title: Transmembrane domains 1 and 2 of the latent membrane protein 1 of Epstein-Barr virus contain a lipid raft targeting signal and play a critical role in cytostasis.
abstract: The latent membrane protein 1 (LMP-1) oncoprotein of Epstein-Barr virus (EBV) is a constitutively active, CD40-like cell surface signaling protein essential for EBV-mediated human B-cell immortalization. Like ligand-activated CD40, LMP-1 activates NF-kappaB and Jun kinase signaling pathways via binding, as a constitutive oligomer, to tumor necrosis factor receptor-associated factors (TRAFs). LMP-1's lipid raft association and oligomerization have been linked to its activation of cell signaling pathways. Both oligomerization and lipid raft association require the function of LMP-1's polytopic multispanning transmembrane domain, a domain that is indispensable for LMP-1's growth-regulatory signaling activities. We have begun to address the sequence requirements of the polytopic hydrophobic transmembrane domain for LMP-1's signaling and biochemical activities. Here we report that transmembrane domains 1 and 2 are sufficient for LMP-1's lipid raft association and cytostatic activity. Transmembrane domains 1 and 2 support NF-kappaB activation, albeit less potently than does the entire polytopic transmembrane domain. Interestingly, LMP-1's first two transmembrane domains are not sufficient for oligomerization or TRAF binding. These results suggest that lipid raft association and oligomerization are mediated by distinct and separable activities of LMP-1's polytopic transmembrane domain. Additionally, lipid raft association, mediated by transmembrane domains 1 and 2, plays a significant role in LMP-1 activation, and LMP-1 can activate NF-kappaB via an oligomerization/TRAF binding-independent mechanism. To our knowledge, this is the first demonstration of an activity's being linked to individual membrane-spanning domains within LMP-1's polytopic transmembrane domain.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: William F
authors.initials: WF
authors.lastname: Coffin
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Geiger
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Martin
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D019281:Dimerization; D017353:Gene Deletion; D005786:Gene Expression Regulation; D004854:Herpesvirus 4, Human / Q000472:pathogenicity* / Q000502:physiology; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D015398:Signal Transduction; D015533:Transcriptional Activation; D014763:Viral Matrix Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: C037662:EBV-associated membrane antigen, Epstein-Barr virus; D016328:NF-kappa B; D014763:Viral Matrix Proteins