Protein kinase PKC delta and c-Abl are required for mitochondrial apoptosis induction by genotoxic stress in the absence of p53, p73 and Fas receptor

Overcoming β-Cell Dysfunction in Type 2 Diabetes Mellitus: CD36 Inhibition and Antioxidant System

Type 2 diabetes mellitus (T2DM) is marked by chronic hyperglycemia, gradually worsening β-cell failure, and insulin resistance. Glucotoxicity and oxidative stress cause β-cell failure by increasing reactive oxygen species (ROS) production, impairing insulin secretion, and disrupting transcription factors such as pancreatic and duodenal homeobox 1 (PDX-1) and musculoaponeurotic fibrosarcoma oncogene family A (MafA). Cluster determinant 36 (CD36), an essential glycoprotein responsible for fatty acid uptake, exacerbates oxidative stress and induces the apoptosis of β-cells under hyperglycemic conditions through pathways involving ceramide, thioredoxin-interacting protein (TXNIP), and Rac1-nicotinamide adenine dinucleotide phosphate oxidase (NOX)-mediated redoxosome formation. Targeting CD36 pathways has emerged as a promising therapeutic strategy. Oral hypoglycemic agents, such as metformin, teneligliptin, and pioglitazone, have shown protective effects on β-cells by enhancing antioxidant defenses. These agents reduce glucotoxicity via mechanisms such as suppressing CD36 expression and stabilizing mitochondrial function. Additionally, novel insights into the glutathione antioxidant system and its role in β-cell survival underscore its therapeutic potential. This review focuses on the key contribution of oxidative stress and CD36 to β-cell impairment, the therapeutic promise of antioxidants, and the need for further research to apply these findings in clinical practice. Promising strategies targeting these mechanisms may help preserve β-cell function and slow T2DM progression.

c-Abl tyrosine kinase inhibition attenuate oxidative stress-induced pancreatic β-Cell dysfunction via glutathione antioxidant system

Chronic oxidative stress, which is caused by aberrant non-receptor tyrosine kinase (c-Abl) signaling, plays a key role in the progression of β-cell loss in diabetes mellitus. Recent studies, however, have linked ferroptotic-like death to the β-cell loss in diabetes mellitus. Here, we report that oxidative stress-driven reduced/oxidized glutathione (GSH/GSSG) loss and proteasomal degradation of glutathione peroxidase 4 (GPX4) promote ferroptotic-like cell damage through increased lipid peroxidation. Mechanistically, treatment with GNF2, a non-ATP competitive c-Abl kinase inhibitor, selectively preserves β-cell function by inducing the orphan nuclear receptor estrogen-related receptor gamma (ERRγ). ERRγ-driven glutaminase 1 (GLS1) expression promotes the elevation of the GSH/GSSG ratio, and this increase leads to the inhibition of lipid peroxidation by GPX4. Strikingly, pharmacological inhibition of ERRγ represses the expression of GLS1 and reverses the GSH/GSSG ratio linked to mitochondrial dysfunction and increased lipid peroxidation mediated by GPX4 degradation. Inhibition of GLS1 suppresses the ERRγ agonist DY131-induced GSH/GSSG ratio linked to ferroptotic-like death owing to the loss of GPX4. Furthermore, immunohistochemical analysis showed enhanced ERRγ and GPX4 expression in the pancreatic islets of GNF2-treated mice compared to that in streptozotocin-treated mice. Altogether, our results provide the first evidence that the orphan nuclear receptor ERRγ-induced GLS1 expression augments the glutathione antioxidant system, and its downstream signaling leads to improved β-cell function and survival under oxidative stress conditions.

Mitochondrial Proteome of Affected Glutamatergic Neurons in a Mouse Model of Leigh Syndrome

Defects in mitochondrial function lead to severe neuromuscular orphan pathologies known as mitochondrial disease. Among them, Leigh Syndrome is the most common pediatric presentation, characterized by symmetrical brain lesions, hypotonia, motor and respiratory deficits, and premature death. Mitochondrial diseases are characterized by a marked anatomical and cellular specificity. However, the molecular determinants for this susceptibility are currently unknown, hindering the efforts to find an effective treatment. Due to the complex crosstalk between mitochondria and their supporting cell, strategies to assess the underlying alterations in affected cell types in the context of mitochondrial dysfunction are critical. Here, we developed a novel virus-based tool, the AAV-mitoTag viral vector, to isolate mitochondria from genetically defined cell types. Expression of the AAV-mitoTag in the glutamatergic vestibular neurons of a mouse model of Leigh Syndrome lacking the complex I subunit Ndufs4 allowed us to assess the proteome and acetylome of a subset of susceptible neurons in a well characterized model recapitulating the human disease. Our results show a marked reduction of complex I N-module subunit abundance and an increase in the levels of the assembly factor NDUFA2. Transiently associated non-mitochondrial proteins such as PKCδ, and the complement subcomponent C1Q were also increased in Ndufs4-deficient mitochondria. Furthermore, lack of Ndufs4 induced ATP synthase complex and pyruvate dehydrogenase (PDH) subunit hyperacetylation, leading to decreased PDH activity. We provide novel insight on the pathways involved in mitochondrial disease, which could underlie potential therapeutic approaches for these pathologies.

Sensitivity of CD3/CD28-stimulated versus non-stimulated lymphocytes to ionizing radiation and genotoxic anticancer drugs: key role of ATM in the differential radiation response

Activation of T cells, a major fraction of peripheral blood lymphocytes (PBLCS), is essential for the immune response. Genotoxic stress resulting from ionizing radiation (IR) and chemical agents, including anticancer drugs, has serious impact on T cells and, therefore, on the immune status. Here we compared the sensitivity of non-stimulated (non-proliferating) vs. CD3/CD28-stimulated (proliferating) PBLC to IR. PBLCs were highly sensitive to IR and, surprisingly, stimulation to proliferation resulted in resistance to IR. Radioprotection following CD3/CD28 activation was observed in different T-cell subsets, whereas stimulated CD34+ progenitor cells did not become resistant to IR. Following stimulation, PBLCs showed no significant differences in the repair of IR-induced DNA damage compared with unstimulated cells. Interestingly, ATM is expressed at high level in resting PBLCs and CD3/CD28 stimulation leads to transcriptional downregulation and reduced ATM phosphorylation following IR, indicating ATM to be key regulator of the high radiosensitivity of resting PBLCs. In line with this, pharmacological inhibition of ATM caused radioresistance of unstimulated, but not stimulated, PBLCs. Radioprotection was also achieved by inhibition of MRE11 and CHK1/CHK2, supporting the notion that downregulation of the MRN-ATM-CHK pathway following CD3/CD28 activation results in radioprotection of proliferating PBLCs. Interestingly, the crosslinking anticancer drug mafosfamide induced, like IR, more death in unstimulated than in stimulated PBLCs. In contrast, the bacterial toxin CDT, damaging DNA through inherent DNase activity, and the DNA methylating anticancer drug temozolomide induced more death in CD3/CD28-stimulated than in unstimulated PBLCs. Thus, the sensitivity of stimulated vs. non-stimulated lymphocytes to genotoxins strongly depends on the kind of DNA damage induced. This is the first study in which the killing response of non-proliferating vs. proliferating T cells was comparatively determined. The data provide insights on how immunotherapeutic strategies resting on T-cell activation can be impacted by differential cytotoxic effects resulting from radiation and chemotherapy.

In vitro identification of mitochondrial oxidative stress production by time-resolved fluorescence imaging of glioma cells

Oxidative phosphorylation and glycolysis are important features, by which cells could bypass oxidative stress. The level of oxidative stress, and the ability of cells to promote oxidative phosphorylation or glycolysis, significantly determined proliferation or cell demise. In the present work, we have employed selective mitochondrial probe MitoTracker™ Orange CMTM/Ros (MTO) to estimate the level of oxidative stress in cancer cells at different stressed conditions. MTO is partially sensitive to decrease of mitochondrial membrane potential and to reactive oxygen species (ROS) generated in mitochondria. We have demonstrated, that fluorescence lifetime of MTO is much more sensitive to oxidative stress than intensity-based approaches. This method was validated in different cancer cell lines. Our approach revealed, at relatively low ROS levels, that Gö 6976, a protein kinase C (PKC) α inhibitor, and rottlerin, an indirect PKCδ inhibitor, increased mitochondrial ROS level in glioma cell. Their involvement in oxidative phosphorylation and apoptosis was investigated with oxygen consumption rate estimation, western blot and flow-cytometric analysis. Our study brings new insight to identify feeble differences in ROS production in living cells.

Enhanced G-Quadruplex DNA Stabilization and Telomerase Inhibition by Novel Fluorescein Derived Salen and Salphen Based Ni(II) and Pd(II) Complexes

Metal based salen complexes have been considered as an important scaffold toward targeting of DNA structures. In the present work, we have synthesized nickel(II) and palladium(II) salen and salphen complexes by using readily available fluorescein as the backbone to provide an extended aromatic surface. The metal complexes exhibit affinity toward the human telomeric G-quadruplex DNA with promising inhibition of telomerase activity. This has been ascertained by their efficiency in the long term cell proliferation assay which showed significant cancer cell toxicity in the presence of the metal complexes. Confocal microscopy showed cellular internalization followed by localization in the nucleus and mitochondria. Considerable population at the sub-G1 phase of the cell cycle showed cell death via apoptotic pathway.

Pro-haloacetate Nanoparticles for Efficient Cancer Therapy via Pyruvate Dehydrogenase Kinase Modulation

Anticancer agents based on haloacetic acids are developed for inhibition of pyruvate dehydrogenase kinase (PDK), an enzyme responsible for reversing the suppression of mitochondria-dependent apoptosis. Through molecular docking studies mono- and dihaloacetates are identified as potent PDK2 binders and matched their efficiency with dichloroacetic acid. In silico screening directed their conversion to phospholipid prodrugs, which were subsequently self-assembled to pro-haloacetate nanoparticles. Following a thorough physico-chemical characterization, the functional activity of these novel agents was established in wide ranges of human cancer cell lines in vitro and in vivo in rodents. Results indicated that the newly explored PDK modulators can act as efficient agent for cancer regression. A Pyruvate dehydrogenase (PDH) assay mechanistically confirmed that these agents trigger their activity through the mitochondria-dependent apoptosis.

Multifunctional roles of PKCδ: Opportunities for targeted therapy in human disease

The serine-threonine protein kinase, protein kinase C-δ (PKCδ), is emerging as a bi-functional regulator of cell death and proliferation. Studies in PKCδ-/- mice have confirmed a pro-apoptotic role for this kinase in response to DNA damage and a tumor promoter role in some oncogenic contexts. In non-transformed cells, inhibition of PKCδ suppresses the release of cytochrome c and caspase activation, indicating a function upstream of apoptotic pathways. Data from PKCδ-/- mice demonstrate a role for PKCδ in the execution of DNA damage-induced and physiologic apoptosis. This has led to the important finding that inhibitors of PKCδ can be used therapeutically to reduce irradiation and chemotherapy-induced toxicity. By contrast, PKCδ is a tumor promoter in mouse models of mammary gland and lung cancer, and increased PKCδ expression is a negative prognostic indicator in Her2+ and other subtypes of human breast cancer. Understanding how these distinct functions of PKCδ are regulated is critical for the design of therapeutics to target this pathway. This review will discuss what is currently known about biological roles of PKCδ and prospects for targeting PKCδ in human disease.

c-Abl silencing reduced the inhibitory effects of TGF-β1 on apoptosis in systemic sclerosis dermal fibroblasts

It is generally accepted that the apoptosis of myofibroblasts is a crucial event in the normal wound healing. Delay in myofibroblasts apoptosis results in fibrotic diseases such as systemic sclerosis (SSc). Transforming growth factor-β1 (TGF-β1) is an important cytokine to induce fibroblasts differentiation into myofibroblasts. Cellular Abelson (c-Abl) is known as a TGF-β1-modulating molecule in fibrosis. The role of c-Abl, TGF-β1, and their interaction in SSc myofibroblasts apoptosis has not yet been fully explored. The aim of this study was to evaluate whether TGF-β1 and inhibition of c-Abl influence Bax to Bcl-2 ratio and apoptosis in SSc and healthy dermal fibroblasts. We also would like to know whether there is interaction between TGF-β1 and c-Abl in connection with fibroblasts apoptosis or not. Bax to Bcl-2 ratio was determined using quantitative real-time polymerase chain reaction and immunoblotting. Apoptosis was detected using annexin V and nuclear staining with Hoechst dye. Our results demonstrated that inhibition of c-Abl increased SSc and healthy dermal fibroblasts susceptibility to apoptosis through increasing in Bax to Bcl-2 mRNA and protein ratios, whereas TGF-β1 promoted healthy fibroblasts resistance to apoptosis via decreasing Bax to Bcl-2 mRNA and protein ratios. In addition, c-Abl silencing reduced the effects of TGF-β1 on Bax to Bcl-2 mRNA and protein ratios. These results suggested that TGF-β1 and c-Abl individually may prevent the deletion of myofibroblasts from wounds and result in fibrosis. Results also proposed that silencing of c-Abl may promote myofibroblasts elimination from wound lesions through reduction in the TGF-β1 inhibitory effects on apoptosis.

Benzo(a)pyrene-7,8-diol-9,10-epoxide induced p53-independent necrosis via the mitochondria-associated pathway involving Bax and Bak activation

Benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE) is a highly reactive DNA damage agent and can induce cell death through both p53-independent and -dependent pathways. However, little is known about the molecular mechanisms of p53-independent pathways in BPDE-induced cell death. To understand the p53-independent mechanisms, we have now examined BPDE-induced cytotoxicity in p53-deficient baby mouse kidney (BMK) cells. The results showed that BPDE could induce Bax and Bak activation, cytochrome c release, caspases activation, and necrotic cell death in the BMK cells. Bax and Bak, two key molecules of mitochondrial permeability transition pore, were interdependently activated by BPDE, with Bax and Bak translocation to and Bax/Bak homo-oligomerization in mitochondria, release of cytochrome c was induced. Importantly, cytochrome c release and necrotic cell death were diminished in BMK cells (Bax−/−), BMK cells (Bak−/−), and BMK cells (Bax−/−/Bak−/−). Furthermore, overexpression of Bcl-2 could ameliorate BPDE-induced cytochrome c release and necrosis. Together the findings suggested that BPDE-induced necrosis was modulated by the p53-independent pathway, which was related to the translocation of Bax and Bak to mitochondria, release of cytochrome c, and activation of caspases.

Inhibiting tyrosine phosphorylation of protein kinase Cδ (PKCδ) protects the salivary gland from radiation damage

Radiation therapy for head and neck cancer can result in extensive damage to normal adjacent tissues such as the salivary gland and oral mucosa. We have shown previously that tyrosine phosphorylation at Tyr-64 and Tyr-155 activates PKCδ in response to apoptotic stimuli by facilitating its nuclear import. Here we have identified the tyrosine kinases that mediate activation of PKCδ in apoptotic cells and have explored the use of tyrosine kinase inhibitors for suppression of irradiation-induced apoptosis. We identify the damage-inducible kinase, c-Abl, as the PKCδ Tyr-155 kinase and c-Src as the Tyr-64 kinase. Depletion of c-Abl or c-Src with shRNA decreased irradiation- and etoposide-induced apoptosis, suggesting that inhibitors of these kinases may be useful therapeutically. Pretreatment with dasatinib, a broad spectrum tyrosine kinase inhibitor, blocked phosphorylation of PKCδ at both Tyr-64 and Tyr-155. Expression of "gate-keeper" mutants of c-Abl or c-Src that are active in the presence of dasatinib restored phosphorylation of PKCδ at Tyr-155 and Tyr-64, respectively. Imatinib, a c-Abl-selective inhibitor, also specifically blocked PKCδ Tyr-155 phosphorylation. Dasatinib and imatinib both blocked binding of PKCδ to importin-α and nuclear import, demonstrating that tyrosine kinase inhibitors can inhibit nuclear accumulation of PKCδ. Likewise, pretreatment with dasatinib also suppressed etoposide and radiation induced apoptosis in vitro. In vivo, pre-treatment of mice with dasatinib blocked radiation-induced apoptosis in the salivary gland by >60%. These data suggest that tyrosine kinase inhibitors may be useful prophylactically for protection of nontumor tissues in patients undergoing radiotherapy of the head and neck.

Loss of protein kinase Cδ/HuR interaction is necessary to doxorubicin resistance in breast cancer cell lines

The protein kinase Cδ (PKCδ) interacts with and phosphorylates HuR, dictating its functionality. We show here that the genotoxic stimulus induced by doxorubicin triggers PKCδ interaction with HuR and leads to HuR phosphorylation on serines 221 and 318 and cytoplasmic translocation. This series of events is crucial to elicit the death pathway triggered by doxorubicin and is necessary to promote HuR function in post-transcriptional regulation of gene expression, because genetic ablation of PKCδ caused the inability of HuR to bind its target mRNAs, topoisomerase IIα (TOP2A) included. In in vitro select doxorubicin-resistant human breast cancer cell lines upregulating the multidrug resistance marker ABCG2, PKCδ, and HuR proteins were coordinately downregulated together with the doxorubicin target TOP2A protein whose mRNA was HuR-regulated. Therefore, we show here that PKCδ, HuR, and TOP2A constitute a network mediating doxorubicin efficacy in breast cancer cells. The importance of these molecular events in cancer therapy is suggested by their being profoundly suppressed in cells selected for doxorubicin resistance.

The sodium/iodide symporter NIS is a transcriptional target of the p53-family members in liver cancer cells

Thyroid iodide accumulation via the sodium/iodide symporter (NIS; SLC5A5) has been the basis for the longtime use of radio-iodide in the diagnosis and treatment of thyroid cancers. NIS is also expressed, but poorly functional, in some non-thyroid human cancers. In particular, it is much more strongly expressed in cholangiocarcinoma (CCA) and hepatocellular carcinoma (HCC) cell lines than in primary human hepatocytes (PHH). The transcription factors and signaling pathways that control NIS overexpression in these cancers is largely unknown. We identified two putative regulatory clusters of p53-responsive elements (p53REs) in the NIS core promoter, and investigated the regulation of NIS transcription by p53-family members in liver cancer cells. NIS promoter activity and endogenous NIS mRNA expression are stimulated by exogenously expressed p53-family members and significantly reduced by member-specific siRNAs. Chromatin immunoprecipitation analysis shows that the p53–REs clusters in the NIS promoter are differentially occupied by the p53-family members to regulate basal and DNA damage-induced NIS transcription. Doxorubicin strongly induces p53 and p73 binding to the NIS promoter, leading to an increased expression of endogenous NIS mRNA and protein in HCC and CCA cells, but not in PHH. Silencing NIS expression reduced doxorubicin-induced apoptosis in HCC cells, pointing to a possible role of a p53-family-dependent expression of NIS in apoptotic cell death. Altogether, these results indicate that the NIS gene is a direct target of the p53 family and suggests that the modulation of NIS by DNA-damaging agents is potentially exploitable to boost NIS upregulation in vivo.

Receptor tyrosine kinase ErbB2 translocates into mitochondria and regulates cellular metabolism

It is well known that ErbB2, a receptor tyrosine kinase, localizes on the plasma membrane. Here we describe a novel observation that ErbB2 also localizes in mitochondria of cancer cells and patient samples. We found that ErbB2 translocates into mitochondria through the association with mtHSP70. Additionally, mitochondrial ErbB2 (mtErbB2) negatively regulates mitochondrial respiratory functions. Oxygen consumption and activities of complexes of the mitochondrial electron transport chain were decreased in mtErbB2-overexpressing cells. Mitochondrial membrane potential and the cellular ATP level also were decreased. In contrast, mtErbB2 enhanced cellular glycolysis. The translocation of ErbB2 and its impact on mitochondrial function are kinase dependent. Interestingly, cancer cells with higher levels of mtErbB2 were more resistant to ErbB2 targeting antibody trastuzumab. Our study provides a novel perspective on the metabolic regulatory function of ErbB2 and reveals that mtErbB2 plays an important role in the regulation of cellular metabolism and cancer cell resistance to therapeutics.

ΔNp73 enhances promoter activity of TGF-β induced genes

The p53 homolog p73 is frequently overexpressed in cancers. Especially the transactivation domain truncated isoform ΔNp73 has oncogenic properties and its upregulation is associated with poor patient survival. It has been shown that ΔNp73 has an inhibitory effect on the transactivation capacity of p53 and other p73 isoforms. Here, we confirm this finding but surprisingly find that ΔNp73 may also stimulate the expression of TGF-β signaling targets. Promoter-reporter analysis indicated that the presence of Smad Binding Elements (SBE) in the promoter is sufficient for stimulation of gene expression by ΔNp73. TGF-β signaling was less efficient in ΔNp73 downregulated cells, whereas tetracycline induced ΔNp73 increased expression of endogenous TGF-β regulated genes PAI-1 and Col1a1. Pull-down assays with SBE DNA suggest that ΔNp73 enhances smad3/4 binding to SBEs, thereby stimulating TGF-β signaling. Chromatin immunoprecipitation assays confirmed a direct interaction between ΔNp73 and SBE. Given the role of TGF-β signaling in carcinogenesis, tumor invasion and metastasis via targets like PAI-1 and Col1a1, our data suggest a model on how this effect of ΔNp73 could be a contributing factor in cancer progression.

Protein kinase cδ in apoptosis: a brief overview

Protein kinase C-delta (PKCδ), a member of the lipid-regulated serine/threonine PKC family, has been implicated in a wide range of important cellular processes. In the past decade, the critical role of PKCδ in the regulation of both intrinsic and extrinsic apoptosis pathways has been widely explored. In most cases, over-expression or activation of PKCδ results in the induction of apoptosis. The phosphorylations and multiple cell organelle translocations of PKCδ initiate apoptosis by targeting multiple downstream effectors. During apoptosis, PKCδ is proteolytically cleaved by caspase-3 to generate a constitutively activated catalytic fragment, which amplifies apoptosis cascades in nucleus and mitochondria. However, PKCδ also exerts its anti-apoptotic and pro-survival roles in some cases. Therefore, the complicated role of PKCδ in apoptosis appears to be stimulus and cell type dependent. This review is mainly focused on how PKCδ gets activated in diverse ways in response to apoptotic signals and how PKCδ targets different downstream regulators to sponsor or restrain apoptosis induction.

Src kinases are important regulators of mitochondrial functions

Mitochondria produce the most part of the energy used by the cells. This energetic production occurs through the oxidative phosphorylation (OXPHOS) process. Mitochondrial functions such as OXPHOS need to be tightly regulated to respect the needs of cells. Phosphorylation of mitochondrial proteins now appears as a major regulation pathway of mitochondrial functions. Several kinases and phosphatases are specifically targeted to mitochondria where they modulate mitochondrial functions. However, we still poorly understand the extent of tyrosine phosphorylation events on mitochondrial metabolism. Among the tyrosine-kinases observed in mitochondria, Src kinases emerge as key players. In the past years, several mitochondrial proteins were shown to be substrates of Src kinases. Notably, these kinases can impact greatly OXPHOS and apoptosis. Important regulators of Src kinases activity are also observed in mitochondria. The aim of this review is to summarize the recent findings on how overall mitochondrial tyrosine phosphorylation events and more specifically Src kinases can influence mitochondrial functions. The different mechanisms of Src kinases regulation and translocation into mitochondria will be also discussed. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Targeting malignant mitochondria with therapeutic peptides

The current status of peptides that target the mitochondria in the context of cancer is the focus of this review. Chemotherapy and radiotherapy used to kill tumor cells are principally mediated by the process of apoptosis that is governed by the mitochondria. The failure of anticancer therapy often resides at the level of the mitochondria. Therefore, the mitochondrion is a key pharmacological target in cancer due to many of the differences that arise between malignant and healthy cells at the level of this ubiquitous organelle. Additionally, targeting the characteristics of malignant mitochondira often rely on disruption of protein--protein interactions that are not generally amenable to small molecules. We discuss anticancer peptides that intersect with pathological changes in the mitochondrion.

Mitochondrial DNA maintenance is regulated in human hepatoma cells by glycogen synthase kinase 3β and p53 in response to tumor necrosis factor α

During chronic liver inflammation, up-regulated Tumor Necrosis Factor alpha (TNF-α) targets hepatocytes and induces abnormal reactive oxygen species (ROS) production responsible for mitochondrial DNA (mtDNA) alterations. The serine/threonine Glycogen Synthase Kinase 3 beta (GSK3β) plays a pivotal role during inflammation but its involvement in the maintenance of mtDNA remains unknown. The aim of this study was to investigate its involvement in TNF-α induced mtDNA depletion and its interrelationship with p53 a protein known to maintain mtDNA copy numbers. Using quantitative polymerase chain reaction (qPCR) we found that at 30 min in human hepatoma HepG2 cells TNF-α induced 0.55±0.10 mtDNA lesions per 10 Kb and a 52.4±2.8% decrease in mtDNA content dependent on TNF-R1 receptor and ROS production. Both lesions and depletion returned to baseline from 1 to 6 h after TNF-α exposure. Luminol-amplified chemiluminescence (LAC) was used to measure the rapid (10 min) and transient TNF-α induced increase in ROS production (168±15%). A transient 8-oxo-dG level of 1.4±0.3 ng/mg DNA and repair of abasic sites were also measured by ELISA assays. Translocation of p53 to mitochondria was observed by Western Blot and co-immunoprecipitations showed that TNF-α induced p53 binding to GSK3β and mitochondrial transcription factor A (TFAM). In addition, mitochondrial D-loop immunoprecipitation (mtDIP) revealed that TNF-α induced p53 binding to the regulatory D-loop region of mtDNA. The knockdown of p53 by siRNAs, inhibition by the phosphoSer(15)p53 antibody or transfection of human mutant active GSK3βS9A pcDNA3 plasmid inhibited recovery of mtDNA content while blockade of GSK3β activity by SB216763 inhibitor or knockdown by siRNAs suppressed mtDNA depletion. This study is the first to report the involvement of GSK3β in TNF-α induced mtDNA depletion. We suggest that p53 binding to GSK3β, TFAM and D-loop could induce recovery of mtDNA content through mtDNA repair.

Implication of NADPH oxidases in the early inflammation process generated by cystic fibrosis cells

In cystic fibrosis (CF) patients, pulmonary inflammation is a major cause of morbidity and mortality. The aim of this study was to further investigate whether oxidative stress could be involved in the early inflammatory process associated with CF pathogenesis. We used a model of CFTR defective epithelial cell line (IB3-1) and its reconstituted CFTR control (S9) cell line cultured in various ionic conditions. This study showed that IB3-1 and S9 cells expressed the NADPH oxidases (NOXs) DUOX1/2 and NOX2 at the same level. Nevertheless, several parameters participating in oxidative stress (increased ROS production and apoptosis, decreased total thiol content) were observed in IB3-1 cells cultured in hypertonic environment as compared to S9 cells and were inhibited by diphenyleneiodonium (DPI), a well-known inhibitor of NOXs; besides, increased production of the proinflammatory cytokines IL-6 and IL-8 by IB3-1 cells was also inhibited by DPI as compared to S9 cells. Furthermore, calcium ionophore (A23187), which upregulates DUOX and NOX2 activities, strongly induced oxidative stress and IL-8 and IL-6 overexpression in IB3-1 cells. All these events were suppressed by DPI, supporting the involvement of NOXs in the oxidative stress, which can upregulate proinflammatory cytokine production by the airway CFTR-deficient cells and trigger early pulmonary inflammation in CF patients.

Oxidative Stress, DNA Damage, and c-Abl Signaling: At the Crossroad in Neurodegenerative Diseases?

The c-Abl tyrosine kinase is implicated in diverse cellular activities including growth factor signaling, cell adhesion, oxidative stress, and DNA damage response. Studies in mouse models have shown that the kinases of the c-Abl family play a role in the development of the central nervous system. Recent reports show that aberrant c-Abl activation causes neuroinflammation and neuronal loss in the forebrain of transgenic adult mice. In line with these observations, an increased c-Abl activation is reported in human neurodegenerative pathologies, such as Parkinson's, and Alzheimer's diseases. This suggests that aberrant nonspecific posttranslational modifications induced by c-Abl may contribute to fuel the recurrent phenotypes/features linked to neurodegenerative disorders, such as an impaired mitochondrial function, oxidative stress, and accumulation of protein aggregates. Herein, we review some reports on c-Abl function in neuronal cells and we propose that modulation of different aspects of c-Abl signaling may contribute to mediate the molecular events at the interface between stress signaling, metabolic regulation, and DNA damage. Finally, we propose that this may have an impact in the development of new therapeutic strategies.

Graphene as a nanocarrier for tamoxifen induces apoptosis in transformed cancer cell lines of different origins

A cationic amphiphile, cholest-5en-3β-oxyethyl pyridinium bromide (PY(+) -Chol), is able to efficiently disperse exfoliated graphene (GR) in water by the physical adsorption of PY(+) -Chol on the surface of GR to form stable, dark aqueous suspensions at room temperature. The GR-PY(+) -Chol suspension can then be used to solubilize Tamoxifen Citrate (TmC), a breast cancer drug, in water. The resulting TmC-GR-PY(+) -Chol is stable for a long time without any precipitation. Fluorescence emission and UV absorption spectra indicate the existence of noncovalent interactions between TmC, GR, and PY(+) -Chol in these suspensions. Electron microscopy shows the existence of segregated GR sheets and TmC 'ribbons' in the composite suspensions. Atomic force microscopy indicates the presence of 'extended' structures of GR-PY(+) -Chol, which grows wider in the presence of TmC. The slow time-dependent release of TmC is noticed in a reconstituted cell culture medium, a property useful as a drug carrier. TmC-GR-PY(+) -Chol selectively enhanced the cell death (apoptosis) of the transformed cancer cells compared to normal cells. This potency is found to be true for a wide range of transformed cancer cells viz. HeLa, A549, ras oncogene-transformed NIH3T3, HepG2, MDA-MB231, MCF-7, and HEK293T compared to the normal cell HEK293 in vitro. Confocal microscopy confirmed the high efficiency of TmC-GR-PY(+) -Chol in delivering the drug to the cells, compared to the suspensions devoid of GR.

Central role of mitochondria in drug-induced liver injury

A frequent mechanism for drug-induced liver injury (DILI) is the formation of reactive metabolites that trigger hepatitis through direct toxicity or immune reactions. Both events cause mitochondrial membrane disruption. Genetic or acquired factors predispose to metabolite-mediated hepatitis by increasing the formation of the reactive metabolite, decreasing its detoxification, or by the presence of critical human leukocyte antigen molecule(s). In other instances, the parent drug itself triggers mitochondrial membrane disruption or inhibits mitochondrial function through different mechanisms. Drugs can sequester coenzyme A or can inhibit mitochondrial β-oxidation enzymes, the transfer of electrons along the respiratory chain, or adenosine triphosphate (ATP) synthase. Drugs can also destroy mitochondrial DNA, inhibit its replication, decrease mitochondrial transcripts, or hamper mitochondrial protein synthesis. Quite often, a single drug has many different effects on mitochondrial function. A severe impairment of oxidative phosphorylation decreases hepatic ATP, leading to cell dysfunction or necrosis; it can also secondarily inhibit ß-oxidation, thus causing steatosis, and can also inhibit pyruvate catabolism, leading to lactic acidosis. A severe impairment of β-oxidation can cause a fatty liver; further, decreased gluconeogenesis and increased utilization of glucose to compensate for the inability to oxidize fatty acids, together with the mitochondrial toxicity of accumulated free fatty acids and lipid peroxidation products, may impair energy production, possibly leading to coma and death. Susceptibility to parent drug-mediated mitochondrial dysfunction can be increased by factors impairing the removal of the toxic parent compound or by the presence of other medical condition(s) impairing mitochondrial function. New drug molecules should be screened for possible mitochondrial effects.

The impact of Fli1 deficiency on the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune inflammatory disease with unknown etiology characterized by microvascular injury and fibrosis of the skin and internal organs. A growing body of evidence suggests that deficiency of the transcription factor Fli1 (Friend leukemia integration-1) has a pivotal role in the pathogenesis of SSc. Fli1 is expressed in fibroblasts, endothelial cells, and immune cells, and has important roles in the activation, differentiation, development, and survival of these cells. Previous studies demonstrated that Fli1 is downregulated in SSc fibroblasts by an epigenetic mechanism and a series of experiments with Fli1-deficient animal models revealed that Fli1 deficiency in fibroblasts and endothelial cells reproduces the histopathologic features of fibrosis and vasculopathy in SSc, respectively. In this article, we review the impact of Fli1 deficiency on the pathogenesis of SSc and discuss a new therapeutic strategy for SSc by targeting the transcription factor Fli1.

Cisplatin-induced apoptosis in p53-deficient renal cells via the intrinsic mitochondrial pathway

Nephrotoxicity is the major limiting factor for the use of cisplatin in cancer therapy. Recent studies have demonstrated an important role for p53 in cisplatin-induced renal injury. Nevertheless, pharmacological and genetic blockade of p53 only provides partial renoprotective effects, suggesting the presence of p53-independent injury mechanisms. To understand the p53-independent mechanisms, we have now examined cisplatin-induced apoptosis in p53-deficient kidney cells. We show that cisplatin could induce Bax activation, cytochrome c release, and apoptosis in primary cultures of p53-deficient renal tubular cells, albeit at a level that was lower than in the wild-type cells. Cisplatin could also induce typical apoptosis in p53-deficient baby mouse kidney (BMK) cells. The apoptosis was caspase dependent and could be completely blocked by general caspase inhibitors. Bax and Bak, two key molecules in the mitochondrial pathway of apoptosis, were interdependently activated by cisplatin, with Bax translocation to and Bax/Bak oligomerization in mitochondria, leading to cytochrome c release. Importantly, cytochrome c release and apoptosis were diminished in Bax/Bak single or double-knockout BMK cells. Furthermore, overexpression of Bcl-2 could ameliorate cisplatin-induced cytochrome c release and apoptosis. Together, the results have demonstrated a p53-independent mechanism of cisplatin nephrotoxicity that involves the mitochondrial pathway of apoptosis.

Protein kinase Cdelta negatively regulates hedgehog signaling by inhibition of Gli1 activity

Constitutive activation of the hedgehog pathway is implicated in the development of many human malignancies; hedgehog targets, PTCH1 and Gli1, are markers of hedgehog signaling activation and are expressed in most hedgehog-associated tumors. Protein kinase Cdelta (PKCdelta) generally slows proliferation and induces cell cycle arrest of various cell lines. In this study, we show that activated PKCdelta (wild-type PKCdelta stimulated by phorbol 12-myristate 13-acetate or constitutively active PKCdelta) decreased Gli-luciferase reporter activity in NIH/3T3 cells, as well as the endogenous hedgehog-responsive gene PTCH1. In human hepatoma (i.e. Hep3B) cells, wild-type PKCdelta and constitutively active PKCdelta decreased the expression levels of endogenous Gli1 and PTCH1. In contrast, PKCdelta siRNA increased the expression levels of these target genes. Silencing of PKCdelta by siRNA rescued the inhibition of cell growth by KAAD-cyclopamine, an antagonist of hedgehog signaling element Smoothened, suggesting that PKCdelta acts downstream of Smoothened. The biological relevance of our study is shown in hepatocellular carcinoma where we found that hepatocellular carcinoma with detectable hedgehog signaling had weak or no detectable expression of PKCdelta, whereas PKCdelta highly expressing tumors had no detectable hedgehog signaling. Our results demonstrate that PKCdelta alters hedgehog signaling by inhibition of Gli protein transcriptional activity. Furthermore, our findings suggest that, in certain cancers, PKCdelta plays a role as a negative regulator of tumorigenesis by regulating hedgehog signaling.

Wogonin induced differentiation and G1 phase arrest of human U-937 leukemia cells via PKCdelta phosphorylation

Wogonin, a natural monoflavonoid, has been shown to have tumor therapeutic potential in vitro and in vivo. Recently many studies have focused on the induction of apoptosis of tumor cells by wogonin. In this study, we found that wogonin could induce differentiation and G1 phase arrest of human U-937 leukemia cells. The growth of U-937 cells incubated with wogonin was inhibited in a time- and concentration-dependent manner. After treatment with wogonin, U-937 cells exhibited the characteristics of mature granulocytes, such as increased cytoplasmic-to-nuclear ratio, enhanced prominence of cytoplasmic granules, membrane ruffling, a higher NBT-reducing ability, and an increased expression of CD11b. Moreover, wogonin could induce G1 phase arrest and influenced the expression of associated proteins. For example, the expression of phorsphorylated protein kinase C (PKC) delta, p21 increased, while that of cyclin D1/cyclin-dependent kinase (CDK) 4, p-Rb decreased. The upregulation of p21 could be reversed by rottlerin, an inhibitor of PKCdelta. Taken together, wogonin induced U-937 cells to undergo granulocytic differentiation and G1 phase arrest via PKCdelta phosphorylation-induced upregulation of p21 proteins.

Positive and negative regulation of radiation-induced apoptosis by protein kinase C

Indicators such as clonogenic survival, transformation, and chromosomal aberrations are used to evaluate the effects of radiation on cells. Apoptosis, another such indicator, is a mode of cell death, and radiation-induced apoptosis contributes to eliminating damaged cells and preventing malformation and carcinogenesis. Understanding radiation-induced apoptosis will assist in radiotherapy for cancer and treatment of patients in accidental radiation exposure. Protein kinase C (PKC) is a serine/threonine kinase that is related to cell proliferation, differentiation, metabolism, and apoptosis, and has many roles in the radiation-induced cellular responses involving apoptosis. This review describes the functions of PKC, including its relationship with other signaling networks and oxidative stress in the regulation of radiation-induced apoptosis. Such information might provide clues for evaluating the effects of radiation and for identifying clinical applications.

The protein kinase C (PKC) family of proteins in cytokine signaling in hematopoiesis

The members of the protein kinase C (PKC) family of proteins play important roles in signaling for various growth factors, cytokines, and hormones. Extensive work over the years has led to the identification of three major groups of PKC isoforms. These include the classic PKCs (PKCalpha, PKCbeta(I), PKCbeta(II), PKCgamma), the novel PKCs (PKCdelta, PKCepsilon, PKCeta, PKCmu, PKCtheta), and the atypical PKCs (PKCzeta, PKCiota/lambda). All these PKC subtypes have been shown to participate in the generation of signals for important cellular processes and to mediate diverse and, in some cases, opposing biologic responses. There is emerging evidence that these kinases also play key functional roles in the regulation of cell growth, apoptosis, and differentiation of hematopoietic cells. In this review, both the engagement of the various PKC members in cytokine and growth factor signaling and their role in the regulation of hematopoiesis are discussed.

Nuclear expression of E2F4 induces cell death via multiple pathways in normal human intestinal epithelial crypt cells but not in colon cancer cells

E2F transcription factors control cell cycle progression. The localization of E2F4 in intestinal epithelial cells is cell cycle dependent, being cytoplasmic in quiescent differentiated cells but nuclear in proliferative cells. However, whether nuclear translocation of E2F4 alone is sufficient to trigger intestinal epithelial cell proliferation remains to be established. Adenoviruses expressing fusion proteins between green fluorescent protein (GFP) and wild-type (wt)E2F4 or GFP and nuclear localization signal (NLS)-tagged E2F4 were used to infect normal human intestinal epithelial crypt cells (HIEC). In contrast to expression of wtE2F4, persistent expression of E2F4 into the nucleus of HIEC triggered phosphatidylserine exposure, cytoplasmic shrinkage, zeiosis, formation of apoptotic bodies, and activation of caspase 9 and caspase 3. Inhibition of caspase activities by zVAD-fmk partially inhibited cell death induced by E2F4-NLS. An induction of p53, phosphorylated Ser15-p53, PUMA, FAS, BAX, RIP, and phosphorylated JNK1 was also observed in HIEC expressing E2F4-NLS compared with wtE2F4-expressing cells. E2F1 and p14ARF expression remained unaltered. Downregulation of p53 expression by RNA interference attenuated cell death induced by E2F4-NLS. By contrast, the level of cell death was negligible in colon cancer cells despite the strong expression of E2F4 into the nucleus. In conclusion, deregulated nuclear E2F4 expression induces apoptosis via multiple pathways in normal intestinal epithelial cells but not in colon cancer cells. Hence, mutations that deregulate E2F4 localization may provide an initial proliferative advantage but at the same time accelerate cell death. However, intestinal cells acquiring mutations (e.g., p53, Bax loci, etc.) may escape apoptosis, thereby revealing the full mitogenic potential of the E2F4 transcription factor.

Cadmium induces mitochondria-dependent apoptosis of normal human hepatocytes

The heavy metal cadmium, an environmental pollutant, has been widely demonstrated to be toxic, in particular for liver. In murines, cadmium induces apoptosis of hepatocytes and hepatomas. In human cells, apoptosis induced by cadmium has been exclusively demonstrated in tumoral cell lines. Nothing was known in normal liver, in vitro or in vivo. In the present study, we examined the effects of cadmium in nonmalignant human hepatocytes. For that purpose, we investigated whether cadmium was able to induce apoptosis of normal human hepatocytes (NHH) in primary culture and of a SV40-immortalized human hepatocyte (IHH) cell line. Treatment of IHH and NHH with cadmium induced the presence of a sub-G(1) population at 10 and 100 micromol/L, respectively. DAPI staining of both cell types treated with cadmium 100 micromol/L revealed the induction of nuclear apoptotic bodies, supporting the hypothesis of apoptosis. In IHH and NHH, cadmium 100 micromol/L induced PARP cleavage into a 85 kDa fragment. In order to investigate the involvement of mitochondria in cadmium-induced apoptosis, we measured the mitochondrial membrane potential (Delta(Psim)). We observed that in IHH and NHH, cadmium 100 micromol/L induced a decrease of Delta(Psim). As expected, cadmium under the same conditions enhanced caspase-9 and caspase-3 activities. In addition, cadmium from 1 to 100 micromol/L induced the expression of p53 and phosphorylation of its Ser15 in IHH and NHH. In conclusion, we showed in this study that human hepatocytes were sensitive to cadmium and apoptosis induced at concentrations suggested in the literature to inhibit p53 DNA-binding and DNA repair.

Protein Kinase Cζ Abrogates the Proapoptotic Function of Bax through Phosphorylation

Protein kinase Czeta (PKCzeta) is an atypical PKC isoform that plays an important role in supporting cell survival but the mechanism(s) involved is not fully understood. Bax is a major member of the Bcl-2 family that is required for apoptotic cell death. Because Bax is extensively co-expressed with PKCzeta in both small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cells, it is possible that Bax may act as the downstream target of PKCzeta in regulating survival and chemosensitivity of lung cancer cells. Here we discovered that treatment of cells with nicotine not only enhances PKCzeta activity but also results in Bax phosphorylation and prolonged cell survival, which is suppressed by a PKCzeta specific inhibitor (a myristoylated PKCzeta pseudosubstrate peptide). Purified, active PKCzeta directly phosphorylates Bax in vitro. Overexpression of wild type or the constitutively active A119D but not the dominant negative K281W PKCzeta mutant results in Bax phosphorylation at serine 184. PKCzeta co-localizes and interacts with Bax at the BH3 domain. Specific depletion of PKCzeta by RNA interference blocks nicotine-stimulated Bax phosphorylation and enhances apoptotic cell death. Intriguingly, forced expression of wild type or A119D but not K281W PKCzeta mutant results in accumulation of Bax in cytoplasm and prevents Bax from undergoing a conformational change with prolonged cell survival. Purified PKCzeta can directly dissociate Bax from isolated mitochondria of C2-ceramide-treated cells. Thus, PKCzeta may function as a physiological Bax kinase to directly phosphorylate and interact with Bax, which leads to sequestration of Bax in cytoplasm and abrogation of the proapoptotic function of Bax.

Excretory-secretory products from Fasciola hepatica induce eosinophil apoptosis by a caspase-dependent mechanism

Eosinophils (Eo) are known to be important effector cells in the host defense against helminth parasites. Excretory-secretory products (ESP) released by helminths have shown wide immunomodulatory properties, such as the induction of cellular apoptosis. We investigated the ability of ESP from Fasciola hepatica to induce Eo apoptosis. In this work, we observed that ESP induced an early apoptosis of rat peritoneal eosinophils and that this phenomenon was time- and concentration-dependent. Furthermore, we demonstrated that activation of protein tyrosine kinases (TyrK) and caspases were necessary to mediate the Eo apoptosis induced by the ESP, and that carbohydrate components present in these antigens were involved in this effect. We have described for the first time the ability of ESP from F. hepatica to modify the viability of Eo by apoptosis induction. Besides that, we have observed Eo apoptosis in the liver of rats 21 days after F. hepatica infection. The diminution in Eo survival in early infection could be a parasite strategy in order to prevent a host immune response.

The role of the mitochondria in mediating cytotoxicity of anti-cancer therapies

Optimal cytotoxic anticancer therapy, at the cellular level, requires effective and selective induction of cell death to achieve a net reduction of biomass of malignant tissues. Standard cytotoxic chemotherapeutics have been developed based on the observations that mitotically active cancer cells are more susceptible than quiescent normal cells to chromosomal, microtubular or metabolic poisons. More recent development of molecularly targeted drugs for cancer focuses on exploiting biological differentials between normal and transformed cells for selective eradication of cancers. The common thread of "standard" and "novel" cytotoxic drugs is their ability to activate the apoptosis-inducing machinery mediated by mitochondria, also known as the intrinsic death signaling cascade. The aim of this article is to provide an overview of the role of the mitochondria, an energy-generating organelle essential for life, in mediating death when properly activated by cytotoxic stresses.

Tyrosine 311 is phosphorylated by c-Abl and promotes the apoptotic effect of PKCdelta in glioma cells

In this study we characterized the phosphorylation of tyrosine 311 and its role in the apoptotic function of PKCdelta in glioma cells. We found that c-Abl phosphorylated PKCdelta on tyrosine 311 in response to H2O2 and that this phosphorylation contributed to the apoptotic effect of H2O2. In contrast, Src, Lyn, and Yes were not involved in the phosphorylation of tyrosine 311 by H2O2. A phosphomimetic PKCdelta mutant, in which tyrosine 311 was mutated to glutamic acid (PKCdeltaY311E), induced a large degree of cell apoptosis. Overexpression of the PKCdeltaY311E mutant induced the phosphorylation of p38 and inhibition of p38 abolished the apoptotic effect of the PKCdelta mutant. These results suggest an important role of tyrosine 311 in the apoptotic function of PKCdelta and implicate c-Abl as the kinase that phosphorylates this tyrosine.

p63 and p73, members of the p53 gene family, transactivate PKCδ

The p53 family comprises three genes that encode for p53, p63 and p73. These genes have a significant degree of sequence homology, especially in the central sequence-specific DNA-binding domain. The high homology among the three DNA-binding domains indicates that these transcription factors have identical residues interacting with DNA, and thus potentially can recognize the same transcriptional targets. In this study, we demonstrate that PKCdelta is induced by p63 and p73 in Saos2 cells. The putative human PKCdelta promoter harbours three p53-like binding sites (RE I, RE II, RE III). In order to confirm the transactivation of PKCdelta by p53 family members, we performed transcription assays using the entire or selected regions of the promoter upstream of a luciferase reporter gene. The results obtained demonstrated that, at least in vitro, the p53 family members tested (TAp63alpha, TAp73alpha, DeltaNp63alpha, but not DeltaNp73alpha) were able to drive transcription from the PKCdelta promoter.