-
The Journal of Biological Chemistry May 2024ATP-citrate lyase (ACLY) links carbohydrate and lipid metabolism and provides nucleocytosolic acetyl-CoA necessary for protein acetylation. ACLY has two major splice...
ATP-citrate lyase (ACLY) links carbohydrate and lipid metabolism and provides nucleocytosolic acetyl-CoA necessary for protein acetylation. ACLY has two major splice isoforms: the full-length canonical "long" isoform and an uncharacterized "short" isoform in which exon 14 is spliced out. Exon 14 encodes 10 amino acids within a disordered region of the protein and includes at least 1 site that is dynamically phosphorylated. Both isoforms are expressed in healthy tissues to varying degrees. Analysis of human transcriptomic data revealed that the Percent Spliced In (PSI) of exon 14, i.e., the proportion of long isoform, is increased in several cancers and correlated with poorer overall survival in a pan-cancer analysis, though not in individual tumor types, which prompted us to explore potential biochemical and functional differences between ACLY isoforms. Here, we show that there are no discernible differences in enzymatic activity or stability between isoforms or phosphomutants of ACLY in vitro. Similarly, both isoforms and phosphomutants were able to rescue ACLY functions, including fatty acid synthesis and bulk histone acetylation, when re-expressed in Acly knockout cells. Deletion of Acly exon 14 in mice did not overtly impact development or metabolic physiology, nor did it attenuate tumor burden in a genetic model of intestinal cancer. Notably, expression of epithelial splicing regulatory protein 1 (ESRP1) is highly correlated with ACLY PSI. We report that ACLY splicing is regulated by ESRP1. In turn, both ESRP1 expression and ACLY PSI are correlated with specific immune signatures in tumors. Despite these intriguing patterns of ACLY splicing in healthy and cancer tissues, functional differences between the isoforms remain elusive.
PubMed: 38815867
DOI: 10.1016/j.jbc.2024.107418 -
PLoS Pathogens May 2024The influenza A virus (IAV) consists of 8 single-stranded, negative-sense viral RNA (vRNA) segments. After infection, vRNA is transcribed, replicated, and wrapped by...
The influenza A virus (IAV) consists of 8 single-stranded, negative-sense viral RNA (vRNA) segments. After infection, vRNA is transcribed, replicated, and wrapped by viral nucleoprotein (NP) to form viral ribonucleoprotein (vRNP). The transcription, replication, and nuclear export of the viral genome are regulated by the IAV protein, NS2, which is translated from spliced mRNA transcribed from viral NS vRNA. This splicing is inefficient, explaining why NS2 is present in low abundance after IAV infection. The levels of NS2 and its subsequent accumulation are thought to influence viral RNA replication and vRNP nuclear export. Here we show that NS2 is ubiquitinated at the K64 and K88 residues by K48-linked and K63-linked polyubiquitin (polyUb) chains, leading to the degradation of NS2 by the proteasome. Additionally, we show that a host deubiquitinase, OTUB1, can remove polyUb chains conjugated to NS2, thereby stabilizing NS2. Accordingly, knock down of OTUB1 by siRNA reduces the nuclear export of vRNP, and reduces the overall production of IAV. These results collectively demonstrate that the levels of NS2 in IAV-infected cells are regulated by a ubiquitination-deubiquitination system involving OTUB1 that is necessary for optimal IAV replication.
PubMed: 38814988
DOI: 10.1371/journal.ppat.1012279 -
The Journal of Biological Chemistry May 2024Ataxin-2 (Atx2) is a polyglutamine (polyQ) tract-containing RNA-binding protein, while its polyQ expansion may cause protein aggregation that is implicated in the...
Ataxin-2 (Atx2) is a polyglutamine (polyQ) tract-containing RNA-binding protein, while its polyQ expansion may cause protein aggregation that is implicated in the pathogenesis of neurodegenerative diseases such as spinocerebellar ataxia type 2 (SCA2). However, the molecular mechanism underlying how Atx2 aggregation contributes to the proteinopathies remains elusive. Here, we investigated the influence of Atx2 aggregation on the assembly and functionality of cellular processing bodies (P-bodies) by using biochemical and fluorescence imaging approaches. We have revealed that polyQ-expanded (PQE) Atx2 sequesters the DEAD-box RNA helicase (DDX6), an essential component of P-bodies, into aggregates or puncta via some RNA sequences. The N-terminal like-Sm (LSm) domain of Atx2 (residues 82-184) and the C-terminal helicase domain of DDX6 are responsible for the interaction and specific sequestration. Moreover, sequestration of DDX6 may aggravate pre-mRNA mis-splicing, and interfere with the assembly of cellular P-bodies, releasing the endoribonuclease MARF1 that promotes mRNA decay and translational repression. Rescuing the DDX6 protein level can recover the assembly and functionality of P-bodies preventing targeted mRNA from degradation. This study provides a line of evidence for sequestration of the P-body components and impairment of the P-body homeostasis in dysregulating RNA metabolism, which is implicated in the disease pathologies and a potential therapeutic target.
PubMed: 38810698
DOI: 10.1016/j.jbc.2024.107413 -
The Journal of Biological Chemistry May 2024Lysyl oxidase-like 2 (LOXL2) is a member of the lysyl oxidase family and has the ability to catalyze the cross-linking of extracellular matrix collagen and elastin. High...
Lysyl oxidase-like 2 (LOXL2) is a member of the lysyl oxidase family and has the ability to catalyze the cross-linking of extracellular matrix collagen and elastin. High expression of LOXL2 is related to tumor cell proliferation, invasion and metastasis. LOXL2 contains 14 exons. Previous studies have found that LOXL2 has abnormal alternative splicing and exon skipping in a variety of tissues and cells, resulting in a new alternatively-spliced isoform denoted LOXL2Δ13. LOXL2Δ13 lacks LOXL2WT exon 13, but its encoded protein has greater ability to induce tumor cell proliferation, invasion and metastasis. However, the molecular events that produce LOXL2Δ13 are still unclear. In this study, we found that overexpression of the splicing factor hnRNPA1 in cells can regulate the alternative splicing of LOXL2 and increase the expression of LOXL2Δ13. The exonic splicing silencer (ESS) exists at the 3' splice site (3' SS) and 5' splice site (5' SS) of LOXL2 exon 13. HnRNPA1 can bind to the ESS and inhibit the inclusion of exon 13. The RRM domain of hnRNPA1 and phosphorylation of hnRNPA1 at S91 and S95 are important for the regulation of LOXL2 alternative splicing. These results show that hnRNPA1 is a splicing factor that enhances the production of LOXL2Δ13.
PubMed: 38810697
DOI: 10.1016/j.jbc.2024.107414 -
Science Advances May 2024Structural maintenance of chromosomes flexible hinge domain-containing 1 (SMCHD1) is a noncanonical SMC protein and an epigenetic regulator. Mutations in SMCHD1 cause...
Structural maintenance of chromosomes flexible hinge domain-containing 1 (SMCHD1) is a noncanonical SMC protein and an epigenetic regulator. Mutations in SMCHD1 cause facioscapulohumeral muscular dystrophy (FSHD), by overexpressing DUX4 in muscle cells. Here, we demonstrate that SMCHD1 is a key regulator of alternative splicing in various cell types. We show how SMCHD1 loss causes splicing alterations of DNMT3B, which can lead to hypomethylation and DUX4 overexpression. Analyzing RNA sequencing data from muscle biopsies of patients with FSHD and Smchd1 knocked out cells, we found mis-splicing of hundreds of genes upon SMCHD1 loss. We conducted a high-throughput screen of splicing factors, revealing the involvement of the splicing factor RBM5 in the mis-splicing of DNMT3B. Subsequent RNA immunoprecipitation experiments confirmed that SMCHD1 is required for RBM5 recruitment. Last, we show that mis-splicing of DNMT3B leads to hypomethylation of the D4Z4 region and to DUX4 overexpression. These results suggest that DNMT3B mis-splicing due to SMCHD1 loss plays a major role in FSHD pathogenesis.
Topics: Muscular Dystrophy, Facioscapulohumeral; Humans; DNA Methyltransferase 3B; Homeodomain Proteins; DNA (Cytosine-5-)-Methyltransferases; Chromosomal Proteins, Non-Histone; DNA Methylation; Alternative Splicing; RNA-Binding Proteins; RNA Splicing; Gene Expression Regulation
PubMed: 38809976
DOI: 10.1126/sciadv.adn7732 -
Journal of Biomedical Research May 2024The current study aimed to investigate associations of circRNAs and related genetic variants with risk of prostate cancer (PCa) as well as to elucidate biological...
The current study aimed to investigate associations of circRNAs and related genetic variants with risk of prostate cancer (PCa) as well as to elucidate biological mechanisms underlying the associations. By using the MiOncoCirc database, we first compared expression levels of circRNAs between 25 paired PCa and adjacent normal tissues to identify risk-associated circRNAs. We then used logistic regression models to evaluate associations between genetic variants in candidate circRNAs and PCa risk among 4662 prostate cancer patients and 3114 healthy controls, and identified rs11973492 as a significant risk-associated variant (odds ratio = 1.20, 95% confidence interval: 1.08-1.34, = 7.06 × 10 ) in a dominant genetic model, which altered the secondary structure of the corresponding RNA chain. In the analysis, we found to sponge and silence 21 RNA-binding proteins (RPBs) enriched in the RNA splicing pathway, among which HNRNPA1 was identified and validated as a hub RBP using an external RNA-sequencing data as well as the in-house (four tissue samples) and publicly available single-cell transcriptomes. Additionally, we demonstrated that HNRNPA1 might influence hallmarks including MYC, DNA repair, and E2F target signaling pathways, thereby promoting carcinogenesis. In conclusion, genetic variants in may act as a sponge and inhibitor of RNA splicing-associated RBPs including HNRNPA1, playing an oncogenic role in PCa.
PubMed: 38808547
DOI: 10.7555/JBR.38.20240030 -
Genome Biology May 2024RNA-binding proteins (RBPs) regulate key aspects of RNA processing including alternative splicing, mRNA degradation and localization by physically binding RNA molecules....
RNA-binding proteins (RBPs) regulate key aspects of RNA processing including alternative splicing, mRNA degradation and localization by physically binding RNA molecules. Current methods to map these interactions, such as CLIP, rely on purifying single proteins at a time. Our new method, ePRINT, maps RBP-RNA interaction networks on a global scale without purifying individual RBPs. ePRINT uses exoribonuclease XRN1 to precisely map the 5' end of the RBP binding site and uncovers direct and indirect targets of an RBP of interest. Importantly, ePRINT can also uncover RBPs that are differentially activated between cell fate transitions, including neural progenitor differentiation into neurons.
Topics: RNA-Binding Proteins; Binding Sites; Exoribonucleases; Humans; RNA; Animals; Protein Binding
PubMed: 38807229
DOI: 10.1186/s13059-024-03271-1 -
Nature Communications May 2024Alternative splicing events are a major causal mechanism for complex traits, but they have been understudied due to the limitation of short-read sequencing. Here, we...
Alternative splicing events are a major causal mechanism for complex traits, but they have been understudied due to the limitation of short-read sequencing. Here, we generate a full-length isoform annotation of human immune cells from an individual by long-read sequencing for 29 cell subsets. This contains a number of unannotated transcripts and isoforms such as a read-through transcript of TOMM40-APOE in the Alzheimer's disease locus. We profile characteristics of isoforms and show that repetitive elements significantly explain the diversity of unannotated isoforms, providing insight into the human genome evolution. In addition, some of the isoforms are expressed in a cell-type specific manner, whose alternative 3'-UTRs usage contributes to their specificity. Further, we identify disease-associated isoforms by isoform switch analysis and by integration of several quantitative trait loci analyses with genome-wide association study data. Our findings will promote the elucidation of the mechanism of complex diseases via alternative splicing.
Topics: Humans; Alternative Splicing; Protein Isoforms; Quantitative Trait Loci; Genome-Wide Association Study; 3' Untranslated Regions; Alzheimer Disease; Genome, Human; Mitochondrial Precursor Protein Import Complex Proteins
PubMed: 38806455
DOI: 10.1038/s41467-024-48615-4 -
Molecular Neurodegeneration May 2024Microglia play diverse pathophysiological roles in Alzheimer's disease (AD), with genetic susceptibility factors skewing microglial cell function to influence AD risk....
Microglia play diverse pathophysiological roles in Alzheimer's disease (AD), with genetic susceptibility factors skewing microglial cell function to influence AD risk. CD33 is an immunomodulatory receptor associated with AD susceptibility through a single nucleotide polymorphism that modulates mRNA splicing, skewing protein expression from a long protein isoform (CD33M) to a short isoform (CD33m). Understanding how human CD33 isoforms differentially impact microglial cell function in vivo has been challenging due to functional divergence of CD33 between mice and humans. We address this challenge by studying transgenic mice expressing either of the human CD33 isoforms crossed with the 5XFAD mouse model of amyloidosis and find that human CD33 isoforms have opposing effects on the response of microglia to amyloid-β (Aβ) deposition. Mice expressing CD33M have increased Aβ levels, more diffuse plaques, fewer disease-associated microglia, and more dystrophic neurites compared to 5XFAD control mice. Conversely, CD33m promotes plaque compaction and microglia-plaque contacts, and minimizes neuritic plaque pathology, highlighting an AD protective role for this isoform. Protective phenotypes driven by CD33m are detected at an earlier timepoint compared to the more aggressive pathology in CD33M mice that appears at a later timepoint, suggesting that CD33m has a more prominent impact on microglia cell function at earlier stages of disease progression. In addition to divergent roles in modulating phagocytosis, scRNAseq and proteomics analyses demonstrate that CD33m microglia upregulate nestin, an intermediate filament involved in cell migration, at plaque contact sites. Overall, our work provides new functional insights into how CD33, as a top genetic susceptibility factor for AD, modulates microglial cell function.
Topics: Animals; Alzheimer Disease; Microglia; Sialic Acid Binding Ig-like Lectin 3; Mice, Transgenic; Humans; Mice; Protein Isoforms; Disease Models, Animal; Amyloid beta-Peptides; Plaque, Amyloid
PubMed: 38802940
DOI: 10.1186/s13024-024-00734-8 -
Scientific Reports May 2024SH-SY5Y, a neuroblastoma cell line, can be converted into mature neuronal phenotypes, characterized by the expression of mature neuronal and neurotransmitter markers....
SH-SY5Y, a neuroblastoma cell line, can be converted into mature neuronal phenotypes, characterized by the expression of mature neuronal and neurotransmitter markers. However, the mature phenotypes described across multiple studies appear inconsistent. As this cell line expresses common neuronal markers after a simple induction, there is a high chance of misinterpreting its maturity. Therefore, sole reliance on common neuronal markers is presumably inadequate. The Alzheimer's disease (AD) central gene, amyloid precursor protein (APP), has shown contrasting transcript variant dynamics in various cell types. We differentiated SH-SY5Y cells into mature neuron-like cells using a concise protocol and observed the upregulation of total APP throughout differentiation. However, APP transcript variant-1 was upregulated only during the early to middle stages of differentiation and declined in later stages. We identified the maturity state where this post-transcriptional shift occurs, terming it "true maturity." At this stage, we observed a predominant expression of mature neuronal and cholinergic markers, along with a distinct APP variant pattern. Our findings emphasize the necessity of using a differentiation state-sensitive marker system to precisely characterize SH-SY5Y differentiation. Moreover, this study offers an APP-guided, alternative neuronal marker system to enhance the accuracy of the conventional markers.
Topics: Humans; Amyloid beta-Protein Precursor; Neurons; Cell Line, Tumor; Cell Differentiation; Neuroblastoma; Biomarkers; Alzheimer Disease; Alternative Splicing; Protein Isoforms
PubMed: 38802572
DOI: 10.1038/s41598-024-63005-y