LMP1 Transmembrane Domain 1 and 2 (TM1-2) FWLY Mediates Intermolecular Interactions with TM3-6 To Activate NF-κB

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Abstract
The Epstein-Barr virus oncoprotein LMP1 has six transmembrane domains (TMs) that enable intermolecular aggregation and constitutive signaling through two C-terminal cytosolic domains. Expression of both TMs 1 and 2 without the C terminus (TM1-2ΔC) and TMs 3 to 6 fused to the C terminus (TM3-6) results in partial association, which is substantially decreased by TM1 F 38 WLY 41 mutation to A 38 ALA 41 . We now investigate whether TM1-2ΔC can functionally interact with TM3-6. TM1-2ΔC induced TM3-6 to mediate NF-κB activation at 59% of LMP1 levels, and the effect was dependent on TM1-2 F 38 WLY 41 . TM1-2ΔC even induced TM3-4 C terminus-mediated NF-κB activation to 44% of LMP1 levels. Surprisingly, this effect was TM1 F 38 WLY 41 independent, indicative of a role for TMs 5 and 6 in TM1 F 38 WLY 41 effects. TM3 W 98 was also important for TM1-2ΔC induction of TM3-6-mediated NF-κB activation, for association, and for TM1 F 38 WLY 41 dependence on C-terminal NF-κB activation. These data support models in which the TM1 F 38 WLY 41 effects are at least partially dependent on TM3 W 98 and a residue(s) in TMs 5 and 6.