Cleavage of a hydrophilic C-terminal domain increases growth-inhibitory activity of oncostatin M

Methylmercury directly modifies the 105th cysteine residue in oncostatin M to promote binding to tumor necrosis factor receptor 3 and inhibit cell growth

We previously found that methylmercury induces expression of oncostatin M (OSM), which is released extracellularly and binds to tumor necrosis factor receptor 3 (TNFR3), possibly enhancing its own toxicity. However, the mechanism by which methylmercury causes OSM to bind to TNFR3 rather than to its known receptors, OSM receptor and LIFR, is unknown. In this study, we aimed to elucidate the effect of methylmercury modification of cysteine residues in OSM on binding to TNFR3. Immunostaining of TNFR3-V5-expressing cells suggested that methylmercury promoted binding of OSM to TNFR3 on the cell membrane. In an in vitro binding assay, OSM directly bound to the extracellular domain of TNFR3, and this binding was promoted by methylmercury. Additionally, the formation of a disulfide bond in the OSM molecule was essential for the binding of both proteins, and LC/MS analysis revealed that methylmercury directly modified the 105th cysteine residue (Cys105) in OSM. Next, mutant OSM, in which Cys105 was replaced by serine or methionine, increased the binding to TNFR3, and a similar effect was observed in immunoprecipitation using cultured cells. Furthermore, cell proliferation was inhibited by treatment with Cys105 mutant OSMs compared with wildtype OSM, and this effect was cancelled by TNFR3 knockdown. In conclusion, we revealed a novel mechanism of methylmercury toxicity, in which methylmercury directly modifies Cys105 in OSM, thereby inhibiting cell proliferation via promoting binding to TNFR3. This indicates a chemical disruption in the interaction between the ligand and the receptor is a part of methylmercury toxicity.

Exploring the oncostatin M (OSM) feed-forward signaling of glioblastoma via STAT3 in pan-cancer analysis

Background

Oncostatin M (OSM) has been reported to be a key regulating factor in the process of tumor development. Previous studies have demonstrated both the promotion and inhibition effects of OSM in tumors, therefore inspiring controversies. However, no systematic assessment of OSM across various cancers is available, and the mechanisms behind OSM-related cancer progression remain to be elucidated.

Methods

Based on The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) databases, we conducted a pan-cancer analysis on OSM to explore its tumor-related functions across cancers as well as its correlations with specific molecules, cells in the tumor microenvironment. Considering the results of pan-cancer analysis, we chose the specific tumor glioblastoma multiforme (GBM) to screen out the OSM-induced signaling pathways and intercellular communications in tumor progression. Wound scratch assay, invasion assay and qRT-PCR were performed to verify the biological effects of OSM on glioblastoma cells.

Results

Higher OSM level was found in most tumor tissues compared with corresponding normal tissues, and the enhanced OSM expression was observed to be strongly related to patients’ poor prognosis in several cancers. Moreover, the expression of OSM was associated with stromal and immune cell infiltration in the tumor microenvironment, and OSM-related immune checkpoint and chemokine co-expression were also observed. Our results suggested that OSM could communicate extensively with the tumor microenvironment. Taking GBM as an example, our study found that two critical signaling pathways in OSM-related tumor progression by KEGG enrichment analysis: Jak-STAT and NF-κB pathways. Single-cell RNA sequencing data analysis of GBM revealed that OSM was mainly secreted by microglia, and cell–cell interaction analysis proved that OSM-OSMR is an important pathway for OSM to stimulate malignant cells. In vitro, OSM treatment could facilitate the migration and invasion of glioblastoma cells, meanwhile promote the proneural-mesenchymal transition. The administration of STAT3 inhibitors effectively suppressed the OSM-mediated biological effects, which proved the key role of STAT3 in OSM signaling.

Conclusion

Taken together, our study provides a comprehensive understanding with regard to the tumor progression under the regulation of OSM. OSM seems to be closely related to chronic inflammation and tumor development in the tumor microenvironment. As an important inflammatory factor in the tumor microenvironment, OSM may serve as a potential immunotherapeutic target for cancer treatment, especially for GBM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02260-9.

Bioactive recombinant human oncostatin M for NMR-based screening in drug discovery

Oncostatin M (OSM) is a pleiotropic, interleukin-6 family inflammatory cytokine that plays an important role in inflammatory diseases, including inflammatory bowel disease, rheumatoid arthritis, and cancer progression and metastasis. Recently, elevated OSM levels have been found in the serum of COVID-19 patients in intensive care units. Multiple anti-OSM therapeutics have been investigated, but to date no OSM small molecule inhibitors are clinically available. To pursue a high-throughput screening and structure-based drug discovery strategy to design a small molecule inhibitor of OSM, milligram quantities of highly pure, bioactive OSM are required. Here, we developed a reliable protocol to produce highly pure unlabeled and isotope enriched OSM from E. coli for biochemical and NMR studies. High yields (ca. 10 mg/L culture) were obtained in rich and minimal defined media cultures. Purified OSM was characterized by mass spectrometry and circular dichroism. The bioactivity was confirmed by induction of OSM/OSM receptor signaling through STAT3 phosphorylation in human breast cancer cells. Optimized buffer conditions yielded ¹H, ¹⁵N HSQC NMR spectra with intense, well-dispersed peaks. Titration of ¹⁵N OSM with a small molecule inhibitor showed chemical shift perturbations for several key residues with a binding affinity of 12.2 ± 3.9 μM. These results demonstrate the value of bioactive recombinant human OSM for NMR-based small molecule screening.

Prokaryotic soluble overexpression and purification of oncostatin M using a fusion approach and genetically engineered E. coli strains

Human Oncostatin M (OSM), initially discovered as a tumour inhibitory factor secreted from U-937 cells, is a gp130 (IL-6/LIF) cytokine family member that exhibits pleiotropic effects in inflammation, haematopoiesis, skeletal tissue alteration, liver regeneration, cardiovascular and metabolic diseases. Cytoplasmic expression of OSM in Escherichia coli results in inclusion bodies, and complex solubilisation, refolding and purification is required to prepare bioactive protein. Herein, eight N-terminal fusion variants of OSM with hexahistidine (His6) tag and seven solubility-enhancing tags, including thioredoxin (Trx), small ubiquitin-related modifier (Sumo), glutathione S-transferase (GST), maltose-binding protein (MBP), N-utilisation substance protein A (Nusa), human protein disulphide isomerase (PDI) and the b‘a’ domain of PDI (PDIb‘a’), were tested for soluble OSM expression in E. coli. The His6-OSM plasmid was also introduced into genetically engineered Origami 2 and SHuffle strains to test expression of the protein. At 18 °C, MBP-tagged OSM was highly expressed and solubility was dramatically enhanced. In addition, His6-OSM was more highly expressed and soluble in Origami 2 and SHuffle strains than in BL21(DE3). MBP-OSM and His6-OSM were purified more than 95% with yields of 11.02 mg and 3.27 mg from a 500 mL culture. Protein identity was confirmed by mass spectroscopy, and bioactivity was demonstrated by in vitro inhibition of Th17 cell differentiation.

A quick and efficient method to generate mammalian stable cell lines based on a novel inducible alphavirus DNA/RNA layered system

We report a new method to generate high-expressing mammalian cell lines in a quick and efficient way. For that purpose, we developed a master cell line (MCL) containing an inducible alphavirus vector expressing GFP integrated into the genome. In the MCL, recombinant RNA levels increased >4,600-fold after induction, due to a doxycycline-dependent RNA amplification loop. The MCL maintained inducibility and expression during 50 passages, being more efficient for protein expression than a conventional cell line. To generate new cell lines, mutant LoxP sites were inserted into the MCL, allowing transgene and selection gene exchange by Cre-directed recombination, leading to quick generation of inducible cell lines expressing proteins of therapeutic interest, like human cardiotrophin-1 and oncostatin-M at several mg/l/24 h. These proteins contained posttranslational modifications, showed bioactivity, and were efficiently purified. Remarkably, this system allowed production of toxic proteins, like oncostatin-M, since cells able to express it could be grown to the desired amount before induction. These cell lines were easily adapted to growth in suspension, making this methodology very attractive for therapeutic protein production.

The enigmatic cytokine oncostatin m and roles in disease

Oncostatin M is a secreted cytokine involved in homeostasis and in diseases involving chronic inflammation. It is a member of the gp130 family of cytokines that have pleiotropic functions in differentiation, cell proliferation, and hematopoetic, immunologic, and inflammatory networks. However, Oncostatin M also has activities novel to mediators of this cytokine family and others and may have fundamental roles in mechanisms of inflammation in pathology. Studies have explored Oncostatin M functions in cancer, bone metabolism, liver regeneration, and conditions with chronic inflammation including rheumatoid arthritis, lung and skin inflammatory disease, atherosclerosis, and cardiovascular disease. This paper will review Oncostatin M biology in a historical fashion and focus on its unique activities, in vitro and in vivo, that differentiate it from other cytokines and inspire further study or consideration in therapeutic approaches.

Characterization of the rat oncostatin M receptor complex which resembles the human, but differs from the murine cytokine receptor

Evaluation of a pathophysiological role of the interleukin-6-type cytokine oncostatin M (OSM) for human diseases has been complicated by the fact that mouse models of diseases targeting either OSM or the OSM receptor (OSMR) complex cannot fully reflect the human situation. This is due to earlier findings that human OSM utilizes two receptor complexes, glycoprotein 130 (gp130)/leukemia inhibitory factor receptor (LIFR) (type I) and gp130/OSMR (type II), both with wide expression profiles. Murine OSM on the other hand only binds to the gp130/OSMR (type II) receptor complex with high affinity. Here, we characterize the receptor usage for rat OSM. Using different experimental approaches (knock-down of the OSMR expression by RNA interference, blocking of the LIFR by LIF-05, an antagonistic LIF variant and stably transfected Ba/F3 cells) we can clearly show that rat OSM surprisingly utilizes both, the type I and type II receptor complex, therefore mimicking the human situation. Furthermore, it displays cross-species activities and stimulates cells of human as well as murine origin. Its signaling capacities closely mimic those of human OSM in cell types of different origin in the way that strong activation of the Jak/STAT, the MAP kinase as well as the PI3K/Akt pathways can be observed. Therefore, rat disease models would allow evaluation of the relevance of OSM for human biology.

Oncostatin M and leukemia inhibitory factor increase hepcidin expression in hepatoma cell lines

Overproduction of hepcidin by interleukin-6 (IL-6) is considered to be the main factor responsible for the development of anemia in inflammatory conditions. Since oncostatin M (OSM), a member of the IL-6 family, plays an important role in immune and inflammatory responses, we assessed the effect of OSM on hepcidin expression, as well as that of leukemia inhibitory factor (LIF), another member of the IL-6 family. We found that hepcidin expression was markedly induced by OSM and LIF in a time- and dose-dependent manner in hepatoma cell lines, and this expression was induced independent of IL-6/IL-6 receptor signaling. Luciferase assay revealed that OSM and LIF stimulated a -1.3-kb hepcidin promoter. This effect was markedly reduced when the signal transducer and activator of transcription (STAT) site of the promoter was mutated, and was almost completely abolished in the presence of AG-490, a Janus kinase (JAK) inhibitor. Hence, the JAK/STAT pathway plays a major role in OSM- and LIF-induced activation of the hepcidin promoter. In conclusion, we demonstrated that OSM and LIF can induce hepcidin expression mainly through the JAK/STAT pathways. Further studies are warranted to evaluate the clinical significance of OSM and LIF in the development of anemia in various inflammatory diseases.

Developmental abnormalities in mice transgenic for bovine oncostatin M

Oncostatin M belongs to the subfamily of hematopoietin cytokines that binds a receptor complex containing gp130. To date, only the human form of oncostatin M has been identified, and its evolutionary conservation is unresolved. We have isolated a bovine gene whose open reading frame encodes a precursor protein that is 58% identical to human oncostatin M. A comparison of the bovine and human amino acid sequences predicts significant similarity, including the four-alpha-helical-bundle structure and the placement of disulfide bridges. As with the human protein, bovine oncostatin M binds specific receptors on human H2981 cells and inhibits the proliferation of human A375 tumor cells and mouse M1 leukemia cells. To identify activities regulated in vivo, we injected bovine oncostatin M fusion genes containing various tissue-specific promoters into mouse embryos. The frequencies of transgenic mice were reduced significantly, suggesting that overexpression of the bovine cytokine is detrimental to normal mouse development. In addition to deaths associated with expression in neurons and keratinized epithelia, bovine oncostatin M caused abnormalities in bone growth and spermatogenesis, stimulated fibrosis surrounding islets in the pancreas, and disrupted normal lymphoid tissue development. This work establishes the existence of a nonprimate oncostatin M gene and provides the first demonstration that this cytokine can function in a pleiotropic manner in vivo. Information regarding bovine oncostatin M may help characterize the structure and function of this cytokine in other vertebrate species.

Structure-function studies of human ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) is a polypeptide that promotes the survival and/or differentiation of a number of neural cell types. Here we present a structural and functional analysis of the human CNTF molecule. Variant proteins were synthesized by Escherichia coli transformed with mutant cDNA constructs, and purified by SDS-polyacrylamide gel electrophoresis and reverse phase high pressure liquid chromatography. Most variant CNTF proteins lacked neurotrophic activity, but two N- and C-terminal deletions (delta 2-14 and delta 173-200, respectively) actually displayed a several-fold increase in specific activity. Loss of biological activity was accompanied by changes in the alpha-helical nature of CNTF as measured by circular dichroism. These data strengthen the proposed similarity between CNTF and the family of hematopoietic cytokines.