# USP7 targeting by HHV-8 vIRFs

> **NIH NIH R01** · JOHNS HOPKINS UNIVERSITY · 2020 · $409,375

## Abstract

Human herpesvirus 8 (HHV-8) is involved etiologically in AIDS-associated diseases Kaposi’s sarcoma, primary
effusion lymphoma (PEL), and multicentric Castleman’s disease; in all, viral latent and lytic functions are believed
to contribute. HHV-8 encodes four interferon regulatory factor homologues (vIRFs) that can interact in inhibitory
fashion with cellular IRFs and/or a variety of other cellular proteins involved in innate immunity and antiviral
stress signaling. However, very few of these interactions have been detected and assessed functionally in the
context of virus infection. It has recently been reported that both vIRF-1 and vIRF-4 interact with the
deubiquitinase USP7 [ubiquitin-specific protease 7, also called herpesvirus-associated USP (HAUSP)], and we
have identified vIRF-3 (published) and vIRF-2 (new data in this revised application) as additional interaction
partners of USP7. While vIRF-4 interacts with the USP7 N-terminal TRAF domain via a core motif, ASTS,
matching the consensus USP7-interaction motif, A/PxxS, present in many cellular and viral proteins, vIRF-1 and
vIRF-3 have, respectively, a single and duplicated TRAF domain-interacting EGPS core motif and vIRF-2
appears to interact with USP7 in a novel manner. vIRFs 1, 2 and 3 are expressed in latently (in addition to
lytically) infected PEL cells, but in other examined cell types, all vIRFs appear to be expressed only during lytic
replication. Through depletion-based analyses in PEL cells and gene ablation in the context of HHV-8 bacmid
(BAC16) virus-infected iSLK (inducible, epithelial) cells, we have determined that vIRF-1, like vIRF-3, is important
for the viability of latently infected PEL cells and that vIRF-3, in contrast to vIRF-1, negatively regulates HHV-8
productive replication. Furthermore, using WT or USP7-refractory (EGPS motif-mutated) vIRF-1/3 “rescue” of
vIRF depletion phenotypes in PEL cells and BAC16 mutants expressing USP7-refractory variants of vIRFs 1 and
3, we have determined that vIRF-1 and vIRF-3 interactions with USP7 are involved centrally in the respective
latent and lytic activities. USP7 depletion revealed directly the importance of the deubiquitinase for latent PEL
cell viability and HHV-8 productive replication. We have also identified ubiquitin modifications of vIRFs 1 and 3,
raising the possibility of USP7 modulation of vIRF expression and/or activities via ubiquitin editing. In this
application we propose to: (1) examine the functional and biological consequences of vIRF-2 targeting of USP7;
(2) characterize structurally and functionally vIRF ubiquitination and USP7 editing thereof; (3) identify vIRF-
regulated USP7 targets in the context of HHV-8 infected cells and the functional significance of these proteins
in HHV-8 biology. The proposed work will, for the first time, characterize vIRF-2 targeting of USP7 and identify
mechanisms underlying biological activities mediated via vIRF-USP7 interactions, of demonstrated importance
to both latent ...

## Key facts

- **NIH application ID:** 9883702
- **Project number:** 5R01AI140855-02
- **Recipient organization:** JOHNS HOPKINS UNIVERSITY
- **Principal Investigator:** John Nicholas
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $409,375
- **Award type:** 5
- **Project period:** 2019-03-01 → 2024-02-29

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9883702

## Citation

> US National Institutes of Health, RePORTER application 9883702, USP7 targeting by HHV-8 vIRFs (5R01AI140855-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9883702. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*