Backgrounds: Infection by virus or treatment with double-stranded RNA (dsRNA) results in the activation of transcription factors including IRF-3, IRF-7 and a pleiotropic regulator NF-kB by specific phosphorylation. These factors are important in triggering a cascade of antiviral responses. A protein kinase that is yet to be identified is responsible for the activation of these factors and plays a key role in the responses.

The candidate oncoprotein BCL‐3 has been shown to function as a transcriptional co‐activator for homodimers of NF‐κB p50 and p50B. We expressed BCL‐3 ectopically in pro‐B cell lines and found that these cells exhibited a dramatic increase in nuclear κB motif binding activity of p50 homodimers containing BCL‐3 in the complex. Co‐transfection and in vitro reconstitution experiments revealed that the complex of p50 with its precursor p105 (p50–p105), which was shown to accumulate in the cytoplasm of the pro‐B cell lines, is required for induction of DNA binding of p50 homodimers by BCL‐3. However, we could see no in vivo or in vitro evidence of a BCL‐3‐induced increase in proteolytic processing. Instead, BCL‐3‐mediated reorganization of NFKB1 subunits was demonstrated in vitro. Immunofluorescence staining clearly demonstrated that the transition from cytoplasmic p50–p105 to nuclear p50 homodimers was induced by BCL‐3 expression. Thus BCL‐3 has versatile functions: cytoplasmic activation of p50 homodimers, their nuclear translocation and, as previously shown, modulation of the transcriptional machinery in the nucleus.

Cellular genes including the type I interferon genes are activated in response to viral infection. We previously reported that IRF-3 (interferon regulatory factor 3) is specifically phosphorylated on serine residues and directly transmits a virus-induced signal from the cytoplasm to the nucleus, and then participates in the primary phase of gene induction. In this study, we analyzed the molecular mechanism of IRF-3 activation further. The formation of a stable homomeric complex of IRF-3 between the specifically phosphorylated IRF-3 molecules occurred. While virus-induced IRF-7 did not bind to p300, the phosphorylated IRF-3 complex formed a stable multimeric complex with p300 (active holocomplex). Competition using a synthetic phosphopeptide corresponding to the activated IRF-3 demonstrated that p300 directly recognizes the structure in the vicinity of the phosphorylated residues of IRF-3. These results indicated that the phosphorylation of serine residues at positions 385 and 386 is critical for the formation of the holocomplex, presumably through a conformational switch facilitating homodimer formation and the generation of the interaction interface with CBP/p300.

Hepatic insulin signalling involves insulin receptor substrates (Irs) 1/2, and is normally associated with the inhibition of gluconeogenesis and activation of lipogenesis. In diabetes and obesity, insulin no longer suppresses hepatic gluconeogenesis, while continuing to activate lipogenesis, a state referred to as ‘selective insulin resistance'. Here, we show that ‘selective insulin resistance' is caused by the differential expression of Irs1 and Irs2 in different zones of the liver. We demonstrate that hepatic Irs2-knockout mice develop ‘selective insulin resistance', whereas mice lacking in Irs1, or both Irs1 and Irs2, develop ‘total insulin resistance'. In obese diabetic mice, Irs1/2-mediated insulin signalling is impaired in the periportal zone, which is the primary site of gluconeogenesis, but enhanced in the perivenous zone, which is the primary site of lipogenesis. While hyperinsulinaemia reduces Irs2 expression in both the periportal and perivenous zones, Irs1 expression, which is predominantly in the perivenous zone, remains mostly unaffected. These data suggest that ‘selective insulin resistance' is induced by the differential distribution, and alterations of hepatic Irs1 and Irs2 expression.

Infections of bacteria and viruses induce host defense reactions known as innate responses that include the production of cytokines and chemokines. The production of type I interferon (IFN) is known to be induced by viral double-stranded (ds) RNA or bacterial lipopolysaccharide (LPS). Although important functions for the transcription factors NF-U UB and interferon regulatory factor-3 (IRF-3) are indicated, the molecular signals leading to the activation of IFN genes have yet to be elucidated. We provide several lines of evidence that LPS and dsRNA trigger distinct intracellular signals upstream. Notably, our investigation revealed a critical function for TIRAP/MAL, a signaling adapter for Toll-like receptor (TLR) 4, in LPS-induced but not dsRNA-induced activation of IRF-3. These results highlight cross-talk between TLR-mediated and virus/dsRNA-induced signals resulting in activation of the IFN system. ß