title: Inhibition of transforming growth factor beta signaling and Smad-dependent activation of transcription by the Latent Membrane Protein 1 of Epstein-Barr virus.
abstract: Inhibition of transforming growth factor beta (TGFbeta) signaling by the Epstein-Barr virus Latent Membrane Protein 1 (LMP1) may account, at least in part, for the oncogenic activity of LMP1. We found that LMP1 is a potent inhibitor of TGFbeta signaling and Smad-dependent activation of transcription in 293 epithelial cells and COS-7 fibroblasts. LMP1 strongly inhibited the uninduced and the Smad-inducible activity of the promoters of the human p21/WAF1/Cip1 gene and the mouse Smad7 gene. Inhibition of TGFbeta signaling and Smad-dependent activation of transcription by LMP1 was greatly reduced by deletion of both C-terminal activating regions 1 and 2 of LMP1 as well as by overexpression of a non-degradable form of IkappaB. In contrast, specific inhibitors of p38 kinase or MEK kinase did not reverse the inhibitory activity of LMP1. TGFbeta signaling was enhanced by overexpression of dominant negative forms of the LMP1 effectors TRAF2, NIK, and IKKbeta and was abolished by overexpression of p65/RelA or a p50/p65 fusion protein. Deletion of the transactivation domain of p65 abolished its inhibitory activity. Immunoblotting and immunofluorescence microscopy indicated that suppression of TGFbeta signaling and Smad transcriptional activity by LMP1 was not due to Smad degradation or cytoplasmic retention suggesting that LMP1 affects the nuclear function of Smad proteins. Our data are consistent with an essential role of NF-kappaB activation by LMP1 in the inhibition of TGFbeta signaling and Smad-mediated transcriptional responses.
authors.affiliation: Department of Basic Sciences, University of Crete Medical School and Institute of Molecular Biology and Biotechnology, Heraklion GR-71110, Greece.
authors.forename: Vassiliki
authors.initials: V
authors.lastname: Prokova
authors.forename: George
authors.initials: G
authors.lastname: Mosialos
authors.forename: Dimitris
authors.initials: D
authors.lastname: Kardassis
mesh_terms: D000818:Animals; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology; D005656:Fungal Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D016328:NF-kappa B / Q000737:chemistry / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D051785:Smad Proteins; D051900:Smad3 Protein; D015534:Trans-Activators / Q000037:antagonists & inhibitors* / Q000502:physiology; D014157:Transcription Factors / Q000037:antagonists & inhibitors*; D015533:Transcriptional Activation / Q000187:drug effects*; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors*; D014763:Viral Matrix Proteins / Q000494:pharmacology*
chemical_list: D004268:DNA-Binding Proteins; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D016328:NF-kappa B; C497790:SMAD3 protein, human; D029701:Saccharomyces cerevisiae Proteins; D051785:Smad Proteins; D051900:Smad3 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D014763:Viral Matrix Proteins