ARGLU1 is a transcriptional coactivator and splicing regulator important for stress hormone signaling and development

Proximity labeling reveals dynamic changes in the SQSTM1 protein network

Sequestosome1 (SQSTM1) is an autophagy receptor that mediates the degradation of intracellular cargo, including protein aggregates, through multiple protein interactions. These interactions form the SQSTM1 protein network, and these interactions are mediated by SQSTM1 functional interaction domains, which include LIR, PB1, UBA, and KIR. Technological advances in cell biology continue to expand our knowledge of the SQSTM1 protein network and the relationship between the actions of the SQSTM1 protein network in cellular physiology and disease states. Here we apply proximity profile labeling to investigate the SQSTM1 protein interaction network by fusing TurboID with the human protein SQSTM1 (TurboID::SQSTM1). This chimeric protein displayed well-established SQSTM1 features including production of SQSTM1 intracellular bodies, binding to known SQSTM1 interacting partners, and capture of novel SQSTM1 protein interactors. Strikingly, aggregated tau protein altered the protein interaction network of SQSTM1 to include many stress-associated proteins. We demonstrate the importance of the PB1 and/or UBA domains for binding network members, including the K18 domain of tau. Overall, our work reveals the dynamic landscape of the SQSTM1 protein network and offers a resource to study SQSTM1 function in cellular physiology and disease state.

Proximity labeling reveals dynamic changes in the SQSTM1 protein network

Sequestosome1 (SQSTM1) is an autophagy receptor that mediates degradation of intracellular cargo, including protein aggregates, through multiple protein interactions. These interactions form the SQSTM1 protein network, and these interactions are mediated by SQSTM1 functional interaction domains, which include LIR, PB1, UBA and KIR. Technological advances in cell biology continue to expand our knowledge of the SQSTM1 protein network and of the relationship of the actions of the SQSTM1 protein network in cellular physiology and disease states. Here we apply proximity profile labeling to investigate the SQSTM1 protein interaction network by fusing TurboID with the human protein SQSTM1 (TurboID::SQSTM1). This chimeric protein displayed well-established SQSTM1 features including production of SQSTM1 intracellular bodies, binding to known SQSTM1 interacting partners, and capture of novel SQSTM1 protein interactors. Strikingly, aggregated tau protein altered the protein interaction network of SQSTM1 to include many stress-associated proteins. We demonstrate the importance of the PB1 and/or UBA domains for binding network members, including the K18 domain of tau. Overall, our work reveals the dynamic landscape of the SQSTM1 protein network and offers a resource to study SQSTM1 function in cellular physiology and disease state.

ARGLU1 enhances promoter-proximal pausing of RNA polymerase II and stimulates DNA damage repair

Arginine and glutamate rich 1 (ARGLU1) is a poorly understood cellular protein with functions in RNA splicing and transcription. Computational prediction suggests that ARGLU1 contains intrinsically disordered regions and lacks any known structural or functional domains. We used adenovirus Early protein 1A (E1A) to probe for critical regulators of important cellular pathways and identified ARGLU1 as a significant player in transcription and the DNA damage response pathway. Transcriptional effects induced by ARGLU1 occur via enhancement of promoter-proximal RNA polymerase II pausing, likely by inhibiting the interaction between JMJD6 and BRD4. When overexpressed, ARGLU1 increases the growth rate of cancer cells, while its knockdown leads to growth arrest. Significantly, overexpression of ARGLU1 increased cancer cell resistance to genotoxic drugs and promoted DNA damage repair. These results identify new roles for ARGLU1 in cancer cell survival and the DNA damage repair pathway, with potential clinical implications for chemotherapy resistance.

Molecular characteristics and clinical implications of serine/arginine-rich splicing factors in human cancer

As critical splicing regulators, serine/arginine-rich splicing factors (SRSFs) play pivotal roles in carcinogenesis. As dysregulation of SRSFs may confer potential cancer risks, targeting SRSFs could provide important insights into cancer therapy. However, a global and comprehensive pattern to elaborate the molecular characteristics, mechanisms, and clinical links of SRSFs in a wide variety of human cancer is still lacking. In this study, a systematic analysis was conducted to reveal the molecular characteristics and clinical implications of SRSFs covering more than 10000 tumour samples of 33 human cancer types. We found that SRSFs experienced prevalent genomic alterations and expression perturbations in multiple cancer types. The DNA methylation, m6A modification, and miRNA regulation of SRSFs were all cancer context-dependent. Importantly, we found that SRSFs were strongly associated with cancer immunity, and were capable of predicting response to immunotherapy. And SRSFs had colossal potential for predicting survival in multiple cancer types, including those that have received immunotherapy. Moreover, we also found that SRSFs could indicate the drug sensitivity of targeted therapy and chemotherapy. Our research highlights the significance of SRSFs in cancer occurrence and development, and provides sufficient resources for understanding the biological characteristics of SRSFs, offering a new and unique perspective for developing cancer therapeutic strategies.

Single-Cell RNA Sequencing of Coronary Perivascular Adipose Tissue From End-Stage Heart Failure Patients Identifies SPP1+ Macrophage Subpopulation as a Target for Alleviating Fibrosis

BACKGROUND

Perivascular adipose tissue (PVAT) is vital for vascular homeostasis, and PVAT dysfunction is associated with increased atherosclerotic plaque burden. But the mechanisms underlining coronary PVAT dysfunction in coronary atherosclerosis remain elusive.

METHODS

We performed single-cell RNA sequencing of the stromal vascular fraction of coronary PVAT from 3 groups of heart transplant recipients with end-stage heart failure, including 3 patients with nonobstructive coronary atherosclerosis, 3 patients with obstructive coronary artery atherosclerosis, and 4 nonatherosclerosis control subjects. Bioinformatics was used to annotate the cellular populations, depict the cellular developmental trajectories and interactions, and explore the differences among 3 groups of coronary PVAT at the cellular and molecular levels. Pathological staining, quantitative real-time polymerase chain reaction, and in vitro studies were performed to validate the key findings.

RESULTS

Ten cell types were identified among 67 936 cells from human coronary PVAT. Several cellular subpopulations, including SPP1+ (secreted phosphoprotein 1) macrophages and profibrotic fibroadipogenic progenitor cells, were accumulated in PVAT surrounding atherosclerotic coronary arteries compared with nonatherosclerosis coronary arteries. The fibrosis percentage was increased in PVAT surrounding atherosclerotic coronary arteries, and it was positively associated with the grade of coronary artery stenosis. Cellular interaction analysis suggested OPN (osteopontin) secreted by SPP1+ macrophages interacted with CD44 (cluster of differentiation 44)/integrin on fibroadipogenic progenitor cells. Strikingly, correlation analyses uncovered that higher level of SPP1 in PVAT correlates with a more severe fibrosis degree and a higher coronary stenosis grade. In vitro studies showed that conditioned medium from atherosclerotic coronary PVAT promoted the migration and proliferation of fibroadipogenic progenitor cells, while such effect was prevented by blocking CD44 or integrin.

CONCLUSIONS

SPP1+ macrophages accumulated in the PVAT surrounding atherosclerotic coronary arteries, and they promoted the migration and proliferation of fibroadipogenic progenitor cells via OPN-CD44/integrin interaction and thus aggravated the fibrosis of coronary PVAT, which was positively correlated to the coronary stenosis burden. Therefore, SPP1+ macrophages in coronary PVAT may participate in the progression of coronary atherosclerosis.

Targeting PDK2 rescues stress-induced impaired brain energy metabolism

Depression is a mental illness frequently accompanied by disordered energy metabolism. A dysregulated hypothalamus pituitary adrenal axis response with aberrant glucocorticoids (GCs) release is often observed in patients with depression. However, the associated etiology between GCs and brain energy metabolism remains poorly understood. Here, using metabolomic analysis, we showed that the tricarboxylic acid (TCA) cycle was inhibited in chronic social defeat stress (CSDS)-exposed mice and patients with first-episode depression. Decreased mitochondrial oxidative phosphorylation was concomitant with the impairment of the TCA cycle. In parallel, the activity of pyruvate dehydrogenase (PDH), the gatekeeper of mitochondrial TCA flux, was suppressed, which is associated with the CSDS-induced neuronal pyruvate dehydrogenase kinase 2 (PDK2) expression and consequently enhanced PDH phosphorylation. Considering the well-acknowledged role of GCs in energy metabolism, we further demonstrated that glucocorticoid receptors (GR) stimulated PDK2 expression by directly binding to its promoter region. Meanwhile, silencing PDK2 abrogated glucocorticoid-induced PDH inhibition, restored the neuronal oxidative phosphorylation, and improved the flux of isotope-labeled carbon (U-13C] glucose) into the TCA cycle. Additionally, in vivo, pharmacological inhibition and neuron-specific silencing of GR or PDK2 restored CSDS-induced PDH phosphorylation and exerted antidepressant activities against chronic stress exposure. Taken together, our findings reveal a novel mechanism of depression manifestation, whereby elevated GCs levels regulate PDK2 transcription via GR, thereby impairing brain energy metabolism and contributing to the onset of this condition.

Deletion of ARGLU1 causes global defects in alternative splicing in vivo and mouse cortical malformations primarily via apoptosis

Haploinsufficient mutation in arginine and glutamine-rich protein 1 (Arglu1), a newly identified pre-mRNA splicing regulator, may be linked to neural developmental disorders associated with mental retardation and epilepsy in human patients, but the underlying causes remain elusive. Here we show that ablation of Arglu1 promotes radial glial cell (RG) detachment from the ventricular zone (VZ), leading to ectopic localized RGs in the mouse embryonic cortex. Although they remain proliferative, ectopic progenitors, as well as progenitors in the VZ, exhibit prolonged mitosis, p53 upregulation and cell apoptosis, leading to reduced neuron production, neuronal loss and microcephaly. RNA seq analysis reveals widespread changes in alternative splicing in the mutant mouse embryonic cortex, preferentially affecting genes involved in neuronal functions. Mdm2 and Mdm4 are found to be alternatively spliced at the exon 3 and exon 5 respectively, leading to absence of the p53-binding domain and nonsense-mediated mRNA decay (NMD) and thus relieve inhibition of p53. Removal of p53 largely rescues the microcephaly caused by deletion of Arglu1. Our findings provide mechanistic insights into cortical malformations of human patients with Arglu1 haploinsufficient mutation.

Distinct biogenesis pathways may have led to functional divergence of the human and Drosophila Arglu1 sisRNA

Stable intronic sequence RNAs (sisRNAs) are stable, long noncoding RNAs containing intronic sequences. While sisRNAs have been found across diverse species, their level of conservation remains poorly understood. Here we report that the biogenesis and functions of a sisRNA transcribed from the highly conserved Arglu1 locus are distinct in human and Drosophila melanogaster. The Arglu1 genes in both species show similar exon-intron structures where the intron 2 is orthologous and positionally conserved. In humans, Arglu1 sisRNA retains the entire intron 2 and promotes host gene splicing. Mechanistically, Arglu1 sisRNA represses the splicing-inhibitory activity of ARGLU1 protein by binding to ARGLU1 protein and promoting its localization to nuclear speckles, away from the Arglu1 gene locus. In contrast, Drosophila dArglu1 sisRNA forms via premature cleavage of intron 2 and represses host gene splicing. This repression occurs through a local accumulation of dARGLU1 protein and inhibition of telescripting by U1 snRNPs at the dArglu1 locus. We propose that distinct biogenesis of positionally conserved Arglu1 sisRNAs in both species may have led to functional divergence.

Identification of potentially functional modules and diagnostic genes related to amyotrophic lateral sclerosis based on the WGCNA and LASSO algorithms

Amyotrophic lateral sclerosis (ALS) is a genetically and phenotypically heterogeneous disease results in the loss of motor neurons. Mounting information points to involvement of other systems including cognitive impairment. However, neither the valid biomarker for diagnosis nor effective therapeutic intervention is available for ALS. The present study is aimed at identifying potentially genetic biomarker that improves the diagnosis and treatment of ALS patients based on the data of the Gene Expression Omnibus. We retrieved datasets and conducted a weighted gene co-expression network analysis (WGCNA) to identify ALS-related co-expression genes. Functional enrichment analysis was performed to determine the features and pathways of the main modules. We then constructed an ALS-related model using the least absolute shrinkage and selection operator (LASSO) regression analysis and verified the model by the receiver operating characteristic (ROC) curve. Besides we screened the non-preserved gene modules in FTD and ALS-mimic disorders to distinct ALS-related genes from disorders with overlapping genes and features. Altogether, 4198 common genes between datasets with the most variation were analyzed and 16 distinct modules were identified through WGCNA. Blue module had the most correlation with ALS and functionally enriched in pathways of neurodegeneration-multiple diseases', 'amyotrophic lateral sclerosis', and 'endocytosis' KEGG terms. Further, some of other modules related to ALS were enriched in 'autophagy' and 'amyotrophic lateral sclerosis'. The 30 top of hub genes were recruited to a LASSO regression model and 5 genes (BCLAF1, GNA13, ARL6IP5, ARGLU1, and YPEL5) were identified as potentially diagnostic ALS biomarkers with validating of the ROC curve and AUC value.

Functional characterization of the human Cdk10/Cyclin Q complex

Cyclin-dependent kinases (CDKs) are key players in cell cycle regulation and transcription. The CDK-family member Cdk10 is important for neural development and can act as a tumour suppressor, but the underlying molecular mechanisms are largely unknown. Here, we provide an in-depth analysis of Cdk10 substrate specificity and function. Using recombinant Cdk10/CycQ protein complexes, we characterize RNA pol II CTD, c-MYC and RB1 as in vitro protein substrates. Using an analogue-sensitive mutant kinase, we identify 89 different Cdk10 phosphosites in HEK cells originating from 66 different proteins. Among these, proteins involved in cell cycle, translation, stress response, growth signalling, as well as rRNA, and mRNA transcriptional regulation, are found. Of a set of pan-selective CDK- and Cdk9-specific inhibitors tested, all inhibited Cdk10/CycQ at least five times weaker than their proposed target kinases. We also identify Cdk10 as an in vitro substrate of Cdk1 and Cdk5 at multiple sites, allowing for a potential cross-talk between these CDKs. With this functional characterization, Cdk10 adopts a hybrid position in both cell cycle and transcriptional regulation.

Comprehensive Characterization of Ageing-Relevant Subtypes Associated With Different Tumorigenesis and Tumor Microenvironment in Prostate Cancer

Objective: Accumulated evidence demonstrates that ageing is a robust risk factor of prostate cancer prognosis. Herein, we conducted a systematic analysis about ageing-relevant molecules and relevant tumor microenvironment features in prostate cancer.

Methods: Transcriptome data, clinical information, and mutational data of prostate cancer patients were retrospectively collected from the Cancer Genome Atlas cohort. In accordance with the expression of specific ageing-relevant genes, prostate cancer patients were clustered with consensus clustering analyses. WGCNA was adopted for determination of subtype-associated co-expression modules and genes. Thereafter, characteristic genes were further screened with random forest algorithm and a prognostic model was conducted with multivariate cox regression analyses. Tumor microenvironment-infiltrating immune cells were estimated with ssGSEA and ESTIMATE. Activities of the cancer immunity cycle and expressions of HLA and immune checkpoint molecules were then quantified across prostate cancer cases. A serious experiment was conducted to investigate the roles of EIF2S2 in prostate tumorigenesis.

Results: This study characterized three ageing-relevant subtypes (C1, C2, and C3) with diverse clinical prognosis. Subtype C1 presented the features of low mutational frequency and immune activation; C2 was characterized by stromal and immune activation; and C3 showed immune suppression. An ageing-derived gene signature was conducted, which independently and robustly predicted patients’ prognosis. Additionally, this signature was in relation to immune inactivation. Among the genes in the signature, EIF2S2 triggered proliferation, invasion, and migration of LNCaP and PC-3 cells.

Conclusion: Collectively, ageing-relevant molecular subtypes and gene signature might be of great significance to determine clinical outcomes and tumor microenvironment features and immunotherapeutic responses in prostate cancer.

miR-335-5p Inhibits Progression of Uterine Leiomyoma by Targeting ARGLU1

Studies have demonstrated that miR-335-5p exhibits an essential role in the progress of multiple tumors, including thyroid cancer, pancreatic cancer, and non-small-cell lung cancer. However, the possible expression, the detailed role, and the underlying mechanisms of miR-335-5p in uterine leiomyoma (UL) still remained unclear. Therefore, the present study was designed to investigate the mechanism and function of miR-335-5p in UL. In our study, microRNA-335-5p (miR-335-5p) is significantly downregulated in UL tissues and UL cell lines, especially in HCC1688 and SK-UT-1 cells. Functionally, overexpression of miR-335-5p notably inhibits the viability of UL cell lines by CCK-8 assay. Besides, upregulation of miR-335-5p inhibits proliferation of UL cell lines by colony formation assay and decreases the protein levels of PCNA and Ki-67 detected by western blot assay. In addition, overexpression of miR-335-5p induces UL cell cycle arrest at G1 phase. Upregulation of miR-335-5p decreases the levels of Cyclin A1, Cyclin B1, and Cyclin D2 and upregulates the expression of p27 protein. Additionally, upregulation of miR-335-5p promotes the apoptosis of UL cell lines, increases the protein levels of Bax, Cleaved caspase-3, and Cleaved caspase-9, and decreases the protein expression of Bcl-2. Moreover, Arginine and Glutamate-Rich protein 1 (ARGLU1) is predicted as a target of miR-335-5p by ENCORI and miRDB and confirmed by dual-luciferase reporter assay. ARGLU1 is negatively associated with miR-335-5p. Furthermore, overexpression of ARGLU1 partly restores the effects of miR-335-5p mimic on the viability, proliferation, cell cycle, and apoptosis of UL cell lines. To conclude, miR-335-5p may play a repressive role in UL by targeting ARGLU1 and serve as a potential therapeutic target for the treatment of UL.

Identification of ARGLU1 as a potential therapeutic target for gastric cancer based on genome-wide functional screening data

BACKGROUND

Due to the molecular mechanism complexity and heterogeneity of gastric cancer (GC), mechanistically interpretable biomarkers were required for predicting prognosis and discovering therapeutic targets for GC patients.

METHODS

Based on a total of 824 GC-specific fitness genes from the Project Score database, LASSOCox regression was performed in TCGA-STAD cohort to construct a GC Prognostic (GCP) model which was then evaluated on 7 independent GC datasets. Targets prioritization was performed in GC organoids. ARGLU1 was selected to further explore the biological function and molecular mechanism. We evaluated the potential of ARGLU1 serving as a promising therapeutic target for GC using patients derived xenograft (PDX) model.

FINDINGS

The 9-gene GCP model showed a statistically significant prognostic performance for GC patients in 7 validation cohorts. Perturbation of SSX4, DDX24, ARGLU1 and TTF2 inhibited GC organoids tumor growth. The results of tissue microarray indicated lower expression of ARGLU1 was correlated with advanced TNM stage and worse overall survival. Over-expression ARGLU1 significantly inhibited GC cells viability in vitro and in vivo. ARGLU1 could enhance the transcriptional level of mismatch repair genes including MLH3, MSH2, MSH3 and MSH6 by potentiating the recruitment of SP1 and YY1 on their promoters. Moreover, inducing ARGLU1 by LNP-formulated saRNA significantly inhibited tumor growth in PDX model.

INTERPRETATION

Based on genome-wide functional screening data, we constructed a 9-gene GCP model with satisfactory predictive accuracy and mechanistic interpretability. Out of nine prognostic genes, ARGLU1 was verified to be a potential therapeutic target for GC.

FUNDING

National Natural Science Foundation of China.

Silencing of SRRM4 suppresses microexon inclusion and promotes tumor growth across cancers

RNA splicing is widely dysregulated in cancer, frequently due to altered expression or activity of splicing factors (SFs). Microexons are extremely small exons (3–27 nucleotides long) that are highly evolutionarily conserved and play critical roles in promoting neuronal differentiation and development. Inclusion of microexons in mRNA transcripts is mediated by the SF Serine/Arginine Repetitive Matrix 4 (SRRM4), whose expression is largely restricted to neural tissues. However, microexons have been largely overlooked in prior analyses of splicing in cancer, as their small size necessitates specialized computational approaches for their detection. Here, we demonstrate that despite having low expression in normal nonneural tissues, SRRM4 is further silenced in tumors, resulting in the suppression of normal microexon inclusion. Remarkably, SRRM4 is the most consistently silenced SF across all tumor types analyzed, implying a general advantage of microexon down-regulation in cancer independent of its tissue of origin. We show that this silencing is favorable for tumor growth, as decreased SRRM4 expression in tumors is correlated with an increase in mitotic gene expression, and up-regulation of SRRM4 in cancer cell lines dose-dependently inhibits proliferation in vitro and in a mouse xenograft model. Further, this proliferation inhibition is accompanied by induction of neural-like expression and splicing patterns in cancer cells, suggesting that SRRM4 expression shifts the cell state away from proliferation and toward differentiation. We therefore conclude that SRRM4 acts as a proliferation brake, and tumors gain a selective advantage by cutting off this brake.

Using data from The Cancer Genome Atlas, this study shows that the splicing factor SRRM4 and its program of differentiation-promoting microexons are downregulated across tumor types with remarkable consistency, providing tumors with a proliferative advantage.

MiR-3613-3p inhibits hypertrophic scar formation by down-regulating arginine and glutamate-rich 1

Hypertrophic scar (HS) is a severe skin disorder characterized by excessive extracellular matrix production and abnormal function of fibroblasts. Recent studies have demonstrated that microRNAs (miRNAs) play critical roles in HS formation. This study aims to investigate the role of miR-3613-3p in the formation of HS. The mRNA and miRNA levels were measured by quantitative RT-PCR analysis. The protein levels were examined by Western blot assay. Cell proliferation was determined by Cell Counting Kit-8 assay. The Caspase-3 and Caspase-9 activities were measured using flow cytometry assay. Dual-luciferase activity reporter assay and mRNA-miRNA pulldown assay were conducted to validate the target of miR-3613-3p. miR-3613-3p was downregulated, while arginine and glutamate-rich 1 (ARGLU1) was upregulated in HS fibroblasts (HSFs) and tissues. Overexpression of miR-3613-3p or knockdown of ARGLU1 markedly inhibited the expression of extracellular matrix (ECM) production-associated proteins and promoted Caspase-3 and Caspase-9 activations in HSFs. ARGLU1 was further identified as a direct target of miR-3613-3p. Restoration of ARGLU1 abrogated the suppressive effect of miR-3613-3p on cell proliferation and ECM protein expression of HSFs. Our results demonstrated that miR-3613-3p inhibited HS formation via targeting ARGLU1, which may provide potential therapeutic targets for the management of HS.

Eph/ephrin signalling in the development and function of the mammalian cochlea

In mammals, the functional development of the cochlea requires the tight regulation of multiple molecules and signalling pathways including fibroblast growth factors, bone morphogenetic proteins, Wnt and Notch signalling pathways. Over the last decade, the Eph/ephrin system also emerged as a key player of the development and function of the mammalian cochlea. In this review, we discuss the recent advances on the role of Eph/ephrin signalling in patterning the cochlear sensory epithelium and the complex innervation of mechanosensory hair cells by spiral ganglion neurons. Finally, we address the issue of a syndromic form of hearing loss caused by a deficient member of the Eph/ephrin family.