Inken Lorenzen

Soluble Interleukin-15 Receptor α (IL-15Rα)-sushi as a Selective and Potent Agonist of IL-15 Action through IL-15Rβ/γ HYPERAGONIST IL-15·IL-15Rα FUSION PROTEINS

Interleukin-15 (IL-15) is crucial for the generation of multiple lymphocyte subsets (natural killer (NK), NK-T cells, and memory CD8 T cells), and transpresentation of IL-15 by monocytes and dendritic cells has been suggested to be the dominant activating process of these lymphocytes. We have previously shown that a natural soluble form of IL-15Rα chain corresponding to the entire extracellular domain of IL-15Rα behaves as a high affinity IL-15 antagonist. In sharp contrast with this finding, we demonstrate in this report that a recombinant, soluble sushi domain of IL-15Rα, which bears most of the binding affinity for IL-15, behaves as a potent IL-15 agonist by enhancing its binding and biological effects (proliferation and protection from apoptosis) through the IL-15Rβ/γ heterodimer, whereas it does not affect IL-15 binding and function of the tripartite IL-15Rα/β/γ membrane receptor. Our results suggest that, if naturally produced, such soluble sushi domains might be involved in the IL-15 transpresentation mechanism. Fusion proteins (RLI and ILR), in which IL-15 and IL-15Rα-sushi are attached by a flexible linker, are even more potent than the combination of IL-15 plus sIL-15Rα-sushi. After binding to IL-15Rβ/γ, RLI is internalized and induces a biological response very similar to the IL-15 high affinity response. Such hyper-IL-15 fusion proteins appear to constitute potent adjuvants for the expansion of lymphocyte subsets.

Inhibition of Classic Signaling Is a Novel Function of Soluble Glycoprotein 130 (sgp130), Which Is Controlled by the Ratio of Interleukin 6 and Soluble Interleukin 6 Receptor

Background: IL-6 trans-signaling plays a critical role in chronic inflammation and cancer. Results: The trans-signaling inhibitor sgp130(Fc) also inhibits classic signaling depending on IL-6/sIL-6R ratios. Conclusion: The additional function of sgp130(Fc) suggests that in vivo only low therapeutic concentrations guarantee blockade of trans-signaling but not classic signaling. Significance: The demonstration that the trans-signaling inhibitor can also inhibit classic signaling is central for the field of IL-6 biology. IL-6 trans-signaling via the soluble IL-6 receptor (sIL-6R) plays a critical role in chronic inflammation and cancer. Soluble gp130 (sgp130) specifically inhibits IL-6 trans-signaling but was described to not interfere with classic signaling via the membrane-bound IL-6R. Physiological and most pathophysiological conditions are characterized by a molar excess of serum sIL-6R over IL-6 characterized by free IL-6 and IL-6 found in IL-6·sIL-6R complexes allowing both classic and trans-signaling. Surprisingly, under these conditions, sgp130 was able to trap all free IL-6 molecules in IL-6·sIL-6R·sgp130 complexes, resulting in inhibition of classic signaling. Because a significant fraction of IL-6 molecules did not form complexes with sIL-6R, our results demonstrate that compared with the anti-IL-6R antibody tocilizumab or the anti-trans-signaling monoclonal antibody 25F10, much lower concentrations of the dimeric sgp130Fc were sufficient to block trans-signaling. In vivo, sgp130Fc blocked IL-6 signaling in the colon but not in liver and lung, indicating that the colon is a prominent target of IL-6 trans-signaling. Our results point to a so far unanticipated role of sgp130 in the blockade of classic signaling and indicate that in vivo only low therapeutic concentrations of sgp130Fc guarantee blockade of IL-6 trans-signaling without affecting IL-6 classic signaling.

An Interleukin-6 Receptor-dependent Molecular Switch Mediates Signal Transduction of the IL-27 Cytokine Subunit p28 (IL-30) via a gp130 Protein Receptor Homodimer

Background: Anti-inflammatory signaling of IL-27, p28, and EBI3 is mediated by gp130 and Wsx-1. Results: Signaling of p28 via IL-6R is mediated by a gp130 homodimer. Conclusion: Signaling of p28 via IL-6R is likely not anti-inflammatory. Significance: We identify the signal receptor complex of p28/IL-6R. IL-27 consists of the cytokine subunit p28 and the non-signaling α-receptor EBI3. p28 was shown to additionally act via the non-signaling membrane-bound IL-6 α-receptor (IL-6R) as an agonistic cytokine but also as a gp130 β-receptor antagonist, leading to inhibition of IL-6 signaling. Here, we developed a strategy for bacterial expression, purification, and refolding of murine p28. We show that p28 did not interfere with IL-6- or IL-27-induced signaling, indicating that p28 has no antagonistic properties. Moreover, we demonstrate that murine p28 acts as an agonistic cytokine via the murine and human IL-6R, indicating that p28 exhibits no species specificity. p28 was able to induce p28-trans-signaling via the soluble IL-6R (sIL-6R), a characteristic property that was initially described for trans-signaling of IL-6 via the sIL-6R. Of notice, p28/sIL-6R trans-signaling was inhibited by the IL-6 trans-signaling antagonist, soluble gp130. At higher concentrations, p28 but not IL-6 was able to induce signaling even in the absence of IL-6R or EBI3. Although IL-27 signals via a heterodimer of the β-receptor chains gp130 and Wsx-1, p28/IL-6R specifically recruits two gp130 β-receptor chains for signal transduction. The binding of p28 to a gp130/Wsx-1 heterodimer or a gp130 homodimer is highly selective and controlled by a novel molecular switch induced by EBI3 or IL-6R, respectively.

Membrane-proximal domain of a disintegrin and metalloprotease-17 represents the putative molecular switch of its shedding activity operated by protein-disulfide isomerase.

A disintegrin and metalloprotease-17 (ADAM17) is a major sheddase responsible for the regulation of a wide range of biological processes, like cellular differentiation, regeneration, or cancer progression. Hitherto, the mechanism regulating the enzymatic activity of ADAM17 is poorly understood. Recently, protein-disulfide isomerase (PDI) was shown to interact with ADAM17 and to down-regulate its enzymatic activity. Here we demonstrate by NMR spectroscopy and tandem-mass spectrometry that PDI directly interacts with the membrane-proximal domain (MPD), a domain of ADAM17 involved in its dimerization and substrate recognition. PDI catalyzes an isomerization of disulfide bridges within the thioredoxin motif C600XXC603 of the MPD and results in a drastic structural change between an active open state and an inactive closed conformation. This conformational change of the MPD putatively acts as a molecular switch, facilitating a global reorientation of the extracellular domains in ADAM17 and regulating its shedding activity.

Interleukin-6 receptor specific RNA aptamers for cargo delivery into target cells

Aptamers represent an emerging strategy to deliver cargo molecules, including dyes, drugs, proteins or even genes, into specific target cells. Upon binding to specific cell surface receptors aptamers can be internalized, for example by macropinocytosis or receptor mediated endocytosis. Here we report the in vitro selection and characterization of RNA aptamers with high affinity (Kd = 20 nM) and specificity for the human IL-6 receptor (IL-6R). Importantly, these aptamers trigger uptake without compromising the interaction of IL-6R with its natural ligands the cytokine IL-6 and glycoprotein 130 (gp130). We further optimized the aptamers to obtain a shortened, only 19-nt RNA oligonucleotide retaining all necessary characteristics for high affinity and selective recognition of IL-6R on cell surfaces. Upon incubation with IL-6R presenting cells this aptamer was rapidly internalized. Importantly, we could use our aptamer, to deliver bulky cargos, exemplified by fluorescently labeled streptavidin, into IL-6R presenting cells, thereby setting the stage for an aptamer-mediated escort of drug molecules to diseased cell populations or tissues.

Multimerisation of A disintegrin and metalloprotease protein-17 (ADAM17) is mediated by its EGF-like domain.

A disintegrin and metalloprotease protein 17 (ADAM17) is a transmembrane zinc dependent metalloprotease. The catalytic activity of the enzyme results in the shedding of a broad range of membrane proteins. The release of the corresponding ectodomains induces a switch in various physiological and pathophysiological processes. So far there is not much information about the molecular mechanism of ADAM17 activation available. As for other transmembrane proteases, multimerisation may play a critical role in the activation and function of ADAM17. The present work demonstrates that ADAM17 indeed exists as a multimer in the cell membrane and that this multimerisation is mediated by its EGF-like domain.

Human β-Defensin 2 and β-Defensin 3 Chimeric Peptides Reveal the Structural Basis of the Pathogen Specificity of Their Parent Molecules

ABSTRACT Despite partial sequence identity and structural similarity, human β-defensin 3 (HBD3) kills Staphylococcus aureus with a 4- to 8-fold higher efficiency than human β-defensin 2 (HBD2), whereas the activities against Escherichia coli are identical. The design and characterization of HBD2/HBD3 chimeric peptides revealed that distinct molecular regions are responsible for their divergent killing properties. Two of the chimeras killed both E. coli and S. aureus with an even higher efficacy than the wild-type molecules. Moreover, one of these two chimeras maintained its high killing activities in the presence of physiologic salt concentrations. Due to the broad spectrum of their antimicrobial activities against many human multidrug-resistant pathogens, these two designer peptides of human origin represent promising templates for a new class of antibiotics.

The structure of the interleukin-15 alpha receptor and its implications for ligand binding.

Interleukin (IL)-15 is a member of the small four α-helix bundle family of cytokines. IL-15 was discovered by its ability to mimic IL-2-mediated T-cell proliferation. Both cytokines share the β and γ receptor chains of the IL-2 receptor for signal transduction. However, in addition, they target specific α chain receptors IL-15Rα and IL-2Rα, respectively. The exceptionally high affinity binding of IL-15 to IL-15Rα is mediated by its sushi domain. Here we present the solution structure of the IL-15Rα sushi domain solved by NMR spectroscopy and a model of its complex with IL-15. The model shows that, rather than the familiar hydrophobic forces dominating the interaction interface between cytokines and their cognate receptors, the interaction between the IL-15 and IL-15Rα complex involves a large network of ionic interactions. This type of interaction explains the exceptionally high affinity of the IL-15·IL-15Rα complex, which is essential for the biological effects of this important cytokine and which is not observed in other cytokine/cytokine receptor complexes.

A novel bispecific single-chain antibody for ADAM17 and CD3 induces T-cell-mediated lysis of prostate cancer cells

ADAM17 (A disintegrin and metalloproteinase 17) is a membrane-bound protease that cleaves various cell surface proteins, including cytokines and cytokine receptors. Recently it was shown that ADAM17 is highly expressed on the surface of many cancer cells, whereas normal cells express low levels of ADAM17, implying that ADAM17 is a potential immunotherapeutic target. We have generated a monoclonal antibody against human ADAM17, which recognized the membrane proximal cysteine-rich extension of the ADAM17 protein. Unlike normal cells, tumour cell lines, such as a prostate cancer cell line, pancreatic cancer cell lines, a breast cancer cell line and a non-small lung cancer cell line, expressed ADAM17 on the cell surface. Using the sequence of the antibody we generated an ADAM17-specific scFv (single-chain variable fragment) and fused this to a CD3-specific scFv to generate a bispecific T-cell engager antibody [A300E-BiTE (bispecific T-cell engager antibody)]. Specificity was demonstrated on cells in which ADAM17 was knocked down with a specific shRNA (short hairpin RNA). A300E-BiTE recognized ADAM17 and CD3 on the cell surface of tumour cells and T-cells respectively. In the presence of primary human peripheral blood mononuclear cells or human T-cells the addition of A300E-BiTE led to ADAM17-specific killing of prostate tumour cells indicating a novel strategy for the treatment of cancer.

A disintegrin and metalloprotease 17 dynamic interaction sequence, the sweet tooth for the human interleukin 6 receptor.

Background: A disintegrin and metalloprotease 17 (ADAM17) releases many proinflammatory mediators. Results: The conserved ADAM seventeen dynamic interaction sequence (CANDIS) mediates effective substrate binding and is controlled by the disulfide-regulated conformation of the preceding membrane-proximal domain (MPD). Conclusion: CANDIS, together with the MPD, represents a novel key regulatory element. Significance: We investigate the molecular details of a novel kind of regulation. A disintegrin and metalloprotease 17 (ADAM17) is a major sheddase involved in the regulation of a wide range of biological processes. Key substrates of ADAM17 are the IL-6 receptor (IL-6R) and TNF-α. The extracellular region of ADAM17 consists of a prodomain, a catalytic domain, a disintegrin domain, and a membrane-proximal domain as well as a small stalk region. This study demonstrates that this juxtamembrane segment is highly conserved, α-helical, and involved in IL-6R binding. This process is regulated by the structure of the preceding membrane-proximal domain, which acts as molecular switch of ADAM17 activity operated by a protein-disulfide isomerase. Hence, we have termed the conserved stalk region “Conserved ADAM seventeen dynamic interaction sequence” (CANDIS). Finally, we identified the region in IL-6R that binds to CANDIS. In contrast to the type I transmembrane proteins, the IL-6R, and IL-1RII, CANDIS does not bind the type II transmembrane protein TNF-α, demonstrating fundamental differences in the respective shedding by ADAM17.