Two Carboxyl-terminal Activation Regions of Epstein-Barr Virus Latent Membrane Protein 1 Activate NF-κB through Distinct Signaling Pathways in Fibroblast Cell Lines

Abstract

Latent membrane protein 1 (LMP1), an Epstein-Barr virus transforming protein, is able to activate NF-κB through its carboxyl-terminal activation region 1 (CTAR1) and 2 (CTAR2), but the exact role of each domain is not fully understood. Here we show that LMP1 activates NF-κB in different NF-κB essential modulator (NEMO)-defective cell lines, but not in cells lacking both IκB kinase 1 (IKK1) and 2 (IKK2). Mutational studies reveal that CTAR1, but not CTAR2, mediates NEMO-independent NF-κB activation and that this process largely depends on IKK1. Retroviral expression of LMP1 mutants in cells lacking either functional NF-κB inducing kinase (NIK), NEMO, IKK1, or IKK2 further illustrates distinct signals from the two activation regions of LMP1 for persistent NF-κB activation. One originates in CTAR2, operates through the canonical NEMO-dependent pathway, and induces NFKB2 p100 production; the second signal originates in CTAR1, utilizes NIK and IKK1, and induces the processing of p100. Our results thus help clarify how two functional domains of LMP1 persistently activate NF-κB through distinct signaling pathways.