Panoply™ Human OSM Knockdown Stable Cell Line

Homeobox protein B13 (HOXB13) is a transcription factor associated with methylmercury toxicity; however, the specific downstream factors contributing to the enhancement of this toxicity remain unclear. Here, researchers found that methylmercury induces the expression of oncostatin M (OSM, an interleukin-6 family cytokine), and that HOXB13 knockdown significantly suppresses this induction. In HEK293 cells, OSM knockdown conferred resistance to methylmercury, and simultaneous knockdown of both HOXB13 and OSM did not further enhance this resistance. Methylmercury promoted the binding of HOXB13 to the OSM gene promoter, indicating that HOXB13 participates in the process of enhancing methylmercury toxicity. Supplementing the culture medium with recombinant OSM increased the sensitivity of OSM-knockdown cells to methylmercury, suggesting that extracellularly released OSM enhances methylmercury toxicity via membrane receptors. Researchers identified tumor necrosis factor receptor 3 (TNFR3) as a potential candidate receptor mediating OSM-enhanced methylmercury toxicity. This toxicity mechanism was also confirmed in mouse neural stem cells.

OSM is a cytokine belonging to the IL-6 family that exerts various physiological functions-such as inducing cell death, inhibiting cell growth, and promoting bone regeneration-after being secreted into the extracellular space. Research has shown that in HEK293 cells treated with methylmercury, the level of OSM in the culture medium increased over time (Figure 1A). Although recombinant OSM was added to the HEK293 cell culture medium, this did not affect methylmercury-induced cell death. Given that the quantity of endogenous OSM released extracellularly following methylmercury treatment might be sufficient to exacerbate methylmercury toxicity, researchers added recombinant OSM to OSM-knockdown cells. The results demonstrated that the addition of recombinant OSM increased the cells' sensitivity to methylmercury in a dose-dependent manner (Figure 1B), indicating that OSM-induced by methylmercury and released extracellularly-contributes to methylmercury-induced cytotoxicity. In HOXB13-knockdown cells that were resistant to methylmercury, WP9QY showed almost no protective effect against methylmercury toxicity (Figure 1C); interestingly, OSM-knockdown cells exhibited similar results (Figure 1D). These findings suggest that after being induced by methylmercury via HOXB13 and released extracellularly, OSM may trigger cytotoxicity by binding to a TNF receptor that can be inhibited by WP9QY.

Figure 1. Effects of methylmercury on extracellular release of OSM and of the TNF receptor inhibitor on HOXB13/OSM-mediated methylmercury toxicity. (Toyama T, et al., 2019)