Cell structure and function最新文献

Interleukin-1 receptor type 2 (IL-1R2) functions as a decoy receptor that suppresses IL-1-induced inflammatory signaling. Both membrane-bound IL-1R2 (WT IL-1R2) and its soluble form (sIL-1R2) bind interleukin-1α (IL-1α) at the cell surface or in the extracellular space, thereby inhibiting downstream signaling. However, the anti-inflammatory role of IL-1R2 varies depending on the cellular context and receptor structure. In this study, we generated two IL-1R2 deletion mutants-ΔTM, lacking the transmembrane domain, and ΔTMCP, lacking both the transmembrane and cytoplasmic domains-and compared their functions with those of WT IL-1R2 in HeLa cells. Western blotting, immunoprecipitation, and enzyme-linked immunosorbent assay were used to assess receptor expression, IL-1α binding, and IL-1β-induced interleukin-8 (IL-8) production, respectively. Both ΔTM and ΔTMCP were secreted more efficiently than WT IL-1R2. WT IL-1R2 exhibited weak intracellular interaction with IL-1α, whereas the deletion mutants showed minimal binding. WT IL-1R2 most effectively suppressed IL-1α extracellular release; however, ΔTM and ΔTMCP also reduced secretion. Notably, both deletion mutants suppressed IL-1β-induced IL-8 production more effectively than WT IL-1R2, indicating enhanced extracellular decoy activity. These findings demonstrate that structural modifications of IL-1R2 influence its function as a decoy receptor, and the enhanced inhibitory effects of the deletion mutants on IL-1 signaling provide new insight into the anti-inflammatory potential of soluble IL-1R2 in non-immune cells.Key words: Interleukin-1, Interleukin-1 receptor type 2, decoy receptor, Transmembrane, Soluble interleukin-1 receptor type 2.

During early embryogenesis, gastrulation occurs within a specific region of the pluripotent epiblast, where cells undergo significant changes in their context. The induction of these cellular transformations in particular cell populations suggests the involvement of non-diffusible factors that activate signaling pathways in a spatiotemporal manner. Syntaxin4 (Stx4), a type IV membrane protein that functions as an intravesicular fusion mediator, often translocates across membranes to perform a latent extracellular role in locally regulating cellular behaviors. Through the culture of mouse embryonic egg cylinders isolated from E6.0 embryos and embryonic stem cells (ESCs), we demonstrate that the membrane translocation of Stx4 may play a crucial role in this early stage of development. Using membrane-impermeable antagonistic peptides against extracellular Stx4, along with several small-molecule inhibitors and activators, we found that cells with extracellular Stx4 deactivate focal adhesion kinase (FAK), which then impacts AKT/PI3K signaling and results in increased expression of P-cadherin, ultimately inducing the expression of the gastrulation marker brachyury. Activation of this signaling pathway also triggers Rho/ROCK signaling in ESCs, leading to morphological changes. These findings offer important insights into gastrulation by shedding light on the molecular mechanisms that initiate the spatiotemporal changes in the uniform pluripotent cell sheet.Key words: gastrulation, FAK, P-cadherin, Rho/ROCK, membrane flip.

Phospholipids are major components of biological membranes. They play an essential role in intracellular signaling and organelle dynamics; however, the availability of suitable lipid-specific probes is limited, which has hindered studies on their spatial distribution and functional dynamics in living cells. Previously, we demonstrated that octadecyl rhodamine B chloride (R18) is transported to the endoplasmic reticulum via nonvesicular membrane transport. In this study, we showed that R18 is internalized in a phosphatidylethanolamine (PE)-dependent manner in vivo. The internalization of R18 in Saccharomyces cerevisiae is blocked in PE-deficient mutants, but restored by ethanolamine supplementation, which suggests strict PE dependence. Moreover, R18 delivered to vacuoles through autophagy was not terminally retained, but underwent Pep4- and Atg15-dependent export from the vacuoles. The exported R18 was then redirected to endosomes following prolonged autophagy. These results suggest that R18 may serve as an indicator of PE dynamics and vacuole-endosome lipid transport, which contributes to lipid homeostasis inside vacuoles.Key words: autophagy, in vivo lipid dynamics, octadecyl rhodamine B (R18), phospholipase, phospholipid, vacuole, yeast.

Afadin and ZO-1 are actin-binding scaffold proteins localized at cell-cell junctions. Although these proteins contain multiple protein-binding motifs for various junctional proteins, their binding partners within cells are strictly regulated. Here, we investigated the mutual interactions among afadin, ZO-1, and actin filaments using cells lacking cellular junctions derived from EL and F9 non-epithelial cells. In EL-derived cells, afadin and ZO-1 independently colocalized with various types of actin filaments. In F9-derived cells, afadin and ZO-1 colocalized as aggregates. Gene disruption analyses revealed that afadin and ZO-1 independently form aggregates in the absence of cadherin-catenin complex. Nectin-2, an afadin-binding membrane protein, was detected in afadin aggregates but not in ZO-1 aggregates, suggesting the existence of a membrane protein that binds to ZO-1. We identified this protein as JAM-C. A comparison between α-catenin-deficient and β-catenin-deficient F9 cells suggested that the extracellular domain of E-cadherin interferes with afadin and ZO-1 aggregate formation. Furthermore, gene disruption of nectin-2 suggested that JAM-C-bound ZO-1, rather than unbound ZO-1, preferentially interacts with afadin. Together, these findings indicate that interactions among afadin, ZO-1, and actin filaments are strictly regulated by various cellular contexts.Key words: afadin, ZO-1, actin, F9 cell, L cell.

Quantitative morphological analysis is crucial for understanding cellular processes. While 3D Z-stack imaging offers high-resolution data, the complexity of 3D structures makes direct interpretation and manual annotation challenging and time-consuming, especially for large datasets. Maximum Intensity Projection (MIP) is a common strategy to create more interpretable 2D representations, but this inevitably leads to artificial overlaps between structures, significantly hindering accurate automated segmentation of individual instances by conventional methods or standard deep learning tools. To address this critical challenge in 2D projection analysis, we developed DeMemSeg, a deep learning pipeline based on Mask R-CNN, specifically designed to segment overlapping membrane structures, called prospore membranes (PSMs) during yeast sporulation. DeMemSeg was trained on a custom-annotated dataset, leveraging a systematic image processing workflow. Our optimized model accurately identifies and delineates individual, overlapping PSMs, achieving segmentation performance and derived morphological measurements that are statistically indistinguishable from expert manual annotation. Notably, DeMemSeg successfully generalized to segment PSMs from unseen data acquired from gip1Δ mutant cells, capturing the distinct morphological defects in PSMs. DeMemSeg thus provides a robust, automated solution for objective quantitative analysis of complex, overlapping membrane morphologies directly from widely used 2D MIP images, offering a practical tool and adaptable workflow to advance cell biology research.Key words: deep learning-based segmentation, microscopy image processing, cellular morphology, yeast sporulation, membrane structure.

As the outermost organ, the skin is particularly susceptible to physical damage. Keratinocytes are a major component of the epidermis, and their migration plays a crucial role in skin wound healing. Supersulfides contribute to energy production to sustain the life activities of organisms and are anticipated to play a role in various physiological functions; however, minimal studies have investigated their presence and functions in the skin. This study aimed to determine the presence of supersulfides in the skin and investigate their effect on keratinocyte migration. Using sulfane sulfur probe 4 (SSP4), a fluorescent probe that detects sulfane sulfur, the presence of supersulfides in both skin tissue and keratinocytes was revealed. Moreover, the primary supersulfide biosynthetic enzyme, cysteinyl-tRNA synthetase 2 (CARS2), was expressed at both the tissue and cellular levels. CARS2 expression and SSP4 fluorescence intensity in keratinocytes increased during wound healing, suggesting that supersulfide is involved in the regulation of cell migration. Knockdown of CARS2 suppressed keratinocyte migration and markedly downregulated gene expression of various chemokines. Protein expression analysis revealed that supersulfides regulate E-cadherin and matrix metalloproteinase (MMP)-9 via extracellular signal-regulated kinase (ERK) and protein kinase B (Akt). Furthermore, Na₂S₄ treatment of keratinocytes with CARS2 knockdown restored cell migration. We propose that supersulfide in the skin represents a novel mechanism of re-epithelialization and may serve as a therapeutic target for skin wounds.Key words: supersulfide, cysteinyl-tRNA synthetase 2, keratinocyte, cell migration, wound healing.

For the biogenesis and maintenance of cilia, bidirectional protein trafficking within cilia is crucial, and is conducted by intraflagellar transport (IFT) trains containing the IFT-A and IFT-B complexes that are powered by dynein-2 and kinesin-II motors. We have recently shown that before the assembly of anterograde IFT trains, the IFT-A, IFT-B, and dynein-2 complexes are independently recruited to the mother centriole/basal body. The IFT-B complex, which consists of 16 subunits, can be divided into the IFT-B1 and IFT-B2 subcomplexes, and IFT-B1 can be further divided into the IFT-B1a and IFT-B1b subgroups. Here we investigated how the IFT-B complex is assembled and recruited to the mother centriole for ciliogenesis. Analyses using cells with knockouts of individual IFT-B subunits, and analyses of proteins coimmunoprecipitated with EGFP-fused IFT-B2, IFT-B1b, and IFT-B1a subunits expressed in these knockout cells demonstrated the following: (i) although IFT-B2 is dispensable for the linkage between IFT-B1b and IFT-B1a, it is essential for their localization to the mother centriole; (ii) IFT-B1b is essential both for bridging IFT-B2 and IFT-B1a, and for their localization to the mother centriole; (iii) IFT-B1a is not required for the linkage between IFT-B2 and IFT-B1b nor for their localization to the mother centriole; and (iv) all IFT-B components (IFT-B2, IFT-B1b, and IFT-B1a) are essential for ciliogenesis. Thus, although ciliogenesis is not a prerequisite for the recruitment of the IFT-B complex to the mother centriole, the linkage between IFT-B2 and IFT-B1b is crucial for the mother centriole localization of the IFT-B complex for ciliogenesis.Key words: cilia, ciliogenesis, distal appendages, IFT-B complex, mother centriole.

p53 protein, a crucial transcription factor in cellular responses to a wide variety of stress, regulates multiple target genes involved in tumor suppression, senescence induction, and metabolic functions. To characterize the context-dependent roles of p53, it is still needed to develop an experimental system that enables selective activation of p53 in cells and tissues. In this study, we developed an optogenetic tool, Opto-p53, to control p53 signaling by light. Opto-p53 was designed to trigger p53 signaling by reconstituting p53 N-terminal and C-terminal fragments with a light-inducible dimerization (LID) system. Upon light exposure, cells expressing Opto-p53 demonstrated p53 transcriptional activation, resulting in cell death and cell cycle arrest. We further enhanced the efficacy of light-induced p53 activation by introducing specific mutations into Opto-p53 fragments. Our findings unveil the capability of Opto-p53 to serve as a powerful tool for dissecting the complex roles of p53 in cellular processes, thereby contributing to the field of synthetic biology and providing general design principles for optogenetic tools using endogenous transcription factors.Key words: synthetic biology, transcriptional factor, p53, optogenetics.

Stimulator of interferon genes (STING) is an endoplasmic reticulum (ER)-localized transmembrane protein. STING induces type I interferon and inflammatory responses against a variety of double-stranded DNA (dsDNA) viruses, which is critical for limiting their infection and replication. In certain settings where self-DNAs (genomic or mitochondrial DNA) emerge in the cytosol or when intracellular membrane traffic is impaired, STING becomes activated and triggers inflammation, which may contribute to the pathogenesis of various autoinflammatory and neurodegenerative diseases, including COPA syndrome and Parkinson's disease. The human STING gene exhibits genetic heterogeneity with R232, HAQ (R71H-G230A-R293Q), and H232 being the most common variants, along with population stratification. A very recent study has shown that HAQ, not R232 or H232, mediates complete clinical protection in the pathogenesis of COPA syndrome. These results reveal, for the first time, the distinct activities of the major variants in the context of the pathogenesis of autoinflammatory diseases. Besides these major variants, there exist minor pathogenic STING variants that cause an autoinflammatory disease called STING-associated vasculopathy with onset in infancy (SAVI). This review summarizes recent insights into human STING variants and their inflammatory activities.Key words: innate immunity, STING variants, COPA syndrome, membrane traffic, the Golgi.

The accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) activates the unfolded protein response (UPR) to maintain the homeostasis of the ER. The UPR consists of the IRE1, PERK and ATF6 pathways in vertebrates. Knockout of the IRE1 and PERK pathways causes defects in liver and pancreatic β cells, respectively, in mice, whereas knockout of the ATF6 pathway causes very early embryonic lethality in mice and medaka fish, a vertebrate model organism. We previously showed that ATF6 knockout in medaka causes a defect in the development of the notochord-the notochord becomes shorter-but that transient overexpression of the ER chaperone BiP via microinjection of BiP mRNA into one-cell stage embryos of these ATF6 knockout rescues this defect. Here, we microinjected mRNA encoding various ER chaperones and found that GRP94, calreticulin and calnexin also partially rescued this defect. Thus, BiP/GRP94 and calreticulin/calnexin greatly contribute to the development of the notochord by controlling the quality of collagens and N-glycosylated proteins (such as laminin and fibrillin), respectively, which have been confirmed necessary for the formation of the notochord in zebrafish.Key words: endoplasmic reticulum, protein folding, molecular chaperone, collagen, glycoprotein.