Disulfide bond assignment in human interleukin-7 by matrix-assisted laser desorption/ionization mass spectroscopy and site-directed cysteine to serine mutational analysis

In what area of biology has a "new" type of cell death been discovered?

Cell death is a fundamental physiological process that occurs in all organisms and is crucial to each organism's evolution, ability to maintain a stable internal environment, and the development of multiple organ systems. Disulfidptosis is a new mode of cell death that is triggered when cells with high expression of solute carrier family 7 member 11 (SLC7A11) are exposed to glucose starvation to initiate the process of cell death. The disulfidptosis mechanism is a programmed cell death mode that triggers cell death through reduction-oxidation (REDOX) reactions and disulfur bond formation. In disulfidptosis, disulfur bonds play a crucial role and cause the protein in the cell to undergo conformational changes, eventually leading to cell death. This mode of cell death has unique characteristics and regulatory mechanisms in comparison with other modes of cell death. In recent years, an increasing number of studies have shown that the disulfidptosis mechanism plays a key role in the occurrence and development of a variety of diseases. For example, cancer, cardiovascular diseases, neurodegenerative diseases, and liver diseases are all closely related to cell disulfidptosis mechanisms. Therefore, it is of paramount clinical significance to conduct in-depth research regarding this mechanism. This review summarizes the research progress on the disulfidptosis mechanism, including its discovery history, regulatory mechanism, related proteins, and signaling pathways. Potential applications of the disulfidptosis mechanism in disease therapy and future research directions are also discussed. This mechanism represents another subversive discovery after ferroptosis, and provides both a fresh perspective and an innovative strategy for the treatment of cancer, as well as inspiration for the treatment of other diseases.

Modulation of Signaling Mediated by TSLP and IL-7 in Inflammation, Autoimmune Diseases, and Cancer

Thymic Stromal Lymphopoietin (TSLP) and Interleukin-7 (IL-7) are widely studied cytokines within distinct branches of immunology. On one hand, TSLP is crucially important for mediating type 2 immunity at barrier surfaces and has been linked to widespread allergic and inflammatory diseases of the airways, skin, and gut. On the other hand, IL-7 operates at the foundations of T-cell and innate lymphoid cell (ILC) development and homeostasis and has been associated with cancer. Yet, TSLP and IL-7 are united by key commonalities in their structure and the structural basis of the receptor assemblies they mediate to initiate cellular signaling, in particular their cross-utilization of IL-7Rα. As therapeutic targeting of TSLP and IL-7 via diverse approaches is reaching advanced stages and in light of the plethora of mechanistic and structural data on receptor signaling mediated by the two cytokines, the time is ripe to provide integrated views of such knowledge. Here, we first discuss the major pathophysiological roles of TSLP and IL-7 in autoimmune diseases, inflammation and cancer. Subsequently, we curate structural and mechanistic knowledge about receptor assemblies mediated by the two cytokines. Finally, we review therapeutic avenues targeting TSLP and IL-7 signaling. We envision that such integrated view of the mechanism, structure, and modulation of signaling assemblies mediated by TSLP and IL-7 will enhance and fine-tune the development of more effective and selective approaches to further interrogate the role of TSLP and IL-7 in physiology and disease.

Essential cell-extrinsic requirement for PDIA6 in lymphoid and myeloid development

In a forward genetic screen of N-ethyl-N-nitrosourea (ENU)–induced mutant mice for aberrant immune function, we identified mice with a syndromic disorder marked by growth retardation, diabetes, premature death, and severe lymphoid and myeloid hypoplasia together with diminished T cell–independent (TI) antibody responses. The causative mutation was in Pdia6, an essential gene encoding protein disulfide isomerase A6 (PDIA6), an oxidoreductase that functions in nascent protein folding in the endoplasmic reticulum. The immune deficiency caused by the Pdia6 mutation was, with the exception of a residual T cell developmental defect, completely rescued in irradiated wild-type recipients of PDIA6-deficient bone marrow cells, both in the absence or presence of competition. The viable hypomorphic allele uncovered in these studies reveals an essential role for PDIA6 in hematopoiesis, but one extrinsic to cells of the hematopoietic lineage. We show evidence that this role is in the proper folding of Wnt3a, BAFF, IL-7, and perhaps other factors produced by the extra-hematopoietic compartment that contribute to the development and lineage commitment of hematopoietic cells.

Isoform-specific domain organization determines conformation and function of the peroxisomal biogenesis factor PEX26

Peroxisomal biogenesis factor PEX26 is a membrane anchor for the multi-subunit PEX1-PEX6 protein complex that controls ubiquitination and dislocation of PEX5 cargo receptors for peroxisomal matrix protein import. PEX26 associates with the peroxisomal translocation pore via PEX14 and a splice variant (PEX26Δex5) of unknown function has been reported. Here, we demonstrate PEX26 homooligomerization mediated by two heptad repeat domains adjacent to the transmembrane domain. We show that isoform-specific domain organization determines PEX26 oligomerization and impacts peroxisomal β-oxidation and proliferation. PEX26 and PEX26Δex5 displayed different patterns of interaction with PEX2-PEX10 or PEX13-PEX14 complexes, which relate to distinct pre-peroxisomes in the de novo synthesis pathway. Our data support an alternative PEX14-dependent mechanism of peroxisomal membrane association for the splice variant, which lacks a transmembrane domain. Structure-function relationships of PEX26 isoforms explain an extended function in peroxisomal homeostasis and these findings may improve our understanding of the broad phenotype of PEX26-associated human disorders.

A combinatorial approach of N-terminus blocking and codon optimization strategies to enhance the soluble expression of recombinant hIL-7 in E. coli fed-batch culture

Human interleukin-7 (hIL-7) is a therapeutically important cytokine involved in lymphocyte development and survival. In previous reports, a uniformly poor expression of hIL-7 has been shown in Escherichia coli host with the problem of inclusion body formation. In this study, the role of codon optimization and N-terminus blocking using various solubility enhancer fusion tags was explored to improve its soluble expression. The use of codon optimization strategy improved its expression to 80 ± 5 mg/L at shake flask level. The utilization of pelB leader sequence resulted in an unprocessed protein in the form of cytoplasmic inclusion bodies with lower expression yields. The N-terminus fusion of small ubiquitin-like modifier (SUMO), thioredoxin (Trx), and NusA tags increased the expression in the range of 90-140 mg/L, where >90 % of the fusion protein was obtained in soluble form. The fed-batch fermentation of SUMO-tagged hIL-7 protein was optimized at bioreactor level, where a high volumetric product concentration of 2.65 g/L was achieved by controlling the plasmid segregation instability using high antibiotic concentration. The specific product yield (Y_P/X) and volumetric product concentration were 1.38 and 2.55-fold higher compared to batch results, respectively. A preparative scale affinity chromatography resulted in a high recovery yield of 50.6 mg/L with ∼90 % purity. The conformational property of purified recombinant hIL-7 from CD spectroscopy showed a typical helical structure with 31.5 % α-helix and 26.43 % β-sheet. The biological activity of purified protein was tested using IL-7-dependent murine immature B lymphocyte (2E8) cell line by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide salt (MTT) assay, where it showed a similar biological activity as standard control.

Cloning and characterization of novel tumor-targeting immunocytokines based on murine IL7

We generated and characterized novel antibody-cytokine fusion proteins ("immunocytokines") based on murine interleukin-7 (IL7), an immunomodulatory protein which has previously shown anti-cancer activity in preclinical models and whose human counterpart is currently being investigated in clinical trials. The sequential fusion of the clinical-stage antibody fragment scFv(F8), specific to a tumor-associated splice isoform of fibronectin, yielded an immunocytokine (termed "F8-mIL7") of insufficient pharmaceutical quality and in vivo tumor targeting performance, with a striking dose dependence on tumor targeting selectivity. By contrast, a novel immunocytokine design (termed "F8-mIL7-F8"), in which two scFv moieties were fused at the N- and C-terminus of murine IL7, yielded a protein of excellent pharmaceutical quality and with improved tumor-targeting performance [tumor: blood ratio=16:1, 24h after injection]. Both F8-mIL7 and F8-mIL7-F8 could induce tumor growth retardation in immunocompetent mice, but were not able to eradicate F9 tumors. The combination of F8-mIL7-F8 with paclitaxel led to improved therapeutic results, which were significantly better compared to those obtained with saline treatment. The study indicates how the engineering of novel immunocytokine formats may help generate fusion proteins of acceptable pharmaceutical quality, for those immunomodulatory proteins which do not lend themselves to a direct fusion with antibody fragments.

Gas-phase scrambling of disulfide bonds during matrix-assisted laser desorption/ionization mass spectrometry analysis

Evidence for photo-induced radical disulfide bond scrambling in the gas phase during matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is described. The phenomenon was observed during the analysis of tryptic peptides from insulin and was confirmed in the determination of disulfide bonds in the rhamnose-binding lectin SEL24K from the Chinook salmon Oncorhynchus tshawytscha. A possible mechanism for this surprising scrambling is proposed. Despite this finding, the disulfide bond pattern in SEL24K was assigned unambiguously by a multi-enzyme digestion strategy in combination with MALDI mass spectrometry. The pattern was found to be symmetrical in the tandem repeat sequence of SEL24K. To the best of our knowledge, this is the first report of disulfide bond scrambling in the gas phase during MALDI-MS analysis. This observation has important ramifications for unambiguous assignment of disulfide bonds.

Structural and biophysical studies of the human IL-7/IL-7Ralpha complex

IL-7 and IL-7Ralpha bind the gamma(c) receptor, forming a complex crucial to several signaling cascades leading to the development and homeostasis of T and B cells. We report that the IL-7Ralpha ectodomain uses glycosylation to modulate its binding constants to IL-7, unlike the other receptors in the gamma(c) family. IL-7 binds glycosylated IL-7Ralpha 300-fold more tightly than unglycosylated IL-7Ralpha, and the enhanced affinity is attributed primarily to an accelerated on rate. Structural comparison of IL-7 in complex to both forms of IL-7Ralpha reveals that glycosylation does not participate directly in the binding interface. The SCID mutations of IL-7Ralpha locate outside the binding interface with IL-7, suggesting that the expressed mutations cause protein folding defects in IL-7Ralpha. The IL-7/IL-7Ralpha structures provide a window into the molecular recognition events of the IL-7 signaling cascade and provide sites to target for designing new therapeutics to treat IL-7-related diseases.

Expression and production of human interleukin-7 in insect cells using baculovirus expression vector system (BEVS)

Interleukin-7 (IL-7) is a glycoprotein cytokine with significant clinical and biomedical potential, such as cancer therapy and HIV infections. Earlier it has been cloned and expressed in various protein expression systems; however, they are not efficient for large-scale production. To address this inadequacy, we report in this paper the production of recombinant human interleukin-7 (hIL-7) in insect cells. A recombinant bacmid containing hIL-7 was constructed, purified, and characterized. It was used to infect Trichoplusia ni (BT1-TN-5B1/High Fivetrade mark) insect cells. Result shows that T. ni cells successfully produce hIL-7 in shake flask cultures. A scale up to 2.5-L laboratory batch bioreactor showed the efficacy of this system for large-scale production. Our results offer a highly efficient, inexpensive, and convenient system for the large-scale expression and production of recombinant hIL-7.

Crystallization and preliminary X-ray diffraction of human interleukin-7 bound to unglycosylated and glycosylated forms of its alpha-receptor

The interleukin-7 (IL-7) signaling pathway plays an essential role in the development, proliferation and homeostasis of T and B cells in cell-mediated immunity. Understimulation and overstimulation of the IL-7 signaling pathway leads to severe combined immunodeficiency, autoimmune reactions, heart disease and cancers. Stimulation of the IL-7 pathway begins with IL-7 binding to its alpha-receptor, IL-7R alpha. Protein crystals of unglycosylated and glycosylated complexes of human IL-7-IL-7R alpha extracellular domain (ECD) obtained using a surface entropy-reduction approach diffract to 2.7 and 3.0 A, respectively. Anomalous dispersion methods will be used to solve the unglycosylated IL-7-IL-7R alpha ECD complex structure and this unglycosylated structure will then serve as a model in molecular-replacement attempts to solve the structure of the glycosylated IL-7-alpha-receptor complex.

Molecular and functional evidence for activity of murine IL-7 on human lymphocytes

Although interleukin-7 (IL-7) is essential for human and murine lymphopoiesis and homeostasis, clear disparities between these species regarding the role of IL-7 during B-cell development suggest that other, subtler differences may exist. One basic unsolved issue of IL-7 biology concerns cross-species activity, because in contrast to the human ortholog, the ability of murine (m)IL-7 to stimulate human cells remains unresolved. Establishing whether two-way cross-species reactivity occurs is fundamental for evaluating the role of IL-7 in chimeric human-mouse models, which are the most versatile tools for studying human lymphoid development and disease in vivo. Here, we show that mIL-7 triggers the same signaling pathways as human (h)IL-7 in human T cells, promoting similar changes in viability, proliferation, size, and immunophenotype, even at low concentrations. This ability is not confined to T cells, because mIL-7 mediates cell growth and protects human B-cell precursors from dexamethasone-induced apoptosis. Importantly, endogenous mIL-7 produced in the mouse thymic microenvironment stimulates human T cells, because their expansion in chimeric fetal thymic organ cultures is inhibited by a mIL-7-specific neutralizing antibody. Our results demonstrate that mIL-7 affects human lymphocytes and indicate that mouse models of human lymphoid development and disease must integrate the biological effects of endogenous IL-7 on human cells.

Cell biology of IL-7, a key lymphotrophin

IL-7 is essential for the development and survival of T lymphocytes. This review is primarily from the perspective of the cell biology of the responding T cell. Beginning with IL-7 receptor structure and regulation, the major signaling pathways appear to be via PI3K and Stat5, although the requirement for either has yet to be verified by published knockout experiments. The proliferation pathway induced by IL-7 differs from conventional growth factors and is primarily through posttranslational regulation of p27, a Cdk inhibitor, and Cdc25a, a Cdk-activating phosphatase. The survival function of IL-7 is largely through maintaining a favorable balance of bcl-2 family members including Bcl-2 itself and Mcl-1 on the positive side, and Bax, Bad and Bim on the negative side. There are also some remarkable metabolic effects of IL-7 withdrawal. Studies of IL-7 receptor signaling have yet to turn up unique pathways, despite the unique requirement for IL-7 in T cell biology. There remain significant questions regarding IL-7 production and the major producing cells have yet to be fully characterized.

Production and purification of refolded recombinant human IL-7 from inclusion bodies

A recombinant form of human rhIL-7 was overexpressed in Escherichia coli HMS174 (DE3) pLysS under the control of a T7 promoter. The resulting insoluble inclusion bodies were separated from cellular debris by cross-flow filtration and solubilized by homogenization with 6 M guanidine HCl. Attempts at refolding rhIL-7 from solubilized inclusion bodies without prior purification of monomeric, denatured rhIL-7 were not successful. Denatured, monomeric rhIL-7 was therefore initially purified by size-exclusion chromatography using Prep-Grade Pharmacia Superdex 200. Correctly folded rhIL-7 monomer was generated by statically refolding the denatured protein at a final protein concentration of 80-100 microg/ml in 100 mM Tris, 2mM EDTA, 500 mM L-arginine, pH 9.0, buffer with 0.55 g/l oxidized glutathione at 2-8 degrees C for at least 48 h. The refolded rhIL-7 was subsequently purified by low-pressure liquid chromatography, using a combination of hydrophobic interaction, cation-exchange, and size-exclusion chromatography. The purified final product was >95% pure by SDS-PAGE stained with Coomassie brilliant blue, high-pressure size-exclusion chromatography (SEC-HPLC), and reverse-phase HPLC. The endotoxin level was <0.05 EU/mg. The final purified product was biologically active in a validated IL-7 dependent pre-B-cell bioassay. In anticipation of human clinical trials, this material is currently being evaluated for safety and efficacy in non-human primate toxicology studies.

Altered biological activity associated with C-terminal modifications of IL-7

Interleukin 7 (IL-7) is a pleiotropic cytokine which plays a role in both T and B cell function as well as in establishment and maintenance of immunological barriers in epithelial tissues. The heterodimeric IL-7 receptor (IL-7R) consists of the p76 IL-7Ralpha subunit and the p64 common gamma (gammac) subunit. Ligand-binding induces signal transduction through tyrosine phosphorylation of the janus (Jak) and src-related kinases as well as by activation of phosphatidinositol-3 kinase (P13-kinase). In an effort to further define the requirements for ligand-receptor interactions and to subsequently develop candidate receptor binding antagonists with selective biological activities, we examined a series of IL-7 mutants in which the carboxy terminal hydrophobic residues were substituted with aliphatic amino acids. In this study we describe abrogation of IL-7 driven proliferation and attenuated phosphotyrosine signaling by IL-7(143) (Trp-Ala) and IL-7(143) (Trp-His) in IL-7R expressing T and B leukemia cells. Decreased phosphorylation of Jak3 kinase by IL-7W143A, IL-7W143P and IL-7W143H suggest that alterations in this region of the carboxyterminal region of IL-7 affects its interaction with the gammac subunit of the IL-7R.

Interleukin-7 receptor expression and activation in nonhaematopoietic neoplastic cell lines

The high-affinity human interleukin-7 (IL-7)R is a heterodimeric complex consisting of the IL-7Ralpha and common interleukin-2 receptor gamma (IL-2Rgamma(c)) chains. Activation of the IL-7R complex is associated with tyrosine and serine residue phosphorylation of a number of intracellular substrates leading to proliferation and induction of various cellular differentiation processes. In this study, we demonstrate, by S1 nuclease protection assay, immunoprecipitation and in vitro kinase assay that functional human (h) IL-7R is expressed in haematopoietic and nonhaematopoietic cell lines. The National Cancer Institute (NCI) tumour panel of 60 cell lines (NCI60) was screened for the expression of IL-7R mRNA by S1 nuclease protection assay, and IL-7R mRNA was detected in 9 of 12 leukemia, 3 of 7 lung, 4 of 6 CNS, 2 of 7 melanoma, 2 of 7 renal, 1 of 6 colon and 1 of 6 breast cancer cell lines. Immunoblot analysis of haematopoietic, lung cancer and brain tumour cell lines demonstrated expression of IL-7R, IL-2Rgamma(c) and p59 fyn, suggesting that the components of an IL-7R signalling network are present in nonhaematopoietic neoplastic cells. Immunoprecipitation of IL-7Ralpha followed by an in vitro kinase assay demonstrated functional receptor phosphorylation events in the lung cancer cells but not in the brain tumour cell lines. The expression of functional IL-7R on epithelial tumour cells may represent a potential target for receptor-directed therapy.

Structure function analysis of interleukin 7: requirement for an aromatic ring at position 143 of helix D

The residues located at the carboxyl terminus of helix D in interleukin-7 (IL-7) have previously been targeted as important for recruitment and binding to the gamma chain component of the IL-7 receptor (IL-7R). In this study, Trp 143 of helix D was mutated to His, Phe, Tyr and Pro and these mutants, along with a W143A mutant previously described, were studied to determine the effects on activation of DNA synthesis and binding affinity to IL-7R positive 2E8 cells. The W143F and W143Y mutants were similar to wild type IL-7 in their binding properties and retained 85% and 74% of their activating properties, respectively. In contrast, the W143H mutant possessed a lower binding affinity and a corresponding decrease in activation, the W143A mutant possessed an over 100-fold decreased binding affinity and some residual activation activity and the W143P mutant possessed a greatly decreased binding affinity and did not activate. These results strongly suggest an aromatic residue is required at position 143 for IL-7R binding and subsequent signal transduction.

Comparative model building of interleukin-7 using interleukin-4 as a template: a structural hypothesis that displays atypical surface chemistry in helix D important for receptor activation

Using a combination of theoretical sequence structure recognition predictions and experimental disulfide bond assignments, a three-dimensional (3D) model of human interleukin-7 (hIL-7) was constructed that predicts atypical surface chemistry in helix D that is important for receptor activation. A 3D model of hIL-7 was built using the X-ray crystal structure of interleukin-4 (IL-4) as a template (Walter MR et al., 1992, J Mol Biol. 224:1075-1085; Walter MR et al., 1992, J Biol Chem 267:20371-20376). Core secondary structures were constructed from sequences of hIL-7 predicted to form helices. The model was constructed by superimposing IL-7 helices onto the IL-4 template and connecting them together in an up-up down-down topology. The model was finished by incorporating the disulfide bond assignments (Cys3, Cys142), (Cys35, Cys130), and (Cys48, Cys93), which were determined by MALDI mass spectroscopy and site-directed mutagenesis (Cosenza L, Sweeney E, Murphy JR, 1997, J Biol Chem 272:32995-33000). Quality analysis of the hIL-7 model identified poor structural features in the carboxyl terminus that, when further studied using hydrophobic moment analysis, detected an atypical structural property in helix D, which contains Cys 130 and Cys142. This analysis demonstrated that helix D had a hydrophobic surface exposed to bulk solvent that accounted for the poor quality of the model, but was suggestive of a region in IL-7 that maybe important for protein interactions. Alanine (Ala) substitution scanning mutagenesis was performed to test if the predicted atypical surface chemistry of helix D in the hIL-7 model is important for receptor activation. This analysis resulted in the construction, purification, and characterization of four hIL-7 variants, hIL-7(K121A), hIL-7(L136A), hIL-7(K140A), and hIL-7(W143A), that displayed reduced or abrogated ability to stimulate a murine IL-7 dependent pre-B cell proliferation. The mutant hIL-7(W143A), which is biologically inactive and displaces [125I]-hIL-7, is the first reported IL-7R system antagonist.

Assignment of the three disulfide bonds of Selenocosmia huwena lectin-I from the venom of spider Selenocosmia huwena

The positions of the disulfide bonds of Selenocosmia huwena lectin-I (SHL-I) from the venom of the Chinese bird spider S. huwena have been determined. The existence of three disulfide bonds in the native SHL-I was proved by matrix-assisted laser desorption ionization time-of-flight mass spectroscopic analysis. To map the disulfide bonds, native SHL-I was proteolytically digested. The resulting peptides were separated by reverse phase high-performance liquid chromatography. Matrix-assisted laser desorption ionization time-of-flight mass spectroscopic analysis indicated the presence of one disulfide bond Cys7-Cys19. The partially reduced peptides by using Tris-(2-carboxyethyl)-phosphine at pH 3.0 were purified by reverse phase high-performance liquid chromatography. Four M Guanidine-HCl was found to increase the yields of partially reduced peptides prominently. The free thiols were carboxamidomethlate by iodoacetamide. The specific location of another disulfide bond Cys2-Cys14 was proved by comparing N-terminal sequencing analysis of the partially reduced and alkylated SHL-I with that of the intact peptide. Finally, the three disulfide linkage of SHL-I could be assigned as Cys2-Cys14, Cys7-Cys19, Cys13-Cys26.

Interleukin 7 (IL-7) receptor-specific cell killing by DAB389 IL-7: a novel agent for the elimination of IL-7 receptor positive cells

Interleukin 7 (IL-7) induces the proliferation of B cell progenitors in long-term bone marrow cultures, promotes the growth of resting fetal and adult thymocytes, and costimulates mature human T cell proliferation. IL-7 also induces cell growth in hematologic malignancies such as acute lymphoblastic leukemia, chronic lymphocytic leukemia, acute myelogenous leukemia, and Sezary syndrome. We have constructed a recombinant fusion protein, DAB389 IL-7, composed of the catalytic and transmembrane domains of diphtheria toxin (DT), fused to IL-7. We demonstrate that DAB389 IL-7 is selectively cytotoxic for only those cells bearing the IL-7 receptor and that entry into target cells is mediated through the receptor. The nontoxic mutant, DA(E149S)B389 IL-7, was constructed and used to demonstrate that the catalytic domain of DT is responsible for the ADP ribosylation of elongation factor 2 that results in cytotoxicity. Finally, we demonstrate that DA(E149S)B389 IL-7 induces the growth of IL-7-dependent cells, verifying the bioactivity of the IL-7 binding domain of DAB389 IL-7. We propose that DAB389 IL-7 may be an important reagent in studying the IL-7--IL-7 receptor complex and may possess potential as a therapeutic agent against IL-7 receptor-bearing hematologic malignancies.