Characterization of the transcriptional repressor RBP in Epstein-Barr virus-transformed B cells

A novel RBP-J kappa-dependent switch from C/EBP beta to C/EBP zeta at the C/EBP binding site on the C-reactive protein promoter

Regulation of basal and cytokine (IL-6 and IL-1beta)-induced expression of C-reactive protein (CRP) in human hepatoma Hep3B cells occurs during transcription. A critical transcriptional regulatory element on the CRP promoter is a C/EBP binding site overlapping a NF-kappaB p50 binding site. In response to IL-6, C/EBPbeta and p50 occupy the C/EBP-p50 site on the CRP promoter. The aim of this study was to identify the transcription factors occupying the C/EBP-p50 site in the absence of C/EBPbeta. Accordingly, we treated Hep3B nuclear extract with a C/EBP-binding consensus oligonucleotide to generate an extract lacking active C/EBPbeta. Such treated nuclei contain only C/EBPzeta (also known as CHOP10 and GADD153) because the C/EBP-binding consensus oligonucleotide binds to all C/EBP family proteins except C/EBPzeta. EMSA using this extract revealed formation of a C/EBPzeta-containing complex at the C/EBP-p50 site on the CRP promoter. This complex also contained RBP-Jkappa, a transcription factor known to interact with kappaB sites. RBP-Jkappa was required for the formation of C/EBPzeta-containing complex. The RBP-Jkappa-dependent C/EBPzeta-containing complexes were formed at the C/EBP-p50 site on the CRP promoter in the nuclei of primary human hepatocytes also. In luciferase transactivation assays, overexpressed C/EBPzeta abolished both C/EBPbeta-induced and (IL-6 + IL-1beta)-induced CRP promoter-driven luciferase expression. These results indicate that under basal conditions, C/EBPzeta occupies the C/EBP site, an action that requires RBP-Jkappa. Under induced conditions, C/EBPzeta is replaced by C/EBPbeta and p50. We conclude that the switch between C/EBPbeta and C/EBPzeta participates in regulating CRP transcription. This process uses a novel phenomenon, that is, the incorporation of RBP-Jkappa into C/EBPzeta complexes solely to support the binding of C/EBPzeta to the C/EBP site.

Pathogenic roles for Epstein-Barr virus (EBV) gene products in EBV-associated proliferative disorders

Epstein-Barr virus (EBV) is associated with a still growing spectrum of clinical disorders, ranging from acute and chronic inflammatory diseases to lymphoid and epithelial malignancies. Based on a combination of in vitro and in vivo findings, EBV is thought to contribute in the pathogenesis of these diseases. The different EBV gene expression patterns in the various disorders, suggest different EBV-mediated pathogenic mechanisms. In the following pages, an overview of the biology of EBV-infection is given and functional aspects of EBV-proteins are discussed and their putative role in the various EBV-associated disorders is described. EBV gene expression patterns and possible pathogenic mechanisms are discussed. In addition, expression of the cellular genes upregulated by EBV in vitro is discussed, and a comparison with the in vivo situation is made.