Src kinases are important regulators of mitochondrial functions

Multiomics analysis identifies oxidative phosphorylation as a cancer vulnerability arising from myristoylation inhibition

BACKGROUND

In humans, two ubiquitously expressed N-myristoyltransferases, NMT1 and NMT2, catalyze myristate transfer to proteins to facilitate membrane targeting and signaling. We investigated the expression of NMTs in numerous cancers and found that NMT2 levels are dysregulated by epigenetic suppression, particularly so in hematologic malignancies. This suggests that pharmacological inhibition of the remaining NMT1 could allow for the selective killing of these cells, sparing normal cells with both NMTs.

METHODS AND RESULTS

Transcriptomic analysis of 1200 NMT inhibitor (NMTI)-treated cancer cell lines revealed that NMTI sensitivity relates not only to NMT2 loss or NMT1 dependency, but also correlates with a myristoylation inhibition sensitivity signature comprising 54 genes (MISS-54) enriched in hematologic cancers as well as testis, brain, lung, ovary, and colon cancers. Because non-myristoylated proteins are degraded by a glycine-specific N-degron, differential proteomics revealed the major impact of abrogating NMT1 genetically using CRISPR/Cas9 in cancer cells was surprisingly to reduce mitochondrial respiratory complex I proteins rather than cell signaling proteins, some of which were also reduced, albeit to a lesser extent. Cancer cell treatments with the first-in-class NMTI PCLX-001 (zelenirstat), which is undergoing human phase 1/2a trials in advanced lymphoma and solid tumors, recapitulated these effects. The most downregulated myristoylated mitochondrial protein was NDUFAF4, a complex I assembly factor. Knockout of NDUFAF4 or in vitro cell treatment with zelenirstat resulted in loss of complex I, oxidative phosphorylation and respiration, which impacted metabolomes.

CONCLUSIONS

Targeting of both, oxidative phosphorylation and cell signaling partly explains the lethal effects of zelenirstat in select cancer types. While the prognostic value of the sensitivity score MISS-54 remains to be validated in patients, our findings continue to warrant the clinical development of zelenirstat as cancer treatment.

Hippocampal Pyk2 regulates specific social skills: Implications for schizophrenia

Pyk2 has been shown previously to be involved in several psychological and cognitive alterations related to stress, Huntington's disease, and Alzheimer's disease. All these disorders are accompanied by different types of impairments in sociability, which has recently been linked to improper mitochondrial function. We hypothesize that Pyk2, which regulates mitochondria, could be associated with the regulation of mitochondrial dynamics and social skills. In the present manuscript, we report that a reduction of Pyk2 levels in mouse pyramidal neurons of the hippocampus decreased social dominance and aggressivity. Furthermore, social interactions induced robust Pyk2-dependent hippocampal changes in several oxidative phosphorylation complexes. We also observed that Pyk2 levels were increased in the CA1 pyramidal neurons of schizophrenic subjects, occurring alongside changes in different direct and indirect regulators of mitochondrial function including DISC1 and Grp75. Accordingly, overexpressing Pyk2 in hippocampal CA1 pyramidal cells mimicked some specific schizophrenia-like social behaviors in mice. In summary, our results indicate that Pyk2 might play a role in regulating specific social skills likely via mitochondrial dynamics and that there might be a link between Pyk2 levels in hippocampal neurons and social disturbances in schizophrenia.

Superbinder based phosphoproteomic landscape revealed PRKCD_pY313 mediates the activation of Src and p38 MAPK to promote TNBC progression

Phosphorylation proteomics is the basis for the study of abnormally activated kinase signaling pathways in breast cancer, which facilitates the discovery of new oncogenic agents and drives the discovery of potential targets for early diagnosis and therapy of breast cancer. In this study, we have explored the aberrantly active kinases in breast cancer development and to elucidate the role of PRKCD_pY313 in triple negative breast cancer (TNBC) progression. We collected 47 pairs of breast cancer and paired far-cancer normal tissues and analyzed phosphorylated tyrosine (pY) peptides by Superbinder resin and further enriched the phosphorylated serine/threonine (pS/pT) peptides using TiO2 columns. We mapped the kinases activity of different subtypes of breast cancer and identified PRKCD_pY313 was upregulated in TNBC cell lines. Gain-of-function assay revealed that PRKCD_pY313 facilitated the proliferation, enhanced invasion, accelerated metastasis, increased the mitochondrial membrane potential and reduced ROS level of TNBC cell lines, while Y313F mutation and low PRKCD_pY313 reversed these effects. Furthermore, PRKCD_pY313 significantly upregulated Src_pY419 and p38_pT180/pY182, while low PRKCD_pY313 and PRKCD_Y313F had opposite effects. Dasatinib significantly inhibited the growth of PRKCD_pY313 overexpression cells, and this effect could be enhanced by Adezmapimod. In nude mice xenograft model, PRKCD_pY313 significantly promoted tumor progression, accompanied by increased levels of Ki-67, Bcl-xl and Vimentin, and decreased levels of Bad, cleaved caspase 3 and ZO1, which was opposite to the trend of Y313F group. Collectively, the heterogeneity of phosphorylation exists in different molecular subtypes of breast cancer. PRKCD_pY313 activates Src and accelerates TNBC progression, which could be inhibited by Dasatinib.

Health position paper and redox perspectives on reactive oxygen species as signals and targets of cardioprotection

The present review summarizes the beneficial and detrimental roles of reactive oxygen species in myocardial ischemia/reperfusion injury and cardioprotection. In the first part, the continued need for cardioprotection beyond that by rapid reperfusion of acute myocardial infarction is emphasized. Then, pathomechanisms of myocardial ischemia/reperfusion to the myocardium and the coronary circulation and the different modes of cell death in myocardial infarction are characterized. Different mechanical and pharmacological interventions to protect the ischemic/reperfused myocardium in elective percutaneous coronary interventions and coronary artery bypass grafting, in acute myocardial infarction and in cardiotoxicity from cancer therapy are detailed. The second part keeps the focus on ROS providing a comprehensive overview of molecular and cellular mechanisms involved in ischemia/reperfusion injury. Starting from mitochondria as the main sources and targets of ROS in ischemic/reperfused myocardium, a complex network of cellular and extracellular processes is discussed, including relationships with Ca2+ homeostasis, thiol group redox balance, hydrogen sulfide modulation, cross-talk with NAPDH oxidases, exosomes, cytokines and growth factors. While mechanistic insights are needed to improve our current therapeutic approaches, advancements in knowledge of ROS-mediated processes indicate that detrimental facets of oxidative stress are opposed by ROS requirement for physiological and protective reactions. This inevitable contrast is likely to underlie unsuccessful clinical trials and limits the development of novel cardioprotective interventions simply based upon ROS removal.

Phosphorylation of mammalian mitochondrial EF-Tu by Fyn and c-Src kinases

Src Family Kinases (SFKs) are tyrosine kinases known to regulate glucose and fatty acid metabolism as well as oxidative phosphorylation (OXPHOS) in mammalian mitochondria. We and others discovered the association of the SFK kinases Fyn and c-Src with mitochondrial translation components. This translational system is responsible for the synthesis of 13 mitochondrial (mt)-encoded subunits of the OXPHOS complexes and is, thus, essential for energy generation. Mitochondrial ribosomal proteins and various translation elongation factors including Tu (EF-Tu_mt) have been identified as possible Fyn and c-Src kinase targets. However, the phosphorylation of specific residues in EF-Tu_mt by these kinases and their roles in the regulation of protein synthesis are yet to be explored. In this study, we report the association of EF-Tu_mt with cSrc kinase and mapping of phosphorylated Tyr (pTyr) residues by these kinases. We determined that a specific Tyr residue in EF-Tu_mt at position 266 (EF-Tu_mt-Y266), located in a highly conserved c-Src consensus motif is one of the major phosphorylation sites. The potential role of EF-Tu_mt-Y266 phosphorylation in regulation of mitochondrial translation investigated by site-directed mutagenesis. Its phosphomimetic to Glu residue (EF-Tu_mt-E266) inhibited ternary complex (EF-Tu_mt•GTP•aatRNA) formation and translation in vitro. Our findings along with data mining analysis of the c-Src knock out (KO) mice proteome suggest that the SFKs have possible roles for regulation of mitochondrial protein synthesis and oxidative energy metabolism in animals.

Crosstalk between Lipid Rafts and Aging: New Frontiers for Delaying Aging

With the rapid aging in the global population, delay of aging has become a hot research topic. Lipid rafts (LRs) are microdomains in the plasma membrane that contain sphingolipids and cholesterol. Emerging evidence indicates an interesting interplay between LRs and aging. LRs and their components are altered with aging. Further, the aging process is strongly influenced by LRs. In recent years, LRs and their component signaling molecules have been recognized to affect aging by interfering with its hallmarks. Therefore, targeting LRs is a promising strategy to delay aging.

Angiopteris cochinchinensis de Vriese Ameliorates LPS-Induced Acute Lung Injury via Src Inhibition

Growing demand for treatment options against acute lung injury (ALI) emphasizes studies on plant extracts harboring anti-inflammatory effects. According to GC-MS analysis, Angiopteris cochinchinensis de Vriese consists of various flavonoids with anti-inflammatory activities. Thus, in this study, the anti-inflammatory effects of an extract of Angiopteris cochinchinensis de Vriese (Ac-EE) were assessed using RAW264.6 murine macrophages and a lipopolysaccharide (LPS)-induced ALI model. Ac-EE reduced the nitric oxide production in murine macrophages increased by LPS induction. Moreover, protective effects of Ac-EE on lung tissue were demonstrated by shrinkage of edema and lung injury. Reduced neutrophil infiltration and formation of hyaline membranes were also detected in lung tissues after H&E staining. Semiquantitative RT-PCR, quantitative real-time PCR, and ELISA showed that Ac-EE inhibits the production of proinflammatory mediators, including iNOS and COX-2, and cytokines, such as TNF-α, IL-1β, and IL-6. An Ac-EE-mediated anti-inflammatory response was derived from inhibiting the NF-κB signaling pathway, which was evaluated by luciferase reporter assay and Western blotting analysis. A cellular thermal shift assay revealed that the prime target of Ac-EE in alleviating inflammation was Src. With its direct binding with Src, Angiopteris cochinchinensis de Vriese significantly mitigates lung injury, showing possibilities of its potential as an effective botanical drug.

PPFIA4 promotes castration-resistant prostate cancer by enhancing mitochondrial metabolism through MTHFD2

Background

The development of castration-resistant prostate cancer (CRPC) remains a major obstacle in the treatment of prostate cancer (PCa). Dysregulated mitochondrial function has been linked to the initiation and progression of diverse human cancers. Deciphering the novel molecular mechanisms underlying mitochondrial function may provide important insights for developing novel therapeutics for CRPC.

Methods

We investigate the expression of the protein tyrosine phosphatase receptor type F polypeptide interacting protein alpha 4 (PPFIA4) using public datasets and tumor specimens from PCa cases by immunohistochemistry. Gain- and loss-of-function studies are performed in PCa cell lines and mouse models of subcutaneous xenograft to characterize the role of PPFIA4 in CRPC. Gene expression regulation is evaluated by a series of molecular and biochemical experiments in PCa cell lines. The therapeutic effects of methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) inhibitor combined enzalutamide are assessed using in vitro functional assays and in vivo mouse models.

Results

We show that the increase of PPFIA4 exacerbates aggressive phenotype resembling CRPC. A fraction of PPFIA4 localizes to mitochondria and interacts with MTHFD2, a key enzyme for one-carbon metabolism. Androgen deprivation increases the translocation of PPFIA4 into mitochondria and increases the interaction between PPFIA4 and MTHFD2, which result in the elevation of tyrosine phosphorylated MTHFD2. Consequently, the levels of NADPH synthesis increase, resulting in protection against androgen deprivation-induced mitochondrial dysfunction, as well as promotion of tumor growth. Clinically, PPFIA4 expression is significantly increased in CRPC tissues compared with localized PCa ones. Importantly, an MTHFD2 inhibitor, DS18561882, combined with enzalutamide can significantly inhibit CRPC cell proliferation in vitro and tumor growth in vivo.

Conclusion

Overall, our findings reveal a PPFIA4-MTHFD2 complex in mitochondria that links androgen deprivation to mitochondrial metabolism and mitochondrial dysfunction, which suggest a potential strategy to inhibit CRPC progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02331-3.

Drug Repositioning in Friedreich Ataxia

Friedreich ataxia is a rare neurodegenerative disorder caused by insufficient levels of the essential mitochondrial protein frataxin. It is a severely debilitating disease that significantly impacts the quality of life of affected patients and reduces their life expectancy, however, an adequate cure is not yet available for patients. Frataxin function, although not thoroughly elucidated, is associated with assembly of iron-sulfur cluster and iron metabolism, therefore insufficient frataxin levels lead to reduced activity of many mitochondrial enzymes involved in the electron transport chain, impaired mitochondrial metabolism, reduced ATP production and inefficient anti-oxidant response. As a consequence, neurons progressively die and patients progressively lose their ability to coordinate movement and perform daily activities. Therapeutic strategies aim at restoring sufficient frataxin levels or at correcting some of the downstream consequences of frataxin deficiency. However, the classical pathways of drug discovery are challenging, require a significant amount of resources and time to reach the final approval, and present a high failure rate. Drug repositioning represents a viable alternative to boost the identification of a therapy, particularly for rare diseases where resources are often limited. In this review we will describe recent efforts aimed at the identification of a therapy for Friedreich ataxia through drug repositioning, and discuss the limitation of such strategies.

Mitochondrial matrix-localized Src kinase regulates mitochondrial morphology

The architecture of mitochondria adapts to physiological contexts: while mitochondrial fragmentation is usually associated to quality control and cell death, mitochondrial elongation often enhances cell survival during stress. Understanding how these events are regulated is important to elucidate how mitochondrial dynamics control cell fate. Here, we show that the tyrosine kinase Src regulates mitochondrial morphology. Deletion of Src increased mitochondrial size and reduced cellular respiration independently of mitochondrial mass, mitochondrial membrane potential or ATP levels. Re-expression of Src targeted to the mitochondrial matrix, but not of Src targeted to the plasma membrane, rescued mitochondrial morphology in a kinase activity-dependent manner. These findings highlight a novel function for Src in the control of mitochondrial dynamics.

Src activates retrograde membrane traffic through phosphorylation of GBF1

The Src tyrosine kinase controls cancer-critical protein glycosylation through Golgi to ER relocation of GALNTs enzymes. How Src induces this trafficking event is unknown. Golgi to ER transport depends on the GTP exchange factor (GEF) GBF1 and small GTPase Arf1. Here, we show that Src induces the formation of tubular transport carriers containing GALNTs. The kinase phosphorylates GBF1 on 10 tyrosine residues; two of them, Y876 and Y898, are located near the C-terminus of the Sec7 GEF domain. Their phosphorylation promotes GBF1 binding to the GTPase; molecular modeling suggests partial melting of the Sec7 domain and intramolecular rearrangement. GBF1 mutants defective for these rearrangements prevent binding, carrier formation, and GALNTs relocation, while phosphomimetic GBF1 mutants induce tubules. In sum, Src promotes GALNTs relocation by promoting GBF1 binding to Arf1. Based on residue conservation, similar regulation of GEF-Arf complexes by tyrosine phosphorylation could be a conserved and widespread mechanism.

Oxidative Phosphorylation Is a Metabolic Vulnerability in Chemotherapy-Resistant Triple-Negative Breast Cancer

Oxidative phosphorylation (OXPHOS) is an active metabolic pathway in many cancers. RNA from pretreatment biopsies from patients with triple-negative breast cancer (TNBC) who received neoadjuvant chemotherapy demonstrated that the top canonical pathway associated with worse outcome was higher expression of OXPHOS signature. IACS-10759, a novel inhibitor of OXPHOS, stabilized growth in multiple TNBC patient-derived xenografts (PDX). On gene expression profiling, all of the sensitive models displayed a basal-like 1 TNBC subtype. Expression of mitochondrial genes was significantly higher in sensitive PDXs. An in vivo functional genomics screen to identify synthetic lethal targets in tumors treated with IACS-10759 found several potential targets, including CDK4. We validated the antitumor efficacy of the combination of palbociclib, a CDK4/6 inhibitor, and IACS-10759 in vitro and in vivo. In addition, the combination of IACS-10759 and multikinase inhibitor cabozantinib had improved antitumor efficacy. Taken together, our data suggest that OXPHOS is a metabolic vulnerability in TNBC that may be leveraged with novel therapeutics in combination regimens. SIGNIFICANCE: These findings suggest that triple-negative breast cancer is highly reliant on OXPHOS and that inhibiting OXPHOS may be a novel approach to enhance efficacy of several targeted therapies.

Mitochondrial Kinases and the Role of Mitochondrial Protein Phosphorylation in Health and Disease

The major role of mitochondria is to provide cells with energy, but no less important are their roles in responding to various stress factors and the metabolic changes and pathological processes that might occur inside and outside the cells. The post-translational modification of proteins is a fast and efficient way for cells to adapt to ever changing conditions. Phosphorylation is a post-translational modification that signals these changes and propagates these signals throughout the whole cell, but it also changes the structure, function and interaction of individual proteins. In this review, we summarize the influence of kinases, the proteins responsible for phosphorylation, on mitochondrial biogenesis under various cellular conditions. We focus on their role in keeping mitochondria fully functional in healthy cells and also on the changes in mitochondrial structure and function that occur in pathological processes arising from the phosphorylation of mitochondrial proteins.

Characterization of the interactome of c-Src within the mitochondrial matrix by proximity-dependent biotin identification

C-Src kinase is localized in several subcellular compartments, including mitochondria where it is involved in the regulation of organelle functions and overall metabolism. Surprisingly, the characterization of the intramitochondrial Src interactome has never been fully determined. Using in vitro proximity-dependent biotin identification (BioID) coupled to mass spectrometry, we identified 51 candidate proteins that may interact directly or indirectly with c-Src within the mitochondrial matrix. Pathway analysis suggests that these proteins are involved in a large array of mitochondrial functions such as protein folding and import, mitochondrial organization and transport, oxidative phosphorylation, tricarboxylic acid cycle and metabolism of amino and fatty acids. Among these proteins, we identified 24 tyrosine phosphorylation sites in 17 mitochondrial proteins (AKAP1, VDAC1, VDAC2, VDAC3, LonP1, Hsp90, SLP2, PHB2, MIC60, UBA1, EF-Tu, LRPPRC, ACO2, OAT, ACAT1, ETFβ and ATP5β) as potential substrates for intramitochondrial Src using in silico prediction of tyrosine phospho-sites. Interaction of c-Src with SLP2 and ATP5β was confirmed using coimmunoprecipitation. This study suggests that the intramitochondrial Src could target several proteins and regulate different mitochondrial functions.

Oxidation Impacts the Intracellular Signaling Machinery in Hematological Disorders

The dynamic coordination between kinases and phosphatases is crucial for cell homeostasis, in response to different stresses. The functional connection between oxidation and the intracellular signaling machinery still remains to be investigated. In the last decade, several studies have highlighted the role of reactive oxygen species (ROS) as modulators directly targeting kinases, phosphatases, and downstream modulators, or indirectly acting on cysteine residues on kinases/phosphatases resulting in protein conformational changes with modulation of intracellular signaling pathway(s). Translational studies have revealed the important link between oxidation and signal transduction pathways in hematological disorders. The intricate nature of intracellular signal transduction mechanisms, based on the generation of complex networks of different types of signaling proteins, revealed the novel and important role of phosphatases together with kinases in disease mechanisms. Thus, therapeutic approaches to abnormal signal transduction pathways should consider either inhibition of overactivated/accumulated kinases or homeostatic signaling resetting through the activation of phosphatases. This review discusses the progress in the knowledge of the interplay between oxidation and cell signaling, involving phosphatase/kinase systems in models of globally distributed hematological disorders.

c-Src kinase impairs the expression of mitochondrial OXPHOS complexes in liver cancer

Src family kinases (SFKs) play a crucial role in the regulation of multiple cellular pathways, including mitochondrial oxidative phosphorylation (OXPHOS). Aberrant activities of one of the most predominant SFKs, c-Src, was identified as a fundamental cause for dysfunctional cell signaling and implicated in cancer development and metastasis, especially in human hepatocellular carcinoma (HCC). Recent work in our laboratory revealed that c-Src is implicated in the regulation of mitochondrial energy metabolism in cancer. In this study, we investigated the effect of c-Src expression on mitochondrial energy metabolism by examining changes in the expression and activities of OXPHOS complexes in liver cancer biopsies and cell lines. An increased expression of c-Src was correlated with an impaired expression of nuclear- and mitochondrial-encoded subunits of OXPHOS complexes I and IV, respectively, in metastatic biopsies and cell lines. Additionally, we observed a similar association between high c-Src and reduced OXPHOS complex expression and activity in mouse embryonic fibroblast (MEF) cell lines. Interestingly, the inhibition of c-Src kinase activity with the SFK inhibitor PP2 and c-Src siRNA stimulated the expression of complex I and IV subunits and increased their enzymatic activities in both cancer and normal cells. Evidence provided in this study reveals that c-Src impairs the expression and function of mitochondrial OXPHOS complexes, resulting in a significant defect in mitochondrial energy metabolism, which can be a contributing factor to the development and progression of liver cancer. Furthermore, our findings strongly suggest that SFK inhibitors should be used in the treatment of HCC and other cancers with aberrant c-Src kinase activity to improve mitochondrial energy metabolism.

trans-Fatty acids facilitate DNA damage-induced apoptosis through the mitochondrial JNK-Sab-ROS positive feedback loop

trans-Fatty acids (TFAs) are unsaturated fatty acids that contain one or more carbon-carbon double bonds in trans configuration. Epidemiological evidence has linked TFA consumption with various disorders, including cardiovascular diseases. However, the underlying pathological mechanisms are largely unknown. Here, we show a novel toxic mechanism of TFAs triggered by DNA damage. We found that elaidic acid (EA) and linoelaidic acid, major TFAs produced during industrial food manufacturing (so-called as industrial TFAs), but not their corresponding cis isomers, facilitated apoptosis induced by doxorubicin. Consistently, EA enhanced UV-induced embryonic lethality in C. elegans worms. The pro-apoptotic action of EA was blocked by knocking down Sab, a c-Jun N-terminal kinase (JNK)-interacting protein localizing at mitochondrial outer membrane, which mediates mutual amplification of mitochondrial reactive oxygen species (ROS) generation and JNK activation. EA enhanced doxorubicin-induced mitochondrial ROS generation and JNK activation, both of which were suppressed by Sab knockdown and pharmacological inhibition of either mitochondrial ROS generation, JNK, or Src-homology 2 domain-containing protein tyrosine phosphatase 1 (SHP1) as a Sab-associated protein. These results demonstrate that in response to DNA damage, TFAs drive the mitochondrial JNK-Sab-ROS positive feedback loop and ultimately apoptosis, which may provide insight into the common pathogenetic mechanisms of diverse TFA-related disorders.

Metabolic reprogramming by tobacco-specific nitrosamines (TSNAs) in cancer

Metabolic reprogramming is a hallmark of cancer and the link between oncogenes activation, tumor supressors inactivation and bioenergetics modulation is well established. However, numerous carcinogenic environmental factors are responsible for early cancer initiation and their impact on metabolic reprogramming just starts to be deciphered. For instance, it was recently shown that UVB irradiation triggers metabolic reprogramming at the pre-cancer stage with implication for skin cancer detection and therapy. These observations foster the need to study the early changes in tissue metabolism following exposure to other carcinogenic events. According to the International Agency for Research on Cancer (IARC), tobacco smoke is a major class I-carcinogenic environmental factor that contains different carcinogens, but little is known on the impact of tobacco smoke on tissue metabolism and its participation to cancer initiation. In particular, tobacco-specific nitrosamines (TSNAs) play a central role in tobacco-smoke mediated cancer initiation. Here we describe the recent advances that have led to a new hypothesis regarding the link between nitrosamines signaling and metabolic reprogramming in cancer.

Intramitochondrial Src kinase links mitochondrial dysfunctions and aggressiveness of breast cancer cells

High levels and activity of Src kinase are common among breast cancer subtypes, and several inhibitors of the kinase are currently tested in clinical trials. Alterations in mitochondrial activity is also observed among the different types of breast cancer. Src kinase is localized in several subcellular compartments, including mitochondria where it targets several proteins to modulate the activity of the organelle. Although the subcellular localization of other oncogenes modulates the potency of known treatments, nothing is known about the specific role of intra-mitochondrial Src (mtSrc) in breast cancer. The aim of this work was to determine whether mtSrc kinase has specific impact on breast cancer cells. We first observed that activity of mtSrc is higher in breast cancer cells of the triple negative subtype. Over-expression of Src specifically targeted to mitochondria reduced mtDNA levels, mitochondrial membrane potential and cellular respiration. These alterations of mitochondrial functions led to lower cellular viability, shorter cell cycle and increased invasive capacity. Proteomic analyses revealed that mtSrc targets the mitochondrial single-stranded DNA-binding protein, a regulator of mtDNA replication. Our findings suggest that mtSrc promotes aggressiveness of breast cancer cells via phosphorylation of mitochondrial single-stranded DNA-binding protein leading to reduced mtDNA levels and mitochondrial activity. This study highlights the importance of considering the subcellular localization of Src kinase in the development of potent therapy for breast cancer.

Bisphenol A induces human uterine leiomyoma cell proliferation through membrane-associated ERα36 via nongenomic signaling pathways

The role of ERα36 in regulating BPA's effects and its potential as a risk factor for human uterine fibroids were evaluated. BPA at low concentrations (10^-6 μM - 10 μM) increased proliferation by facilitating progression of hormonally regulated, immortalized human uterine leiomyoma (ht-UtLM; fibroid) cells from G₀-G₁ into S phase of the cell cycle; whereas, higher concentrations (100 μM-200 μM) decreased growth. BPA upregulated ERα36 gene and protein expression, and induced increased SOS1 and Grb2 protein expression, both of which are mediators of the MAPK_p44/42/ERK1/2 pathway. EGFR (pEGFR), Ras, and MAPK_p44/42 were phosphorylated with concurrent Src activation in ht-UtLM cells within 10 min of BPA exposure. BPA enhanced colocalization of phosphorylated Src (pSrc) to ERα36 and coimmunoprecipitation of pSrc with pEGFR. Silencing ERα36 with siERα36 abolished the above effects. BPA induced proliferation in ht-UtLM cells through membrane-associated ERα36 with activation of Src, EGFR, Ras, and MAPK nongenomic signaling pathways.

HER2 Signaling Hijacks the Creatine Shuttle to Fuel Breast Cancer Cell Growth

Alteration of cell energy metabolism represents a major determinant of cancer progression; however, our understanding of oncogenic mechanisms underlying this rewiring remains elusive. In this issue of Cell Metabolism, Kurmi et al. (2018) show that HER2 signaling promotes ABL-mediated phosphorylation of the mitochondrial creatine kinase (MtCK1), providing ATP to support breast tumor growth.

A Disintegrin and Metalloproteinase Domain-8: A Novel Protective Proteinase in Chronic Obstructive Pulmonary Disease

RATIONALE

ADAM8 (a disintegrin and metalloproteinase domain-8) is expressed by leukocytes and epithelial cells in health, but its contribution to the pathogenesis of chronic obstructive pulmonary disease (COPD) is unknown.

OBJECTIVES

To determine whether the expression of ADAM8 is increased in the lungs of patients with COPD and cigarette smoke (CS)-exposed mice, and whether ADAM8 promotes the development of COPD.

METHODS

ADAM8 levels were measured in lung, sputum, plasma, and/or BAL fluid samples from patients with COPD, smokers, and nonsmokers, and wild-type (WT) mice exposed to CS versus air. COPD-like lung pathologies were compared in CS-exposed WT versus Adam8-/- mice.

MEASUREMENTS AND MAIN RESULTS

ADAM8 immunostaining was reduced in macrophages, and alveolar and bronchial epithelial cells in the lungs of patients with COPD versus control subjects, and CS- versus air-exposed WT mice. ADAM8 levels were similar in plasma, sputum, and BAL fluid samples from patients with COPD and control subjects. CS-exposed Adam8-/- mice had greater airspace enlargement and airway mucus cell metaplasia than WT mice, but similar small airway fibrosis. CS-exposed Adam8-/- mice had higher lung macrophage counts, oxidative stress levels, and alveolar septal cell death rates, but lower alveolar septal cell proliferation rates and soluble epidermal growth factor receptor BAL fluid levels than WT mice. Adam8 deficiency increased lung inflammation by reducing CS-induced activation of the intrinsic apoptosis pathway in macrophages. Human ADAM8 proteolytically shed the epidermal growth factor receptor from bronchial epithelial cells to reduce mucin expression in vitro. Adam8 bone marrow chimera studies revealed that Adam8 deficiency in leukocytes and lung parenchymal cells contributed to the exaggerated COPD-like disease in Adam8-/- mice.

CONCLUSIONS

Adam8 deficiency increases CS-induced lung inflammation, emphysema, and airway mucus cell metaplasia. Strategies that increase or prolong ADAM8's expression in the lung may have therapeutic efficacy in COPD.

Metabolic Plasticity of Tumor Cell Mitochondria

Mitochondria are dynamic organelles that exchange a multiplicity of signals with other cell compartments, in order to finely adjust key biological routines to the fluctuating metabolic needs of the cell. During neoplastic transformation, cells must provide an adequate supply of the anabolic building blocks required to meet a relentless proliferation pressure. This can occur in conditions of inconstant blood perfusion leading to variations in oxygen and nutrient levels. Mitochondria afford the bioenergetic plasticity that allows tumor cells to adapt and thrive in this ever changing and often unfavorable environment. Here we analyse how mitochondria orchestrate the profound metabolic rewiring required for neoplastic growth.

Mitochondrial cAMP-PKA signaling: What do we really know?

Mitochondria are key organelles for cellular homeostasis. They generate the most part of ATP that is used by cells through oxidative phosphorylation. They also produce reactive oxygen species, neurotransmitters and other signaling molecules. They are important for calcium homeostasis and apoptosis. Considering the role of this organelle, it is not surprising that most mitochondrial dysfunctions are linked to the development of pathologies. Various mechanisms adjust mitochondrial activity according to physiological needs. The cAMP-PKA signaling emerged in recent years as a direct and powerful mean to regulate mitochondrial functions. Multiple evidence demonstrates that such pathway can be triggered from cytosol or directly within mitochondria. Notably, specific anchor proteins target PKA to mitochondria whereas enzymes necessary for generation and degradation of cAMP are found directly in these organelles. Mitochondrial PKA targets proteins localized in different compartments of mitochondria, and related to various functions. Alterations of mitochondrial cAMP-PKA signaling affect the development of several physiopathological conditions, including neurodegenerative diseases. It is however difficult to discriminate between the effects of cAMP-PKA signaling triggered from cytosol or directly in mitochondria. The specific roles of PKA localized in different mitochondrial compartments are also not completely understood. The aim of this work is to review the role of cAMP-PKA signaling in mitochondrial (patho)physiology.

Diet-resistant obesity is characterized by a distinct plasma proteomic signature and impaired muscle fiber metabolism

Background/Objectives:

Inter-individual variability in weight loss during obesity treatment is complex and poorly understood. Here we use whole body and tissue approaches to investigate fuel oxidation characteristics in skeletal muscle fibers, cells and distinct circulating protein biomarkers before and after a high fat meal (HFM) challenge in those who lost the most (obese diet-sensitive; ODS) vs the least (obese diet-resistant; ODR) amount of weight in a highly controlled weight management program.

Subjects/Methods:

In 20 weight stable-matched ODS and ODR women who previously completed a standardized clinical weight loss program, we analyzed whole-body energetics and metabolic parameters in vastus lateralis biopsies and plasma samples that were obtained in the fasting state and 6 h after a defined HFM, equivalent to 35% of total daily energy requirements.

Results:

At baseline (fasting) and post-HFM, muscle fatty acid oxidation and maximal oxidative phosphorylation were significantly greater in ODS vs ODR, as was reactive oxygen species emission. Plasma proteomics of 1130 proteins pre and 1, 2, 5 and 6 h after the HFM demonstrated distinct group and interaction differences. Group differences identified S-formyl glutathione hydratase, heat shock 70 kDA protein 1A/B (HSP72), and eukaryotic translation initiation factor 5 (eIF5) to be higher in ODS vs ODR. Group-time differences included aryl hydrocarbon interacting protein (AIP), peptidylpropyl isomerase D (PPID) and tyrosine protein-kinase Fgr, which increased in ODR vs ODS over time. HSP72 levels correlated with muscle oxidation and citrate synthase activity. These proteins circulate in exosomes; exosomes isolated from ODS plasma increased resting, leak and maximal respiration rates in C2C12 myotubes by 58%, 21% and 51%, respectively, vs those isolated from ODR plasma.

Conclusions:

Findings demonstrate distinct muscle metabolism and plasma proteomics in fasting and post-HFM states corresponding in diet-sensitive vs diet-resistant obese women.

ERα36, a variant of estrogen receptor α, is predominantly localized in mitochondria of human uterine smooth muscle and leiomyoma cells

ERα36 is a naturally occurring, membrane-associated, isoform of estrogen receptor α. The expression of ERα36 is due to alternative splicing and different promoter usage. ERα36 is a dominant-negative effector of ERα66-mediated transactivational activities and has the potential to trigger membrane-initiated mitogenic, nongenomic, estrogen signaling; however, the subcellular localization of ERα36 remains controversial. To determine the cellular localization of ERα36 in estrogen-responsive human uterine smooth muscle (ht-UtSMC) and leiomyoma (fibroid; ht-UtLM) cells, we conducted systematic confocal microscopy and subcellular fractionation analysis using ERα36 antibodies. With Image J colocalizaton analysis plugin, confocal images were analyzed to obtain a Pearson’s Correlation Coefficient (PCC) to quantify signal colocalization of ERα36 with mitochondrial, endoplasmic reticulum, and cytoskeletal components in both cell lines. When cells were double-stained with an ERα36 antibody and a mitochondrial-specific dye, MitoTracker, the PCC for the two channel signals were both greater than 0.75, indicating strong correlation between ERα36 and mitochondrial signals in the two cell lines. A blocking peptide competition assay confirmed that the mitochondria-associated ERα36 signal detected by confocal analysis was specific for ERα36. In contrast, confocal images double-stained with an ERα36 antibody and endoplasmic reticulum or cytoskeletal markers, had PCCs that were all less than 0.4, indicating no or very weak signal correlation. Fractionation studies showed that ERα36 existed predominantly in membrane fractions, with minimal or undetected amounts in the cytosol, nuclear, chromatin, and cytoskeletal fractions. With isolated mitochondrial preparations, we confirmed that a known mitochondrial protein, prohibitin, was present in mitochondria, and by co-immunoprecipitation analysis that ERα36 was associated with prohibitin in ht-UtLM cells. The distinctive colocalization pattern of ERα36 with mitochondria in ht-UtSMC and ht-UtLM cells, and the association of ERα36 with a mitochondrial-specific protein suggest that ERα36 is localized primarily in mitochondria and may play a pivotal role in non-genomic signaling and mitochondrial functions.

Exogenous spermine preserves mitochondrial bioenergetics via regulating Src kinase signaling in the spinal cord

Regulation of mitochondrial metabolism is becoming an important target in inhibiting necrosis and apoptosis following secondary spinal cord injury, and physiological compounds that reduce mitochondrial dysfunction are regarded as efficient protective reagents following injury. It has been demonstrated that spermine, a polyamine composed of four primary amines, may be taken up by a mitochondria‑specific uniporter and may preserve mitochondrial bioenergetics, suggesting that it may be important in the pathophysiology of mitochondria. However, the protective mechanism has not yet been definitively clarified. In the present study, isolated spinal cord mitochondria were incubated with spermine to evaluate its physiological functions and Src kinase activities. The results revealed that spermine increased oxidative phosphorylation, attenuated mitochondrial swelling and maintained the membrane potential. An inhibitor of Src kinases, amino‑5-(4‑chlorophenyl)‑7‑(t‑butyl)pyrazolo[3,4‑d]pyrimidine (PP2), markedly reduced the effects of spermine. However, inhibition of tyrosine phosphatases by vanadate led to marginal increases in the effects of spermine. Therefore, the present study hypothesized that tyrosine phosphorylation sites are present in the subunits of respiratory chains and mitochondrial permeability transition pore proteins, which may be modified via phosphorylation and dephosphorylation. Furthermore, spermine may upregulate the phosphorylation of Src kinases, and PP2 and vanadate conversely regulate Src phosphorylation. The results of the present study suggest that spermine is a strategic regulator within mitochondria that may activate Src kinases in the spinal cord, and tyrosine phosphorylation signaling is a primary regulatory pathway of mitochondrial metabolism.

The Chaperone TRAP1 As a Modulator of the Mitochondrial Adaptations in Cancer Cells

Mitochondria can receive, integrate, and transmit a variety of signals to shape many biochemical activities of the cell. In the process of tumor onset and growth, mitochondria contribute to the capability of cells of escaping death insults, handling changes in ROS levels, rewiring metabolism, and reprograming gene expression. Therefore, mitochondria can tune the bioenergetic and anabolic needs of neoplastic cells in a rapid and flexible way, and these adaptations are required for cell survival and proliferation in the fluctuating environment of a rapidly growing tumor mass. The molecular bases of pro-neoplastic mitochondrial adaptations are complex and only partially understood. Recently, the mitochondrial molecular chaperone TRAP1 (tumor necrosis factor receptor associated protein 1) was identified as a key regulator of mitochondrial bioenergetics in tumor cells, with a profound impact on neoplastic growth. In this review, we analyze these findings and discuss the possibility that targeting TRAP1 constitutes a new antitumor approach.

Fyn kinase regulates translation in mammalian mitochondria

BACKGROUND

Mitochondrial translation machinery solely exists for the synthesis of 13 mitochondrially-encoded subunits of the oxidative phosphorylation (OXPHOS) complexes in mammals. Therefore, it plays a critical role in mitochondrial energy production. However, regulation of the mitochondrial translation machinery is still poorly understood. In comprehensive proteomics studies with normal and diseased tissues and cell lines, we and others have found the majority of mitochondrial ribosomal proteins (MRPs) to be phosphorylated. Neither the kinases for these phosphorylation events nor their specific roles in mitochondrial translation are known.

METHODS

Mitochondrial kinases are responsible for phosphorylation of MRPs enriched from bovine mitoplasts by strong cation-exchange chromatography and identified by mass spectrometry-based proteomics analyses of kinase rich fractions. Phosphorylation of recombinant MRPs and 55S ribosomes was assessed by in vitro phosphorylation assays using the kinase-rich fractions. The effect of identified kinase on OXPHOS and mitochondrial translation was assessed by various cell biological and immunoblotting approaches.

RESULTS

Here, we provide the first evidence for the association of Fyn kinase, a Src family kinase, with mitochondrial translation components and its involvement in phosphorylation of 55S ribosomal proteins in vitro. Modulation of Fyn expression in human cell lines has provided a link between mitochondrial translation and energy metabolism, which was evident by the changes in 13 mitochondrially encoded subunits of OXPHOS complexes.

CONCLUSIONS AND GENERAL SIGNIFICANCE

Our findings suggest that Fyn kinase is part of a complex mechanism that regulates protein synthesis and OXPHOS possibly by tyrosine phosphorylation of translation components in mammalian mitochondria.

Post-translational modifications in mitochondria: protein signaling in the powerhouse

There is an intimate interplay between cellular metabolism and the pathophysiology of disease. Mitochondria are essential to maintaining and regulating metabolic function of cells and organs. Mitochondrial dysfunction is implicated in diverse diseases, such as cardiovascular disease, diabetes and metabolic syndrome, neurodegeneration, cancer, and aging. Multiple reversible post-translational protein modifications are located in the mitochondria that are responsive to nutrient availability and redox conditions, and which can act in protein-protein interactions to modify diverse mitochondrial functions. Included in this are physiologic redox signaling via reactive oxygen and nitrogen species, phosphorylation, O-GlcNAcylation, acetylation, and succinylation, among others. With the advent of mass proteomic screening techniques, there has been a vast increase in the array of known mitochondrial post-translational modifications and their protein targets. The functional significance of these processes in disease etiology, and the pathologic response to their disruption, are still under investigation. However, many of these reversible modifications act as regulatory mechanisms in mitochondria and show promise for mitochondrial-targeted therapeutic strategies. This review addresses the current knowledge of post-translational processing and signaling mechanisms in mitochondria, and their implications in health and disease.

Tyrosine kinase inhibition reverses TDP-43 effects on synaptic protein expression, astrocytic function and amino acid dis-homeostasis

The trans-activating response of DNA/RNA-binding protein (TDP)-43 pathology is associated with many neurodegenerative diseases via unknown mechanisms. Here, we use a transgenic mouse model over-expressing human wild-type neuronal TDP-43 to study the effects of TDP-43 pathology on glutamate metabolism and synaptic function. We found that neuronal TDP-43 over-expression affects synaptic protein expression, including Synapsin I, and alters surrounding astrocytic function. TDP-43 over-expression is associated with an increase in glutamate and γ-amino butyric acid and reduction of glutamine and aspartate levels, indicating impairment of presynaptic terminal. TDP-43 also decreases tricarboxylic acid cycle metabolism and induces oxidative stress via lactate accumulation. Neuronal TDP-43 does not alter microglia activity or significantly changes systemic and brain inflammatory markers compared to control. We previously demonstrated that brain-penetrant tyrosine kinase inhibitors (TKIs), nilotinib and bosutinib, reduce TDP-43-induced cell death in transgenic mice. Here, we show that TKIs reverse the effects of TDP-43 on synaptic proteins, increase astrocytic function and restore glutamate and neurotransmitter balance in TDP-43 mice. Nilotinib, but not bosutinib, reverses mitochondrial impairment and oxidative metabolism. Taken together, these data suggest that TKIs can attenuate TDP-43 toxicity and improve synaptic and astrocytic function, independent of microglial or other inflammatory effects. In conclusion, our data demonstrate novel mechanisms of the effects of neuronal TDP-43 over-expression on synaptic protein expression and alteration of astrocytic function.

Integration of superoxide formation and cristae morphology for mitochondrial redox signaling

The mitochondrial network provides the central cell's energetic and regulatory unit, which besides ATP and metabolite production participates in cellular signaling through regulated reactive oxygen species (ROS) production and various protein/ion fluxes. The inner membrane forms extensive folds, called cristae, i.e. cavities enfolded from and situated perpendicularly to its inner boundary membrane portion, which encompasses an inner cylinder within the outer membrane tubule. Mitochondrial cristae ultramorphology reflects various metabolic, physiological or pathological states. Since the mitochondrion is typically a predominant superoxide source and generated ROS also serve for the creation of information redox signals, we review known relationships between ROS generation within the respiratory chain complexes of cristae and cristae morphology. Notably, it is emphasized that cristae shape is governed by ATP-synthase dimers, MICOS complexes, OPA1 isoforms and the umbrella of their regulation, and also dependent on local protonmotive force (electrical potential component) in cristae. Cristae are also affected by redox-sensitive kinases/phosphatases or p66SHC. ATP-synthase dimers decrease in the inflated intracristal space, diminishing pH and hypothetically having minimal superoxide formation. Matrix-released signaling superoxide/H₂O₂ is predominantly integrated along mitochondrial tubules, whereas the diffusion of intracristal signaling ROS species is controlled by crista junctions, the widening of which enables specific retrograde redox signaling such as during hypoxic cell adaptation. Other physiological cases of H₂O₂ release from the mitochondrion include the modulation of insulin release in pancreatic β-cells, enhancement of insulin signaling in peripheral tissues, signaling by T-cell receptors, retrograde signaling during the cell cycle and cell differentiation, specifically that of adipocytes.

Fatty Acid Oxidation-Driven Src Links Mitochondrial Energy Reprogramming and Oncogenic Properties in Triple-Negative Breast Cancer

Transmitochondrial cybrids and multiple OMICs approaches were used to understand mitochondrial reprogramming and mitochondria-regulated cancer pathways in triple-negative breast cancer (TNBC). Analysis of cybrids and established breast cancer (BC) cell lines showed that metastatic TNBC maintains high levels of ATP through fatty acid β oxidation (FAO) and activates Src oncoprotein through autophosphorylation at Y419. Manipulation of FAO including the knocking down of carnitine palmitoyltransferase-1A (CPT1) and 2 (CPT2), the rate-limiting proteins of FAO, and analysis of patient-derived xenograft models confirmed the role of mitochondrial FAO in Src activation and metastasis. Analysis of TCGA and other independent BC clinical data further reaffirmed the role of mitochondrial FAO and CPT genes in Src regulation and their significance in BC metastasis.

A novel mechanism of action for salidroside to alleviate diabetic albuminuria: effects on albumin transcytosis across glomerular endothelial cells

Salidroside (SAL) is a phenylethanoid glycoside isolated from the medicinal plant Rhodiola rosea. R. rosea has been reported to have beneficial effects on diabetic nephropathy (DN) and high-glucose (HG)-induced mesangial cell proliferation. Given the importance of caveolin-1 (Cav-1) in transcytosis of albumin across the endothelial barrier, the present study was designed to elucidate whether SAL could inhibit Cav-1 phosphorylation and reduce the albumin transcytosis across glomerular endothelial cells (GECs) to alleviate diabetic albuminuria as well as to explore its upstream signaling pathway. To assess the therapeutic potential of SAL and the mechanisms involved in DN albuminuria, we orally administered SAL to db/db mice, and the effect of SAL on the albuminuria was measured. The albumin transcytosis across GECs was explored in a newly established in vitro cellular model. The ratio of albumin to creatinine was significantly reduced upon SAL treatment in db/db mice. SAL decreased the albumin transcytosis across GECs in both normoglycemic and hyperglycemic conditions. SAL reversed the HG-induced downregulation of AMP-activated protein kinase and upregulation of Src kinase and blocked the upregulation Cav-1 phosphorylation. Meanwhile, SAL decreased mitochondrial superoxide anion production and moderately depolarized mitochondrial membrane potential. We conclude that SAL exerts its proteinuria-alleviating effects by downregulation of Cav-1 phosphorylation and inhibition of albumin transcytosis across GECs. These studies provide the first evidence of interference with albumin transcytosis across GECs as a novel approach to the treatment of diabetic albuminuria.

The Src non-receptor tyrosine kinase paradigm: New insights into mammalian Sertoli cell biology

Src kinases are non-receptor tyrosine kinases that phosphorylate diverse substrates, which control processes such as cell proliferation, differentiation and survival; cell adhesion; and cell motility. c-Src, the prototypical member of this protein family, is widely expressed by several organs that include the testis. In the seminiferous epithelium of the adult rat testis, c-Src is highest at the tubule lumen during the release of mature spermatids. Other studies show that testosterone regulates spermatid adhesion to Sertoli cells via c-Src, indicating Src phosphorylates key substrates that prompt the disassembly of Sertoli cell-spermatid junctions. A more recent in vitro study reveals that c-Src participates in the internalization of proteins that constitute the blood-testis barrier, which is present between Sertoli cells, suggesting a similar mechanism of junction disassembly is at play during spermiation. In this review, we discuss recent findings on c-Src, with an emphasis on its role in spermatogenesis in the mammalian testis.

Src regulates insulin secretion and glucose metabolism by influencing subcellular localization of glucokinase in pancreatic β-cells

Aims/Introduction

Src, a non‐receptor tyrosine kinase, regulates a wide range of cellular functions, and hyperactivity of Src is involved in impaired glucose metabolism in pancreatic β‐cells. However, the physiological role of Src in glucose metabolism in normal, unstressed β‐cells remains unclear. In the present study, we investigated the role of Src in insulin secretion and glucose metabolism.

Materials and Methods

Src was downregulated using small interfering ribonucleic acid in INS‐1 cells, and glucose‐induced insulin secretion, adenosine triphosphate content, intracellular calcium concentration, glucose utilization and glucokinase activity were measured. Expression levels of messenger ribonucleic acid and protein of glucokinase were examined by semiquantitative real‐time polymerase chain reaction and immunoblotting, respectively. Cells were fractionated by digitonin treatment, and subcellular localization of glucokinase was examined by immunoblotting. Interaction between glucokinase and neuronal nitric oxide synthase was estimated by immunoprecipitation.

Results

In Src downregulated INS‐1 cells, glucose‐induced insulin secretion was impaired, whereas insulin secretion induced by high K⁺ was not affected. Intracellular adenosine triphosphate content and elevation of intracellular calcium concentration by glucose stimulation were suppressed by Src downregulation. Src downregulation reduced glucose utilization in the presence of high glucose, which was accompanied by a reduction in glucokinase activity without affecting its expression. However, Src downregulation reduced glucokinase in soluble, cytoplasmic fraction, and increased it in pellet containing intaracellular organelles. In addition, interaction between glucokinase and neuronal nitric oxide synthase was facilitated by Src downregulation.

Conclusions

Src plays an important role in glucose‐induced insulin secretion in pancreatic β‐cells through maintaining subcellular localization and activity of glucokinase.

Src inhibitors modulate frataxin protein levels

Defective expression of frataxin is responsible for the inherited, progressive degenerative disease Friedreich's Ataxia (FRDA). There is currently no effective approved treatment for FRDA and patients die prematurely. Defective frataxin expression causes critical metabolic changes, including redox imbalance and ATP deficiency. As these alterations are known to regulate the tyrosine kinase Src, we investigated whether Src might in turn affect frataxin expression. We found that frataxin can be phosphorylated by Src. Phosphorylation occurs primarily on Y118 and promotes frataxin ubiquitination, a signal for degradation. Accordingly, Src inhibitors induce accumulation of frataxin but are ineffective on a non-phosphorylatable frataxin-Y118F mutant. Importantly, all the Src inhibitors tested, some of them already in the clinic, increase frataxin expression and rescue the aconitase defect in frataxin-deficient cells derived from FRDA patients. Thus, Src inhibitors emerge as a new class of drugs able to promote frataxin accumulation, suggesting their possible use as therapeutics in FRDA.

New Insight into the Role of Reactive Oxygen Species (ROS) in Cellular Signal-Transduction Processes

Reactive oxygen species (ROS) were once considered to be deleterious agents, contributing to a vast range of pathologies. But, now their protective effects are being appreciated. Both their damaging and beneficial effects are initiated when they target distinct molecules and consequently begin functioning as part of complex signal-transduction pathways. The recognition of ROS as signaling mediators has driven a wealth of research into their roles in both normal and pathophysiological states. The present review assesses the relevant recent literature to outline the current perspectives on redox-signaling mechanisms, physiological implications, and therapeutic strategies. This study highlights that a more fundamental knowledge about many aspects of redox signaling will allow better targeting of ROS, which would in turn improve prophylactic and pharmacotherapy for redox-associated diseases.

Lymphocyte-specific protein tyrosine kinase (Lck) interacts with CR6-interacting factor 1 (CRIF1) in mitochondria to repress oxidative phosphorylation

BACKGROUND

Many cancer cells exhibit reduced mitochondrial respiration as part of metabolic reprogramming to support tumor growth. Mitochondrial localization of several protein tyrosine kinases is linked to this characteristic metabolic shift in solid tumors, but remains largely unknown in blood cancer. Lymphocyte-specific protein tyrosine kinase (Lck) is a key T-cell kinase and widely implicated in blood malignancies. The purpose of our study is to determine whether and how Lck contributes to metabolic shift in T-cell leukemia through mitochondrial localization.

METHODS

We compared the human leukemic T-cell line Jurkat with its Lck-deficient derivative Jcam cell line. Differences in mitochondrial respiration were measured by the levels of mitochondrial membrane potential, oxygen consumption, and mitochondrial superoxide. Detailed mitochondrial structure was visualized by transmission electron microscopy. Lck localization was evaluated by subcellular fractionation and confocal microscopy. Proteomic analysis was performed to identify proteins co-precipitated with Lck in leukemic T-cells. Protein interaction was validated by biochemical co-precipitation and confocal microscopy, followed by in situ proximity ligation assay microscopy to confirm close-range (<16 nm) interaction.

RESULTS

Jurkat cells have abnormal mitochondrial structure and reduced levels of mitochondrial respiration, which is associated with the presence of mitochondrial Lck and lower levels of mitochondrion-encoded electron transport chain proteins. Proteomics identified CR6-interacting factor 1 (CRIF1) as the novel Lck-interacting protein. Lck association with CRIF1 in Jurkat mitochondria was confirmed biochemically and by microscopy, but did not lead to CRIF1 tyrosine phosphorylation. Consistent with the role of CRIF1 in functional mitoribosome, shRNA-mediated silencing of CRIF1 in Jcam resulted in mitochondrial dysfunction similar to that observed in Jurkat. Reduced interaction between CRIF1 and Tid1, another key component of intramitochondrial translational machinery, in Jurkat further supports the role of mitochondrial Lck as a negative regulator of CRIF1 through competitive binding.

CONCLUSIONS

This is the first report demonstrating the role of mitochondrial Lck in metabolic reprogramming of leukemic cells. Mechanistically, it is distinct from other reported mitochondrial protein tyrosine kinases. In a kinase-independent manner, mitochondrial Lck interferes with mitochondrial translational machinery through competitive binding to CRIF1. These findings may reveal novel approaches in cancer therapy by targeting cancer cell metabolism.

Sepsis-induced brain mitochondrial dysfunction is associated with altered mitochondrial Src and PTP1B levels

Sepsis-induced brain dysfunction (SIBD) is often the first manifestation of sepsis, and its pathogenesis is associated with mitochondrial dysfunction. In this study, we investigated the roles of the tyrosine kinase Src and protein tyrosine phosphatase 1B (PTP1B) in brain mitochondrial dysfunction using a rat model of lipopolysaccharide (LPS)-induced sepsis. We found that there was a gradual and significant increase of PTP1B levels in the rat brain after sepsis induction. In contrast, brain Src levels were reduced in parallel with the PTP1B increase. Sepsis led to significantly reduced tyrosine phosphorylation of mitochondrial oxidative phosphorylation (OXPHOS) complexes I, II and III. Pretreatment of mitochondrial proteins with active PTP1B significantly inhibited complexes I and III activities in vitro, whereas Src enhanced complexes I, II, and III activities. PTP1B and Src were each co-immunoprecipitated with OXPHOS complexes I and III, suggesting direct interactions between both proteins and complexes I and III. Src also directly interacted with complex II. Furthermore, pretreatment of mitochondrial proteins with active PTP1B resulted in overproduction of reactive oxygen species and decreased mitochondrial membrane potential. Pretreatment with active Src produced the opposite effect. These results suggest that brain mitochondrial dysfunction following LPS-induced sepsis in rats is partly attributed to PTP1B and Src mediated decrease in mitochondrial protein tyrosine phosphorylation.

CPUY11018, an azimilide derivative, ameliorates isoproterenol-induced cardiac insufficiency through relieving dysfunctional mitochondria and endoplasmic reticulum

Objectives

Deterioration of cardiac performance under stress may be partly mediated by dysfunctional mitochondria and endoplasmic reticulum (ER) that is likely related to an activation of NADPH oxidase (NOX) and an increase in pro-inflammatory factors. We investigated if a new compound CPUY11018 (CPUY) derived from Azimilide could ameliorate the stress impaired cardiac performance.

Methods

Forty-eight male Sprague Dawley rats were randomly divided into six groups and were injected with isoproterenol (ISO, 1 ml/kg, s.c.) for 10 days. Cardiac myocytes and fibroblasts from neonate rats were incubated with ISO. CPUY was employed and compared with apocynin (APO) – an inhibitor of NOX.

Key findings

In ISO-treated group, the compromised haemodynamics and cardiac remodelling were significant with dysfunctional mitochondria indicated by decreased MnSOD and mitochondrial membrane potential, and an enhanced reactive oxygen species genesis. Downregulation of FKBP12.6, CASQ2 and SERCA2a was also remarkable in vivo and in vitro implying an abnormal ER. Upregulated Nox4, p22phox and p47phox were significant, associated with upregulation of Src, IκBβ and NFκB, and downregulation of pAMPK/AMPK and Cx40 in vivo and in vitro. These abnormalities were relieved by CPUY and APO.

Conclusions

CPUY is potential in managing cardiac insufficiency through normalizing mitochondria and ER in the affected heart.

Pathophysiological implications of mitochondrial oxidative stress mediated by mitochondriotropic agents and polyamines: the role of tyrosine phosphorylation

Mitochondria, once merely considered as the "powerhouse" of cells, as they generate more than 90 % of cellular ATP, are now known to play a central role in many metabolic processes, including oxidative stress and apoptosis. More than 40 known human diseases are the result of excessive production of reactive oxygen species (ROS), bioenergetic collapse and dysregulated apoptosis. Mitochondria are the main source of ROS in cells, due to the activity of the respiratory chain. In normal physiological conditions, ROS generation is limited by the anti-oxidant enzymatic systems in mitochondria. However, disregulation of the activity of these enzymes or interaction of respiratory complexes with mitochondriotropic agents may lead to a rise in ROS concentrations, resulting in oxidative stress, mitochondrial permeability transition (MPT) induction and triggering of the apoptotic pathway. ROS concentration is also increased by the activity of amine oxidases located inside and outside mitochondria, with oxidation of biogenic amines and polyamines. However, it should also be recalled that, depending on its concentration, the polyamine spermine can also protect against stress caused by ROS scavenging. In higher organisms, cell signaling pathways are the main regulators in energy production, since they act at the level of mitochondrial oxidative phosphorylation and participate in the induction of the MPT. Thus, respiratory complexes, ATP synthase and transition pore components are the targets of tyrosine kinases and phosphatases. Increased ROS may also regulate the tyrosine phosphorylation of target proteins by activating Src kinases or phosphatases, preventing or inducing a number of pathological states.

The azaindole framework in the design of kinase inhibitors

This review article illustrates the growing use of azaindole derivatives as kinase inhibitors and their contribution to drug discovery and innovation. The different protein kinases which have served as targets and the known molecules which have emerged from medicinal chemistry and Fragment-Based Drug Discovery (FBDD) programs are presented. The various synthetic routes used to access these compounds and the chemical pathways leading to their synthesis are also discussed. An analysis of their mode of binding based on X-ray crystallography data gives structural insights for the design of more potent and selective inhibitors.

Adrenergic signaling regulates mitochondrial Ca2+ uptake through Pyk2-dependent tyrosine phosphorylation of the mitochondrial Ca2+ uniporter

AIMS

Mitochondrial Ca2+ homeostasis is crucial for balancing cell survival and death. The recent discovery of the molecular identity of the mitochondrial Ca2+ uniporter pore (MCU) opens new possibilities for applying genetic approaches to study mitochondrial Ca2+ regulation in various cell types, including cardiac myocytes. Basal tyrosine phosphorylation of MCU was reported from mass spectroscopy of human and mouse tissues, but the signaling pathways that regulate mitochondrial Ca2+ entry through posttranslational modifications of MCU are completely unknown. Therefore, we investigated α1-adrenergic-mediated signal transduction of MCU posttranslational modification and function in cardiac cells.

RESULTS

α1-adrenoceptor (α1-AR) signaling translocated activated proline-rich tyrosine kinase 2 (Pyk2) from the cytosol to mitochondrial matrix and accelerates mitochondrial Ca2+ uptake via Pyk2-dependent MCU phosphorylation and tetrametric MCU channel pore formation. Moreover, we found that α1-AR stimulation increases reactive oxygen species production at mitochondria, mitochondrial permeability transition pore activity, and initiates apoptotic signaling via Pyk2-dependent MCU activation and mitochondrial Ca2+ overload.

INNOVATION

Our data indicate that inhibition of α1-AR-Pyk2-MCU signaling represents a potential novel therapeutic target to limit or prevent mitochondrial Ca2+ overload, oxidative stress, mitochondrial injury, and myocardial death during pathophysiological conditions, where chronic adrenergic stimulation is present.

CONCLUSION

The α1-AR-Pyk2-dependent tyrosine phosphorylation of the MCU regulates mitochondrial Ca2+ entry and apoptosis in cardiac cells.

Coenzyme q and the respiratory chain: coenzyme q pool and mitochondrial supercomplexes

Two alternative models of organization of the mitochondrial electron transport chain (mETC) have been alternatively favored or questioned by the accumulation evidences of different sources, the solid model or the random collision model. Both agree in the number of respiratory complexes (I-IV) that participate in the mETC, but while the random collision model proposes that Complexes I-IV do not interact physically and that electrons are transferred between them by coenzyme Q and cytochrome c, the solid model proposes that all complexes super-assemble in the so-called respirasome. Recently, the plasticity model has been developed to incorporate the solid and the random collision model as extreme situations of a dynamic organization, allowing super-assembly free movement of the respiratory complexes. In this review, we evaluate the supporting evidences of each model and the implications of the super-assembly in the physiological role of coenzyme Q.

Phosphorylation of flotillin-1 by mitochondrial c-Src is required to prevent the production of reactive oxygen species

We have shown that mitochondrial c-Src regulates reactive oxygen species (ROS) production by phosphorylating the succinate dehydrogenase A of respiratory complex II (CxII). To elucidate the molecular mechanisms underlying ROS production regulated by c-Src in the CxII, we investigated the CxII protein complex derived from cells treated with Src family kinase inhibitor PP2. We identified flotillin-1 as a c-Src target that prevents ROS production from CxII. Phosphorylation-site analysis suggests Tyr56 and Tyr149 on flotillin-1 as sites for phosphorylation by c-Src. A comparison of cells expressing flotillin-1 and its phosphorylation defective mutants confirms the requirement for flotillin-1 phosphorylation for its interaction with CxII and subsequent reduction in ROS production. Our findings suggest a critical role of flotillin-1 in ROS production mediated by c-Src.