been demonstrated.…”