SIRT4 inhibits malignancy progression of NSCLCs, through mitochondrial dynamics mediated by the ERK-Drp1 pathway

Mitochondrial signaling pathways and their role in cancer drug resistance

Mitochondria, traditionally known as cellular powerhouses, now emerge as critical signaling centers influencing cancer progression and drug resistance. The review highlights the role that apoptotic signaling, DNA mutations, mitochondrial dynamics and metabolism play in the development of resistance mechanisms and the advancement of cancer. Targeted approaches are discussed, with an emphasis on managing mitophagy, fusion, and fission of the mitochondria to make resistant cancer cells more susceptible to traditional treatments. Additionally, metabolic reprogramming can be used to effectively target metabolic enzymes such GLUT1, HKII, PDK, and PKM2 in order to avoid resistance mechanisms. Although there are potential possibilities for therapy, the complex structure of mitochondria and their subtle role in tumor development hamper clinical translation. Novel targeted medicines are put forth, providing fresh insights on combating drug resistance in cancer. The study also emphasizes the significance of glutamine metabolism, mitochondrial respiratory complexes, and apoptotic pathways as potential targets to improve treatment effectiveness against drug-resistant cancers. Combining complementary and nanoparticle-based techniques to target mitochondria has demonstrated encouraging results in the treatment of cancer, opening doors to reduce resistance and enable individualized treatment plans catered to the unique characteristics of each patient. Suggesting innovative approaches such as drug repositioning and mitochondrial drug delivery to enhance the efficacy of mitochondria-targeting therapies, presenting a pathway for advancements in cancer treatment. This thorough investigation is a major step forward in the treatment of cancer and has the potential to influence clinical practice and enhance patient outcomes.

Emerging role of sirtuins in non‑small cell lung cancer (Review)

Non‑small cell lung cancer (NSCLC) is a highly prevalent lung malignancy characterized by insidious onset, rapid progression and advanced stage at the time of diagnosis, making radical surgery impossible. Sirtuin (SIRT) is a histone deacetylase that relies on NAD+ for its function, regulating the aging process through modifications in protein activity and stability. It is intricately linked to various processes, including glycolipid metabolism, inflammation, lifespan regulation, tumor formation and stress response. An increasing number of studies indicate that SIRTs significantly contribute to the progression of NSCLC by regulating pathophysiological processes such as energy metabolism, autophagy and apoptosis in tumor cells through the deacetylation of histones or non‑histone proteins. The present review elaborates on the roles of different SIRTs and their mechanisms in NSCLC, while also summarizing novel therapeutic agents based on SIRTs. It aims to present new ideas and a theoretical basis for NSCLC treatment.

SIRT4 Protects Müller Glial Cells Against Apoptosis by Mediating Mitochondrial Dynamics and Oxidative Stress

SIRT4 is a member of the sirtuin family, which is related to mitochondrial function and possesses antioxidant and regulatory redox effects. Currently, the roles of SIRT4 in retinal Müller glial cells, oxidative stress, and mitochondrial function are still unclear. We confirmed, by immunofluorescence staining, that SIRT4 is located mainly in the mitochondria of retinal Müller glial cells. Using flow cytometry and Western blotting, we analyzed cell apoptosis, intracellular reactive oxygen species (ROS) levels, apoptotic and proapoptotic proteins, mitochondrial dynamics-related proteins, and mitochondrial morphology and number after the overexpression and downregulation of SIRT4 in rMC-1 cells. Neither the upregulation nor the downregulation of SIRT4 alone affected apoptosis. SIRT4 overexpression reduced intracellular ROS, reduced the BAX/BCL2 protein ratio, and increased the L-OPA/S-OPA1 ratio and the levels of the mitochondrial fusion protein MFN2 and the mitochondrial cleavage protein FIS1, increasing mitochondrial fusion. SIRT4 downregulation had the opposite effect. Mitochondria tend to divide after serum starvation for 24 h, and SIRT4 downregulation increases mitochondrial fragmentation and oxidative stress, leading to aggravated cell damage. The mitochondrial division inhibitor Mdivi-1 reduced oxidative stress levels and thus reduced cell damage caused by serum starvation. The overexpression of SIRT4 in rMC-1 cells reduced mitochondrial fragmentation caused by serum starvation, leading to mitochondrial fusion and reduced expression of cleaved caspase-3, thus alleviating the cellular damage caused by oxidative stress. Thus, we speculate that SIRT4 may protect retinal Müller glial cells against apoptosis by mediating mitochondrial dynamics and oxidative stress.

Mitochondrial dynamics in pulmonary disease: Implications for the potential therapeutics

Mitochondria are dynamic organelles that continuously undergo fusion/fission to maintain normal cell physiological activities and energy metabolism. When mitochondrial dynamics is unbalanced, mitochondrial homeostasis is broken, thus damaging mitochondrial function. Accumulating evidence demonstrates that impairment in mitochondrial dynamics leads to lung tissue injury and pulmonary disease progression in a variety of disease models, including inflammatory responses, apoptosis, and barrier breakdown, and that the role of mitochondrial dynamics varies among pulmonary diseases. These findings suggest that modulation of mitochondrial dynamics may be considered as a valid therapeutic strategy in pulmonary diseases. In this review, we discuss the current evidence on the role of mitochondrial dynamics in pulmonary diseases, with a particular focus on its underlying mechanisms in the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis (PF), pulmonary arterial hypertension (PAH), lung cancer and bronchopulmonary dysplasia (BPD), and outline effective drugs targeting mitochondrial dynamics-related proteins, highlighting the great potential of targeting mitochondrial dynamics in the treatment of pulmonary disease.

Sirtuin insights: bridging the gap between cellular processes and therapeutic applications

The greatest challenges that organisms face today are effective responses or detection of life-threatening environmental changes due to an obvious semblance of stress and metabolic fluctuations. These are associated with different pathological conditions among which cancer is most important. Sirtuins (SIRTs; NAD+-dependent enzymes) are versatile enzymes with diverse substrate preferences, cellular locations, crucial for cellular processes and pathological conditions. This article describes in detail the distinct roles of SIRT isoforms, unveiling their potential as either cancer promoters or suppressors and also explores how both natural and synthetic compounds influence the SIRT function, indicating promise for therapeutic applications. We also discussed the inhibitors/activators tailored to specific SIRTs, holding potential for diseases lacking effective treatments. It may uncover the lesser-studied SIRT isoforms (e.g., SIRT6, SIRT7) and their unique functions. This article also offers a comprehensive overview of SIRTs, linking them to a spectrum of diseases and highlighting their potential for targeted therapies, combination approaches, disease management, and personalized medicine. We aim to contribute to a transformative era in healthcare and innovative treatments by unraveling the intricate functions of SIRTs.

SIRT4 as a novel interactor and candidate suppressor of C-RAF kinase in MAPK signaling

Cellular responses leading to development, proliferation, and differentiation depend on RAF/MEK/ERK signaling, which integrates and amplifies signals from various stimuli for downstream cellular responses. C-RAF activation has been reported in many types of tumor cell proliferation and developmental disorders, necessitating the discovery of potential C-RAF protein regulators. Here, we identify a novel and specific protein interaction between C-RAF among the RAF kinase paralogs, and SIRT4 among the mitochondrial sirtuin family members SIRT3, SIRT4, and SIRT5. Structurally, C-RAF binds to SIRT4 through the N-terminal cysteine-rich domain, whereas SIRT4 predominantly requires the C-terminus for full interaction with C-RAF. Interestingly, SIRT4 specifically interacts with C-RAF in a pre-signaling inactive (serine 259-phosphorylated) state. Consistent with this finding, the expression of SIRT4 in HEK293 cells results in an up-regulation of pS259-C-RAF levels and a concomitant reduction in MAPK signaling as evidenced by strongly decreased phospho-ERK signals. Thus, we propose an additional extra-mitochondrial function of SIRT4 as a cytosolic tumor suppressor of C-RAF-MAPK signaling, besides its metabolic tumor suppressor role of glutamate dehydrogenase and glutamate levels in mitochondria.

The mitochondria-related gene risk mode revealed p66Shc as a prognostic mitochondria-related gene of glioblastoma

Numerous studies have highlighted the pivotal role of mitochondria-related genes (MRGs) in the initiation and progression of glioblastoma (GBM). However, the specific contributions of MRGs coding proteins to GBM pathology remain incompletely elucidated. The identification of prognostic MRGs in GBM holds promise for the development of personalized targeted therapies and the enhancement of patient prognosis. We combined differential expression with univariate Cox regression analysis to screen prognosis-associated MRGs in GBM. Based on the nine MRGs, the hazard ratio model was conducted using a multivariate Cox regression algorithm. SHC-related survival, pathway, and immune analyses in GBM cohorts were obtained from the Biomarker Exploration of the Solid Tumor database. The proliferation and migration of U87 cells were measured by CCK-8 and transwell assay. Apoptosis in U87 cells was evaluated using flow cytometry. Confocal microscopy was employed to measure mitochondrial reactive oxygen species (ROS) levels and morphology. The expression levels of SHC1 and other relevant proteins were examined via western blotting. We screened 15 prognosis-associated MRGs and constructed a 9 MRGs-based model. Validation of the model's risk score confirmed its efficacy in predicting the prognosis of patients with GBM. Furthermore, analysis revealed that SHC1, a constituent MRG of the prognostic model, was upregulated and implicated in the progression, migration, and immune infiltration of GBM. In vitro experiments elucidated that p66Shc, the longest isoform of SHC1, modulates mitochondrial ROS production and morphology, consequently promoting the proliferation and migration of U87 cells. The 9 MRGs-based prognostic model could predict the prognosis of GBM. SHC1 was upregulated and correlated with the prognosis of patients by involvement in immune infiltration. Furthermore, in vitro experiments demonstrated that p66Shc promotes U87 cell proliferation and migration by mediating mitochondrial ROS production. Thus, p66Shc may serve as a promising biomarker and therapeutic target for GBM.

Mitochondria act as a key regulatory factor in cancer progression: Current concepts on mutations, mitochondrial dynamics, and therapeutic approach

The diversified impacts of mitochondrial function vs. dysfunction have been observed in almost all disease conditions including cancers. Mitochondria play crucial roles in cellular homeostasis and integrity, however, mitochondrial dysfunctions influenced by alterations in the mtDNA can disrupt cellular balance. Many external stimuli or cellular defects that cause cellular integrity abnormalities, also impact mitochondrial functions. Imbalances in mitochondrial activity can initiate and lead to accumulations of genetic mutations and can promote the processes of tumorigenesis, progression, and survival. This comprehensive review summarizes epigenetic and genetic alterations that affect the functionality of the mitochondria, with considerations of cellular metabolism, and as influenced by ethnicity. We have also reviewed recent insights regarding mitochondrial dynamics, miRNAs, exosomes that play pivotal roles in cancer promotion, and the impact of mitochondrial dynamics on immune cell mechanisms. The review also summarizes recent therapeutic approaches targeting mitochondria in anti-cancer treatment strategies.

IRF2BP2 drives lymphatic metastasis in OSCC cells by elevating mitochondrial fission-dependent fatty acid oxidation

Lymph node metastasis (LNM) is a major determinant for the poor outcome of oral squamous cell carcinoma (OSCC). Interferon regulatory factor 2 binding protein 2 (IRF2BP2) has been reported to modulate the development and progression of several types of cancers, while its role in OSCC with LNM has not been reported yet. The expression of IRF2BP2 and its association with LNM were evaluated by immunohistochemistry and qualitative reverse transcription polymerase chain reaction in clinically collected OSCC tissues. Then, loss-of-function and rescue assays were conducted to identify the role of IRF2BP2-mediated fatty acid oxidation (FAO) in the invasion, lymphoinvasion, and epithelial-mesenchymal transition (EMT) in OSCC cells. Importantly, confocal microscope, transmission electron microscope, immunofluorescence, and Western blot were applied to identify the involvement of mitochondrial fission in IRF2BP2-regulated FAO. Lastly, the in vivo models were established to evaluate the role of IRF2BP2 in OSCC. IRF2BP2 overexpression has been associated with LNM in OSCC, whose knockdown inhibited invasion, lymphoinvasion, and EMT of OSCC cells, as well as retarded FAO rate with CPT1A downregulation. And CPT1A overexpression rescued invasion, lymphoinvasion, and induced EMT in IRF2BP2-silenced OSCC cells. Mechanically, IRF2BP2 accelerated mitochondrial fission by contributing to Drp1 S616 phosphorylation and mitochondrial localization, resulting in the upregulation of CPT1A. In addition, IRF2BP2 knockdown significantly inhibited tumor growth and LNM in vivo. The highly expressed IRF2BP2 may induce the phosphorylation and mitochondrial translocation of Drp1 to activate mitochondrial fission, which upregulated CPT1A expression and FAO rate, resulting in LNM in OSCC. This highlighted a potential therapeutic vulnerability for the treatment of LNM+ OSCC via targeting IRF2BP2-FAO.

DRP1: At the Crossroads of Dysregulated Mitochondrial Dynamics and Altered Cell Signaling in Cancer Cells

In the past decade, compelling evidence has accumulated that highlights the role of various subcellular structures in human disease conditions. Dysregulation of these structures greatly impacts cellular function and, thereby, disease conditions. One such organelle extensively studied for its role in several human diseases, especially cancer, is the mitochondrion. DRP1 is a GTPase that is considered the master regulator of mitochondrial fission and thereby also affects the proper functioning of the organelle. Altered signaling pathways are a distinguished characteristic of cancer cells. In this review, we aim to summarize our current understanding of the interesting crosstalk between the mitochondrial structure-function maintained by DRP1 and the signaling pathways that are affected in cancer cells. We highlight the structural aspects of DRP1, its regulation by various modifications, and the association of the protein with various cellular pathways altered in cancer. A better understanding of this association may help in identifying potential pharmacological targets for novel therapies in cancer.

Inhibition of mitochondrial fusion via SIRT1/PDK2/PARL axis breaks mitochondrial metabolic plasticity and sensitizes cancer cells to glucose restriction therapy

Mitochondria dynamically change their morphology via fusion and fission, a process called mitochondrial dynamics. Dysregulated mitochondrial dynamics respond rapidly to metabolic cues, and are linked to the initiation and progression of diverse human cancers. Metabolic adaptations significantly contribute to tumor development and escape from tissue homeostatic defenses. In this work, we identified oroxylin A (OA), a dual GLUT1/mitochondrial fusion inhibitor, which restricted glucose catabolism of hepatocellular carcinoma cells and simultaneously inhibited mitochondrial fusion by disturbing SIRT1/PDK2/PARL axis. Based the dual action of OA in metabolic regulation and mitochondrial dynamics, further results revealed that mitochondrial functional status and spare respiratory capacity (SRC) of cancer cells had a close correlation with mitochondrial metabolic plasticity, and played important roles in the susceptibility to cancer therapy aiming at glucose restriction. Cancer cells with healthy mitochondria and high SRC exhibit greater metabolic flexibility and higher resistance to GLUT1 inhibitors. This phenomenon is attributed to the fact that high SRC cells fuse mitochondria in response to glucose restriction, enhancing tolerance to energy deficiency, but undergo less mitochondrial oxidative stress compared to low SRC cells. Thus, inhibiting mitochondrial fusion breaks mitochondrial metabolic plasticity and increases cancer cell susceptibility to glucose restriction therapy. Collectively, these finding indicate that combining a GLUT1 inhibitor with a mitochondrial fusion inhibitor can work synergistically in cancer therapy and, more broadly, suggest that the incorporations of mitochondrial dynamics and metabolic regulation may become the targetable vulnerabilities bypassing the genotypic heterogeneity of multiple malignancies.

Mitochondrial dynamics in health and disease: mechanisms and potential targets

Mitochondria are organelles that are able to adjust and respond to different stressors and metabolic needs within a cell, showcasing their plasticity and dynamic nature. These abilities allow them to effectively coordinate various cellular functions. Mitochondrial dynamics refers to the changing process of fission, fusion, mitophagy and transport, which is crucial for optimal function in signal transduction and metabolism. An imbalance in mitochondrial dynamics can disrupt mitochondrial function, leading to abnormal cellular fate, and a range of diseases, including neurodegenerative disorders, metabolic diseases, cardiovascular diseases and cancers. Herein, we review the mechanism of mitochondrial dynamics, and its impacts on cellular function. We also delve into the changes that occur in mitochondrial dynamics during health and disease, and offer novel perspectives on how to target the modulation of mitochondrial dynamics.

The Role of Mitochondrial Dynamics and Mitotic Fission in Regulating the Cell Cycle in Cancer and Pulmonary Arterial Hypertension: Implications for Dynamin-Related Protein 1 and Mitofusin2 in Hyperproliferative Diseases

Mitochondria, which generate ATP through aerobic respiration, also have important noncanonical functions. Mitochondria are dynamic organelles, that engage in fission (division), fusion (joining) and translocation. They also regulate intracellular calcium homeostasis, serve as oxygen-sensors, regulate inflammation, participate in cellular and organellar quality control and regulate the cell cycle. Mitochondrial fission is mediated by the large GTPase, dynamin-related protein 1 (Drp1) which, when activated, translocates to the outer mitochondrial membrane (OMM) where it interacts with binding proteins (Fis1, MFF, MiD49 and MiD51). At a site demarcated by the endoplasmic reticulum, fission proteins create a macromolecular ring that divides the organelle. The functional consequence of fission is contextual. Physiological fission in healthy, nonproliferating cells mediates organellar quality control, eliminating dysfunctional portions of the mitochondria via mitophagy. Pathological fission in somatic cells generates reactive oxygen species and triggers cell death. In dividing cells, Drp1-mediated mitotic fission is critical to cell cycle progression, ensuring that daughter cells receive equitable distribution of mitochondria. Mitochondrial fusion is regulated by the large GTPases mitofusin-1 (Mfn1) and mitofusin-2 (Mfn2), which fuse the OMM, and optic atrophy 1 (OPA-1), which fuses the inner mitochondrial membrane. Mitochondrial fusion mediates complementation, an important mitochondrial quality control mechanism. Fusion also favors oxidative metabolism, intracellular calcium homeostasis and inhibits cell proliferation. Mitochondrial lipids, cardiolipin and phosphatidic acid, also regulate fission and fusion, respectively. Here we review the role of mitochondrial dynamics in health and disease and discuss emerging concepts in the field, such as the role of central versus peripheral fission and the potential role of dynamin 2 (DNM2) as a fission mediator. In hyperproliferative diseases, such as pulmonary arterial hypertension and cancer, Drp1 and its binding partners are upregulated and activated, positing mitochondrial fission as an emerging therapeutic target.

SIRT4 in ageing

Ageing is a phenomenon in which cells, tissues and organs undergo systemic pathological changes as individuals age, leading to the occurrence of ageing-related diseases and the end of life. It is associated with many phenotypes known as ageing characteristics, such as genomic instability, nutritional imbalance, mitochondrial dysfunction, cell senescence, stem cell depletion, and an altered microenvironment. The sirtuin family (SIRT), known as longevity proteins, is thought to delay ageing and prolong life, and mammals, including humans, have seven family members (SIRT1-7). SIRT4 has been studied less among the sirtuin family thus far, but it has been reported that it has important physiological functions in organisms, such as promoting DNA damage repair, participating in the energy metabolism of three substances, inhibiting inflammatory reactions and apoptosis, and regulating mitochondrial function. Recently, some studies have demonstrated the involvement of SIRT4 in age-related processes, but knowledge in this field is still scarce. Therefore, this review aims to analyse the relationship between SIRT4 and ageing characteristics as well as some age-related diseases (e.g., cardiovascular diseases, metabolic diseases, neurodegenerative diseases and cancer).

Unraveling the Post-Translational Modifications and therapeutical approach in NSCLC pathogenesis

Non-Small Cell Lung Cancer (NSCLC) is the most prevalent kind of lung cancer with around 85% of total lung cancer cases. Despite vast therapies being available, the survival rate is low (5 year survival rate is 15%) making it essential to comprehend the mechanism for NSCLC cell survival and progression. The plethora of evidences suggests that the Post Translational Modification (PTM) such as phosphorylation, methylation, acetylation, glycosylation, ubiquitination and SUMOylation are involved in various types of cancer progression and metastasis including NSCLC. Indeed, an in-depth understanding of PTM associated with NSCLC biology will provide novel therapeutic targets and insight into the current sophisticated therapeutic paradigm. Herein, we reviewed the key PTMs, epigenetic modulation, PTMs crosstalk along with proteogenomics to analyze PTMs in NSCLC and also, highlighted how epi‑miRNA, miRNA and PTM inhibitors are key modulators and serve as promising therapeutics.

Rab32 promotes glioblastoma migration and invasion via regulation of ERK/Drp1-mediated mitochondrial fission

The highly widespread and infiltrative nature of glioblastoma multiforme (GBM) makes complete surgical resection hard, causing high recurrence rate and poor patients' prognosis. However, the mechanism underlying GBM migration and invasion is still unclear. In this study, we investigated the role of a Ras-related protein Rab32 on GBM and uncovered its underlying molecular and subcellular mechanisms that contributed to GBM aggressiveness. The correlation of Rab32 expression with patient prognosis and tumor grade was investigated by public dataset analysis and clinical specimen validation. The effect of Rab32 on migration and invasion of GBM had been evaluated using wound healing assay, cell invasion assay, as well as protein analysis upon Rab32 manipulations. Mitochondrial dynamics of cells upon Rab32 alterations were detected by immunofluorescence staining and western blotting. Both the subcutaneous and intracranial xenograft tumor model were utilized to evaluate the effect of Rab32 on GBM in vivo. The expression level of Rab32 is significantly elevated in the GBM, especially in the most malignant mesenchymal subtype, and is positively correlated with tumor pathological grade and poor prognosis. Knockdown of Rab32 attenuated the capability of GBM's migration and invasion. It also suppressed the expression levels of invasion-related proteins (MMP2 and MMP9) as well as mesenchymal transition markers (N-cadherin, vimentin). Interestingly, Rab32 transported Drp1 to mitochondrial from the cytoplasm and modulated mitochondrial fission in an ERK_1/2 signaling-dependent manner. Furthermore, silencing of Rab32 in vivo suppressed tumor malignancy via ERK/Drp1 axis. Rab32 regulates ERK_1/2/Drp1-dependent mitochondrial fission and causes mesenchymal transition, promoting migration and invasion of GBM. It serves as a novel therapeutic target for GBM, especially for the most malignant mesenchymal subtype. Schematic of Rab32 promotes GBM aggressiveness via regulation of ERK/Drp1-mediated mitochondrial fission. Rab32 transports Drp1 from the cytoplasm to the mitochondria and recruits ERK_1/2 to activate the ser616 site of Drp1, which in turn mediates mitochondrial fission and promotes mesenchymal transition, migration and invasion of GBM.

Sirtuin 4 activates autophagy and inhibits tumorigenesis by upregulating the p53 signaling pathway

The role of autophagy in cancer is context-dependent. In the present study, we aimed to investigate the regulator and underlying mechanism of autophagy. We found that a sirtuin (SIRT) family member, SIRT4, was significantly associated autophagy pathway in pancreatic ductal adenocarcinoma (PDAC). Specifically, in vitro cell culture experiments and in vivo transgenic and xenografted animal models revealed that SIRT4 could inhibit tumor growth and promote autophagy in PDAC. In terms of the mechanism, we demonstrated that SIRT4 activated the phosphorylation of p53 protein by suppressing glutamine metabolism, which was crucial in SIRT4-induced autophagy. AMPKα was implicated in the regulation of autophagy and phosphorylation of p53 mediated by SIRT4, contributing to the suppression of pancreatic tumorigenesis. Notably, the clinical significance of the SIRT4/AMPKα/p53/autophagy axis was demonstrated in human PDAC specimens. Collectively, these findings suggested that SIRT4-induced autophagy further inhibited tumorigenesis and progression of PDAC, highlighting the potential of SIRT4 as a therapeutic target for cancer.

Shedding light on structure, function and regulation of human sirtuins: a comprehensive review

Sirtuins play an important role in signalling pathways associated with various metabolic regulations. They possess mono-ADP-ribosyltransferase or deacylase activity like demalonylase, deacetylase, depalmitoylase, demyristoylase and desuccinylase activity. Sirtuins are histone deacetylases which depends upon nicotinamide adenine dinucleotide (NAD) that deacetylate lysine residues. There are a total of seven human sirtuins that have been identified namely, SIRT1, SIRT2, SIRT3, SIRT4, SIRT5, SIRT6 and SIRT7. The subcellular location of mammalian sirtuins, SIRT1, SIRT6, and SIRT7 are in the nucleus; SIRT3, SIRT4, and SIRT5 are in mitochondria, and SIRT2 is in cytoplasm. Structurally sirtuins contains a N-terminal, a C-terminal and a Zn+ binding domain. The sirtuin family has been found to be crucial for maintaining lipid and glucose homeostasis, and also for regulating insulin secretion and sensitivity, DNA repair pathways, neurogenesis, inflammation, and ageing. Based on the literature, sirtuins are overexpressed and play an important role in tumorigenicity in various types of cancer such as non-small cell lung cancer, colorectal cancer, etc. In this review, we have discussed about the different types of human sirtuins along with their structural and functional features. We have also discussed about the various natural and synthetic regulators of sirtuin activities like resveratrol. Our overall study shows that the correct regulation of sirtuins can be a good target for preventing and treating various diseases for improving the human lifespan. To investigate the true therapeutic potential of sirtuin proteins and their efficacy in a variety of pathological diseases, a better knowledge of the link between the structure and function of sirtuin proteins would be necessary.

Mitochondrial dysfunction in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by the increased pulmonary vascular resistance due to pulmonary vasoconstriction and vascular remodeling. PAH has high disability, high mortality and poor prognosis, which is becoming a more common global health issue. There is currently no drug that can permanently cure PAH patients. The pathogenesis of PAH is still not fully elucidated. However, the role of metabolic theory in the pathogenesis of PAH is becoming clearer, especially mitochondrial metabolism. With the deepening of mitochondrial researches in recent years, more and more studies have shown that the occurrence and development of PAH are closely related to mitochondrial dysfunction, including the tricarboxylic acid cycle, redox homeostasis, enhanced glycolysis, and increased reactive oxygen species production, calcium dysregulation, mitophagy, etc. This review will further elucidate the relationship between mitochondrial metabolism and pulmonary vasoconstriction and pulmonary vascular remodeling. It might be possible to explore more comprehensive and specific treatment strategies for PAH by understanding these mitochondrial metabolic mechanisms.

SIRT4 Expression Ameliorates the Detrimental Effect of Heat Stress via AMPK/mTOR Signaling Pathway in BMECs

Sirtuin 4 (SIRT4), a member of the SIRT family, has been reported to be a key factor involved in antioxidant defense in mitochondria. This study aimed to explore the potential molecular mechanism via which SIRT4 regulates heat stress-induced oxidative stress and lactoprotein synthesis in bovine mammary epithelial cells (BMECs). Our results showed that SIRT4 was significantly decreased in heat stressed mammary tissue. Depletion of SIRT4 in BMECs induced the generation of ROS, which, as exhibited by the decreased activity of antioxidant enzymes, changed mitochondrial morphology through mediating protein and mRNA levels related to mitochondrial fission and fusion. Moreover, we found that depletion of SIRT4 or stress conditions inhibited the expression of milk proteins, as well as lipid and glucose synthesis-related genes, and activated the AMPK/mTOR signaling pathway. Increased SIRT4 expression was found to have the opposite effect. However, blocking the AMPK/mTOR signaling pathway could inhibit the regulatory function of SIRT4 in milk synthesis-related gene expression. In summary, our results suggest that SIRT4 may play critical roles in maintaining mammary gland function by regulating the AMPK/mTOR signaling pathway in dairy cows, indicating that SIRT4 may be a potential molecular target for curing heat stress-induced BMEC injury and low milk production in dairy cows.

Sanggenon C Suppresses Tumorigenesis of Gastric Cancer by Blocking ERK-Drp1-Mediated Mitochondrial Fission

Sanggenon C is a flavonoid extracted from the root bark of white mulberry, which is a traditional Chinese medicine with anti-inflammatory, antioxidative, and antitumor pharmacological effects. In this study, sanggenon C was found to inhibit human gastric cancer (GC) cell proliferation and colony formation, induce GC cell cycle arrest in the G0-G1 phase, and promote GC cell apoptosis. Moreover, sanggenon C was found to decrease the level of mitochondrial membrane potential in GC cells and inhibit mitochondrial fission. Mechanistically, RNA sequencing, bioinformatics analysis, and a series of functional analyses confirmed that sanggenon C inhibited mitochondrial fission to induce apoptosis by blocking the extracellular regulated protein kinases (ERK) signaling pathway, and constitutive activation of ERK significantly abrogated these effects. Finally, sanggenon C was found to suppress the growth of tumor xenografts in nude mice without obvious side effects to the vital organs of animals. This study reveals that sanggenon C could be a novel therapeutic strategy for GC treatment.

The role of protein acetylation in carcinogenesis and targeted drug discovery

Protein acetylation is a reversible post-translational modification, and is involved in many biological processes in cells, such as transcriptional regulation, DNA damage repair, and energy metabolism, which is an important molecular event and is associated with a wide range of diseases such as cancers. Protein acetylation is dynamically regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs) in homeostasis. The abnormal acetylation level might lead to the occurrence and deterioration of a cancer, and is closely related to various pathophysiological characteristics of a cancer, such as malignant phenotypes, and promotes cancer cells to adapt to tumor microenvironment. Therapeutic modalities targeting protein acetylation are a potential therapeutic strategy. This article discussed the roles of protein acetylation in tumor pathology and therapeutic drugs targeting protein acetylation, which offers the contributions of protein acetylation in clarification of carcinogenesis, and discovery of therapeutic drugs for cancers, and lays the foundation for precision medicine in oncology.

Significant position of C-myc in colorectal cancer: a promising therapeutic target

Colorectal cancer (CRC) is a malignant tumor initiating from the mucosa of the colorectum. According to the 2020 statistics from the World Health Organization, there are 10.0% CRC cases among all 19.3 million new cancers, followed by lung and breast cancer, and 9.4% CRC cases among all 9.9 million cancer deaths, ranking second. The population of CRC patients in China is large, and its incidence and mortality continue to increase each year. Despite the continuous development of surgical methods, chemotherapy, radiotherapy, targeted therapy and immunotherapy, the overall survival of CRC patients remains low. Past research has suggested that c-myc plays a pivotal role in the development of CRC. A higher expression level of c-Myc is a negative prognostic marker in CRC. However, there are few drugs targeting c-myc directly. Therefore, we focused on discovering the mechanism of c-myc in CRC to provide a reference for a better therapy choice for patients.

The histone deacetylase SIRT6 promotes glycolysis through the HIF-1α/HK2 signaling axis and induces erlotinib resistance in non-small cell lung cancer

Erlotinib is a first-generation epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI). Overcoming erlotinib resistance is crucial to improve the survival of advanced non-small cell lung cancer (NSCLC) patients with sensitive EGFR mutations. It is also an important clinical problem that urgently needs a solution. In this study, we explored strategies to overcome erlotinib resistance from the perspective of energy metabolism. SIRT6 is a histone deacetylase. Here, we found that high expression of SIRT6 is associated with poor prognosis of lung adenocarcinoma, especially in EGFR-mutated NSCLC patients. The next cell experiment found that SIRT6 expression increased in erlotinib-resistant cells, and SIRT6 expression was negatively correlated with the sensitivity of NSCLC to erlotinib. Inhibition of SIRT6 promoted erlotinib-induced apoptosis in erlotinib-resistant cells, and glycolysis in drug-resistant cells was also inhibited. Functional studies have shown that SIRT6 increases glycolysis through the HIF-1α/HK2 signaling axis in drug-resistant cells and inhibits the sensitivity of NSCLC cells to erlotinib. In addition, the HIF-1α blocker PX478-2HCL attenuated the glycolysis and erlotinib resistance induced by SIRT6. More importantly, we confirmed the antitumor effect of SIRT6 inhibition combined with erlotinib in NSCLC-bearing mice. Our findings indicate that the cancer metabolic pathway regulated by SIRT6 may be a new target for attenuating NSCLC erlotinib resistance and has potential as a biomarker or therapeutic target to improve outcomes in NSCLC patients.

Mitochondrial Homeostasis–Related lncRNAs are Potential Biomarkers for Predicting Prognosis and Immune Response in Lung Adenocarcinoma

The prognosis of the most common histological subtype of lung cancer, lung adenocarcinoma (LUAD), is relatively poor. Mitochondrial homeostasis depends to a great extent on the coordination between mitophagy and mitochondrial biogenesis, the deregulation of which causes various human diseases, including cancer. There is accumulating evidence that long noncoding RNAs (lncRNAs) are critical in predicting the prognosis and immune response in carcinoma. Therefore, it is critical to discern lncRNAs related to mitochondrial homeostasis in LUAD patients. In this study, we identified mitochondrial homeostasis–related lncRNAs (MHRlncRNAs) by coexpression analysis. In order to construct a prognostic signature composed of three MHRlncRNAs, univariate and multivariate Cox regression analyses were performed. Kaplan–Meier analysis, stratification analysis, principal component analysis (PCA), receiver operating characteristic (ROC) curve, gene set enrichment analysis (GSEA), and nomogram were applied to evaluate and optimize the risk model. Subsequently, we identified the mitochondrial homeostasis–related lncRNA signature (MHLncSig) as an independent predictive factor of prognosis. Based on the LUAD subtypes regrouped by this risk model, we further investigated the underlying tumor microenvironment, tumor mutation burden, and immune landscape behind different risk groups. Likewise, individualized immunotherapeutic strategies and candidate compounds were screened to aim at different risk subtypes of LUAD patients. Finally, we validated the expression trends of lncRNAs included in the risk model using quantitative real-time polymerase chain reaction (qRT-PCR) assays. The established MHLncSig may be a promising tool for predicting the prognosis and guiding individualized treatment in LUAD.

Association of sirtuins (SIRT1-7) with lung and intestinal diseases

"Exterior-interior correlation between the lung and large intestine" is one of the important contents of traditional Chinese medicine. This theory describes the role of the lung and the intestine in association with disease treatment. The "lung-gut" axis is a modern extension of the "exterior-interior correlation between lung and large intestine" theory in TCM. Sirtuin (SIRT) is a nicotinamide adenine dinucleotide (NAD⁺)-dependent enzyme family with deacetylase properties, which is highly conserved from bacteria to humans. The sirtuin defines seven silencing regulatory proteins (SIRT1-7) in human cells. It can regulate aging, metabolism, and certain diseases. Current studies have shown that sirtuins have dual characteristics, acting as both tumor promoters and tumor inhibitors in cancers. This paper provides a comparative summary of the roles of SIRT1-7 in the intestine and lung (both inflammatory diseases and tumors), and the promoter/suppressor effects of targeting SIRT family microRNAs and modulators of inflammation or tumors. Sirtuins have great potential as drug targets for the treatment of intestinal and respiratory diseases. Meanwhile, it may provide new ideas of future drug target research.

AIM2 Promotes Gastric Cancer Cell Proliferation via the MAPK Signaling Pathway

Background

Gastric cancer (GC) is a highly prevalent tumor type. The dysregulated expression of melanoma deficiency factor 2 (AIM2) has been observed in a range of tumor types. Herein, we explore the role of AIM2 in the regulation of GC progression.

Methods

Gastric cancer cells BGC-823 and MGC-803 in logarithmic growth phase were divided into blank group (control), Control group (NC) and SH-AIM2 group, respectively. Control group and SH-AIM2 group were transfected with AIM2 NC and SH-AIM2, respectively. Nude mice were divided into blank group (control) and SH-AIM2 group, and the treatment methods were the same as above. Differential AIM2 expression in GC tissues was assessed via bioinformatics analyses, after which western blotting was used for analyzing the AIM2 levels in tumor and paracancerous tissues from five stomach cancer patients. In addition, qPCR and protein imprinting were used to assess AIM2 expression levels in GC cells, and AIM2 knockdown was conducted in MGC-803 and BGC-823cells, after which colony formation and EdU incorporation assay were utilized to assess cell proliferation. The oncogenic role of AIM2 was then assessed in mice and validated through immunohistochemical analyses.

Results

GC tissues and cell lines exhibited marked AIM2 overexpression. AIM2 knockdown significantly impaired GC cell proliferation and migration, as confirmed through in vitro assays. In vivo experiments showed that both the increment ability and invasion and migration ability of AIM2 knockdown group were significantly lower than that of control and NC the change of AIM2 protein level would affect the change of MAPK pathway related protein level.

Conclusions

AIM2 knockdown markedly suppresses the proliferation, migration, as well as invasion of GC cells via the inhibition of MAPK signaling, thereby slowing tumor progression. Overall, these results suggest that further analyses of AIM2 may offer clinically valuable insights that can aid in the treatment of human GC.

Apelin-13 Pretreatment Promotes the Cardioprotective Effect of Mesenchymal Stem Cells against Myocardial Infarction by Improving Their Survival

Although mesenchymal stem cell- (MSC-) based therapy has shown promising results for myocardial infarction (MI), low cell survival heavily limits its beneficial effects. Apelin plays an essential regulatory role in cell proliferation. This study was aimed at determining whether Apelin-13 pretreatment could improve the survival of MSCs in the ischemic heart and enhance their cardioprotective efficacy against MI. MSCs were pretreated with or without Apelin-13 for 24 hours and then exposed to serum deprivation and hypoxia (SD/H) for 48 hours. The mitochondrial morphology of MSCs was assessed by MitoTracker staining. The apoptosis of MSCs was determined by TUNEL staining. The level of mitochondrial reactive oxygen species (ROS) of MSCs was detected by Mito-Sox staining. MSCs and Apelin-13-pretreated MSCs were transplanted into the peri-infarct region in a mouse MI model. Apelin-13 pretreatment protected MSCs against SD/H-induced mitochondrial fragmentation and apoptosis. Apelin-13 pretreatment reduced ROS generation induced by SD/H in MSCs. Furthermore, Apelin-13 pretreatment enhanced the angiogenesis of MSCs under SD/H conditions. Mechanistically, Apelin-13 pretreatment inhibited SD/H-induced MSC apoptosis by downregulating mitochondrial fission via activation of the ERK pathway, and these effects were partially abrogated by ERK inhibitor U0126. Apelin-13 pretreatment promoted the survival of MSCs in the ischemic heart. Moreover, transplantation with Apelin-13-pretreated MSCs improved heart function and increased angiogenesis accompanied by decreased fibrosis compared with MSC transplantation at 28 days following MI. These findings reveal that pretreatment with Apelin-13 improves MSCs survival and enhances their therapeutic efficacy for MI. Our study provides a novel approach to improve MSC-based therapy for cardiovascular disease.

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.

The role of protein acetylation in regulating mitochondrial fusion and fission

The dynamic processes of mitochondrial fusion and fission determine the shape of mitochondria, which can range from individual fragments to a hyperfused network, and influence mitochondrial function. Changes in mitochondrial shape can occur rapidly, allowing mitochondria to adapt to specific cues and changing cellular demands. Here, we will review what is known about how key proteins required for mitochondrial fusion and fission are regulated by their acetylation status, with acetylation promoting fission and deacetylation enhancing fusion. In particular, we will examine the roles of NAD+ dependant sirtuin deacetylases, which mediate mitochondrial acetylation, and how this post-translational modification provides an exquisite regulatory mechanism to co-ordinate mitochondrial function with metabolic demands of the cell.

Mitochondrial Tumor Suppressors-The Energetic Enemies of Tumor Progression

Tumor suppressors represent a critical line of defense against tumorigenesis. Their mechanisms of action and the pathways they are involved in provide important insights into cancer progression, vulnerabilities, and treatment options. Although nuclear and cytosolic tumor suppressors have been extensively investigated, relatively little is known about tumor suppressors localized within the mitochondria. However, recent research has begun to uncover the roles of these important proteins in suppressing tumorigenesis. Here, we review this newly developing field and summarize available information on mitochondrial tumor suppressors.

Circular RNA OMA1 regulates the progression of breast cancer via modulation of the miR‑1276/SIRT4 axis

Mounting evidence has indicated that circular RNAs (circRNAs) serve essential roles in the tumorigenesis and development of various types of cancer. However, the biological functions and the underlying mechanisms of circRNAs in breast cancer (BC) remain largely elusive. In the present study, the expression pattern of circRNAs in three pairs of BC tissues and adjacent normal tissues was determined using a circRNA microarray. The expression and prognostic value of circOMA1 were evaluated by reverse transcription‑quantitative PCR in 64 pairs of BC tissues and adjacent normal tissues. Survival curves were generated by the Kaplan‑Meier method, and statistical significance was estimated using the log‑rank test. A series of in vitro functional experiments were then performed to investigate the role of circOMA1 in the tumorigenesis of BC. The results revealed that the expression levels of circOMA1 were upregulated in BC tissues, and its expression was markedly associated with tumor size and lymph node metastasis. Receiver operating characteristic analysis demonstrated that the expression of circOMA1 could be used to discriminate between BC tissues and adjacent normal tissues. Functionally, overexpression of circOMA1 promoted the viability, migration and invasion of BC cells, whereas circOMA1 knockdown had the opposite effect. Mechanistic investigations showed that circOMA1 promoted the progression of BC by sponging microRNA (miR)‑1276 and upregulating sirtuin 4 (SIRT4) expression. In conclusion, circOMA1 may act as an oncogenic circRNA in BC via regulation of the miR‑1276/SIRT4 axis.

Mammalian SIRT4 is a tumor suppressor of clear cell renal cell carcinoma by inhibiting cancer proliferation, migration and invasion

OBJECTIVE

Sirtuins family are defined as class III histone deacetylases (HDACs). Recently, mammalian silent information regulator two 4 (SIRT4) has been reported to be a tumor suppressor gene in multiple cancers. The objective of the present study was to explore the potential role of SIRT4 in clear cell renal cell carcinoma (ccRCC).

METHODS

We estimated SIRT4 expression levels in ccRCC and its adjacent non-neoplastic tissue by Western blotting (WB), quantitative real-time polymerase chain reaction (qRT-PCR) and bioinformatics data, the clinical and survival data were also collected and analyzed. In vitro study, ccRCC cell lines were transfected with SIRT4-siRNA or lentivirus to downregulate or overexpress the expression level of SIRT4. Then, the proliferation capacity of tumor cell was assessed by 5-Ethynyl-2'-deoxyuridine (EDU) assay, cell migration and invasion capacity were assessed by Transwell assays.

RESULTS

Our results indicated that the expression level of SIRT4 in ccRCC was significantly lower than the corresponding normal tissues (P< 0.001). Meanwhile, bioinformatics data and the result of WB showed that low SIRT4 expression level was obviously involved with poor overall survival and advanced tumor stage in ccRCC patients. Biological experiments demonstrated that overexpression of SIRT4 significantly reduced the proliferation, migration and invasion ability of ccRCC cells. Conversely, downregulation of SIRT4 enhanced the proliferation, migration and invasion ability of ccRCC cells.

CONCLUSIONS

These findings support that SIRT4 acts as a tumor suppressor in ccRCC and might be a novel biomarker and new therapeutic target for ccRCC.

Characterization of Histone Deacetylase Mechanisms in Cancer Development

Over decades of studies, accumulating evidence has suggested that epigenetic dysregulation is a hallmark of tumours. Post-translational modifications of histones are involved in tumour pathogenesis and development mainly by influencing a broad range of physiological processes. Histone deacetylases (HDACs) and histone acetyltransferases (HATs) are pivotal epigenetic modulators that regulate dynamic processes in the acetylation of histones at lysine residues, thereby influencing transcription of oncogenes and tumour suppressor genes. Moreover, HDACs mediate the deacetylation process of many nonhistone proteins and thus orchestrate a host of pathological processes, such as tumour pathogenesis. In this review, we elucidate the functions of HDACs in cancer.

SIRT4 and SIRT6 Serve as Novel Prognostic Biomarkers With Competitive Functions in Serous Ovarian Cancer

Sirtuins (SIRTs) are class III histone deacetylases (HDACs) that include seven members and are widely expressed in mammals. Accumulating evidence shows that sirtuins may have contradictory roles in various malignancies. They mainly participate in metabolic homeostasis, DNA damage repair, cell survival, and differentiation, as well as other cancer-related biological processes. To better understand their prognostic role and biological functions, we used comprehensive bioinformatic analyses to demonstrate the expression and mutation of sirtuin family member genes in ovarian cancer (OC), with a detailed focus on prognostic prediction, including the effectiveness of anti-OC drugs. Furthermore, the co-expression genes of SIRT4 and SIRT6 with contradictory survival prediction values in both overall and progression-free survival (PFS) times were further analyzed through Gene Ontology enrichment and Kyoto Encyclopedia annotation. Additionally, we performed and obtained the immunohistochemical staining patterns of these two biomarkers from the serous OC patient database and clinical patient samples to demonstrate their potential applicability in clinical pathology. According to our findings, SIRT4 and SIRT6 are novel prognostic biomarkers that may serve as contradictory competitors for OC cell survival. They are also sensitive biomarkers for the prediction of Avastin's anticancer effect. While SIRT4 is related to the immune response during oocyte maturation, SIRT6 participates in immune-related disease pathways and mitochondrial metabolism-mediated DNA translation. These findings contribute to the novel hypothesis that SIRT4 and SIRT6 act as contradictory competitors in the regulation of OC behavior. Further studies are required to validate our hypothesis.

TRIM66 Overexpression Promotes Glioma Progression and Regulates Glucose Uptake Through cMyc/GLUT3 Signaling

OBJECTIVE

Tripartite motif 66 (TRIM66) is reported to be closely associated with human cancers. However, the roles of TRIM66 in glioma remain unclear. The present study aimed to investigate the clinical significance and biological roles of TRIM66 in human glioma.

METHODS

TRIM66 expression in glioma tissues was examined by immunohistochemistry. TRIM66 overexpression and siRNA knockdown were performed in glioblastoma cell lines. CCK8, colony formation assay, transwell assay, Annexin V and JC1 staining, glucose uptake assay, and Western blotting were used to explore the biological roles and potential underlying mechanisms of TRIM66 in glioma progression.

RESULTS

Our results showed that TRIM66 was overexpressed in 52/95 glioma cases. The rates of TRIM66 overexpression in Grade I, Grade II, Grade III, and Grade IV gliomas were 16.6%, 41.3%, 58.6%, and 70.9%, respectively. Oncomine data showed that TRIM66 was upregulated in glioblastoma and oligodendroglioma compared with normal brain tissues. TRIM66 expression was higher in glioblastoma cell lines compared with normal SVG p12 glial cell line. TRIM66 promoted in vitro and in vivo proliferation, invasion, and inhibited temozolomide (TMZ)-induced apoptosis. Notably, TRIM66 increased glucose metabolism by upregulating glucose uptake, glucose consumption, and ATP production. Western blotting showed that TRIM66 positively regulated cMyc and GLUT3. Depletion of cMyc by siRNA abolished the effect of TRIM66 on GLUT3. Chromatin immunoprecipitation (ChIP) assay showed that cMyc could bind to the promoter regions of GLUT3 in glioblastoma cells.

CONCLUSION

TRIM66 was upregulated in human gliomas, where it promoted cell growth and chemoresistance. Our data also identified novel roles of TRIM66 in glioma progression. TRIM66 upregulates glucose uptake and mitochondrial function through the cMyc/GLUT3 signaling, which makes it a potential therapeutic target.

Mitochondrial Sirtuins in Reproduction

Mitochondria act as hubs of numerous metabolic pathways. Mitochondrial dysfunctions contribute to altering the redox balance and predispose to aging and metabolic alterations. The sirtuin family is composed of seven members and three of them, SIRT3-5, are housed in mitochondria. They catalyze NAD+-dependent deacylation and the ADP-ribosylation of mitochondrial proteins, thereby modulating gene expression and activities of enzymes involved in oxidative metabolism and stress responses. In this context, mitochondrial sirtuins (mtSIRTs) act in synergistic or antagonistic manners to protect from aging and aging-related metabolic abnormalities. In this review, we focus on the role of mtSIRTs in the biological competence of reproductive cells, organs, and embryos. Most studies are focused on SIRT3 in female reproduction, providing evidence that SIRT3 improves the competence of oocytes in humans and animal models. Moreover, SIRT3 protects oocytes, early embryos, and ovaries against stress conditions. The relationship between derangement of SIRT3 signaling and the imbalance of ROS and antioxidant defenses in testes has also been demonstrated. Very little is known about SIRT4 and SIRT5 functions in the reproductive system. The final goal of this work is to understand whether sirtuin-based signaling may be taken into account as potential targets for therapeutic applications in female and male infertility.

SIRT4 is the molecular switch mediating cellular proliferation in colorectal cancer through GLS mediated activation of AKT/GSK3β/CyclinD1 pathway

Mitochondria-localized sirtuin 4 (SIRT4) is associated with malignant phenotypes in colorectal cancer (CRC). However, the molecular mechanisms that drive SIRT4-mediated carcinogenesis are unclear. Initially, we confirmed expression of SIRT4 in CRC through public database and in CRC patient tissues using quantitative real-time reverse transcription PCR. We established HCT116 colorectal cells that overexpressed SIRT4 and HT29 cells were transfected with plasmids bearing a small interfering RNA construct to silence SIRT4. Assays to determine the malignant phenotypes (proliferation, invasion and migration) were performed. Xenograft in vivo models were also constructed. A protein interactome network was built using differentially expressed proteins identified using the liquid chromatography/tandem mass spectrophotometry, the findings of which were confirmed using co-immunoprecipitation, western blotting and phenotype rescue experiments. Decreased SIRT4 expression was associated with malignant phenotypes in vitro and in vivo. The ribosomal biogenesis pathway was enriched in the interactome network. SIRT4 suppression activated glutaminase, thereby initiating AKT activation. Our research provided novel insights into the molecular mechanisms underlying CRC, and identified that SIRT4 exerts its antitumor activity in CRC possibly dependent on glutaminase to inhibit proliferation, migration and invasion via the AKT/GSK3β/CyclinD1 pathway.

ERK/Drp1-dependent mitochondrial fission contributes to HMGB1-induced autophagy in pulmonary arterial hypertension

OBJECTIVES

High-mobility group box-1 (HMGB1) and aberrant mitochondrial fission mediated by excessive activation of GTPase dynamin-related protein 1 (Drp1) have been found to be elevated in patients with pulmonary arterial hypertension (PAH) and critically implicated in PAH pathogenesis. However, it remains unknown whether Drp1-mediated mitochondrial fission and which downstream targets of mitochondrial fission mediate HMGB1-induced pulmonary arterial smooth muscle cells (PASMCs) proliferation and migration leading to vascular remodelling in PAH. This study aims to address these issues.

METHODS

Primary cultured PASMCs were obtained from male Sprague-Dawley (SD) rats. We detected RNA levels by qRT-PCR, protein levels by Western blotting, cell proliferation by Cell Counting Kit-8 (CCK-8) and EdU incorporation assays, migration by wound healing and transwell assays. SD rats were injected with monocrotaline (MCT) to establish PAH. Hemodynamic parameters were measured by closed-chest right heart catheterization.

RESULTS

HMGB1 increased Drp1 phosphorylation and Drp1-dependent mitochondrial fragmentation through extracellular signal-regulated kinases 1/2 (ERK1/2) signalling activation, and subsequently triggered autophagy activation, which further led to bone morphogenetic protein receptor 2 (BMPR2) lysosomal degradation and inhibitor of DNA binding 1 (Id1) downregulation, and eventually promoted PASMCs proliferation/migration. Inhibition of ERK1/2 cascade, knockdown of Drp1 or suppression of autophagy restored HMGB1-induced reductions of BMPR2 and Id1, and diminished HMGB1-induced PASMCs proliferation/migration. In addition, pharmacological inhibition of HMGB1 by glycyrrhizin, suppression of mitochondrial fission by Mdivi-1 or blockage of autophagy by chloroquine prevented PAH development in MCT-induced rats PAH model.

CONCLUSIONS

HMGB1 promotes PASMCs proliferation/migration and pulmonary vascular remodelling by activating ERK1/2/Drp1/Autophagy/BMPR2/Id1 axis, suggesting that this cascade might be a potential novel target for management of PAH.

Mitochondrial sirtuins in stem cells and cancer

The mammalian sirtuin family consists of seven proteins, three of which (SIRT3, SIRT4, and SIRT5) localise specifically within mitochondria and preserve mitochondrial function and homeostasis. Mitochondrial sirtuins are involved in diverse functions such as deacetylation, ADP-ribosylation, demalonylation and desuccinylation, thus affecting various aspects of cell fate. Intriguingly, mitochondrial sirtuins are able to manage these delicate processes with accuracy mediated by crosstalk between the nucleus and mitochondria. Previous studies have provided ample information about their substrates and targets, whereas less is known about their role in cancer and stem cells. Here, we review and discuss recent advances in our understanding of the structural and functional properties of mitochondrial sirtuins, including their targets in cancer and stem cells. These advances could help to improve the understanding of their interplay with signalling cascades and pathways, leading to new avenues for developing novel drugs for sirtuin-related disease treatments. We also highlight the complex network of mitochondrial sirtuins in cancer and stem cells, which may be important in deciphering the molecular mechanism for their activation and inhibition.

BCAT1 overexpression regulates proliferation and c‑Myc/GLUT1 signaling in head and neck squamous cell carcinoma

Branched chain amino acid transaminase 1 (BCAT1) overexpression has been reported in various cancers; however, at present, its significance and biological role in head and neck squamous cell carcinoma (HNSCC) remain unknown. BCAT1 protein expression was upregulated in 56/106 (52.8%) cases of HNSCC. BCAT1 overexpression was associated with tumor-node-metastasis stage, tumor stage and nodal metastasis. The Cancer Genome Atlas data suggested that high BCAT1 expression was associated with poor patient survival. Oncomine data suggested that BCAT1 expression was increased in HNSCC. Functionally, BCAT1 overexpression promoted cell proliferation, colony formation, invasion and cisplatin resistance in FaDu cells. BCAT1 overexpression also upregulated the mitochondrial membrane potential, and increased ATP production, glucose consumption and glucose uptake. Western blotting demonstrated that BCAT1 overexpression upregulated c-Myc and glucose transporter 1 (GLUT1) protein levels. Depletion of c-Myc using small interfering RNA abolished the influence of BCAT1 on GLUT1. Chromatin immunoprecipitation assays demonstrated that c-Myc has binding sites in the GLUT1 promoter. Collectively, the present findings suggested that BCAT1 is upregulated in human HNSCC and regulates HNSCC cell proliferation, invasion, cisplatin sensitivity and c-Myc/GLUT1 signaling.

Mitochondrial Sirtuins and Doxorubicin-induced Cardiotoxicity

Doxorubicin (DOX) is the most effective and extensively used treatment for many tumors. However, its clinical use is hampered by its cardiotoxicity. DOX-induced mitochondrial dysfunction, which causes reactive oxygen species (ROS) generation, cardiomyocyte death, bioenergetic failure, and decreased cardiac function, is a very important mechanism of cardiotoxicity. These cellular processes are all linked by mitochondrial sirtuins (SIRT3-SIRT4). Mitochondrial sirtuins preserve mitochondrial function by increasing mitochondrial metabolism, inhibiting ROS generation by activating the antioxidant enzyme manganese-dependent superoxide dismutase (MnSOD), decreasing apoptosis by activating the forkhead homeobox type O (FOXO) and P53 pathways, and increasing autophagy through AMP-activated protein kinase (AMPK)/mTOR signaling. Thus, sirtuins function at the control point of many mechanisms involved in DOX-induced cardiotoxicity. In this review, we focus on the role of mitochondrial sirtuins in mitochondrial biology and DOX-induced cardiotoxicity. A further aim is to highlight other mitochondrial processes, such as autophagy (mitophagy) and mitochondrial quality control (MQC), for which the effect of mitochondrial sirtuins on cardiotoxicity is unknown.

Research Progress of Sirtuin4 in Cancer

Sirtuins (SIRTs) are members of the silent information regulator-2 family. They are a conserved family of nicotinamide adenine dinucleotide-dependent protein lysine deacylases. SIRTS are involved in intricate cellular processes. There are seven subtypes of SIRTs (1–7) in mammals. SIRT4 is located mainly in mitochondria and has various catalytic activities. These enzyme activities give it a diverse range of important biologic functions, such as energy metabolism, oxidative stress, and aging. Cancer is characterized as reprogramming of energy metabolism and redox imbalance, and SIRT4 can affect tumorigenesis. Here, we review the structure, localization, and enzyme activity of SIRT4 and its role in various neoplasms.

Resveratrol's Anti-Cancer Effects through the Modulation of Tumor Glucose Metabolism

Simple Summary

The prevention and treatment of cancer is an ongoing medical challenge. In the context of personalized medicine, the well-studied polyphenol resveratrol could complement classical tumor therapy. It may affect key processes such as inflammation, angiogenesis, proliferation, metastasis, glucose metabolism, and apoptosis in various cancers because resveratrol acts as a multi-targeting agent by modulating multiple signal transduction pathways. This review article focuses on resveratrol’s ability to modify tumor glucose metabolism and its associated therapeutic capacity. Resveratrol reduces glucose uptake and glycolysis by affecting Glut1, PFK1, HIF-1α, ROS, PDH, and the CamKKB/AMPK pathway. It also inhibits cell growth, invasion, and proliferation by targeting NF-kB, Sirt1, Sirt3, LDH, PI-3K, mTOR, PKM2, R5P, G6PD, TKT, talin, and PGAM. In addition, resveratrol induces apoptosis by targeting integrin, p53, LDH, and FAK. In conclusion, resveratrol has many potentials to intervene in tumor processes if bioavailability can be increased and this natural compound can be used selectively.

Abstract

Tumor cells develop several metabolic reprogramming strategies, such as increased glucose uptake and utilization via aerobic glycolysis and fermentation of glucose to lactate; these lead to a low pH environment in which the cancer cells thrive and evade apoptosis. These characteristics of tumor cells are known as the Warburg effect. Adaptive metabolic alterations in cancer cells can be attributed to mutations in key metabolic enzymes and transcription factors. The features of the Warburg phenotype may serve as promising markers for the early detection and treatment of tumors. Besides, the glycolytic process of tumors is reversible and could represent a therapeutic target. So-called mono-target therapies are often unsafe and ineffective, and have a high prevalence of recurrence. Their success is hindered by the ability of tumor cells to simultaneously develop multiple chemoresistance pathways. Therefore, agents that modify several cellular targets, such as energy restriction to target tumor cells specifically, have therapeutic potential. Resveratrol, a natural active polyphenol found in grapes and red wine and used in many traditional medicines, is known for its ability to target multiple components of signaling pathways in tumors, leading to the suppression of cell proliferation, activation of apoptosis, and regression in tumor growth. Here, we describe current knowledge on the various mechanisms by which resveratrol modulates glucose metabolism, its potential as an imitator of caloric restriction, and its therapeutic capacity in tumors.

Anti-allergic drug azelastine suppresses colon tumorigenesis by directly targeting ARF1 to inhibit IQGAP1-ERK-Drp1-mediated mitochondrial fission

This study aimed to screen novel anticancer strategies from FDA-approved non-cancer drugs and identify potential biomarkers and therapeutic targets for colorectal cancer (CRC).

Methods: A library consisting of 1056 FDA-approved drugs was screened for anticancer agents. WST-1, colony-formation, flow cytometry, and tumor xenograft assays were used to determine the anticancer effect of azelastine. Quantitative proteomics, confocal imaging, Western blotting and JC-1 assays were performed to examine the effects on mitochondrial pathways. The target protein of azelastine was analyzed and confirmed by DARTS, WST-1, Biacore and tumor xenograft assays. Immunohistochemistry, gain- and loss-of-function experiments, WST-1, colony-formation, immunoprecipitation, and tumor xenograft assays were used to examine the functional and clinical significance of ARF1 in colon tumorigenesis.

Results: Azelastine, a current anti-allergic drug, was found to exert a significant inhibitory effect on CRC cell proliferation in vitro and in vivo, but not on ARF1-deficient or ARF1-T48S mutant cells. ARF1 was identified as a direct target of azelastine. High ARF1 expression was associated with advanced stages and poor survival of CRC. ARF1 promoted colon tumorigenesis through its interaction with IQGAP1 and subsequent activation of ERK signaling and mitochondrial fission by enhancing the interaction of IQGAP1 with MEK and ERK. Mechanistically, azelastine bound to Thr-48 in ARF1 and repressed its activity, decreasing Drp1 phosphorylation. This, in turn, inhibited mitochondrial fission and suppressed colon tumorigenesis by blocking IQGAP1-ERK signaling.

Conclusions: This study provides the first evidence that azelastine may be novel therapeutics for CRC treatment. ARF1 promotes colon tumorigenesis, representing a promising biomarker and therapeutic target in CRC.

Long non-coding RNA RACGAP1P promotes breast cancer invasion and metastasis via miR-345-5p/RACGAP1-mediated mitochondrial fission

Long non-coding RNAs (lncRNAs) are emerging as key molecules in various cancers, yet their potential roles in the pathogenesis of breast cancer are not fully understood. Herein, using microarray analysis, we revealed that the lncRNA RACGAP1P, the pseudogene of Rac GTPase activating protein 1 (RACGAP1), was up-regulated in breast cancer tissues. Its high expression was confirmed in 25 pairs of breast cancer tissues and 8 breast cell lines by qRT-PCR. Subsequently, we found that RACGAP1P expression was positively correlated with lymph node metastasis, distant metastasis, TNM stage, and shorter survival time in 102 breast cancer patients. Then, in vitro and in vivo experiments were designed to investigate the biological function and regulatory mechanism of RACGAP1P in breast cancer cell lines. Overexpression of RACGAP1P in MDA-MB-231 and MCF7 breast cell lines increased their invasive ability and enhanced their mitochondrial fission. Conversely, inhibition of mitochondrial fission by Mdivi-1 could reduce the invasive ability of RACGAP1P-overexpressing cell lines. Furthermore, the promotion of mitochondrial fission by RACGAP1P depended on its competitive binding with miR-345-5p against its parental gene RACGAP1, leading to the activation of dynamin-related protein 1 (Drp1). In conclusion, lncRNA RACGAP1P promotes breast cancer invasion and metastasis via miR-345-5p/RACGAP1 pathway-mediated mitochondrial fission.

Sirtuins' control of autophagy and mitophagy in cancer

Mammalian cells use a specialized and complex machinery for the removal of altered proteins or dysfunctional organelles. Such machinery is part of a mechanism called autophagy. Moreover, when autophagy is specifically employed for the removal of dysfunctional mitochondria, it is called mitophagy. Autophagy and mitophagy have important physiological implications and roles associated with cellular differentiation, resistance to stresses such as starvation, metabolic control and adaptation to the changing microenvironment. Unfortunately, transformed cancer cells often exploit autophagy and mitophagy for sustaining their metabolic reprogramming and growth to a point that autophagy and mitophagy are recognized as promising targets for ongoing and future antitumoral therapies. Sirtuins are NAD+ dependent deacylases with a fundamental role in sensing and modulating cellular response to external stresses such as nutrients availability and therefore involved in aging, oxidative stress control, inflammation, differentiation and cancer. It is clear, therefore, that autophagy, mitophagy and sirtuins share many common aspects to a point that, recently, sirtuins have been linked to the control of autophagy and mitophagy. In the context of cancer, such a control is obtained by modulating transcription of autophagy and mitophagy genes, by post translational modification of proteins belonging to the autophagy and mitophagy machinery, by controlling ROS production or major metabolic pathways such as Krebs cycle or glutamine metabolism. The present review details current knowledge on the role of sirtuins, autophagy and mitophagy in cancer to then proceed to discuss how sirtuins can control autophagy and mitophagy in cancer cells. Finally, we discuss sirtuins role in the context of tumor progression and metastasis indicating glutamine metabolism as an example of how a concerted activation and/or inhibition of sirtuins in cancer cells can control autophagy and mitophagy by impinging on the metabolism of this fundamental amino acid.

Different Effects of Metformin and A769662 on Sodium Iodate-Induced Cytotoxicity in Retinal Pigment Epithelial Cells: Distinct Actions on Mitochondrial Fission and Respiration

Oxidative stress-associated retinal pigment epithelium (RPE) cell death is critically implicated in the pathogenesis of visual dysfunction and blindness of retinal degenerative diseases. Sodium iodate (NaIO₃) is an oxidative retinotoxin and causes RPE damage. Previously, we found that NaIO₃ can induce human ARPE-19 cell death via inducing mitochondrial fission and mitochondrial dysfunction. Although metformin has been demonstrated to benefit several diseases possibly via AMP-activated protein kinase (AMPK) activation, it remains unknown how AMPK affects retinopathy in NaIO₃ model. Therefore, in this study, we compared the effects of metformin and AMPK activator A769662 on NaIO₃-induced cellular stress and toxicity. We found that A769662 can protect cells against NaIO₃-induced cytotoxicity, while metformin exerts an enhancement in cell death. The mitochondrial reactive oxygen species (ROS) production as well as mitochondrial membrane potential loss induced by NaIO₃ were not altered by both agents. In addition, NaIO₃-induced cytosolic ROS production, possibly from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and counteracting cell death, was not altered by A769662 and metformin. Notably, NaIO₃-induced mitochondrial fission and inhibition of mitochondrial respiration for ATP turnover were reversed by A769662 but not by metformin. In agreement with the changes on mitochondrial morphology, the ERK-Akt signal axis dependent Drp-1 phosphorylation at S616 (an index of mitochondrial fission) under NaIO₃ treatment was blocked by A769662, but not by metformin. In summary, NaIO₃-induced cell death in ARPE cells primarily comes from mitochondrial dysfunction due to dramatic fission and inhibition of mitochondrial respiration. AMPK activation can exert a protection by restoring mitochondrial respiration and inhibition of ERK/Akt/Drp-1 phosphorylation, leading to a reduction in mitochondrial fission. However, inhibition of respiratory complex I by metformin might deteriorate mitochondrial dysfunction and cell death under NaIO₃ stress.

Mitochondrial Dynamics: Fission and Fusion in Fate Determination of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are pivotal to tissue homeostasis, repair, and regeneration due to their potential for self-renewal, multilineage differentiation, and immune modulation. Mitochondria are highly dynamic organelles that maintain their morphology via continuous fission and fusion, also known as mitochondrial dynamics. MSCs undergo specific mitochondrial dynamics during proliferation, migration, differentiation, apoptosis, or aging. Emerging evidence suggests that mitochondrial dynamics are key contributors to stem cell fate determination. The coordination of mitochondrial fission and fusion is crucial for cellular function and stress responses, while abnormal fission and/or fusion causes MSC dysfunction. This review focuses on the role of mitochondrial dynamics in MSC commitment under physiological and stress conditions. We highlight mechanistic insights into modulating mitochondrial dynamics and mitochondrial strategies for stem cell-based regenerative medicine. These findings shed light on the contribution of mitochondrial dynamics to MSC fate and MSC-based tissue repair.

miR-424-5p regulates cell proliferation and migration of esophageal squamous cell carcinoma by targeting SIRT4

Objective: The present research is aimed to elucidate the expression patterns of miR-424-5p and its role in tumorigenesis and progression of esophageal squamous cell carcinoma (ESCC).

Methods: Both starBase and TCGA were utilized to assess miR-424-5p expression status in ESCC. The endogenous mRNA expression levels of miR-424-5p in ESCC and normal esophagus cell lines were detected by qRT-PCR. CCK8 and colony-forming assays were applied to determine the effects of miR-424-5p on ESCC proliferation. Transwell migration and wound healing assays were carried out to observe the changes of ESCC cell mobility after miR-424-5p mimic or inhibitor transfection. Impact of miR-424-5p on malignancy growth in vivo was further verified in a mouse xenograft model. The regulatory relationships between miR-424-5p and SIRT4 were validated by dual luciferase reporter assay, qRT-PCR and Western blot.

Results: miR-424-5p expression was found upregulated in ESCC. miR-424-5p overexpression dramatically facilitated ESCC cells proliferation and migration capacity in vitro, while downregulation of miR-424-5p displayed the opposite trend. Inhibition of xenograft tumor growth was further evidenced in vivo. Moreover, SIRT4 was confirmed to be a specific target gene of miR-424-5p in ESCC and negatively modulated by miR-424-5p. Finally, SIRT4 overexpression strongly rescued the promoting influence of miR-424-5p on the proliferative and migratory capacity of ESCC cells.

Conclusions: miR-424-5p had tumor promoting functions in proliferation and migration of ESCC by targeting SIRT4, suggesting that miR-424-5p may serve as a potential diagnostic biomarker and manipulation of miR-424-5p/SIRT4 axis could provide a novel therapeutic strategy for further ESCC treatment.