Department of Biochemistry, La Trobe University, Melbourne, Victoria, Australia.
PLoS One. 2007 Sep 12;2(9):e874. doi: 10.1371/journal.pone.0000874.
In an accompanying paper, we show that the mitochondrial Unfolded Protein Response or mtUPR is initiated by the activation of transcription of chop through an AP-1 element in the chop promoter. Further, we show that the c/ebp beta gene is similarly activated and CHOP and C/EBP beta subsequently hetero-dimerise to activate transcription of mtUPR responsive genes. Here, we report the discovery of six additional mtUPR responsive genes. We found that these genes encoding mitochondrial proteases YME1L1 and MPP beta, import component Tim17A and enzymes NDUFB2, endonuclease G and thioredoxin 2, all contain a CHOP element in their promoters. In contrast, genes encoding mitochondrial proteins Afg3L2, Paraplegin, Lon and SAM 50, which do not have a CHOP element, were not up-regulated. Conversely, genes with CHOP elements encoding cytosolic proteins were not induced by the accumulation of unfolded proteins in mitochondria. These results indicate that mtUPR responsive genes appear to share a requirement for a CHOP element, but that this is not sufficient for the regulation of the mtUPR. A more detailed analysis of promoters of mtUPR responsive genes revealed at least two additional highly conserved, putative regulatory sites either side of the CHOP element, one a motif of 12 bp which lies 14 bp upstream of the CHOP site and another 9 bp element, 2 bp downstream of the CHOP site. Both of these additional elements are conserved in the promoters of 9 of the ten mtUPR responsive genes we have identified so far, the exception being the Cpn60/10 bidirectional promoter. Mutation of each of these elements substantially reduced the mtUPR responsiveness of the promoters suggesting that these elements coordinately regulate mtUPR.
在一篇伴随论文中，我们表明线粒体未折叠蛋白反应（mtUPR）是通过 chop 启动子中的 AP-1 元件激活 chop 的转录而启动的。此外，我们表明 c/ebp beta 基因也被类似地激活，随后 CHOP 和 C/EBP beta 异二聚化以激活 mtUPR 反应基因的转录。在这里，我们报告了六个额外的 mtUPR 反应基因的发现。我们发现，这些基因编码线粒体蛋白酶 YME1L1 和 MPPβ、导入成分 Tim17A 以及酶 NDUFB2、endonuclease G 和硫氧还蛋白 2，它们的启动子中都含有 CHOP 元件。相比之下，编码线粒体蛋白 Afg3L2、Paraplegin、Lon 和 SAM 50 的基因没有 CHOP 元件，它们没有上调。相反，没有 CHOP 元件的编码细胞质蛋白的基因不会因线粒体中未折叠蛋白的积累而被诱导。这些结果表明，mtUPR 反应基因似乎共享对 CHOP 元件的需求，但这不足以调节 mtUPR。对 mtUPR 反应基因启动子的更详细分析揭示了至少两个额外的高度保守的、假定的调节位点，位于 CHOP 元件的两侧，一个是位于 CHOP 位点上游 14 个碱基的 12 个碱基的基序，另一个是位于 CHOP 位点下游 2 个碱基的 9 个碱基元件。这两个额外的元件都在我们迄今为止鉴定的十个 mtUPR 反应基因中的九个基因的启动子中保守，唯一的例外是 Cpn60/10 双向启动子。这些元件中的每一个的突变都大大降低了启动子的 mtUPR 反应性，表明这些元件协同调节 mtUPR。
