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Epstein-Barr virus EBNA2 blocks Nur77- mediated apoptosis
Jae Myun Lee1, Kyoung-Ho Lee, Magdalena Weidner
1Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, 1650 Orleans Street, Baltimore, MD 21231, USA.
Abstract:
Epstein-Barr virus infection in vitro immortalizes primary B cells. EBNA2 is an Epstein-Barr virus-encoded transcriptional transactivator that mimics the effects of activated Notch signaling and is essential for this proliferative response. An assay using Sindbis virus (SV) as a cell death inducer revealed that, like Notch, EBNA2 also has antiapoptotic activity. We show that Nur77 is a mediator of SV-induced cell death and that EBNA2 antiapoptotic activity results from interaction with Nur77. EBNA2 colocalized with Nur77 in transfected cells and coprecipitated with Nur77 in IB4 B cells. EBNA2 binds to Nur77 through sequences in the EBNA2 amino acid 123-147 conserved domain and an EBNA2 mutant unable to bind Nur77 also lost the ability to protect cells from SV-induced apoptosis. EBNA2 exerted its antideath function by retaining Nur77 in the nucleus and preventing Nur77 from targeting mitochondria in response to apoptotic stimuli. Thus, targeting of Nur77 can be added to the list of strategies used by viruses to counter apoptosis.
Insights
Epstein-Barr virus protein EBNA2 prevents B cell death by interacting with the Nur77 protein. This interaction keeps Nur77 in the nucleus, blocking its pro-apoptotic function and aiding viral survival.
Area of Science:
- Virology
- Cell Biology
- Immunology
Background:
- Epstein-Barr virus (EBV) infection immortalizes primary B cells, a process crucial for viral latency.
- EBV nuclear antigen 2 (EBNA2) is essential for B cell proliferation and mimics activated Notch signaling.
- EBNA2 exhibits antiapoptotic activity, similar to Notch signaling.
Purpose of the Study:
- To elucidate the mechanism by which EBNA2 confers antiapoptotic activity.
- To identify the cellular targets of EBNA2 involved in apoptosis regulation.
- To investigate the role of Nur77 in EBV-mediated B cell survival.
Main Methods:
- Sindbis virus (SV) was used as an inducer of apoptosis in B cells.
- Co-localization and co-precipitation assays were performed to study protein interactions.
- EBNA2 mutants were utilized to map binding domains and functional consequences.
- Cellular localization studies tracked Nur77 in response to apoptotic stimuli.
Main Results:
- EBNA2 possesses antiapoptotic activity, protecting B cells from SV-induced cell death.
- Nur77 was identified as a mediator of SV-induced cell death.
- EBNA2 directly interacts with Nur77, colocalizing and co-precipitating in B cells.
- EBNA2 binds Nur77 via a conserved domain (amino acids 123-147) and prevents Nur77 nuclear export.
- This interaction retains Nur77 in the nucleus, inhibiting its translocation to mitochondria and subsequent apoptosis.
Conclusions:
- EBNA2's antiapoptotic function is mediated through direct interaction with the Nur77 protein.
- EBNA2 prevents apoptosis by sequestering Nur77 in the nucleus, thereby blocking its pro-apoptotic mitochondrial pathway.
- Viral manipulation of host cell death pathways, specifically targeting Nur77, is a key strategy for Epstein-Barr virus survival.