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Nature Communications Dec 2023Selective autophagy of the endoplasmic reticulum (ER), known as ER-phagy, is an important regulator of ER remodeling and essential to maintain cellular homeostasis...
Selective autophagy of the endoplasmic reticulum (ER), known as ER-phagy, is an important regulator of ER remodeling and essential to maintain cellular homeostasis during environmental changes. We recently showed that members of the FAM134 family play a critical role during stress-induced ER-phagy. However, the mechanisms on how they are activated remain largely unknown. In this study, we analyze phosphorylation of FAM134 as a trigger of FAM134-driven ER-phagy upon mTOR (mechanistic target of rapamycin) inhibition. An unbiased screen of kinase inhibitors reveals CK2 to be essential for FAM134B- and FAM134C-driven ER-phagy after mTOR inhibition. Furthermore, we provide evidence that ER-phagy receptors are regulated by ubiquitination events and that treatment with E1 inhibitor suppresses Torin1-induced ER-phagy flux. Using super-resolution microscopy, we show that CK2 activity is essential for the formation of high-density FAM134B and FAM134C clusters. In addition, dense clustering of FAM134B and FAM134C requires phosphorylation-dependent ubiquitination of FAM134B and FAM134C. Treatment with the CK2 inhibitor SGC-CK2-1 or mutation of FAM134B and FAM134C phosphosites prevents ubiquitination of FAM134 proteins, formation of high-density clusters, as well as Torin1-induced ER-phagy flux. Therefore, we propose that CK2-dependent phosphorylation of ER-phagy receptors precedes ubiquitin-dependent activation of ER-phagy flux.
Topics: Phosphorylation; Membrane Proteins; Autophagy; Endoplasmic Reticulum; Carrier Proteins; Endoplasmic Reticulum Stress; TOR Serine-Threonine Kinases; Ubiquitination
PubMed: 38102139
DOI: 10.1038/s41467-023-44101-5 -
Acta Biomaterialia Oct 2023Although mitochondrial morphology and function are considered to be closely related to matrix stiffness-driven tumor progression, it remains poorly understood how...
Although mitochondrial morphology and function are considered to be closely related to matrix stiffness-driven tumor progression, it remains poorly understood how extracellular matrix (ECM) stiffness affects mitochondrial dynamics and mitophagy. Here, we found that soft substrate triggered calcium transport by increasing endoplasmic reticulum (ER) calcium release and mitochondrial (MITO) calcium uptake. ER-MITO calcium transport promoted the recruitment of dynamin-related protein 1 (Drp1) to mitochondria and phosphorylation at the serine 616 site, which induced mitochondrial fragmentation and Parkin/PINK1-mediated mitophagy. Furthermore, in vivo experiments demonstrated that soft ECM enhanced calcium levels in tumor tissue, Drp1 activity was required for soft ECM-induced mitochondrial dynamics impairment, and inhibition of Drp1 activity enhanced soft ECM-induced tumor necrosis. In conclusion, we revealed a new mechanism whereby ER-MITO calcium transport regulated mitochondrial dynamics and mitophagy through Drp1 translocation in response to soft substrates. These findings provide valuable insights into ECM stiffness as a potential target for antitumor therapy. STATEMENT OF SIGNIFICANCE: Here, we examined the relationship between substrate stiffness and mitochondrial dynamics by using polyacrylamide (PAA) substrates to simulate the stages of breast cancer or BAPN to reduce tumor tissue stiffness. The results elucidated that soft substrate triggered the recruitment of DRP1 and subsequent mitochondrial fission and mitophagy by ER-MITO calcium transport. Furthermore, mitophagy partly attenuated soft ECM-mediated tumor tissue necrosis and contributed to tumor survival in vivo. Our discoveries revealed the molecular mechanisms by which mechanical stimulation regulates mitochondrial dynamics, providing valuable insights into ECM stiffness as a target for anti-tumor approaches, which could be beneficial for both biomechanics research and clinical applications.
Topics: Humans; Female; Mitophagy; Mitochondrial Dynamics; Calcium; Dynamins; Endoplasmic Reticulum; Necrosis; Breast Neoplasms
PubMed: 37541606
DOI: 10.1016/j.actbio.2023.07.060 -
Journal of Proteome Research Nov 2023Most proteins secreted into the extracellular space are first recruited from the endoplasmic reticulum into coat protein complex II (COPII)-coated vesicles or tubules...
Most proteins secreted into the extracellular space are first recruited from the endoplasmic reticulum into coat protein complex II (COPII)-coated vesicles or tubules that facilitate their transport to the Golgi apparatus. Although several secreted proteins have been shown to be actively recruited into COPII vesicles and tubules by the cargo receptors LMAN1 and SURF4, the full cargo repertoire of these receptors is unknown. We now report mass spectrometry analysis of conditioned media and cell lysates from HuH7 cells CRISPR targeted to inactivate the or gene. We found that LMAN1 has limited clients in HuH7 cells, whereas SURF4 traffics a broad range of cargoes. Analysis of putative SURF4 cargoes suggests that cargo recognition is governed by complex mechanisms rather than interaction with a universal binding motif..
Topics: Humans; Carrier Proteins; Endoplasmic Reticulum; Golgi Apparatus; Membrane Proteins; Protein Transport
PubMed: 37844105
DOI: 10.1021/acs.jproteome.3c00259 -
Journal of Molecular Medicine (Berlin,... Dec 2023The unfolded protein response (UPR) is a cellular stress response mechanism induced by the accumulation of unfolded or misfolded proteins. Within the endoplasmic... (Review)
Review
The unfolded protein response (UPR) is a cellular stress response mechanism induced by the accumulation of unfolded or misfolded proteins. Within the endoplasmic reticulum and mitochondria, a dynamic balance exists between protein folding mechanisms and unfolded protein levels under normal conditions. Disruption of this balance or an accumulation of unfolded proteins in these organelles can result in stress responses and UPR. The UPR restores organelle homeostasis and promotes cell survival by increasing the expression of chaperone proteins, regulating protein quality control systems, and enhancing the protein degradation pathway. However, prolonged or abnormal UPR can also have negative effects, including cell death. Therefore, many diseases, especially neurodegenerative diseases, are associated with UPR dysfunction. Neurodegenerative diseases are characterized by misfolded proteins accumulating and aggregating, and neuronal cells are particularly sensitive to misfolded proteins and are prone to degeneration. Many studies have shown that the UPR plays an important role in the pathogenesis of neurodegenerative diseases. Here, we will discuss the possible contributions of the endoplasmic reticulum unfolded protein response (UPR) and the mitochondrial unfolded protein response (UPR) in the development of several neurodegenerative diseases.
Topics: Humans; Neurodegenerative Diseases; Endoplasmic Reticulum Stress; Unfolded Protein Response; Endoplasmic Reticulum; Mitochondria
PubMed: 37817014
DOI: 10.1007/s00109-023-02382-9 -
EMBO Reports Nov 2023Compartmentalization by membranes is a common feature of eukaryotic cells and serves to spatiotemporally confine biochemical reactions to control physiology.... (Review)
Review
Compartmentalization by membranes is a common feature of eukaryotic cells and serves to spatiotemporally confine biochemical reactions to control physiology. Membrane-bound organelles such as the endoplasmic reticulum (ER), the Golgi complex, endosomes and lysosomes, and the plasma membrane, continuously exchange material via vesicular carriers. In addition to vesicular trafficking entailing budding, fission, and fusion processes, organelles can form membrane contact sites (MCSs) that enable the nonvesicular exchange of lipids, ions, and metabolites, or the secretion of neurotransmitters via subsequent membrane fusion. Recent data suggest that biomolecule and information transfer via vesicular carriers and via MCSs share common organizational principles and are often mediated by proteins with intrinsically disordered regions (IDRs). Intrinsically disordered proteins (IDPs) can assemble via low-affinity, multivalent interactions to facilitate membrane tethering, deformation, fission, or fusion. Here, we review our current understanding of how IDPs drive the formation of multivalent protein assemblies and protein condensates to orchestrate vesicular and nonvesicular transport with a special focus on presynaptic neurotransmission. We further discuss how dysfunction of IDPs causes disease and outline perspectives for future research.
Topics: Intrinsically Disordered Proteins; Endoplasmic Reticulum; Golgi Apparatus; Cell Membrane; Lysosomes
PubMed: 37680133
DOI: 10.15252/embr.202357758 -
Environmental Science and Pollution... Jul 2023Copper (Cu) can be harmful to host physiology at high levels, although it is still unclear exactly how it causes nephrotoxicity. Mitochondrial dysfunction and...
Copper (Cu) can be harmful to host physiology at high levels, although it is still unclear exactly how it causes nephrotoxicity. Mitochondrial dysfunction and endoplasmic reticulum (ER) stress are associated with heavy metal intoxication. Meanwhile, mitochondria and ER are connected via mitochondria-associated ER membranes (MAM). In order to reveal the crosstalk between them, a total of 144 1-day-old Peking ducks were randomly divided into four groups: control (basal diet), 100 mg/kg Cu, 200 mg/kg Cu, and 400 mg/kg Cu groups. Results found that excessive Cu disrupted MAM integrity, reduced the co-localization of IP3R and VDAC1, and significantly changed the MAM-related factors levels (Grp75, Mfn2, IP3R, MCU, PACS2, and VDAC1), leading to MAM dysfunction. We further found that Cu exposure induced mitochondrial dysfunction via decreasing the ATP level and the expression levels of COX4, TOM20, SIRT1, and OPA1 and up-regulating Parkin expression level. Meanwhile, Cu exposure dramatically increased the expression levels of Grp78, CRT, and ATF4, resulting in ER stress. Overall, these findings demonstrated MAM plays the critical role in Cu-induced kidney mitochondrial dysfunction and ER stress, which deepened our understanding of Cu-induced nephrotoxicity.
Topics: Animals; Ducks; Copper; Endoplasmic Reticulum; Mitochondria; Kidney; Endoplasmic Reticulum Stress
PubMed: 37253910
DOI: 10.1007/s11356-023-27924-z -
The FEBS Journal Dec 2023Lysosomal degradation of the endoplasmic reticulum (ER) and its components through the autophagy pathway has emerged as a major regulator of ER proteostasis. Commonly... (Review)
Review
Lysosomal degradation of the endoplasmic reticulum (ER) and its components through the autophagy pathway has emerged as a major regulator of ER proteostasis. Commonly referred to as ER-phagy and ER-to-lysosome-associated degradation (ERLAD), how the ER is targeted to the lysosome has been recently clarified by a growing number of studies. Here, we summarize the discoveries of the molecular components required for lysosomal degradation of the ER and their proposed mechanisms of action. Additionally, we discuss how cells employ these machineries to create the different routes of ER-lysosome-associated degradation. Further, we review the role of ER-phagy in viral infection pathways, as well as the implication of ER-phagy in human disease. In sum, we provide a comprehensive overview of the current field of ER-phagy.
Topics: Humans; Secretome; Autophagy; Endoplasmic Reticulum-Associated Degradation; Lysosomes; Endoplasmic Reticulum; Endoplasmic Reticulum Stress
PubMed: 37920925
DOI: 10.1111/febs.16986 -
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 -
Trends in Cell Biology Dec 2023Mechanobiology studies the mechanisms by which cells sense and respond to physical forces, and the role of these forces in shaping cells and tissues themselves.... (Review)
Review
Mechanobiology studies the mechanisms by which cells sense and respond to physical forces, and the role of these forces in shaping cells and tissues themselves. Mechanosensing can occur at the plasma membrane, which is directly exposed to external forces, but also in the cell's interior, for example, through deformation of the nucleus. Less is known on how the function and morphology of organelles are influenced by alterations in their own mechanical properties, or by external forces. Here, we discuss recent advances on the mechanosensing and mechanotransduction of organelles, including the endoplasmic reticulum (ER), the Golgi apparatus, the endo-lysosmal system, and the mitochondria. We highlight open questions that need to be addressed to gain a broader understanding of the role of organelle mechanobiology.
Topics: Humans; Mechanotransduction, Cellular; Organelles; Golgi Apparatus; Endoplasmic Reticulum; Mitochondria; Cell Membrane
PubMed: 37236902
DOI: 10.1016/j.tcb.2023.05.001 -
The International Journal of... Jul 2024The endoplasmic reticulum (ER) regulates essential cellular processes, including protein folding, lipid synthesis, and calcium homeostasis. The ER homeostasis is... (Review)
Review
The endoplasmic reticulum (ER) regulates essential cellular processes, including protein folding, lipid synthesis, and calcium homeostasis. The ER homeostasis is maintained by a conserved set of signaling cascades called the Unfolded Protein Response (UPR). How the UPR senses perturbations in ER homeostasis has been the subject of active research for decades. In metazoans, the UPR consists of three ER-membrane embedded sensors: IRE1, PERK and ATF6. These sensors detect the accumulation of misfolded proteins in the ER lumen and adjust protein folding capacity according to cellular needs. Early work revealed that the ER-resident chaperone BiP binds to all three UPR sensors in higher eukaryotes and BiP binding was suggested to regulate their activity. More recent data have shown that in higher eukaryotes the interaction of the UPR sensors with a complex network of chaperones and misfolded proteins modulates their activation and deactivation dynamics. Furthermore, emerging evidence suggests that the UPR monitors ER membrane integrity beyond protein folding defects. However, the mechanistic and structural basis of UPR activation by proteotoxic and lipid bilayer stress in higher eukaryotes remains only partially understood. Here, we review the current understanding of novel protein interaction networks and the contribution of the lipid membrane environment to UPR activation.
Topics: Unfolded Protein Response; Endoplasmic Reticulum; Humans; Animals; Homeostasis
PubMed: 38768891
DOI: 10.1016/j.biocel.2024.106598