Journal of Molecular Cell Biology

Long noncoding RNAs (LncRNAs) have emerged as a class of important regulatory ncRNAs and are known to fine-tune numerous cellular processes including proliferation, differentiation and development; however, their role in quiescence still remains largely unexplored. A miRNA host gene lncRNA, MIR503HG, has been reported to play important role in cancer development. Here, we demonstrate the role of MIR503HG lncRNA in regulating cellular quiescence. MIR503HG displays elevated levels in human diploid fibroblasts induced to undergo quiescence. Depletion of MIR503HG in HDFs affects the entry of cells into quiescence but has no effect on cell cycle progression, suggesting its role in quiescence attainment and/or maintenance. Additionally, MIR503HG depletion led to a drastic decrease in the levels of miR508 target, PTEN with a concomitant increase in pAkt levels, indicating its role in negative regulation of miR508. Further, we demonstrate that the lncRNA MIR503HG regulates PTEN levels by acting as a ceRNA for miR508 to maintain cellular quiescence. Our studies illustrate that MIR503HG can function synergistically with miR503 to maintain cells under quiescence and both the miRNA-HG and the miRNA encoded by its gene locus synergistically control the same biological process in different ways by regulating different downstream genes.

Tumor heterogeneity highlights the necessity of precision cancer medicine, making the evaluation and screening of anticancer drugs a core challenge in cancer therapy. However, current cell-based efficacy assessment methods struggle to quantify the holistic impact of drugs on cellular behavior through specific target engagement. Here, we proposed a novel approach (DL-TCP-FRET) that integrates phenotypic and target-related evaluations: the logistic fitting analysis is performed on time- and concentration-dependent cellular phenotypic characteristics to construct a phenotypic score (P), while a target score (T) is established based on the FRET efficiency between target proteins. These two scores were then further combined to generate a unified drug efficacy score (PT). Validation in A549 cells demonstrated that our method can reliably distinguish EGFR-TKIs from non-targeted drugs. DL-TCP-FRET simplifies the experimental workflow of drug efficacy evaluation and improves the accuracy of targeted drug identification, providing a novel strategy for advancing precision cancer therapy.

Multicellular organisms comprise various types of cells, which are characterized by gene expression through interactions between chromosomal DNA and nuclear proteins. Many cutting-edge methods have been developed to reveal the three-dimensional organization of chromosomes. The detailed analyses of whole chromosomes have begun to uncover structural features specific to several cell types. Here, we show that cell types are instantly and highly accurately classified using conventional DNA staining and a convolutional neural network (CNN). A high-resolution single slice image of the nucleus is sufficient for the accurate classification of both live and fixed cells, including neurons and non-neural cells. These findings suggest that there may be cell-type-specific features decipherable by deep learning in a thin two-dimensional slice of the nucleus.

During viral infection, viral replication perturbs endoplasmic reticulum (ER) homeostasis and triggers the unfolded protein response (UPR). XBP1s, a transcription factor generated by one branch of the UPR, is known to potentiate both innate and adaptive immunity, but its role in antiviral responses remains incompletely understood beyond its ability to augment type I interferon (IFN) mRNA induction. Here, we show that XBP1s positively regulates the RIG-I-like receptors (RLRs), ribonuclease L (RNase L), and protein kinase R (PKR) pathways, indicating that it enhances all three major antiviral response pathways. We further show that RNase L activation rapidly decreases XBP1 mRNA levels in an RNase activity-dependent manner, leading to a prompt reduction in XBP1s expression. Consistent with this, RNase L deletion significantly increased both thapsigargin-mediated XBP1s induction and XBP1s expression following Japan encephalitis virus infection. Poly(I:C)-induced IFNB mRNA expression was significantly enhanced in RNase L-knockout cells. This enhancement was completely abolished by RNase L reconstitution. XBP1 knockdown also significantly attenuated IFNB mRNA expression in RNase L-knockout cells. These findings suggest a negative-feedback loop in which RNase L suppresses XBP1s, thereby fine-tuning antiviral responsiveness during viral infection. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/713401v1_ufig1.gif" ALT="Figure 1000"> View larger version (19K): org.highwire.dtl.DTLVardef@112d312org.highwire.dtl.DTLVardef@df79a9org.highwire.dtl.DTLVardef@1ac571borg.highwire.dtl.DTLVardef@18ac610_HPS_FORMAT_FIGEXP M_FIG C_FIG

The cell cycle comprises different phases and is a tightly regulated process at the molecular level. During the cell cycle, two key events occurred: DNA duplication during the S phase and chromosome segregation during mitosis. Accurate cell cycle progression, achieved through faithful chromosome segregation, is essential for maintaining cell fidelity. Long noncoding RNAs are a subclass of noncoding RNA that are longer than 200 bp and form RNA protein complexes (RNPs) to regulate various biological processes. Herein, we demonstrate that lncRNA NORM is involved in regulating the cell cycle by maintaining proper chromosome segregation. NORM exhibited G2 phase-specific expression, and the depletion of NORM resulted in a significant G2/M arrest. NORM-depleted cells failed to progress in mitosis and showed defects in chromosome segregation. We further demonstrated that NORM binds to proteins such as Plk1 and Nsun2. Depletion of NORM hindered the interaction between Plk1 and Bub1, resulting in reduced kinetochore localization of Plk1 during prometaphase. Our results also show that the depletion of NORM affects the binding of Nsun2 protein to CDK1 mRNA and, consequently, the stabilization of CDK1 at the protein level. Altogether, our results demonstrate that NORM regulates chromosome segregation by mediating the interaction between Plk1 and Bub1.

ATAD2 possesses a C-terminal bromodomain (BRD) that plays a critical role in recognizing and binding to acetylated lysine residues. However, because the native intracellular structure of ATAD2 remains poorly defined, the mechanisms by which the ATAD2 BRD recruits acetylated histones and the regulatory pathways involved are not yet understood. In this study, we report that the ATAD2 BRD mediates the formation of liquid-liquid phase separation (LLPS) of ATAD2 in cells. This phase separation promotes the process of histone H4 acetylation, leading to the up-regulation of C-MYC, CCND3, and ATF2 gene expression and the facilitation of chromatin remodeling. Our findings elucidate a vital function of ATAD2, wherein BRD-mediated LLPS drives histone acetylation to promote cellular chromatin remodeling.

Mixed-lineage leukemia translocated to 3 (MLLT3) is vital for maintaining the stemness of hematopoietic stem cells. Loss of MLLT3 in megakaryocyte (MK)-erythrocyte progenitor (MEP) cells leads to its differentiation into MKs. Despite its significance in stemness, the regulatory mechanism of MLLT3 during differentiation remains elusive. In this study, we investigate the regulatory role of histone deacetylase 6 (HDAC6) in modulating MLLT3 levels via heat shock protein 90 (Hsp90) activation during myeloid lineage differentiation into MKs, monocytes, and macrophages. We found that HDAC6 activates Hsp90 through deacetylation, enabling Hsp90 to retain MLLT3 in the cytoplasm where protein kinase C (PKC) phosphorylates MLLT3 at serine residues; leading to loss of MLLT3 during MK and macrophage differentiation but not during monocyte differentiation. This research provides valuable insights into the regulatory mechanisms underlying myeloid lineage commitment and opens new avenues for future investigations into stem cell biology and therapeutic applications.

Vascular plasticity is a crucial biological asset enabling our bodies to rapidly adapt to infections and acute inflammation. However, repeated insult during chronic disease can result in these vascular adaptations becoming irreversible, thereby driving disease progression and fibrosis. This study aimed to understand if phenotypic changes in endothelial cell (EC) identity could be indicative of progressive fibrosis and thereby offer new diagnostic and therapeutic opportunities for patients with metabolic dysfunction-associated steatotic liver disease (MASLD). Previous research has documented that a significant shift in EC transcriptomic signature occurs during liver fibrosis in both pre-clinical models and patients. However, the protein expression profile, phenotype and functional role of these new EC subpopulations that are induced during fibrogenesis is unclear. In this study, we integrate high-resolution imaging, proteomic and transcriptomic analysis which collectively highlight a central role for endothelial-to-mesenchymal transition (EndMT)-induced EC plasticity in the derivation of fibrosis-associated EC (FAEC). We demonstrate that: 1) full spectrum flow cytometry can provide new opportunities to categorize and phenotype EC subpopulations, 2) two distinct EndMT-derived FAEC subpopulations expand during fibrogenesis; THY1.2+ICAM1+ and TAGLN+MCAM+ EC that display unique immunomodulatory and metabolic phenotypes, 3) TAGLN+ FAEC are a conserved, pro-fibrotic cell type arising at early stages of MASLD, and 4) increased hepatic expression of TAGLN is significantly associated with detrimental patient outcomes at all stages of liver disease. This study will pave the way for the development of FAEC-specific diagnostic and therapeutic approaches to tackle progressive fibrotic disease.

Circular RNAs (circRNAs) originate from backsplicing of numerous genes in animals, but the functions of most circRNAs remain elusive. We previously demonstrated that circZNF827 forms a complex with hnRNPL/K and its host gene-encoded protein ZNF827 that acts in the nucleus to transcriptionally repress the nerve growth factor receptor (NGFR/p75NTR) gene during neuronal differentiation (Hollensen, 2020) [1]. To explore the mechanism of action, and to assess a potential role of the circZNF827-hnRNP complex on additional loci, we scrutinized the genome-wide consequences of circZNF827 and/or hnRNPL knockdown at the transcriptomic and epigenetic level. RNA-sequencing and CUT&RUN confirmed that NGFR and additional loci are transcriptionally repressed by the circZNF827-protein complex, and that these are primarily enriched for H3K27me3 signatures. Only a fraction of the massive transcriptomic changes could be ascribed to a direct circZNF827 transcription-regulated phenotype, suggesting that initial key regulatory events elicited by the circZNF827-hnRNP complex likely lead to a secondary response, which further augments neuronal differentiation.

Varicella Zoster Virus (VZV) is a dsDNA virus that infects dermal cells and causes characteristic cutaneous lesions. The virus undergoes neurotropism and later causes secondary cycles of infection. In the host nucleus, Promyelocytic Leukaemia Nuclear Bodies (PML-NBs) spontaneously form around the VZV genome to repress viral gene expression. VZV encodes for a ubiquitin E3 ligase ORF61 to disperse PML-NBs and alleviate repression. ORF61 functions as a ubiquitin E3 ligase with a conserved RING domain at the N-terminal end. It carries three SUMO-interacting motifs (SIMs) that mediate interactions with SUMOylated proteins within PML bodies. The mechanism by which ORF61 disperses PML-NBs is poorly understood. To understand how ORF61 interacts with SUMOylated proteins, we investigated its interaction with SUMO and studied its SUMO-Targeted Ubiquitin Ligase (STUbL) activity. Our studies reveal that ORF61 co-opts the E2D family for ubiquitination activity. A specific network of interactions between the E2 enzyme, ORF61, and Ub facilitates polyubiquitination. ORF61 can synthesize branched polyubiquitin chains of K11, K48, and K63 linkages. The C-terminal SIM in ORF61 is a high-affinity binder of SUMO chains. Utilizing the SIM, ORF61 targets specific lysines on SUMO chains for ubiquitination. These studies provide crucial insights into the functional mechanism of viral STUbL ORF61.

Mesenchymal stem cells (MSCs) have garnered significant attention over the past three decades due to their robust regenerative potential, primarily mediated by their paracrine activity by releasing soluble bioactive factors and extracellular vesicles (EVs). The MSC secretome plays a pivotal role in wound healing by influencing cellular migration, inflammation, angiogenesis, extracellular matrix (ECM) remodeling, and re-epithelialization. SPARC (Secreted Protein Acidic and Rich in Cysteine), a multifunctional ECM glycoprotein involved in tissue repair and remodeling, regulates key processes such as cell migration, proliferation, angiogenesis, and survival. Despite its known role in ECM dynamics, the impact of SPARC expression on the regenerative properties of MSCs remains underexplored. In this study, we hypothesized that SPARC overexpression in MSCs enhances their secretomes regenerative capacity. Using lentiviral systems, we generated SPARC-overexpressing (+SPARC) and SPARC-knockdown (KD-SPARC) MSCs to investigate SPARCs role in wound healing. Conditioned media (CM) derived from these MSCs were analyzed in vitro for their effects on human skin keratinocytes and fibroblasts. Our results revealed that SPARC expression significantly influences cell-specific migration and cell cycle. Furthermore, in an in vivo wound healing model, CM from +SPARC MSCs accelerated regeneration, while SPARC absence in MSCs CM delayed the healing process. These findings underscore the critical role of SPARC in modulating MSC secretome composition and enhancing its regenerative efficacy. This study highlights SPARC as a promising therapeutic target for the development of advanced regenerative therapies aimed at improving cutaneous wound healing outcomes.

Presenilin 1 (PS1), a key pathogenic factor in familial Alzheimers disease, is implicated in regulation of mitochondrial functions, yet its precise sub-mitochondrial localization and underlying mechanisms remain poorly understood. In this study, we generated PS1 knockout (PS1 KO) cell lines to investigate the role of PS1 in mitochondrial structure and function. Our results demonstrated that PS1 is directly localized to the mitochondrial inner membrane. PS1 deficiency led to reduced ATP production, impaired mitochondrial respiration capacity, decreased mitochondrial membrane potential, disrupted Ca2+ homeostasis, and elevated reactive oxygen species (ROS) accumulation. Moreover, loss of PS1 caused abnormal mitochondrial cristae structure. Further analysis revealed that PS1 interacts with mitochondrial inner membrane proteins. Its absence promotes ATAD3A oligomerization and disrupts its arrangement at mitochondrial cristae junctions, leading to expansion of the mitochondria-associated membrane (MAM) and instability of mitochondrial DNA (mtDNA). Our findings demonstrate that PS1 acts as a central regulator of mitochondrial cristae morphogenesis by modulating protein interaction networks at cristae junctions, thereby illuminating fundamental molecular mechanisms contributing to mitochondrial dysfunctions in Alzheimers disease.

The maintenance of protein homeostasis is vital for all cells. Alteration in protein handling underlies several diseases. The small molecule sephin1 is a promising clinical candidate against proteostasis disruption, but its mechanism of action is still uncertain. Our experimental evidence shows that sephin1 binds G-actin and drives actin cytoskeleton misfolding, and eventually, Golgi disintegration. At first, sephin1 impairs the autophagic flux and elicits the phosphorylation of the subunit of eIF2 and the ER-stress independent expression of CHOP via GCN2 kinase. Sephin1 also inhibits the mammalian target of rapamycin (mTORC1), activates the transcription Factor EB (TFEB), drives the expression of TFEB-direct target genes, and eventually stimulates the autophagy lysosomal pathway. Our results reveal that the actin cytoskeleton may regulate autophagy via mTORC1-TFEB complemented with the GCN2-eIF2-CHOP signaling pathway.

The activation of thermogenesis in brown adipose tissue (BAT) represents a pivotal target for ameliorating disorders of glucose and lipid metabolism. This study sought to elucidate the regulatory effects of quercetin on thermogenesis and glucose-lipid metabolism within brown adipocytes, alongside its underlying molecular mechanisms. The findings demonstrated that quercetin markedly upregulated the expression of uncoupling protein 1 (UCP1), a critical thermogenic protein in brown adipocytes, thereby enhancing cellular thermogenic capacity and effectively mitigating glucose and lipid metabolism disorders. Subsequent mechanistic investigations confirmed that quercetin activated the COX2-PGE2-EP4-UCP1 signaling axis by augmenting the stability of cyclooxygenase 2 (COX2) protein, thus mediating its thermogenic-promoting and metabolism-improving effects. This study identifies quercetin as a potential therapeutic agent for the improvement of glucose and lipid metabolism disorders, uncovers a novel molecular mechanism through which quercetin regulates brown adipocyte thermogenesis, and provides a theoretical and experimental foundation for the application of quercetin in the prevention and treatment of obesity and related metabolic diseases.

Text abstractsLipid homeostasis is essential for organismal physiology, and its disruption contributes to metabolic disorders. Using an unbiased genetic modifier screen in Drosophila, we identified GAR1, a core component of the box H/ACA small nucleolar ribonucleoprotein complex, as a pivotal regulator of systemic lipid storage. We show that the H/ACA snoRNP complex is essential for maintaining lipid droplet morphology in adipose tissue and preventing ectopic fat accumulation. Moreover, null mutants of Gar1 or Dkc1 exhibit severe developmental defects, including reduced body size and larval lethality. RNA-seq analysis revealed that Gar1 dysfunction triggered widespread alternative splicing defects, specifically targeting key transcripts within the insulin signaling cascade, including chico, Pi3K92E, sgg, and Lip4. Furthermore, knockdown of Gar1 impaired insulin signaling, as evidenced by the reduced membrane localization of the tGPH fluorescence. Genetic epistasis further positions GAR1 upstream of the lin-28/foxo axis, as knocking down lin-28 or foxo fully rescues the lipometabolic defects in GAR1-deficient animals. These findings reveal a previously unrecognized link between the snoRNP machinery and metabolic process, establishing the box H/ACA complex as an important coordinator that integrates RNA processing with insulin-mediated nutrient sensing to ensure developmental and lipid homeostasis. Article summaryLipid metabolism is tightly controlled by multiple factors. To find new regulators, the authors performed a genetic screen and identified a small nucleolar protein GAR1 participate in fat storage and larval development. They demonstrated a critical role of box H/ACA snoRNP complex in modulating alternative splicing and balancing insulin cascade. Blocking two insulin-related genes reversed the lipid defects caused by Gar1 loss. These findings revealed the box H/ACA complex integrates RNA processing with insulin-mediated nutrient sensing to ensure developmental and lipid homeostasis, offering a perspective for understanding the metabolic regulation network.

The newly identified signaling system comprising C-X-C motif chemokine ligand 17 (CXCL17) and G protein-coupled receptor 25 (GPR25) is involved in immune regulation and tumor development. However, the evolutionary origin of this pair has remained unclear because CXCL17 orthologs in lower vertebrates exhibit extreme sequence variation and cannot be identified through conventional homology-based searches. In this study, we identified seven possible CXCL17 orthologs in primitive cartilaginous fishes, including sharks and rays, using an integrated approach based on key amino acid sequence features as well as gene synteny, architecture, and RNA sequencing data in the NCBI gene database. To validate these candidates, a representative ortholog from the cloudy catshark (Scyliorhinus torazame), termed St-CXCL17, was prepared via bacterial overexpression and in vitro refolding. In cell-based functional assays, St-CXCL17 demonstrated high binding affinity and activation potency toward its corresponding receptor, St-GPR25. Further analysis revealed that removing three conserved C-terminal residues almost completely abolished this activity. While these cartilaginous fish CXCL17s share considerable homology with one another, they lack significant overall similarity to orthologs in mammals, amphibians, or bony fishes. These findings identify functional CXCL17 orthologs in cartilaginous fishes for the first time, implying that the CXCL17-GPR25 signaling pair likely originated in ancient cartilaginous fish ancestors or earlier and has been conserved throughout the evolution of jawed vertebrates.

Single-cell expression quantitative trait loci (sc-eQTL) analyses are powerful in identifying context-specific susceptibility genes from genome-wide association studies (GWAS) loci. However, few studies have comprehensively investigated cells of lung cancer origin in non-European populations. Here, we built a lung sc-eQTL dataset from 129 Korean women never-smokers with epithelial cell enrichment. eQTL mapping identified 2,229 genes with an eQTL in 33 cell types, including East Asian-specific findings when compared to predominantly European datasets. Integration with single-cell chromatin accessibility data demonstrated an enrichment of cell-type specific eQTLs in cell-type matched candidate enhancers, while shared eQTLs were more frequently found near promoters. Colocalization and transcriptome-wide association study unveiled 36 susceptibility genes from 22 cell types in 22 lung cancer loci, including 10 loci not achieving genome-wide significance in prior GWAS. Around 47% of these genes were from cells of the alveoli, underscoring their importance, especially in lung adenocarcinoma (LUAD) susceptibility. Focusing on the trajectory of alveolar epithelial cell regeneration, we detected 785 cell-state-interacting QTLs, which overlapped with 28% (10) of the identified susceptibility genes. Finally, we experimentally validated East Asian-and alveolar type 2 cell-specific eQTL of TCF7L2 underlying East Asian LUAD locus, 10q25.2. Consistent with its role as a Wnt/{beta}-catenin effector, TCF7L2 displayed significant effect on lung adenocarcinoma cell growth. Our data highlighted context-specific susceptibility genes, especially from alveolar cells of lung, contributing to lung cancer etiology.

Despite of the highly potent antiretroviral therapies, HIV-1 establishes persistent infection and causes chronic inflammation in AIDS patients. Beyond CD4+ T cells, HIV-1 infects myeloid cells, including circulating monocytes and tissue-resident macrophages, and integrates with host genomes to form stable viral reservoirs. To achieve a functional HIV cure, latency-promoting agents (LPAs) have been developed for the "block-and-lock" strategy to reinforce deep HIV-1 latency and permanently silence proviruses. However, most LPAs have been tested mainly in CD4+ T cells, and their efficacy in myeloid cells remains unclear. In this study, we reported that levosimendan (LSM), a drug approved for clinic use to treat heart failures, is able to inhibit HIV lytic infection and reactivation in myeloid cells. LSM blocked viral lytic reactivation in HIV-1 latently infected monocytic cells (TH89GFP, U1) and microglial cells (HC69). LSM also inhibited HIV infection in human induced pluripotent stem cell (iPSC) derived microglia (iMG), primary human resident liver macrophages (Kupffer cells) as well as human monocyte-derived macrophages (MDMs). Furthermore, we demonstrated that overexpression of a predicted drug target of LSM, the conserved serine/threonine kinase RIOK1 (RIO kinase 1), overcomes LSMs anti-HIV effect. Overall, our studies concluded that LSM is a promising LPA to inhibit HIV-1 infection in myeloid cells in the RIOK1-dependent manner.

PUF60 is a splicing factor related to the polypyrimidine-tract binding protein U2AF2. PUF60 is deleted in developmental disorders such as Verheij syndrome and amplified in approximately 8% of cancers. Thus, both increases and decreases in PUF60 expression can have profound physiological effects. However, little is known about how changes in PUF60 expression impact global splicing patterns. Here, we created a model system of CRISPRa/i in mouse stem cells (mESCs) to transcriptionally upregulate or downregulate Puf60. Our results uncovered extensive transcriptional, post-transcriptional, and post-translational regulation of Puf60 protein expression. We observed that Puf60 protein levels in normal mESCs drop dramatically at a critical cell density, leading to cell death. Puf60 is very essential in stem cells, and its repression causes cell death and impacts specific splicing events, including its own splicing autoregulation, providing valuable insights into the functional consequences of PUF60 dysregulation. Analysis of phosphoprotein data revealed phosphorylation of threonine at the N-terminus of PUF60. Our results showed that mutating threonine to glutamate downregulates the protein and alters its localization. Thus, our study reveals a novel regulatory mechanism of Puf60 phosphorylation that mediates its function and may be related to its frequent overexpression in cancer cells.

ObjectivesLupus nephritis (LN) is a severe complication of systemic lupus erythematosus with heterogeneous clinical outcomes and limited therapeutic options. Although immune dysregulation is central to LN pathogenesis, the underlying cell-type-specific regulatory mechanisms and their genetic determinants remain poorly characterized. MethodsWe generated a single-cell multi-omics atlas of peripheral blood mononuclear cells (PBMCs) from newly diagnosed, minimally treated LN patients by integrating single-cell RNA-seq (scRNA-seq) and single-nucleus ATAC-seq (snATAC-seq) profiles. To elucidate genetically driven regulatory programs in a broaden LN population, we generated a blood expression quantitative trait loci (eQTL) atlas from 99 Chinese LN patients and performed Bayesian colocalization analysis to systematically prioritize putative causal genes for LN. Finally, we investigated how fine-mapped SNPs associated with LN phenotypic manifestations exert regulatory effects within distinct single-cell chromation contexts by leveraging peak-to-gene linkages at single-cell resolution. ResultsOur single-cell multi-omic dataset and orthogonal analytical approaches revealed extensive immune remodeling in LN, characterized by amplified innate immune activation and impaired adaptive immune responses, and identified transcription factors (TFs) orchestrating immune regulatory circuits. Bayesian colocalization analysis nominated 14 high-fidelity causal genes for kidney function and 23 for SLE. Integration with fine-mapped GWAS variants highlighted critical cell type convergence across autoimmune disorders and immune-mediated nephropathies, particularly within B cell subsets, where TF-driven programs delineated stage-specific differentiation networks. ConclusionsTogether, these analyses reconstruct the regulatory architecture underlying immune dysregulation in LN and connect genetic variation to cell-type-specific regulation, guiding genetically informed therapeutic development.