Sharma Shraddha, Wang Jianming, Cortes Gomez Eduardo, Taggart Robert T, Baysal Bora E
Department of Pathology.
Department of Biostatistics and Bioinformatics, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA.
Hum Mol Genet. 2017 Apr 1;26(7):1328-1339. doi: 10.1093/hmg/ddx041.
Mutations in mitochondrial complex II (succinate dehydrogenase; SDH) genes predispose to paraganglioma tumors that show constitutive activation of hypoxia responses. We recently showed that SDHB mRNAs in hypoxic monocytes gain a stop codon mutation by APOBEC3A-mediated C-to-U RNA editing. Here, we test the hypothesis that inhibition of complex II facilitates hypoxic gene expression in monocytes using an integrative experimental approach. By RNA sequencing, we show that specific inhibition of complex II by atpenin A5 in normoxic conditions mimics hypoxia and induces hypoxic transcripts as well as APOBEC3A-mediated RNA editing in human monocytes. Myxothiazol, a complex III inhibitor, has similar effects in normoxic monocytes. Atpenin A5 partially inhibits oxygen consumption, and neither hypoxia nor atpenin A5 in normoxia robustly stabilizes hypoxia-inducible factor (HIF)-1α in primary monocytes. Several earlier studies in transformed cell lines suggested that normoxic stabilization of HIF-1α explains the persistent expression of hypoxic genes upon complex II inactivation. On the contrary, we find that atpenin A5 antagonizes the stabilization of HIF-1α and reduces hypoxic gene expression in transformed cell lines. Accordingly, compound germline heterozygosity of mouse Sdhb/Sdhc/Sdhd null alleles blunts chronic hypoxia-induced increases in hemoglobin levels, an adaptive response mainly regulated by HIF-2α. In contrast, atpenin A5 or myxothiazol does not reduce hypoxia-induced gene expression or RNA editing in monocytes. These results reveal a novel role for mitochondrial respiratory inhibition in induction of the hypoxic transcriptome in monocytes and suggest that inhibition of complex II activates a distinct hypoxia signaling pathway in a cell-type specific manner.
线粒体复合物II（琥珀酸脱氢酶；SDH）基因的突变易导致副神经节瘤肿瘤，这些肿瘤表现出缺氧反应的组成性激活。我们最近发现，缺氧单核细胞中的SDHB mRNA通过载脂蛋白B编辑酶催化多肽3A（APOBEC3A）介导的C到U RNA编辑获得了一个终止密码子突变。在这里，我们使用综合实验方法来检验复合物II的抑制促进单核细胞中缺氧基因表达这一假设。通过RNA测序，我们发现，在常氧条件下，atpenin A5对复合物II的特异性抑制模拟了缺氧状态，并在人类单核细胞中诱导了缺氧转录本以及APOBEC3A介导的RNA编辑。黏噻唑，一种复合物III抑制剂，在常氧单核细胞中具有类似的作用。Atpenin A5部分抑制氧气消耗，并且无论是缺氧还是常氧条件下的atpenin A5都不能在原代单核细胞中强有力地稳定缺氧诱导因子（HIF）-1α。之前在转化细胞系中的几项研究表明，HIF-1α的常氧稳定解释了复合物II失活后缺氧基因的持续表达。相反，我们发现atpenin A5拮抗HIF-1α的稳定，并降低转化细胞系中缺氧基因的表达。因此，小鼠Sdhb/Sdhc/Sdhd无效等位基因的复合种系杂合性减弱了慢性缺氧诱导的血红蛋白水平升高，这是一种主要由HIF-2α调节的适应性反应。相比之下，atpenin A5或黏噻唑不会降低单核细胞中缺氧诱导的基因表达或RNA编辑。这些结果揭示了线粒体呼吸抑制在单核细胞缺氧转录组诱导中的新作用，并表明复合物II的抑制以细胞类型特异性方式激活了一条独特的缺氧信号通路。
