BNIP3 and NIX Mediate Mieap-Induced Accumulation of Lysosomal Proteins within Mitochondria

Abstract

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.

Local Mitochondrial-Endolysosomal Microfusion Cleaves Voltage-Dependent Anion Channel 1 To Promote Survival in Hypoxia

“…It is known that a TP53-inducible protein, Mieap (18), controls mitochondrial quality (19). Using TP53-specific siRNA, we confirmed, as published previously (19), that Mieap is TP53 inducible (Fig. 2A).…”

“…In addition, TP53 has been reported to activate necrosis by opening the mitochondrial permeability transition pore (42). Although our results point to the involvement of TP53-induced Mieap and BNIP3-mediated regulation of the hypoxic processing of VDAC1, we do not conclude, as suggested previously (19,20), that lysosome-like organelles or lysosomal proteins accumulate in mitochondria. However, the latter studies examined exogenous overexpression of adenovirus-infected Mieap in normoxia, which contrasts with the conditions of the present study, which examined endogenous proteins in hypoxic cells.…”

“…3F; Table 1), which further implicates lysosome involvement in resistance to apoptosis in hypoxia. However, Mieap was not pulled down, suggesting that BNIP3 and Mieap did not bind directly, which contrasts with the findings of a previous report (19). Since pulldown experiments showed that clathrin bound BNIP3 in hypoxic cells and that clathrin is involved in vesicle trafficking, the effect of brefeldin A, an inhibitor of transport of secretory proteins from the endoplasmic reticulum to the Golgi apparatus, was examined.…”

“…It is known that a TP53-inducible protein, Mieap (also referred to as Spata18) (18), controls mitochondrial quality through interaction with the HIF-1-inducible protein BNIP3 (19). In addition, Mieap has been proposed to induce the accumulation of lysosomal proteins within mitochondria by way of repairing damaged mitochondria (20).…”

p53 and mitochondrial function in neurons

“…In response to stress, such as DNA damage, Mieap is induced and translocates to the mitochondrial matrix in a ROS-dependent manner [89], allowing lysosomal enzymes to move into the matrix thereby facilitating degradation of oxidatively damaged mitochondrial proteins (designated MALM for Mieap-induced accumulation of lysosome-like organelles within mitochondria [88]). This occurs only when BNIP3 and NIX coexist at the mitochondrial surface [90]. The interaction between Mieap, BNIP3 and NIX appears to facilitate the formation of a mitochondrial membrane pore involving both mitochondrial membranes, thus causing a drop in membrane potential.…”