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 activate transcription by binding to TRAFs, JAK3 and/or TRADD. CD40's association with CD40L activates signaling. However, LMP-1 signals independently of a ligand but dependently on self-association. We demonstrate that activated CD40 and LMP-1 co-localize in lipid rafts and recruit TRAF3 there, findings consistent with signals of CD40 and LMP-1 being initiated from lipid rafts. To elucidate their signaling, we compared requirements for their aggregation and subcellular localization. Targeting CD40's monomeric C-terminal signaling domain to lipid rafts activates signaling, as does rendering it trimeric. Addition of both modifications supports signaling more efficiently. Parallel experiments with LMP-1 indicate that targeting the monomeric C-terminal signaling domain of LMP-1 to lipid rafts activates signaling, but trimerizing 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 ligand or CD40's trimerized and/or localized derivatives. An activity of LMP-1's N-terminus and membrane-spanning domains other than trimerization must contribute to its efficient signaling.
Kaykas
A
A
McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, WI 53706, USA.
Worringer
K
K
Sugden
B
B
D048868:Adaptor Proteins, Signal Transducing; D001402:B-Lymphocytes; D001665:Binding Sites; D019013:CD40 Antigens / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D023201:CD40 Ligand / Q000494:pharmacology / Q000502:physiology; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002461:Cell Line, Transformed; D003598:Cytoskeletal Proteins; D004854:Herpesvirus 4, Human; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; D021962:Membrane Microdomains / Q000502:physiology*; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D048008:TNF Receptor-Associated Factor 3; D014162:Transfection; D016335:Zinc Fingers
D048868:Adaptor Proteins, Signal Transducing; D019013:CD40 Antigens; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; C484380:PDLIM7 protein, human; D011506:Proteins; D011994:Recombinant Proteins; D048008:TNF Receptor-Associated Factor 3; D023201:CD40 Ligand