Fiorentino Valeria, Brancaleoni Valentina, Granata Francesca, Graziadei Giovanna, Di Pierro Elena
Dipartimento di Scienze Cliniche e di Comunità, Università Degli Studi di Milano, Milano, Italy.
Fondazione IRCCS Cà Granda-Ospedale Maggiore Policlinico, U.O. di Medicina Interna, Milano, Italy.
Blood Cells Mol Dis. 2016 Oct;61:48-53. doi: 10.1016/j.bcmd.2016.08.002. Epub 2016 Aug 17.
The PPOX gene encodes for the protoporphyrinogen oxidase, which is involved in heme production. The partial deficiency of protoporphyrinogen oxidase causes variegate porphyria. The tissue-specific regulation of other heme biosynthetic enzymes is extensively studied, but the information concerning transcriptional and post-transcriptional regulation of PPOX gene expression is scarcely available. In this study, we characterized functions of three variants identified in the regulatory regions of the PPOX gene, which show a novel role for the 5' untranslated exon 1. Using luciferase assays and RNA analysis, we demonstrated that only c.1-883G>C promoter variant causes a significant loss in the transcriptional activity of PPOX gene whereas c.1-413G>T 5' UTR variant inhibits translation of PPOX mRNA and c.1-176G>A splicing variant causes 4bp deletion in 5' UTR of PPOX mRNA variant 2. These observations indicate that the regulation of PPOX gene expression can also occur through a post-transcriptional modulation of the amount of gene product and that this modulation can be mediated by 5' untranslated exon 1. Moreover this study confirms that these regulatory regions represent an important molecular target for the pathogenesis of variegate porphyria.
PPOX基因编码原卟啉原氧化酶，该酶参与血红素的生成。原卟啉原氧化酶的部分缺陷会导致混合型卟啉症。对其他血红素生物合成酶的组织特异性调控已进行了广泛研究，但关于PPOX基因表达的转录和转录后调控的信息却很少。在本研究中，我们对在PPOX基因调控区域中鉴定出的三种变体的功能进行了表征，这些变体显示出5'非翻译外显子1的新作用。通过荧光素酶测定和RNA分析，我们证明只有c.1-883G>C启动子变体导致PPOX基因的转录活性显著丧失，而c.1-413G>T 5'UTR变体抑制PPOX mRNA的翻译，c.1-176G>A剪接变体导致PPOX mRNA变体2的5'UTR缺失4bp。这些观察结果表明，PPOX基因表达的调控也可以通过对基因产物量的转录后调节来实现，并且这种调节可以由5'非翻译外显子1介导。此外，本研究证实这些调控区域是混合型卟啉症发病机制的重要分子靶点。
