Jun N-terminal kinase (JNK) is a stress-activated protein kinase that can be induced by inflammatory cytokines, bacterial endotoxin, osmotic shock, UV radiation, and hypoxia. We report the identification of an anthrapyrazolone series with significant inhibition of JNK1, -2, and -3 (K i ‫؍‬ 0.19 M). SP600125 is a reversible ATPcompetitive inhibitor with >20-fold selectivity vs. a range of kinases and enzymes tested. In cells, SP600125 dose dependently inhibited the phosphorylation of c-Jun, the expression of inflammatory genes COX-2, IL-2, IFN-␥, TNF-␣, and prevented the activation and differentiation of primary human CD4 cell cultures. In animal studies, SP600125 blocked (bacterial) lipopolysaccharideinduced expression of tumor necrosis factor-␣ and inhibited anti-CD3-induced apoptosis of CD4 ؉ CD8 ؉ thymocytes. Our study supports targeting JNK as an important strategy in inflammatory disease, apoptotic cell death, and cancer.

Activation of the transcription factor nuclear factor kappa B (NF-kappaB) is controlled by sequential phosphorylation, ubiquitination, and degradation of its inhibitory subunit IkappaB. A large multiprotein complex, the IkappaB kinase (IKK) signalsome, was purified from HeLa cells and found to contain a cytokine-inducible IkappaB kinase activity that phosphorylates IkappaB-alpha and IkappaB-beta. Two components of the IKK signalsome, IKK-1 and IKK-2, were identified as closely related protein serine kinases containing leucine zipper and helix-loop-helix protein interaction motifs. Mutant versions of IKK-2 had pronounced effects on RelA nuclear translocation and NF-kappaB-dependent reporter activity, consistent with a critical role for the IKK kinases in the NF-kappaB signaling pathway.

Interleukin-1 (IL-1) and tumor necrosis factor (TNF-␣

Activation of the transcription factor NF-B is controlled by the sequential phosphorylation, ubiquitination, and degradation of its inhibitory subunit, IB. We recently purified a large multiprotein complex, the IB kinase (IKK) signalsome, which contains two regulated IB kinases, IKK1 and IKK2, that can each phosphorylate IB␣ and IB␤. The IKK signalsome contains several additional proteins presumably required for the regulation of the NFB signal transduction cascade in vivo. In this report, we demonstrate reconstitution of IB kinase activity in vitro by using purified recombinant IKK1 and IKK2. Recombinant IKK1 or IKK2 forms homo-or heterodimers, suggesting the possibility that similar IKK complexes exist in vivo. Indeed, in HeLa cells we identified two distinct IKK complexes, one containing IKK1-IKK2 heterodimers and the other containing IKK2 homodimers, which display differing levels of activation following tumor necrosis factor alpha stimulation. To better elucidate the nature of the IKK signalsome, we set out to identify IKK-associated proteins. To this end, we purified and cloned a novel component common to both complexes, named IKKassociated protein 1 (IKKAP1). In vitro, IKKAP1 associated specifically with IKK2 but not IKK1.