Nonproductive Splicing Prevents Expression of MYH7b Protein in the Mammalian Heart.
Nonproductive Splicing Prevents Expression of MYH7b Protein in the Mammalian Heart.
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DOI：
10.1161/jaha.121.020965
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发表时间：
2021-07-20
影响因子：
5.4
通讯作者：
Leinwand LA
中科院分区：
文献类型：
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作者：
Lee LA;Broadwell LJ;Buvoli M;Leinwand LA
尽管α-肌球蛋白重链(α-MYHC)和β-肌球蛋白重链(β-MYHC)蛋白在心肌收缩中的作用早已被认识到，但另一个密切相关的肌球蛋白家族成员MYH7b(肌球蛋白重链7b)的生物学贡献一直存在争议。在哺乳动物中，MYH7b mRNA被转录，但经历了非生产性的选择性剪接，从而阻止了蛋白质以组织特异性的方式表达，包括在心脏中。然而，最近有几项研究将MYH7b变异与不同的心肌病联系起来，或者报道了MYH7b蛋白在哺乳动物心脏中的表达。通过对哺乳动物心脏转录组和蛋白质组数据的分析，我们发现绝大多数MYH7b RNA受到外显子跳跃的影响，不能翻译成具有功能的肌球蛋白分子。值得注意的是，我们发现在选择性剪接外显子两侧的内含子的移除存在滞后，这可能会将非编码RNA保留在细胞核中。这一过程可能在控制MYH7b的表达以及其他心脏基因的活性方面发挥重要作用。通过Western印迹分析，在成年小鼠、大鼠和人的心脏中没有检测到MYH7b蛋白的表达，这与可以忽略的全长蛋白编码mRNA的水平一致。此外，包括定量质谱分析在内的蛋白质组调查显示，只有微量的心脏MYH7b蛋白，即使这样，也只在个别样本的子集中。这里提出的综合分析表明，先前的研究表明，心脏MYH7b蛋白的表达可能归因于抗体的交叉反应。更重要的是，我们的数据预测，与MYH7b疾病相关的变体可能通过交替剪接的RNA本身发挥作用。
Although the roles of alpha‐myosin heavy chain (α‐MyHC) and beta‐myosin heavy chain (β‐MyHC) proteins in cardiac contractility have long been appreciated, the biological contribution of another closely related sarcomeric myosin family member, MYH7b (myosin heavy chain 7b), has become a matter of debate. In mammals, MYH7b mRNA is transcribed but undergoes non‐productive alternative splicing that prevents protein expression in a tissue‐specific manner, including in the heart. However, several studies have recently linked MYH7b variants to different cardiomyopathies or have reported MYH7b protein expression in mammalian hearts. By analyzing mammalian cardiac transcriptome and proteome data, we show that the vast majority of MYH7b RNA is subject to exon skipping and cannot be translated into a functional myosin molecule. Notably, we discovered a lag in the removal of introns flanking the alternatively spliced exon, which could retain the non‐coding RNA in the nucleus. This process could play a significant role in controlling MYH7b expression as well as the activity of other cardiac genes. Consistent with the negligible level of full‐length protein coding mRNA, no MYH7b protein expression was detected in adult mouse, rat, and human hearts by Western blot analysis. Furthermore, proteome surveys including quantitative mass spectrometry analyses revealed only traces of cardiac MYH7b protein and even then, only in a subset of individual samples. The comprehensive analysis presented here suggests that previous studies showing cardiac MYH7b protein expression were likely attributable to antibody cross‐reactivity. More importantly, our data predict that the MYH7b disease‐associated variants may operate through the alternately spliced RNA itself.