EPSTEIN-BARR-VIRUS-ENCODED LMP1 AND CD40 MEDIATE IL-6 PRODUCTION IN EPITHELIAL-CELLS VIA AN NF-KAPPA-B PATHWAY INVOLVING TNF RECEPTOR-ASSOCIATED FACTORS

Expression of the Epstein-Barr virus (EBV) transforming LMP1 in B cell s activates the transcription factor NF-kappa B and induces phenotypic changes through two distinct domains in the cytoplasmic C-terminus of the protein, The aa 187-231 domain of LMP1, which is important for gr owth transformation, binds tumour necrosis factor (TNF) receptor assoc iated factor (TRAF) 1 and TRAF3 and this interaction mediates subseque nt signalling events, The TRAFs also associate with CD40, a member of the TNFR family, which upon ligation activates NF-kappa B and induces phenotypic changes similar to those mediated by LMP1. This study demon strates that LMP1 expression in carcinoma cell lines and SV40-transfor med keratinocytes results in induction of the pleiotropic cytokine int erleukin 6 (IL6), an effect which is also observed upon CD40 Ligation. The mechanism by which either LMP1 expression or CD40 ligation induce s IL6 production was found to be NF-kappa B-dependent. Mutational anal ysis identified domains in the C-terminus of LMP1 which are important for NF-KB activation and IL6 secretion, LMP1 and CD40 share a common P xQxT core TRAF binding motif and mutations in or adjacent to this sequ ence impaired the ability of LMP1 or CD40 to induce NF-kappa B activat ion and IL6 secretion, The importance of TRAF interactions in mediatin g these effects was confirmed using dominant negative TRAF2 and TRAF3 mutants which also identified differences in the signalling events med iated by the two NF-kappa B activating domains of LMP1. A20, an anti-a poptotic protein which interacts with TRAF2 and blocks CD40-mediated N F-kappa B activity, also blocked NF-kappa B and IL6 secretion in LMP1- transfected epithelial cells, These results suggest that LMP1 regulate s IL6 production in epithelial cells in a manner similar to CD40 ligat ion and implicate TRAFs as common mediators in the transduction of sig nals generated via the CD40 and LMP1 pathways, As a role for IL6 in re gulating epithelial cell growth has previously been suggested, the con trol of IL6 secretion via the CD4O and LMP1 pathways may have implicat ions for the growth of both normal and transformed epithelial cells.