Viral latent membrane protein 1 (LMP-1)-induced CD99 down-regulation in B cells leads to the generation of cells with Hodgkin's and Reed-Sternberg phenotype

Recently we reported that the downregulation of CD99 (Mic2) is a primary re quirement for the generation of Hodgkin's and Reed-Sternberg (H-RS) cells s een in Hodgkin's disease. In this study, we provide evidence that the down- regulation of CD99 is induced by high expression of Epstein-Barr virus (EBV ) latent membrane protein 1 (LMP-I), which is highly expressed in H-RS cell s of EBV-associated Hodgkin's disease. To investigate the effect of LMP-1 o n the expression of CD99 in vitro, we established a stable cell line by tra nsfecting an SV40-early promoter driven-LMP-l expression construct into a n eoplastic lymphoblastoid B cell line, IM9, in which the level of endogenous LMP-1 expression is almost negligible. In this cell line, the overexpressi on of LMP-I led to the downregulation of CD99 and the acquisition of morpho logical and functional characteristics of H-RS cells indistinguishable from those in lymph nodes of Hodgkin's disease patients and in CD99-deficient B cells. In addition, induced LMP-I expression in an EBV-negative B cell clo ne, BJAB, directly caused the down-regulation of surface CD99 expression. N orthern and Western analysis data, showing that overexpression of LMP-1 neg atively influenced the expression of CD99, were supported by experiments in which a CD99 promoter-driven luciferase promoter reporter construct transf ected into 293T cells was down-regulated when LMP-1 was coexpressed. Theref ore, our data strongly suggest that the EBV LMP-1 protein plays a pivotal r ole in the downregulation of CD99 via transcriptional regulation, which lea ds to the generation of the H-RS cells, (C) 2000 by The American Society of Hematology.