CD40 and LMP-1 both signal from lipid rafts but LMP-1 assembles a distinct, more efficient signaling complex

CD40, a member of the TNFR-1 receptor family, shares several features with LMP-1, an oncoprotein encoded by Epstein-Barr virus. CD40 and LMP-1 activat e transcription by binding to TRAFs, JAK3 and/or TRADD, CD40's association with CD40L activates signaling. However, LMP-1 signals independently of a l igand but dependently on self-association. We demonstrate that activated CD 40 and LMP-1 co-localize in lipid rafts and recruit TRAF3 there, findings c onsistent with signals of CD40 and LMP-1 being initiated from lipid rafts. To elucidate their signaling, we compared requirements for their aggregatio n and subcellular localization. Targeting CD40's monomeric C-terminal signa ling domain to lipid rafts activates signaling, as does rendering it trimer ic, Addition of both modifications supports signaling more efficiently. Par allel experiments with LMP-1 indicate that targeting the monomeric C-termin al signaling domain of LMP-1 to lipid rafts activates signaling, but trimer izing it does not. Fusing LMP-1's N-terminus and membrane-spanning domains to CD40's C-terminus supports signaling more efficiently than CD40 plus lig and or CD40's trimerized and/or localized derivatives. An activity of LMP-1 's N-terminus and membrane-spanning domains other than trimerization must c ontribute to its efficient signaling.