The residues between the two transformation effector sites of Epstein-Barrvirus latent membrane protein 1 are not critical for B-lymphocyte growth transformation

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) is essential for EBV-mediated transformation of primary B lymphocytes. LMP1 spontaneously ag gregates in the plasma membrane and enables two transformation effector sit es (TES1 and TES2) within the 200-amino acid cytoplasmic carboxyl terminus to constitutively engage the tumor necrosis factor receptor (TNFR)-associat ed factors TRAF1, TRAF2, TRAF3, and TRAF5 and the TNFR-associated death dom ain proteins TRADD and RIP, thereby activating NF-kappa B and c-Jun N-termi nal kinase (JNK). To investigate the importance of the 60% of the LMP1 carb oxyl terminus that lies between the TES1-TRAF and TES2-TRADD and -RIP bindi ng sites, an EBV recombinant was made that contains a specific deletion of LMP1 codons 232 to 351. Surprisingly, the deletion mutant was similar to wi ldtype (wt) LMP1 EBV recombinants in its efficiency in transforming primary B lymphocytes into lymphoblastoid cell Lines (LCLs). Mutant and wt EBV-tra nsformed LCLs were similarly efficient in long-term outgrowth and in regrow th after endpoint dilution. Mutant and wt LMP1 proteins were also similar i n their constitutive association with TRAF1, TRAF2, TRAF3, TRADD, and RIP. Mutant and wt EBV-transformed LCLs were similar in steady-state levels of B cl2, JNK and activated JNK proteins. The wt phenotype of recombinants with LMP1 codons 232 to 351 deleted further demarcates TES1 and TES2, underscore s their central importance in B-lymphocyte growth transformation and provid es a new perspective on LMP1 sequence variation between TES1 and TES2.