Epstein-Barr Virus Latent Membrane Protein 1 Modulates Distinctive NF-κB Pathways through C-Terminus-Activating Region 1 To Regulate Epidermal Growth Factor Receptor Expression

Abstract

ABSTRACT Epstein-Barr Virus (EBV) latent membrane protein 1 (LMP1) is required for EBV B-lymphocyte transformation, transforms rodent fibroblasts, and can induce lymphoma and epithelial hyperplasia in transgenic mice. Two domains have been identified within the intracellular carboxy terminus that can activate NF-κB, C-terminus-activating region 1 (CTAR1) and CTAR2, through interactions with tumor necrosis receptor-associated factors (TRAFs). CTAR1 can activate both the canonical and noncanonical NF-κB pathways and has unique effects on cellular gene expression. The epidermal growth factor receptor (EGFR) is highly induced by LMP1-CTAR1 in epithelial cells through activation of a novel NF-κB form containing p50 homodimers and Bcl-3. To further understand the regulation of NF-κB in CTAR1-induced EGFR expression, we evaluated the ability of CTAR1 to induce EGFR in mouse embryonic fibroblasts (MEFs) defective for different NF-κB effectors. CTAR1-mediated EGFR induction required the N F-κB- i nducing k inase (NIK) but not the IκB kinase (IKK) complex components that regulate canonical or noncanonical NF-κB pathways. CTAR1-mediated induction of nuclear p50 occurred in IKKβ-, IKKγ-, and NIK-defective MEFs, indicating that this induction is not dependent on the canonical or noncanonical NF-κB pathways. EGFR and nuclear p50 were expressed at high levels in TRAF2 −/− fibroblasts and were not induced by CTAR1. In TRAF3 −/− MEFs, CTAR1 induced nuclear p50 but did not affect basal levels of STAT3 serine phosphorylation or induce EGFR expression. EGFR was induced by LMP1 in TRAF6 −/− MEFs. These findings suggest that this novel NF-κB pathway is differentially regulated by TRAF2 and TRAF3, and that distinct interactions of LMP1 and its effectors regulate LMP1-mediated gene expression.