Ghost mitochondria drive metastasis through adaptive GCN2/Akt therapeutic vulnerability

Cardiolipin Dysregulation in Glioblastoma-Effects on Mitochondrial Function Tumor Cell Death and Sensitivity to Mitochondria-Targeting Drugs

Biological systems do not exist in isolation. Analogous to the intricate design of a spider web, the metabolic adaptations propagated by glioblastoma cells are interlaced, creating a "defense mechanism" that increases the likelihood of mutagenesis and proliferation, while mitigating stress-induced tumor cell death and immune evasion. Previous studies have observed the role of cardiolipin (CL) in the electron transport chain (ETC) function and several other intracellular signaling pathways. Our review provides a synopsis of the existing knowledge about CL in glioblastoma and its complex relationship with metabolic reprogramming at the subcellular level. Through a meticulous examination of CL defects due to its biogenesis and stress-induced modifications, we seek to elucidate the multifaceted connections between aberrant CL variants and the metabolic alterations that underlie glioblastoma progression. A comprehensive grasp of these mechanisms could provide future direction in designing chemotherapeutic agents that selectively target glioblastoma, are less harmful to normal cells, and therefore, may extend patient survival.

Transcription factor A, mitochondrial promotes lymph node metastasis and lymphangiogenesis in epithelial ovarian carcinoma

Background

Mitochondria play a central, multifunctional role in cancer progression. However, the mechanism of mitochondrial genes in epithelial ovarian cancer (EOC) remains unclear. This study aimed to screen candidate mitochondrial genes in EOC and then to investigate their biological functions and potential mechanisms.

Methods

We downloaded Gene Expression Omnibus RNA-seq profiles and identified mitochondrial differentially expressed genes in EOC by bioinformatics analysis. Transcription factor A, mitochondrial (TFAM) expression in EOC tissues was determined by immunohistochemistry. In vitro assays were applied to clarify TFAM function in EOC.

Results

The bioinformatics analysis results showed that the mitochondrial genes TFAM, HSPE1, and CYC1 were significantly upregulated (P < 0.05) in EOC, and their upregulation was associated with a poor prognosis. TFAM was highly expressed in EOC tissues and significantly associated with clinical stage (P = 0.004), lymph node metastasis (P = 0.043), and overall survival (P < 0.05). Silencing TFAM in EOC cells significantly inhibited cell proliferation and migration and induced cell apoptosis (P < 0.05).

Conclusion

TFAM promotes EOC cell secretion of VEGF-A, VEGF-C, VEGF-D, lymphangiogenesis, and EOC lymph node metastasis. Our results may provide new insights into the biological functions and potential mechanisms of TFAM in EOC, which might provide new targets for EOC diagnosis and treatment.

BRAFV600 and ErbB inhibitors directly activate GCN2 in an off-target manner to limit cancer cell proliferation

Targeted kinase inhibitors are well known for their promiscuity and off-target effects. Herein, we define an off-target effect in which several clinical BRAFV600 inhibitors, including the widely used dabrafenib and encorafenib, interact directly with GCN2 to activate the Integrated Stress Response and ATF4. Blocking this off-target effect by co-drugging with a GCN2 inhibitor in A375 melanoma cells causes enhancement rather than suppression of cancer cell outgrowth, suggesting that the off-target activation of GCN2 is detrimental to these cells. This result is mirrored in PC9 lung cancer cells treated with erlotinib, an EGFR inhibitor, that shares the same off-target activation of GCN2. Using an in silico kinase inhibitor screen, we identified dozens of FDA-approved drugs that appear to share this off-target activation of GCN2 and ATF4. Thus, GCN2 activation may modulate the therapeutic efficacy of some kinase inhibitors, depending on the cancer context.

Clinical research framework proposal for ketogenic metabolic therapy in glioblastoma

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, with a universally lethal prognosis despite maximal standard therapies. Here, we present a consensus treatment protocol based on the metabolic requirements of GBM cells for the two major fermentable fuels: glucose and glutamine. Glucose is a source of carbon and ATP synthesis for tumor growth through glycolysis, while glutamine provides nitrogen, carbon, and ATP synthesis through glutaminolysis. As no tumor can grow without anabolic substrates or energy, the simultaneous targeting of glycolysis and glutaminolysis is expected to reduce the proliferation of most if not all GBM cells. Ketogenic metabolic therapy (KMT) leverages diet-drug combinations that inhibit glycolysis, glutaminolysis, and growth signaling while shifting energy metabolism to therapeutic ketosis. The glucose-ketone index (GKI) is a standardized biomarker for assessing biological compliance, ideally via real-time monitoring. KMT aims to increase substrate competition and normalize the tumor microenvironment through GKI-adjusted ketogenic diets, calorie restriction, and fasting, while also targeting glycolytic and glutaminolytic flux using specific metabolic inhibitors. Non-fermentable fuels, such as ketone bodies, fatty acids, or lactate, are comparatively less efficient in supporting the long-term bioenergetic and biosynthetic demands of cancer cell proliferation. The proposed strategy may be implemented as a synergistic metabolic priming baseline in GBM as well as other tumors driven by glycolysis and glutaminolysis, regardless of their residual mitochondrial function. Suggested best practices are provided to guide future KMT research in metabolic oncology, offering a shared, evidence-driven framework for observational and interventional studies.

Novel insights into the GCN2 pathway and its targeting. Therapeutic value in cancer and lessons from lung fibrosis development

Defining the mechanisms that allow cells to adapt to environmental stress is critical for understanding the progression of chronic diseases and identifying relevant drug targets. Among these, activation of the pathway controlled by the eIF2-alpha kinase GCN2 is critical for translational and metabolic reprogramming of the cell in response to various metabolic, proteotoxic, and ribosomal stressors. However, its role has frequently been investigated through the lens of a stress pathway signaling via the eIF2α-activating transcription factor 4 (ATF4) downstream axis, while recent advances in the field have revealed that the GCN2 pathway is more complex than previously thought. Indeed, this kinase can be activated through a variety of mechanisms, phosphorylate substrates other than eIF2α, and regulate cell proliferation in a steady state. This review presents recent findings regarding the fundamental mechanisms underlying GCN2 signaling and function, as well as the development of drugs that modulate its activity. Furthermore, by comparing the literature on GCN2's antagonistic roles in two challenging pathologies, cancer and pulmonary diseases, the benefits, and drawbacks of GCN2 targeting, particularly inhibition, are discussed.

Multifaceted role of GCN2 in tumor adaptation and therapeutic targeting

Tumor cells voraciously consume nutrients from their environment to facilitate rapid proliferation, necessitating effective strategies to manage nutrient scarcity during tumor growth and progression. A pivotal regulatory mechanism in this context is the Integrated Stress Response (ISR), which ensures cellular homeostasis under conditions such as endoplasmic reticulum stress, the unfolded protein response, and nutrient deprivation. Within the ISR framework, the kinase GCN2 is critical, orchestrating a myriad of cellular processes including the inhibition of protein synthesis, the enhancement of amino acid transport, autophagy initiation, and angiogenesis. These processes collectively enable tumor survival and adaptation under nutrient-limited conditions. Furthermore, GCN2-mediated pathways may induce apoptosis, a property exploited by specific therapeutic agents. Leveraging extensive datasets from TCGA, GEO, and GTEx projects, we conducted a pan-cancer analysis to investigate the prognostic significance of GCN2 expression across diverse cancer types. Our analysis indicates that GCN2 expression significantly varies and correlates with both adverse and favorable prognoses depending on the type of cancer, illustrating its complex role in tumorigenesis. Importantly, GCN2 also modulates the tumor immune microenvironment, influencing immune checkpoint expression and the functionality of immune cells, thereby affecting immunotherapy outcomes. This study highlights the potential of targeting GCN2 with specific inhibitors, as evidenced by their efficacy in preclinical models to augment treatment responses and combat resistance in oncology. These findings advocate for a deeper exploration of GCN2's multifaceted roles, which could pave the way for novel targeted therapies in cancer treatment, aiming to improve clinical outcomes.

Emerging Paradigms in Cancer Metastasis: Ghost Mitochondria, Vasculogenic Mimicry, and Polyploid Giant Cancer Cells

The capacity of cancer cells to migrate from a primary tumor, disseminate throughout the body, and eventually establish secondary tumors is a fundamental aspect of metastasis. A detailed understanding of the cellular and molecular mechanisms underpinning this multifaceted process would facilitate the rational development of therapies aimed at treating metastatic disease. Although various hypotheses and models have been proposed, no single concept fully explains the mechanism of metastasis or integrates all observations and experimental findings. Recent advancements in metastasis research have refined existing theories and introduced new ones. This review evaluates several novel/emerging theories, focusing on ghost mitochondria (GM), vasculogenic mimicry (VM), and polyploid giant cancer cells (PGCCs).

Suppressing mitochondrial inner membrane protein (IMMT) inhibits the proliferation of breast cancer cells through mitochondrial remodeling and metabolic regulation

Metabolic reprogramming is widely recognized as a hallmark of malignant tumors, and the targeting of metabolism has emerged as an appealing approach for cancer treatment. Mitochondria, as pivotal organelles, play a crucial role in the metabolic regulation of tumor cells, and their morphological and functional alterations are intricately linked to the biological characteristics of tumors. As a key regulatory subunit of mitochondria, mitochondrial inner membrane protein (IMMT), plays a vital role in degenerative diseases, but its role in tumor is almost unknown. The objective of this research was to investigate the roles that IMMT play in the development and progression of breast cancer (BC), as well as to elucidate the underlying biological mechanisms that drive these effects. In this study, it was confirmed that the expression of IMMT in BC tissues was significantly higher than that in normal tissues. The analysis of The Cancer Genome Atlas (TCGA) database revealed that IMMT can serve as an independent prognostic factor for BC patients. Additionally, verification in clinical specimens of BC demonstrated a positive association between high IMMT expression and larger tumor size (> 2 cm), Ki-67 expression (> 15%), and HER-2 status. Furthermore, in vitro experiments have substantiated that the suppression of IMMT expression resulted in a reduction in cell proliferation and alterations in mitochondrial cristae, concomitant with the liberation of cytochrome c, but it did not elicit mitochondrial apoptosis. Through Gene Set Enrichment Analysis (GSEA) analysis, we have predicted the associated metabolic genes and discovered that IMMT potentially modulates the advancement of BC through its interaction with 16 metabolic-related genes, and the changes in glycolysis related pathways have been validated in BC cell lines after IMMT inhibition. Consequently, this investigation furnishes compelling evidence supporting the classification of IMMT as prognostic marker in BC, and underscoring its prospective utility as a novel target for metabolic therapy.

Loss of Myo19 increases metastasis by enhancing microenvironmental ROS gradient and chemotaxis

Tumor metastasis involves cells migrating directionally in response to external chemical signals. Reactive oxygen species (ROS) in the form of H2O2 has been demonstrated as a chemoattractant for neutrophils but its spatial characteristics in tumor microenvironment and potential role in tumor cell dissemination remain unknown. Here we investigate the spatial ROS distribution in 3D tumor spheroids and identify a ROS concentration gradient in spheroid periphery, which projects into a H2O2 gradient in tumor microenvironment. We further reveal the role of H2O2 gradient to induce chemotaxis of tumor cells by activating Src and subsequently inhibiting RhoA. Finally, we observe that the absence of mitochondria cristae remodeling proteins including the mitochondria-localized actin motor Myosin 19 (Myo19) enhances ROS gradient and promotes tumor dissemination. Myo19 downregulation is seen in many tumors, and Myo19 expression is negatively associated with tumor metastasis in vivo. Together, our study reveals the chemoattractant role of tumor microenvironmental ROS and implies the potential impact of mitochondria cristae disorganization on tumor invasion and metastasis.

Human and animal intestinal commensals and probiotics vs modern challenges of biosafety: problems and prospects

The appearance of an array of data on the study of the intestinal microbiota in Metazoa has significantly expanded our understanding of the role of commensals in the control of a wide range of physiological functions in higher organisms in norm and pathology. In the intestine, where the microbial load significantly exceeds the number of microorganisms of other ecosystems, the components of the intestinal microbiota are a constant source of stimuli that induce activation of the host immune system. The introduction into practice of biomedical research of innovative high-resolution methods, including   multi-omics technologies, has brought data that change our understanding of intestinal commensals, including probiotics with GRAS status, widely used in medicine, agriculture and biotechnology. The ability of these bacteria to induce negative processes in the host body that are beneficial for bacterial proliferation and expansion revealed a clear lack of our knowledge about the logic of their life and the mechanisms of interaction with eukaryotic cells. This determines the urgent need for comprehensive research of probiotics and the development of standardization of their safety assessment. Apriori's confidence in the exceptional benefit of the bacteria widely used in medicine, agriculture and biotechnology has determined the seriously omission in our control system today - the lack of standardization of studies for the safety assessment of bacteria with GRAS status . The moment has come when it became clear that this gap should be promptly filled and that only exact understanding the molecular base of interacting the microbes with eukaryotic cells can provide the foundation for effective practical developments in controlling the evolution of bacterial virulence and probiotic safety strategy, as well as the competent use of genetic technologies for monitoring the environment and managing infectious processes, thus avoiding the dramatic consequences of large-scale interventions in the micro and macro worlds.

Therapeutic targets for endometriosis: Genome-wide Mendelian randomization and colocalization analyses

BACKGROUND

Endometriosis (EM) greatly affects women's reproductive health, identifying new drug targets for EM is urgently needed. This study utilizes comprehensive genome-wide Mendelian randomization (MR) and colocalization analyses, using genomic data, to identify potential therapeutic approaches for EM.

METHODS

Genome-wide cis-expression quantitative trait loci (cis-eQTL) data were obtained from GTEx V8, which included 838 participants across 49 tissues or cells, and the eQTLGen consortium, which included 31,684 participants. Genome-wide association analysis (GWAS) data for EM were sourced from the FinnGen study, which consisted of 8,288 cases and 68,969 controls, as well as the UK Biobank study, which included 1,496 cases and 359,698 controls. This study utilized MR analysis to assess the correlation between genes and the risk of EM. Subsequently, colocalization analysis was conducted to investigate potential shared causal variants between the identified genes and EM.

RESULTS

After conducting MR and colocalization analyses, we identified a total of 13 genes that showed significant evidence of colocalization. These genes are considered promising therapeutic candidates for treating EM. Among them, inner membrane mitochondrial protein (IMMT), src kinase associated phosphoprotein 1 (SKAP1), lysine methyltransferase 5A (KMT5A), KLF transcription factor 12 (KLF12), GRB10 interacting GYF protein 1 (GIGYF1), Wnt family member 7A (WNT7A), Sad1 and UNC84 domain containing 1 (SUN1), and poly (ADP-ribose) polymerase family member 3 (PARP3) were found to have positive associations with the risk of EM. On the other hand, progestin and adipoQ receptor family member 8 (PAQR8), adaptor related protein complex 3 subunit mu 1 (AP3M1), surfeit 6 (SURF6), TUB bipartite transcription factor (TUB), and DNA polymerase delta interacting protein 2 (POLDIP2) were found to have inverse relationships with the risk of EM.

CONCLUSIONS

Through genome-wide MR studies, a comprehensive set of genes associated with EM has been identified. Among them, IMMT, PAQR8, SKAP1, KMT5A, AP3M1, SURF6, KLF12, GIGYF1, TUB, WNT7A, SUN1, POLDIP2, and PARP3 show potential as therapeutic targets for EM treatment. Nonetheless, it is crucial to conduct further rigorous investigations to validate these prospects.

Role of mitochondrial alterations in human cancer progression and cancer immunity

Dysregulating cellular metabolism is one of the emerging cancer hallmarks. Mitochondria are essential organelles responsible for numerous physiologic processes, such as energy production, cellular metabolism, apoptosis, and calcium and redox homeostasis. Although the "Warburg effect," in which cancer cells prefer aerobic glycolysis even under normal oxygen circumstances, was proposed a century ago, how mitochondrial dysfunction contributes to cancer progression is still unclear. This review discusses recent progress in the alterations of mitochondrial DNA (mtDNA) and mitochondrial dynamics in cancer malignant progression. Moreover, we integrate the possible regulatory mechanism of mitochondrial dysfunction-mediated mitochondrial retrograde signaling pathways, including mitochondrion-derived molecules (reactive oxygen species, calcium, oncometabolites, and mtDNA) and mitochondrial stress response pathways (mitochondrial unfolded protein response and integrated stress response) in cancer progression and provide the possible therapeutic targets. Furthermore, we discuss recent findings on the role of mitochondria in the immune regulatory function of immune cells and reveal the impact of the tumor microenvironment and metabolism remodeling on cancer immunity. Targeting the mitochondria and metabolism might improve cancer immunotherapy. These findings suggest that targeting mitochondrial retrograde signaling in cancer malignancy and modulating metabolism and mitochondria in cancer immunity might be promising treatment strategies for cancer patients and provide precise and personalized medicine against cancer.

Global Impacts of Western Diet and Its Effects on Metabolism and Health: A Narrative Review

The Western diet is a modern dietary pattern characterized by high intakes of pre-packaged foods, refined grains, red meat, processed meat, high-sugar drinks, candy, sweets, fried foods, conventionally raised animal products, high-fat dairy products, and high-fructose products. The present review aims to describe the effect of the Western pattern diet on the metabolism, inflammation, and antioxidant status; the impact on gut microbiota and mitochondrial fitness; the effect of on cardiovascular health, mental health, and cancer; and the sanitary cost of the Western diet. To achieve this goal, a consensus critical review was conducted using primary sources, such as scientific articles, and secondary sources, including bibliographic indexes, databases, and web pages. Scopus, Embase, Science Direct, Sports Discuss, ResearchGate, and the Web of Science were used to complete the assignment. MeSH-compliant keywords such "Western diet", "inflammation", "metabolic health", "metabolic fitness", "heart disease", "cancer", "oxidative stress", "mental health", and "metabolism" were used. The following exclusion criteria were applied: (i) studies with inappropriate or irrelevant topics, not germane to the review's primary focus; (ii) Ph.D. dissertations, proceedings of conferences, and unpublished studies. This information will allow for a better comprehension of this nutritional behavior and its effect on an individual's metabolism and health, as well as the impact on national sanitary systems. Finally, practical applications derived from this information are made.

Supervised Learning and Multi-Omics Integration Reveals Clinical Significance of Inner Membrane Mitochondrial Protein (IMMT) in Prognostic Prediction, Tumor Immune Microenvironment and Precision Medicine for Kidney Renal Clear Cell Carcinoma

Kidney renal clear cell carcinoma (KIRC) accounts for approximately 75% of all renal cancers. The prognosis for patients with metastatic KIRC is poor, with less than 10% surviving five years after diagnosis. Inner membrane mitochondrial protein (IMMT) plays a crucial role in shaping the inner mitochondrial membrane (IMM), regulation of metabolism and innate immunity. However, the clinical relevance of IMMT in KIRC is not yet fully understood, and its role in shaping the tumor immune microenvironment (TIME) remains unclear. This study aimed to investigate the clinical significance of IMMT in KIRC using a combination of supervised learning and multi-omics integration. The supervised learning principle was applied to analyze a TCGA dataset, which was downloaded and split into training and test datasets. The training dataset was used to train the prediction model, while the test and the entire TCGA dataset were used to evaluate its performance. Based on the risk score, the cutoff between the low and high IMMT group was set at median value. A Kaplan-Meier curve, receiver operating characteristic (ROC) curve, principal component analysis (PCA) and Spearman's correlation were conducted to evaluate the prediction ability of the model. Gene Set Enrichment Analysis (GSEA) was used to investigate the critical biological pathways. Immunogenicity, immunological landscape and single-cell analysis were performed to examine the TIME. Databases including Gene Expression Omnibus (GEO), Human Protein Atlas (HPA) and Clinical Proteomic Tumor Analysis Consortium (CPTAC) were employed for inter-database verification. Pharmacogenetic prediction was analyzed via single-guide RNA (sgRNA)-based drug sensitivity screening using Q-omics v.1.30. Low expressions of IMMT in tumor predicted dismal prognosis in KIRC patients and correlated with KIRC progression. GSEA revealed that low expressions of IMMT were implicated in mitochondrial inhibition and angiogenetic activation. In addition, low IMMT expressions had associations with reduced immunogenicity and an immunosuppressive TIME. Inter-database verification corroborated the correlation between low IMMT expressions, KIRC tumors and the immunosuppressive TIME. Pharmacogenetic prediction identified lestaurtinib as a potent drug for KIRC in the context of low IMMT expressions. This study highlights the potential of IMMT as a novel biomarker, prognostic predictor and pharmacogenetic predictor to inform the development of more personalized and effective cancer treatments. Additionally, it provides important insights into the role of IMMT in the mechanism underlying mitochondrial activity and angiogenesis development in KIRC, which suggests IMMT as a promising target for the development of new therapies.

Mitochondria in cancer: clean windmills or stressed tinkerers?

There is now a consensus that mitochondria are important tumor drivers, sophisticated biological machines that can engender a panoply of key disease traits. How this happens, however, is still mostly elusive. The opinion presented here is that what cancer exploits are not the normal mitochondria of oxygenated and nutrient-replete tissues, but the unfit, damaged, and dysfunctional organelles generated by the hostile environment of tumor growth. These 'ghost' mitochondria survive quality control and thwart cell death to relay multiple comprehensive 'danger signals' of metabolic starvation, cellular stress, and reprogrammed gene expression. The result is a new, treacherous cellular phenotype, proliferatively quiescent but highly motile, that enables tumor cell escape from a threatening environment and colonization of distant, more favorable sites (metastasis).

Multi-omics and experimental analysis unveil theragnostic value and immunological roles of inner membrane mitochondrial protein (IMMT) in breast cancer

BACKGROUND

The inner membrane mitochondrial protein (IMMT) is a central unit of the mitochondrial contact site and cristae organizing system (MICOS). While researchers continue to demonstrate the physiological function of IMMT in regulating mitochondrial dynamics and preserving mitochondrial structural integrity, the roles of IMMT in clinicopathology, the tumor immune microenvironment (TIME), and precision oncology in breast cancer (BC) remain unclear.

METHODS

Multi-omics analysis was used here to evaluate the diagnostic and prognostic value of IMMT. Web applications aimed at analyzing the whole tumor tissue, single cells, and spatial transcriptomics were used to examine the relationship of IMMT with TIME. Gene set enrichment analysis (GSEA) was employed to determine the primary biological impact of IMMT. Experimental verification using siRNA knockdown and clinical specimens of BC patients confirmed the mechanisms behind IMMT on BC cells and the clinical significance, respectively. Potent drugs were identified by accessing the data repositories of CRISPR-based drug screenings.

RESULTS

High IMMT expression served as an independent diagnostic biomarker, correlated with advanced clinical status, and indicated a poor relapse-free survival (RFS) rate for patients with BC. Although, the contents of Th1, Th2, MSC, macrophages, basophil, CD4 + T cell and B cell, and TMB levels counteracted the prognostic significance. Single-cell level and whole-tissue level analyses revealed that high IMMT was associated with an immunosuppressive TIME. GSEA identified IMMT perturbation as involved in cell cycle progression and mitochondrial antioxidant defenses. Experimental knockdown of IMMT impeded the migration and viability of BC cells, arrested the cell cycle, disturbed mitochondrial function, and increased the ROS level and lipid peroxidation. The clinical values of IMMT were amenable to ethnic Chinese BC patients, and can be extrapolated to some other cancer types. Furthermore, we discovered that pyridostatin acted as a potent drug candidate in BC cells harboring an elevated IMMT expression.

CONCLUSION

This study combined a multi-omics survey with experimental verification to reveal the novel clinical significance of IMMT in BC, demonstrating its role in TIME, cancer cell growth and mitochondrial fitness, and identified pyridostatin as a promising drug candidate for the development of precision medicine.

Radiation resistance of cancer cells caused by mitochondrial dysfunction depends on SIRT3-mediated mitophagy

Radiation resistance is the leading cause of radiotherapy failure in patients with cancer. Enhanced DNA damage repair is the main reason for cancer cells to develop resistance to radiation. Autophagy has been widely reported to be linked to increased genome stability and radiation resistance. Mitochondria are highly involved in the cell response to radiotherapy. However, the autophagy subtype mitophagy has not been studied in terms of genome stability. We have previously demonstrated that mitochondrial dysfunction is the cause of radiation resistance in tumour cells. In the present study, we found that SIRT3 was highly expressed in colorectal cancer cells with mitochondrial dysfunction, leading to PINK1/Parkin-mediated mitophagy. Excessive activation of mitophagy enhanced DNA damage repair, therefore promoting the resistance of tumour cells to radiation. Mechanistically, mitophagy resulted in decreased RING1b expression, which led to a reduction in the ubiquitination of histone H2A at K119, thereby enhancing the repair of DNA damage caused by radiation. Additionally, high expression of SIRT3 was related to a poor tumour regression grade in rectal cancer patients treated with neoadjuvant radiotherapy. These findings suggest that restoring mitochondrial function could be an effective method for increasing the radiosensitivity of patients with colorectal cancer.

Mitochondrial fitness and cancer risk

Changes in metabolism are a hallmark of cancer, but molecular signatures of altered bioenergetics to aid in clinical decision-making do not currently exist. We recently identified a group of human tumors with constitutively reduced expression of the mitochondrial structural protein, Mic60, also called mitofilin or inner membrane mitochondrial protein (IMMT). These Mic60-low tumors exhibit severe loss of mitochondrial fitness, paradoxically accompanied by increased metastatic propensity and upregulation of a unique transcriptome of Interferon (IFN) signaling and Senescence-Associated Secretory Phenotype (SASP). Here, we show that an optimized, 11-gene signature of Mic60-low tumors is differentially expressed in multiple malignancies, compared to normal tissues, and correlates with poor patient outcome. When analyzed in three independent patient cohorts of pancreatic ductal adenocarcinoma (PDAC), the Mic60-low gene signature was associated with aggressive disease variants, local inflammation, FOLFIRINOX failure and shortened survival, independently of age, gender, or stage. Therefore, the 11-gene Mic60-low signature may provide an easily accessible molecular tool to stratify patient risk in PDAC and potentially other malignancies.

Miro proteins and their role in mitochondrial transfer in cancer and beyond

Mitochondria are organelles essential for tumor cell proliferation and metastasis. Although their main cellular function, generation of energy in the form of ATP is dispensable for cancer cells, their capability to drive their adaptation to stress originating from tumor microenvironment makes them a plausible therapeutic target. Recent research has revealed that cancer cells with damaged oxidative phosphorylation import healthy (functional) mitochondria from surrounding stromal cells to drive pyrimidine synthesis and cell proliferation. Furthermore, it has been shown that energetically competent mitochondria are fundamental for tumor cell migration, invasion and metastasis. The spatial positioning and transport of mitochondria involves Miro proteins from a subfamily of small GTPases, localized in outer mitochondrial membrane. Miro proteins are involved in the structure of the MICOS complex, connecting outer and inner-mitochondrial membrane; in mitochondria-ER communication; Ca²⁺ metabolism; and in the recycling of damaged organelles via mitophagy. The most important role of Miro is regulation of mitochondrial movement and distribution within (and between) cells, acting as an adaptor linking organelles to cytoskeleton-associated motor proteins. In this review, we discuss the function of Miro proteins in various modes of intercellular mitochondrial transfer, emphasizing the structure and dynamics of tunneling nanotubes, the most common transfer modality. We summarize the evidence for and propose possible roles of Miro proteins in nanotube-mediated transfer as well as in cancer cell migration and metastasis, both processes being tightly connected to cytoskeleton-driven mitochondrial movement and positioning.

GCN2: roles in tumour development and progression

GCN2 (general control nonderepessible 2) is an eIF2α kinase responsible for entirely rewiring the metabolism of cells when they are put under amino acid starvation stress. Recently, there has been renewed interest in GCN2 as a potential oncotarget, with several studies reporting the development of small molecule inhibitors. The foundation of this work is built upon biochemical and cellular data which suggest GCN2 may be aberrantly overexpressed and is responsible for keeping cells on ‘life-support’ while tumours undergo significant nutritional stress during tumorigenesis, allowing cancer stem cells to develop chemotherapeutic resistance. However, most studies which have investigated the role of GCN2 in cancer have been conducted in various cancer model systems, often under a specific set of stresses, mutational backgrounds and drug cocktails. This review aims to comprehensively summarise the biochemical, molecular and cellular literature associated with GCN2 and its role in various cancers and determine whether a consensus can be developed to discern under which circumstances we may wish to target GCN2.