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TRADD Domain of Epstein-Barr Virus Transforming Protein LMP1 Is Essential for Inducing Immortalization and Suppressing Senescence of Primary Rodent Fibroblasts

ABSTRACT Mutation analysis of latent membrane protein 1 (LMP1) in Epstein-Barr virus (EBV)-induced B-cell immortalization revealed two transformation effector sites, TES1 and TES2. TES2 mediates the interaction with tumor necrosis factor receptor-associated death domain protein (TRADD) and plays a key role in transactivating NF-κB and AP-1. Recombinant EBV containing LMP1 with TES2 deleted induces a limited proliferation of B cells. The present study shows that a mutant with an LMP1 site-specific mutation at TES2, LMP1TRADD, initially stimulates cell growth and significantly extends the life span of MEF. However, it is not sufficient for the immortalization of MEF, and MEF-LMP1TRADD cells eventually enter growth arrest. Further analysis reveals that although LMP1TRADDpromotes cell growth, it does not prevent the eventual onset of senescence and the expression of tumor suppressor p16Ink4a.