FEBS Letters最新文献

Exogenous fatty acids are directly incorporated into bacterial membranes, heavily influencing cell envelope properties, antibiotic susceptibility, and bacterial ecology. Here, we quantify fatty acid biosynthesis metabolites and enzymes of the fatty acid synthesis pathway to determine how exogenous fatty acids inhibit fatty acid synthesis in Escherichia coli. We find that acyl-CoA synthesized from exogenous fatty acids rapidly increases concentrations of long-chain acyl-acyl carrier protein (acyl-ACP), which inhibits fatty acid synthesis initiation. Accumulation of long-chain acyl-ACP is caused by competition with acyl-CoA for phospholipid synthesis enzymes. Furthermore, we find that transcriptional regulation rebalances saturated and unsaturated acyl-ACP while maintaining overall expression levels of fatty acid synthesis enzymes. Rapid feedback inhibition of fatty acid synthesis by exogenous fatty acids thus allows E. coli to benefit from exogenous fatty acids while maintaining fatty acid synthesis capacity. We hypothesize that this indirect feedback mechanism is ubiquitous across bacterial species.

Fused in sarcoma (FUS) is a causative factor of amyotrophic lateral sclerosis (ALS) and is believed to propagate pathologically by transmission from cell to cell. However, the mechanism underlying FUS release from cells, which is a critical step for the propagation system, remains poorly understood. This study conducted an analysis of the release of human and mouse FUS from neurons, revealing that human FUS is significantly released into the media compared to its mouse counterpart. Further study using chimeric FUS proteins identified the amino-terminal region of human FUS as essential for its release. These findings indicate that human FUS is released directly from neurons and underscore the novel functional role of its amino-terminal region in this process.

FOXO3a is a transcription factor involved in cell growth inhibition and apoptosis. FOXO3a is localized in the cytoplasm in cancer cells, and its nuclear translocation by small molecules is expected to prevent cancer cell growth. In this study, we screened a fungal broth library in HeLa cells using fluorescently labeled FOXO3a and an AI-based imaging system. We identified violaceoid F, which translocates FOXO3a into the nucleus by inhibiting CRM1, which is responsible for nuclear protein export. Violaceoid F was observed to target the reactive cysteine of CRM1 through its α, β-epoxyketone. However, because violaceoid F did not inhibit Crm1 in fission yeast cells, it seems to target cysteine residue(s) other than Cys528 of human CRM1 which are not targeted by other known CRM1 inhibitors, indicating that violaceoid F inhibits CRM1 via a novel mechanism.

Phospholipids are asymmetrically distributed in the plasma membrane (PM), and scramblases disrupt this asymmetry by shuffling phospholipids. We recently identified mouse Tmem63b as a membrane structure-responsive scramblase. Tmem63b belongs to the TMEM63/OSCA family of ion channels; however, the conservation of the scramblase activity within this family remains unclear. We expressed human TMEM63 paralogs, TMEM63B orthologs, and plant OSCA1.1 in Tmem63b-deficient mouse pro-B cells and found that vertebrate TMEM63B orthologs exhibit scramblase activity at the PM. Previously, ten pathogenic human TMEM63B variants were identified, some of which exhibited constitutive scramblase activity. Upon expressing all variants, we found that nine variants displayed constitutive scramblase activity. These results suggest that membrane structure-responsive scramblase activity at the PM is conserved among vertebrate TMEM63B orthologs.

The colonic epithelium plays a crucial role in gastrointestinal homeostasis, and colon organoids enable investigation into the molecular mechanisms underlying colonic physiology. However, the method for differentiating induced pluripotent stem cells (iPSCs) into human colon organoids (HCOs) is not necessarily standardized, and studies using HCOs are limited. This study refines the differentiation of HCOs by comparing two protocols reported in Cell Stem Cell and Nature Medicine journals. The former protocol, which uses transient bone morphogenetic protein 2 (BMP2) signaling activation, demonstrated superior efficacy in upregulating colon-specific markers. Additionally, adenovirus-mediated transduction of the transcription factors HOXD13 or SATB2 during hindgut endoderm development, together with BMP2 treatment, enhanced colonic identity, suggesting improved colonic maturation. This optimized protocol advances the generation of mature HCOs, offering a better model for investigating colonic epithelial biology and pathology.

Cell adhesion is warranted by proteins that are crucial for the maintenance of tissue integrity and homeostasis. Most of these proteins behave as receptors to link adhesion to the control of cell survival and their expression or regulation are often altered in cancers. B-cell malignancies do not evade this principle as they are sustained in relapsed niches by interacting with the microenvironment that includes cells and their secreted factors. Focusing on chronic lymphocytic leukemia and mantle cell lymphoma, this Review delves with the molecules involved in the dialog between the adhesion platforms and signaling pathways known to regulate both cell adhesion and survival. Current therapeutic strategies disrupt adhesive structures and compromise the microenvironment support to tumor cells, rendering them sensitive to immune recognition. The development of organ-on-chip and 3D culture systems, such as spheroids, have revealed the importance of mechanical cues in regulating signaling pathways to organize cell adhesion and survival. All these elements contribute to the elaboration of the crosstalk of lymphoma cells with the microenvironment and the education processes that allow the establishment of the supportive niche.

Promyelocytic leukemia (PML) protein forms the scaffold for PML nuclear bodies (PML NB) that reorganize into Lipid-Associated PML Structures (LAPS) under fatty acid stress. We determined how the fatty acid oleate alters the interactome of PMLI or PMLII by expressing fusions with the ascorbate peroxidase APEX2 in U2OS cells. The resultant interactome included ESCRT and COPII transport protein nodes. Proximity ligation assay (PLA) revealed that COPII proteins SEC23B, SEC24A and USO1 preferentially associated with PML NBs. Nuclear localization of USO1, but not SEC23B and SEC24A, was reduced in PML knockout cells and restored by PMLII expression. Thus, proximity-labelling methods identified COPII transport protein interactions with PML NBs that are disrupted by fatty acid stress.

Genome maintenance is essential for the integrity of the genetic blueprint, of which only a small fraction is transcribed in higher eukaryotes. DNA lesions occurring in the transcribed genome trigger transcription pausing and transcription-coupled DNA repair. There are two major transcription-coupled DNA repair pathways. The transcription-coupled nucleotide excision repair (TC-NER) pathway has been well studied for decades, while the transcription-coupled homologous recombination repair (TC-HR) pathway has recently gained attention. Importantly, recent studies have uncovered crucial roles of RNA transcripts in TC-HR, opening exciting directions for future research. Transcription also plays pivotal roles in regulating the stability of highly specialized genomic structures such as telomeres, centromeres, and fragile sites. Despite their positive function in genome maintenance, transcription and RNA transcripts can also be the sources of genomic instability, especially when colliding with DNA replication and forming unscheduled pathological RNA:DNA hybrids (R-loops), respectively. Pathological R-loops can result from transcriptional stress, which may be induced by transcription dysregulation. Future investigation into the interplay between transcription and DNA repair will reveal novel molecular bases for genome maintenance and transcriptional stress-associated genomic instability, providing therapeutic targets for human disease intervention.

The transcription-coupled repair (TCR) pathway resolves transcription-blocking DNA lesions to maintain cellular function and prevent transcriptional arrest. Stalled RNA polymerase II (RNAPII) triggers repair mechanisms, including RNAPII ubiquitination, which recruit UVSSA and TFIIH. Defects in TCR-associated genes cause disorders like Cockayne syndrome, UV-sensitive syndrome, xeroderma pigmentosum, and recently defined AMeDS. TCR safeguards transcription, linking its failure to neurodegeneration and disease phenotypes.

Yeast is a poikilothermic organism and adapts its lipid composition to the environmental temperature to maintain membrane physical properties. Studies addressing temperature-dependent adaptation of the lipidome have described changes in the phospholipid composition at the level of sum composition (e.g. PC 32:1) and molecular composition (e.g. PC 16:0_16:1). However, there is little information at the level of positional isomers (e.g. PC 16:0/16:1 versus PC 16:1/16:0). Here, we used collision- and ozone-induced dissociation (CID/OzID) mass spectrometry to investigate homeoviscous adaptation of PC, PE and PS to determine the phospholipid acyl chains at the sn-1 and sn-2 position. Our data establish the sn-molecular species composition of PC, PE and PS in the lipidome of yeast cultured at different temperatures.