Necroptosis is an alternative programmed cell death pathway that is unleashed in the absence of apoptosis and mediated by signaling complexes containing receptor-interating protein kinase 1 (RIPK1) and RIPK3. This form of cell death has recently been implicated in host defense system to eliminate pathogen-infected cells. However, only a few viral species such as herpes simplex virus (HSV) and cytomegalovirus (CMV) have evolved mechanisms inhibiting necroptosis to overcome host antiviral defense, which is important for successful pathogenesis. Here, we show that the γ-herpesvirus Epstein-Barr virus (EBV) blocks necroptosis in EBV-infected human nasopharyngeal epithelial cells and nasopharyngeal carcinoma cells. Our findings indicate that EBV-encoded latent membrane protein 1 (LMP1), which lacks an RIP homotypic interaction motif (RHIM) domain, has mechanisms distinct from RHIM signaling competition to inhibit this necroptotic pathway. Intriguingly, LMP1 interacts directly with both RIPK1 and RIPK3 through its C-terminal activation region. More importantly, LMP1 can modulate the post-translational modification of the two receptor-interacting proteins. We then show that LMP1-mediated promotion of K63-polyubiquitinated RIPK1, suppression of RIPK1 protein expression and inhibition of K63-polyubiquitinated RIPK3 induced a switch in cell fate from necroptotic death to survival. These findings provide direct evidence for the suppression of necroptosis by EBV and define a mechanism of LMP1 to interrupt the initiation process of necroptosis before necrosome formation.
Bibliographical noteFunding Information:
We thank Dr. Xiaodong Wang (National Institute of Biological Sciences, Beijing, China) for providing the Flag-RIPK3 plasmid and Dr Kenneth M Izumi (Brigham and Women’s Hospital, Boston, MA, USA) for the pSG5-LMP1 plasmid. We also thank Dr. Junpu Wang (Department of Electron Microscope, Central South University, Changsha, China) for technical assistance with TEM measurements. This work was supported by the National Natural Science Foundation of China (No. 81430064 and 81602402), the Fundamental Research Funds for the Central Universities (No. 502042004) and the Fundamental Research Funds for the Central Universities of Central South University (No. 2014zzts068).