Requirement for LMP1-induced RON receptor tyrosine kinase in Epstein-Barr virus-mediated B-cell proliferation.

EBV, an oncogenic human herpesvirus, can transform primary B lymphocytes into immortalized lymphoblastoid cell lines (LCLs) through multiple regulatory mechanisms. However, the involvement of protein tyrosine kinases in the infinite proliferation of B cells is not clear. In this study, we performed kinase display assays to investigate this subject and identified a specific cellular target, Recepteur d'Origine Nantais (RON) tyrosine kinase, expressed in LCLs but not in primary B cells. Furthermore, we found that latent membrane protein 1 (LMP1), an important EBV oncogenic protein, enhanced RON expression through its C-terminal activation region-1 (CTAR1) by promoting NF-κB binding to the RON promoter. RON knockdown decreased the proliferation of LCLs, and transfection with RON compensated for the growth inhibition caused by knockdown of LMP1. Immunohistochemical analysis revealed a correlation between LMP1 and RON expression in biopsies from posttransplantation lymphoproliferative disorder (PTLD), suggesting that LMP1-induced RON expression not only is essential for the growth of LCLs but also may contribute to the pathogenesis of EBV-associated PTLD. Our study is the first to reveal the impact of RON on the proliferation of transformed B cells and to suggest that RON may be a novel therapeutic target for EBV-associated lymphoproliferative diseases.