bims-apauto Biomed News
on Apoptosis and autophagy
Issue of 2021‒03‒14
ten papers selected by
Su Hyun Lee
Seoul National University

  1. Pharmacol Rep. 2021 Mar 07.
      BACKGROUND: Human epidermal growth factor receptor 2 (HER2) is well-known as the therapeutic marker in breast cancer. Therefore, we evaluated anti-cancer activity of arctigenin (ATG) on in SK-BR-3 HER2-overexpressing human breast cancer cells.METHODS: Cell viability and cytotoxicity were analyzed with MTT and colony-forming assay and cell cycle analysis was performed by flow cytometry. The expression and/or phosphorylation of proteins in whole cell lysate and mitochondrial fraction were analyzed by Western blotting. Cellular levels of LC3 and sequestosome 1 (SQSTM1/P62) were observed by immunofluorescence analysis.
    RESULTS: The result showed that ATG decreased cell viability of SK-BR-3 cells in a concentration-dependent manner. Moreover, ATG increased the sub G1 population linked to the suppression of HER2/EGFR1 signaling pathway. Furthermore, ATG increased the phosphorylation of H2AX and down-regulated RAD51 and survivin expressions, indicating that ATG induced DNA damage and inhibited the DNA repair system. We also found that cleavages of caspase-7 and PARP by releasing mitochondrial cytochrome c into the cytoplasm were induced by ATG treatment for 72 h through the reduction of Bcl-2 and Bcl-xL levels in mitochondria. In contrast, the levels of LC-3 and SQSTM1/P62 were increased by ATG for 24 h through the Akt/mTOR and AMPK signaling pathway.
    CONCLUSIONS: Taken together, this study indicates that autophagy-linked apoptosis is responsible for the anti-cancer activity of ATG in SK-BR-3 cells, and suggests that ATG is considered a potential therapeutic for the treatment of HER2-overexpressing breast cancer.
    Keywords:  Apoptosis; Arctigenin; Autophagy; Cell death; HER2-overexpressing breast cancer
  2. Nat Commun. 2021 03 11. 12(1): 1589
      Glutathione peroxidase 4 (GPX4) utilizes glutathione (GSH) to detoxify lipid peroxidation and plays an essential role in inhibiting ferroptosis. As a selenoprotein, GPX4 protein synthesis is highly inefficient and energetically costly. How cells coordinate GPX4 synthesis with nutrient availability remains unclear. In this study, we perform integrated proteomic and functional analyses to reveal that SLC7A11-mediated cystine uptake promotes not only GSH synthesis, but also GPX4 protein synthesis. Mechanistically, we find that cyst(e)ine activates mechanistic/mammalian target of rapamycin complex 1 (mTORC1) and promotes GPX4 protein synthesis at least partly through the Rag-mTORC1-4EBP signaling axis. We show that pharmacologic inhibition of mTORC1 decreases GPX4 protein levels, sensitizes cancer cells to ferroptosis, and synergizes with ferroptosis inducers to suppress patient-derived xenograft tumor growth in vivo. Together, our results reveal a regulatory mechanism to coordinate GPX4 protein synthesis with cyst(e)ine availability and suggest using combinatorial therapy of mTORC1 inhibitors and ferroptosis inducers in cancer treatment.
  3. Front Cell Dev Biol. 2020 ;8 596655
      Despite the activation of autophagy may enable residual cancer cells to survive and allow tumor relapse, excessive activation of autophagy may eventually lead to cell death. However, the details of the association of autophagy with primary resistance in hepatocellular carcinoma (HCC) remain less clear. In this study, cohort analysis revealed that HCC patients receiving sorafenib with HBV had higher mortality risk. We found that high epidermal growth factor receptor (EGFR) expression and activity may be linked to HBV-induced sorafenib resistance. We further found that the resistance of EGFR-overexpressed liver cancer cells to sorafenib is associated with low activity of AMP-activated protein kinase (AMPK) and CCAAT/enhancer binding protein delta (CEBPD) as well as insufficient autophagic activation. In response to metformin, the AMPK/cAMP-response element binding protein (CREB) pathway contributes to CEBPD activation, which promotes autophagic cell death. Moreover, treatment with metformin can increase sorafenib sensitivity through AMPK activation in EGFR-overexpressed liver cancer cells. This study suggests that AMPK/CEBPD-activated autophagy could be a potent strategy for improving the efficacy of sorafenib in HCC patients.
    Keywords:  AMPK; CEBPD; autophagy; metformin; sorafenib
  4. J Cell Physiol. 2021 Mar 08.
      Autophagy, an evolutionarily conserved lysosomal degradation pathway, is known to regulate a variety of physiological and pathological processes. At present, the function and the precise mechanism of autophagy regulation in kidney and renal cells remain elusive. Here, we explored the role of ERK1 and ERK2 (referred as ERK1/2 hereafter) in autophagy regulation in renal cells in response to hypoglycemia. Glucose starvation potently and transiently activated ERK1/2 in renal cells, and this was concomitant with an increase in autophagic flux. Perturbing ERK1/2 activation by treatment with inhibitors of RAF or MEK1/2, via the expression of a dominant-negative mutant form of MEK1/2 or RAS, blocked hypoglycemia-mediated ERK1/2 activation and autophagy induction in renal cells. Glucose starvation also induced the accumulation of reactive oxygen species in renal cells, which was involved in the activation of the ERK1/2 cascade and the induction of autophagy in renal cells. Interestingly, ATG13 and FIP200, the members of the ULK1 complex, contain the ERK consensus phosphorylation sites, and glucose starvation induced an association between ATG13 or FIP200 and ERK1/2. Moreover, the expression of the phospho-defective mutants of ATG13 and FIP200 in renal cells blocked glucose starvation-induced autophagy and rendered cells more susceptible to hypoglycemia-induced cell death. However, the expression of the phospho-mimic mutants of ATG13 and FIP200 induced autophagy and protected renal cells from hypoglycemia-induced cell death. Taken together, our results demonstrate that hypoglycemia activates the ERK1/2 signaling to regulate ATG13 and FIP200, thereby stimulating autophagy to protect the renal cells from hypoglycemia-induced cell death.
    Keywords:  ATG13; ERK1/2; FIP200; autophagy; hypoglycemia; renal cells
  5. Chem Biol Interact. 2021 Mar 06. pii: S0009-2797(21)00069-7. [Epub ahead of print] 109433
      Pancreatic cancer is one of the most malignant cancers around the world. The co-occurrence of mutation in KRAS and p53 makes it highly aggressive, proliferative, metastatic, and resistant to apoptotic cell death. Therefore, there is a need to trigger an alternate mechanism of cancer cell death in apoptosis-resistant pancreatic cancer. Autophagic cell death could be an alternate viable option for treatment in such cases.Thus, identification of small molecules as autophagy modulators with potent anticancer efficacy would be of great importance in pancreatic cancer. The present study investigates fluorinated thiazolidionol (FTZ) driven autophagy modulation, underlying mechanism and regulation of critical sentinels of oncogenic signaling by FTZ in pancreatic cancer cells. We identified that FTZ triggered autophagic cell death in pancreatic cancer cells, independent of apoptosis evidenced by an increase in cytoplasmic vacuoles formation, autophagy flux, LC3-II expression, and p62 degradation. Further, the crucial events of apoptosis i.e., Caspase-3 activation and PARP cleavage, were not observed, indicating the non-occurrence of apoptotic cell death. Moreover, FTZ was able to activate AMPK and suppress PI3k/Akt/mTOR and MEK/ERK, the key oncogenic signaling pathways in cancer cells. Furthermore, treatment with FTZ suppressed migration, invasion, and angiogenesis in pancreatic cancer cells. Studies in vivo revealed significant regression of tumors by FTZ in nude mice model. Overall, our study demonstrates that FTZ induces autophagic cell death in pancreatic cancer cells independent of apoptosis, which is accompanied by AMPK activation and supression of critical sentinels of oncogenic signaling in pancreatic cancer cells.
    Keywords:  AMPK activation; Fluorinated thiazolidinol; Pancreatic cancer; autophagy; caspase independent cell death; tumor regression
  6. Autophagy. 2021 Mar 11. 1-18
      Preconditioning with a mild stressor such as fasting is a promising way to reduce severe side effects from subsequent chemo- or radiotherapy. However, the underlying mechanisms have been largely unexplored. Here, we demonstrate that the TP53/p53-FBXO22-TFEB (transcription factor EB) axis plays an essential role in this process through upregulating basal macroautophagy/autophagy. Mild stress-activated TP53 transcriptionally induced FBXO22, which in turn ubiquitinated KDM4B (lysine-specific demethylase 4B) complexed with MYC-NCOR1 suppressors for degradation, leading to transcriptional induction of TFEB. Upregulation of autophagy-related genes by increased TFEB dramatically enhanced autophagic activity and cell survival upon following a severe stressor. Mitogen-induced AKT1 activation counteracted this process through the phosphorylation of KDM4B, which inhibited FBXO22-mediated ubiquitination. Additionally, fbxo22-/- mice died within 10 h of birth, and their mouse embryonic fibroblasts (MEFs) showed a lowered basal autophagy, whereas FBXO22-overexpressing mice were resistant to chemotherapy. Taken together, these results suggest that TP53 upregulates basal autophagy through the FBXO22-TFEB axis, which governs the hormetic effect in chemotherapy.Abbreviations: BBC3/PUMA: BCL2 binding component 3; CDKN1A/p21: cyclin dependent kinase inhibitor 1A; ChIP-seq: chromatin immunoprecipitation followed by sequencing; DDB2: damage specific DNA binding protein 2; DRAM: DNA damage regulated autophagy modulator; ESR/ER: estrogen receptor 1; FMD: fasting mimicking diet; HCQ: hydroxychloroquine; KDM4B: lysine-specific demethylase 4B; MAP1LC3/LC3: microtubule associated protein 1 light chain 3 alpha; MEFs: mouse embryonic fibroblasts; MTOR: mechanistic target of rapamycin kinase; NCOR1: nuclear receptor corepressor 1; SCF: SKP1-CUL-F-box protein; SQSTM1: sequestosome 1; TFEB: transcription factor EB.
    Keywords:  AKT1; FBXO22; KDM4B; MYC; TP53; autophagy; hormesis; ubiquitination
  7. Biochim Biophys Acta Mol Cell Res. 2021 Mar 08. pii: S0167-4889(21)00055-0. [Epub ahead of print] 119001
      Endoplasmic Reticulum (ER) stress signaling is an adaptive mechanism triggered when protein folding demand overcomes the folding capacity of this compartment, thereby leading to the accumulation of improperly folded proteins. This stress signaling pathway is named the Unfolded Protein Response (UPR) and aims at restoring ER homeostasis. However, if this fails, mechanisms orienting cells towards death processes are initiated. Herein, we summarize the most recent findings connecting ER stress and the UPR with identified death mechanisms including apoptosis, necrosis, pyroptosis, ferroptosis, and autophagy. We highlight new avenues that could be investigated and controlled through actionable mechanisms in physiology and pathology.
    Keywords:  Apoptosis; Autophagy; Cell death; Endoplasmic reticulum; Ferroptosis; Pyroptosis; Unfolded protein response
  8. Chem Biol Interact. 2021 Mar 05. pii: S0009-2797(21)00068-5. [Epub ahead of print] 109432
      Mitochondrial dependent oxidative stress (OS) and subsequent cell death are considered as the major cytotoxicity caused by Triethylene glycol dimethacrylate (TEGDMA), a commonly monomer of many resin-based dental composites. Under OS microenvironment, autophagy serves as a cell homeostatic mechanism and maintains redox balance through degradation or turnover of cellular components in order to promote cell survival. However, whether autophagy is involved in the mitochondrial oxidative damage and apoptosis induced by TEGDMA, and the cellular signaling pathways underlying this process remain unclear. In the present study, we demonstrated that TEGDMA induced mouse preodontoblast cell line (mDPC6T) dysfunctional mitochondrial oxidative response. In further exploring the underlying mechanisms, we found that TEGDMA impaired autophagic flux, as evidenced by increased LC3-II expression and hindered p62 degradation, thereby causing both mitochondrial oxidative damage and cell apoptosis. These results were further verified by treatment with chloroquine (autophagy inhibitor) and rapamycin (autophagy promotor). More importantly, we found that the JNK/MAPK pathway was the key upstream regulator of above injury process. Collectively, our finding firstly demonstrated that TEGDMA induced JNK-dependent autophagy, thereby promoting mitochondrial dysfunction-associated oxidative damage and apoptosis in preodontoblast.
    Keywords:  Apoptosis; Autophagy; Dental pulp cell; Mitochondrial dysfunction; Oxidative stress; TEGDMA
  9. Mol Biol Rep. 2021 Mar 09.
      The plasma membrane performs a central role in maintaining cellular homeostasis and viability by acting as a semi-permeable barrier separating the cell from its surroundings. Under physiological conditions, it is constantly exposed to different kinds of stress, such as from pore-forming proteins/toxins and mechanical activity, that compromises its integrity resulting in cells developing various ways to cope with these dangers to survive. These plasma membrane repair mechanisms are initiated by the rapid influx of extracellular Ca2+ ions and are thus hinged on the activity of various Ca2+-binding proteins. The cell's response to membrane damage also depends on the nature and extent of the stimuli as well as the cell type, and the mechanisms involved are believed to be not mutually exclusive. In regulated necrotic cell death, specifically necroptosis, pyroptosis, and ferroptosis, plasma membrane damage ultimately causes cell lysis and the release of immunomodulating damage-associated molecular patterns. Here, I will discuss how these three cell death pathways are counterbalanced by the action of ESCRT (Endosomal Sorting Complex Required for Transport)-III-dependent plasma membrane repair mechanism, that eventually affects the profile of released cytokines and cell-to-cell communication. These highlight a crucial role that plasma membrane repair play in regulated necrosis, and its potential as a viable target to modulate the immune responses associated with these pathways in the context of the various human pathologies where these cell death modalities are implicated.
    Keywords:  ESCRT; Ferroptosis; Membrane pores; Necroptosis; Plasma membrane repair; Pyroptosis
  10. Autophagy. 2021 Mar 08. 1-27
      Autophagosome formation requires PROPPIN/WIPI proteins and monophosphorylated phosphoinositides, such as phosphatidylinositol-3-phosphate (PtdIns3P) or PtdIns5P. This process occurs in association with mammalian endosomes, where the PROPPIN WIPI1 has additional, undefined roles in vesicular traffic. To explore whether these functions are interconnected, we dissected routes and subreactions of endosomal trafficking requiring WIPI1. WIPI1 specifically acts in the formation and fission of tubulo-vesicular endosomal transport carriers. This activity supports the PtdIns(3,5)P2-dependent transport of endosomal cargo toward the plasma membrane, Golgi, and lysosomes, suggesting a general role of WIPI1 in endosomal protein exit. Three features differentiate the endosomal and macroautophagic/autophagic activities of WIPI1: phosphoinositide binding site II, the requirement for PtdIns(3,5)P2, and bilayer deformation through a conserved amphipathic α-helix. Their inactivation preserves autophagy but leads to a strong enlargement of endosomes, which accumulate micrometer-long endosomal membrane tubules carrying cargo proteins. WIPI1 thus supports autophagy and protein exit from endosomes by different modes of action. We propose that the type of phosphoinositides occupying its two lipid binding sites, the most unusual feature of PROPPIN/WIPI family proteins, switches between these effector functions.AbbreviationsEGF: epidermal growth factorEGFR: epidermal growth factor receptorKD: knockdownKO: knockoutPtdIns3P: phosphatidylinositol-3-phosphatePtdIns5P: phosphatidylinositol-5-phosphatePtdIns(3,5)P2: phosphatidylinositol-3,5-bisphosphateTF: transferrinTFRC: transferrin receptorWT: wildtype.
    Keywords:  Autophagy; EGF receptor; PROPPIN; WIPI proteins; autophagosome; endosomal transport carrier; endosome; lysosome; transferrin receptor; vacuole