Temporal Analysis of Cell Protein Ubiquitination during Epstein-Barr Virus Reactivation by BCR Cross-linking

Epstein-Barr virus (EBV) reactivation in latently infected B cells is essential for persistent infection and B cell receptor (BCR) activation is a physiologically relevant stimulus for EBV reactivation. Post-translational modifications, such as phosphorylation and ubiquitination, are known to be regulated by antigen binding to BCR within minutes. However, a detailed understanding of the signaling alterations at later time when EBV is being actively replicated remains elusive. To gain insights into BCR activation-mediated reprogramming of the cellular environment in both Akata-BX1 (EBV+) and Akata-4E3 (EBV-) B cells, we utilized a 3-plex stable isotope labeling by amino acid in cell culture (SILAC)-based quantitative proteomic approach to monitor the dynamic changes of protein ubiquitination during the course of immunoglobulin G (IgG) cross-linking of BCRs. We observed temporal alterations in the level of ubiquitination on approximately 150 sites in both Akata-BX1 (EBV+) and Akata-4E3 (EBV-) B cells post-IgG cross-linking compared with no cross-linking controls, with the majority of protein ubiquitination down-regulated. Our analysis revealed that IgG cross-linking plays a major role in the regulation of protein ubiquitination in both EBV+ and EBV- B cells. Bioinformatic analyses of up-regulated ubiquitination events revealed significant enrichment of proteins involved in RNA processing. Among the down-regulated ubiquitination events are proteins enriched in apoptosis and the ubiquitin-proteasome pathway. The comparative and quantitative studies provide a foundation for further understanding how BCR activation regulates cellular protein ubiquitination and how EBV utilizes or subverts BCR engagement-mediated changes to facilitate viral replication.