Two carboxyl-terminal activation regions of Epstein-Barr virus latent membrane protein 1 activate NF-κB through distinct signaling pathways in fibroblast cell lines

Latent membrane protein 1 ( LMP1), an Epstein- Barr virus transforming protein, is able to activate NF-kappaB 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-kappaB in different NF-kappaB essential modulator ( NEMO)- defective cell lines, but not in cells lacking both IkappaB kinase 1 ( IKK1) and 2 ( IKK2). Mutational studies reveal that CTAR1, but not CTAR2, mediates NEMO-independent NF-kappaB activation and that this process largely depends on IKK1. Retroviral expression of LMP1 mutants in cells lacking either functional NF-kappaB inducing kinase ( NIK), NEMO, IKK1, or IKK2 further illustrates distinct signals from the two activation regions of LMP1 for persistent NF-kappaB 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-kappaB through distinct signaling pathways.