Examples of associations between human disease and defects in pre-messenger RNA splicing/alternative splicing are accumulating. Although many alterations are caused by mutations in splicing signals ...or regulatory sequence elements, recent studies have noted the disruptive impact of mutated generic spliceosome components and splicing regulatory proteins. This review highlights recent progress in our understanding of how the altered splicing function of RNA-binding proteins contributes to myelodysplastic syndromes, cancer, and neuropathologies.
Summary
Deregulation of precursor mRNA splicing is associated with many illnesses and has been linked to age‐related chronic diseases. Here we review recent progress documenting how defects in the ...machinery that performs intron removal and controls splice site selection contribute to cellular senescence and organismal aging. We discuss the functional association linking p53, IGF‐1, SIRT1, and ING‐1 splice variants with senescence and aging, and review a selection of splicing defects occurring in accelerated aging (progeria), vascular aging, and Alzheimer's disease. Overall, it is becoming increasingly clear that changes in the activity of splicing factors and in the production of key splice variants can impact cellular senescence and the aging phenotype.
The number of factors known to participate in the DNA damage response (DDR) has expanded considerably in recent years to include splicing and alternative splicing factors. While the binding of ...splicing proteins and ribonucleoprotein complexes to nascent transcripts prevents genomic instability by deterring the formation of RNA/DNA duplexes, splicing factors are also recruited to, or removed from, sites of DNA damage. The first steps of the DDR promote the post-translational modification of splicing factors to affect their localization and activity, while more downstream DDR events alter their expression. Although descriptions of molecular mechanisms remain limited, an emerging trend is that DNA damage disrupts the coupling of constitutive and alternative splicing with the transcription of genes involved in DNA repair, cell-cycle control and apoptosis. A better understanding of how changes in splice site selection are integrated into the DDR may provide new avenues to combat cancer and delay aging.
The R2TP/Prefoldin-like (R2TP/PFDL) complex has emerged as a cochaperone complex involved in the assembly of a number of critical protein complexes including snoRNPs, nuclear RNA polymerases and ...PIKK-containing complexes. Here we report on the use of multiple target affinity purification coupled to mass spectrometry to identify two additional complexes that interact with R2TP/PFDL: the TSC1-TSC2 complex and the U5 small nuclear ribonucleoprotein (snRNP). The interaction between R2TP/PFDL and the U5 snRNP is mostly mediated by the previously uncharacterized factor ZNHIT2. A more general function for the zinc-finger HIT domain in binding RUVBL2 is exposed. Disruption of ZNHIT2 and RUVBL2 expression impacts the protein composition of the U5 snRNP suggesting a function for these proteins in promoting the assembly of the ribonucleoprotein. A possible implication of R2TP/PFDL as a major effector of stress-, energy- and nutrient-sensing pathways that regulate anabolic processes through the regulation of its chaperoning activity is discussed.
The poly(A)-binding protein nuclear 1 is encoded by the PABPN1 gene, whose mutations result in oculopharyngeal muscular dystrophy, a late-onset disorder for which the molecular basis remains unknown. ...Despite recent studies investigating the functional roles of PABPN1, little is known about its regulation. Here, we show that PABPN1 negatively controls its own expression to maintain homeostatic levels in human cells. Transcription from the PABPN1 gene results in the accumulation of two major isoforms: an unspliced nuclear transcript that retains the 3′-terminal intron and a fully spliced cytoplasmic mRNA. Increased dosage of PABPN1 protein causes a significant decrease in the spliced/unspliced ratio, reducing the levels of endogenous PABPN1 protein. We also show that PABPN1 autoregulation requires inefficient splicing of its 3′-terminal intron. Our data suggest that autoregulation occurs via the binding of PABPN1 to an adenosine (A)-rich region in its 3′ untranslated region, which promotes retention of the 3′-terminal intron and clearance of intron-retained pre-mRNAs by the nuclear exosome. Our findings unveil a mechanism of regulated intron retention coupled to nuclear pre-mRNA decay that functions in the homeostatic control of PABPN1 expression.
Protein phosphorylation constitutes a major post-translational modification that critically regulates the half-life, intra-cellular distribution, and activity of proteins. Among the large number of ...kinases that compose the human kinome tree, those targeting RNA-binding proteins, in particular serine/arginine-rich (SR) proteins, play a major role in the regulation of gene expression by controlling constitutive and alternative splicing. In humans, these kinases belong to the CMGC Cyclin-dependent kinases (CDKs), Mitogen-activated protein kinases (MAPKs), Glycogen synthase kinases (GSKs), and Cdc2-like kinases (CLKs) group and several studies indicate that they also control viral replication
direct or indirect mechanisms. The aim of this review is to describe known and emerging activities of CMGC kinases that share the common property to phosphorylate SR proteins, as well as their interplay with different families of viruses, in order to advance toward a comprehensive knowledge of their pro- or anti-viral phenotype and better assess possible translational opportunities.
See Fratta and Isaacs (doi:10.1093/brain/awy091) for a scientific commentary on this article.
Mutations in the RNA binding proteins TDP-43 and hnRNP A1 are associated with ALS. Deshaies et al. report ...that TDP-43 modulates hnRNP A1 splicing so as to elevate levels of an isoform containing an elongated prion-like domain, hnRNP A1B. Patients with documented TDP-43 pathology show neuronal hnRNP A1B cytoplasmic accumulation.
Abstract
See Fratta and Isaacs (doi:10.1093/brain/awy091) for a scientific commentary on this article.
The RNA binding proteins TDP-43 (encoded by TARDBP) and hnRNP A1 (HNRNPA1) are each mutated in certain amyotrophic lateral sclerosis cases and are often mislocalized in cytoplasmic aggregates within motor neurons of affected patients. Cytoplasmic inclusions of TDP-43, which are accompanied by a depletion of nuclear TDP-43, are observed in most amyotrophic lateral sclerosis cases and nearly half of frontotemporal dementia cases. Here, we report that TDP-43 binds HNRNPA1 pre-mRNA and modulates its splicing, and that depletion of nuclear TDP-43 results in increased inclusion of a cassette exon in the HNRNPA1 transcript, and consequently elevated protein levels of an isoform containing an elongated prion-like domain, referred to as hnRNP A1B. Combined in vivo and in vitro approaches demonstrated greater fibrillization propensity for hnRNP A1B, which drives protein aggregation and is toxic to cells. Moreover, amyotrophic lateral sclerosis patients with documented TDP-43 pathology showed neuronal hnRNP A1B cytoplasmic accumulation, indicating that TDP-43 mislocalization may contribute to neuronal vulnerability and loss via altered HNRNPA1 pre-mRNA splicing and function. Given that TDP-43 and hnRNP A1 each bind, and thus modulate, a third of the transcriptome, our data suggest a much broader disruption in RNA metabolism than previously considered.
When targeting promoter regions, small interfering RNAs (siRNAs) trigger a previously proposed pathway known as transcriptional gene silencing by promoting heterochromatin formation. Here we show ...that siRNAs targeting intronic or exonic sequences close to an alternative exon regulate the splicing of that exon. The effect occurred in hepatoma and HeLa cells with siRNA antisense strands designed to enter the silencing pathway, suggesting hybridization with nascent pre-mRNA. Unexpectedly, in HeLa cells the sense strands were also effective, suggesting that an endogenous antisense transcript, detectable in HeLa but not in hepatoma cells, acts as a target. The effect depends on Argonaute-1 and is counterbalanced by factors favoring chromatin opening or transcriptional elongation. The increase in heterochromatin marks (dimethylation at Lys9 and trimethylation at Lys27 of histone H3) at the target site, the need for the heterochromatin-associated protein HP1alpha and the reduction in RNA polymerase II processivity suggest a mechanism involving the kinetic coupling of transcription and alternative splicing.
We have performed a survey of soluble human protein complexes containing components of the transcription and RNA processing machineries using protein affinity purification coupled to mass ...spectrometry. Thirty-two tagged polypeptides yielded a network of 805 high-confidence interactions. Remarkably, the network is significantly enriched in proteins that regulate the formation of protein complexes, including a number of previously uncharacterized proteins for which we have inferred functions. The RNA polymerase II (RNAP II)-associated proteins (RPAPs) are physically and functionally associated with RNAP II, forming an interface between the enzyme and chaperone/scaffolding proteins. BCDIN3 is the 7SK snRNA methylphosphate capping enzyme (MePCE) present in an snRNP complex containing both RNA processing and transcription factors, including the elongation factor P-TEFb. Our results define a high-density protein interaction network for the mammalian transcription machinery and uncover multiple regulatory factors that target the transcription machinery.
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