Article

Microtubule-associated Protein 1 Light Chain 3 (LC3) Interacts with Bnip3 Protein to Selectively Remove Endoplasmic Reticulum and Mitochondria via Autophagy

Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, California 92093, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2012; 287(23):19094-104. DOI: 10.1074/jbc.M111.322933
Source: PubMed

ABSTRACT

Autophagy plays an important role in cellular quality control and is responsible for removing protein aggregates and dysfunctional organelles. Bnip3 is an atypical BH3-only protein that is known to cause mitochondrial dysfunction and cell death. Interestingly, Bnip3 can also protect against cell death by inducing mitochondrial autophagy. The mechanism for this process, however, remains poorly understood. Bnip3 contains a C-terminal transmembrane domain that is essential for homodimerization and proapoptotic function. In this study, we show that homodimerization of Bnip3 is also a requirement for induction of autophagy. Several Bnip3 mutants that do not interfere with its mitochondrial localization but disrupt homodimerization failed to induce autophagy in cells. In addition, we discovered that endogenous Bnip3 is localized to both mitochondria and the endoplasmic reticulum (ER). To investigate the effects of Bnip3 at mitochondria or the ER on autophagy, Bnip3 was targeted specifically to each organelle by substituting the Bnip3 transmembrane domain with that of Acta or cytochrome b(5). We found that Bnip3 enhanced autophagy in cells from both sites. We also discovered that Bnip3 induced removal of both ER (ERphagy) and mitochondria (mitophagy) via autophagy. The clearance of these organelles was mediated in part via binding of Bnip3 to LC3 on the autophagosome. Although ablation of the Bnip3-LC3 interaction by mutating the LC3 binding site did not impair the prodeath activity of Bnip3, it significantly reduced both mitophagy and ERphagy. Our data indicate that Bnip3 regulates the apoptotic balance as an autophagy receptor that induces removal of both mitochondria and ER.

    • "But, in the same model, CIT supplementation led to a decrease in protein carbonylation in the muscle and it is well known that post-translational oxidative protein modifications are associated to a loss of the protein function related to an increase of protein degradation[108]. Additionally, Ham et al.[109]demonstrated in limb-casted mice studied over a period of 14 days that CIT supplementation did not alter the mRNA expression of genes involved in the proteasome muscle protein breakdown system (Fbxo32, tripartite-motif-containing 63 gene, Foxo1, and Foxo4) but CIT could modulate the autophagosome system : The same authors showed that CIT induced an upregulation of the mRNA expression of the Bnip3 gene -which mediates the recruitment of the growing autophagosome to damaged mitochondria[110]-but not on the LC3BII:LC3B1 ratio, a reliable marker of the number of autophagosomes[111]. Interestingly, in another model[2], data showed a probable down-regulation of the expression of a proteolysis activator protein (subunit 1 of the proteasome activator complex) by CIT, which could lead to a decrease in muscle protein catabolism. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Beside their main contribution as substrates for protein synthesis, amino acids as signaling molecules could exert some regulatory functions on protein synthesis and/or proteolysis that have been emphasized in a number of recent studies. Several publications have highlighted supplemental roles of those amino acids in protein metabolism as well as in immunity, heat shock response or apoptosis processes. In this way, via their regulatory properties, selected amino acids (like leucine, glutamine, arginine, citrulline or methionine) directly influence the proteome. In this review, we are proposing an overview of the regulation of the proteome by amino acids in mammals. This article is protected by copyright. All rights reserved.
    No preview · Article · Jan 2016 · Proteomics
  • Source
    • "The LC3-II protein is bound to an oligomeric Atg12-Atg5-Atg-16 complex and facilitates the conjugation of autophagosomes. It is LC3-II that directly interacts with autophagy adapter proteins containing LC3-interacting receptors (i.e., BNIP3, NIX, and p62) [13] [14] [15]. Given this essential function of LC3-II in autophagy, it has been used as a defining protein marker of autophagy [16] [17]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Autophagy is an evolutionarily conserved catabolic process for maintaining cellular homeostasis during both normal and stress conditions. Metabolic reprogramming in tissues of dead bodies is inevitable due to chronic ischemia and nutrient deprivation, which are well-known features that stimulate autophagy. Currently, it is not fully elucidated whether postmortem autophagy, also known as thanatophagy, occurs in dead bodies is a function of the time of death. In this study, we tested the hypothesis that thanatophagy would increase in proportion to time elapsed since death for tissues collected from cadavers. Brain and heart tissue from corpses at different time intervals after death were analyzed by Western blot. Densitometry analysis demonstrated that thanatophagy occurred in a manner that was dependent on the time of death. The autophagy-associated proteins, LC3 II, p62, Beclin-1 and Atg7, increased in a time-dependent manner in heart tissues. A potent inducer of autophagy, BNIP3, decreased in the heart tissues as time of death increased, whereas the protein levels increased in brain tissues. However, there was no expression of BNIP3 at extended postmortem intervals in both brain and heart samples. Collectively, the present study demonstrates for the first time that thanatophagy occurs in brain and heart tissues of cadavers in a time-dependent manner. Further, our data suggest that cerebral thanatophagy may occur in a Beclin-1- independent manner. This unprecedented study provides potential insight into thanatophagy as a novel method for the estimation of the time of death in criminal investigationsAbstract: Autophagy is an evolutionarily conserved catabolic process for maintaining cellular homeostasis during both normal and stress conditions. Metabolic reprogramming in tissues of dead bodies is inevitable due to chronic ischemia and nutrient deprivation, which are well-known features that stimulate autophagy. Currently, it is not fully elucidated whether postmortem autophagy, also known as thanatophagy, occurs in dead bodies is a function of the time of death. In this study, we tested the hypothesis that thanatophagy would increase in proportion to time elapsed since death for tissues collected from cadavers. Brain and heart tissue from corpses at different time intervals after death were analyzed by Western blot. Densitometry analysis demonstrated that thanatophagy occurred in a manner that was dependent on the time of death. The autophagy-associated proteins, LC3 II, p62, Beclin-1 and Atg7, increased in a time-dependent manner in heart tissues. A potent inducer of autophagy, BNIP3, decreased in the heart tissues as time of death increased, whereas the protein levels increased in brain tissues. However, there was no expression of BNIP3 at extended postmortem intervals in both brain and heart samples. Collectively, the present study demonstrates for the first time that thanatophagy occurs in brain and heart tissues of cadavers in a time-dependent manner. Further, our data suggest that cerebral thanatophagy may occur in a Beclin-1- independent manner. This unprecedented study provides potential insight into thanatophagy as a novel method for the estimation of the time of death in criminal investigations
    Full-text · Article · Nov 2015
  • Source
    • "xia - induced macroautophagy or mitophagy ( Sowter et al . , 2001 ; Tracy et al . , 2007 ; Zhang et al . , 2008 ; Bellot et al . , 2009 ) . While BH3 domains of BNIP3 and NIX are sufficient to induce the general autophagy response ( Bellot et al . , 2009 ) , induction of mitophagy requires the LIR domain of NIX ( Novak et al . , 2010 ) and BNIP3 ( Hanna et al . , 2012 ; Zhu et al . , 2013 ) . Phosphorylation of BNIP3 at serines flanking its LIR domain promotes binding to LC3 family members and thereby increases mitophagy ( Zhu et al . , 2013 ) , however , involved kinases are unknown ( Figure 3B ) . It is not clear how phosphorylation of BNIP3 is regulated under hypoxia and if phosphorylation regulate"
    [Show abstract] [Hide abstract]
    ABSTRACT: Oxygen (O2) is an essential substrate in cellular metabolism, bioenergetics, and signaling and as such linked to the survival and normal function of all metazoans. Low O2 tension (hypoxia) is a fundamental feature of physiological processes as well as pathophysiological conditions such as cancer and ischemic diseases. Central to the molecular mechanisms underlying O2 homeostasis are the hypoxia-inducible factors-1 and -2 alpha (HIF-1α and EPAS1/HIF-2α) that function as master regulators of the adaptive response to hypoxia. HIF-induced genes promote characteristic tumor behaviors, including angiogenesis and metabolic reprogramming. The aim of this review is to critically explore current knowledge of how HIF-α signaling regulates the abundance and function of major O2-consuming organelles. Abundant evidence suggests key roles for HIF-1α in the regulation of mitochondrial homeostasis. An essential adaptation to sustained hypoxia is repression of mitochondrial respiration and induction of glycolysis. HIF-1α activates several genes that trigger mitophagy and represses regulators of mitochondrial biogenesis. Several lines of evidence point to a strong relationship between hypoxia, the accumulation of misfolded proteins in the endoplasmic reticulum, and activation of the unfolded protein response. Surprisingly, although peroxisomes depend highly on molecular O2 for their function, there has been no evidence linking HIF signaling to peroxisomes. We discuss our recent findings that establish HIF-2α as a negative regulator of peroxisome abundance and suggest a mechanism by which cells attune peroxisomal function with O2 availability. HIF-2α activation augments peroxisome turnover by pexophagy and thereby changes lipid composition reminiscent of peroxisomal disorders. We discuss potential mechanisms by which HIF-2α might trigger pexophagy and place special emphasis on the potential pathological implications of HIF-2α-mediated pexophagy for human health.
    Full-text · Article · Aug 2015 · Frontiers in Cell and Developmental Biology
Show more