The prohibitin protein complex promotes mitochondrial stabilization and cell survival in hematologic malignancies

Emerging roles of prohibitins in cancer: an update

The prohibitin (PHB) family, including PHB1 and its homolog PHB2, is ubiquitously located in different cellular compartments and plays roles in fundamental cellular processes such as proliferation, differentiation, and apoptosis. Accumulating evidence has indicated that this family contributes to the development of numerous diseases in particular cancers. Aberrant expressions of PHBs can been observed in diverse types of human cancer. Depending on their cell compartment-specific attributes and interacting proteins, PHBs are tightly linked to almost all aspects of cancer biology and have distinct bidirectional functions of tumor-suppression or tumor-promotion. However, the roles of PHBs in cancer have yet to be fully characterized and understood. This review provides an updated overview of the pleiotropic effects of PHBs and emphasizes their characteristic roles in each cancer respectively, with the great expectation to identify potential targets for therapeutic approaches and promising molecular biomarkers for cancer diagnosis and prognostic monitor.

Unravelling the anti-apoptotic role of Plasmodium falciparum Prohibitin-2 (PfPhb2) in maintaining mitochondrial homeostasis

The functional mitochondrion is vital for the propagation of the malaria parasite in the human host. Members of the SPFH protein family, Prohibitins (PHBs), are known to play crucial roles in maintaining mitochondrial homeostasis and cellular functions. Here, we have functionally characterized the homologue of the Plasmodium falciparumProhibitin-2 (PfPhb2) protein. A transgenic parasite line, generated using the selection-linked integration (SLI) strategy for C-terminal tagging, was utilized for cellular localization as well as for inducible knock-down of PfPhb2. We show that PfPhb2 localizes in the parasite mitochondrion during the asexual life cycle. Inducible knock-down of PfPhb2 by GlmS ribozyme caused no significant effect on the growth and multiplication of parasites. However, depletion of PfPhb2 under mitochondrial-specific stress conditions, induced by inhibiting the essential mitochondrial AAA-protease, ClpQ protease, results in enhanced inhibition of parasite growth, mitochondrial ROS production, mitochondrial membrane potential loss and led to mitochondrial fission/fragmentation, ultimately culminating in apoptosis-like cell-death. Further, PfPhb2 depletion renders the parasites more susceptible to mitochondrial targeting drug proguanil. These data suggest the functional involvement of PfPhb2 along with ClpQ protease in stabilization of various mitochondrial proteins to maintain mitochondrial homeostasis and functioning. Overall, we show that PfPhb2 has an anti-apoptotic role in maintaining mitochondrial homeostasis in the parasite.

Sesaminol alters phospholipid metabolism and alleviates obesity-induced NAFLD

The prevalence of obesity-induced non-alcoholic fatty liver disease (NAFLD) and insulin resistance is increasing worldwide. We previously demonstrated that sesaminol increases thermogenesis in adipocytes, improves insulin sensitivity, and mitigates obesity in mice. In this study, we demonstrated that sesaminol increased mitochondrial activity and reduced ROS production in hepatocytes. Therefore, we delve into the metabolic action of sesaminol in obesity-induced NAFLD or metabolic dysfunction-associated liver disease (MAFLD). Here, we report that sesaminol induces OXPHOS proteins and mitochondrial function in vivo. Further, our data suggest that sesaminol administration reduces hepatic triacylglycerol accumulation and LDL-C levels. Prominently, the lipidomics analyses revealed that sesaminol administration decreased the major phospholipids such as PC, PE, PI, CL, and PS to maintain membrane lipid homeostasis in the liver upon HFD challenge. Besides, SML reduced ePC and SM molecular species and increased PA levels in the HFD-fed mice. Also, sesaminol renders anti-inflammatory properties and dampens fibrosis markers in the liver. Remarkably, SML lowers the hepatic levels of ALT and AST enzymes and alleviates NAFLD in diet-induced obese mice. The molecular docking analysis identifies peroxisome proliferator-activated receptors as potential endogenous receptors for sesaminol. Together, our study demonstrates plant lignan sesaminol as a potential small molecule that alters the molecular species of major phospholipids, including sphingomyelin and ether-linked PCs in the liver tissue, improves metabolic parameters, and alleviates obesity-induced fatty liver disease in mice.

Moringin, an isothiocyanate modulates multiple cellular signalling molecules in breast cancer cells

Prohibitin (PHB) is a pleiotropic molecule with a variety of known functions and subcellular locations. PHB's function in breast cancer is poorly understood. Herein, we report that PHB is expressed in cancer types of diverse origin including breast cancer. The cancer patients with changes in PHB were reported to have significantly reduced 'overall survival' in comparison to the cases without alterations in PHB. The expression of PHB was increased by H2O2 and also by Moringin (MG), which is an isothiocyanate derived from the seeds of Moringa oleifera. MG interacted with PHB, DRP1, and SLP2 and inhibited the growth of MCF-7 and MDAMB-231 cells. The isothiocyanate triggered apoptosis in breast cancer cells as revealed by AO/PI assay, phosphatidylserine externalization, cell cycle analysis and DAPI staining. MG induced proapoptotic proteins expression such as cytochrome c, p53, and cleaved caspase-7. Further, cell survival proteins such as survivin, Bcl-2, and Bcl-xL were suppressed. A depolarization of membrane potential suggested that the apoptosis was triggered through mitochondria. The isothiocyanate suppressed the cancer cell migration and interacted with NF-κB subunits. MG suppressed p65 nuclear translocation induced by TNF-α. The reactive oxygen species generation was also induced by the isothiocyanate in breast cancer cells. MG also modulated the expression of lncRNAs. Collectively, the functions of PHB in breast cancer growth is evident from this study. The activities of MG against breast cancer might result from its ability to modulate multiple cancer-related targets.

UBXN1 promotes liver tumorigenesis by regulating mitochondrial homeostasis

BACKGROUND

The maintenance of mitochondrial homeostasis is critical for tumor initiation and malignant progression because it increases tumor cell survival and growth. The molecular events controlling mitochondrial integrity that facilitate the development of hepatocellular carcinoma (HCC) remain unclear. Here, we report that UBX domain-containing protein 1 (UBXN1) hyperactivation is essential for mitochondrial homeostasis and liver tumorigenesis.

METHODS

Oncogene-induced mouse liver tumor models were generated with the Sleeping Beauty (SB) transposon delivery system. Assessment of HCC cell growth in vivo and in vitro, including tumour formation, colony formation, TUNEL and FACS assays, was conducted to determine the effects of UBXN1 on HCC cells, as well as the involvement of the UBXN1-prohibitin (PHB) interaction in mitochondrial function. Coimmunoprecipitation (Co-IP) was used to assess the interaction between UBXN1 and PHB. Liver hepatocellular carcinoma (LIHC) datasets and HCC patient samples were used to assess the expression of UBXN1.

RESULTS

UBXN1 expression is commonly upregulated in human HCCs and mouse liver tumors and is associated with poor overall survival in HCC patients. UBXN1 facilitates the growth of human HCC cells and promotes mouse liver tumorigenesis driven by the NRas/c-Myc or c-Myc/shp53 combination. UBXN1 interacts with the inner mitochondrial membrane protein PHB and sustains PHB expression. UBXN1 inhibition triggers mitochondrial damage and liver tumor cell apoptosis.

CONCLUSIONS

UBXN1 interacts with PHB and promotes mitochondrial homeostasis during liver tumorigenesis.

Dual-specificity phosphatase 1 interacts with prohibitin 2 to improve mitochondrial quality control against type-3 cardiorenal syndrome

Type-3 cardiorenal syndrome (CRS-3) is acute kidney injury followed by cardiac injury/dysfunction. Mitochondrial injury may impair myocardial function during CRS-3. Since dual-specificity phosphatase 1 (DUSP1) and prohibitin 2 (PHB2) both promote cardiac mitochondrial quality control, we assessed whether these proteins were dysregulated during CRS-3-related cardiac depression. We found that DUSP1 was downregulated in heart tissues from a mouse model of CRS-3. DUSP1 transgenic (DUSP1Tg) mice were protected from CRS-3-induced myocardial damage, as evidenced by their improved heart function and myocardial structure. CRS-3 induced the inflammatory response, oxidative stress and mitochondrial dysfunction in wild-type hearts, but not in DUSP1Tg hearts. DUSP1 overexpression normalized cardiac mitochondrial quality control during CRS-3 by suppressing mitochondrial fission, restoring mitochondrial fusion, re-activating mitophagy and augmenting mitochondrial biogenesis. We found that DUSP1 sustained cardiac mitochondrial quality control by binding directly to PHB2 and maintaining PHB2 phosphorylation, while CRS-3 disrupted this physiological interaction. Transgenic knock-in mice carrying the Phb2S91D variant were less susceptible to cardiac depression upon CRS-3, due to a reduced inflammatory response, suppressed oxidative stress and improved mitochondrial quality control in their heart tissues. Thus, CRS-3-induced myocardial dysfunction can be attributed to reduced DUSP1 expression and disrupted DUSP1/PHB2 binding, leading to defective cardiac mitochondrial quality control.

Essential Protein PHB2 and Its Regulatory Mechanisms in Cancer

Prohibitins (PHBs) are a highly conserved class of proteins and have an essential role in transcription, epigenetic regulation, nuclear signaling, mitochondrial structural integrity, cell division, and cellular membrane metabolism. Prohibitins form a heterodimeric complex, consisting of two proteins, prohibitin 1 (PHB1) and prohibitin 2 (PHB2). They have been discovered to have crucial roles in regulating cancer and other metabolic diseases, functioning both together and independently. As there have been many previously published reviews on PHB1, this review focuses on the lesser studied prohibitin, PHB2. The role of PHB2 in cancer is controversial. In most human cancers, overexpressed PHB2 enhances tumor progression, while in some cancers, it suppresses tumor progression. In this review, we focus on (1) the history, family, and structure of prohibitins, (2) the essential location-dependent functions of PHB2, (3) dysfunction in cancer, and (4) the promising modulators to target PHB2. At the end, we discuss future directions and the clinical significance of this common essential gene in cancer.

Overexpression of Prohibitin 2 Protein is Associated with Adverse Prognosis in Cytogenetically Normal Acute Myeloid Leukemia

Cytogenetically normal acute myeloid leukemia (CN-AML) accounts for 40%–50% of all AML cases. Despite advances in understanding the molecular pathophysiology of CN-AML, its clinical outcome remains unsatisfactory and unpredictable. To investigate its clinical implication in CN-AML, we measured the expression of prohibitin 2 (PHB2) using immunohistochemical staining (IHCS) of paraffin-embedded bone marrow sections from 134 CN-AML patients. IHCS results were semi-quantitatively scored. Clinical outcome was analyzed in comparison with other prognostic markers, including NPM1 polymorphism and FLT3 internal tandem duplication, and WT1 and BAALC mRNA expression. Except for BAALC mRNA expression, the known molecular markers showed no prognostic effect in the CN-AML patients. PHB2 protein overexpression was significantly associated with adverse prognosis in CN-AML patients. The PHB2 protein expression status may serve as an independent prognostic indicator in CN-AML.

Genome-wide DNA hypermethylation opposes healing in chronic wound patients by impairing epithelial-to-mesenchymal transition

An extreme chronic wound tissue microenvironment causes epigenetic gene silencing. An unbiased whole-genome methylome was studied in the wound-edge tissue of patients with chronic wounds. A total of 4,689 differentially methylated regions (DMRs) were identified in chronic wound-edge skin compared with unwounded human skin. Hypermethylation was more frequently observed (3,661 DMRs) in the chronic wound-edge tissue compared with hypomethylation (1,028 DMRs). Twenty-six hypermethylated DMRs were involved in epithelial-mesenchymal transition (EMT). Bisulfite sequencing validated hypermethylation of a predicted specific upstream regulator TP53. RNA-Seq analysis was performed to qualify findings from methylome analysis. Analysis of the downregulated genes identified the TP53 signaling pathway as being significantly silenced. Direct comparison of hypermethylation and downregulated genes identified 4 genes, ADAM17, NOTCH, TWIST1, and SMURF1, that functionally represent the EMT pathway. Single-cell RNA-Seq studies revealed that these effects on gene expression were limited to the keratinocyte cell compartment. Experimental murine studies established that tissue ischemia potently induces wound-edge gene methylation and that 5′-azacytidine, inhibitor of methylation, improved wound closure. To specifically address the significance of TP53 methylation, keratinocyte-specific editing of TP53 methylation at the wound edge was achieved by a tissue nanotransfection-based CRISPR/dCas9 approach. This work identified that reversal of methylation-dependent keratinocyte gene silencing represents a productive therapeutic strategy to improve wound closure.

Elucidation of the changes occurring at the proteome level in ovaries of high-fat diet-induced obese rats

High-fat diet-induced obesity adversely affects the female reproductive system. The metabolic changes that the high-fat diet causes on the ovaries have not been elucidated. Herein, to understand the molecular and cellular mechanisms underlying the effects of long-term high-fat diet-fed, the changes in the global proteomic profile of the rat ovaries were investigated. The female rats were randomly divided into two groups based on their diets: the ones that were fed with the high-fat diet and the other ones that were fed with the control diet for 18 weeks. To identify differentially expressed proteins, the changes in ovary proteomes were investigated by two-dimensional electrophoresis coupled to matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight and label-free quantification with nano-high performance liquid chromatography to tandem mass spectrometry (nHPLC-MS/MS). A total of 80 proteins were differentially regulated. The upregulated proteins were involved in responses to chemical and organic substances, cytokines, external stimuli, and lipids. These proteins were particularly associated with vesicles, microbodies, and cell surface proteins. The downregulated proteins were involved in biological processes associated with cellular respiration. Those proteins created a network consisting of proteins involved in aerobic respiration and energy generation. Our results demonstrated that the mechanisms related to energy production in the ovary tissue were particularly affected by the high-fat diet.

Sensitive electrochemical immunosensor to detect prohibitin 2, a potential blood cancer biomarker

Blood cancers are difficult to cure completely and frequently show a poor prognosis. Recently, prohibitin 2 (PHB2) has been shown to be a potential biomarker for blood cancers. Sandwich ELISA can be used as a reference method for quantitative analysis of PHB2; however, ELISA can be challenging for early diagnosis and continuous monitoring method due to the need for large sample volumes (25 μL <), technical expertise, complex procedure, relative high cost, and non-portability. Thus, this study developed a sensitive and time efficient electrochemical immunosensor for detecting PHB2 from a blood cancer patient. It is a simple and portable platform consisting of a disposable electrode and blood sample volume of 4 μL. The sensor uses a gold nanostructured electrode and square wave voltammetry (SWV) measurement of a horseradish peroxidase (HRP) label to amplify the electrochemical signal. The immunosensor could quantitatively detect PHB2 with high sensitivity (limit of detection [LoD] = 0.04 ng/mL) and satisfactory reproducibility (relative standard deviation [RSD] <5.2%). The sensor achieved an LoD of 0.63 ng/mL with satisfactory recovery (89.1-104.7%) and reproducibility (RSD <6.4%) with PHB2 spiked into white blood cell (WBC) lysates. When the sensor was compared to a reference ELISA to determine the PHB2 concentrations in WBC lysate samples from healthy patients and those with blood cancer, the correlation coefficient (R²) was 0.996. A 3.3-fold difference was detected in the measured PHB2 concentration between blood cancer patients and healthy individuals. Accordingly, this study suggests a sensitive and accurate analytical method for quantitatively detecting the PHB2 in blood samples.

Quadruple and Truncated MEK3 Mutants Identified from Acute Lymphoblastic Leukemia Promote Degradation and Enhance Proliferation

Compared to other ethnicities, Hispanic children incur the highest rates of leukemia, and most cases are diagnosed as Acute Lymphoblastic Leukemia (ALL). Despite improved treatment and survival for ALL, disproportionate health outcomes in Hispanics persist. Thus, it is essential to identify oncogenic mutations within this demographic to aid in the development of new strategies to diagnose and treat ALL. Using whole-exome sequencing, five single nucleotide polymorphisms within mitogen-activated protein kinase 3 (MAP2K3) were identified in an ALL cancer patient library from the U.S./Mexico border. MAP2K3 R26T and P11T are located near the substrate-binding site, while R65L and R67W localized to the kinase domain. Truncated-MAP2K3 mutant Q73* was also identified. Transfection in HEK293 cells showed that the quadruple-MEK3 mutant (4M-MEK3) impacted protein stability, inducing degradation and reducing expression. The expression of 4M-MEK3 could be rescued by cysteine/serine protease inhibition, and proteasomal degradation of truncated-MEK3 occurred in a ubiquitin-independent manner. MEK3 mutants displayed reduced auto-phosphorylation and enzymatic activity, as seen by decreases in p38 phosphorylation. Furthermore, uncoupling of the MEK3/p38 signaling pathway resulted in less suppressive activity on HEK293 cell viability. Thus, disruption of MEK3 activation may promote proliferative signals in ALL. These findings suggest that MEK3 represents a potential therapeutic target for treating ALL.

Role of Prohibitins in Aging and Therapeutic Potential Against Age-Related Diseases

A decline in mitochondrial function has long been associated with age-related health decline. Several lines of evidence suggest that interventions that stimulate mitochondrial autophagy (mitophagy) can slow aging and prolong healthy lifespan. Prohibitins (PHB1 and PHB2) assemble at the mitochondrial inner membrane and are critical for mitochondrial homeostasis. In addition, prohibitins (PHBs) have diverse roles in cell and organismal biology. Here, we will discuss the role of PHBs in mitophagy, oxidative phosphorylation, cellular senescence, and apoptosis. We will also discuss the role of PHBs in modulating lifespan. In addition, we will review the links between PHBs and diseases of aging. Finally, we will discuss the emerging concept that PHBs may represent an attractive therapeutic target to counteract aging and age-onset disease.

GOLPH3 promotes glioma progression by enhancing PHB2-mediated autophagy

Due to the hypoxia and nutrient deficiency microenvironment, malignant glioma exhibits high autophagy activity and autophagy plays a significant role in the occurrence and development of glioma. However, the potential molecular mechanism of autophagy in glioma remains unknown. In this study, we demonstrated that Golgi phosphorylation protein 3 (GOLPH3), a highly conserved protein basically concentrates in the trans-Golgi network, promoted glioma autophagy. Inhibiting autophagy by using chloroquine suppressed the stimulating effect of GOLPH3 on glioma malignant development both in vitro and in vivo. Mechanistically, GOLPH3 interacted with and recruited prohibitin-2 (PHB2), an autophagy receptor of mitochondrion, and LC3-II. PHB2 promoted cell autophagy and down-regulation of PHB2 abolished the effect of GOLPH3 on autophagy. On the side, the relative mRNA and protein levels of GOLPH3 and PHB2 were positively associated with each other and both also correlated with autophagy in glioma tissues. Together, our results revealed that GOLPH3 promotes glioma progression by enhancing PHB2-mediated autophagy and inhibiting autophagy may benefit glioma patients with GOLPH3 high level. The novel GOLPH3-PHB2-autophagy axis maybe a potential and prospective therapeutic target for gliomas.

Can Prohibitin 1 be a Safeguard against liver disease?

Prohibitin (PHB) 1 is involved in multiple regulatory pathways in liver disease to protect hepatocytes, and its function is associated with subcellular localization. PHB1 located in the nucleus, cytoplasm and the mitochondrial inner membrane has anti-oxidative stress and anti-inflammatory effects in hepatitis and cirrhosis, which can protect liver cells from damage caused by inflammatory factors and reactive oxygen species (ROS) stimulation. The low expression of PHB1 located in the nucleus of liver cancer cells inhibits the proliferation and metastasis of liver cancer; thus, PHB1 exhibits the function of a tumor suppressor gene. Understanding the mechanisms of PHB1 in liver diseases may be useful for further research on the disease and may provide new ideas for the development of targeted therapeutic drugs in the future. Therefore, this review puts forward an overview of the role of PHB1 and its protective mechanism in liver diseases.

The BCL-2 family members NOXA and BIM mediate fluorizoline-induced apoptosis in multiple myeloma cells

Fluorizoline is a new synthetic molecule that induces apoptosis by selectively targeting prohibitins. In this study, we have assessed the pro-apoptotic effect of fluorizoline in 3 different multiple myeloma cell lines and 12 primary samples obtained from treatment-naïve multiple myeloma patients. Fluorizoline induced apoptosis in both multiple myeloma cell lines and primary samples at concentrations in the low micromolar range. All primary samples were sensitive to fluorizoline. Moreover, fluorizoline increased the mRNA and protein levels of the pro-apoptotic BCL-2 family member NOXA both in cell lines and primary samples analyzed. Finally, NOXA-depletion by CRISPR/Cas9 in cells that do not express BIM conferred resistance to fluorizoline-induced apoptosis in multiple myeloma cells. These results suggest that targeting prohibitins could be a new therapeutic strategy for myeloma multiple.

Aberrant Expression of Prohibitin Is Related to Prognosis of Nasal Extranodal Natural Killer/T Cell Lymphoma, Nasal Type

INTRODUCTION

Nasal extranodal natural killer (NK)/T cell lymphoma, nasal type (ENKTCL) is a high-grade Epstein-Barr virus (EBV)-associated malignancy with poor outcomes. There are few biomarkers for the accurate diagnosis and prognostic prediction of the disease. The aim of this study was to investigate the clinicopathological significance of prohibitin (PHB) expression in nasal ENKTCL.

METHODS

The expression level of PHB was detected via immunohistochemical staining in 49 nasal ENKTCL tissues and age- and sex-matched controls of 30 nasal mucosa-reactive lymphoid hyperplasia (NRLH) tissues. The correlations between the PHB expression and clinicopathological features of patients with nasal ENKTCL were evaluated.

RESULTS

The results indicated a significantly decreased expression of PHB in nasal ENKTCL tissues compared with in NRLH tissues. Low-level PHB expression was significantly associated with younger age and fever (p = 0.008 and 0.018, respectively). The Kaplan-Meier analysis showed that the cytoplasm expression level of PHB in nasal ENKTCL was inversely related to overall survival (p = 0.046).

CONCLUSIONS

PHB may be a potential diagnostic marker and prognostic predictor of nasal ENKTCL.

Prohibitin 2/PHB2 in Parkin-Mediated Mitophagy: A Potential Therapeutic Target for Non-Small Cell Lung Carcinoma

Background

Mitophagy, a selective autophagy process, plays various roles in tumors. Prohibitin 2 (PHB2) is an inner-mitochondrial membrane protein that participates in parkin-induced mitophagy. However, the role of PHB2 in non-small cell lung carcinoma (NSCLC) has not been previously reported.

Material/Methods

PHB2 protein or PHB2-mRNA in NSCLC and paired normal tissues was determined by Western blot, qRT-PCR, and immunohistochemical staining. Cell proliferation was detected by CCK-8 assay. Cell migration was evaluated by wound healing and transwell migration assays. A 3D live-cell confocal system was used to monitor autophagic flux. Mitochondrial autolysosomes were observed by transmission electron microscopy (TEM). Finally, we performed JC-1 assay to measure mitochondrial membrane potential (MMP).

Results

The level of PHB2 was significantly increased in human NSCLC specimens compared to paired adjacent specimens. Inhibition of PHB2 expression attenuated mitophagy in A549 and H1299 cells, as indicated by decreased levels of LC3 II/I and parkin markers and increased level of p62 protein. Furthermore, the inhibition caused reduction in mitochondrial autolysosomes and autophagic flux, as shown by TEM and live-cell imaging, respectively. In addition, PHB2 inhibition caused a remarkable increase in MMP and suppressed the proliferation and migration of A549 and H1299 cells.

Conclusions

Our results suggest that downregulation of PHB2 reduced parkin-mediated mitophagy, which suppressed proliferation and migration of A549 and H1299 cells.

PBMC of Multiple Sclerosis Patients Show Deregulation of OPA1 Processing Associated with Increased ROS and PHB2 Protein Levels

Multiple sclerosis (MS) is an autoimmune disease in which activated lymphocytes affect the central nervous system. Increase of reactive oxygen species (ROS), impairment of mitochondria-mediated apoptosis and mitochondrial alterations have been reported in peripheral lymphocytes of MS patients. Mitochondria-mediated apoptosis is regulated by several mechanisms and proteins. Among others, optic atrophy 1 (OPA1) protein plays a key role in the regulating mitochondrial dynamics, cristae architecture and release of pro-apoptotic factors. Very interesting, mutations in OPA1 gene, have been associated with multiple sclerosis-like disorder. We have analyzed OPA1 and some factors involved in its regulation. Fifteen patients with MS and fifteen healthy control subjects (HC) were enrolled into the study and peripheral blood mononuclear cells (PBMCs) were isolated. H₂O₂ level was measured spectrofluorimetrically, OPA1, PHB2, SIRT3, and OMA1 were analyzed by western blotting. Statistical analysis was performed using Student's t-test. The results showed that PBMC of MS patients were characterized by a deregulation of OPA1 processing associated with increased H₂O₂ production, inactivation of OMA1 and increase of PHB2 protein level. The presented data suggest that the alteration of PHB2, OMA1, and OPA1 processing could be involved in resistance towards apoptosis. These molecular parameters could also be useful to assess disease activity.

Enhancing Glycolysis Protects against Ischemia-Reperfusion Injury by Reducing ROS Production

After myocardial ischemia-reperfusion, fatty acid oxidation shows fast recovery while glucose oxidation rates remain depressed. A metabolic shift aimed at increasing glucose oxidation has shown to be beneficial in models of myocardial ischemia-reperfusion. However, strategies aimed at increasing glucose consumption in the clinic have provided mixed results and have not yet reached routine clinical practice. A better understanding of the mechanisms underlying the protection afforded by increased glucose oxidation may facilitate the transfer to the clinic. The purpose of this study was to evaluate if the modulation of reactive oxygen species (ROS) was involved in the protection afforded by increased glucose oxidation. Firstly, we characterized an H9C2 cellular model in which the use of glucose or galactose as substrates can modulate glycolysis and oxidative phosphorylation pathways. In this model, there were no differences in morphology, cell number, or ATP and PCr levels. However, galactose-grown cells consumed more oxygen and had an increased Krebs cycle turnover, while cells grown in glucose had increased aerobic glycolysis rate as demonstrated by higher lactate and alanine production. Increased aerobic glycolysis was associated with reduced ROS levels and protected the cells against simulated ischemia-reperfusion injury. Furthermore, ROS scavenger N-acetyl cysteine (NAC) was able to reduce the amount of ROS and to prevent cell death. Lastly, cells grown in galactose showed higher activation of mTOR/Akt signaling pathways. In conclusion, our results provide evidence indicating that metabolic shift towards increased glycolysis reduces mitochondrial ROS production and prevents cell death during ischemia-reperfusion injury.

Prohibitin (PHB) expression is associated with aggressiveness in DLBCL and flavagline-mediated inhibition of cytoplasmic PHB functions induces anti-tumor effects

BACKGROUND

Diffuse large B-cell lymphomas (DLBCLs) are aggressive lymphomas accounting for approximately a third of non-Hodgkin lymphomas. Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are scaffold proteins that promote mitochondria homeostasis and consequently cell survival, but biological functions of cytoplasmic PHBs remain largely unknown in DLBCL.

METHODS

PHB expression was analyzed in 82 DLBCL biopsies and five DLBCL cell lines by immunohistochemistry (IHC) and Western blotting. Pharmacological inhibition of PHB using the synthetic flavagline FL3 was realized in vitro to gain insight PHB cellular functions. Effects of FL3 on DLBCL cell line viability, apoptosis, C-Raf-ERK-MNK-eIF4E signaling pathway and eIF4F complex formation and activity were evaluated by XTT assay, annexin V-FITC/PI dual staining and Western blotting respectively. Subcutaneous DLBCL xenograft model in SCID mice was also performed to determine in vivo FL3 effect.

RESULTS

As in DLBCL cell lines, PHB1 and PHB2 were expressed in germinal center B-cell-like (GCB) and activated B-cell-like (ABC) subtypes. In patient samples, high PHB levels were associated with higher serum LDH (PHB1 and PHB2), IPIaa (PHB2), and Ki-67 (PHB2) expression. Higher PHB1 expression tends to be associated with shorter event-free survival (EFS) in patients, especially in male patients. FL3 induced apoptosis of DLBCL cell lines that was associated with inhibition of the ERK-MNK-eIF4E signaling pathway, including aggressive double/triple-hit DLBCL cell lines. This resulted in altered eIF4F complex formation and activity leading to a reduction of Bcl-2 and c-Myc expression levels. Moreover, FL3 strongly downregulated DLBCL cellular levels of Akt protein and AKT mRNA. FL3 antitumor activity was also confirmed in vivo in a murine xenograft model.

CONCLUSION

Our data indicate that PHB overexpression is associated with markers of tumor aggressiveness in DLBCL, and that targeting PHBs may be a therapeutic option, notably in aggressive subtypes.

Human Ovarian Cancer Tissue Exhibits Increase of Mitochondrial Biogenesis and Cristae Remodeling

Ovarian cancer (OC) is the most lethal gynecologic cancer characterized by an elevated apoptosis resistance that, potentially, leads to chemo-resistance in the recurrent disease. Mitochondrial oxidative phosphorylation was found altered in OC, and mitochondria were proposed as a target for therapy. Molecular evidence suggests that the deregulation of mitochondrial biogenesis, morphology, dynamics, and apoptosis is involved in carcinogenesis. However, these mitochondrial processes remain to be investigated in OC. Eighteen controls and 16 OC tissues (serous and mucinous) were collected. Enzymatic activities were performed spectrophotometrically, mitochondrial DNA (mtDNA) content was measured by real-time-PCR, protein levels were determined by Western blotting, and mitochondrial number and structure were measured by electron microscopy. Statistical analysis was performed using Student’s t-test, Mann-Whitney U test, and principal component analysis (PCA). We found, in OC, that increased mitochondrial number associated with increased peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) and mitochondrial transcription factor A (TFAM) protein levels, as well as mtDNA content. The OC mitochondria presented an increased maximum length, as well as reduced cristae width and junction diameter, associated with increased optic atrophy 1 protein (OPA1) and prohibitin 2 (PHB2) protein levels. In addition, in OC tissues, augmented cAMP and sirtuin 3 (SIRT3) protein levels were observed. PCA of the 25 analyzed biochemical parameters classified OC patients in a distinct group from controls. We highlight a “mitochondrial signature” in OC that could result from cooperation of the cAMP pathway with the SIRT3, OPA1, and PHB2 proteins.

In vivo stabilization of OPA1 in hepatocytes potentiates mitochondrial respiration and gluconeogenesis in a prohibitin-dependent way

Patients with fatty liver diseases present altered mitochondrial morphology and impaired metabolic function. Mitochondrial dynamics and related cell function require the uncleaved form of the dynamin-like GTPase OPA1. Stabilization of OPA1 might then confer a protective mechanism against stress-induced tissue damages. To study the putative role of hepatic mitochondrial morphology in a sick liver, we expressed a cleavage-resistant long form of OPA1 (L-OPA1Δ) in the liver of a mouse model with mitochondrial liver dysfunction (i.e. the hepatocyte-specific prohibitin-2 knockout (Hep-Phb2^-/-) mice). Liver prohibitin-2 deficiency caused excessive proteolytic cleavage of L-OPA1, mitochondrial fragmentation, and increased apoptosis. These molecular alterations were associated with lipid accumulation, abolished gluconeogenesis, and extensive liver damage. Such liver dysfunction was associated with severe hypoglycemia. In prohibitin-2 knockout mice, expression of L-OPA1Δ by in vivo adenovirus delivery restored the morphology but not the function of mitochondria in hepatocytes. In prohibitin-competent mice, elongation of liver mitochondria by expression of L-OPA1Δ resulted in excessive glucose production associated with increased mitochondrial respiration. In conclusion, mitochondrial dynamics participates in the control of hepatic glucose production.

Mitophagy in Cancer: A Tale of Adaptation

：In the past years, we have learnt that tumors co-evolve with their microenvironment, and that the active interaction between cancer cells and stromal cells plays a pivotal role in cancer initiation, progression and treatment response. Among the players involved, the pathways regulating mitochondrial functions have been shown to be crucial for both cancer and stromal cells. This is perhaps not surprising, considering that mitochondria in both cancerous and non-cancerous cells are decisive for vital metabolic and bioenergetic functions and to elicit cell death. The central part played by mitochondria also implies the existence of stringent mitochondrial quality control mechanisms, where a specialized autophagy pathway (mitophagy) ensures the selective removal of damaged or dysfunctional mitochondria. Although the molecular underpinnings of mitophagy regulation in mammalian cells remain incomplete, it is becoming clear that mitophagy pathways are intricately linked to the metabolic rewiring of cancer cells to support the high bioenergetic demand of the tumor. In this review, after a brief introduction of the main mitophagy regulators operating in mammalian cells, we discuss emerging cell autonomous roles of mitochondria quality control in cancer onset and progression. We also discuss the relevance of mitophagy in the cellular crosstalk with the tumor microenvironment and in anti-cancer therapy responses.

Targeted OMA1 therapies for cancer

The mitochondrial inner membrane proteins OMA1 and OPA1 belong to the BAX/BAK1-dependent apoptotic signaling pathway, which can be regulated by tumor protein p53 and the prohibitins PHB and PHB2 in the context of neoplastic disease. For the most part these proteins have been studied separate from each other. Here, I argue that the OMA1 mechanism of action represents the missing link between p53 and cytochrome c release. The mitochondrial fusion protein OPA1 is cleaved by OMA1 in a stress-dependent manner generating S-OPA1. Excessive S-OPA1 can facilitate outer membrane permeabilization upon BAX/BAK1 activation through its membrane shaping properties. p53 helps outer membrane permeabilization in a 2-step process. First, cytosolic p53 activates BAX/BAK1 at the mitochondrial surface. Then, in a second step, p53 binds to prohibitin thereby releasing the restraint on OMA1. This activates OMA1, which cleaves OPA1 and promotes cytochrome c release. Clearly, OMA1 and OPA1 are not root causes for cancer. Yet many cancer cells rely on this pathway for survival, which can explain why loss of p53 function promotes tumor growth and confers resistance to chemotherapies.

Prohibitins: A Critical Role in Mitochondrial Functions and Implication in Diseases

Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are proteins that are ubiquitously expressed, and are present in the nucleus, cytosol, and mitochondria. Depending on the cellular localization, PHB1 and PHB2 have distinctive functions, but more evidence suggests a critical role within mitochondria. In fact, PHB proteins are highly expressed in cells that heavily depend on mitochondrial function. In mitochondria, these two proteins assemble at the inner membrane to form a supra-macromolecular structure, which works as a scaffold for proteins and lipids regulating mitochondrial metabolism, including bioenergetics, biogenesis, and dynamics in order to determine the cell fate, death, or life. PHB alterations have been found in aging and cancer, as well as neurodegenerative, cardiac, and kidney diseases, in which significant mitochondrial impairments have been observed. The molecular mechanisms by which prohibitins regulate mitochondrial function and their role in pathology are reviewed and discussed herein.

Prohibitin 1 Acts As a Negative Regulator of Wingless/Integrated-Beta-Catenin Signaling in Murine Liver and Human Liver Cancer Cells

Prohibitin1 (PHB1) is a mitochondrial chaperone with diverse functions that include cell proliferation, apoptosis, and mitochondrial homoeostasis. Liver‐specific Phb1 knockout (KO) mice develop spontaneous injury and hepatocellular carcinoma (HCC). Our previous work demonstrated that PHB1 negatively regulates the H19‐insulin‐like growth factor 2 (IGF2)‐H19‐IGF2 axis signaling pathway and E‐box activity in hepatocytes and HCC cells. Phb1 KO livers exhibited increased expression of multiple wingless/integrated (WNT) target genes compared to control littermates. Therefore, we hypothesized that PHB1 is a negative regulator of WNT‐beta‐catenin signaling in the liver. Analysis of livers from Phb1 KO mice demonstrated an activation of the WNT‐beta‐catenin pathway as determined by phosphorylation of glycogen synthase kinase 3 (GSK3)beta^{serine [Ser]9} and protein kinase B (AKT)^Ser473. Phb1 KO livers showed increased messenger RNA (mRNA) levels of multiple WNT ligands, with Wnt7a (79‐fold), Wnt10a (12‐fold), and Wnt16 (48‐fold) being most highly overexpressed compared to control littermates. Subcellular fractionation of liver cells from Phb1 KO mice indicated that hepatocytes are the main source of WNT ligands. Immunostaining and cellular colocalization analysis of Phb1 KO livers demonstrated expression of WNT7a, WNT10a, and WNT16 in hepatocytes. Chromatin immunoprecipitation revealed increased binding of transcription factor E2F1 (E2F1) to the Wnt10a promoter in Phb1 KO livers and WNT9A in HepG2 cells. PHB1 silencing in HepG2 cells activated WNT signaling, whereas its overexpression caused inactivation of this pathway. PHB1 silencing in HepG2 cells induced the expression of multiple WNT ligands of which WNT9A induction was partly regulated through E2F1. Conclusion: PHB1 acts as a negative regulator of WNT signaling, and its down‐regulation causes the induction of multiple WNT ligands and downstream activation of canonical WNT‐beta‐catenin signaling in murine liver and human HCC cells, in part through E2F1.