Myc Regulation of a Mitochondrial Trafficking Network Mediates Tumor Cell Invasion and Metastasis

Emerging roles for Mitochondrial Rho GTPases in tumor biology

Mitochondrial Rho GTPases (MIRO1 and MIRO2) are primarily studied for their role as resident mitochondrial anchor proteins that facilitate mitochondria trafficking in neurons. However, it is now appreciated that these proteins have critical roles in cancer. In this review, we focus on examining the role of MIROs in cancer, including expression changes in tumors and the molecular mechanisms by which MIROs impact tumor cell growth, invasion, and metastasis. Additionally, we give an overview of how MIRO's functions in normal cells within the tumor microenvironment can support or inhibit tumor growth and metastasis. Although this is still an emerging field, the current consensus is that the MIROs primarily promote tumor progression of disparate tumor types. As mitochondrial proteins are now being targeted in the clinic, we discuss their potential as novel proteins to target in cancer.

The Up-Regulated Expression of Mitochondrial Membrane Molecule RHOT1 in Gastric Cancer Predicts the Prognosis of Patients and Promotes the Malignant Biological Behavior of Cells

Gastric cancer (GC) remains a major disease of high morbidity and mortality worldwide despite advances in diagnosis and treatment. Ras homolog family member T1 (RHOT1) plays an important role in several cancers. Our study aimed to analyze RHOT1 expression, to assess the relationship between its expression and the prognosis of patients, and know the impact of RHOT1 on GC cells. The Cancer Genome Atlas (TCGA) RNA-seq data was used for gene expression analysis, survival and prognostic analysis. Nomograms were created to analyze the pathological factors of GC patients. RHOT1 expression was up-regulated by analyzed TCGA-Stomach adenocarcinoma (STAD) data and verified by Polymerase Chain Reaction (PCR) assay in GC tissues and cell lines. Furthermore, RHOT1 up-regulation was significantly associated with shorter survival of GC patients. At last, after silencing the expression of RHOT1 in AGS cell lines, we found that the proliferative ability of the cells was significantly reduced, the cell invasion ability was significantly inhibited, the cell migration ability was also significantly weakened, the cell cycle was arrested in the G0/G1 phase, and apoptosis was significantly increased. So RHOT1 could impact the apoptosis, proliferation, invasion, and migration behavior of GC cells. We trust RHOT1 has the potential to become a new oncogene biomarker for diagnosis and prognosis as well as a new therapeutic target in GC.

Le transport mitochondrial

La reprogrammation métabolique est l’un des marqueurs de la carcinogenèse. Au cœur de cette reprogrammation se trouvent les mitochondries qui produisent l’énergie sous forme de molécules d’ATP. La régulation spatio-temporelle de la production d’ATP, indispensable pour fournir l’énergie au bon endroit et au bon moment, est assurée par le transport intracellulaire des mitochondries. Les complexes Miro/TRAK présents à la surface des mitochondries se lient aux protéines motrices de la cellule (dynéine, kinésine, myosine) pour transporter les mitochondries le long du cytosquelette. Ces acteurs du transport mitochondrial sont souvent dérégulés dans le cancer. Nous présentons dans cette revue les mécanismes par lesquels le transport mitochondrial contribue à la migration, à la division cellulaire et à la réponse au stress des cellules cancéreuses. Décrypter ces mécanismes pourrait ouvrir la voie à de nouvelles approches thérapeutiques en oncologie.

Map7D2 and Map7D1 facilitate microtubule stabilization through distinct mechanisms in neuronal cells

The microtubule-associated proteins Map7D2 and Map7D1, which belong to the MAP7 family, stabilize microtubules through distinct mechanisms for the control of cell motility and neurite outgrowth.

Microtubule (MT) dynamics are modulated through the coordinated action of various MT-associated proteins (MAPs). However, the regulatory mechanisms underlying MT dynamics remain unclear. We show that the MAP7 family protein Map7D2 stabilizes MTs to control cell motility and neurite outgrowth. Map7D2 directly bound to MTs through its N-terminal half and stabilized MTs in vitro. Map7D2 localized prominently to the centrosome and partially on MTs in mouse N1-E115 neuronal cells, which expresses two of the four MAP7 family members, Map7D2 and Map7D1. Map7D2 loss decreased the resistance to the MT-destabilizing agent nocodazole without affecting acetylated/detyrosinated stable MTs, suggesting that Map7D2 stabilizes MTs via direct binding. In addition, Map7D2 loss increased the rate of random cell migration and neurite outgrowth, presumably by disturbing the balance between MT stabilization and destabilization. Map7D1 exhibited similar subcellular localization and gene knockdown phenotypes to Map7D2. However, in contrast to Map7D2, Map7D1 was required for the maintenance of acetylated stable MTs. Taken together, our data suggest that Map7D2 and Map7D1 facilitate MT stabilization through distinct mechanisms in cell motility and neurite outgrowth.

Hsa_circ_0005230 is up-regulated and promotes gastric cancer cell invasion and migration via regulating the miR-1299/RHOT1 axis

Gastric cancer (GC) is one of the most common cancers in the world. Circular RNAs (circRNAs) are a class of non-coding RNAs that are widely expressed in eukaryotic cells. However, their role has been poorly understood in GC. This report aimed to explore the biological functions of hsa_circ_0005230 and its action mechanism in GC. This study validated that hsa_circ_0005230 was significantly up-regulated in 130 cases of GC tissues using qRT-PCR, and clinicopathological feature analysis revealed that its high expression was positively associated with histological grade, lymph node metastasis, TNM stages, and poor prognosis. In vitro, functional experiments showed that silencing hsa_circ_0005230 significantly decreased GC cell proliferation, invasion and migration capabilities. In addition, the major proteins of EMT (epithelial-mesenchymal transition) relevance have changed. In mechanism studies, bioinformatics analyses were used to predict the hsa_circ_0005230/miR-1299/RHOT1 axis and hsa_circ_0005230 may serve as a sponge for miR-1299 and indirectly regulate the expression of RHOT1. The regulated relationships between the molecules on the axis were verified using qRT-PCR and correlation analysis. Dual-luciferase reporter gene assay has been used to verify the binding site between miR-1299 and RHOT1. WB (Western blotting) and IHC (Immunohistochemical) were used to verify that RHOT1 may play the role of oncoprotein and affect the biological behavior of GC. Overall, hsa_circ_0005230 could enhance the EMT phenotype by promoting RHOT1 expression through sponging miR-1299, thus affecting the biological behavior of GC. Hsa_circ_0005230 can be easily identified as a potential diagnostic biomarker and assessment prognosis target for GC.

Targeting the ERK mitogen-activated protein kinase cascade for the treatment of KRAS-mutant pancreatic cancer

Mutational activation of the KRAS oncogene is found in ~95% of pancreatic ductal adenocarcinoma (PDAC), the major form of pancreatic cancer. With substantial experimental evidence that continued aberrant KRAS function is essential for the maintenance of PDAC tumorigenic growth, the National Cancer Institute has identified the development of effective anti-KRAS therapies as one of four major initiatives for pancreatic cancer research. The recent clinical success in the development of an anti-KRAS therapy targeting one specific KRAS mutant (G12C) supports the significant potential impact of anti-KRAS therapies. However, KRAS^G12C mutations comprise only 2% of KRAS mutations in PDAC. Thus, there remains a dire need for additional therapeutic approaches for targeting the majority of KRAS-mutant PDAC. Among the different directions currently being pursued for anti-KRAS drug development, one of the most promising involves inhibitors of the key KRAS effector pathway, the three-tiered RAF-MEK-ERK mitogen-activated protein kinase (MAPK) cascade. We address the promises and challenges of targeting ERK MAPK signaling as an anti-KRAS therapy for PDAC. In particular, we also summarize the key role of the MYC transcription factor and oncoprotein in supporting ERK-dependent growth of KRAS-mutant PDAC.

MIRO2 regulates prostate cancer cell growth via GCN1-dependent stress signaling

There is a continued need to identify novel therapeutic targets to prevent the mortality associated with prostate cancer. In this context, Mitochondrial Rho GTPase 2 (MIRO2) mRNA was upregulated in metastatic prostate cancer compared to localized tumors, and higher MIRO2 levels were correlated with poor patient survival. Using human cell lines that represent androgen-independent or -sensitive prostate cancer, we showed that MIRO2 depletion impaired cell growth, colony formation and tumor growth in mice. Network analysis of MIRO2's binding partners identified metabolism and cellular responses to extracellular stimuli as top over-represented pathways. The top hit on our screen, General Control Non-derepressible 1 (GCN1), was overexpressed in prostate cancer, and interacted with MIRO2 in prostate cancer cell lines and in primary prostate cancer cells. Functional analysis of MIRO2 mutations present in prostate cancer patients led to the identification of MIRO2 159L, which increased GCN1 binding. Importantly, MIRO2 was necessary for efficient GCN1-mediated GCN2 kinase signaling and induction of the transcription factor ATF4 levels. Further, MIRO2's effect on regulating prostate cancer cell growth was mediated by ATF4. Finally, levels of activated GCN2 and ATF4 were correlated with MIRO2 expression in prostate cancer xenografts. Both MIRO2 and activated GCN2 levels were higher in hypoxic areas of prostate cancer xenografts. Overall, we propose that targeting the MIRO2-GCN1 axis may be a valuable strategy to halt prostate cancer growth. Implications: MIRO2/GCN1/GCN2 constitute a novel mitochondrial signaling pathway that controls androgen-independent and androgen-sensitive prostate cancer cell growth.

Mitochondrial Fission and Fusion in Tumor Progression to Metastasis

Mitochondria are highly dynamic organelles which can change their shape, via processes termed fission and fusion, in order to adapt to different environmental and developmental contexts. Due to the importance of these processes in maintaining a physiologically healthy pool of mitochondria, aberrant cycles of fission/fusion are often seen in pathological contexts. In this review we will discuss how dysregulated fission and fusion promote tumor progression. We focus on the molecular mechanisms involved in fission and fusion, discussing how altered mitochondrial fission and fusion change tumor cell growth, metabolism, motility, and invasion and, finally how changes to these tumor-cell intrinsic phenotypes directly and indirectly impact tumor progression to metastasis. Although this is an emerging field of investigation, the current consensus is that mitochondrial fission positively influences metastatic potential in a broad variety of tumor types. As mitochondria are now being investigated as vulnerable targets in a variety of cancer types, we underscore the importance of their dynamic nature in potentiating tumor progression.

Mitochondrial fragmentation is crucial for c-Myc-driven hepatoblastoma-like liver tumor

Hepatoblastoma is the most common liver cancer in children, and the aggressive subtype often has a poor prognosis and lacks effective targeted therapy. Although aggressive hepatoblastoma (HB) is often accompanied by abnormally high expression of the transcription factor c-Myc, the underlying mechanism remains unclear. In this study, we found that mitochondrial fragmentation was enhanced by c-Myc overexpression in human aggressive HB tissues and was associated with poor prognosis. Then, a mouse model resembling human HB was established via hydrodynamic injection of c-Myc plasmids. We observed that liver-specific knockout of the mitochondrial fusion molecule MFN1 or overexpression of mitochondrial fission molecule DRP1 promoted the occurrence of c-Myc-driven liver cancer. In contrast, when MFN1 was overexpressed in the liver, tumor formation was delayed. In vitro experiments showed that c-Myc transcriptionally upregulated the expression of DRP1 and decreased MFN1 expression through upregulation of miR-373-3p. Moreover, enhanced mitochondrial fragmentation significantly promoted aerobic glycolysis and the proliferation of HB cells by significantly increasing reactive oxygen species (ROS) production and activating the RAC-alpha serine/threonine-protein kinase (AKT)/mammalian target of rapamycin (mTOR) and nuclear factor κB (NF-κB) pathways. Taken together, our results indicate that c-Myc-mediated mitochondrial fragmentation promotes the malignant transformation and progression of HB by activating ROS-mediated multi-oncogenic signaling.

Mitochondrial Dysfunction as a Hallmark of Environmental Injury

Environmental factors including diet, sedentary lifestyle and exposure to pollutants largely influence human health throughout life. Cellular and molecular events triggered by an exposure to environmental pollutants are extremely variable and depend on the age, the chronicity and the doses of exposure. Only a fraction of all relevant mechanisms involved in the onset and progression of pathologies in response to toxicants has probably been identified. Mitochondria are central hubs of metabolic and cell signaling responsible for a large variety of biochemical processes, including oxidative stress, metabolite production, energy transduction, hormone synthesis, and apoptosis. Growing evidence highlights mitochondrial dysfunction as a major hallmark of environmental insults. Here, we present mitochondria as crucial organelles for healthy metabolic homeostasis and whose dysfunction induces critical adverse effects. Then, we review the multiple mechanisms of action of pollutants causing mitochondrial toxicity in link with chronic diseases. We propose the Aryl hydrocarbon Receptor (AhR) as a model of “exposome receptor”, whose activation by environmental pollutants leads to various toxic events through mitochondrial dysfunction. Finally, we provide some remarks related to mitotoxicity and risk assessment.

Mitochondria and Their Relationship with Common Genetic Abnormalities in Hematologic Malignancies

Hematologic malignancies are known to be associated with numerous cytogenetic and molecular genetic changes. In addition to morphology, immunophenotype, cytochemistry and clinical characteristics, these genetic alterations are typically required to diagnose myeloid, lymphoid, and plasma cell neoplasms. According to the current World Health Organization (WHO) Classification of Tumors of Hematopoietic and Lymphoid Tissues, numerous genetic changes are highlighted, often defining a distinct subtype of a disease, or providing prognostic information. This review highlights how these molecular changes can alter mitochondrial bioenergetics, cell death pathways, mitochondrial dynamics and potentially be related to mitochondrial genetic changes. A better understanding of these processes emphasizes potential novel therapies.

Ral GEF with the PH Domain and SH3 Binding Motif 1 Regulated by Splicing Factor Junction Plakoglobin and Pyrimidine Metabolism Are Prognostic in Uterine Carcinosarcoma

Uterine carcinosarcoma (UCS) is a highly invasive malignant tumor that originated from the uterine epithelium. Many studies suggested that the abnormal changes of alternative splicing (AS) of pre-mRNA are related to the occurrence and metastasis of the tumor. This study investigates the mechanism of alternative splicing events (ASEs) in the tumorigenesis and metastasis of UCS. RNA-seq of UCS samples and alternative splicing event (ASE) data of UCS samples were downloaded from The Cancer Genome Atlas (TCGA) and TCGASpliceSeq databases, several times. Firstly, we performed the Cox regression analysis to identify the overall survival-related alternative splicing events (OSRASEs). Secondly, a multivariate model was applied to approach the prognostic values of the risk score. Afterwards, a coexpressed network between splicing factors (SFs) and OSRASEs was constructed. In order to explore the relationship between the potential prognostic signaling pathways and OSRASEs, we fabricated a network between these pathways and OSRASEs. Finally, validations from multidimension platforms were used to explain the results unambiguously. 1,040 OSRASEs were identified by Cox regression. Then, 6 OSRASEs were incorporated in a multivariable model by Lasso regression. The area under the curve (AUC) of the receiver operator characteristic (ROC) curve was 0.957. The risk score rendered from the multivariate model was corroborated to be an independent prognostic factor (P < 0.001). In the network of SFs and ASEs, junction plakoglobin (JUP) noteworthily regulated RALGPS1-87608-AT (P < 0.001, R = 0.455). Additionally, RALGPS1-87608-AT (P = 0.006) showed a prominent relationship with distant metastasis. KEGG pathways related to prognosis of UCS were selected by gene set variation analysis (GSVA). The pyrimidine metabolism (P < 0.001, R = -0.470) was the key pathway coexpressed with RALGPS1. We considered that aberrant JUP significantly regulated RALGPS1-87608-AT and the pyrimidine metabolism pathway might play a significant part in the metastasis and prognosis of UCS.

Apoptosis - Fueling the oncogenic fire

Apoptosis, the most extensively studied form of programmed cell death, is essential for organismal homeostasis. Apoptotic cell death has widely been reported as a tumor suppressor mechanism. However, recent studies have shown that apoptosis exerts noncanonical functions and may paradoxically promote tumor growth and metastasis. The hijacking of apoptosis by cancer cells may arise at different levels, either via the interaction of apoptotic cells with their local or distant microenvironment, or through the abnormal pro-oncogenic roles of the main apoptosis effectors, namely caspases and mitochondria, particularly upon failed apoptosis. In this review, we highlight some of the recently described mechanisms by which apoptosis and these effectors may promote cancer aggressiveness. We believe that a better understanding of the noncanonical roles of apoptosis may be crucial for developing more efficient cancer therapies.

A cancer ubiquitome landscape identifies metabolic reprogramming as target of Parkin tumor suppression

Changes in metabolism that affect mitochondrial and glycolytic networks are hallmarks of cancer, but their impact in disease is still elusive. Using global proteomics and ubiquitome screens, we now show that Parkin, an E3 ubiquitin ligase and key effector of mitophagy altered in Parkinson's disease, shuts off mitochondrial dynamics and inhibits the non-oxidative phase of the pentose phosphate pathway. This blocks tumor cell movements, creates metabolic and oxidative stress, and inhibits primary and metastatic tumor growth. Uniformly down-regulated in cancer patients, Parkin tumor suppression requires its E3 ligase function, is reversed by antioxidants, and is independent of mitophagy. These data demonstrate that cancer metabolic networks are potent oncogenes directly targeted by endogenous tumor suppression.

Identification and Functional Characterization of Novel MYC-Regulated Long Noncoding RNAs in Group 3 Medulloblastoma

Simple Summary

Medulloblastoma is the most common malignant pediatric brain tumor, which accounts for approximately 20% of all childhood brain tumors. To date, no pharmacological approaches are decisive in the treatment of this cancer, while the secondary effects of conventional therapies as chemotherapy, radiotherapy or surgical interventions heavily affect the quality of life of patients. This requires the rapid development of alternative molecular therapies, which are the future challenge of personalized medicine. In this context, we addressed our research towards the most aggressive form of Medulloblastoma to identify novel genes responsible for its onset and/or progression. We discovered three newly implicated genes, for which we highlighted a contribution in the control of cancer cell features. Deepening into the Medulloblastoma biology, this study represents a further step forward for the development of molecular therapies in the era of precision oncology.

Abstract

The impact of protein-coding genes on cancer onset and progression is a well-established paradigm in molecular oncology. Nevertheless, unveiling the contribution of the noncoding genes—including long noncoding RNAs (lncRNAs)—to tumorigenesis represents a great challenge for personalized medicine, since they (i) constitute the majority of the human genome, (ii) are essential and flexible regulators of gene expression and (iii) present all types of genomic alterations described for protein-coding genes. LncRNAs have been increasingly associated with cancer, their highly tissue- and cancer type-specific expression making them attractive candidates as both biomarkers and therapeutic targets. Medulloblastoma is one of the most common malignant pediatric brain tumors. Group 3 is the most aggressive subgroup, showing the highest rate of metastasis at diagnosis. Transcriptomics and reverse genetics approaches were combined to identify lncRNAs implicated in Group 3 Medulloblastoma biology. Here we present the first collection of lncRNAs dependent on the activity of the MYC oncogene, the major driver gene of Group 3 Medulloblastoma. We assessed the expression profile of selected lncRNAs in Group 3 primary tumors and functionally characterized these species. Overall, our data demonstrate the direct involvement of three lncRNAs in Medulloblastoma cancer cell phenotypes.

Targeting Mitochondrial Metabolism in Clear Cell Carcinoma of the Ovaries

Ovarian clear cell carcinoma (OCCC) is a rare but chemorefractory tumor. About 50% of all OCCC patients have inactivating mutations of ARID1A, a member of the SWI/SNF chromatin-remodeling complex. Members of the SWI/SNF remodeling have emerged as regulators of the energetic metabolism of mammalian cells; however, the role of ARID1A as a modulator of the mitochondrial metabolism in OCCCs is yet to be defined. Here, we show that ARID1A loss results in increased mitochondrial metabolism and renders ARID1A-mutated cells increasingly and selectively dependent on it. The increase in mitochondrial activity following ARID1A loss is associated with increase in c-Myc expression and increased mitochondrial number and reduction of their size consistent with a higher mitochondrial cristae/outer membrane ratio. Significantly, preclinical testing of the complex I mitochondrial inhibitor IACS-010759 showed it extends overall survival in a preclinical model of ARID1A-mutated OCCC. These findings provide for the targeting mitochondrial activity in ARID1A-mutated OCCCs.

Mitochondrial dynamics in cancer stem cells

Many tumors are now understood to be heterogenous cell populations arising from a minority of epithelial-like cancer stem cells (CSCs). CSCs demonstrate distinctive metabolic signatures from the more differentiated surrounding tumor bulk that confer resistance to traditional chemotherapeutic regimens and potential for tumor relapse. Many CSC phenotypes including metabolism, epithelial-to-mesenchymal transition, cellular signaling pathway activity, and others, arise from altered mitochondrial function and turnover, which are regulated by constant cycles of mitochondrial fusion and fission. Further, recycling of mitochondria through mitophagy in CSCs is associated with maintenance of reactive oxygen species levels that dictate gene expression. The protein machinery that drives mitochondrial dynamics is surprisingly simple and may represent attractive new therapeutic avenues to target CSC metabolism and selectively eradicate tumor-generating cells to reduce the risks of metastasis and relapse for a variety of tumor types.

Mitochondria: The metabolic switch of cellular oncogenic transformation

Mitochondria, well recognized as the "powerhouse" of cells, are maternally inherited organelles with bacterial ancestry that play essential roles in a myriad of cellular functions. It has become profoundly evident that mitochondria regulate a wide array of cellular and metabolic functions, including biosynthetic metabolism, cell signaling, redox homeostasis, and cell survival. Correspondingly, defects in normal mitochondrial functioning have been implicated in various human malignancies. Cancer development involves the activation of oncogenes, inactivation of tumor suppressor genes, and impairment of apoptotic programs in cells. Mitochondria have been recognized as the site of key metabolic switches for normal cells to acquire a malignant phenotype. This review outlines the role of mitochondria in human malignancies and highlights potential aspects of mitochondrial metabolism that could be targeted for therapeutic development.

Roles of mitochondria in the hallmarks of metastasis

Although mitochondrial contributions to cancer have been recognised for approximately a century, given that mitochondrial DNA (mtDNA) is dwarfed by the size of the nuclear genome (nDNA), nuclear genetics has represented a focal point in cancer biology, often at the expense of mtDNA and mitochondria. However, genomic sequencing and advances in in vivo models underscore the importance of mtDNA and mitochondria in cancer and metastasis. In this review, we explore the roles of mitochondria in the four defined 'hallmarks of metastasis': motility and invasion, microenvironment modulation, plasticity and colonisation. Biochemical processes within the mitochondria of both cancer cells and the stromal cells with which they interact are critical for each metastatic hallmark. We unravel complex dynamics in mitochondrial contributions to cancer, which are context-dependent and capable of either promoting metastasis or being leveraged to prevent it at various points of the metastatic cascade. Ultimately, mitochondrial contributions to cancer and metastasis are rooted in the capacity of these organelles to tune metabolic and genetic responses to dynamic microenvironmental cues.

Small Extracellular Vesicle Regulation of Mitochondrial Dynamics Reprograms a Hypoxic Tumor Microenvironment

The crosstalk between tumor cells and the adjacent normal epithelium contributes to cancer progression, but its regulators have remained elusive. Here, we show that breast cancer cells maintained in hypoxia release small extracellular vesicles (sEVs) that activate mitochondrial dynamics, stimulate mitochondrial movements, and promote organelle accumulation at the cortical cytoskeleton in normal mammary epithelial cells. This results in AKT serine/threonine kinase (Akt) activation, membrane focal adhesion turnover, and increased epithelial cell migration. RNA sequencing profiling identified integrin-linked kinase (ILK) as the most upregulated pathway in sEV-treated epithelial cells, and genetic or pharmacologic targeting of ILK reversed mitochondrial reprogramming and suppressed sEV-induced cell movements. In a three-dimensional (3D) model of mammary gland morphogenesis, sEV treatment induced hallmarks of malignant transformation, with deregulated cell death and/or cell proliferation, loss of apical-basal polarity, and appearance of epithelial-to-mesenchymal transition (EMT) markers. Therefore, sEVs released by hypoxic breast cancer cells reprogram mitochondrial dynamics and induce oncogenic changes in a normal mammary epithelium.

Impact of pharmacological agents on mitochondrial function: a growing opportunity?

Present-day drug therapies provide clear beneficial effects as many diseases can be driven into remission and the symptoms of others can be efficiently managed; however, the success of many drugs is limited due to both patient non-compliance and adverse off-target or toxicity-induced effects. There is emerging evidence that many of these side effects are caused by drug-induced impairment of mitochondrial function and eventual mitochondrial dysfunction. It is imperative to understand how and why drug-induced side effects occur and how mitochondrial function is affected. In an aging population, age-associated drug toxicity is another key area of focus as the majority of patients on medication are older. Therefore, with an aging population possessing subtle or even more dramatic individual differences in mitochondrial function, there is a growing necessity to identify and understand early on potentially significant drug-associated off-target effects and toxicity issues. This will not only reduce the number of unwanted side effects linked to mitochondrial toxicity but also identify useful mitochondrial-modulating agents. Mechanistically, many successful drug classes including diabetic treatments, antibiotics, chemotherapies and antiviral agents have been linked to mitochondrial targeted effects. This is a growing area, with research to repurpose current medications affecting mitochondrial function being assessed in cancer, the immune system and neurodegenerative disorders including Parkinson's disease. Here, we review the effects that pharmacological agents have on mitochondrial function and explore the opportunities from these effects as potential disease treatments. Our focus will be on cancer treatment and immune modulation.

Identification of Prognostic and Metastatic Alternative Splicing Signatures in Kidney Renal Clear Cell Carcinoma

Background: Kidney renal clear cell carcinoma (KIRC) is the malignancy originated from the renal epithelium, with a high rate of distant metastasis. Aberrant alternative splicing (AS) of pre-mRNA are widely reported to be involved in the tumorigenesis and metastasis of multiple cancers. The aim of this study is to explore the mechanism of alternative splicing events (ASEs) underlying tumorigenesis and metastasis of KIRC. Methods: RNA-seq of 537 KIRC samples downloaded from the TCGA database and ASEs data from the TCGASpliceSeq database were used to identify ASEs in patients with KIRC. The univariate and Lasso regression analysis were used to screen the most significant overall survival-related ASEs (OS-SEs). Based on those, the OS-SEs model was proposed. The interaction network of OS-SEs and splicing factors (SFs) with absolute value of correlation coefficient value >0.750 was constructed by Pearson correlation analysis. The OS-SEs significantly related to distant metastasis and clinical stage were identified by non-parametric test, and those were also integrated into co-expression analysis with prognosis-related Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways identified by Gene Set Variation Analysis (GSVA). ASEs with significance were selected for multiple online database validation. Results: A total of prognostic 6,081 overall survival-related ASEs (OS-SEs) were identified by univariate Cox regression analysis and a prediction model was constructed based on 5 OS-SEs screened by Lasso regression with the Area Under Curve of 0.788. Its risk score was also illustrated to be an independent predictor, which the good reliability of the model. Among 390 identified candidate SFs, DExD-Box Helicase 39B (DDX39B) was significantly correlated with OS and metastasis. After external database validation, Retained Intron of Ras Homolog Family Member T2 (RHOT2) and T-Cell Immune Regulator 1 (TCIRG1) were identified. In the co-expression analysis, overlapped co-expression signal pathways for RHOT2 and TCIRG1 were sphingolipid metabolism and N-glycan biosynthesis. Conclusions: Based on the results of comprehensive bioinformatic analysis, we proposed that aberrant DDX39B regulated RHOT2-32938-RI and TCIRG1-17288-RI might be associated with the tumorigenesis, metastasis, and poor prognosis of KIRC via sphingolipid metabolism or N-glycan biosynthesis pathway.

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.