Development of human IL-6 receptor antagonists

Interleukin-6 N-terminal peptides modulate the expression of junB protooncogene and the production of fibrinogen in HepG2 cells

Interleukin-6 (IL-6) is a helical cytokine exerting pleiotropic activities including the regulation of hematopoiesis, B cell activation and acute-phase reaction. The structure-function relationship of the molecule is the subject of intensive investigation using point and deletion mutants. Our objective was to analyse the role of the N-terminal 18-46 region in IL-6-mediated expression of junB protooncogene and fibrinogen production, reflecting the acute phase response, with synthetic overlapping peptides. mRNA expression of junB was monitored by competitive RT-PCR, while sandwich ELISA was used for the detection of fibrinogen in the supernatant of HepG2 human hepatoma cells. We found that even short synthetic octapeptides can be stimulatory (in the absence of IL-6) or inhibitory (in the presence of IL-6) in both assays. To establish the molecular mechanism by which synthetic peptides exert their biological effects electromobility shift assay was carried out using HepG2 nuclear extracts. Peptides inducing junB expression initiate gel shifts of STAT3/DNA complexes, which may indicate the involvement of this signal transduction pathway. Circular dicroism spectroscopy data suggest that 8-11-mer peptides representing different parts of the 18-46 region have a marked tendency to adopt ordered conformations in a water/trifluoroethanol (1:1 v/v) mixture. Competition studies with rhIL-6 and selected fluorophore-labelled peptides indicate the presence of more than one binding site on soluble IL-6 receptor. Considering the possible multiple etiologic role of IL-6 in the pathogenesis of various diseases, these peptides could be useful for dissection of IL-6 related biological effects.

Solution structure of recombinant human interleukin-6

Interleukin-6 (IL-6) is a 185 amino acid cytokine which exerts multiple biological effects in vivo and whose dysregulation underlies several disease processes. The solution structure of recombinant human interleukin-6 has now been determined using heteronuclear three and four-dimensional NMR spectroscopy. The structure of the molecule was determined using 3044 distance and torsion restraints derived by NMR spectroscopy to generate an ensemble of 32 structures using a combined distance geometry/simulated annealing protocol. The protein contains five alpha-helices interspersed with variable-length loops; four of these helices constitute a classical four-helix bundle with the fifth helix located in the CD loop. There were no distance violations greater than 0.3 A in any of the final 32 structures and the ensemble has an average-to-the-mean backbone root-mean-square deviation of 0.50 A for the core four-helix bundle. Although the amino-terminal 19 amino acids are disordered in solution, the remainder of the molecule has a well defined structure that shares many features displayed by other long-chain four-helix bundle cytokines. The high-resolution NMR structure of hIL-6 is used to rationalize available mutagenesis data in terms of a heteromeric receptor complex.

Identification of residues in the putative 5th helical region of human interleukin-6, important for activation of the IL-6 signal transducer, gp130

We have previously shown that L58 in the putative 5th helical region of human interleukin-6 (IL-6) is important for activation of the IL-6 signal transducer gp130 [de Hon et al. (1995) FEBS Lett. 369, 187-191]. To further explore the importance of individual residues in this region for gp130 activation we have now combined Ala substitutions of residues E52, S53, S54, K55, E56, L58 and E60 with other substitutions in IL-6, known to affect gp130 activation (Q160E and T163P). The combination mutant protein with L58A completely lost the capacity to induce the proliferation of XG-1 myeloma cells, and could effectively antagonize wild type IL-6 activity on these cells. Moreover, the data suggest that besides L58, S54 particularly, but also E52, S53, K55 and E56 contribute to gp130 activation.