Regulation of cargo selection in exosome biogenesis and its biomedical applications in cancer.

Extracellular vesicles (EVs), including exosomes, are increasingly recognized as potent mediators of intercellular communication due to their capacity to transport a diverse array of bioactive molecules. They assume vital roles in a wide range of physiological and pathological processes and hold significant promise as emerging disease biomarkers, therapeutic agents, and carriers for drug delivery. Exosomes encompass specific groups of membrane proteins, lipids, nucleic acids, cytosolic proteins, and other signaling molecules within their interior. These cargo molecules dictate targeting specificity and functional roles upon reaching recipient cells. Despite our growing understanding of the significance of exosomes in diverse biological processes, the molecular mechanisms governing the selective sorting and packaging of cargo within exosomes have not been fully elucidated. In this review, we summarize current insights into the molecular mechanisms that regulate the sorting of various molecules into exosomes, the resulting biological functions, and potential clinical applications, with a particular emphasis on their relevance in cancer and other diseases. A comprehensive understanding of the loading processes and mechanisms involved in exosome cargo sorting is essential for uncovering the physiological and pathological roles of exosomes, identifying therapeutic targets, and advancing the clinical development of exosome-based therapeutics.

Thrap3 promotes nonalcoholic fatty liver disease by suppressing AMPK-mediated autophagy.

Autophagy functions in cellular quality control and metabolic regulation. Dysregulation of autophagy is one of the major pathogenic factors contributing to the progression of nonalcoholic fatty liver disease (NAFLD). Autophagy is involved in the breakdown of intracellular lipids and the maintenance of healthy mitochondria in NAFLD. However, the mechanisms underlying autophagy dysregulation in NAFLD remain unclear. Here, we demonstrate that the hepatic expression level of Thrap3 was significantly increased in NAFLD conditions. Liver-specific Thrap3 knockout improved lipid accumulation and metabolic properties in a high-fat diet (HFD)-induced NAFLD model. Furthermore, Thrap3 deficiency enhanced autophagy and mitochondrial function. Interestingly, Thrap3 knockout increased the cytosolic translocation of AMPK from the nucleus and enhanced its activation through physical interaction. The translocation of AMPK was regulated by direct binding with AMPK and the C-terminal domain of Thrap3. Our results indicate a role for Thrap3 in NAFLD progression and suggest that Thrap3 is a potential target for NAFLD treatment.

Patulin alleviates hepatic lipid accumulation by regulating lipogenesis and mitochondrial respiration.

AIMS: The aim of this study is to evaluate the effects of patulin on hepatic lipid metabolism and mitochondrial oxidative function and elucidate the underlying molecular mechanisms. MAIN METHODS: The effects of patulin on hepatic lipid accumulation were evaluated in free fatty acid-treated AML12 or HepG2 cells through oil red O staining, triglyceride assay, real-time polymerase chain reaction, and western blotting. Alteration of mitochondrial oxidative capacity by patulin treatment was determined using Seahorse analysis to measure the oxygen consumption rate. KEY FINDINGS: The increased amounts of lipid droplets induced by free fatty acids were significantly reduced by patulin treatment. Patulin markedly activated the CaMKII/AMP-activated protein kinase (AMPK)/proliferator-activated receptor-γ coactivator (PGC)-1α signaling pathway in hepatocytes, reduced the expression of sterol regulatory element binding protein 1c (SREBP-1c) and lipogenic genes, and increased the expression of genes related to mitochondrial fatty acid oxidation. In addition, patulin treatment enhanced the mitochondrial consumption rate and increased the expression of mitochondrial oxidative phosphorylation proteins in HepG2 hepatocytes. The effects of patulin on anti-lipid accumulation; SREBP-1c, PGC-1α, and carnitine palmitoyltransferase 1 expression; and mitochondrial oxidative capacity were significantly prevented by compound C, an AMPK inhibitor. SIGNIFICANCE: Patulin is a potent inducer of the AMPK pathway, and AMPK-mediated mitochondrial activation is required for the efficacy of patulin to inhibit hepatic lipid accumulation. This study is the first to report that patulin is a promising bioactive compound that prevents the development and worsening of fatty liver diseases, including non-alcoholic fatty liver disease, by improving mitochondrial quality and lipid metabolism.

GPR143 controls ESCRT-dependent exosome biogenesis and promotes cancer metastasis.

Exosomes transport a variety of macromolecules and modulate intercellular communication in physiology and disease. However, the regulation mechanisms that determine exosome contents during exosome biogenesis remain poorly understood. Here, we find that GPR143, an atypical GPCR, controls the endosomal sorting complex required for the transport (ESCRT)-dependent exosome biogenesis pathway. GPR143 interacts with HRS (an ESCRT-0 Subunit) and promotes its association to cargo proteins, such as EGFR, which subsequently enables selective protein sorting into intraluminal vesicles (ILVs) in multivesicular bodies (MVBs). GPR143 is elevated in multiple cancers, and quantitative proteomic and RNA profiling of exosomes in human cancer cell lines showed that the GPR143-ESCRT pathway promotes secretion of exosomes that carry unique cargo, including integrins signaling proteins. Through gain- and loss-of-function studies in mice, we show that GPR143 promotes metastasis by secreting exosomes and increasing cancer cell motility/invasion through the integrin/FAK/Src pathway. These findings provide a mechanism for regulating the exosomal proteome and demonstrate its ability to promote cancer cell motility.

Potential involvement of neutrophils on exercise effects in breast cancer malignancy.

PURPOSE: This review aimed to comprehensively explore and elucidate multifaceted neutrophils in breast cancer, particularly in the context of physical activity. Neutrophils play a critical role in the tumor microenvironment and systemic immune response, despite their short half-life and terminal differentiation. Through a thorough review of research related to changes in immunity in breast cancer during exercise, this review aims to provide comprehensive insights into immunological changes, especially focusing on neutrophils. Recognizing that much of the existing research has predominantly focused on T cells and nature killer (NK) cells, our review seeks to shift the spotlight toward understanding how exercise affects neutrophils, a less-explored but critical immune response component in breast cancer. METHODS: This study involved an extensive review of the literature (from 2000 to 2023) using the PubMed, Science Direct, and Google Scholar databases. The keywords chosen for the searches were "immune cells and exercise," "exercise and breast cancer," "tumor microenvironment and neutrophils," and "neutrophils and exercise and breast cancers." RESULTS: Neutrophils in the tumor microenvironment can exhibit distinct phenotypes and functions. These differences have yielded conflicting results regarding tumor progression. Exercise plays a positive role in breast cancer and alters the immune system. Physical activity can quantitatively and functionally regulate neutrophils under various conditions such as metabolic disruption or senescence. CONCLUSION: This short communication outlines exercise-induced neutrophil diversification and its role in breast cancer progression, both within and systemically within the tumor microenvironment. Exercise may provide benefits through the potential neutrophil involvement in breast cancer.

TRAIL & EGFR affibody dual-display on a protein nanoparticle synergistically suppresses tumor growth.

The TNF-related apoptosis-inducing ligand (TRAIL) is a promising anticancer drug candidate because it selectively binds to the proapoptotic death receptors, which are frequently overexpressed in a wide range of cancer cells, subsequently inducing strong apoptosis in these cells. However, the therapeutic benefit of TRAIL has not been clearly proven, mainly because of its poor pharmacokinetic characteristics and frequent resistance to its application caused by the activation of a survival signal via the EGF/epidermal growth factor receptor (EGFR) signaling pathway. Here, a lumazine synthase protein cage nanoparticle isolated from Aquifex aeolicus (AaLS) was used as a multiple ligand-displaying nanoplatform to display polyvalently both TRAIL and EGFR binding affibody molecules (EGFRAfb) via a SpyTag/SpyCatcher protein-ligation system, to form AaLS/TRAIL/EGFRAfb. The dual-ligand-displaying AaLS/TRAIL/EGFRAfb exhibited a dramatically enhanced cytotoxicity on TRAIL-resistant and EGFR-overexpressing A431 cancer cells in vitro, effectively disrupting the EGF-mediated EGFR survival signaling pathway by blocking EGF/EGFR binding as well as strongly activating both the extrinsic and intrinsic apoptotic pathways synergistically. The AaLS/TRAIL/EGFRAfb selectively targeted A431 cancer cells in vitro and actively reached the tumor sites in vivo. The A431 tumor-bearing mice treated with AaLS/TRAIL/EGFRAfb exhibited a significant suppression of the tumor growth without any significant side effects. Collectively, these findings showed that the AaLS/TRAIL/EGFRAfb could be used as an effective protein-based therapeutic for treating EGFR-positive cancers, which are difficult to manage using mono-therapeutic approaches.

Role of Mitochondrial Stress Response in Cancer Progression.

Mitochondria are subcellular organelles that are a hub for key biological processes, such as bioenergetic, biosynthetic, and signaling functions. Mitochondria are implicated in all oncogenic processes, from malignant transformation to metastasis and resistance to chemotherapeutics. The harsh tumor environment constantly exposes cancer cells to cytotoxic stressors, such as nutrient starvation, low oxygen, and oxidative stress. Excessive or prolonged exposure to these stressors can cause irreversible mitochondrial damage, leading to cell death. To survive hostile microenvironments that perturb mitochondrial function, cancer cells activate a stress response to maintain mitochondrial protein and genome integrity. This adaptive mechanism, which is closely linked to mitochondrial function, enables rapid adjustment and survival in harsh environmental conditions encountered during tumor dissemination, thereby promoting cancer progression. In this review, we describe how the mitochondria stress response contributes to the acquisition of typical malignant traits and highlight the potential of targeting the mitochondrial stress response as an anti-cancer therapeutic strategy.

Phospholipase Cγ1 represses colorectal cancer growth by inhibiting the Wnt/ß-catenin signaling axis.

As essential phospholipid signaling regulators, phospholipase C (PLC)s are activated by various extracellular ligands and mediate intracellular signal transduction. PLCγ1 is involved in regulating various cancer cell functions. However, the precise in vivo link between PLCγ1 and cancer behavior remains undefined. To investigate the role of PLCγ1 in colorectal carcinogenesis, we generated an intestinal tissue-specific Plcg1 knock out (KO) in adenomatous polyposis coli (Apc) Min/+ mice. Plcg1 deficiency in ApcMin/+ mice showed earlier death, with a higher colorectal tumor incidence in both number and size than in wild-type mice. Mechanistically, inhibition of PLCγ1 increased the levels of its substrate phosphoinositol 4,5-bisphosphate (PIP2) at the plasma membrane and promoted the activation of Wnt receptor low-density lipoprotein receptor-related protein 6 (LRP6) by glycogen synthase kinase 3ß (GSK3ß) to enhance ß-catenin signaling. Enhanced cell proliferation and Wnt/ß-catenin signaling were observed in colon tumors from Plcg1 KO mice. Furthermore, low PLCγ1 expression was associated with a poor prognosis of colon cancer patients. Collectively, we demonstrated the role of PLCγ1 in vivo as a tumor suppressor relationship between the regulation of the PIP2 level and Wnt/ß-catenin-dependent intestinal tumor formation.

LONP1 and ClpP cooperatively regulate mitochondrial proteostasis for cancer cell survival.

Mitochondrial proteases are key components in mitochondrial stress responses that maintain proteostasis and mitochondrial integrity in harsh environmental conditions, which leads to the acquisition of aggressive phenotypes, including chemoresistance and metastasis. However, the molecular mechanisms and exact role of mitochondrial proteases in cancer remain largely unexplored. Here, we identified functional crosstalk between LONP1 and ClpP, which are two mitochondrial matrix proteases that cooperate to attenuate proteotoxic stress and protect mitochondrial functions for cancer cell survival. LONP1 and ClpP genes closely localized on chromosome 19 and were co-expressed at high levels in most human cancers. Depletion of both genes synergistically attenuated cancer cell growth and induced cell death due to impaired mitochondrial functions and increased oxidative stress. Using mitochondrial matrix proteomic analysis with an engineered peroxidase (APEX)-mediated proximity biotinylation method, we identified the specific target substrates of these proteases, which were crucial components of mitochondrial functions, including oxidative phosphorylation, the TCA cycle, and amino acid and lipid metabolism. Furthermore, we found that LONP1 and ClpP shared many substrates, including serine hydroxymethyltransferase 2 (SHMT2). Inhibition of both LONP1 and ClpP additively increased the amount of unfolded SHMT2 protein and enhanced sensitivity to SHMT2 inhibitor, resulting in significantly reduced cell growth and increased cell death under metabolic stress. Additionally, prostate cancer patients with higher LONP1 and ClpP expression exhibited poorer survival. These results suggest that interventions targeting the mitochondrial proteostasis network via LONP1 and ClpP could be potential therapeutic strategies for cancer.

Accessibility-dependent topology studies of membrane proteins using a SpyTag/SpyCatcher protein-ligation system.

Covalent protein-ligation methods were used not only to visualize the localization of proteins of interest in cells, but also to study the topology of plasma and subcellular organelle membrane proteins using fluorescent cell imaging. A 13-amino-acid SpyTag (ST) peptide was genetically introduced either into a variety of subcellular proteins of interest or into different positions of plasma or subcellular organelle membrane proteins individually. Conversely, a 15 kDa SpyCatcher (SC) protein was chemically conjugated with either fluorescent dyes or horseradish peroxidase (HRP) via a thiol-maleimide reaction. The extracellular ST-fused plasma membrane proteins were efficiently labeled with the fluorescent-dye-conjugated SC in both live and permeabilized cells, whereas the intracellularly localized ST-fused subcellular proteins were only labeled in permeabilized cells because of the limited accessibility of the fluorescent-dye-conjugated SC to the membrane. The fluorescent-dye-labeled SC together with selective membrane-permeabilizing agents successfully labeled the plasma or the subcellular organelle membrane proteins in a topology-dependent manner. Moreover, the HRP-conjugated SC not only successfully labeled the ST-fused plasma membrane proteins, thus significantly enhancing fluorescent signals in combination with the tyramide signal amplification agents, but also ligated with an external ST-fused target ligand, thus selectively binding to the endogenously expressed cellular receptors of the target cancer cells.

Flightless-1 inhibits ER stress-induced apoptosis in colorectal cancer cells by regulating Ca2+ homeostasis.

The endoplasmic reticulum (ER) stress response is an adaptive mechanism that is activated upon disruption of ER homeostasis and protects the cells against certain harmful environmental stimuli. However, critical and prolonged cell stress triggers cell death. In this study, we demonstrate that Flightless-1 (FliI) regulates ER stress-induced apoptosis in colon cancer cells by modulating Ca2+ homeostasis. FliI was highly expressed in both colon cell lines and colorectal cancer mouse models. In a mouse xenograft model using CT26 mouse colorectal cancer cells, tumor formation was slowed due to elevated levels of apoptosis in FliI-knockdown (FliI-KD) cells. FliI-KD cells treated with ER stress inducers, thapsigargin (TG), and tunicamycin exhibited activation of the unfolded protein response (UPR) and induction of UPR-related gene expression, which eventually triggered apoptosis. FliI-KD increased the intracellular Ca2+ concentration, and this upregulation was caused by accelerated ER-to-cytosolic efflux of Ca2+. The increase in intracellular Ca2+ concentration was significantly blocked by dantrolene and tetracaine, inhibitors of ryanodine receptors (RyRs). Dantrolene inhibited TG-induced ER stress and decreased the rate of apoptosis in FliI-KD CT26 cells. Finally, we found that knockdown of FliI decreased the levels of sorcin and ER Ca2+ and that TG-induced ER stress was recovered by overexpression of sorcin in FliI-KD cells. Taken together, these results suggest that FliI regulates sorcin expression, which modulates Ca2+ homeostasis in the ER through RyRs. Our findings reveal a novel mechanism by which FliI influences Ca2+ homeostasis and cell survival during ER stress.

Unleashing the full potential of Hsp90 inhibitors as cancer therapeutics through simultaneous inactivation of Hsp90, Grp94, and TRAP1.

The Hsp90 family proteins Hsp90, Grp94, and TRAP1 are present in the cell cytoplasm, endoplasmic reticulum, and mitochondria, respectively; all play important roles in tumorigenesis by regulating protein homeostasis in response to stress. Thus, simultaneous inhibition of all Hsp90 paralogs is a reasonable strategy for cancer therapy. However, since the existing pan-Hsp90 inhibitor does not accumulate in mitochondria, the potential anticancer activity of pan-Hsp90 inhibition has not yet been fully examined in vivo. Analysis of The Cancer Genome Atlas database revealed that all Hsp90 paralogs were upregulated in prostate cancer. Inactivation of all Hsp90 paralogs induced mitochondrial dysfunction, increased cytosolic calcium, and activated calcineurin. Active calcineurin blocked prosurvival heat shock responses upon Hsp90 inhibition by preventing nuclear translocation of HSF1. The purine scaffold derivative DN401 inhibited all Hsp90 paralogs simultaneously and showed stronger anticancer activity than other Hsp90 inhibitors. Pan-Hsp90 inhibition increased cytotoxicity and suppressed mechanisms that protect cancer cells, suggesting that it is a feasible strategy for the development of potent anticancer drugs. The mitochondria-permeable drug DN401 is a newly identified in vivo pan-Hsp90 inhibitor with potent anticancer activity.

Glucosylceramide synthase regulates adipo-osteogenic differentiation through synergistic activation of PPARγ with GlcCer.

Dysregulation of the adipo-osteogenic differentiation balance of mesenchymal stem cells (MSCs), which are common progenitor cells of adipocytes and osteoblasts, has been associated with many pathophysiologic diseases, such as obesity, osteopenia, and osteoporosis. Growing evidence suggests that lipid metabolism is crucial for maintaining stem cell homeostasis and cell differentiation; however, the detailed underlying mechanisms are largely unknown. Here, we demonstrate that glucosylceramide (GlcCer) and its synthase, glucosylceramide synthase (GCS), are key determinants of MSC differentiation into adipocytes or osteoblasts. GCS expression was increased during adipogenesis and decreased during osteogenesis. Targeting GCS using RNA interference or a chemical inhibitor enhanced osteogenesis and inhibited adipogenesis by controlling the transcriptional activity of peroxisome proliferator-activated receptor γ (PPARγ). Treatment with GlcCer sufficiently rescued adipogenesis and inhibited osteogenesis in GCS knockdown MSCs. Mechanistically, GlcCer interacted directly with PPARγ through A/B domain and synergistically enhanced rosiglitazone-induced PPARγ activation without changing PPARγ expression, thereby treatment with exogenous GlcCer increased adipogenesis and inhibited osteogenesis. Animal studies demonstrated that inhibiting GCS reduced adipocyte formation in white adipose tissues under normal chow diet and high-fat diet feeding and accelerated bone repair in a calvarial defect model. Taken together, our findings identify a novel lipid metabolic regulator for the control of MSC differentiation and may have important therapeutic implications.

ITGB4-mediated metabolic reprogramming of cancer-associated fibroblasts.

Integrin beta 4 (ITGB4) overexpression in cancer cells contributes to cancer progression. However, the role of stromal ITGB4 expression in cancer progression remains poorly understood, despite stromal ITGB4 overexpression in malignant cancers. In our study, ITGB4-overexpressing triple negative breast cancer (TNBC) cells provided cancer-associated fibroblasts (CAFs) with ITGB4 proteins via exosomes, which induced BNIP3L-dependent mitophagy and lactate production in CAFs. In coculture assays, the ITGB4-induced mitophagy and glycolysis were suppressed in CAFs by knocking down ITGB4 or inhibiting exosome generation in MDA-MB-231, or blocking c-Jun or AMPK phosphorylation in CAFs. ITGB4-overexpressing CAF-conditioned medium promoted the proliferation, epithelial-to-mesenchymal transition, and invasion of breast cancer cells. In a co-transplant mouse model, MDA-MB-231 made a bigger tumor mass with CAFs than ITGB4 knockdown MDA-MB-231. Herein, we presented how TNBC-derived ITGB4 protein triggers glycolysis in CAFs via BNIP3L-dependent mitophagy and suggested the possibility that ITGB4-induced mitophagy could be targeted as a cancer therapy.

MFF Regulation of Mitochondrial Cell Death Is a Therapeutic Target in Cancer.

The regulators of mitochondrial cell death in cancer have remained elusive, hampering the development of new therapies. Here, we showed that protein isoforms of mitochondrial fission factor (MFF1 and MFF2), a molecule that controls mitochondrial size and shape, that is, mitochondrial dynamics, were overexpressed in patients with non-small cell lung cancer and formed homo- and heterodimeric complexes with the voltage-dependent anion channel-1 (VDAC1), a key regulator of mitochondrial outer membrane permeability. MFF inserted into the interior hole of the VDAC1 ring using Arg225, Arg236, and Gln241 as key contact sites. A cell-permeable MFF Ser223-Leu243 d-enantiomeric peptidomimetic disrupted the MFF-VDAC1 complex, acutely depolarized mitochondria, and triggered cell death in heterogeneous tumor types, including drug-resistant melanoma, but had no effect on normal cells. In preclinical models, treatment with the MFF peptidomimetic was well-tolerated and demonstrated anticancer activity in patient-derived xenografts, primary breast and lung adenocarcinoma 3D organoids, and glioblastoma neurospheres. These data identify the MFF-VDAC1 complex as a novel regulator of mitochondrial cell death and an actionable therapeutic target in cancer. SIGNIFICANCE: These findings describe mitochondrial fission regulation using a peptidomimetic agent that disturbs the MFF-VDAC complex and displays anticancer activity in multiple tumor models.See related commentary by Rao, p. 6074.

Mitochondrial fission factor is a novel Myc-dependent regulator of mitochondrial permeability in cancer.

BACKGROUND: Mitochondrial functions are exploited in cancer and provide a validated therapeutic target. However, how this process is regulated has remained mostly elusive and the identification of new pathways that control mitochondrial integrity in cancer is an urgent priority. METHODS: We studied clinically-annotated patient series of primary and metastatic prostate cancer, representative cases of multiple myeloma (MM) and publicly available genetic databases. Gene regulation studies involved chromatin immunoprecipitation, PCR amplification and Western blotting of conditional Myc-expressing cell lines. Transient or stable gene silencing was used to quantify mitochondrial functions in bioenergetics, outer membrane permeability, Ca2+ homeostasis, redox balance and cell death. Tumorigenicity was assessed by cell proliferation, colony formation and xenograft tumour growth. FINDINGS: We identified Mitochondrial Fission Factor (MFF) as a novel transcriptional target of oncogenic Myc overexpressed in primary and metastatic cancer, compared to normal tissues. Biochemically, MFF isoforms, MFF1 and MFF2 associate with the Voltage-Dependent Anion Channel-1 (VDAC1) at the mitochondrial outer membrane, in vivo. Disruption of this complex by MFF silencing induces general collapse of mitochondrial functions with increased outer membrane permeability, loss of inner membrane potential, Ca2+ unbalance, bioenergetics defects and activation of cell death pathways. In turn, this inhibits tumour cell proliferation, suppresses colony formation and reduces xenograft tumour growth in mice. INTERPRETATION: An MFF-VDAC1 complex is a novel regulator of mitochondrial integrity and actionable therapeutic target in cancer.

Phospholipase C-ß1 potentiates glucose-stimulated insulin secretion.

PLC-ß exerts biologic influences through GPCR. GPCRs are involved in regulating glucose-stimulated insulin secretion (GSIS). Previous studies have suggested that PLC-ßs might play an important role in pancreatic ß cells. However, because of a lack of the specific inhibitors of PLC-ß isozymes and appropriate genetic models, the in vivo function of specific PLC-ß isozymes in pancreatic ß cells and their physiologic relevance in the regulation of insulin secretion have not been studied so far. The present study showed that PLC-ß1 was crucial for ß-cell function by generation of each PLC-ß conditional knockout mouse. Mice lacking PLC-ß1 in ß cells exhibited a marked defect in GSIS, leading to glucose intolerance. In ex vivo studies, the secreted insulin level and Ca2+ response in Plcb1f/f; pancreas/duodenum homeobox protein 1 (Pdx1)-Cre recombinase-estrogen receptor T2 (CreERt2) islets was lower than those in the Plcb1f/f islets under the high-glucose condition. PLC-ß1 led to potentiate insulin secretion via stimulation of particular Gq-protein-coupled receptors. Plcb1f/f; Pdx1-CreERt2 mice fed a high-fat diet developed more severe glucose intolerance because of a defect in insulin secretion. The present study identified PLC-ß1 as an important molecule that regulates ß cell insulin secretion and can be considered a candidate for therapeutic intervention in diabetes mellitus.-Hwang, H.-J., Yang, Y. R., Kim, H. Y., Choi, Y., Park, K.-S., Lee, H., Ma, J. S., Yamamoto, M., Kim, J., Chae, Y. C., Choi, J. H., Cocco, L., Berggren, P.-O., Jang, H.-J., Suh, P.-G. Phospholipase Cß1 potentiates glucose-stimulated insulin secretion.

Interplay between TRAP1 and Sirtuin-3 Modulates Mitochondrial Respiration and Oxidative Stress to Maintain Stemness of Glioma Stem Cells.

Glioblastoma (GBM) cancer stem cells (CSC) are primarily responsible for metastatic dissemination, resistance to therapy, and relapse of GBM, the most common and aggressive brain tumor. Development and maintenance of CSCs require orchestrated metabolic rewiring and metabolic adaptation to a changing microenvironment. Here, we show that cooperative interplay between the mitochondrial chaperone TRAP1 and the major mitochondria deacetylase sirtuin-3 (SIRT3) in glioma stem cells (GSC) increases mitochondrial respiratory capacity and reduces production of reactive oxygen species. This metabolic regulation endowed GSCs with metabolic plasticity, facilitated adaptation to stress (particularly reduced nutrient supply), and maintained "stemness." Inactivation of TRAP1 or SIRT3 compromised their interdependent regulatory mechanisms, leading to metabolic alterations, loss of stemness, and suppression of tumor formation by GSC in vivo. Thus, targeting the metabolic mechanisms regulating interplay between TRAP1 and SIRT3 may provide a novel therapeutic option for intractable patients with GBM. SIGNIFICANCE: Discovery and functional analysis of a TRAP1-SIRT3 complex in glioma stem cells identify potential target proteins for glioblastoma treatment.

Cancer stem cell metabolism: target for cancer therapy.

Increasing evidence suggests that cancer stem cell (CSC) theory represents an important mechanism underlying the observed failure of existing therapeutic modalities to fully eradicate cancers. In addition to their more established role in maintaining minimal residual disease after treatment and forming the new bulk of the tumor, CSCs might also critically contribute to tumor recurrence and metastasis. For this reason, specific elimination of CSCs may thus represent one of the most important treatment strategies. Emerging evidence has shown that CSCs have a different metabolic phenotype to that of differentiated bulk tumor cells, and these specific metabolic activities directly participate in the process of CSC transformation or support the biological processes that enable tumor progression. Exploring the role of CSC metabolism and the mechanism of the metabolic plasticity of CSCs has become a major focus in current cancer research. The targeting of CSC metabolism may provide new effective therapies to reduce the risk of recurrence and metastasis. In this review, we summarize the most significant discoveries regarding the metabolism of CSCs and highlight recent approaches in targeting CSC metabolism. [BMB Reports 2018; 51(7): 319-326].

Hypoxia-dependent mitochondrial fission regulates endothelial progenitor cell migration, invasion, and tube formation.

Tumor undergo uncontrolled, excessive proliferation leads to hypoxic microenvironment. To fulfill their demand for nutrient, and oxygen, tumor angiogenesis is required. Endothelial progenitor cells (EPCs) have been known to the main source of angiogenesis because of their potential to differentiation into endothelial cells. Therefore, understanding the mechanism of EPC-mediated angiogenesis in hypoxia is critical for development of cancer therapy. Recently, mitochondrial dynamics has emerged as a critical mechanism for cellular function and differentiation under hypoxic conditions. However, the role of mitochondrial dynamics in hypoxia-induced angiogenesis remains to be elucidated. In this study, we demonstrated that hypoxia-induced mitochondrial fission accelerates EPCs bioactivities. We first investigated the effect of hypoxia on EPC-mediated angiogenesis. Cell migration, invasion, and tube formation was significantly increased under hypoxic conditions; expression of EPC surface markers was unchanged. And mitochondrial fission was induced by hypoxia time-dependent manner. We found that hypoxia-induced mitochondrial fission was triggered by dynamin-related protein Drp1, specifically, phosphorylated DRP1 at Ser637, a suppression marker for mitochondrial fission, was impaired in hypoxia time-dependent manner. To confirm the role of DRP1 in EPC-mediated angiogenesis, we analyzed cell bioactivities using Mdivi-1, a selective DRP1 inhibitor, and DRP1 siRNA. DRP1 silencing or Mdivi-1 treatment dramatically reduced cell migration, invasion, and tube formation in EPCs, but the expression of EPC surface markers was unchanged. In conclusion, we uncovered a novel role of mitochondrial fission in hypoxia-induced angiogenesis. Therefore, we suggest that specific modulation of DRP1-mediated mitochondrial dynamics may be a potential therapeutic strategy in EPC-mediated tumor angiogenesis.