The Close Interconnection between Mitochondrial Dynamics and Mitophagy in Cancer

Transcriptomics analysis revealed that TAZ regulates the proliferation of KIRC cells through mitophagy

Transcriptional Co-Activator with PDZ-Binding Motif (TAZ, also known as WWTR1) is a downstream effector of the Hippo pathway, involved in the regulation of organ regeneration and cell differentiation in processes such as development and regeneration. TAZ has been shown to play a tumor-promoting role in various cancers. Currently, many studies focus on the role of TAZ in the process of mitophagy. However, the molecular mechanism and biological function of TAZ in renal clear cell carcinoma (KIRC) are still unclear. Therefore, we systematically analyzed the mRNA expression profile and clinical data of KIRC in The Cancer Genome Atlas (TCGA) dataset. We found that TAZ expression was significantly upregulated in KIRC compared with normal kidney tissue and was closely associated with poor prognosis of patients. Combined with the joint analysis of 36 mitophagy genes, it was found that TAZ was significantly negatively correlated with the positive regulators of mitophagy. Finally, our results confirmed that high expression of TAZ in KIRC inhibits mitophagy and promotes KIRC cell proliferation. In conclusion, our findings reveal the important role of TAZ in KIRC and have the potential to be a new target for KIRC therapy.

Multiomics Reveals Induction of Neuroblastoma SK-N-BE(2)C Cell Death by Mitochondrial Division Inhibitor 1 through Multiple Effects

Mitochondrial division inhibitor 1 (Mdivi-1) is a well-known synthetic compound aimed at inhibiting dynamin-related protein 1 (Drp1) to suppress mitochondrial fission, making it a valuable tool for studying mitochondrial dynamics. However, its specific effects beyond Drp1 inhibition remain to be confirmed. In this study, we employed integrative proteomics and phosphoproteomics to delve into the molecular responses induced by Mdivi-1 in SK-N-BE(2)C cells. A total of 3070 proteins and 1945 phosphorylation sites were identified, with 880 of them represented as phosphoproteins. Among these, 266 proteins and 97 phosphorylation sites were found to be sensitive to the Mdivi-1 treatment. Functional enrichment analysis unveiled their involvement in serine biosynthesis and extrinsic apoptotic signaling pathways. Through targeted metabolomics, we observed that Mdivi-1 enhanced intracellular serine biosynthesis while reducing the production of C24:1-ceramide. Within these regulated phosphoproteins, dynamic dephosphorylation of proteasome subunit alpha type 3 serine 250 (PSMA3-S250) occurred after Mdivi-1 treatment. Further site-directed mutagenesis experiments revealed that the dephosphorylation-deficient mutant PSMA3-S250A exhibited a decreased cell survival. This research confirms that Mdivi-1's inhibition of mitochondrial division leads to various side effects, ultimately influencing cell survival, rather than solely targeting Drp1 inhibition.

Cigarette smoke causes a bioenergetic crisis in RPE cells involving the downregulation of HIF-1α under normoxia

Age-related macular degeneration (AMD) is the most common blinding disease in the elderly population. However, there are still many uncertainties regarding the pathophysiology at the molecular level. Currently, impaired energy metabolism in retinal pigment epithelium (RPE) cells is discussed as one major hallmark of early AMD pathophysiology. Hypoxia-inducible factors (HIFs) are important modulators of mitochondrial function. Moreover, smoking is the most important modifiable risk factor for AMD and is known to impair mitochondrial integrity. Therefore, our aim was to establish a cell-based assay that enables us to investigate how smoking affects mitochondrial function in conjunction with HIF signaling in RPE cells. For this purpose, we treated a human RPE cell line with cigarette smoke extract (CSE) under normoxia (21% O2), hypoxia (1% O2), or by co-treatment with Roxadustat, a clinically approved HIF stabilizer. CSE treatment impaired mitochondrial integrity, involving increased mitochondrial reactive oxygen species, disruption of mitochondrial membrane potential, and altered mitochondrial morphology. Treatment effects on cell metabolism were analyzed using a Seahorse Bioanalyzer. Mitochondrial respiration and ATP production were impaired in CSE-treated cells under normoxia. Surprisingly, CSE-treated RPE cells also exhibited decreased glycolytic rate under normoxia, causing a bioenergetic crisis, because two major metabolic pathways that provide ATP were impaired by CSE. Downregulation of glycolytic rate was HIF-dependent because HIF-1α, the α-subunit of HIF-1, was downregulated by CSE on the protein level, especially under normoxia. Moreover, hypoxia incubation and treatment with Roxadustat restored glycolytic flux. Taken together, our in vitro model provides interesting insights into HIF-dependent regulation of glycolysis under normoxic conditions, which will enable us to investigate signaling pathways involved in RPE metabolism in health and disease.

Erythrose inhibits the progression to invasiveness and reverts drug resistance of cancer stem cells of glioblastoma

Glioblastoma (GBM) is the most frequent brain cancer and more lethal than other cancers. Characteristics of this cancer are its high drug resistance, high recurrence rate and invasiveness. Invasiveness in GBM is related to overexpression of matrix metalloproteinases (MMPs) which are mediated by wnt/β-catenin and induced by the activation of signaling pathways extracellularly activated by the cytokine neuroleukin (NLK) in cancer stem cells (CSC). Therefore, in this work we evaluated the effect of the tetrose saccharide, erythrose (Ery), a NLK inhibitor of invasiveness and drug sensitization in glioblastoma stem cells (GSC). GSC were obtained from parental U373 cell line by a CSC phenotype enrichment protocol based on microenvironmental stress conditions such as hypoxia, hipoglycemia, drug exposition and serum starvation. Enriched fraction of GSC overexpressed the typical markers of brain CSC: low CD133+ and high CD44; in addition, epithelial to mesenchyme transition (EMT) markers and MMPs were increased several times in GSC vs. U373 correlating with higher invasiveness, elongated and tubular mitochondrion and temozolomide (TMZ) resistance. IC₅₀ of Ery was found at nM concentration and at 24 h induced a severe diminution of EMT markers, MMPs and invasiveness in GSC. Furthermore, the phosphorylation pattern of NLK after Ery exposition also was affected. In addition, when Ery was administered to GSC at subIC₅₀, it was capable of reverting TMZ resistance at concentrations innocuous to non-tumor cancer cells. Moreover, Ery added daily induced the death of all GSC. Those findings indicated that the phytodrug Ery could be used as adjuvant therapy in GBM.

TPGS loaded triphenyltin (IV) micelles induced apoptosis by upregulating p53 in breast cancer cells and inhibit tumor progression in T-cell lymphoma bearing mice

AIMS

Currently, breast cancer is one of the most frequently diagnosed and the second leading cause of cancer related deaths in women worldwide. Our present study aimed to investigate the major mechanistic effects of micelles (TSD-30-F, TSD-34-F) on breast cancer cells as well as their antitumor efficacy in in vivo DL bearing BALB/c mice.

METHODS

Apoptotic death by micelles was investigated by mitochondrial aggregation, membrane potential and DNA fragmentation assay in MCF-7 and MDA-MB-231 cells. Molecular mode of action of micelles were determined by RT-PCR and western blot analysis, drug-ligand interaction was analyzed by in silico methods, while, in vivo antitumor activity was investigated by Kaplen-Meier survival curve, T/C value, body weight and belly size of BALB/c mice.

KEY FINDINGS

TSD-30-F and TSD-34-F micelles displayed significant apoptotic induction. At molecular level, TSD-30 and TSD-34 micelles showed up-regulation of p53, Bax, Bak, Caspase-3 and down-regulation of Bcl-2 genes as well as proteins in tested breast cancer cells. In silico analysis revealed that TSD-30 and TSD-34 showed efficient binding affinity with p53, Caspase-3, Bax and Bcl-2 proteins. Significant in vivo antitumor efficacy was exhibited by the micelles formulations by increasing life span with reduced bodyweight and belly size growth pattern in BALB/c mice compared to DTX-F micelles.

SIGNIFICANCE

Our results suggest that triphenyltin (IV) micelles could be a very promising therapeutic candidate for treatment of breast cancer patients and occupy a new place in targeted breast cancer therapeutic.

Reprogramming of arachidonate metabolism confers temozolomide resistance to glioblastoma through enhancing mitochondrial activity in fatty acid oxidation

Background

Sp1 is involved in the recurrence of glioblastoma (GBM) due to the acquirement of resistance to temozolomide (TMZ). Particularly, the role of Sp1 in metabolic reprogramming for drug resistance remains unknown.

Methods

RNA-Seq and mass spectrometry were used to analyze gene expression and metabolites amounts in paired GBM specimens (primary vs. recurrent) and in paired GBM cells (sensitive vs. resistant). ω-3/6 fatty acid and arachidonic acid (AA) metabolism in GBM patients were analyzed by targeted metabolome. Mitochondrial functions were determined by Seahorse XF Mito Stress Test, RNA-Seq, metabolome and substrate utilization for producing ATP. Therapeutic options targeting prostaglandin (PG) E2 in TMZ-resistant GBM were validated in vitro and in vivo.

Results

Among the metabolic pathways, Sp1 increased the prostaglandin-endoperoxide synthase 2 expression and PGE2 production in TMZ-resistant GBM. Mitochondrial genes and metabolites were obviously increased by PGE2, and these characteristics were required for developing resistance in GBM cells. For inducing TMZ resistance, PGE2 activated mitochondrial functions, including fatty acid β-oxidation (FAO) and tricarboxylic acid (TCA) cycle progression, through PGE2 receptors, E-type prostanoid (EP)1 and EP3. Additionally, EP1 antagonist ONO-8713 inhibited the survival of TMZ-resistant GBM synergistically with TMZ.

Conclusion

Sp1-regulated PGE2 production activates FAO and TCA cycle in mitochondria, through EP1 and EP3 receptors, resulting in TMZ resistance in GBM. These results will provide us a new strategy to attenuate drug resistance or to re-sensitize recurred GBM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00804-3.

Characterization of Mitochondrial Proteome and Function in Luminal A and Basal-like Breast Cancer Subtypes Reveals Alteration in Mitochondrial Dynamics and Bioenergetics Relevant to Their Diagnosis

Breast cancer (BC) is the most prevalent cancer and the one with the highest mortality among women worldwide. Although the molecular classification of BC has been a helpful tool for diagnosing and predicting the treatment of BC, developments are still being made to improve the diagnosis and find new therapeutic targets. Mitochondrial dysfunction is a crucial feature of cancer, which can be associated with cancer aggressiveness. Although the importance of mitochondrial dynamics in cancer is well recognized, its involvement in the mitochondrial function and bioenergetics context in BC molecular subtypes has been scantly explored. In this study, we combined mitochondrial function and bioenergetics experiments in MCF7 and MDA-MB-231 cell lines with statistical and bioinformatics analyses of the mitochondrial proteome of luminal A and basal-like tumors. We demonstrate that basal-like tumors exhibit a vicious cycle between mitochondrial fusion and fission; impaired but not completely inactive mitochondrial function; and the Warburg effect, associated with decreased oxidative phosphorylation (OXPHOS) complexes I and III. Together with the results obtained in the cell lines and the mitochondrial proteome analysis, two mitochondrial signatures were proposed: one signature reflecting alterations in mitochondrial functions and a second signature exclusively of OXPHOS, which allow us to distinguish between luminal A and basal-like tumors.

Mitochondrial connections with immune system in Zebrafish

Mitochondria are organelles commonly associated with adenosine triphosphate (ATP) formation through the oxidative phosphorylation (OXPHOS) process. However, mitochondria are also responsible for functions such as calcium homeostasis, apoptosis, autophagy, and production of reactive oxygen species (ROS) that, in conjunction, can lead to different cell fate decisions. Mitochondrial morphology changes rely on nutrients' availability and the bioenergetics demands of the cells, in a process known as mitochondrial dynamics, which includes both fusion and fission. This organelle senses the microenvironment and can modify the cells to either a pro or anti-inflammatory profile. The zebrafish has been increasingly used to research mitochondrial dynamics and its connection with the immune system since the pathways and molecules involved in these processes are conserved on this fish. Several genetic tools and technologies are currently available to analyze the behavior of mitochondria in zebrafish. However, even though zebrafish presents several similar processes known in mammals, the effect of the mitochondria in the immune system has not been so broadly studied in this model. In this review, we summarize the current knowledge in zebrafish studies regarding mitochondrial function and immuno metabolism.

BNIP3L-mediated mitophagy is required for mitochondrial remodeling during the differentiation of optic nerve oligodendrocytes

Retinal ganglion cell axons are heavily myelinated (98%) and myelin damage in the optic nerve (ON) severely affects vision. Understanding the molecular mechanism of oligodendrocyte progenitor cell (OPC) differentiation into mature oligodendrocytes will be essential for developing new therapeutic approaches for ON demyelinating diseases. To this end, we developed a new method for isolation and culture of ON-derived oligodendrocyte lineage cells and used it to study OPC differentiation. A critical aspect of cellular differentiation is macroautophagy/autophagy, a catabolic process that allows for cell remodeling by degradation of excess or damaged cellular molecules and organelles. Knockdown of ATG9A and BECN1 (pro-autophagic proteins involved in the early stages of autophagosome formation) led to a significant reduction in proliferation and survival of OPCs. We also found that autophagy flux (a measure of autophagic degradation activity) is significantly increased during progression of oligodendrocyte differentiation. Additionally, we demonstrate a significant change in mitochondrial dynamics during oligodendrocyte differentiation, which is associated with a significant increase in programmed mitophagy (selective autophagic clearance of mitochondria). This process is mediated by the mitophagy receptor BNIP3L (BCL2/adenovirus E1B interacting protein 3-like). BNIP3L-mediated mitophagy plays a crucial role in the regulation of mitochondrial network formation, mitochondrial function and the viability of newly differentiated oligodendrocytes. Our studies provide novel evidence that proper mitochondrial dynamics is required for establishment of functional mitochondria in mature oligodendrocytes. These findings are significant because targeting BNIP3L-mediated programmed mitophagy may provide a novel therapeutic approach for stimulating myelin repair in ON demyelinating diseases.Abbreviations: A2B5: a surface antigen of oligodendrocytes precursor cells, A2B5 clone 105; ACTB: actin, beta; APC: an antibody to label mature oligodendrocytes, anti-adenomatous polyposis coli clone CC1; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG9A: autophagy related 9A; AU: arbitrary units; BafA1: bafilomycin A1; BCL2: B cell leukemia/lymphoma 2; BECN1: beclin 1, autophagy related; BNIP3: BCL2/adenovirus E1B interacting protein 3; BNIP3L/NIX: BCL2/adenovirus E1B interacting protein 3-like; CASP3: caspase 3; CNP: 2',3'-cyclic nucleotide 3'-phosphodiesterase; Ctl: control; COX8: cytochrome c oxidase subunit; CSPG4/NG2: chondroitin sulfate proteoglycan 4; DAPI: 4'6-diamino-2-phenylindole; DNM1L: dynamin 1-like; EGFP: enhanced green fluorescent protein; FACS: fluorescence-activated cell sorting; FIS1: fission, mitochondrial 1; FUNDC1: FUN14 domain containing 1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFAP: glial fibrillary growth factor; GFP: green fluorescent protein; HsESC: human embryonic stem cell; IEM: immunoelectron microscopy; LAMP1: lysosomal-associated membrane protein 1; LC3B: microtubule-associated protein 1 light chain 3; MBP: myelin basic protein; MFN2: mitofusin 2; Mito-Keima: mitochondria-targeted monomeric keima-red; Mito-GFP: mitochondria-green fluorescent protein; Mito-RFP: mitochondria-red fluorescent protein; MitoSOX: red mitochondrial superoxide probe; MKI67: antigen identified by monoclonal antibody Ki 67; MMP: mitochondrial membrane potential; O4: oligodendrocyte marker O4; OLIG2: oligodendrocyte transcription factor 2; ON: optic nerve; OPA1: OPA1, mitochondrial dynamin like GTPase; OPC: oligodendrocyte progenitor cell; PDL: poly-D-lysine; PINK1: PTEN induced putative kinase 1; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; RFP: red fluorescent protein; RGC: retinal ganglion cell; ROS: reactive oxygen species; RT-PCR: real time polymerase chain reaction; SEM: standard error of the mean; SOD2: superoxide dismutase 2, mitochondrial; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy; TMRM: tetramethylrhodamine methyl ester; TOMM20: translocase of outer mitochondrial membrane 20; TUBB: tubulin, beta; TUBB3: tubulin, beta 3 class III.

DNMT1 maintains metabolic fitness of adipocytes through acting as an epigenetic safeguard of mitochondrial dynamics

White adipose tissue (WAT) is a key regulator of systemic energy metabolism, and impaired WAT plasticity characterized by enlargement of preexisting adipocytes associates with WAT dysfunction, obesity, and metabolic complications. However, the mechanisms that retain proper adipose tissue plasticity required for metabolic fitness are unclear. Here, we comprehensively showed that adipocyte-specific DNA methylation, manifested in enhancers and CTCF sites, directs distal enhancer-mediated transcriptomic features required to conserve metabolic functions of white adipocytes. Particularly, genetic ablation of adipocyte Dnmt1, the major methylation writer, led to increased adiposity characterized by increased adipocyte hypertrophy along with reduced expansion of adipocyte precursors (APs). These effects of Dnmt1 deficiency provoked systemic hyperlipidemia and impaired energy metabolism both in lean and obese mice. Mechanistically, Dnmt1 deficiency abrogated mitochondrial bioenergetics by inhibiting mitochondrial fission and promoted aberrant lipid metabolism in adipocytes, rendering adipocyte hypertrophy and WAT dysfunction. Dnmt1-dependent DNA methylation prevented aberrant CTCF binding and, in turn, sustained the proper chromosome architecture to permit interactions between enhancer and dynamin-1-like protein gene Dnm1l (Drp1) in adipocytes. Also, adipose DNMT1 expression inversely correlated with adiposity and markers of metabolic health but positively correlated with AP-specific markers in obese human subjects. Thus, these findings support strategies utilizing Dnmt1 action on mitochondrial bioenergetics in adipocytes to combat obesity and related metabolic pathology.

Glutamine deficiency promotes stemness and chemoresistance in tumor cells through DRP1-induced mitochondrial fragmentation

Glutamine is essential for maintaining the TCA cycle in cancer cells yet they undergo glutamine starvation in the core of tumors. Cancer stem cells (CSCs), responsible for tumor recurrence are often found in the nutrient limiting cores. Our study uncovers the molecular basis and cellular links between glutamine deprivation and stemness in the cancer cells. We showed that glutamine is dispensable for the survival of ovarian and colon cancer cells while it is required for their proliferation. Glutamine starvation leads to the metabolic reprogramming in tumor cells with enhanced glycolysis and unaltered oxidative phosphorylation. Production of reactive oxygen species (ROS) in glutamine limiting condition induces MAPK-ERK1/2 signaling pathway to phosphorylate dynamin-related protein-1(DRP1) at Ser616. Moreover, p-DRP1 promotes mitochondrial fragmentation and enhances numbers of CD44 and CD117/CD45 positive CSCs. Besides the established features of cancer stem cells, glutamine deprivation induces perinuclear localization of fragmented mitochondria and reduction in proliferation rate which are usually observed in CSCs. Treatment with glutaminase inhibitor (L-DON) mimics the effects of glutamine starvation without altering cell survival in in vitro as well as in in vivo model. Interestingly, the combinatorial treatment of L-DON with DRP1 inhibitor (MDiVi-1) reduces the stem cell population in tumor tissue in mouse model. Collectively our data suggest that glutamine deficiency in the core of tumors can increase the cancer stem cell population and the combination therapy with MDiVi-1 and L-DON is a useful approach to reduce CSCs population in tumor.

DRP1 Promotes BRAFV600E-Driven Tumor Progression and Metabolic Reprogramming in Colorectal Cancer

Background

Mitochondria are highly dynamic organelles which remain in a continuous state of fission/ fusion dynamics to meet the metabolic needs of a cell. However, this fission/fusion dynamism has been reported to be dysregulated in most cancers. Such enhanced mitochondrial fission is demonstrated to be positively regulated by some activating oncogenic mutations; such as those of KRAS (Kristen rat sarcoma viral oncogene homologue) or BRAF (B- rapidly accelerated fibrosarcoma), thereby increasing tumor progression/ chemotherapeutic resistance and metabolic deregulation. However, the underlying mechanism(s) are still not clear, thus highlighting the need to further explore possible mechanism(s) of intervention. We sought to investigate how BRAF^V600E driven CRC (colorectal cancer) progression is linked to mitochondrial fission/fusion dynamics and whether this window could be exploited to target CRC progression.

Methods

Western blotting was employed to study the differences in expression levels of key proteins regulating mitochondrial dynamics, which was further confirmed by confocal microscopy imaging of mitochondria in endogenously expressing BRAF^WT and BRAF^V600E CRC cells. Proliferation assays, soft agar clonogenic assays, glucose uptake/lactate production, ATP/ NADPH measurement assays were employed to study the extent of carcinogenesis and metabolic reprograming in BRAF^V600E CRC cells. Genetic knockdown (shRNA/ siRNA) and/or pharmacologic inhibition of Dynamin related protein1/Pyruvate dehydrogenase kinase1 (DRP1/PDK1) and/or BRAF^V600E were employed to study the involvement and possible mechanism of these proteins in BRAF^V600E driven CRC. Statistical analyses were carried out using Graph Pad Prism v 5.0, data was analyzed by unpaired t-test and two-way ANOVA with appropriate post hoc tests.

Results

Our results demonstrate that BRAF^V600E CRC cells have higher protein levels of mitochondrial fission factor- DRP1/pDRP1^S616 leading to a more fragmented mitochondrial state compared to those harboring BRAF^WT . This fragmented mitochondrial state was found to confer glycolytic phenotype, clonogenic potential and metastatic advantage to cells harboring BRAF^V600E . Interestingly, such fragmented mitochondrial state seemed positively regulated by mitochondrial PDK1 as observed through pharmacologic as well as genetic inhibition of PDK1.

Conclusion

In conclusion, our data suggest that BRAF^V600E driven colorectal cancers have fragmented mitochondria which confers glycolytic phenotype and growth advantage to these tumors, and such phenotype is dependent at least in part on PDK1- thus highlighting a potential therapeutic target.

Hypoxia-induced mitochondrial abnormalities in cells of the placenta

INTRODUCTION

Impaired utero-placental perfusion is a well-known feature of early preeclampsia and is associated with placental hypoxia and oxidative stress. Although aberrations at the level of the mitochondrion have been implicated in PE pathophysiology, whether or not hypoxia-induced mitochondrial abnormalities contribute to placental oxidative stress is unknown.

METHODS

We explored whether abnormalities in mitochondrial metabolism contribute to hypoxia-induced placental oxidative stress by using both healthy term placentae as well as a trophoblast cell line (BeWo cells) exposed to hypoxia. Furthermore, we explored the therapeutic potential of the antioxidants MitoQ and quercetin in preventing hypoxia-induced placental oxidative stress.

RESULTS

Both in placental explants as well as BeWo cells, hypoxia resulted in reductions in mitochondrial content, decreased abundance of key molecules involved in the electron transport chain and increased expression and activity of glycolytic enzymes. Furthermore, expression levels of key regulators of mitochondrial biogenesis were decreased while the abundance of constituents of the mitophagy, autophagy and mitochondrial fission machinery was increased in response to hypoxia. In addition, placental hypoxia was associated with increased oxidative stress, inflammation, and apoptosis. Moreover, experiments with MitoQ revealed that hypoxia-induced reactive oxygen species originated from the mitochondria in the trophoblasts.

DISCUSSION

This study is the first to demonstrate that placental hypoxia is associated with mitochondrial-generated reactive oxygen species and significant alterations in the molecular pathways controlling mitochondrial content and function. Furthermore, our data indicate that targeting mitochondrial oxidative stress may have therapeutic benefit in the management of pathologies related to placental hypoxia.

The Mitochondrial Proteome of Tumor Cells: A SnapShot on Methodological Approaches and New Biomarkers

Simple Summary

Mitochondria are central hubs of cellular signaling, energy metabolism, and redox balance. The plasticity of these cellular organelles is an essential requisite for the cells to cope with different stimuli and stress conditions. Cancer cells are characterized by changes in energy metabolism, mitochondrial signaling, and dynamics. These changes are driven by alterations in the mitochondrial proteome. For this reason, in the last years a focus of basic and cancer research has been the implementation and optimization of technologies to investigate changes in the mitochondrial proteome during cancer initiation and progression. This review presents an overview of the most used technologies to investigate the mitochondrial proteome and recent evidence on changes in the expression levels and delocalization of certain proteins in and out the mitochondria for shaping the functional properties of tumor cells.

Abstract

Mitochondria are highly dynamic and regulated organelles implicated in a variety of important functions in the cell, including energy production, fatty acid metabolism, iron homeostasis, programmed cell death, and cell signaling. Changes in mitochondrial metabolism, signaling and dynamics are hallmarks of cancer. Understanding whether these modifications are associated with alterations of the mitochondrial proteome is particularly relevant from a translational point of view because it may contribute to better understanding the molecular bases of cancer development and progression and may provide new potential prognostic and diagnostic biomarkers as well as novel molecular targets for anti-cancer treatment. Making an inventory of the mitochondrial proteins has been particularly challenging given that there is no unique consensus targeting sequence that directs protein import into mitochondria, some proteins are present at very low levels, while other proteins are expressed only in some cell types, in a particular developmental stage or under specific stress conditions. This review aims at providing the state-of-the-art on methodologies used to characterize the mitochondrial proteome in tumors and highlighting the biological relevance of changes in expression and delocalization of proteins in and out the mitochondria in cancer biology.

SIRT3, a metabolic target linked to ataxia-telangiectasia mutated (ATM) gene deficiency in diffuse large B-cell lymphoma

Inactivation of Ataxia-telangiectasia mutated (ATM) gene results in an increased risk to develop cancer. We show that ATM deficiency in diffuse large B-cell lymphoma (DLBCL) significantly induce mitochondrial deacetylase sirtuin-3 (SIRT3) activity, disrupted mitochondrial structure, decreased mitochondrial respiration, and compromised TCA flux compared with DLBCL cells expressing wild type (WT)-ATM. This corresponded to enrichment of glutamate receptor and glutamine pathways in ATM deficient background compared to WT-ATM DLBCL cells. ATM^−/− DLBCL cells have decreased apoptosis in contrast to radiosensitive non-cancerous A-T cells. In vivo studies using gain and loss of SIRT3 expression showed that SIRT3 promotes growth of ATM CRISPR knockout DLBCL xenografts compared to wild-type ATM control xenografts. Importantly, screening of DLBCL patient samples identified SIRT3 as a putative therapeutic target, and validated an inverse relationship between ATM and SIRT3 expression. Our data predicts SIRT3 as an important therapeutic target for DLBCL patients with ATM null phenotype.

Mitochondrial functional and structural impairment is involved in the antitumor activity of δ-tocotrienol in prostate cancer cells

The therapeutic options for castration-resistant prostate cancer (CRPC) are still limited. Natural bioactive compounds were shown to possess pro-death properties in different tumors. We previously reported that δ-tocotrienol (δ-TT) induces apoptosis, paraptosis and autophagy in CRPC cells. Here, we investigated whether δ-TT might exert its activity by impairing mitochondrial functions. We demonstrated that, in PC3 and DU145 cells, δ-TT impairs mitochondrial respiration and structural dynamics. In both cell lines, δ-TT triggers mitochondrial Ca²⁺ and ROS overload. In PC3 cells, both Ca²⁺ and ROS mediate the δ-TT-related anticancer activities (decrease of cell viability, apoptosis, paraptosis, autophagy and mitophagy). As expected, in autophagy-defective DU145 cells, Ca²⁺ overload was involved in δ-TT-induced pro-death effects but not in autophagy and mitophagy. In this cell line, we also demonstrated that ROS overload is not involved in the anticancer activities of δ-TT, supporting a low susceptibility of these cells to ROS-related oxidative stress. Taken together, these data demonstrate that, in CRPC cells, δ-TT triggers cell death by inducing mitochondrial functional and structural impairments, providing novel mechanistic insights in its antitumor activity.

Canonical and Noncanonical Roles of Fanconi Anemia Proteins: Implications in Cancer Predisposition

Simple Summary

Fanconi anemia (FA) is a genetic disorder that is characterized by bone marrow failure (BMF), developmental abnormalities, and predisposition to cancer. In this review, we present an overview of both canonical (regulation of interstrand cross-links repair, ICLs) and noncanonical roles of FA proteins. We divide noncanonical alternative functions in two types: nuclear (outside ICLs such as FA action in replication stress or DSB repair) and cytosolic (such as in mitochondrial quality control or selective autophagy). We further discuss the involvement of FA genes in the predisposition to develop different types of cancers and we examine current DNA damage response-targeted therapies. Finally, we promote an insightful perspective regarding the clinical implication of the cytosolic noncanonical roles of FA proteins in cancer predisposition, suggesting that these alternative roles could be of critical importance for disease progression.

Abstract

Fanconi anemia (FA) is a clinically and genetically heterogeneous disorder characterized by the variable presence of congenital somatic abnormalities, bone marrow failure (BMF), and a predisposition to develop cancer. Monoallelic germline mutations in at least five genes involved in the FA pathway are associated with the development of sporadic hematological and solid malignancies. The key function of the FA pathway is to orchestrate proteins involved in the repair of interstrand cross-links (ICLs), to prevent genomic instability and replication stress. Recently, many studies have highlighted the importance of FA genes in noncanonical pathways, such as mitochondria homeostasis, inflammation, and virophagy, which act, in some cases, independently of DNA repair processes. Thus, primary defects in DNA repair mechanisms of FA patients are typically exacerbated by an impairment of other cytoprotective pathways that contribute to the multifaceted clinical phenotype of this disease. In this review, we summarize recent advances in the understanding of the pathogenesis of FA, with a focus on the cytosolic noncanonical roles of FA genes, discussing how they may contribute to cancer development, thus suggesting opportunities to envisage novel therapeutic approaches.

NIX-Mediated Mitophagy Promotes Effector Memory Formation in Antigen-Specific CD8+ T Cells

Autophagy plays a critical role in the maintenance of immunological memory. However, the molecular mechanisms involved in autophagy-regulated effector memory formation in CD8⁺ T cells remain unclear. Here we show that deficiency in NIX-dependent mitophagy leads to metabolic defects in effector memory T cells. Deletion of NIX caused HIF1α accumulation and altered cellular metabolism from long-chain fatty acid to short/branched-chain fatty acid oxidation, thereby compromising ATP synthesis during effector memory formation. Preventing HIF1α accumulation restored long-chain fatty acid metabolism and effector memory formation in antigen-specific CD8⁺ T cells. Our study suggests that NIX-mediated mitophagy is critical for effector memory formation in T cells.

Gupta et al. demonstrate that mitophagy mediated by NIX, a mitochondrial outer membrane protein, plays a critical role in CD8⁺ T cell effector memory formation by regulating mitochondrial superoxide-dependent HIF1α protein accumulation and fatty acid metabolism. These findings elucidate the molecular mechanisms regulating T cell effector memory formation against viruses.

The Activity of KIF14, Mieap, and EZR in a New Type of the Invasive Component, Torpedo-Like Structures, Predetermines the Metastatic Potential of Breast Cancer

Intratumor morphological heterogeneity reflects patterns of invasive growth and is an indicator of the metastatic potential of breast cancer. In this study, we used this heterogeneity to identify molecules associated with breast cancer invasion and metastasis. The gene expression microarray data were used to identify genes differentially expressed between solid, trabecular, and other morphological arrangements of tumor cells. Immunohistochemistry was applied to evaluate the association of the selected proteins with metastasis. RNA-sequencing was performed to analyze the molecular makeup of metastatic tumor cells. High frequency of metastases and decreased metastasis-free survival were detected in patients either with positive expression of KIF14 or Mieap or negative expression of EZR at the tips of the torpedo-like structures in breast cancers. KIF14- and Mieap-positive and EZR-negative cells were mainly detected in the torpedo-like structures of the same breast tumors; however, their transcriptomic features differed. KIF14-positive cells showed a significant upregulation of genes involved in ether lipid metabolism. Mieap-positive cells were enriched in genes involved in mitophagy. EZR-negative cells displayed upregulated genes associated with phagocytosis and the chemokine-mediated signaling pathway. In conclusion, the positive expression of KIF14 and Mieap and negative expression of EZR at the tips of the torpedo-like structures are associated with breast cancer metastasis.

The wasting-associated metabolite succinate disrupts myogenesis and impairs skeletal muscle regeneration

BACKGROUND

Muscle wasting is a debilitating co-morbidity affecting most advanced cancer patients. Alongside enhanced muscle catabolism, defects in muscle repair/regeneration contribute to cancer-associated wasting. Among the factors implicated in suppression of muscle regeneration are cytokines that interfere with myogenic signal transduction pathways. Less understood is how other cancer/wasting-associated cues, such as metabolites, contribute to muscle dysfunction. This study investigates how the metabolite succinate affects myogenesis and muscle regeneration.

METHODS

We leveraged an established ectopic metabolite treatment (cell permeable dimethyl-succinate) strategy to evaluate the ability of intracellular succinate elevation to 1) affect myoblast homeostasis (proliferation, apoptosis), 2) disrupt protein dynamics and induce wasting-associated atrophy, and 3) modulate in vitro myogenesis. In vivo succinate supplementation experiments (2% succinate, 1% sucrose vehicle) were used to corroborate and extend in vitro observations. Metabolic profiling and functional metabolic studies were then performed to investigate the impact of succinate elevation on mitochondria function.

RESULTS

We found that in vitro succinate supplementation elevated intracellular succinate about 2-fold, and did not have an impact on proliferation or apoptosis of C2C12 myoblasts. Elevated succinate had minor effects on protein homeostasis (~25% decrease in protein synthesis assessed by OPP staining), and no significant effect on myotube atrophy. Succinate elevation interfered with in vitro myoblast differentiation, characterized by significant decreases in late markers of myogenesis and fewer nuclei per myosin heavy chain positive structure (assessed by immunofluorescence staining). While mice orally administered succinate did not exhibit changes in overall body composition or whole muscle weights, these mice displayed smaller muscle myofiber diameters (~6% decrease in the mean of non-linear regression curves fit to the histograms of minimum feret diameter distribution), which was exacerbated when muscle regeneration was induced with barium chloride injury. Significant decreases in the mean of non-linear regression curves fit to the histograms of minimum feret diameter distributions were observed 7 days and 28 days post injury. Elevated numbers of myogenin positive cells (3-fold increase) supportive of the differentiation defects observed in vitro were observed 28 days post injury. Metabolic profiling and functional metabolic assessment of myoblasts revealed that succinate elevation caused both widespread metabolic changes and significantly lowered maximal cellular respiration (~35% decrease).

CONCLUSIONS

This study broadens the repertoire of wasting-associated factors that can directly modulate muscle progenitor cell function and strengthens the hypothesis that metabolic derangements are significant contributors to impaired muscle regeneration, an important aspect of cancer-associated muscle wasting.

The Role of Reactive Oxygen Species in the Life Cycle of the Mitochondrion

Currently, it is known that, in living systems, free radicals and other reactive oxygen and nitrogen species play a double role, because they can cause oxidative damage and tissue dysfunction and serve as molecular signals activating stress responses that are beneficial to the organism. It is also known that mitochondria, because of their capacity to produce free radicals, play a major role in tissue oxidative damage and dysfunction and provide protection against excessive tissue dysfunction through several mechanisms, including the stimulation of permeability transition pore opening. This process leads to mitoptosis and mitophagy, two sequential processes that are a universal route of elimination of dysfunctional mitochondria and is essential to protect cells from the harm due to mitochondrial disordered metabolism. To date, there is significant evidence not only that the above processes are induced by enhanced reactive oxygen species (ROS) production, but also that such production is involved in the other phases of the mitochondrial life cycle. Accumulating evidence also suggests that these effects are mediated through the regulation of the expression and the activity of proteins that are engaged in processes such as genesis, fission, fusion, and removal of mitochondria. This review provides an account of the developments of the knowledge on the dynamics of the mitochondrial population, examining the mechanisms governing their genesis, life, and death, and elucidating the role played by free radicals in such processes.

PINK1-Dependent Mitophagy Regulates the Migration and Homing of Multiple Myeloma Cells via the MOB1B-Mediated Hippo-YAP/TAZ Pathway

The roles of mitochondrial dysfunction in carcinogenesis remain largely unknown. The effects of PTEN-induced putative kinase 1 (PINK1)-dependent mitophagy on the pathogenesis of multiple myeloma (MM) are determined. The levels of the PINK1-dependent mitophagy markers PINK1 and parkin RBR E3 ubiquitin protein ligase (PARK2) in CD138+ plasma cells are reduced in patients with MM and correlate with clinical outcomes in myeloma patients. Moreover, the induction of PINK1-dependent mitophagy with carbonylcyanide-m-chlorophenylhydrazone (CCCP) or salinomycin, or overexpression of PINK1 leads to inhibition of transwell migration, suppression of myeloma cell homing to calvarium, and decreased osteolytic bone lesions. Furthermore, genetic deletion of pink1 accelerates myeloma development in a spontaneous X-box binding protein-1 spliced isoform (XBP-1s) transgenic myeloma mouse model and in VK*MYC transplantable myeloma recipient mice. Additionally, treatment with salinomycin shows significant antimyeloma activities in vivo in murine myeloma xenograft models. Finally, the effects of PINK1-dependent mitophagy on myeloma pathogenesis are driven by the activation of the Mps one binder kinase activator (MOB1B)-mediated Hippo pathway and the subsequent downregulation of Yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ) expression. These data provide direct evidence that PINK1-dependent mitophagy plays a critical role in the pathogenesis of MM and is a potential therapeutic target.

Mitochondrial Dynamic Dysfunction as a Main Triggering Factor for Inflammation Associated Chronic Non-Communicable Diseases

Mitochondria are organelles with highly dynamic ultrastructure maintained by flexible fusion and fission rates governed by Guanosine Triphosphatases (GTPases) dependent proteins. Balanced control of mitochondrial quality control is crucial for maintaining cellular energy and metabolic homeostasis; however, dysfunction of the dynamics of fusion and fission causes loss of integrity and functions with the accumulation of damaged mitochondria and mitochondrial deoxyribose nucleic acid (mtDNA) that can halt energy production and induce oxidative stress. Mitochondrial derived reactive oxygen species (ROS) can mediate redox signaling or, in excess, causing activation of inflammatory proteins and further exacerbate mitochondrial deterioration and oxidative stress. ROS have a deleterious effect on many cellular components, including lipids, proteins, both nuclear and mtDNA and cell membrane lipids producing the net result of the accumulation of damage associated molecular pattern (DAMPs) capable of activating pathogen recognition receptors (PRRs) on the surface and in the cytoplasm of immune cells. Chronic inflammation due to oxidative damage is thought to trigger numerous chronic diseases including cardiac, liver and kidney disorders, neurodegenerative diseases (Parkinson's disease and Alzheimer's disease), cardiovascular diseases/atherosclerosis, obesity, insulin resistance, and type 2 diabetes mellitus.

Mitochondrial Dysfunction at the Center of Cancer Therapy

Significance: Mitochondria undergo constant morphological changes through fusion, fission, and mitophagy. As the key organelle in cells, mitochondria are responsible for numerous essential cellular functions such as metabolism, regulation of calcium (Ca²⁺), generation of reactive oxygen species, and initiation of apoptosis. Unsurprisingly, mitochondrial dysfunctions underlie many pathologies including cancer. Recent Advances: Currently, the gold standard for cancer treatment is chemotherapy, radiation, and surgery. However, the efficacy of these treatments varies across different cancer cells. It has been suggested that mitochondria may be at the center of these diverse responses. In the past decade, significant advances have been made in understanding distinct types of mitochondrial dysfunctions in cancer. Through investigations of underlying mechanisms, more effective treatment options are developed. Critical Issues: We summarize various mitochondria dysfunctions in cancer progression that have led to the development of therapeutic options. Current mitochondrial-targeted therapies and challenges are discussed. Future Directions: To address the "root" of cancer, utilization of mitochondrial-targeted therapy to target cancer stem cells may be valuable. Investigation of other areas such as mitochondrial trafficking may offer new insights into cancer therapy. Moreover, common antibiotics could be explored as mitocans, and synthetic lethality screens can be utilized to overcome the plasticity of cancer cells.

Crosstalk between autophagy and metabolic regulation of cancer stem cells

Cancer is now considered as a heterogeneous ecosystem in which tumor cells collaborate with each other and with host cells in their microenvironment. As circumstances change, the ecosystem evolves to ensure the survival and growth of the cancer cells. In this ecosystem, metabolism is not only a key player but also drives stemness. In this review, we first summarize our current understanding of how autophagy influences cancer stem cell phenotype. We emphasize metabolic pathways in cancer stem cells and discuss how autophagy-mediated regulation metabolism is involved in their maintenance and proliferation. We then provide an update on the role of metabolic reprogramming and plasticity in cancer stem cells. Finally, we discuss how metabolic pathways in cancer stem cells could be therapeutically targeted.

The Causal Role of Mitochondrial Dynamics in Regulating Innate Immunity in Diabetes

Background: Plenty of evidence suggested that chronic low-grade inflammation triggered by innate immunity activation contributes to the pathogenesis of type 2 diabetes (T2D). Using the trans-mitochondrial cybrid cell model, we have demonstrated that mitochondria independently take part in the pathological process of insulin resistance (IR) and pro-inflammatory phenotype in cybrid cells harboring mitochondrial haplogroup B4, which are more likely to develop T2D. The mitochondrial network is more fragmented, and the expression of fusion-related proteins is low in Cybrid B4. We also discovered the causal role of mitochondrial dynamics (mtDYN) proteins in regulating IR in this cybrid model, and the bidirectional interaction between mtDYN and mitochondrial oxidative stress is considered etiologically important. In this study, we further investigated whether mtDYN bridges the gap between nutrient excess and chronic inflammation in T2D. Methods: Trans-mitochondrial cybrid cells derived from the 143B human osteosarcoma cell line were cultured in a medium containing glucose (25 mM) with or without saturated fatty acid (0.25 mM BSA-conjugated palmitate), and the expression of innate immunity/inflammasome molecules was compared between cybrid B4 (the major T2D-susceptible haplogroup among the Chinese population) and cybrid D4 (the major T2D-resistant haplogroup among the Chinese population). We investigated the causal relationship between mtDYN and nutrient excess-induced inflammation in cybrid B4 by genetic manipulation of mtDYN and by pharmacologically inhibiting mitochondrial fission using the Drp1 inhibitor, mdivi-1, and metformin. Results: Under nutrient excess with high fatty acid, cybrid B4 presented increased mitochondrial pro-fission profiles and enhanced chronic inflammation markers (RIG-I, MDA5, MAVS) and inflammasome (NLRP3, Caspase-1, IL-1β), whereas the levels in cybrid D4 were not or less significantly altered. In cybrid B4 under nutrient excess, overexpression of fusion proteins (Mfn1 or Mfn2) significantly repressed the expression of innate immunity/inflammasome-related molecules, while knockdown had a less significant effect. On the contrary, knockdown of fission proteins (Drp1 or Fis1) significantly repressed the expression of innate immunity/inflammasome-related molecules, while overexpression had a less significant effect. In addition, Drp1 inhibitor mdivi-1 and metformin inhibited mitochondrial fission and attenuated the pro-inflammation expression as well. Conclusion: Our results discovered the causal relationship between mtDYN and nutrient excess-induced chronic inflammation in a diabetes-susceptible cell model. Targeting mtDYN by direct interfering pro-fission can be a therapeutic intervention for chronic inflammation in T2D.

Neutrophil Extracellular Traps Drive Mitochondrial Homeostasis in Tumors to Augment Growth

Neutrophil infiltration and neutrophil extracellular traps (NET) in solid cancers are associated with poorer prognosis, but the mechanisms are incompletely understood. We hypothesized that NETs enhance mitochondrial function in tumor cells, providing extra energy for accelerated growth. Metastatic colorectal cancer tissue showed increased intratumoral NETs and supranormal preoperative serum MPO-DNA, a NET marker. Higher MPO-DNA correlated with shorter survival. In mice, subcutaneous tumor implants and hepatic metastases grew slowly in PAD4-KO mice, genetically incapable of NETosis. In parallel experiments, human cancer cell lines grew slower in nu/nu mice treated with DNAse, which disassembles NETs. PAD4-KO tumors manifested decreased proliferation, increased apoptosis, and increased evidence of oxidative stress. PAD4-KO tumors had decreased mitochondrial density, mitochondrial DNA, a lesser degree of ATP production, along with significantly decreased mitochondrial biogenesis proteins PGC1α, TFAM, and NRF-1. In vitro, cancer cells treated with NETs upregulated mitochondrial biogenesis-associated genes, increased mitochondrial density, increased ATP production, enhanced the percentage of cancer cells with reduced mitochondrial membrane potential, and increased the oxygen consumption rate. Furthermore, NETs increased cancer cells' expression of fission and fusion-associated proteins, DRP-1 and MFN-2, and mitophagy-linked proteins, PINK1 and Parkin. All of which were decreased in PAD4-KO tumors. Mechanistically, neutrophil elastase released from NETs activated TLR4 on cancer cells, leading to PGC1α upregulation, increased mitochondrial biogenesis, and accelerated growth. Taken together, NETs can directly alter the metabolic programming of cancer cells to increase tumor growth. NETs represent a promising therapeutic target to halt cancer progression. SIGNIFICANCE: Neutrophils through the release of NETs facilitate the growth of stressed cancer cells by altering their bioenergetics, the inhibition of which induces cell death.

Role of mitochondria and cardiolipins in growth inhibition of breast cancer cells by retinoic acid

Background

All-trans-retinoic-acid (ATRA) is a promising agent in the prevention/treatment of breast-cancer. There is growing evidence that reprogramming of cellular lipid metabolism contributes to malignant transformation and progression. Lipid metabolism is implicated in cell differentiation and metastatic colonization and it is involved in the mechanisms of sensitivity/resistance to different anti-tumor agents. The role played by lipids in the anti-tumor activity of ATRA has never been studied.

Methods

We used 16 breast cancer cell-lines whose degree of sensitivity to the anti-proliferative action of ATRA is known. We implemented a non-oriented mass-spectrometry based approach to define the lipidomic profiles of each cell-line grown under basal conditions and following treatment with ATRA. To complement the lipidomic data, untreated and retinoid treated cell-lines were also subjected to RNA-sequencing to define the perturbations afforded by ATRA on the whole-genome gene-expression profiles. The number and functional activity of mitochondria were determined in selected ATRA-sensitive and –resistant cell-lines. Bio-computing approaches were used to analyse the high-throughput lipidomic and transcriptomic data.

Results

ATRA perturbs the homeostasis of numerous lipids and the most relevant effects are observed on cardiolipins, which are located in the mitochondrial inner membranes and play a role in oxidative-phosphorylation. ATRA reduces the amounts of cardiolipins and the effect is associated with the growth-inhibitory activity of the retinoid. Down-regulation of cardiolipins is due to a reduction of mitochondria, which is caused by an ATRA-dependent decrease in the expression of nuclear genes encoding mitochondrial proteins. This demonstrates that ATRA anti-tumor activity is due to a decrease in the amounts of mitochondria causing deficits in the respiration/energy-balance of breast-cancer cells.

Conclusions

The observation that ATRA anti-proliferative activity is caused by a reduction in the respiration and energy balance of the tumor cells has important ramifications for the therapeutic action of ATRA in breast cancer. The study may open the way to the development of rational therapeutic combinations based on the use of ATRA and anti-tumor agents targeting the mitochondria.

A Novel MYCN-Specific Antigene Oligonucleotide Deregulates Mitochondria and Inhibits Tumor Growth in MYCN-Amplified Neuroblastoma

Approximately half of high-risk neuroblastoma is characterized by MYCN amplification. N-Myc promotes tumor progression by inducing cell growth and inhibiting differentiation. MYCN has also been shown to play an active role in mitochondrial metabolism, but this relationship is not well understood. Although N-Myc is a known driver of the disease, it remains a target for which no therapeutic drug exists. Here, we evaluated a novel MYCN-specific antigene PNA oligonucleotide (BGA002) in MYCN-amplified (MNA) or MYCN-expressing neuroblastoma and investigated the mechanism of its antitumor activity. MYCN mRNA and cell viability were reduced in a broad set of neuroblastoma cell lines following BGA002 treatment. Furthermore, BGA002 decreased N-Myc protein levels and apoptosis in MNA neuroblastoma. Analysis of gene expression data from patients with neuroblastoma revealed that MYCN was associated with increased reactive oxygen species (ROS), downregulated mitophagy, and poor prognosis. Inhibition of MYCN caused profound mitochondrial damage in MNA neuroblastoma cells through downregulation of the mitochondrial molecular chaperone TRAP1, which subsequently increased ROS. Correspondingly, inhibition of MYCN reactivated mitophagy. Systemic administration of BGA002 downregulated N-Myc and TRAP1, with a concomitant decrease in MNA neuroblastoma xenograft tumor weight. In conclusion, this study highlights the role of N-Myc in blocking mitophagy in neuroblastoma and in conferring protection to ROS in mitochondria through upregulation of TRAP1. BGA002 is a potently improved MYCN-specific antigene oligonucleotide that reverts N-Myc-dysregulated mitochondrial pathways, leading to loss of the protective effect of N-Myc against mitochondrial ROS. SIGNIFICANCE: A second generation antigene peptide oligonucleotide targeting MYCN induces mitochondrial damage and inhibits growth of MYCN-amplified neuroblastoma cells.

Mitochondrial Dysfunction Pathway Networks and Mitochondrial Dynamics in the Pathogenesis of Pituitary Adenomas

Mitochondrion is a multi-functional organelle, which is associated with various signaling pathway networks, including energy metabolism, oxidative stress, cell apoptosis, cell cycles, autophagy, and immunity process. Mitochondrial proteins have been discovered to modulate these signaling pathway networks, and multiple biological behaviors to adapt to various internal environments or signaling events of human pathogenesis. Accordingly, mitochondrial dysfunction that alters the bioenergetic and biosynthetic state might contribute to multiple diseases, including cell transformation and tumor. Multiomics studies have revealed that mitochondrial dysfunction, oxidative stress, and cell cycle dysregulation signaling pathways operate in human pituitary adenomas, which suggest mitochondria play critical roles in pituitary adenomas. Some drugs targeting mitochondria are found as a therapeutic strategy for pituitary adenomas, including melatonin, melatonin inhibitors, temozolomide, pyrimethamine, 18 beta-glycyrrhetinic acid, gossypol acetate, Yougui pill, T-2 toxin, grifolic acid, cyclosporine A, dopamine agonists, and paeoniflorin. This article reviews the latest experimental evidence and potential biological roles of mitochondrial dysfunction and mitochondrial dynamics in pituitary adenoma progression, potential molecular mechanisms between mitochondria and pituitary adenoma progression, and current status and perspectives of mitochondria-based biomarkers and targeted drugs for effective management of pituitary adenomas.

Autophagy Function and Dysfunction: Potential Drugs as Anti-Cancer Therapy

Autophagy is a highly conserved catabolic and energy-generating process that facilitates the degradation of damaged organelles or intracellular components, providing cells with components for the synthesis of new ones. Autophagy acts as a quality control system, and has a pro-survival role. The imbalance of this process is associated with apoptosis, which is a “positive” and desired biological choice in some circumstances. Autophagy dysfunction is associated with several diseases, including neurodegenerative disorders, cardiomyopathy, diabetes, liver disease, autoimmune diseases, and cancer. Here, we provide an overview of the regulatory mechanisms underlying autophagy, with a particular focus on cancer and the autophagy-targeting drugs currently approved for use in the treatment of solid and non-solid malignancies.

Roles of mitochondria in liver cancer stem cells

Primary liver cancer (PLC) is heterogeneous and it is an aggressive malignancy with a poor prognostic outcome. Current evidence suggests that PLC tumorigenesis is driven by rare subpopulations of cancer stem cells (CSCs), which contribute to tumor initiation, progression, and therapy resistance through particular molecular mechanisms. Energy metabolism and mitochondrial function play an important role in the regulation of cancer stemness and stem cell specifications. Since the role of mitochondrial function as central hubs in cell growth and survival, studies on the critical physiological mechanisms of the liver underlying their therapy-resistant phenotype is important. In this review, we focus on liver CSC-related mitochondrial metabolism that contributes to the liver CSC features, in terms of enhanced drug-resistance and increased tumorigenicity, and to discuss their roles on potential therapies windows for PLC therapies.

Understanding sex differences in the regulation of cancer-induced muscle wasting

PURPOSE OF REVIEW

We highlight evidence for sexual dimorphism in preclinical and clinical studies investigating the cause and treatment of cancer cachexia.

RECENT FINDINGS

Cancer cachexia is unintended bodyweight loss occurring with cancer, and skeletal muscle wasting is a critical predictor of negative outcomes in the cancer patient. Skeletal muscle exhibits sexual dimorphism in fiber type, function, and regeneration capacity. Sex differences have been implicated in skeletal muscle metabolism, mitochondrial function, immune response to injury, and myogenic stem cell regulation. All of these processes have the potential to be involved in cancer-induced muscle wasting. Unfortunately, the vast majority of published studies examining cancer cachexia in preclinical models or cancer patients either have not accounted for sex in their design or have exclusively studied males. Preclinical studies have established that ovarian function and estradiol can affect skeletal muscle function, metabolism and mass; ovarian function has also been implicated in the sensitivity of circulating inflammatory cytokines and the progression of cachexia.

SUMMARY

Females and males have unique characteristics that effect skeletal muscle's microenvironment and intrinsic signaling. These differences provide a strong rationale for distinct causes for cancer cachexia development and treatment in males and females.

Cold PSM, but not TRAIL, triggers autophagic cell death: A therapeutic advantage of PSM over TRAIL

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and cold plasma-stimulated medium (PSM) are promising novel anticancer tools due to their strong anticancer activities and high tumor-selectivity. The present study demonstrated that PSM and TRAIL may trigger autophagy in human malignant melanoma and osteosarcoma cells. Live-cell imaging revealed that even under nutritional and stress-free conditions, these cells possessed a substantial level of autophagosomes, which were localized in the cytoplasm separately from tubular mitochondria. In response to cytotoxic levels of PSM, the mitochondria became highly fragmented, and aggregated and colocalized with the autophagosomes. The cytotoxic effects of PSM were suppressed in response to various pharmacological autophagy inhibitors, including 3-methyladenine (3-MA) and bafilomycin A1, thus indicating the induction of autophagic cell death (ACD). Lethal levels of PSM also resulted in non-apoptotic, non-autophagic cell death in a reactive oxygen species-dependent manner under certain circumstances. Furthermore, TRAIL exhibited only a modest cytotoxicity toward these tumor cells, and did not induce ACD and mitochondrial aberration. The combined use of TRAIL and subtoxic concentrations of 3-MA resulted in decreased basal autophagy, increased mitochondrial aberration, colocalization with autophagosomes and apoptosis. These results indicated that PSM may induce ACD, whereas TRAIL may trigger cytoprotective autophagy that compromises apoptosis. To the best of our knowledge, the present study is the first to demonstrate that PSM can induce ACD in human cancer cells. These findings provide a rationale for the advantage of PSM over TRAIL in the destruction of apoptosis-resistant melanoma and osteosarcoma cells.

Inhibition of thioredoxin activates mitophagy and overcomes adaptive bortezomib resistance in multiple myeloma

Background

Although current chemotherapy using bortezomib (Velcade) against multiple myeloma in adults has achieved significant responses and even remission, a majority of patients will develop acquired resistance to bortezomib. Increased thioredoxin level has been reported to be associated with carcinogenesis; however, the role of thioredoxin in bortezomib drug resistance of myeloma remains unclear.

Methods

We generated several bortezomib-resistant myeloma cell lines by serially passaging with increased concentrations of bortezomib over a period of 1.5 years. Thioredoxin expression was measured by real-time PCR and western blot.

Results

The role of thioredoxin in the survival of bortezomib-resistant myeloma cells was determined by specific shRNA knockdown in vitro and in vivo. Thioredoxin inhibitor (PX12) was used to determine the effectiveness of thioredoxin inhibition in the treatment of bortezomib-resistant myeloma cells. The effect of thioredoxin inhibition on mitophagy induction was examined. The correlation of thioredoxin expression with patient overall survival was interrogated. Thioredoxin expression was significantly upregulated in bortezomib-resistant myeloma cells and the change correlated with the increase of bortezomib concentration. Thioredoxin gene knockdown using specific shRNA sensitized bortezomib-resistant myeloma cells to bortezomib efficiency in vitro and in vivo. Similarly, pharmacological inhibition with PX12 inhibited the growth of bortezomib-resistant myeloma cells and overcame bortezomib resistance in vitro and in vivo. Furthermore, inhibition of thioredoxin resulted in the activation of mitophagy and blockage of mitophagy prevented the effects of PX12 on bortezomib-resistant myeloma cells, indicating that mitophagy is the important molecular mechanism for the induction of cell death in bortezomib-resistant myeloma cells by PX12. Moreover, inhibition of thioredoxin resulted in downregulation of phosphorylated mTOR and ERK1/2. Finally, thioredoxin was overexpressed in primary myeloma cells isolated from bortezomib-resistant myeloma patients and overexpression of thioredoxin correlated with poor overall survival in patients with multiple myeloma.

Conclusions

Our findings demonstrated that increased thioredoxin plays a critical role in bortezomib resistance in multiple myeloma through mitophagy inactivation and increased mTOR and ERK1/2 phosphorylation. Thioredoxin provides a potential target for clinical therapeutics against multiple myeloma, particularly for bortezomib-resistant/refractory myeloma patients.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0575-7) contains supplementary material, which is available to authorized users.

Cargo recognition and degradation by selective autophagy

Macroautophagy, initially described as a non-selective nutrient recycling process, is essential for the removal of multiple cellular components. In the past three decades, selective autophagy has been characterized as a highly regulated and specific degradation pathway for removal of unwanted cytosolic components and damaged and/or superfluous organelles. Here, we discuss different types of selective autophagy, emphasizing the role of ligand receptors and scaffold proteins in providing cargo specificity, and highlight unanswered questions in the field.

Reactive Oxygen Species and Mitochondrial Dynamics: The Yin and Yang of Mitochondrial Dysfunction and Cancer Progression

Mitochondria are organelles with a highly dynamic ultrastructure maintained by a delicate equilibrium between its fission and fusion rates. Understanding the factors influencing this balance is important as perturbations to mitochondrial dynamics can result in pathological states. As a terminal site of nutrient oxidation for the cell, mitochondrial powerhouses harness energy in the form of ATP in a process driven by the electron transport chain. Contemporaneously, electrons translocated within the electron transport chain undergo spontaneous side reactions with oxygen, giving rise to superoxide and a variety of other downstream reactive oxygen species (ROS). Mitochondrially-derived ROS can mediate redox signaling or, in excess, cause cell injury and even cell death. Recent evidence suggests that mitochondrial ultrastructure is tightly coupled to ROS generation depending on the physiological status of the cell. Yet, the mechanism by which changes in mitochondrial shape modulate mitochondrial function and redox homeostasis is less clear. Aberrant mitochondrial morphology may lead to enhanced ROS formation, which, in turn, may deteriorate mitochondrial health and further exacerbate oxidative stress in a self-perpetuating vicious cycle. Here, we review the latest findings on the intricate relationship between mitochondrial dynamics and ROS production, focusing mainly on its role in malignant disease.

Mitochondrial fission and mitophagy depend on cofilin-mediated actin depolymerization activity at the mitochondrial fission site

Mitochondria fission and mitophagy are fundamentally crucial to cellular physiology and play important roles in cancer progression. Developing a comprehensive understanding of the molecular mechanism underlying mitochondrial fission and mitophagy will provide novel strategies for cancer prevention and treatment. Actin has been shown to participate in mitochondrial fission and mitophagy regulation. Cofilin is best known as an actin-depolymerizing factor. However, the molecular mechanism by which cofilin regulates mitochondrial fission and mitophagy remains largely unknown. Here we report that knockdown of cofilin attenuates and overexpression of cofilin potentiates mitochondrial fission as well as PINK1/PARK2-dependent mitophagy induced by staurosporine (STS), etoposide (ETO), and carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Cofilin-mediated-PINK1 (PTEN-induced putative kinase 1) accumulation mainly depends on its regulation of mitochondrial proteases, including peptidase mitochondrial processing beta (MPPβ), presenilin-associated rhomboid-like protease (PARL), and ATPase family gene 3-like 2 (AFG3L2), via mitochondrial membrane potential activity. We also found that the interaction and colocalization of G-actin/F-actin with cofilin at mitochondrial fission sites undergo constriction after CCCP treatment. Pretreatment with the actin polymerization inhibitor latrunculin B (LatB) increased and actin-depolymerization inhibitor jasplakinolide (Jas) decreased mitochondrial translocation of actin induced by STS, ETO, and CCCP. Both LatB and Jas abrogated CCCP-mediated mitochondrial fission and mitophagy. Our data suggest that G-actin is the actin form that is translocated to mitochondria, and the actin-depolymerization activity regulated by cofilin at the mitochondrial fission site is crucial for inducing mitochondrial fission and mitophagy.

Melatonin increases human cervical cancer HeLa cells apoptosis induced by cisplatin via inhibition of JNK/Parkin/mitophagy axis

Considering that chemotherapy resistance is vital to the progression of cervical carcinoma, emerging researchers are focused on developing anti-tumor drugs to assist the treatment efficiency of chemotherapy. Melatonin has anti-tumor activity via several mechanisms including its anti-proliferative and pro-apoptotic effects as well as its potent pro-oxidant action in tumor cells. Therefore, melatonin may be useful for the treatment of tumors in association with chemotherapy drugs. Here, we studied the effect and mechanism of melatonin on HeLa cells apoptosis under cisplatin (CIS) treatment, particularly focusing on the caspase-9-related apoptosis pathway and mitophagy-mediated anti-apoptotic mechanism. The result indicated that co-stimulation of HeLa cells with CIS in the presence of melatonin further increased cellular apoptosis. Furthermore, concomitant treatments with melatonin and CIS significantly enhanced the mitochondrial structure and function damage, substantially augmented the caspase-9-dependent mitochondrial apoptosis with evidenced by lower mitochondria membrane potential, higher mitochondria ROS, and more pro-apoptotic proteins compared to the treatment with CIS alone. Mechanistically, melatonin inactivated mitophagy via blockade of JNK/Parkin, leading to the inhibition of anti-apoptotic mitophagy. The mitophagy had the ability to clear and remove damaged mitochondria, impairing CIS-mediated mitochondrial apoptosis. Activation of JNK/Parkin could alleviate the lethal effect of melatonin on HeLa cells. In summary, this study confirmed that melatonin sensitizes human cervical cancer HeLa cells to CIS-induced apoptosis through inhibition of JNK/Parkin/mitophagy pathways.

Mst1 regulates colorectal cancer stress response via inhibiting Bnip3-related mitophagy by activation of JNK/p53 pathway

The Hippo-Mst1 pathway is associated with tumor development and progression. However, little evidence is available for its role in colorectal cancer (CRC) stress response via mitochondrial homeostasis. In this study, we conducted gain-of function assay about Mst1 in CRC via adenovirus transfection. Then, cellular viability and apoptosis were measured via MTT, TUNEL assay, and typan blue staining. Mitochondrial function was detected via JC1 staining, mPTP opening assay, and immunofluorescence of cyt-c. Mitophagy was observed via western blots and immunofluorescence. Cell migration and proliferation were evaluated via Transwell and BrdU assay. Western blots were used to analyze the signaling pathways with JNK inhibitors or p53 siRNA. We found that Mst1 was down-regulated in CRC. Overexpression of Mst1 induced CRC apoptosis and impaired cell proliferation and migration. Functional studies have illustrated that recovery of Mst1 could activate JNK pathway which upregulated the p53 expression. The latter repressed Bnip3 transcription and activity, leading to the mitophagy arrest. The defective mitophagy impaired mitochondrial homeostasis, evoked cellular oxidative stress, and initiated the mitochondrial apoptosis. Meanwhile, bad-structured mitophagy also hindered the cancer proliferation via CyclinD/E. Moreover, Mst1-suppressed mitophagy was associated with CRC migration inhibition via regulation of CXCR4/7 expression. Collectively, our data described the comprehensive role of Mst1 in colorectal cancer stress response involving apoptosis, mobilization, and growth via handling mitophagy by JNK/p53/Bnip3 pathways.

Disrupted Skeletal Muscle Mitochondrial Dynamics, Mitophagy, and Biogenesis during Cancer Cachexia: A Role for Inflammation

Chronic inflammation is a hallmark of cancer cachexia in both patients and preclinical models. Cachexia is prevalent in roughly 80% of cancer patients and accounts for up to 20% of all cancer-related deaths. Proinflammatory cytokines IL-6, TNF-α, and TGF-β have been widely examined for their regulation of cancer cachexia. An established characteristic of cachectic skeletal muscle is a disrupted capacity for oxidative metabolism, which is thought to contribute to cancer patient fatigue, diminished metabolic function, and muscle mass loss. This review's primary objective is to highlight emerging evidence linking cancer-induced inflammation to the dysfunctional regulation of mitochondrial dynamics, mitophagy, and biogenesis in cachectic muscle. The potential for either muscle inactivity or exercise to alter mitochondrial dysfunction during cancer cachexia will also be discussed.