bims-apauto 2021-05-09 papers

Issue of 2021–05–09
five papers selected by
Su Hyun Lee, Seoul National University

Cell Discov. 2021 May 04. 7(1): 31

The SARS-CoV-2 protein ORF3a inhibits fusion of autophagosomes with lysosomes.

Yabin Zhang, Hao Sun, Rongjuan Pei, Binli Mao, Zhenyu Zhao, Huihui Li, Yong Lin, Kefeng Lu.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the ongoing coronavirus disease 2019 pandemic. How SARS-CoV-2 regulates cellular responses to escape clearance by host cells is unknown. Autophagy is an intracellular lysosomal degradation pathway for the clearance of various cargoes, including viruses. Here, we systematically screened 28 viral proteins of SARS-CoV-2 and identified that ORF3a strongly inhibited autophagic flux by blocking the fusion of autophagosomes with lysosomes. ORF3a colocalized with lysosomes and interacted with VPS39, a component of the homotypic fusion and protein sorting (HOPS) complex. The ORF3a-VPS39 interaction prohibited the binding of HOPS with RAB7, which prevented the assembly of fusion machinery, leading to the accumulation of unfused autophagosomes. These results indicated the potential mechanism by which SARS-CoV-2 escapes degradation; that is, the virus interferes with autophagosome-lysosome fusion. Furthermore, our findings will facilitate strategies targeting autophagy for conferring potential protection against the spread of SARS-CoV-2.

DOI: https://doi.org/10.1038/s41421-021-00268-z

Cell Death Dis. 2021 May 05. 12(5): 447

Mitochondrial ferritin attenuates cerebral ischaemia/reperfusion injury by inhibiting ferroptosis.

Peina Wang, Yanmei Cui, Qianqian Ren, Bingqi Yan, Yashuo Zhao, Peng Yu, Guofen Gao, Honglian Shi, Shiyang Chang, Yan-Zhong Chang.

Ischaemic stroke is becoming the most common cerebral disease in aging populations, but the underlying molecular mechanism of the disease has not yet been fully elucidated. Increasing evidence has indicated that an excess of iron contributes to brain damage in cerebral ischaemia/reperfusion (I/R) injury. Although mitochondrial ferritin (FtMt) plays a critical role in iron homeostasis, the molecular function of FtMt in I/R remains unknown. We herein report that FtMt levels are upregulated in the ischaemic brains of mice. Mice lacking FtMt experience more severe brain damage and neurological deficits, accompanied by typical molecular features of ferroptosis, including increased lipid peroxidation and disturbed glutathione (GSH) after cerebral I/R. Conversely, FtMt overexpression reverses these changes. Further investigation shows that Ftmt ablation promotes I/R-induced inflammation and hepcidin-mediated decreases in ferroportin1, thus markedly increasing total and chelatable iron. The elevated iron consequently facilitates ferroptosis in the brain of I/R. In brief, our results provide evidence that FtMt plays a critical role in protecting against cerebral I/R-induced ferroptosis and subsequent brain damage, thus providing a new potential target for the treatment/prevention of ischaemic stroke.

DOI: https://doi.org/10.1038/s41419-021-03725-5

Autophagy. 2021 May 04. 1-3

Upregulation of brain cholesterol levels inhibits mitophagy in Alzheimer disease.

Vicente Roca-Agujetas, Cristina de Dios, Xenia Abadin, Anna Colell.

Mitochondrial dysfunction is behind several neurodegenerative diseases, including Alzheimer disease (AD). Accumulation of damaged mitochondria is already observed at the early stages of AD and has been linked to impaired mitophagy, but the mechanisms underlying this alteration are still not fully known. In our recent study, we show that intracellular cholesterol enrichment can downregulate amyloid beta (Aβ)-induced mitophagy. Mitochondrial glutathione depletion resulting from high cholesterol levels promotes PINK1 (PTEN induced kinase 1)-mediated mitophagosome formation; however, mitophagy flux is ultimately disrupted, most likely due to fusion deficiency of endosomes-lysosomes caused by cholesterol. Meanwhile, in APP-PSEN1-SREBF2 mice, an AD mouse model that overexpresses the cholesterol-related transcription factor SREBF2, cholesterol accumulation prompts an oxidative- and age-dependent cytosolic aggregation of the mitophagy adaptor OPTN (optineurin), which prevents mitophagosome formation despite enhanced PINK1-PRKN/parkin signaling. Hippocampal neurons from postmortem brain of AD individuals reproduce the progressive accumulation of OPTN in aggresome-like structures accompanied by high levels of mitochondrial cholesterol in advanced stages of the disease. Overall, these data provide new insights into the impairment of the PINK1-PRKN mitophagy pathway in AD and suggest the combination of mitophagy inducers with strategies focused on restoring the cholesterol homeostasis and mitochondrial redox balance as a potential disease-modifying therapy for AD.

Keywords: Alzheimer disease; Mitophagy; PINK1; aggresomes; autophagy; cholesterol; optineurin; parkin

DOI: https://doi.org/10.1080/15548627.2021.1920814

Nat Commun. 2021 05 04. 12(1): 2511

Structures of a non-ribosomal peptide synthetase condensation domain suggest the basis of substrate selectivity.

Thierry Izoré, Y T Candace Ho, Joe A Kaczmarski, Athina Gavriilidou, Ka Ho Chow, David L Steer, Robert J A Goode, Ralf B Schittenhelm, Julien Tailhades, Manuela Tosin, Gregory L Challis, Elizabeth H Krenske, Nadine Ziemert, Colin J Jackson, Max J Cryle.

Non-ribosomal peptide synthetases are important enzymes for the assembly of complex peptide natural products. Within these multi-modular assembly lines, condensation domains perform the central function of chain assembly, typically by forming a peptide bond between two peptidyl carrier protein (PCP)-bound substrates. In this work, we report structural snapshots of a condensation domain in complex with an aminoacyl-PCP acceptor substrate. These structures allow the identification of a mechanism that controls access of acceptor substrates to the active site in condensation domains. The structures of this complex also allow us to demonstrate that condensation domain active sites do not contain a distinct pocket to select the side chain of the acceptor substrate during peptide assembly but that residues within the active site motif can instead serve to tune the selectivity of these central biosynthetic domains.

DOI: https://doi.org/10.1038/s41467-021-22623-0

Nat Commun. 2021 05 05. 12(1): 2550

Loss of Ambra1 promotes melanoma growth and invasion.

Melanoma is the deadliest skin cancer. Despite improvements in the understanding of the molecular mechanisms underlying melanoma biology and in defining new curative strategies, the therapeutic needs for this disease have not yet been fulfilled. Herein, we provide evidence that the Activating Molecule in Beclin-1-Regulated Autophagy (Ambra1) contributes to melanoma development. Indeed, we show that Ambra1 deficiency confers accelerated tumor growth and decreased overall survival in Braf/Pten-mutated mouse models of melanoma. Also, we demonstrate that Ambra1 deletion promotes melanoma aggressiveness and metastasis by increasing cell motility/invasion and activating an EMT-like process. Moreover, we show that Ambra1 deficiency in melanoma impacts extracellular matrix remodeling and induces hyperactivation of the focal adhesion kinase 1 (FAK1) signaling, whose inhibition is able to reduce cell invasion and melanoma growth. Overall, our findings identify a function for AMBRA1 as tumor suppressor in melanoma, proposing FAK1 inhibition as a therapeutic strategy for AMBRA1 low-expressing melanoma.

DOI: https://doi.org/10.1038/s41467-021-22772-2