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Autophagy Dec 2023Over the past decade, accumulated studies have reported the presence of non-canonical macroautophagy/autophagy characterized by the shared usage of the autophagy...
Over the past decade, accumulated studies have reported the presence of non-canonical macroautophagy/autophagy characterized by the shared usage of the autophagy machinery and distinct components that function in multiple scenarios but do not involve lysosomal degradation. One type of non-canonical autophagy is secretory autophagy, which facilitates the secretion of various cargoes. In a recent work from Gao et al. the ER-membrane protein STING1 has been identified as a novel substrate of secretory autophagy. The secretion of activated STING1 is mediated by its packing into the rafeesome, a newly identified organelle formed upon the fusion of RAB22A-mediated non-canonical autophagosome with an early endosome. Moreover, extracellular vesicles containing activated STING1 induce antitumor immunity in recipient cells, a process potentially promoted by RAB22A.
Topics: Autophagy; Autophagosomes; Lysosomes; Membrane Proteins; Endoplasmic Reticulum
PubMed: 37543953
DOI: 10.1080/15548627.2023.2240154 -
FEBS Letters Jan 2024Autophagy is an intracellular catabolic process that eliminates cytoplasmic constituents selectively by tight engulfment in an isolation membrane or recycles bulk... (Review)
Review
Autophagy is an intracellular catabolic process that eliminates cytoplasmic constituents selectively by tight engulfment in an isolation membrane or recycles bulk cytoplasm by nonselective sequestration. Completion of the isolation membrane forms a double membrane vesicle, termed autophagosome, that proceeds to fusion with the lysosome, where the inner membrane and its cytoplasmic content are degraded. Autophagosome biogenesis is unique in that the newly-formed membrane, termed phagophore, is elongated by direct lipid flow from a proximal ER-associated donor membrane. Recent years mark a tremendous advancement in delineating the direct regulation of this process by different lipid species and associated protein complexes. Here we schematically summarize the current view of autophagy and autophagosome biogenesis.
Topics: Autophagy; Autophagosomes; Lysosomes; Lipids
PubMed: 37326419
DOI: 10.1002/1873-3468.14679 -
Cancer Biology & Therapy Dec 2023Accumulating studies demonstrated that resistance of colon cancer (CC) to 5-fluorouracil (5-FU) contributes to adverse prognosis. We investigated how Kruppel-like factor...
BACKGROUND
Accumulating studies demonstrated that resistance of colon cancer (CC) to 5-fluorouracil (5-FU) contributes to adverse prognosis. We investigated how Kruppel-like factor 4 (KLF4) affected 5-FU resistance and autophagy in CC cells.
METHODS
KLF4 expression and its downstream target gene RAB26 in CC tissues was analyzed by bioinformatics analysis, and the effect of abnormal KLF4 expression on prognoses of CC patients was predicted. Luciferase reporter assay detected the targeted relationship between KLF4 and RAB26. The viability and apoptosis of CC cells were analyzed by CCK-8 and flow cytometry. The formation of intracellular autophagosomes was detected by confocal laser scanning microscopy and immunofluorescence staining. The mRNA and protein levels were assayed by qRT-PCR and western blot. A xenograft animal model was constructed to verify the function of KLF4. Rescue assay was employed to verify whether KLF4/RAB26 could affect 5-FU resistance in CC cells through autophagy.
RESULTS
KLF4 and RAB26 were lowly expressed in CC. KLF4 correlated with patients' survival. KLF4 was down-regulated in 5-FU resistant CC cells. KLF4 overexpression suppressed the proliferation and 5-FU resistance of CC cells, and inhibited LC3 II/I expression and autophagosome formation. Autophagy activator Rapamycin or sh-RAB26 treatment reversed the impact of KLF4 overexpression on 5-FU resistance. In vivo assay verified that KLF4 inhibited 5-FU resistance in CC cells. Rescue experiments revealed that KLF4 targeted RAB26 to inhibit CC cell autophagy, resulting in decreasing the resistance to 5-FU.
CONCLUSION
KLF4 strengthened the sensitivity of CC cells to 5-FU by targeting RAB26 to restrain autophagy pathway.
Topics: Humans; Animals; Kruppel-Like Factor 4; Colonic Neoplasms; Fluorouracil; Autophagy; Autophagosomes; Disease Models, Animal
PubMed: 37431852
DOI: 10.1080/15384047.2023.2226353 -
Cellular and Molecular Life Sciences :... Jul 2023During phagocytosis, endosomes both contribute with membrane to forming phagosomes and promote phagosome maturation. However, how these vesicles are delivered to the...
During phagocytosis, endosomes both contribute with membrane to forming phagosomes and promote phagosome maturation. However, how these vesicles are delivered to the phagocytic cup and the phagosome has been unknown. Here, we show that Protrudin-mediated endoplasmic reticulum (ER)-endosome contact sites facilitate anterograde translocation of FYCO1 and VAMP7-positive late endosomes and lysosomes (LELys) to forming phagocytic cups in a retinal pigment epithelial-derived cell line (RPE1). Protrudin-dependent phagocytic cup formation required SYT7, which promotes fusion of LELys with the plasma membrane. RPE1 cells perform phagocytosis of dead cells (efferocytosis) that expose phosphatidylserine (PS) on their surface. Exogenous addition of apoptotic bodies increased the formation of phagocytic cups, which further increased when Protrudin was overexpressed. Overexpression of Protrudin also led to elevated uptake of silica beads coated with PS. Conversely, Protrudin depletion or abrogation of ER-endosome contact sites inhibited phagocytic cup formation resulting in reduced uptake of PS-coated beads. Thus, the Protrudin pathway delivers endosomes to facilitate formation of the phagocytic cup important for PS-dependent phagocytosis.
Topics: Phagocytosis; Endoplasmic Reticulum; Lysosomes; Phagosomes; Endosomes
PubMed: 37468729
DOI: 10.1007/s00018-023-04862-0 -
Autophagy Apr 2024Induction of autophagy is a primordial function of the cGAS-STING pathway. However, the molecular mechanisms regulating autophagosome formation during STING-induced...
Induction of autophagy is a primordial function of the cGAS-STING pathway. However, the molecular mechanisms regulating autophagosome formation during STING-induced autophagy remain largely unknown. Recently, we reported that STING directly interacts with WIPI2 to recruit WIPI2 onto STING-positive vesicles for LC3 lipidation and autophagosome formation. We found that STING and PtdIns3P competitively bind to the FRRG motif of WIPI2, resulting in a mutual inhibition between STING-induced and PtdIns3P-dependent autophagy. We also showed that STING-WIPI2 interaction is necessary for cells to clear cytoplasmic DNA and attenuate activated cGAS-STING signaling. In summary, by identifying the interaction between STING and WIPI2, our study revealed a mechanism that allows STING to bypass the canonical upstream machinery to induce autophagosome formation. ATG: autophagy-related; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; cGAMP: cyclic GMP-AMP; cGAS: cyclic GMP-AMP synthase; ER: endoplasmic reticulum; ERGIC: ER-Golgi intermediate compartment; IRF3: interferon regulatory factor 3; PtdIns3P: phosphatidylinositol-3-phosphate; SQSTM1: sequestosome 1; STING: stimulator of interferon genes; TBK1: TANK-binding kinase 1; ULK1: unc-51 like autophagy activating kinase 1; WIPI2: WD repeat domain, phosphoinositide interacting 2.
Topics: Autophagosomes; Membrane Proteins; Humans; Autophagy; Animals; Signal Transduction; Autophagy-Related Proteins; Phosphate-Binding Proteins
PubMed: 37041719
DOI: 10.1080/15548627.2023.2202108 -
The EMBO Journal Oct 2023The regulation of autophagy initiation is a key step in autophagosome biogenesis. However, our understanding of the molecular mechanisms underlying the stepwise assembly...
The regulation of autophagy initiation is a key step in autophagosome biogenesis. However, our understanding of the molecular mechanisms underlying the stepwise assembly of ATG proteins during this process remains incomplete. The Rab GTPase Ypt1/Rab1 is recognized as an essential autophagy regulator. Here, we identify Atg23 and Atg17 as binding partners of Ypt1, with their direct interaction proving crucial for the stepwise assembly of autophagy initiation complexes. Disruption of Ypt1-Atg23 binding results in significantly reduced Atg9 interactions with Atg11, Atg13, and Atg17, thus preventing the recruitment of Atg9 vesicles to the phagophore assembly site (PAS). Likewise, Ypt1-Atg17 binding contributes to the PAS recruitment of Ypt1 and Atg1. Importantly, we found that Ypt1 is phosphorylated by TOR at the Ser174 residue. Converting this residue to alanine blocks Ypt1 phosphorylation by TOR and enhances autophagy. Conversely, the Ypt1 phosphorylation mimic impairs both PAS recruitment and activation of Atg1, thus inhibiting subsequent autophagy. Thus, we propose TOR-mediated Ypt1 as a multifunctional assembly factor that controls autophagy initiation via its regulation of the stepwise assembly of ATG proteins.
Topics: Autophagy; Autophagy-Related Proteins; Phagosomes; Phosphorylation; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 37635626
DOI: 10.15252/embj.2022112814 -
Nature Communications Aug 2023Organelles are shaped by curvature-generating proteins, which include the reticulons and REEPs that are involved in forming the endoplasmic reticulum (ER). A conserved...
Organelles are shaped by curvature-generating proteins, which include the reticulons and REEPs that are involved in forming the endoplasmic reticulum (ER). A conserved REEP subfamily differs from the ER-shaping REEPs in abundance and membrane topology and has unidentified functions. Here, we show that Rop1, the single member of this family in the fission yeast Schizosacharomyces pombe, is crucial for the macroautophagy of organelles and cytosolic proteins. Rop1 is needed for the formation of phagophores, cup-like structures consisting of two closely apposed membrane sheets that encapsulate cargo. It is recruited at early stages to phagophores and is required for their maturation into autophagosomes. Rop1 function relies on its ability to generate high membrane curvature and on its colocalization with the autophagy component Atg2 that is thought to reside at the phagophore rim. We propose that Rop1 facilitates the formation and growth of the double-membrane structure of the autophagosome.
Topics: Membrane Proteins; Autophagosomes; Schizosaccharomyces; Macroautophagy; Autophagy; Autophagy-Related Proteins
PubMed: 37553386
DOI: 10.1038/s41467-023-40530-4 -
Communications Biology Aug 2023Human WIPI β-propellers function as PI3P effectors in autophagy, with WIPI4 and WIPI3 being able to link autophagy control by AMPK and TORC1 to the formation of...
Human WIPI β-propellers function as PI3P effectors in autophagy, with WIPI4 and WIPI3 being able to link autophagy control by AMPK and TORC1 to the formation of autophagosomes. WIPI1, instead, assists WIPI2 in efficiently recruiting the ATG16L1 complex at the nascent autophagosome, which in turn promotes lipidation of LC3/GABARAP and autophagosome maturation. However, the specific role of WIPI1 and its regulation are unknown. Here, we discovered the ABL-ERK-MYC signalling axis controlling WIPI1. As a result of this signalling, MYC binds to the WIPI1 promoter and represses WIPI1 gene expression. When ABL-ERK-MYC signalling is counteracted, increased WIPI1 gene expression enhances the formation of autophagic membranes capable of migrating through tunnelling nanotubes to neighbouring cells with low autophagic activity. ABL-regulated WIPI1 function is relevant to lifespan control, as ABL deficiency in C. elegans increased gene expression of the WIPI1 orthologue ATG-18 and prolonged lifespan in a manner dependent on ATG-18. We propose that WIPI1 acts as an enhancer of autophagy that is physiologically relevant for regulating the level of autophagic activity over the lifespan.
Topics: Animals; Humans; Autophagosomes; Autophagy; Caenorhabditis elegans; Longevity; Macroautophagy; Proto-Oncogene Proteins c-abl
PubMed: 37620393
DOI: 10.1038/s42003-023-05236-9 -
Bioscience Reports May 2024Chloride is a key anion involved in cellular physiology by regulating its homeostasis and rheostatic processes. Changes in cellular Cl- concentration result in... (Review)
Review
Chloride is a key anion involved in cellular physiology by regulating its homeostasis and rheostatic processes. Changes in cellular Cl- concentration result in differential regulation of cellular functions such as transcription and translation, post-translation modifications, cell cycle and proliferation, cell volume, and pH levels. In intracellular compartments, Cl- modulates the function of lysosomes, mitochondria, endosomes, phagosomes, the nucleus, and the endoplasmic reticulum. In extracellular fluid (ECF), Cl- is present in blood/plasma and interstitial fluid compartments. A reduction in Cl- levels in ECF can result in cell volume contraction. Cl- is the key physiological anion and is a principal compensatory ion for the movement of the major cations such as Na+, K+, and Ca2+. Over the past 25 years, we have increased our understanding of cellular signaling mediated by Cl-, which has helped in understanding the molecular and metabolic changes observed in pathologies with altered Cl- levels. Here, we review the concentration of Cl- in various organs and cellular compartments, ion channels responsible for its transportation, and recent information on its physiological roles.
Topics: Humans; Chlorides; Animals; Homeostasis; Chloride Channels; Signal Transduction; Extracellular Fluid; Ion Transport
PubMed: 38573803
DOI: 10.1042/BSR20240029 -
Autophagy Mar 2024Macroautophagy/autophagy receptors target their substrates to phagophores for subsequent sequestration within autophagosomes. During phagophore membrane expansion in...
Macroautophagy/autophagy receptors target their substrates to phagophores for subsequent sequestration within autophagosomes. During phagophore membrane expansion in mammalian cells, autophagy receptors simultaneously interact with the ubiquitinated substrates and the LC3/GABARAP proteins on the expanding membrane. In this punctum, we summarize and discuss our recent research progress on synthetic autophagy receptors (AceTACs). The series of AceTACs were designed by engineering the essential interacting domains and motifs of SQSTM1/p62 (sequestosome 1), a major mammalian autophagy receptor. Particularly, we replaced the ubiquitin-associated domain of SQSTM1 with a target-specific antibody, redirecting the bifunctional interactions of wild-type SQSTM1 and directing the degradation target into the autophagy process. We successfully demonstrated the targeted degradation of aggregation-prone proteins using the AceTAC degraders. Moreover, we presented a model system with a guideline to induce targeted degradation of organelles through the autophagy machinery.
Topics: Animals; Autophagy; Sequestosome-1 Protein; Proteins; Autophagosomes; Ubiquitin; Carrier Proteins; Mammals
PubMed: 37934826
DOI: 10.1080/15548627.2023.2278954