Direct and Indirect Regulation of Cytokine and Cell Cycle Proteins by EBNA-2 during Epstein-Barr Virus Infection

Abstract

We have studied the pathways of regulation of cytokine and cell cycle control proteins during infection of human B lymphocytes by Epstein-Barr virus (EBV). Among 30 cytokine RNAs analyzed by the RNase protection assay, tumor necrosis factor alpha (TNF-α), granulocyte colony-stimulating factor, lymphotoxin (LT), and LTβ were found to be regulated within 20 h of EBV infection of primary B cells. Similar results were obtained using the estrogen-regulated EBNA-2 cell line EREB2.5, in which RNAs for LT and TNF-α were induced within 6 h of activation of EBNA-2. Expression of Notch also caused an induction of TNF-α RNA. The induction of TNF-α RNA by EBNA-2 was indirect, and constitutive expression of either LMP-1 or c-myc proteins did not substitute for EBNA-2 in induction of TNF-α RNA. Cyclin D2 is also an indirect target of EBNA-2-mediated transactivation. EBNA-2 was found to activate the cyclin D2 promoter in a transient-transfection assay. A mutant of EBNA-2 that does not bind RBP-Jκ retained some activity in this assay, and activation did not depend on the presence of B-cell-specific factors. Deletion analysis of the cyclin D2 promoter revealed that removal of sequences containing E-box c-myc consensus DNA binding sequences did not reduce EBNA-2-mediated activation of the cyclin D2 promoter in the transient-transfection assay. The results indicate that cytokines are an early target of EBNA-2 and that EBNA-2 can regulate cyclin D2 transcription in EBV-infected cells by mechanisms additional to the c-myc pathway.