The activity of transcription factor NFκB is regulated by its subcellular localization. In most cell types, NFκB is sequestered in the cytoplasm due to binding of the inhibitory protein IκBα. Stimulation of cells with a wide variety of agents results in degradation of IκBα, which allows translocation of NFκB to the nucleus. Degradation of IκBα is triggered by phosphorylation of two serine residues, i.e. Ser32 and Ser36, by as yet unknown kinases. Here we report that the mitogen‐activated 90 kDa ribosomal S6 kinase (p90rsk1) is an IκBα kinase. p90rsk1 phosphorylates IκBα at Ser32 and it physically associates with IκBα in vivo. Moreover, when the function of p90rsk1 is impaired by expression of a dominant‐negative mutant, IκBα degradation in response to mitogenic stimuli, e.g. 12‐O‐tetradecanoylphorbol 13‐acetate (TPA), is inhibited. Finally, NFκB cannot be activated by TPA in cell lines that have low levels of p90rsk1. We conclude that p90rsk1 is an essential kinase required for phosphorylation and subsequent degradation of IκBα in response to mitogens.

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Gene transfer to synovial tissue by adenoviral vectors (Ad) was studied in vitro in cultured human synoviocytes and in vivo in seven primates with arthritis. Hyperplastic synovium was efficiently transduced with Ad.lacZ in vitro and in vivo in rhesus monkeys with collagen-induced arthritis, whereas chondrocytes were not transduced. Intraarticular injection of recombinant Ad harboring the luciferase gene showed the presence of reporter gene products only in Ad-injected joints. In addition, the feasibility of synovectomy by Ad harboring the herpes simplex virus thymidine kinase gene (tk) was studied. In vitro infection of synovium from rheumatoid arthritis patients with Ad.TK, followed by administration of ganciclovir, resulted in death of >90% of the synoviocytes. By mixing Ad.TK-infected with noninfected cells, it appeared that the presence of 10% infected synoviocytes resulted in the killing of more than 85% of the synoviocytes, demonstrating a substantial bystander effect. Intraarticular injection of Ad.TK in the knees of rhesus monkeys with arthritis, followed by treatment with ganciclovir for 14 days, resulted in increased apoptotic cell death in the synovium of Ad.TK-injected as compared with noninjected joints and ablation of the synovial lining layer. The procedure revealed no toxic side effects. These data suggest that nonsurgical synovectomy by tK gene therapy is feasible.

We have previously demonstrated that expression of major histocompatibility complex (MHC) class I genes is repressed in baby rat kidney cells transformed by early region 1 of oncogenic adenovirus type 12 (Ad12E1). Reduced expression of MHC class I antigens contributes to the escape of Ad12‐transformed cells from T‐cell‐mediated immune surveillance and to tumour induction. In this study, we show that repression of MHC class I expression by Ad12E1A is mediated via the H2TF1 element of the MHC class I promoter. This element binds NF kappa B and KBF1, two factors which play a major role in the regulation of MHC class I expression in vivo. In extracts from Ad12E1‐transformed cells, binding of KBF1 and NF kappa B to the H2TF1 element is decreased. This is caused by reduced production of p50‐NF kappa B1, the 50 kDa subunit shared by KBF1 and NF kappa B, due to interference with p105‐NF kappa B1 processing by Ad12‐13S‐E1A protein. Overexpression of the p105‐NF kappa B1 cDNA, or of a truncated p105‐NF kappa B1 cDNA that codes for p50‐NF kappa B1, restores MHC class I expression in Ad12E1‐transformed cells. These data demonstrate that downregulation of MHC class I expression in Ad12E1‐transformed cells is due to interference with processing of p105‐NF kappa B1 by the Ad12‐13S‐E1A protein.