title: Transcription-coupled RNA surveillance in human genetic diseases caused by splice site mutations.
abstract: Current estimates indicate that approximately one-third of all disease-causing mutations are expected to disrupt splicing. Abnormal splicing often leads to disruption of the reading frame with introduction of a premature termination codon (PTC) that targets the mRNA for degradation in the cytoplasm by nonsense mediated decay (NMD). In addition to NMD there are RNA surveillance mechanisms that act in the nucleus while transcripts are still associated with the chromatin template. However, the significance of nuclear RNA quality control in the context of human genetic diseases is unknown. Here we used patient-derived lymphoblastoid cell lines as disease models to address how biogenesis of mRNAs is affected by splice site mutations. We observed that most of the mutations analyzed introduce PTCs and trigger mRNA degradation in the cytoplasm. However, for some mutant transcripts, RNA levels associated with chromatin were found down-regulated. Quantification of nascent transcripts further revealed that a subset of genes containing splicing mutations (SM) have reduced transcriptional activity. Following treatment with the translation inhibitor cycloheximide the cytoplasmic levels of mutant RNAs increased, while the levels of chromatin-associated transcripts remained unaltered. These results suggest that transcription-coupled surveillance mechanisms operate independently from NMD to reduce cellular levels of abnormal RNAs caused by SM.
authors: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal.
authors: Rita
authors: R
authors: Vaz-Drago
authors: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal.
authors: Marco T
authors: MT
authors: Pinheiro
authors: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal.
authors: Sandra
authors: S
authors: Martins
authors: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal.
authors: Francisco J
authors: FJ
authors: Enguita
authors: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal carmo.fonseca@medicina.ulisboa.pt noelia.custodio@medicina.ulisboa.pt.
authors: Maria
authors: M
authors: Carmo-Fonseca
authors: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal carmo.fonseca@medicina.ulisboa.pt noelia.custodio@medicina.ulisboa.pt.
authors: Noélia
authors: N
authors: Custódio
mesh_terms: D018389:Codon, Nonsense; D030342:Genetic Diseases, Inborn / Q000235:genetics*; D006801:Humans; D009154:Mutation; D022821:RNA Splice Sites; D012326:RNA Splicing; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D018389:Codon, Nonsense; D022821:RNA Splice Sites; D012333:RNA, Messenger