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Abstract FtsZ is highly conserved among bacteria and plays an essential role in bacterial cell division. The tense conformation of FtsZ bound to GTP assembles into a straight filament via head-to-tail associations, and then the upper subunit of FtsZ hydrolyzes GTP bound to the lower FtsZ subunit. The subunit with GDP bound disassembles accompanied by a conformational change in the subunit from the tense to relaxed conformation. Although crystal structures of FtsZ derived from several bacterial species have been determined, the conformational change from the relaxed to tense conformation has only been observed in Staphylococcus aureus FtsZ (SaFtsZ). Recent cryo-electron microscopy analyses revealed the three-dimensional reconstruction of the protofilament, in which tense molecules assemble via head-to-tail associations. However, the lower resolution of the protofilament suggested that the flexibility of the FtsZ protomers between the relaxed and tense conformations caused them to form in less-strict alignments. Furthermore, this flexibility may also prevent FtsZs other than SaFtsZ from crystalizing in the tense conformation, suggesting that the flexibility of bacterial FtsZs differs. In this study, molecular dynamics simulations were performed using SaFtsZ and Bacillus subtilis FtsZ in several situations, which suggested that different features of the FtsZs affect their conformational stability.

Ezrin‐radixin‐moesin‐binding phosphoprotein 50 (EBP50) is a scaffold protein that is required for epithelial polarity. Knockout (KO) of membranous EBP50 (Me‐EBP50) in ovarian clear cell carcinoma (OCCC) cells induced an epithelial–mesenchymal transition (EMT)‐like phenotype, along with decreased proliferation, accelerated migration capability, and induction of cancer stem cell (CSC)‐like properties. Shotgun proteomics analysis of proteins that co‐immunoprecipitated with EBP50 revealed that Me‐EBP50 strongly interacts with myosin 9 (MYH9). Specific inhibition of MYH9 with blebbistatin phenocopied Me‐EBP50 KO, and blebbistatin treatment potentiated the effects of Me‐EBP50 KO. In OCCC cells from clinical samples, Me‐EBP50 and MYH9 were co‐localized at the apical plasma membrane. Patients with a combination of Me‐EBP50‐high and MYH9‐high scores had the best prognosis for overall and progression‐free survival. Our data suggest that Me‐EBP50 has tumor‐suppressive effects through the establishment and maintenance of epithelial polarization. By contrast, loss of Me‐EBP50 expression induces EMT‐like phenotypes, probably due to MYH9 dysfunction; this results in increased cell mobility and enhanced CSC‐like properties, which in turn promote OCCC progression.

The mode of cytokine receptor activation is diverse. Here, the authors find that the marine-sponge derived lectin ThC, a bivalent sugar binding protein, activates human cytokine receptor MPL. This mode of action resembles the pathogenic activation of MPL by mutant molecular chaperon calreticulin in hematologic malignancies.

Abstract TAR DNA-binding protein 43 kDa (TDP-43), a nuclear protein, plays an important role in the molecular pathogenesis of amyotrophic lateral sclerosis (ALS). The long-disordered C-terminal region (CTR) of TDP-43 is known to be aggregation-prone and a hotspot for ALS mutations, so elucidation of the physiological function of CTR will provide insights into the pathogenesis of ALS. The CTR has two Gly, aromatic, and Ser-rich (GaroS) segments and an amyloidogenic core divided into a hydrophobic patch (HP) and a Gln/Asn (Q/N)-rich segment. Although TDP-43 lacking the CTR is known to be unstable, as observed in knock-in mice, it is unclear which of these segments contributes to the stability of TDP-43. Here, we generated 12 mouse lines lacking the various sub-regions of CTR by genome editing and compared the embryonic lethality of homozygotes, and protein and mRNA expression levels of TDP-43. We demonstrated the functional diversity of the four segments of CTR, finding that the presence of the Q/N-rich segment greatly restored the protein stability of TDP-43. In addition, we found that the second GaroS deletion did not affect protein stability and mouse development.

Recent studies utilizing single-cell analysis have unveiled the presence of various fibroblast (Fb) subsets within the synovium under inflammatory conditions in osteoarthritis (OA), distinguishing them from those in rheumatoid arthritis (RA). Moreover, it has been reported that pain in knee OA patients is linked to specific fibroblast subsets. Single-cell expression profiling methods offer an incredibly detailed view of the molecular states of individual cells. However, one limitation of these methods is that they require the destruction of cells during the analysis process, rendering it impossible to directly assess cell function. In our study, we employ flow cytometric analysis, utilizing cell surface markers CD39 and CD55, in an attempt to isolate fibroblast subsets and investigate their relationship with OA pathology. Synovial tissues were obtained from 25 knee OA (KOA) patients. Of these, six samples were analyzed by RNA-seq (n = 3) and LC/MS analysis (n = 3). All 25 samples were analyzed to estimate the proportion of Fb (CD45−CD31−CD90+) subset by flow cytometry. The proportion of Fb subsets (CD39+CD55− and CD39−CD55+) and their association with osteoarthritis pathology were evaluated. CD39+CD55− Fb highly expressed myogenic markers such as CNN1, IGFBP7, MYH11, and TPM1 compared to CD39−CD55+ Fb. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of upregulated differentially expressed genes (DEGs) in CD39+CD55− Fb identified the Apelin pathway and cGMP-PKC-signaling pathway as possibly contributing to pain. LC/MS analysis indicated that proteins encoded by myogenic marker genes, including CNN1, IGFBP7, and MYH11, were also significantly higher than in CD39−CD55+ Fb. CD39−CD55+ Fb highly expressed PRG4 genes and proteins. Upregulated DEGs were enriched for pathways associated with proinflammatory states (‘RA’, ‘TNF signaling pathway’, ‘IL-17 signaling pathway’). The proportion of CD39+CD55− Fb in synovium significantly correlated with both resting and active pain levels in knee OA (KOA) patients (resting pain, ρ = 0.513, p = 0.009; active pain, ρ = 0.483, p = 0.015). There was no correlation between joint space width (JSW) and the proportion of CD39+CD55− Fb. In contrast, there was no correlation between the proportion of CD39−CD55+ Fb and resting pain, active pain, or JSW. In conclusion, CD39+CD55− cells exhibit a myofibroblast phenotype, and its proportion is associated with KOA pain. Our study sheds light on the potential significance of CD39+CD55− synovial fibroblasts in osteoarthritis, their myofibroblast-like phenotype, and their association with joint pain. These findings provide a foundation for further research into the mechanisms underlying fibrosis, the impact of altered gene expression on osteoarthritic joints, and potential therapeutic strategies.