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.

A novel method for residual life assessment of used parts: a case study of used lathe spindles.

In the remanufacturing evaluation process of used spindles, the remaining life of each type is very different due to the differences in the original process, quality, and use conditions. Researching the prediction and evaluation of the remaining life of used spindles has essential engineering significance for improving the accuracy and economics of remanufacturability assessment. Aiming at the fatigue fracture, wear and excessive deformation of the wasted spindle, and considering the factors affecting crack closure and crack development, a residual life prediction evaluation model based on a nonlinear continuous fatigue damage model was proposed. Take the spindle of CAK5085 CNC lathe of a machine tool company as an example to evaluate its remaining life. The accuracy and feasibility of the modified model are verified by comparing the data of the test with the calculated results of the model. The results show that the proposed prediction model can calculate a more accurate stress-life curve, which provides a theoretical basis for the life prediction of remanufactured parts.

The Nuclear Protein HOXB13 Enhances Methylmercury Toxicity by Inducing Oncostatin M and Promoting Its Binding to TNFR3 in Cultured Cells.

Homeobox protein B13 (HOXB13), a transcription factor, is related to methylmercury toxicity; however, the downstream factors involved in enhancing methylmercury toxicity remain unknown. We performed microarray analysis to search for downstream factors whose expression is induced by methylmercury via HOXB13 in human embryonic kidney cells (HEK293), which are useful model cells for analyzing molecular mechanisms. Methylmercury induced the expression of oncostatin M (OSM), a cytokine of the interleukin-6 family, and this was markedly suppressed by HOXB13 knockdown. OSM knockdown also conferred resistance to methylmercury in HEK293 cells, and no added methylmercury resistance was observed when both HOXB13 and OSM were knocked down. Binding of HOXB13 to the OSM gene promoter was increased by methylmercury, indicating the involvement of HOXB13 in the enhancement of its toxicity. Because addition of recombinant OSM to the medium enhanced methylmercury toxicity in OSM-knockdown cells, extracellularly released OSM was believed to enhance methylmercury toxicity via membrane receptors. We discovered tumor necrosis factor receptor (TNF) receptor 3 (TNFR3) to be a potential candidate involved in the enhancement of methylmercury toxicity by OSM. This toxicity mechanism was also confirmed in mouse neuronal stem cells. We report, for the first time, that HOXB13 is involved in enhancement of methylmercury toxicity via OSM-expression induction and that the synthesized OSM causes cell death by binding to TNFR3 extracellularly.

Kindlin-2 Inhibits the Hippo Signaling Pathway by Promoting Degradation of MOB1.

The Hippo signaling pathway plays a key role in development and cancer progression. However, molecules that intrinsically inhibit this pathway are less well known. Here, we report that the focal adhesion molecule Kindlin-2 inhibits Hippo signaling by interacting with and degrading MOB1 and promoting the interaction between MOB1 and the E3 ligase praja2. Kindlin-2 thus inhibits the phosphorylation of LATS1 and YAP and promotes YAP translocation into the nucleus, where it activates downstream Hippo target gene transcription. Kindlin-2 depletion activates Hippo/YAP signaling and alleviates renal fibrosis in Kindlin-2 knockout mice with unilateral ureteral occlusion (UUO). Moreover, Kindlin-2 levels are negatively correlated with MOB1 and phosphorylated (p) YAP in samples from patients with renal fibrosis. Altogether, these results demonstrate that Kindlin-2 inhibits Hippo signaling through degradation of MOB1. A specific long-lasting siRNA against Kindlin-2 effectively alleviated UUO-induced renal fibrosis and could be a potential therapy for renal fibrosis.

Unconventional myosin VIIA promotes melanoma progression.

Unconventional myosin VIIA (Myo7a) is an actin-based motor molecule that normally functions in the cochlear hair cells of the inner ear. Mutations of MYO7A/Myo7a have been implicated in inherited deafness in both humans and mice. However, there is limited information about the functions of Myo7a outside of the specialized cells of the ears. Herein, we report a previously unidentified function of Myo7a by demonstrating that it plays an important role in melanoma progression. We found that silencing Myo7a by means of RNAi inhibited melanoma cell growth through upregulation of cell cycle regulator p21 (also known as CDKN1A) and suppressed melanoma cell migration and invasion through downregulation of RhoGDI2 (also known as ARHGDIB) and MMP9. Furthermore, Myo7a depletion suppressed melanoma cell metastases to the lung, kidney and bone in mice. In contrast, overexpression of Myo7a promoted melanoma xenograft growth and lung metastasis. Importantly, Myo7a levels are remarkably elevated in human melanoma patients. Collectively, we demonstrated for the first time that Myo7a is able to function in non-specialized cells, a finding that reveals the complicated disease-related roles of Myo7a, especially in melanomas.