Reciprocal regulation between alternative splicing and the DNA damage response

Non-canonical functions of spliceosome components in cancer progression

Dysregulation of pre-mRNA splicing is a common hallmark of cancer cells and it is associated with altered expression, localization, and mutations of the components of the splicing machinery. In the last few years, it has been elucidated that spliceosome components can also influence cellular processes in a splicing-independent manner. Here, we analyze open source data to understand the effect of the knockdown of splicing factors in human cells on the expression and splicing of genes relevant to cell proliferation, migration, cell cycle regulation, DNA repair, and cell death. We supplement this information with a comprehensive literature review of non-canonical functions of splicing factors linked to cancer progression. We also specifically discuss the involvement of splicing factors in intercellular communication and known autoregulatory mechanisms in restoring their levels in cells. Finally, we discuss strategies to target components of the spliceosome machinery that are promising for anticancer therapy. Altogether, this review greatly expands understanding of the role of spliceosome proteins in cancer progression.

THO complex deficiency impairs DNA double-strand break repair via the RNA surveillance kinase SMG-1

The integrity and proper expression of genomes are safeguarded by DNA and RNA surveillance pathways. While many RNA surveillance factors have additional functions in the nucleus, little is known about the incidence and physiological impact of converging RNA and DNA signals. Here, using genetic screens and genome-wide analyses, we identified unforeseen SMG-1-dependent crosstalk between RNA surveillance and DNA repair in living animals. Defects in RNA processing, due to viable THO complex or PNN-1 mutations, induce a shift in DNA repair in dividing and non-dividing tissues. Loss of SMG-1, an ATM/ATR-like kinase central to RNA surveillance by nonsense-mediated decay (NMD), restores DNA repair and radio-resistance in THO-deficient animals. Mechanistically, we find SMG-1 and its downstream target SMG-2/UPF1, but not NMD per se, to suppress DNA repair by non-homologous end-joining in favour of single strand annealing. We postulate that moonlighting proteins create short-circuits in vivo, allowing aberrant RNA to redirect DNA repair.

Maturation State-Specific Alternative Splicing in FLT3-ITD and NPM1 Mutated AML

Simple Summary

In hematological malignancies, genome-wide sequencing studies found the process of splicing to be surprisingly frequently disrupted. While recent studies characterized altered splicing in relation to splicing factor mutations in AML, this study explored differential splicing profiles associated with two most common aberrations in AML: FLT3-ITD and NPM1 mutations. We identified the differential splicing of FAB-type specific gene sets in FLT3-ITD+/NPM1+ specimens as compared to FLT3-ITD−/NPM1− samples. The primary functions perturbed by differential splicing in all three FAB types included cell cycle control and DNA damage response. Interestingly, differential expression mainly affected genes involved in hematopoietic differentiation. Our findings increase our understanding of how genetic mutations translate to phenotypic features of AML cells to further improve response predictions and to find innovative therapeutic approaches. Altogether, to the best of our knowledge, this is the first study to report differential splicing profiles associated with FLT3-ITD with a concomitant NPM1 mutation in AML.

Abstract

Despite substantial progress achieved in unraveling the genetics of AML in the past decade, its treatment outcome has not substantially improved. Therefore, it is important to better understand how genetic mutations translate to phenotypic features of AML cells to further improve response predictions and to find innovative therapeutic approaches. In this respect, aberrant splicing is a crucial contributor to the pathogenesis of hematological malignancies. Thus far, altered splicing is well characterized in relation to splicing factor mutations in AML. However, splicing profiles associated with mutations in other genes remain largely unexplored. In this study, we explored differential splicing profiles associated with two of the most common aberrations in AML: FLT3-ITD and NPM1 mutations. Using RNA-sequencing data of a total of 382 primary AML samples, we found that the co-occurrence of FLT3-ITD and mutated NPM1 is associated with differential splicing of FAB-type specific gene sets. Despite the FAB-type specificity of particular gene sets, the primary functions perturbed by differential splicing in all three FAB types include cell cycle control and DNA damage response. Interestingly, we observed functional divergence between alternatively spliced and differentially expressed genes in FLT3-ITD+/NPM1+ samples in all analyzed FAB types, with differential expression affecting genes involved in hematopoietic differentiation. Altogether, these observations indicate that concomitant FLT3-ITD and mutated NPM1 are associated with the maturation state-specific differential splicing of genes with potential oncogenic relevance.

Splicing alterations in healthy aging and disease

Alternative RNA splicing is a key step in gene expression that allows generation of numerous messenger RNA transcripts encoding proteins of varied functions from the same gene. It is thus a rich source of proteomic and functional diversity. Alterations in alternative RNA splicing are observed both during healthy aging and in a number of human diseases, several of which display premature aging phenotypes or increased incidence with age. Age-associated splicing alterations include differential splicing of genes associated with hallmarks of aging, as well as changes in the levels of core spliceosomal genes and regulatory splicing factors. Here, we review the current known links between alternative RNA splicing, its regulators, healthy biological aging, and diseases associated with aging or aging-like phenotypes. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.

Splicing alterations in healthy aging and disease

Alternative RNA splicing is a key step in gene expression that allows generation of numerous messenger RNA transcripts encoding proteins of varied functions from the same gene. It is thus a rich source of proteomic and functional diversity. Alterations in alternative RNA splicing are observed both during healthy aging and in a number of human diseases, several of which display premature aging phenotypes or increased incidence with age. Age-associated splicing alterations include differential splicing of genes associated with hallmarks of aging, as well as changes in the levels of core spliceosomal genes and regulatory splicing factors. Here, we review the current known links between alternative RNA splicing, its regulators, healthy biological aging, and diseases associated with aging or aging-like phenotypes. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.