Role of Defective Oct-2 and OCA-B Expression in Immunoglobulin Production and Kaposi's Sarcoma-Associated Herpesvirus Lytic Reactivation in Primary Effusion Lymphoma▿

Primary effusion lymphoma (PEL) is a distinct type of B-cell non-Hodgkin lymphoma characterized by the presence of Kaposi's sarcoma-associated herpesvirus (KSHV/human herpesvirus 8). Despite having a genotype and gene expression signature of highly differentiated B cells, PEL does not usually express surface or cytoplasmic immunoglobulin (Ig). We show the lack of Oct-2 and OCA-B transcription factors to be responsible, at least in part, for this defect in Ig production. Like Ig genes, ORF50, the key regulator of the switch from latency to lytic reactivation, contains an octamer motif within its promoter. We therefore examined the impact of Oct-2 and OCA-B on ORF50 activation. The binding of Oct-1 to the ORF50 promoter has been shown to significantly enhance ORF50 transactivation. We found that Oct-2, on the other hand, inhibited ORF50 expression and consequently lytic reactivation by competing with Oct-1 for the octamer motif in the ORF50 promoter. Our data suggest that Oct-2 downregulation in infected cells would be favorable to KSHV in allowing for efficient viral reactivation

EBV LMP2A affects LMP1-mediated NF-κB signaling and survival of lymphoma cells by regulating TRAF2 expression

A mechanism used by Epstein-Barr virus (EBV) for in vitro transformation of B cells into lymphoblastoid cell lines (LCLs) is activation of the NF-κB pathway, which is largely mediated by the EBV latent membrane protein 1 (LMP1). LMP1 is coexpressed with LMP2A in many EBV-associated lymphoid malignancies. Since inhibition of NF-κB leads to apoptosis of EBV-infected LCLs and lymphoma cell lines, we sought to determine whether LMP1 alone, or in combination with other viral proteins, is responsible for initiating NF-κB activation in these cells, thereby playing a role in cell survival. We found that suppression of LMP1 by RNA interference results in inhibition of basal NF-κB and induction of apoptosis. Unexpectedly, knockdown of LMP2A also resulted in comparable decrease of NF-κB activity and apoptosis. We report that LMP2A protein controls the expression of TRAF2 mRNA, which in turn is necessary for signaling by LMP1. Our data contrast with previous studies showing that transfected LMP1 can signal in the absence of LMP2A or TRAF2, and demonstrate that both LMP2A and TRAF2 are required for survival in naturally infected lymphoma cells and LCLs. These results also support LMP1, LMP2A, and TRAF2 as potential therapeutic targets in a subset of EBV-associated lymphoid malignancies