陳紀如副教授
Chi-Ju Chen

We sincerely invite Ph.D. program and master degree students who are interested in the studies of Epstein-Barr virus (EBV) to join the lab. Three topics regarding the interplays of EBV and host cells are studied in the lab: (1) the role of cellular kinase MSK1 and (2) protein arginine methyltransferase PRMT1 in EBV reactivation, and (3) EBV BLLF3-mediated interferon inhibition. In addition to EBV, we also study influenza virus.

1.The role of MSK1 in EBV reactivation 

Epstein-Barr virus (EBV) infection causes cancers including Burkitt lymphoma, Hodgkin’s disease,nasopharyngeal carcinoma, and certain types of gastric cancers. EBV establishes a latent infectionright after infection in the form of chromosomal episome, whose genes are mostly repressed, in Bcells and possibly epithelial cells in nasopharynx and oropharynx. The latency can be induced into aproductive infection namely lytic cycle. These two life cycles are interchangeable. People havebeen studying EBV for its association with cancers for a long time. Ample amounts of data suggesthow EBV plays an important role in tumorigenesis. At the same time, new findings regarding itsrole in tumorigenesis are still emerging. However, there are still many unknown. EBV infects tumorcells latently, but high levels of EBV specific antigens and viral titer are high risk factors for EBV-associated malignancies, suggesting genome maintenance and reactivation frequency are bothimportant. We have recently found that mitogen- and stress-associated protein kinase 1 (MSK1)plays an important role in EBV reactivation in Raji cells and EBV maintenance in Akata cells. Weshowed that MSK1 is phosphorylated upon reactivation induced by TPA and sodium butyrate.Activated MSK1 in turn phosphorylates CREB to activate transcription of immediate early gene BZLF1 (Zta) and induces EBV into lytic cycle. We, on the other hand, do not know much abouthow MSK1 plays in maintaining EBV genome in Akata cells.
This proposal focuses on mechanistic studies of MSK1 functions in EBV reactivation and genomemaintenance. Three specific aims are:

1. Investigate if MSK1 regulates EBV reactivation is solely through CREB phosphorylation.
2. Investigate how MSK1 affects maintenance in three aspects including (1) genome replication, (2) genome partition, and (3) genome establishment.
3. Investigate cellular signaling pathways involved in MSK1 activation as well as its role in physiological stimuli known to activate EBV.

2. RIG-I-induced infuenza protein degradation

1. This study aims to understand the stability and degradation of two influenza viral proteins, pro-apoptotic PB1-F2 and ion channel forming M2. Half-lives of proteins are an important aspect of protein functions, however, not much effort was put into this area inthe field of virology.We hope to demonstrate half-lives of proteins and innate immunity-induced proteolysis influence viral protein functions and may affect host-specificity of viral proteins.
   Influenza virus (IAV) is a highly contagious respiratory pathogen. Type I interferon is a crucial innate defense against IAV infection. RIG-I (retinoic acid-inducible gene 1) signaling pathway plays an important role to initiate interferon responses in IVA-infected cells. We found that RIG-I activation induced protein degradation of PB1-F2 and M2, and RNF125, a ubiquitin-E3 ligase and negative regulator for RIG-I, may be responsible. We believe it is part of host defense mechanism against influenza virus infection. We hypothesize that RIG-I activation give rise to a platform for RNF125 to encounter PB1-F2 and M2 to add poly-ubiquitin chains to them. As a consequence ubiquitinated viral proteins are sent to proteasome for degradation. Using pharmacological inhibitors to screen the possible pathways involved in RIG-I induced viral-protein degradation, we found that both autophagic and lysosomal inhibitors increased the presence of viral protein, suggesting the involvement of autophagy-mediated proteolysis. Interestingly our preliminary data shows that mitophagy, an autophagic process used to remove damaged mitochondria, can mediate protein degradation of PB-F2. For the first two parts of this project, we propose to work out the involvement of RNF125 (Aim 1) and autophagy/mitophagy (Aim 2) in RIG-I induced viral protein degradation in details.  This part will help us understand how innate immunity may fight off IAV infection by induce viral protein degradation.
   Previously we found that human PB1-F2 has a three-time longer protein half-life than avian PB1-F2 in human cells. We hypothesize that it may due to their differential responses and promptness to host-specific or signaling-activated protein degradation pathways. For the last part of this proposal, we hope to understand if PB1-F2 and M2 with different host origin response to protein degradation differently in either human or avian cell lines (Aim 3). This part will help us understand the factor deciding viral host range.
   Three specific aims are as follows:
   1. Understand how RNF125 modulates influenza virus during infection
   2. Study the involvement of autophagy/mitophagy in viral protein degradation
   3. Comparing the promptness of PB1-2 and M2 with either human or avian origin to proteolysis