bims-lymeca 2022-10-09 papers

Issue of 2022‒10‒09
six papers selected by
Harilaos Filippakis
University of New England

Biol Pharm Bull. 2022 ;45(10): 1426-1431

V-ATPase a3 Subunit in Secretory Lysosome Trafficking in Osteoclasts.

Mayumi Nakanishi-Matsui, Naomi Matsumoto.

Vacuolar-type ATPase (V-ATPase) shares its structure and rotational catalysis with F-type ATPase (F-ATPase, ATP synthase). However, unlike subunits of F-ATPase, those of V-ATPase have tissue- and/or organelle-specific isoforms. Structural diversity of V-ATPase generated by different combinations of subunit isoforms enables it to play diverse physiological roles in mammalian cells. Among these various roles, this review focuses on the functions of lysosome-specific V-ATPase in bone resorption by osteoclasts. Lysosomes remain in the cytoplasm in most cell types, but in osteoclasts, secretory lysosomes move toward and fuse with the plasma membrane to secrete lysosomal enzymes, which is essential for bone resorption. Through this process, lysosomal V-ATPase harboring the a3 isoform of the a subunit is relocated to the plasma membrane, where it transports protons from the cytosol to the cell exterior to generate the acidic extracellular conditions required for secreted lysosomal enzymes. In addition to this role as a proton pump, we recently found that the lysosomal a3 subunit of V-ATPase is essential for anterograde trafficking of secretory lysosomes. Specifically, a3 interacts with Rab7, a member of the Rab guanosine 5'-triphosphatase (GTPase) family that regulates organelle trafficking, and recruits it to the lysosomal membrane. These findings revealed the multifunctionality of lysosomal V-ATPase in osteoclasts; V-ATPase is responsible not only for the formation of the acidic environment by transporting protons, but also for intracellular trafficking of secretory lysosomes by recruiting organelle trafficking factors. Herein, we summarize the molecular mechanism underlying secretory lysosome trafficking in osteoclasts, and discuss the possible regulatory role of V-ATPase in organelle trafficking.

Keywords: organelle trafficking; osteoclast; proton pump; secretory lysosome; vacuolar-type ATPase

DOI: https://doi.org/10.1248/bpb.b22-00371

J Therm Biol. 2022 Oct;pii: S0306-4565(22)00140-1. [Epub ahead of print]109 103326

ROS/JNK-mediated lysosomal injury in rat intestinal epithelial-6 cells during heat stress.

Zhiguo Pan, Xuan He, Yu Shao, Wenda Chen, Bangjiang Fang.

Injury to the intestinal epithelial cells and loss of the intestinal barrier are critical to heatstroke. To reveal the mechanism through which heatstroke leads to intestinal epithelial injury, the relationship between reactive oxygen species (ROS), c-Jun NH2-terminal kinase (JNK), and lysosomes were studied in intestinal epithelial cells subjected to heat stress. Cells of heat stress groups were incubated at 43 °C for 1 h, then incubated at 37 °C as indicated. Control group cells were incubated at 37 °C. Cell-counting kit-8 assay was used to assess cell viability. Cells were labeled with 2'-7'dichlorofluorescin diacetate and acridine orange (AO) staining, respectively, the total ROS and AO were detected by confocal laser scanning microscopy and flow cytometry. Apoptosis was analyzed by flow cytometry using annexin V-fluorescein isothiocyanate/prodium iodide staining, the expressions of mitogen-activated protein kinases were detected by western blotting. Heat stress induced apoptosis and inhibited cell viability, the production of ROS, and lysosomal injury in IEC-6 cells. After pretreatment with the lysosomal cathepsin inhibitor E64, the JNK inhibitor SP600125, or the ROS scavenger NAC, the effect of heat stress on apoptosis or lysosomal injury was significantly attenuated. In conclusion, heat stress induced apoptosis, lysosomal injury, and the accumulation of ROS in IEC-6 cells; mechanistically, this occurred through the ROS-induced activation of JNK signaling, which mediated the lysosomal injury and ultimately apoptosis.

Keywords: Apoptosis; Heat stress; JNK; Lysosome; ROS

DOI: https://doi.org/10.1016/j.jtherbio.2022.103326

J Physiol. 2022 Oct 02.

Sodium channels and the ionic microenvironment of breast tumours.

Theresa K Leslie, William J Brackenbury.

Cancers of epithelial origin such as breast, prostate, cervical, gastric, colon and lung cancer account for a large proportion of deaths worldwide. Better treatment of metastasis, the main cause of cancer deaths, is therefore urgently required. Several of these tumours have been shown to have an abnormally high concentration of Na+ ([Na+ ]) and emerging evidence points to this accumulation being due to elevated intracellular [Na+ ]. This poses intriguing questions about the cellular mechanisms underlying Na+ dysregulation in cancer, and its pathophysiological significance. Elevated intracellular [Na+ ] may be due to alterations in activity of the Na+ /K+ ATPase, and/or increased influx via Na+ channels and Na+ -linked transporters. Maintenance of the electrochemical Na+ gradient across the plasma membrane is vital to power many cellular processes that are highly active in cancer cells, including glucose and glutamine import. Na+ channels are also upregulated in cancer cells, which in turn promote tumour growth and metastasis. For example, ENaC and ASICs are overexpressed in cancers increasing invasion and proliferation. In addition, voltage-gated Na+ channels are also upregulated in a range of tumour types, where they promote metastatic cell behaviours via various mechanisms, including membrane potential depolarisation and altered pH regulation. Together, recent findings relating to elevated Na+ in the tumour microenvironment and how this may be regulated by several classes of Na+ channels, provide a link between altered Na+ handling and poor clinical outcome. There are new opportunities to leverage this altered Na+ microenvironment for therapeutic benefit, as exemplified by several ongoing clinical trials. Abstract figure legend Mechanisms of Na+ channel and transporter-dependent proliferation, migration, and invasion. Na+ enters through VGSC, ENaC and ASIC channels and through the SGLT2 cotransporter and the NHE1 exchanger. These mechanisms may be responsible for elevating intracellular [Na+ ]. Na+ is removed from the cell via the Na+ /K+ ATPase. VGSCs depolarise the cell membrane potential (Vm ), which leads to increased migration. VGSCs also regulate transcription of genes involved in proliferation, migration and invasion. VGSCs increase the activity of NHE1, further elevating intracellular [Na+ ] and extracellular [H+ ]. This acidifies the extracellular environment and aids cellular invasion through extracellular matrix. The low extracellular pH will then affect the Na+ channels, increasing the inward Na+ current through these in a positive feedback mechanism which increases intracellular [Na+ ] and extracellular [H+ ]. This article is protected by copyright. All rights reserved.

Keywords: breast cancer; ion channels; metastasis; migration; proliferation; sodium

DOI: https://doi.org/10.1113/JP282306

Oncogene. 2022 Oct 04.

Non-genomic activation of the AKT-mTOR pathway by the mitochondrial stress response in thyroid cancer.

Woo Kyung Lee Doolittle, Sunmi Park, Seul Gi Lee, Seonhyang Jeong, Gibbeum Lee, Dongryeol Ryu, Kristina Schoonjans, Johan Auwerx, Jandee Lee, Young Suk Jo.

Cancer progression is associated with metabolic reprogramming and causes significant intracellular stress; however, the mechanisms that link cellular stress and growth signalling are not fully understood. Here, we identified a mechanism that couples the mitochondrial stress response (MSR) with tumour progression. We demonstrated that the MSR is activated in a significant proportion of human thyroid cancers via the upregulation of heat shock protein D family members and the mitokine, growth differentiation factor 15. Our study also revealed that MSR triggered AKT/S6K signalling by activating mTORC2 via activating transcription factor 4/sestrin 2 activation whilst promoting leucine transporter and nutrient-induced mTORC1 activation. Importantly, we found that an increase in mtDNA played an essential role in MSR-induced mTOR activation and that crosstalk between MYC and MSR potentiated mTOR activation. Together, these findings suggest that the MSR could be a predictive marker for aggressive human thyroid cancer as well as a useful therapeutic target.

DOI: https://doi.org/10.1038/s41388-022-02484-7

iScience. 2022 Oct 21. 25(10): 105118

Inhibition of the pseudokinase MLKL alters extracellular vesicle release and reduces tumor growth in glioblastoma.

Gwennan André-Grégoire, Clément Maghe, Tiphaine Douanne, Sara Rosińska, Fiorella Spinelli, An Thys, Kilian Trillet, Kathryn A Jacobs, Cyndie Ballu, Aurélien Dupont, Anne-Marie Lyne, Florence M G Cavalli, Ignacio Busnelli, Vincent Hyenne, Jacky G Goetz, Nicolas Bidère, Julie Gavard.

Extracellular vesicles (EVs) are lipid-based nanosized particles that convey biological material from donor to recipient cells. EVs play key roles in glioblastoma progression because glioblastoma stem-like cells (GSCs) release pro-oncogenic, pro-angiogenic, and pro-inflammatory EVs. However, the molecular basis of EV release remains poorly understood. Here, we report the identification of the pseudokinase MLKL, a crucial effector of cell death by necroptosis, as a regulator of the constitutive secretion of EVs in GSCs. We find that genetic, protein, and pharmacological targeting of MLKL alters intracellular trafficking and EV release, and reduces GSC expansion. Nevertheless, this function ascribed to MLKL appears independent of its role during necroptosis. In vivo, pharmacological inhibition of MLKL reduces the tumor burden and the level of plasmatic EVs. This work highlights the necroptosis-independent role of MLKL in vesicle release and suggests that interfering with EVs is a promising therapeutic option to sensitize glioblastoma cells.

Keywords: Cancer; Cell biology; Functional aspects of cell biology

DOI: https://doi.org/10.1016/j.isci.2022.105118