TUMOR-NECROSIS-FACTOR-ALPHA INDUCES THE ADENOVIRUS EARLY 3-PROMOTER BY ACTIVATION OF NF-KAPPA-B

The early transcription unit 3 (E3) of human adenoviruses encodes prot eins which appear to subvert host defense mechanisms. For example, the E3/19K protein inhibits the transport of major histocompatibility com plex (MHC) class I molecules to the cell surface and thereby prevents cell lysis by cytotoxic T cells. Tumor necrosis factor alpha (TNF) sti mulates expression of MHC molecules on the cell surface of normal cell s but not of E3(+) cells, rather, a further reduction of MHC expressio n is evident. This was attributed to the increased expression of E3/19 K upon TNF treatment, an effect also observed for other E3 proteins. W e investigated the mechanism of the TNF-mediated up-regulation of E3 p roducts. We show that TNF stimulates expression of a luciferase report er gene driven by the E3 promoter. Mutation of individual transcriptio n factor binding sites within the E3 promoter reveals the importance o f the NF-kappa B binding site kappa 2 for TNF inducibility. Electropho retic mobility shift assays using antibodies directed against various members of the NF-kappa B family demonstrate that stimulation by TNF i s mediated by the p50-p65 NF-kappa B complex. TNF inducibility does no t depend on coexpression of E1A and can be observed during infection. Interestingly, the E3 promoter seems to be the only early promoter res ponsive to TNF and the only adenovirus promoter containing an NF-kappa B site. The implications of this regulatory mechanism for the adenovi rus life cycle and its pathogenesis are discussed.