Autophagy contributes to the selective degradation of liquid droplets, including the P-Granule, Ape1-complex and p62/SQSTM1-body, although the molecular mechanisms and physiological relevance of ...selective degradation remain unclear. In this report, we describe the properties of endogenous p62-bodies, the effect of autophagosome biogenesis on these bodies, and the in vivo significance of their turnover. p62-bodies are low-liquidity gels containing ubiquitin and core autophagy-related proteins. Multiple autophagosomes form on the p62-gels, and the interaction of autophagosome-localizing Atg8-proteins with p62 directs autophagosome formation toward the p62-gel. Keap1 also reversibly translocates to the p62-gels in a p62-binding dependent fashion to activate the transcription factor Nrf2. Mice deficient for Atg8-interaction-dependent selective autophagy show that impaired turnover of p62-gels leads to Nrf2 hyperactivation in vivo. These results indicate that p62-gels are not simple substrates for autophagy but serve as platforms for both autophagosome formation and anti-oxidative stress.
p62/SQSTM1 is a multivalent protein that has the ability to cause liquid–liquid phase separation and serves as a receptor protein that participates in cargo isolation during selective autophagy. This ...protein is also involved in the non‐canonical activation of the Keap1‐Nrf2 system, a major oxidative stress response pathway. Here, we show a role of neighbor of BRCA1 gene 1 (NBR1), an autophagy receptor structurally similar to p62/SQSTM1, in p62‐liquid droplet formation and Keap1‐Nrf2 pathway activation. Overexpression of NBR1 blocks selective degradation of p62/SQSTM1 through autophagy and promotes the accumulation and phosphorylation of p62/SQSTM1 in liquid‐like bodies, which is required for the activation of Nrf2. NBR1 is induced in response to oxidative stress, which triggers p62‐mediated Nrf2 activation. Conversely, loss of Nbr1 suppresses not only the formation of p62/SQSTM1‐liquid droplets, but also of p62‐dependent Nrf2 activation during oxidative stress. Taken together, our results show that NBR1 mediates p62/SQSTM1‐liquid droplet formation to activate the Keap1‐Nrf2 pathway.
Synopsis
SQSTM1/p62 can induce liquid‐liquid phase separation and serves as a cargo receptor during selective autophagy. NBR1 and p62 collaborate during the activation of the Keap1‐Nrf2 oxidative stress response pathway, promoting the formation of p62‐liquid droplets.
The autophagy receptor NBR1 is an oxidative stress‐inducible protein.
Overexpression of NBR1 facilitates phase separation of p62 and activates the p62‐Keap1‐Nrf2 pathway.
Loss of NBR1 impedes full activation of the Nrf2 antioxidant response.
SQSTM1/p62 can induce liquid‐liquid phase separation and serves as a cargo receptor during selective autophagy. NBR1 and p62 collaborate during the activation of the Keap1‐Nrf2 oxidative stress response pathway, promoting the formation of p62‐liquid droplets.
Parkinson's disease (PD) is a prevalent neurodegenerative disorder. Recent identification of genes linked to familial forms of PD such as Parkin and PINK1 (PTEN-induced putative kinase 1) has ...revealed that ubiquitylation and mitochondrial integrity are key factors in disease pathogenesis. However, the exact mechanism underlying the functional interplay between Parkin-catalyzed ubiquitylation and PINK1-regulated mitochondrial quality control remains an enigma. In this study, we show that PINK1 is rapidly and constitutively degraded under steady-state conditions in a mitochondrial membrane potential-dependent manner and that a loss in mitochondrial membrane potential stabilizes PINK1 mitochondrial accumulation. Furthermore, PINK1 recruits Parkin from the cytoplasm to mitochondria with low membrane potential to initiate the autophagic degradation of damaged mitochondria. Interestingly, the ubiquitin ligase activity of Parkin is repressed in the cytoplasm under steady-state conditions; however, PINK1-dependent mitochondrial localization liberates the latent enzymatic activity of Parkin. Some pathogenic mutations of PINK1 and Parkin interfere with the aforementioned events, suggesting an etiological importance. These results provide crucial insight into the pathogenic mechanisms of PD.
The Keap1-Nrf2 system and autophagy are both involved in the oxidative-stress response, metabolic pathways, and innate immunity, and dysregulation of these processes is associated with pathogenic ...processes. However, the interplay between these two pathways remains largely unknown. Here, we show that phosphorylation of the autophagy-adaptor protein p62 markedly increases p62’s binding affinity for Keap1, an adaptor of the Cul3-ubiquitin E3 ligase complex responsible for degrading Nrf2. Thus, p62 phosphorylation induces expression of cytoprotective Nrf2 targets. p62 is assembled on selective autophagic cargos such as ubiquitinated organelles and subsequently phosphorylated in an mTORC1-dependent manner, implying coupling of the Keap1-Nrf2 system to autophagy. Furthermore, persistent activation of Nrf2 through accumulation of phosphorylated p62 contributes to the growth of human hepatocellular carcinomas (HCCs). These results demonstrate that selective autophagy and the Keap1-Nrf2 pathway are interdependent, and that inhibitors of the interaction between phosphorylated p62 and Keap1 have potential as therapeutic agents against human HCC.
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•S351-phosphorylated p62 has higher affinity for Keap1 and activates Nrf2•Phosphorylation of p62 mainly occurs on selective autophagic cargos•Cytotoxic cargos, along with phosphorylated p62 and Keap1, are degraded by autophagy•Hepatocellular carcinoma cells utilize p62 phosphorylation for their growth
The Golgi pH regulator (GPHR) is essential for maintaining the function and morphology of the Golgi apparatus through the regulation of luminal acidic pH. Abnormal morphology of the Golgi apparatus ...is associated with neurodegenerative diseases. Here, we found that knockout of GPHR in the mouse brain led to morphological changes in the Golgi apparatus and neurodegeneration, which included brain atrophy, neuronal cell death, and gliosis. Furthermore, in the GPHR knockout mouse brain, transcriptional activity of sterol regulatory element‐binding protein 2 (SREBP2) decreased, resulting in a reduction in cholesterol levels. GPHR‐deficient cells exhibited suppressed neurite outgrowth, which was recovered by exogenous expression of the active form of SREBP2. Our results show that GPHR‐mediated luminal acidification of the Golgi apparatus maintains proper cholesterol levels and, thereby, neuronal morphology.
The Golgi pH regulator (GPHR) is essential for maintaining the integrity of the Golgi apparatus through the regulation of luminal acidic pH. We show here that loss of GPHR induced neurodegeneration accompanied by Golgi fragmentation. We also provide evidence that the Golgi luminal pH is indispensable for maintaining cholesterol levels via activation of the sterol regulatory element‐binding protein SREBP2.
Impaired selective turnover of p62 by autophagy causes severe liver injury accompanied by the formation of p62-positive inclusions and upregulation of detoxifying enzymes. These phenotypes correspond ...closely to the pathological conditions seen in human liver diseases, including alcoholic hepatitis and hepatocellular carcinoma. However, the molecular mechanisms and pathophysiological processes in these events are still unknown. Here we report the identification of a novel regulatory mechanism by p62 of the transcription factor Nrf2, whose target genes include antioxidant proteins and detoxification enzymes. p62 interacts with the Nrf2-binding site on Keap1, a component of Cullin-3-type ubiquitin ligase for Nrf2. Thus, an overproduction of p62 or a deficiency in autophagy competes with the interaction between Nrf2 and Keap1, resulting in stabilization of Nrf2 and transcriptional activation of Nrf2 target genes. Our findings indicate that the pathological process associated with p62 accumulation results in hyperactivation of Nrf2 and delineates unexpected roles of selective autophagy in controlling the transcription of cellular defence enzyme genes.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
PINK1 and Parkin were first identified as the causal genes responsible for familial forms of early-onset Parkinson's disease (PD), a prevalent neurodegenerative disorder. PINK1 encodes a ...mitochondrial serine/threonine protein kinase, whereas Parkin encodes an ubiquitin-protein ligase. PINK1 and Parkin cooperate to maintain mitochondrial integrity; however, the detailed molecular mechanism of how Parkin-catalyzed ubiquitylation results in mitochondrial integrity remains an enigma. In this study, we show that Parkin-catalyzed K63-linked polyubiquitylation of depolarized mitochondria resulted in ubiquitylated mitochondria being transported along microtubules to cluster in the perinuclear region, which was interfered by pathogenic mutations of Parkin. In addition, p62/SQSTM1 (hereafter referred to as p62) was recruited to depolarized mitochondria after Parkin-directed ubiquitylation. Intriguingly, deletion of p62 in mouse embryonic fibroblasts resulted in a gross loss of mitochondrial perinuclear clustering but did not hinder mitochondrial degradation. Thus, p62 is required for ubiquitylation-dependent clustering of damaged mitochondria, which resembles p62-mediated 'aggresome' formation of misfolded/unfolded proteins after ubiquitylation.
Impairment of autophagic degradation of the ubiquitin- and LC3-binding protein “p62” leads to the formation of cytoplasmic inclusion bodies. However, little is known about the sorting mechanism of ...p62 to autophagic degradation. Here we identified a motif of murine p62 consisting of 11 amino acids (Ser334-Ser344) containing conserved acidic and hydrophobic residues across species, as an LC3 recognition sequence (LRS). The crystal structure of the LC3-LRS complex at 1.56Å resolution revealed interaction of Trp340 and Leu343 of p62 with different hydrophobic pockets on the ubiquitin fold of LC3. In vivo analyses demonstrated that p62 mutants lacking LC3 binding ability accumulated without entrapping into autophagosomes in the cytoplasm and subsequently formed ubiquitin-positive inclusion bodies as in autophagy-deficient cells. These results demonstrate that the intracellular level of p62 is tightly regulated by autophagy through the direct interaction of LC3 with p62 and reveal that selective turnover of p62 via autophagy controls inclusion body formation.
Autophagy is a catabolic process where cytosolic cellular components are delivered to the lysosome for degradation. Recent studies have indicated the existence of specific receptors, such as p62, ...which link ubiquitinated targets to autophagosomal degradation pathways. Here we show that NBR1 (neighbor of BRCA1 gene 1) is an autophagy receptor containing LC3- and ubiquitin (Ub)-binding domains. NBR1 is recruited to Ub-positive protein aggregates and degraded by autophagy depending on an LC3-interacting region (LIR) and LC3 family modifiers. Although NBR1 and p62 interact and form oligomers, they can function independently, as shown by autophagosomal clearance of NBR1 in p62-deficient cells. NBR1 was localized to Ub-positive inclusions in patients with liver dysfunction, and depletion of NBR1 abolished the formation of Ub-positive p62 bodies upon puromycin treatment of cells. We propose that NBR1 and p62 act as receptors for selective autophagosomal degradation of ubiquitinated targets.
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