bims-apauto Biomed News
on Apoptosis and autophagy
Issue of 2022‒09‒04
eight papers selected by
Su Hyun Lee
Seoul National University

  1. Mol Cell. 2022 Aug 23. pii: S1097-2765(22)00761-4. [Epub ahead of print]
      The covalent conjugation of ubiquitin family proteins is a widespread post-translational protein modification. In the ubiquitin family, the ATG8 subfamily is exceptional because it is conjugated mainly to phospholipids. However, it remains unknown whether other ubiquitin family proteins are also conjugated to phospholipids. Here, we report that ubiquitin is conjugated to phospholipids, mainly phosphatidylethanolamine (PE), in yeast and mammalian cells. Ubiquitinated PE (Ub-PE) accumulates at endosomes and the vacuole (or lysosomes), and its level increases during starvation. Ub-PE is also found in baculoviruses. In yeast, PE ubiquitination is catalyzed by the canonical ubiquitin system enzymes Uba1 (E1), Ubc4/5 (E2), and Tul1 (E3) and is reversed by Doa4. Liposomes containing Ub-PE recruit the ESCRT components Vps27-Hse1 and Vps23 in vitro. Ubiquitin-like NEDD8 and ISG15 are also conjugated to phospholipids. These findings suggest that the conjugation to membrane phospholipids is not specific to ATG8 but is a general feature of the ubiquitin family.
    Keywords:  Doa4; Tul1; endosome; lysosome; phosphatidylethanolamine; phospholipids; ubiquitin; ubiquitin-like proteins; vacuole
  2. Autophagy. 2022 Aug 29.
      Autophagy (i.e., macroautophagy) plays a significant role in the replication of hepatitis B virus (HBV). In our recent study, we examined the underlying mechanism and discovered that autophagic membranes participated in different steps of the HBV life cycle. We found that phagophores are involved in the assembly of HBV nucleocapsids, autophagosomes participate in the trafficking of HBV nucleocapsids, amphisomes likely participate in the maturation and egress of mature HBV particles, and autolysosomes negatively regulate HBV replication. Our work provides important insights for understanding the relationship between autophagic membranes and HBV replication and raises the possibility of targeting the autophagic pathway for the development of novel drugs against HBV.
  3. Front Pharmacol. 2022 ;13 961725
      As a noninvasive treatment approach for cancer and other diseases, sonodynamic therapy (SDT) has attracted extensive attention due to the deep penetration of ultrasound, good focusing, and selective irradiation sites. However, intrinsic limitations of traditional sonosensitizers hinder the widespread application of SDT. With the development of nanotechnology, nanoparticles as sonosensitizers or as a vehicle to deliver sonosensitizers have been designed and used to target tissues or tumor cells with high specificity and accuracy. Autophagy is a common metabolic alteration in both normal cells and tumor cells. When autophagy happens, a double-membrane autophagosome with sequestrated intracellular components is delivered and fused with lysosomes for degradation. Recycling these cell materials can promote survival under a variety of stress conditions. Numerous studies have revealed that both apoptosis and autophagy occur after SDT. This review summarizes recent progress in autophagy activation by SDT through multiple mechanisms in tumor therapies, drug resistance, and lipid catabolism. A promising tumor therapy, which combines SDT with autophagy inhibition using a nanoparticle delivering system, is presented and investigated.
    Keywords:  autophagy; cancer; nanoparticles; sonodynamic therapy (SDT); sonosensitizers
  4. Autophagy. 2022 Aug 30.
      Substrates that are selected for degradation by autophagy interact in more complex eukaryotes with Atg8-family proteins via the LC3-interacting region (LIR) that is often preceded by either acidic residues or phosphorylated serine or threonine. These upstream amino acid residues increase binding affinity of the LIR motif to its binding site on the surface of LC3/GABARAP. It is not fully understood whether or how phosphorylation functionally replaces acidic residues in the LIR-Atg8-family protein interactions. A recent study by Chino et al., discussed in this article, analyzed phosphorylation of two serine residues upstream of the LIR motif in TEX264, a reticulophagy receptor that exhibits a high binding affinity to LC3/GABARAP proteins. The authors found a structural basis for the high-affinity interaction yielded by phosphorylation, but not by an acidic residue in place of phosphoserine. Furthermore, finding that phosphorylation of TEX264 generates its high binding affinity to Atg8-family proteins uncovers a mechanistic alternative to that utilized by other reticulophagy receptors when they interact with LC3/GABARAP.
    Keywords:  Casein kinase 2; LC3-interacting region; crystallography; intrinsically disordered protein region; isothermal titration calorimetry
  5. Trends Cell Biol. 2022 Aug 18. pii: S0962-8924(22)00191-X. [Epub ahead of print]
      There is now a consensus that mitochondria are important tumor drivers, sophisticated biological machines that can engender a panoply of key disease traits. How this happens, however, is still mostly elusive. The opinion presented here is that what cancer exploits are not the normal mitochondria of oxygenated and nutrient-replete tissues, but the unfit, damaged, and dysfunctional organelles generated by the hostile environment of tumor growth. These 'ghost' mitochondria survive quality control and thwart cell death to relay multiple comprehensive 'danger signals' of metabolic starvation, cellular stress, and reprogrammed gene expression. The result is a new, treacherous cellular phenotype, proliferatively quiescent but highly motile, that enables tumor cell escape from a threatening environment and colonization of distant, more favorable sites (metastasis).
    Keywords:  Mic60; metabolism; metastasis; mitochondria; tumor plasticity
  6. DNA Cell Biol. 2022 Aug 26.
      Autophagy maintains intracellular homeostasis in the cardiovascular system, including in cardiomyocytes, endothelial cells (ECs), and arterial smooth muscle cells. Mitophagy, a selective autophagy that specifically removes damaged and dysfunctional mitochondria, is particularly important for cardiovascular homeostasis. Dysfunctional mitophagy contributes to cardiovascular disease, particularly atherosclerosis (AS). This review focuses on the advances of regulator mechanisms of mitophagy and its potential roles in AS. The findings are beneficial to understanding the pathological processes of atherosclerotic lesions and provide new ideas for the prevention and clinical treatment of AS.
    Keywords:  atherosclerosis; autophagy; cardiovascular disease; mitochondrial dysfunction; mitophagy
  7. Autophagy. 2022 Aug 29.
      Drug resistance has greatly limited the clinical efficacy of lenvatinib in hepatocellular carcinoma (HCC). However, the underlying molecular mechanisms of lenvatinib resistance remain largely undetermined. Further in-depth exploration of mechanisms underlying lenvatinib resistance is still required for the majority of HCC patients. In this study, integrated unbiased whole-genome CRISPR-Cas9 screen with database analysis indicated LAPTM5 (lysosomal protein transmembrane 5) as the critical contributor to lenvatinib resistance in HCC. We revealed that LAPTM5 could promote intrinsic macroautophagic/autophagic flux by facilitating autolysosome formation to drive lenvatinib resistance. The upregulation of LAPTM5 in HCC was induced by both DNA hypomethylation and driver mutations like TP53. Inhibition of autolysosome formation by either hydroxychloroquine (HCQ) or LAPTM5 abrogation worked synergistically with lenvatinib to inhibit tumor growth. In HCC cell lines, patient-derived primary cell lines and organoids, as well as human HCC xenografts and immunocompetent mouse HCC model, the close association between LAPTM5 and sensitivity to lenvatinib was consistently verified. Importantly, in clinical HCC samples, where lenvatinib was used as the first line or adjuvant therapy, LAPTM5 expression positively correlated with lenvatinib sensitivity, implying it as a biomarker to predict patient response to lenvatinib. In conclusion, the combinational therapy targeting autophagy represented a promising strategy to overcome lenvatinib resistance in HCC, and LAPTM5 expression could provide potential guidance for clinical interference.
    Keywords:  Autophagy; LAPTM5; drug resistance; lenvatinib; liver cancer; whole-genome CRISPR-Cas9 screen
  8. Curr Gene Ther. 2022 Aug 31.
      Cancer stem cells (CSCs) are cancer-initiating cells found in most tumors and hematological cancers. CSCs are involved in cells progression, recurrence of tumors, and drug resistance. Current therapies have been focused on treating the mass of tumor cells and cannot eradicate the CSCs. CSCs drug-specific targeting is considered as an approach to precisely target these cells. Clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) gene-editing systems are making progress and showing promise in the cancer research field. One of the attractive applications of CRISPR/Cas9 as one approach of gene therapy is targeting the critical genes involved in drug resistance and maintenance of CSCs. The synergistic effects of gene editing as a novel gene therapy approach and traditional therapeutic methods, including chemotherapy, can resolve drug resistance challenges and regression of the cancers. This review article considers different aspects of CRISPR/Cas9 ability in the study and targeting of CSCs with the intention to investigate their application in drug resistance.
    Keywords:  CRISPR/Cas9 systems; Cancer stem cells; Drug resistance; Gene editing; Stem cells.; Targeting therapy