title: Pharmacological inhibition of the spliceosome subunit SF3b triggers exon junction complex-independent nonsense-mediated decay.
abstract: Spliceostatin A, meayamycin, and pladienolide B are small molecules that target the SF3b subunit of the spliceosomal U2 small nuclear ribonucleoprotein (snRNP). These compounds are attracting much attention as tools to manipulate splicing and for use as potential anti-cancer drugs. We investigated the effects of these inhibitors on mRNA transport and stability in human cells. Upon splicing inhibition, unspliced pre-mRNAs accumulated in the nucleus, particularly within enlarged nuclear speckles. However, a small fraction of the pre-mRNA molecules were exported to the cytoplasm. We identified the export adaptor ALYREF as being associated with intron-containing transcripts and show its requirement for the nucleo-cytoplasmic transport of unspliced pre-mRNA. In contrast, the exon junction complex (EJC) core protein eIF4AIII failed to form a stable complex with intron-containing transcripts. Despite the absence of EJC, unspliced transcripts in the cytoplasm were degraded by nonsense-mediated decay (NMD), suggesting that unspliced transcripts are degraded by an EJC-independent NMD pathway. Collectively, our results indicate that although blocking the function of SF3b elicits a massive accumulation of unspliced pre-mRNAs in the nucleus, intron-containing transcripts can still bind the ALYREF export factor and be transported to the cytoplasm, where they trigger an alternative NMD pathway.
authors.affiliation: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal.
authors.forename: Teresa
authors.identifier: 0000-0001-7061-8904
authors.initials: T
authors.lastname: Carvalho
authors.affiliation: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal.
authors.forename: Sandra
authors.identifier: 0000-0002-7733-4485
authors.initials: S
authors.lastname: Martins
authors.affiliation: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal.
authors.forename: José
authors.identifier: 0000-0002-0637-4527
authors.initials: J
authors.lastname: Rino
authors.affiliation: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal.
authors.forename: Sérgio
authors.initials: S
authors.lastname: Marinho
authors.affiliation: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal carmo.fonseca@medicina.ulisboa.pt.
authors.forename: Maria
authors.identifier: 0000-0002-3402-7143
authors.initials: M
authors.lastname: Carmo-Fonseca
mesh_terms: D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D039601:Eukaryotic Initiation Factor-4A / Q000378:metabolism; D005091:Exons / Q000235:genetics*; D006801:Humans; D007438:Introns / Q000235:genetics; D059365:Nonsense Mediated mRNA Decay / Q000235:genetics*; D009687:Nuclear Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011485:Protein Binding; D021122:Protein Subunits / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012326:RNA Splicing / Q000235:genetics; D000072260:RNA Splicing Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D017381:Spliceosomes / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: C105242:ALYREF protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D021122:Protein Subunits; D000072260:RNA Splicing Factors; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C112491:SF3B1 protein, human; D014157:Transcription Factors; D039601:Eukaryotic Initiation Factor-4A
keywords: EJC; Meayamycin; NMD; Pladienolide B; RNA transport; Spliceostatin A; Splicing