The nonsense-mediated mRNA decay pathway triggers degradation of most BRCA1 mRNAs bearing premature termination codons
The nonsense-mediated mRNA decay pathway triggers degradation of most BRCA1 mRNAs bearing premature termination codons
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DOI：
10.1093/hmg/11.23.2805
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发表时间：
2002-11-01
影响因子：
3.5
通讯作者：
Mazoyer, S
中科院分区：
文献类型：
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作者：
Perrin-Vidoz, L;Sinilnikova, OM;Mazoyer, S
BRCA1基因的胚系突变分布在22个编码外显子上，其中大多数产生提前终止密码子(PTCs)。众所周知，一种被称为无义介导的mRNA衰退(NMD)的机制可以特异性地降解PTCs的转录本；然而，很少有人测量到突变的BRCA1 mRNAs的稳态量。虽然越来越多的证据表明，下游外显子-外显子连接(EEJs)是区分正常终止密码子和PTC的关键决定因素，但关于PTC和下游EEJs之间的最小和最大距离的要求仍然存在争议。我们评估了从乳腺癌/卵巢癌家族携带者建立的淋巴母细胞系中BRCA1等位基因编码的转录本的相对数量，其中BRCA1等位基因含有30种不同的截断突变。我们发现，NMD是由80%的PTC+等位基因触发的，并导致mRNA丰度降低1.5-5倍。位于3.4kb长的中央外显子的所有截断突变都会受到NMD的影响，无论它们到下游EEJ的距离(305到3395个核苷酸)如何。不导致NMD的PTC要么位于最后一个外显子，要么非常接近翻译起始密码子。我们假设，重新启动可以解释为什么携带早期PTCs的转录本逃脱NMD。这是第一次通过分析一大系列突变的内源性等位基因来挑战NMD规则的研究，这些规则是通过对Miniges的研究而建立的。
Germline mutations in the BRCA1 gene are scattered over the 22 coding exons and most of them generate premature termination codons (PTCs). A mechanism called nonsense-mediated mRNA decay (NMD) is known to specifically degrade transcripts with PTCs; however, steady-state amounts of mutant BRCA1 mRNAs have very rarely been measured. Although growing evidence implicates downstream exon-exon junctions (EEJs) as critical determinants for discrimination between normal stop codons and PTCs, requirements concerning the minimal and maximal distance between PTCs and downstream EEJs are still debated. We assessed the relative amount of transcripts encoded by BRCA1 alleles harbouring 30 different truncating mutations in lymphoblastoid cell lines established from carriers from breast/ovarian cancer families. We found that NMD is triggered by 80% of PTC+ alleles and results in a 1.5- to 5-fold reduction in mRNA abundance. All truncating mutations located in the 3.4 kb long central exon are subject to NMD, irrespective of their distance to the downstream EEJ (305 to 3395 nt). PTCs not leading to NMD are either located in the last exon or very close to the translation initiation codon. We hypothesize that reinitiation could explain why transcripts carrying early PTCs escape NMD. This is the first study challenging the NMD rules, which have been established through the study of minigenes, by analysing a large series of mutant endogenous alleles.