Molecular Biology of the Cell最新文献

Endoplasmic reticulum (ER) homeostasis is maintained through tightly regulated processes that coordinate lipid metabolism and proteostasis. The ER-resident acyl-CoA diphosphatase FIT2, and its yeast homologue Scs3, are key regulators of this balance; their loss disrupts ER morphology and induces chronic ER stress, though the underlying mechanisms remain unclear. To uncover factors involved in Scs3-dependent ER maintenance, we conducted a genome-wide multicopy suppressor screen in SCS3 knockout yeast cells, which display inositol auxotrophy. This analysis identified IZH1, a zinc-related ER membrane protein homologous to the human PAQR (Progestin and AdipoQ Receptor) family, as a genetic interactor of SCS3. IZH1 overexpression enhanced INO1 expression, partially restored the growth of SCS3 knockout cells in inositol-deprived conditions, and reduced ER stress levels without correcting ER morphology defects. Moreover, IZH1 overexpression attenuated unfolded protein response signaling during acute proteotoxic stress and normalized ER-associated degradation kinetics. Together, these findings identify Izh1 as a novel regulator of ER homeostasis and provide new insight into how FIT2/Scs3 influences ER function.

Tardigrades are microscopic animals that can survive exceptional levels of ionizing radiation or desiccation-DNA-damaging conditions that would kill most animals. Irradiation or radiomimetic drug treatment of the tardigrade Hypsibius exemplaris can induce remarkably high expression levels of DNA repair genes, primarily those in the base excision repair and nonhomologous end joining pathways. How tardigrades can repair widespread DNA damage without producing frequent, large-scale chromosome structural abnormalities, like chromosome translocations and fusions, is unknown. Here, we report the results of examining chromosome and nuclear architecture throughout the cell cycle in early embryos of H. exemplaris. We found that H. exemplaris chromosomes are maintained in an individualized form throughout the cell cycle. We were surprised to also find that each chromosome is housed in a fully or partially separate lamin-lined compartment, instead of all chromosomes being housed in a single, nearly spherical nuclear lamina and envelope. Our results reveal unusual chromosomal and nuclear organization in a tardigrade. We speculate that these unexpected features might limit chromosomal rearrangements during DNA damage repair in extreme conditions.

The barriers limiting the number of women appointed, retained, and promoted in academia are well documented. Addressing these barriers is key to increasing participation in science, technology, engineering, and mathematics (STEM), which in turn is essential for maintaining a well-trained and competitive workforce and educational system. The success stories of tenacious individuals who persisted despite the many barriers placed before them serve both as potent reminders of hard-fought gains in equal access and opportunities and as inspiration to current and aspiring scientists. When concepts like diversity, equity, and inclusion are rebranded as discriminatory, how do academic institutions respond to the challenge to encourage broad participation in STEM?

Paclitaxel (PTX), a chemotherapeutic that stabilizes microtubules, induces nociceptive hypersensitivity and sensory neuron damage in humans, mice, and flies. To enhance our basic understanding of PTX-induced effects, we undertook a molecular/genetic dissection of PTX-induced nociceptive hypersensitivity. Larvae fed viable doses of PTX exhibited dose-dependent hypersensitivity to subnoxious thermal stimuli. Hypersensitivity developed rapidly and did not completely resolve at the larval stage. Live imaging of peripheral thermal nociceptors showed that lower doses of PTX (< 10 µM) caused hyper-sprouting of tertiary dendritic branches. At 10 µM and above, dendritic beading was observed. PTX-induced hypersensitivity does not depend on signaling pathways previously implicated in acute injury-induced nociceptive sensitization. However, the insulin-like peptide 4 (ILP4) was required for PTX-induced thermal hypersensitivity at 10 µM PTX. Surprisingly, RNAi targeting the insulin receptor (InR) in nociceptors increased PTX-induced hypersensitivity, suggesting that ILP4 does not activate InR in this context. The salivary gland is likely the primary tissue source of functional ILP4. ILP4 mutant larvae did not exhibit PTX-induced beading (10 µM) but did exhibit hypersprouting at lower PTX concentrations. In summary, our model of PTX-induced hypersensitivity reveals a disconnect between hypersensitivity and neuronal morphology and a genetic separation of ILP4 and InR in PTX-induced hypersensitivity.

The tumor microenvironment contributes to tumorigenesis and tumor progression. Interstitial fluid pressure is elevated in almost all solid malignant tumors, and physical pressure in the tumor microenvironment influences various cancer cell functions, including cell proliferation. However, the direction of the pressure applied to cancer cells has not been considered in previous studies, and the role of physical pressure in the tumor microenvironment in tumor progression remains unclear. Therefore, we investigated the effects of hydrostatic pressure (HP) applied to the basal side on lung cancer cells cultured on Transwell filters. Our data show that HP from the basal side alters various phenotypes of cancer cells, including cell migration, polarity, proliferation, and cell death, all of which are presumed to contribute to tumor progression. These results suggest that physical pressure in the tumor microenvironment provides cancer cells with an advantage in various phenotypes and plays an important role in cancer cell biology.

The mechanical properties of cells are governed by the cytoskeleton, a dynamic network of actin filaments, intermediate filaments, and microtubules. Understanding the individual and collective mechanical contributions of these three different cytoskeletal elements is essential to elucidate how cells maintain mechanical integrity during deformation. Here we use a custom single-cell rheometer to identify the distinct contributions of actin and vimentin to the viscoelastic and nonlinear elastic response of cells to uniaxial compression. We used mouse embryonic fibroblasts (MEFs) isolated from wild type (WT) and vimentin knockout (vim -/-) mice in combination with chemical treatments to manipulate actin polymerization and contractility. We show through small amplitude oscillatory measurements and strain ramp tests that vimentin, often overlooked in cellular mechanics, plays a role comparable to actin in maintaining cell stiffness and resisting large compressive forces. However, actin appears to be more important than vimentin in determining cellular energy dissipation. Finally we show by comparing wild type and enucleated cells that compression stiffening originates from the actin and vimentin cytoskeleton, while the nucleus appears to play little role in this. Our findings provide insight into how cytoskeletal networks collectively determine the mechanical properties of cells, providing a basis to understand the role of the cytoskeleton in the ability of cells to resist external as well as internal forces. [Media: see text] [Media: see text].

Cell movement and division are complex behaviors driven by a dynamic internal cytoskeleton. The molecular components and principles of cytoskeletal assembly are well studied, but less is known about cytoskeletal remodeling events, including how centrioles transition from ciliary base to centrosome. Here, we address this using the chytrid Rhizoclosmatium globosum, a zoosporic fungus that has centrioles and cilia, lost in most fungal lineages. Chytrids undergo reorganization of their microtubule cytoskeleton as they grow from zoospore to multinucleated coenocyte. We use evolutionary comparison, RNA-sequencing, and expansion microscopy to understand this reorganization and further develop this organism as a model for evolutionary cell biology. We find that when motile zoospores transition to sessile sporangia, cilia are retracted into the cytoplasm and degraded, while centrioles detach from the ciliary axoneme yet persist. During the mitotic cycles, short centrioles are associated with a centrosome-like microtubule-organizing center (MTOC) and a dense microtubule array at the spindle pole. After the mitotic cycles, centrioles elongate and form cilia, driven by transcription of genes associated with centriole maturation and ciliogenesis, and microtubule bundles are reorganized. Thus, in chytrids structural remodeling of the centriole is temporally coupled to specific changes in cytoskeletal organization over the coenocytic lifecycle.

Proteasome inhibitors such as bortezomib, carfilzomib, and ixazomib are FDA-approved treatments for multiple myeloma, but resistance frequently limits their effectiveness. The transcription factor Nrf1 (NFE2L1) upregulates proteasome and autophagy genes upon proteasome inhibition, contributing to adaptive resistance. In this study, we identified anthracyclines, including doxorubicin, as suppressors of the Nrf1-driven transcriptional response. Mechanistically, doxorubicin impaired Nrf1 binding to antioxidant response elements (AREs) within promoter regions of target genes without affecting Nrf1 processing or nuclear localization. Importantly, aclarubicin, a non-DNA-damaging anthracycline, also attenuated Nrf1 transcriptional activity, indicating that DNA damage is not required for this inhibition. Doxorubicin cotreatment delayed proteasome recovery after pulse inhibition and partially restored sensitivity to carfilzomib in bortezomib-resistant U266 myeloma cells, consistent with genetic knockout of Nrf1. These findings identify a DNA-damage-independent mechanism by which anthracyclines directly obstruct Nrf1-mediated transcriptional induction. Thus, anthracyclines serve as chemical tools to probe the molecular control of proteostasis and suggest a strategy to mitigate Nrf1-driven adaptive response to proteasome inhibition.

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of rare but severe autoimmune diseases characterized by necrotizing inflammation of small blood vessels, leading to organ damage, particularly in the kidneys and respiratory tract. The current understanding of AAV pathogenesis has moved beyond a simple model of autoantibody-mediated damage to recognize a complex, self-sustaining inflammatory circuit. Central to this circuit is a dysregulated triad between neutrophils, macrophages, and the vascular endothelium. This review synthesizes our current understanding of this innate immune axis, detailing the pathogenic sequence from the initial loss of tolerance to the subsequent inflammatory priming event that triggers the pathogenic activation of neutrophils. The chronicity of AAV arises from powerful feed-forward amplification loops that sustain inflammation, which are cemented by the active suppression of the body's intrinsic resolution pathways. Finally, we discuss how advanced bioengineered platforms, such as vasculitis-on-a-chip models, are essential for deconstructing this complex pathology and are poised to accelerate the development of a new generation of targeted, pro-resolution therapies. This review provides a comprehensive framework for understanding the central role of neutrophil-macrophage cross-talk in the perpetuation of AAV.

Cell-surface glypicans distribute several extracellular ligands, including the Wnts, which are secreted to function at short and long range in a tissue. The Drosophila glypican Dally-like protein (Dlp) interacts with Wnts to inhibit short-range Wnt signaling and promote long-range signaling by the Drosophila Wnt1, Wingless (Wg). Dlp-dependent long-range Wg distribution in the fly ovary is attenuated by metalloproteinase 2 (Mmp2). Here, we report that Mmp2 destabilizes cell-surface Dlp, causing it to be internalized. Further, after Mmp2 cleavage, Dlp sequesters more Wg, suggesting that cleaved Dlp removes Wg from the extracellular space to limit its availability for signaling. Based on these and our previous results, we propose that coordinated activities of uncleaved and cleaved Dlp regulate proper extracellular Wg distribution. Overall, this study identifies the molecular basis of protease-mediated inhibition of a cell-surface glypican to modulate ligand distribution and function.