Division of Cancer Biology, National Cancer Center Research Institute, Tokyo, Japan.
PLoS One. 2012;7(1):e30767. doi: 10.1371/journal.pone.0030767. Epub 2012 Jan 26.
Mieap, a p53-inducible protein, controls mitochondrial quality by repairing unhealthy mitochondria. During repair, Mieap induces the accumulation of intramitochondrial lysosomal proteins (designated MALM for Mieap-induced accumulation of lysosome-like organelles within mitochondria) by interacting with NIX, leading to the elimination of oxidized mitochondrial proteins. Here, we report that an additional mitochondrial outer membrane protein, BNIP3, is also involved in MALM. BNIP3 interacts with Mieap in a reactive oxygen species (ROS)-dependent manner via the BH3 domain of BNIP3 and the coiled-coil domains of Mieap. The knockdown of endogenous BNIP3 expression severely inhibited MALM. Although the overexpression of either BNIP3 or NIX did not cause a remarkable change in the mitochondrial membrane potential (MMP), the co-expression of all three exogenous proteins, Mieap, BNIP3 and NIX, caused a dramatic reduction in MMP, implying that the physical interaction of Mieap, BNIP3 and NIX at the mitochondrial outer membrane may regulate the opening of a pore in the mitochondrial double membrane. This effect was not related to cell death. These results suggest that two mitochondrial outer membrane proteins, BNIP3 and NIX, mediate MALM in order to maintain mitochondrial integrity. The physical interaction of Mieap, BNIP3 and NIX at the mitochondrial outer membrane may play a critical role in the translocation of lysosomal proteins from the cytoplasm to the mitochondrial matrix.
Mieap 是一种 p53 诱导蛋白，通过修复不健康的线粒体来控制线粒体质量。在修复过程中，Mieap 通过与 NIX 相互作用，诱导线粒体中溶酶体样细胞器（称为 MALM）内的内源性溶酶体蛋白积累，从而消除氧化的线粒体蛋白。在这里，我们报告另一种线粒体外膜蛋白 BNIP3 也参与了 MALM。BNIP3 通过其 BH3 结构域和 Mieap 的卷曲螺旋结构域与 ROS 依赖性 Mieap 相互作用。内源性 BNIP3 表达的敲低严重抑制了 MALM。虽然 BNIP3 或 NIX 的过表达都不会显著改变线粒体膜电位 (MMP)，但所有三种外源性蛋白（Mieap、BNIP3 和 NIX）的共表达会导致 MMP 急剧下降，这表明 Mieap、BNIP3 和 NIX 在 线粒体外膜上的物理相互作用可能调节线粒体双层膜中孔的打开。这种效应与细胞死亡无关。这些结果表明，两种线粒体外膜蛋白 BNIP3 和 NIX 介导 MALM 以维持线粒体完整性。Mieap、BNIP3 和 NIX 在 线粒体外膜上的物理相互作用可能在溶酶体蛋白从细胞质到线粒体基质的易位中发挥关键作用。
