Oncostatin M binds to extracellular matrix in a bioactive conformation: Implications for inflammation and metastasis

•OSM binding to ECM is pH-dependent and involves electrostatic bonds.•Immobilized OSM is bioactive and induces prolonged phosphorylation of STAT3.•The novel ‘OSM circle’ assay validates immobilized OSM bioactivity.•Immobilized OSM is protected from proteolysis.•A model for the role of immobilized OSM in inflammation and metastasis is developed.

Oncostatin M (OSM) is an interleukin-6-like inflammatory cytokine reported to play a role in a number of pathological processes including cancer. Full-length OSM is expressed as a 26 kDa protein that can be proteolytically processed into 24 kDa and 22 kDa forms via removal of C-terminal peptides. In this study, we examined both the ability of OSM to bind to the extracellular matrix (ECM) and the activity of immobilized OSM on human breast carcinoma cells. OSM was observed to bind to ECM proteins collagen types I and XI, laminin, and fibronectin in a pH-dependent fashion, suggesting a role for electrostatic bonds that involves charged amino acids of both the ECM and OSM. The C-terminal extensions of 24 kDa and 26 kDa OSM, which contains six and thirteen basic amino acids, respectively, enhanced electrostatic binding to ECM at pH 6.5–7.5 when compared to 22 kDa OSM. The highest levels of OSM binding to ECM, though, were observed at acidic pH 5.5, where all forms of OSM bound to ECM proteins to a similar extent. This indicates additional electrostatic binding properties independent of the OSM C-terminal extensions. The reducing agent dithiothreitol also inhibited the binding of OSM to ECM suggesting a role for disulfide bonds in OSM immobilization. OSM immobilized to ECM was protected from cleavage by tumor-associated proteases and maintained activity following incubation at acidic pH for extended periods of time. Importantly, immobilized OSM remained biologically active and was able to induce and sustain the phosphorylation of STAT3 in T47D and ZR-75-1 human breast cancer cells over prolonged periods, as well as increase levels of STAT1 and STAT3 protein expression. Immobilized OSM also induced epithelial–mesenchymal transition-associated morphological changes in T47D cells. Taken together, these data indicate that OSM binds to ECM in a bioactive state that may have important implications for the development of chronic inflammation and tumor metastasis.

Graphical abstractModel for OSM role in chronic inflammation and tumor metastasis. Inflammatory cells infiltrate into a particular microenvironment and secrete OSM, which binds to ECM and helps to nurture an inflammatory microenvironment. Immobilized bioactive OSM will help to maintain a prolonged OSM response ultimately resulting in chronic inflammation. A non-OSM secreting, proliferating tumor may also come into contact with immobilized OSM secreted from inflammatory cells. The interaction of immobilized OSM with proliferating tumor cells may induce an EMT in the tumor cells and enhance tumor metastasis.Figure optionsDownload full-size imageDownload as PowerPoint slide