Drug targets in inflammation and immunomodulation

Signal transduction in inflammatory processes, current and future therapeutic targets: a mini review

The selective control of inflammatory reactions will continue to be a major issue in the development of new drugs. Many new molecular targets are coming up. This paper highlights a few key mediators that are nowadays considered as interesting therapeutic intervention points. Cytokines play an important regulatory role in the initiation, maintenance and termination of inflammatory reactions. More than 50 cytokines have been identified, and more and more has become known about their receptors and signal transduction pathways. Tumour necrosis factor-alpha (TNF-alpha) is still regarded as one of the initial cytokines of the cascade, and different approaches are followed to control its synthesis, release or effects. Lipopolysaccharide (LPS) is a one of the triggers that is able to induce a strong TNF-response. Inhibitors of cyclic nucleotide phosphodiesterases (PDEs), including rolipram and pentoxifylline suppress the LPS-induced TNF-alpha production in monocytes/macrophages. In our laboratory it has been shown that the alternative way to increase cAMP levels, via stimulation of beta-adrenergic receptors, also provides an effective way, both in vitro and in vivo, to inhibit TNF-alpha release. Other therapeutic ways include the use of antibodies directed to cytokines, TNF receptor fused to IgG, antibody therapy against TNF, the use of MAP kinase inhibitors. The different signal transduction pathways, including the NF-kappa B activation route may provide alternative pharmacological tools. We may surely expect anti-inflammatory drugs of much greater specificity to be developed in the next decade. Despite the relative limited investments in veterinary drug development this will also have consequences for veterinary therapy.

Assay for IkappaB kinases using an in vivo biotinylated IkappaB protein substrate

IkappaB kinases (IKK)-1 and -2 are related kinases that are induced by stimuli such as TNF or IL-1 to phosphorylate serines 32 and 36 of IkappaBalpha, the regulatory subunit of the transcription factor NF-kappaB. A procedure for an IKK protein kinase assay is described that uses an in vivo biotinylated IkappaB protein substrate, [gamma-(33)P]ATP, and capture onto a streptavidin membrane. Residues 1-54 of the IkappaBalpha substrate were expressed as a fusion with glutathione S-transferase (GST) and a short (22 amino acid) biotinylation sequence that allowed modification during bacterial expression. Using the streptavidin capture assay the phosphorylation activities of recombinant IKK-1 and -2 were characterized. The assay provided a convenient way to compare IKK protein and peptide substrate preferences; biotinylated GST-IkappaBalpha(1-54) was more readily phosphorylated by both IKK-1 and IKK-2 compared to biotinylated myelin basic protein or a 20-mer biotinylated peptide containing serines 32 and 36 of IkappaBalpha. IKK-1 had 83-fold less activity than IKK-2, and the IKK-1+2 complex had approximately 2-fold more activity than IKK-2. IKK-1+2 and IKK-2 had similar K(m) values for ATP and GST-biotin-IkappaB(1-54) and were similarly inhibited by staurosporine and two of its analogues K252a and K252b, suggesting that most of the IkappaBalpha kinase activity in the IKK-1+2 complex may be attributed to IKK-2. Several features of the assay including the broad linear binding range of the streptavidin membranes for the protein substrate GST-biotin-IkappaB(1-54) (1-4000 pmol of protein/cm(2)), the low background, and its capacity for both biotinylated peptides and proteins make it a useful tool for quantitating IKK activity. These factors and the ease of expressing in vivo biotinylated GST fusions will make this assay approach suitable for a wide variety of protein kinases.