Targeting of the c-Abl tyrosine kinase to mitochondria in endoplasmic reticulum stress-induced apoptosis

c-Abl Phosphorylates MFN2 to Regulate Mitochondrial Morphology in Cells under Endoplasmic Reticulum and Oxidative Stress, Impacting Cell Survival and Neurodegeneration

The endoplasmic reticulum is a subcellular organelle key in the control of synthesis, folding, and sorting of proteins. Under endoplasmic reticulum stress, an adaptative unfolded protein response is activated; however, if this activation is prolonged, cells can undergo cell death, in part due to oxidative stress and mitochondrial fragmentation. Here, we report that endoplasmic reticulum stress activates c-Abl tyrosine kinase, inducing its translocation to mitochondria. We found that endoplasmic reticulum stress-activated c-Abl interacts with and phosphorylates the mitochondrial fusion protein MFN2, resulting in mitochondrial fragmentation and apoptosis. Moreover, the pharmacological or genetic inhibition of c-Abl prevents MFN2 phosphorylation, mitochondrial fragmentation, and apoptosis in cells under endoplasmic reticulum stress. Finally, in the amyotrophic lateral sclerosis mouse model, where endoplasmic reticulum and oxidative stress has been linked to neuronal cell death, we demonstrated that the administration of c-Abl inhibitor neurotinib delays the onset of symptoms. Our results uncovered a function of c-Abl in the crosstalk between endoplasmic reticulum stress and mitochondrial dynamics via MFN2 phosphorylation.

Mitochondrial Dysfunction in Cardiotoxicity Induced by BCR-ABL1 Tyrosine Kinase Inhibitors -Underlying Mechanisms, Detection, Potential Therapies

The advent of BCR-ABL tyrosine kinase inhibitors (TKIs) targeted therapy revolutionized the treatment of chronic myeloid leukemia (CML) patients. Mitochondria are the key organelles for the maintenance of myocardial tissue homeostasis. However, cardiotoxicity associated with BCR-ABL1 TKIs can directly or indirectly cause mitochondrial damage and dysfunction, playing a pivotal role in cardiomyocytes homeostatic system and putting the cancer survivors at higher risk. In this review, we summarize the cardiotoxicity caused by BCR-ABL1 TKIs and the underlying mechanisms, which contribute dominantly to the damage of mitochondrial structure and dysfunction: endoplasmic reticulum (ER) stress, mitochondrial stress, damage of myocardial cell mitochondrial respiratory chain, increased production of mitochondrial reactive oxygen species (ROS), and other kinases and other potential mechanisms of cardiotoxicity induced by BCR-ABL1 TKIs. Furthermore, detection and management of BCR-ABL1 TKIs will promote our rational use, and cardioprotection strategies based on mitochondria will improve our understanding of the cardiotoxicity from a mitochondrial perspective. Ultimately, we hope shed light on clinical decision-making. By integrate and learn from both research and practice, we will endeavor to minimize the mitochondria-mediated cardiotoxicity and reduce the adverse sequelae associated with BCR-ABL1 TKIs.

Inhibition of Abelson Tyrosine-Protein Kinase 2 Suppresses the Development of Alcohol-Associated Liver Disease by Decreasing PPARgamma Expression

BACKGROUND & AIMS

Alcohol-associated liver disease (ALD) represents a spectrum of alcohol use-related liver diseases. Outside of alcohol abstinence, there are currently no Food and Drug Administration-approved treatments for advanced ALD, necessitating a greater understanding of ALD pathogenesis and potential molecular targets for therapeutic intervention. The ABL-family proteins, including ABL1 and ABL2, are non-receptor tyrosine kinases that participate in a diverse set of cellular functions. We investigated the role of the ABL kinases in alcohol-associated liver disease.

METHODS

We used samples from patients with ALD compared with healthy controls to elucidate a clinical phenotype. We established strains of liver-specific Abl1 and Abl2 knockout mice and subjected them to the National Institute on Alcohol Abuse and Alcoholism acute-on-chronic alcohol feeding regimen. Murine samples were subjected to RNA sequencing, AST, Oil Red O staining, H&E staining, Western blotting, and quantitative polymerase chain reaction to assess phenotypic changes after alcohol feeding. In vitro modeling in HepG2 cells as well as primary hepatocytes from C57BL6/J mice was used to establish this mechanistic link of ALD pathogenesis.

RESULTS

We demonstrate that the ABL kinases are highly activated in ALD patient liver samples as well as in liver tissues from mice subjected to an alcohol feeding regimen. We found that the liver-specific knockout of Abl2, but not Abl1, attenuated alcohol-induced steatosis, liver injury, and inflammation. Subsequent RNA sequencing and gene set enrichment analyses of mouse liver tissues revealed that relative to wild-type alcohol-fed mice, Abl2 knockout alcohol-fed mice exhibited numerous pathway changes, including significantly decreased peroxisome proliferator activated receptor (PPAR) signaling. Further examination revealed that PPARγ, a previously identified regulator of ALD pathogenesis, was induced upon alcohol feeding in wild-type mice, but not in Abl2 knockout mice. In vitro analyses revealed that shRNA-mediated knockdown of ABL2 abolished the alcohol-induced accumulation of PPARγ as well as subsequent lipid accumulation. Conversely, forced overexpression of ABL2 resulted in increased PPARγ protein expression. Furthermore, we demonstrated that the regulation of hypoxia inducible factor 1 subunit alpha (HIF1α) by ABL2 is required for alcohol-induced PPARγ expression. Furthermore, treatment with ABL kinase inhibitors attenuated alcohol-induced PPARγ expression, lipid droplet formation, and liver injury.

CONCLUSIONS

On the basis of our current evidence, we propose that alcohol-induced ABL2 activation promotes ALD through increasing HIF1α and the subsequent PPARγ expression, and ABL2 inhibition may serve as a promising target for the treatment of ALD.

Imatinib Attenuates Pentylenetetrazole Kindled and Pilocarpine Induced Recurrent Spontaneous Seizures in Mice

c-Abl is a non-receptor tyrosine kinase that promotes intracellular apoptotic signaling in prolonged epileptic seizures. PTZ and pilocarpine-induced continuous epileptic convulsions cause neuronal death and gliosis. C-Abl is linked to oxidative stress, neuronal hyperexcitability, mitochondrial malfunction, and subsequent seizures. We investigated the involvement of c-Abl in epileptogenesis by employing its selective inhibitor Imatinib (1 & 3 mg/kg; i.p.) together with conventional medication valproate (110 mg/kg; i.p.) tends to be effective in decreasing seizures threshold provoked by PTZ for 15 days and pilocarpine for 37 days. Further, Imatinib was effective in preventing epileptic seizures arbitrated oxidative stress injury. Oxidative stress has been linked to excitotoxicity that is considered to pathogenic factor in epileptic brain damage. As ELIZA and biochemical estimations showed the high level of c-Abl as an indicator of neuronal oxidative and apoptosis under chronic PTZ & pilocarpine epileptic seizures marked by decreased antioxidants and elevated levels of caspase-3 that were successfully prevented with Imatinib treatment same as valproate (standard drug). Further, the aberrant c-Abl activation is also linked with neuroinflammation that is also predisposing factor in the development of seizures. Selective inhibition of c-Abl by Imatinib also showed anti-inflammatory activity marked with suppressed levels of NF-kB and pro-inflammatory mediators (TNF-alpha, IL-1β, and IL-6) suggesting the neuroprotective effect of Imatinib same as valproate (standard drug) in epilepsy. Therefore, the current study provides preclinical evidence of Imatinib as a potential treatment for seizures, as well as an understanding of potential role of c-Ablin epilepsy.

c-Abl controls BCR signaling and B cell differentiation by promoting B cell metabolism

As a non-receptor tyrosine kinase, c-Abl was first studied in chronic myelogenous leukemia, and its role in lymphocytes has been well characterized. c-Abl is involved in B cell development and CD19 associated B cell antigen receptor (BCR) signaling. Although c-Abl regulates different metabolic pathways, the role of c-Abl is still unknown in B cell metabolism. In this study, B cell specific c-Abl knockout (KO) mice (Mb1^Cre+/- c-Abl^fl/fl ) were used to investigate how c-Abl regulates B cell metabolism and BCR signaling. We found that the levels of activation positive BCR signaling proximal molecules, phosphorylated spleen tyrosine kinase (pSYK) and phosphorylated Bruton tyrosine kinase (pBTK), were decreased, while the level of key negative regulator, phosphorylated SH2-containing inositol phosphatase (pSHIP1), was increased in Mb1^Cre+/- c-Abl^fl/fl mice. Furthermore, we found c-Abl deficiency weakened the B cell spreading, formation of BCR signalosomes, and the polymerization of actin during BCR activation, and also impaired the differentiation of germinal center (GC) B cells both in quiescent condition and after immunization. Moreover, B cell mitochondrial respiration and the expression of B cell metabolism regulating molecules were downregulated in c-Abl deficiency mice. Overall, c-Abl, which involved in actin remodeling and B cell metabolism, positively regulates BCR signaling and promotes GC differentiation. This article is protected by copyright. All rights reserved.

Are off-target effects of imatinib the key to improving beta-cell function in diabetes?

The small tyrosine kinase (TK) inhibitor imatinib mesylate (Gleevec, STI571) protects against both type 1 and type 2 diabetes, but as it inhibits many TKs and other proteins, it is not clear by which mechanisms it acts. This present review will focus on the possibility that imatinib acts, at least in part, by improving beta-cell function and survival via off-target effects on beta-cell signaling/metabolic flow events. Particular attention will be given to the possibility that imatinib and other TK inhibitors function as inhibitors of mitochondrial respiration. A better understanding of how imatinib counteracts diabetes will possibly help to clarify the pathogenic role of beta-cell signaling events and mitochondrial function, and hopefully leading to improved treatment of the disease.

Serum Starvation Sensitizes Anticancer Effect of Anemarrhena asphodeloides via p38/JNK-Induced Cell Cycle Arrest and Apoptosis in Colorectal Cancer Cells

The molecular mechanism underlying the anticancer effects of Anemarrhena asphodeloides (A. asphodeloides) on colon cancer is unknown. This is the first study evaluating the anticancer effect of A. asphodeloides extract (AA-Ex) in serum-starved colorectal cancer cells. Changes in cell proliferation and morphology in serum-starved MC38 and HCT116 colorectal cancer cells were investigated using MTS assay. Cell cycle and apoptosis were investigated using flow cytometry, and cell cycle regulator expression was determined using qRT-PCR. Apoptosis regulator protein levels and mitogen-activated protein kinase (MAPK) phosphorylation were assessed using western blotting. AA-Ex sensitively suppressed proliferation of serum-starved colorectal cancer cells, with MC38 and HCT116 cells showing greater changes in proliferation after treatment with AA-Ex under serum starvation than HaCaT and RAW 264.7 cells. AA-Ex inhibited cell cycle progression in serum-starved MC38 and HCT116 cells and increased the expression of cell cycle inhibitors (p53, p21, and p27). Furthermore, AA-Ex induced apoptosis in serum-starved MC38 and HCT116 cells. Consistently, AA-Ex suppressed the expression of the anti-apoptotic molecule Bcl-2 and upregulated pro-apoptotic molecules (cytochrome c, cleaved caspase-9, cleaved caspase-3, and cleaved-PARP) in serum-starved cells. AA-Ex treatment under serum starvation decreased AKT and ERK1/2 phosphorylation in the cell survival signaling pathway but increased p38 and JNK phosphorylation. Furthermore, AA-Ex treatment with serum starvation increased the levels of the transcription factors of the p38 and JNK pathway. Serum starvation sensitizes colorectal cancer cells to the anticancer effect of A. asphodeloidesvia p38/JNK-induced cell cycle arrest and apoptosis. Hence, AA-Ex possesses therapeutic potential for colon cancer treatment.

Niemann-Pick type C disease: cellular pathology and pharmacotherapy

Niemann-Pick type C disease (NPCD) was first described in 1914 and affects approximately 1 in 150 000 live births. It is characterized clinically by diverse symptoms affecting liver, spleen, motor control, and brain; premature death invariably results. Its molecular origins were traced, as late as 1997, to a protein of late endosomes and lysosomes which was named NPC1. Mutation or absence of this protein leads to accumulation of cholesterol in these organelles. In this review, we focus on the intracellular events that drive the pathology of this disease. We first introduce endocytosis, a much-studied area of dysfunction in NPCD cells, and survey the various ways in which this process malfunctions. We briefly consider autophagy before attempting to map the more complex pathways by which lysosomal cholesterol storage leads to protein misregulation, mitochondrial dysfunction, and cell death. We then briefly introduce the metabolic pathways of sphingolipids (as these emerge as key species for treatment) and critically examine the various treatment approaches that have been attempted to date.

Targeting Type 1 Diabetes: Selective Approaches for New Therapies

The clinical onset of type 1 diabetes is characterized by the destruction of the insulin-producing β cells of the pancreas and is caused by autoantigen-induced inflammation (insulitis) of the islets of Langerhans. The current standard of care for type 1 diabetes mellitus patients allows for management of the disease with exogenous insulin, but patients eventually succumb to many chronic complications such as limb amputation, blindness, and kidney failure. New therapeutic approaches now on the horizon are looking beyond glycemic management and are evaluating new strategies from protecting and regenerating endogenous islets to treating the underlying autoimmunity through selective modulation of key immune cell populations. Currently, there are no effective treatments for the autoimmunity that causes the disease, and strategies that aim to delay or prevent the onset of the disease will play an important role in the future of diabetes research. In this review, we summarize many of the key efforts underway that utilize molecular approaches to selectively modulate this disease and look at new therapeutic paradigms that can transform clinical treatment.

Angiotensin II-induced podocyte apoptosis is mediated by endoplasmic reticulum stress/PKC-δ/p38 MAPK pathway activation and trough increased Na+/H+ exchanger isoform 1 activity

Background

Angiotensin II (Ang II) contributes to the progression of renal diseases associated with proteinuria and glomerulosclerosis mainly by inducing podocyte apoptosis. In the present study, we investigated whether the chronic effects of Ang II via AT1 receptor (AT1R) would result in endoplasmic reticulum (ER) stress/PKC-delta/p38 MAPK stimulation, and consequently podocyte apoptosis.

Methods

Wistar rats were treated with Ang II (200 ng·kg⁻¹·min⁻¹, 42 days) and or losartan (10 mg·kg⁻¹·day⁻¹, 14 days). Immortalized mouse podocyte were treated with 1 μM Ang II and/or losartan (1 μM) or SB203580 (0.1 μM) (AT1 receptor antagonist and p38 MAPK inhibitor) for 24 h. Kidney sections and cultured podocytes were used to evaluate protein expression by immunofluorescence and immunoblotting. Apoptosis was evaluated by flow cytometry and intracellular pH (pHi) was analyzed using microscopy combined with the fluorescent probe BCECF/AM.

Results

Compared with controls, Ang II via AT1R increased chaperone GRP 78/Bip protein expression in rat glomeruli (p < 0.001) as well as in podocyte culture (p < 0.01); increased phosphorylated eIf2-α (p < 0.05), PKC-delta (p < 0.01) and p38 MAPK (p < 0.001) protein expression. Furthermore, Ang II induced p38 MAPK-mediated late apoptosis and increased the Bax/Bcl-2 ratio (p < 0.001). Simultaneously, Ang II via AT1R induced p38 MAPK-NHE1-mediated increase of pHi recovery rate after acid loading.

Conclusion

Together, our results indicate that Ang II-induced podocyte apoptosis is associated with AT1R/ER stress/PKC-delta/p38 MAPK axis and enhanced NHE1-mediated pHi recovery rate.

High expression of active ATF6 aggravates endoplasmic reticulum stress‑induced vascular endothelial cell apoptosis through the mitochondrial apoptotic pathway

Activating transcription factor 6 (ATF6), one of three sensor proteins in the endoplasmic reticulum (ER), is an important regulatory factor in the ER stress‑induced apoptosis pathway. Although recent studies have made some progress in elucidating the regulation mechanism of ATF6, the specific regulatory mechanism of ER stress‑induced vascular endothelial cell (VEC) apoptosis is still unclear. The present study was designed to investigate the role of ATF6 in VECs under thapsigargin (TG)‑induced ER stress. ATF6 (1‑366aa; ATF6 high‑expressed plasmid) and ATF6 (151‑366aa; plasmid without transcriptional activity) were transfected into VECs to yield an ATF6 high‑expression model and a positive control model, respectively. High expression of ATF6 decreased viability and aggravated ER stress‑induced apoptosis in VECs. Increased expression of apoptosis‑related genes, including those encoding caspase‑3, caspase‑9, C/EBP homologous protein (CHOP), cytochrome c and B‑cell lymphoma‑associated protein X (Bax)/B‑cell lymphoma (Bcl‑)2, was detected by polymerase chain reaction and western blotting in the ATF6 (1‑366aa) + TG group. No significant effect of TG treatment and high ATF6 expression was indicated on the expression of death receptor‑related genes, including those encoding caspase‑8 and Fas. The results demonstrated that high expression of activated ATF6 aggravates ER stress‑induced VEC apoptosis through the mitochondrial apoptotic pathway. Furthermore, in response to ER stress, ATF6 upregulates the expression of caspase‑3, caspase‑9, CHOP, cytochrome c and Bax/Bcl‑2.

Opposing roles of KIT and ABL1 in the therapeutic response of gastrointestinal stromal tumor (GIST) cells to imatinib mesylate

Most gastrointestinal stromal tumors (GISTs) are caused by activating mutations of the KIT receptor tyrosine kinase. The small molecule inhibitor imatinib mesylate was initially developed to target the ABL1 kinase, which is constitutively activated through chromosomal translocation in BCR-ABL1-positive chronic myeloid leukemia. Because of cross-reactivity of imatinib against the KIT kinase, the drug is also successfully used for the treatment of GIST. Although inhibition of KIT clearly has a major role in the therapeutic response of GIST to imatinib, the contribution of concomitant inhibition of ABL in this context has never been explored. We show here that ABL1 is expressed in the majority of GISTs, including human GIST cell lines. Using siRNA-mediated knockdown, we demonstrate that depletion of KIT in conjunction with ABL1 – hence mimicking imatinib treatment – leads to reduced apoptosis induction and attenuated inhibition of cellular proliferation when compared to depletion of KIT alone. These results are explained by an increased activity of the AKT survival kinase, which is mediated by the cyclin-dependent kinase CDK2, likely through direct phosphorylation. Our results highlight that distinct inhibitory properties of targeted agents can impede antitumor effects and hence provide insights for rational drug development. Novel KIT-targeted agents to treat GIST should therefore comprise an increased specificity for KIT while at the same time displaying a reduced ability to inhibit ABL1.

Critical Roles of the Histone Methyltransferase MLL4/KMT2D in Murine Hepatic Steatosis Directed by ABL1 and PPARγ2

The pathophysiologic continuum of non-alcoholic fatty liver disease begins with steatosis. Despite recent advances in our understanding of the gene regulatory program directing steatosis, how it is orchestrated at the chromatin level is unclear. PPARγ2 is a hepatic steatotic transcription factor induced by overnutrition. Here, we report that the histone H3 lysine 4 methyltransferase MLL4/KMT2D directs overnutrition-induced murine steatosis via its coactivator function for PPARγ2. We demonstrate that overnutrition facilitates the recruitment of MLL4 to steatotic target genes of PPARγ2 and their transactivation via H3 lysine 4 methylation because PPARγ2 phosphorylated by overnutrition-activated ABL1 kinase shows enhanced interaction with MLL4. We further show that Pparg2 (encoding PPARγ2) is also a hepatic target gene of ABL1-PPARγ2-MLL4. Consistently, inhibition of ABL1 improves the fatty liver condition of mice with overnutrition by suppressing the pro-steatotic action of MLL4. Our results uncover a murine hepatic steatosis regulatory axis consisting of ABL1-PPARγ2-MLL4, which may serve as a target of anti-steatosis drug development.

ICG-001 affects DRP1 activity and ER stress correlative with its anti-proliferative effect

Mitochondria form a highly dynamic network driven by opposing scission and fusion events. DRP1 is an essential modulator of mitochondrial fission and dynamics within mammalian cells. Its fission activity is regulated by posttranslational modifications such as activating phosphorylation at serine 616. DRP1 activity has recently been implicated as being dysregulated in numerous human disorders such as cancer and neurodegenerative diseases. Here we describe the development of a cell-based screening assay to detect DRP1 activation. We utilized this to undertake focused compound library screening and identified potent modulators that affected DRP1 activity including ICG-001, which is described as WNT/β-catenin signaling inhibitor. Our findings elucidate novel details about ICG-001’s mechanism of action (MOA) in mediating anti-proliferative activity. We show ICG-001 both inhibits mitochondrial fission and activates an early endoplasmic reticulum (ER) stress response to induce cell death in susceptible colorectal cancer cell lines.

Protein Lipidation As a Regulator of Apoptotic Calcium Release: Relevance to Cancer

Calcium is a critical regulator of cell death pathways. One of the most proximal events leading to cell death is activation of plasma membrane and endoplasmic reticulum-resident calcium channels. A large body of evidence indicates that defects in this pathway contribute to cancer development. Although we have a thorough understanding of how downstream elevations in cytosolic and mitochondrial calcium contribute to cell death, it is much less clear how calcium channels are activated upstream of the apoptotic stimulus. Recently, it has been shown that protein lipidation is a potent regulator of apoptotic signaling. Although classically thought of as a static modification, rapid and reversible protein acylation has emerged as a new signaling paradigm relevant to many pathways, including calcium release and cell death. In this review, we will discuss the role of protein lipidation in regulating apoptotic calcium signaling with direct therapeutic relevance to cancer.

The Src/c-Abl pathway is a potential therapeutic target in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), a fatal disease causing progressive loss of motor neurons, still has no effective treatment. We developed a phenotypic screen to repurpose existing drugs using ALS motor neuron survival as readout. Motor neurons were generated from induced pluripotent stem cells (iPSCs) derived from an ALS patient with a mutation in superoxide dismutase 1 (SOD1). Results of the screen showed that more than half of the hits targeted the Src/c-Abl signaling pathway. Src/c-Abl inhibitors increased survival of ALS iPSC-derived motor neurons in vitro. Knockdown of Src or c-Abl with small interfering RNAs (siRNAs) also rescued ALS motor neuron degeneration. One of the hits, bosutinib, boosted autophagy, reduced the amount of misfolded mutant SOD1 protein, and attenuated altered expression of mitochondrial genes. Bosutinib also increased survival in vitro of ALS iPSC-derived motor neurons from patients with sporadic ALS or other forms of familial ALS caused by mutations in TAR DNA binding protein (TDP-43) or repeat expansions in C9orf72 Furthermore, bosutinib treatment modestly extended survival of a mouse model of ALS with an SOD1 mutation, suggesting that Src/c-Abl may be a potentially useful target for developing new drugs to treat ALS.

Targeting ABL-IRE1α Signaling Spares ER-Stressed Pancreatic β Cells to Reverse Autoimmune Diabetes

In cells experiencing unrelieved endoplasmic reticulum (ER) stress, the ER transmembrane kinase/endoribonuclease (RNase)-IRE1α-endonucleolytically degrades ER-localized mRNAs to promote apoptosis. Here we find that the ABL family of tyrosine kinases rheostatically enhances IRE1α's enzymatic activities, thereby potentiating ER stress-induced apoptosis. During ER stress, cytosolic ABL kinases localize to the ER membrane, where they bind, scaffold, and hyperactivate IRE1α's RNase. Imatinib-an anti-cancer tyrosine kinase inhibitor-antagonizes the ABL-IRE1α interaction, blunts IRE1α RNase hyperactivity, reduces pancreatic β cell apoptosis, and reverses type 1 diabetes (T1D) in the non-obese diabetic (NOD) mouse model. A mono-selective kinase inhibitor that allosterically attenuates IRE1α's RNase-KIRA8-also efficaciously reverses established diabetes in NOD mice by sparing β cells and preserving their physiological function. Our data support a model wherein ER-stressed β cells contribute to their own demise during T1D pathogenesis and implicate the ABL-IRE1α axis as a drug target for the treatment of an autoimmune disease.

Homocysteine induces PUMA-mediated mitochondrial apoptosis in SH-SY5Y cells

Previous studies have reported that homocysteine induced endoplasmic reticulum (ER) stress in neuronal cells, proposing the underlying mechanism by which it could induce neurotoxicity. Induction of pro-apoptotic transcription factor C/EBP homologous protein (CHOP) and activation of caspase-4 by calpain have been suggested to be an important route in inducing apoptosis in response to ER stress. In this study, we investigated the molecular pathway of homocysteine-induced apoptosis in caspase-4 deficient SH-SY5Y human neuroblastoma cells. Homocysteine significantly increased mRNA levels of CHOP and p53, resulting in the upregulation of their downstream target gene, p53 up-regulated modulator of apoptosis (PUMA). In cells treated with homocysteine, Bcl-2-associated X protein (BAX) protein levels, cytochrome c release from the mitochondria, and caspase-9 activation were significantly increased. Consistently, a caspase-9 inhibitor significantly alleviated homocysteine-induced cytotoxicity. Significantly lower BAX mRNA levels and caspase-9 activation were observed in cells transfected with siRNA for PUMA. Taken together, our findings suggest that PUMA would be involved in the possible crosstalk between the ER and the mitochondria in the homocysteine-induced apoptosis of caspase-4 deficient SH-SY5Y cells.

Regulation of mitochondrial functions by protein phosphorylation and dephosphorylation

The mitochondria are double membrane-bound organelles found in most eukaryotic cells. They generate most of the cell’s energy supply of adenosine triphosphate (ATP). Protein phosphorylation and dephosphorylation are critical mechanisms in the regulation of cell signaling networks and are essential for almost all the cellular functions. For many decades, mitochondria were considered autonomous organelles merely functioning to generate energy for cells to survive and proliferate, and were thought to be independent of the cellular signaling networks. Consequently, phosphorylation and dephosphorylation processes of mitochondrial kinases and phosphatases were largely neglected. However, evidence accumulated in recent years on mitochondria-localized kinases/phosphatases has changed this longstanding view. Mitochondria are increasingly recognized as a hub for cell signaling, and many kinases and phosphatases have been reported to localize in mitochondria and play important functions. However, the strength of the evidence on mitochondrial localization and the activities of the reported kinases and phosphatases vary greatly, and the detailed mechanisms on how these kinases/phosphatases translocate to mitochondria, their subsequent function, and the physiological and pathological implications of their localization are still poorly understood. Here, we provide an updated perspective on the recent advancement in this area, with an emphasis on the implications of mitochondrial kinases/phosphatases in cancer and several other diseases.

Melatonin and endoplasmic reticulum stress: relation to autophagy and apoptosis

Endoplasmic reticulum (ER) is a dynamic organelle that participates in a number of cellular functions by controlling lipid metabolism, calcium stores, and proteostasis. Under stressful situations, the ER environment is compromised, and protein maturation is impaired; this causes misfolded proteins to accumulate and a characteristic stress response named unfolded protein response (UPR). UPR protects cells from stress and contributes to cellular homeostasis re-establishment; however, during prolonged ER stress, UPR activation promotes cell death. ER stressors can modulate autophagy which in turn, depending of the situation, induces cell survival or death. Interactions of different autophagy- and apoptosis-related proteins and also common signaling pathways have been found, suggesting an interplay between these cellular processes, although their dynamic features are still unknown. A number of pathologies including metabolic, neurodegenerative and cardiovascular diseases, cancer, inflammation, and viral infections are associated with ER stress, leading to a growing interest in targeting components of the UPR as a therapeutic strategy. Melatonin has a variety of antioxidant, anti-inflammatory, and antitumor effects. As such, it modulates apoptosis and autophagy in cancer cells, neurodegeneration and the development of liver diseases as well as other pathologies. Here, we review the effects of melatonin on the main ER stress mechanisms, focusing on its ability to regulate the autophagic and apoptotic processes. As the number of studies that have analyzed ER stress modulation by this indole remains limited, further research is necessary for a better understanding of the crosstalk between ER stress, autophagy, and apoptosis and to clearly delineate the mechanisms by which melatonin modulates these responses.

Akt is translocated to the mitochondria during etoposide-induced apoptosis of HeLa cells

Akt, or protein kinase B, is a key serine-threonine kinase, which exerts anti-apoptotic effects and promotes cell proliferation in response to various stimuli. Recently, however, it was demonstrated that Akt exhibits a proapoptotic role in certain contexts. During etoposide‑induced apoptosis of HeLa cells, Akt enhances the interaction of second mitochondria‑derived activator of caspases/direct IAP binding protein with low pI (Smac/DIABLO) and X‑linked inhibitor of apoptosis protein by phosphorylating Smac at serine 67, and thus promotes apoptosis. However, the detailed mechanisms underlying Akt regulation in etoposide‑mediated apoptosis remain to be determined. The present study investigated whether etoposide triggers the translocation of Akt into the mitochondria. It was found that Akt activity was increased and sustained during apoptosis triggered by etoposide in HeLa cells. During apoptosis, Akt was translocated from the cytoplasm into the mitochondria in a phosphoinositide 3‑kinase-dependent manner at the early and late stages of apoptosis. Concomitantly, the depletion of Akt in the nuclear fraction was observed after etoposide treatment from analysis of confocal microscopy. The results suggest that etoposide‑stimulated Akt is translocated into the mitochondria, thereby possibly enhancing its interaction with Smac and promoting apoptosis in HeLa cells. These results indicate that Akt may be a promising candidate for a pro-apoptotic approach in cancer treatment.

Caspase-12 mediates carbon tetrachloride-induced hepatocyte apoptosis in mice

AIM: To investigate the role of caspase-12 and its downstream targets in carbon tetrachloride (CCl₄)-induced hepatocyte apoptosis.

METHODS: The role of caspase-12 was determined by using caspase-12 knock-out (^-/-) mice. CCl₄ (300 μL/kg body weight) or vehicle (corn oil) was administered to caspase-12^+/+ or caspase-12^-/- mice as a single intraperitoneal injection. The animals were sacrificed 24 h after the CCl₄ treatment. Blood was collected to evaluate liver function by the measurement of the activity of alanine aminotransferase. Liver samples were used for the measurements of reactive oxygen species using plasma malondialdehyde as biomarker, hepatocyte apoptosis was evaluated via terminal transferase-mediated dUTP nick-end labeling and controlled by morphologic study, and cytochrome C release and caspase activations were measured by Western blotting.

RESULTS: Administration of a low dose of CCl₄ resulted in hepatocyte apoptosis and acute liver injury in wild-type mice. CCl₄ also induced the generation of reactive oxygen species and induction of endoplasmic reticulum stress in the liver followed by activations of caspase-12, -9 and -3 as well as release of small amounts of cytochrome C. However, in the CCl₄-treated caspase-12^-/- mice, activation of caspase-9 and -3 were significantly attenuated (P < 0.05); no effect was seen in cytochrome C release. CCl₄-induced apoptosis and liver damage was markedly reduced in caspase-12^-/- mice compared to caspase-12^+/+ mice (P < 0.05). The active form of caspase-8 was not detected in either caspase-12^+/+ or caspase-12^-/- mice. There was no significant different in the formation of reactive oxygen species in the livers of caspase-12^+/+ and caspase-12^-/- mice treated with CCl₄.

CONCLUSION: Caspase-12 plays a pivotal role in CCl₄-induced hepatic apoptosis through the activation of the downstream effector caspase-3 directly and/or indirectly via capase-9 activation.

Defying c-Abl signaling circuits through small allosteric compounds

Many extracellular and intracellular signals promote the c-Abl tyrosine kinase activity. c-Abl in turn triggers a multitude of changes either in protein phosphorylation or in gene expression in the cell. Yet, c-Abl takes part in diverse signaling routes because of several domains linked to its catalytic core. Complex conformational changes turn on and off its kinase activity. These changes affect surface features of the c-Abl kinase and likely its capability to bind actin and/or DNA. Two specific inhibitors (ATP-competitive or allosteric compounds) regulate the c-Abl kinase through different mechanisms. NMR studies show that a c-Abl fragment (SH3-SH2-linker-SH1) adopts different conformational states upon binding to each inhibitor. This supports an unconventional use for allosteric compounds to unraveling physiological c-Abl signaling circuits.

Progesterone induces apoptosis of insulin-secreting cells: insights into the molecular mechanism

Progesterone has been associated with the development of gestational diabetes (GD) due to the enhancement of insulin resistance. As β-cell apoptosis participates in type 1 and type 2 diabetes pathophysiology, we proposed the hypothesis that progesterone might contribute to the development of GD through a mechanism that also involves β-cell death. To address this question, RINm5F insulin-producing cells were incubated with progesterone (25-100 μM), in the presence or absence of α-tocopherol (40 μM). After 24 or 48 h, membrane integrity and DNA fragmentation were analyzed by flow cytometry. Caspase activity was used to identify the mode of cell death. The involvement of endoplasmic reticulum stress in the action of progesterone was investigated by western blotting. Oxidative stress was measured by 2',7'-dichlorofluorescein diacetate (DCFDA) oxidation. Isolated rat islets were used in similar experiments in order to confirm the effect of progesterone in primary β-cells. Incubation of RINm5F cells with progesterone increased the number of cells with loss of membrane integrity and DNA fragmentation. Progesterone induced generation of reactive species. Pre-incubation with α-tocopherol attenuated progesterone-induced apoptosis. Western blot analyses revealed increased expression of CREB2 and CHOP in progesterone-treated cells. Progesterone caused apoptotic death of rat islet cells and enhanced generation of reactive species. Our results show that progesterone can be toxic to pancreatic β-cells through an oxidative-stress-dependent mechanism that induces apoptosis. This effect may contribute to the development of GD during pregnancy, particularly under conditions that require administration of pharmacological doses of this hormone.

The role of mitochondria in the oncogenic signal transduction

Mitochondria are intracellular organelles thought to have evolved from an alphaproteobacterium engulfed by the ancestor of the eukaryotic cell, an archeon, two billion years ago. Although mitochondria are frequently recognised as the "power plant" of the cell, the function of these organelles go beyond the simple generation of ATP. In fact, mounting evidence suggests that mitochondria are involved in several cellular processes, from regulation of cell death to signal transduction. Given this important role in cell physiology, mitochondrial dysfunction has been frequently associated with human diseases including cancer. Importantly, recent evidence suggests that mitochondrial function is directly regulated by oncogenes and tumour suppressors. However, the consequences of deregulation of mitochondrial function in tumour formation are still unclear. In this review, I propose that mitochondria play a pivotal role in shaping the oncogenic signalling cascade and that mitochondrial dysfunction, in some circumstances, is a required step for cancer transformation.

Tyrosine kinase inhibitors as novel drugs for the treatment of diabetes

INTRODUCTION

Some inhibitors of tyrosine kinase, as imatinib, erlotinib and sunitinib have antihyperglycemic effects but the mechanisms are not totally clear.

AREAS COVERED

It is well established that insulin resistance and beta-cell failure are hallmarks of type 2 diabetes mellitus (DM2). The present review will discuss the molecular mechanisms that account for insulin resistance and beta-cell failure in DM2, and also the effect of tyrosine kinase inhibitors in these processes.

EXPERT OPINION

A better understanding of how these drugs improve the two most important mechanisms of DM2 associated with suggestions of clinical studies will lead to improve the treatment of this disease.

The essential biology of the endoplasmic reticulum stress response for structural and computational biologists

The endoplasmic reticulum (ER) stress response is a cytoprotective mechanism that maintains homeostasis of the ER by upregulating the capacity of the ER in accordance with cellular demands. If the ER stress response cannot function correctly, because of reasons such as aging, genetic mutation or environmental stress, unfolded proteins accumulate in the ER and cause ER stress-induced apoptosis, resulting in the onset of folding diseases, including Alzheimer's disease and diabetes mellitus. Although the mechanism of the ER stress response has been analyzed extensively by biochemists, cell biologists and molecular biologists, many aspects remain to be elucidated. For example, it is unclear how sensor molecules detect ER stress, or how cells choose the two opposite cell fates (survival or apoptosis) during the ER stress response. To resolve these critical issues, structural and computational approaches will be indispensable, although the mechanism of the ER stress response is complicated and difficult to understand holistically at a glance. Here, we provide a concise introduction to the mammalian ER stress response for structural and computational biologists.

Small-molecule inhibition of inflammatory β-cell death

With the worldwide increase in diabetes prevalence there is a pressing unmet need for novel antidiabetic therapies. Insufficient insulin production due to impaired β-cell function and apoptotic reduction of β-cell mass is a common denominator in the pathogenesis of diabetes. Current treatments are directed at improving insulin sensitivity, and stimulating insulin secretion or replacing the hormone, but do not target progressive apoptotic β-cell loss. Here we review the current development of small-molecule inhibitors designed to rescue β-cells from apoptosis. Several distinct classes of small molecules have been identified that protect β-cells from inflammatory, oxidative and/or metabolically induced apoptosis. Although none of these have yet reached the clinic, β-cell protective small molecules alone or in combination with current therapies provide exciting opportunities for the development of novel treatments for diabetes.

The cloning and inducible expression of the rainbow trout ERp57 gene

ERp57 is a member of a protein disulfide isomerase family and is a chaperone responsible for the correct folding of newly synthesized glycoproteins in the endoplasmic reticulum and in the assembly of the major histocompatibility complex class I in the endogenous pathway of antigen presentation. This study reports the identification of a full length ERp57 cDNA in rainbow trout that encodes a putative 477aa mature protein with an additional signal sequence of 16aa. The trout protein shared 75% identity with the human homolog, but interestingly did not include either a C terminal endoplasmic reticulum retention signal, Q/KEDL in humans, or a nuclear localization signal which is highly conserved in mammals. Amino acid sequence alignment revealed conservation of four classical domains in trout ERp57 and two conserved active CXXC redox motifs. Trout ERp57 protein was identified as a single band around 57 kDa. Southern blotting analysis revealed that there two copies of the ERp57 gene in the trout genome and northern blotting showed a wide tissue distribution of gene expression in various tissues with the highest expression in liver and egg. This study showed for the first time in teleost that ERp57 transcript is upregulated in response to immune stimuli such as double stranded RNA or phytohemagglutinin. Furthermore, upon treatment with ER stress inducer A23187, trout ERp57 protein expression levels were increased both in peripheral blood leukocytes and the RTS11 macrophage like cell line after 6 and 8 h respectively. These findings suggest a possible conserved function for trout ERp57 in the ER and during the activation of the immune response.

Mig6 is a sensor of EGF receptor inactivation that directly activates c-Abl to induce apoptosis during epithelial homeostasis

A fundamental aspect of epithelial homeostasis is the dependence on specific growth factors for cell survival, yet the underlying mechanisms remain obscure. We found an “inverse” mode of receptor tyrosine kinase signaling that directly links ErbB receptor inactivation to the induction of apoptosis. Upon ligand deprivation Mig6 dissociates from the ErbB receptor and binds to and activates the tyrosine kinase c-Abl to trigger p73-dependent apoptosis in mammary epithelial cells. Deletion of Errfi1 (encoding Mig6) and inhibition or RNAi silencing of c-Abl causes impaired apoptosis and luminal filling of mammary ducts. Mig6 activates c-Abl by binding to the kinase domain, which is prevented in the presence of epidermal growth factor (EGF) by Src family kinase-mediated phosphorylation on c-Abl-Tyr488. These results reveal a receptor-proximal switch mechanism by which Mig6 actively senses EGF deprivation to directly activate proapoptotic c-Abl. Our findings challenge the common belief that deprivation of growth factors induces apoptosis passively by lack of mitogenic signaling.

c-Abl inhibition delays motor neuron degeneration in the G93A mouse, an animal model of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive death of motor neurons. Although the pathogenesis of ALS remains unclear, several cellular processes are known to be involved, including apoptosis. A previous study revealed the apoptosis-related gene c-Abl to be upregulated in sporadic ALS motor neurons.

METHODOLOGY/FINDINGS

We investigated the possibility that c-Abl activation is involved in the progression of ALS and that c-Abl inhibition is potentially a therapeutic strategy for ALS. Using a mouse motor neuron cell line, we found that mutation of Cu/Zn-superoxide dismutase-1 (SOD1), which is one of the causative genes of familial ALS, induced the upregulation of c-Abl and decreased cell viability, and that the c-Abl inhibitor dasatinib inhibited cytotoxicity. Activation of c-Abl with a concomitant increase in activated caspase-3 was observed in the lumbar spine of G93A-SOD1 transgenic mice (G93A mice), a widely used model of ALS. The survival of G93A mice was improved by oral administration of dasatinib, which also decreased c-Abl phosphorylation, inactivated caspase-3, and improved the innervation status of neuromuscular junctions. In addition, c-Abl expression in postmortem spinal cord tissues from sporadic ALS patients was increased by 3-fold compared with non-ALS patients.

CONCLUSIONS/SIGNIFICANCE

The present results suggest that c-Abl is a potential therapeutic target for ALS and that the c-Abl inhibitor dasatinib has neuroprotective properties in vitro and in vivo.

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.

Does the small tyrosine kinase inhibitor Imatinib mesylate counteract diabetes by affecting pancreatic islet amyloidosis and fibrosis?

INTRODUCTION

The small tyrosine kinase inhibitor Imatinib Mesylate (Gleevec) protects against diabetes, but it is not known how.

AREAS COVERED

It has been suggested that islet amyloid and fibrotic deposits promote beta-cell failure and death, leading to Type-2 diabetes. As Imatinib is known to possess anti-fibrotic/amyloid properties, in for example systemic sclerosis and mouse models for Alzheimer's disease, the present review will discuss the possibility that Imatinib acts, at least in part, by ameliorating islet hyalinization and its consequences in the pathogenesis of Type-2 diabetes.

EXPERT OPINION

A better understanding of how Imatinib counteracts Type-2 diabetes will possibly help to clarify the pathogenic role of islet amyloid and fibrosis, and hopefully lead to improved treatment of the disease.

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.

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.

Mechanistic investigation of imatinib-induced cardiac toxicity and the involvement of c-Abl kinase

The Bcr-abl tyrosine kinase inhibitor imatinib mesylate is the frontline therapy for chronic myeloid leukemia. Imatinib has been reported to cause congestive heart failure and left ventricular contractile dysfunction in patients and cardiomyopathy in rodents, findings proposed to be associated with its pharmacological activity. To investigate the specific role of Abelson oncogene 1 (c-Abl) in imatinib-induced cardiac toxicity, we performed targeted gene inhibition of c-Abl by RNA interference in neonatal cardiomyocytes (NCMs). Suppression of c-Abl did not lead to cytotoxicity or induction of endoplasmic reticulum (ER) stress. To further dis associate c-Abl from imatinib-induced cardiac toxicity, we designed imatinib structural analogs that do not have appreciable c-Abl inhibition in NCMs. The c-Abl inactive analogs induced cytotoxicity and ER stress, at similar or greater potencies and magnitudes as imatinib. Furthermore, combining c-Abl gene silencing with imatinib and analogs treatment did not significantly shift the cytotoxicity dose response curves. Imatinib and analogs were shown to accumulate in lysosomes, likely due to their physicochemical properties, and disrupt autophagy. The toxicity induced by imatinib and analogs can be rescued by bafilomycin A pretreatment, demonstrating the involvement of lysosomal accumulation in cardiac toxicity. The results from our studies strongly suggest that imatinib induces cardiomyocyte dysfunction through disruption of autophagy and induction of ER stress, independent of c-Abl inhibition.

Selective targeting of c-Abl via a cryptic mitochondrial targeting signal activated by cellular redox status in leukemic and breast cancer cells

PURPOSE

The tyrosine kinase c-Abl localizes to the mitochondria under cell stress conditions and promotes apoptosis. However, c-Abl has not been directly targeted to the mitochondria. Fusing c-Abl to a mitochondrial translocation signal (MTS) that is activated by reactive oxygen species (ROS) will selectively target the mitochondria of cancer cells exhibiting an elevated ROS phenotype. Mitochondrially targeted c-Abl will thereby induce malignant cell death.

METHODS

Confocal microscopy was used to determine mitochondrial colocalization of ectopically expressed c-Abl-EGFP/cMTS fusion across three cell lines (K562, Cos-7, and 1471.1) with varying levels of basal (and pharmacologically modulated) ROS. ROS were quantified by indicator dye assay. The functional consequences of mitochondrial c-Abl were assessed by DNA accessibility to 7-AAD using flow cytometry.

RESULTS

The cMTS and cMTS/c-Abl fusions colocalized to the mitochondria in leukemic (K562) and breast (1471.1) cancer phenotypes (but not Cos-7 fibroblasts) in a ROS and PKC dependent manner.

CONCLUSIONS

We confirm and extend oxidative stress activated translocation of the cMTS by demonstrating that the cMTS and Abl/cMTS fusion selectively target the mitochondria of K562 leukemia and mammary adenocarcinoma 1471.1 cells. c-Abl induced K562 leukemia cell death when targeted to the matrix but not the outer membrane of the mitochondria.

The unfolded protein response at the crossroads of cellular life and death during endoplasmic reticulum stress

One of the early cellular responses to endoplasmic reticulum (ER) stress is the activation of the unfolded protein response (UPR). ER stress and the UPR are both implicated in numerous human diseases and pathologies. In spite of this, our knowledge of the molecular mechanisms that regulate cell fate following ER stress is limited. The UPR is initiated by three ER transmembrane receptors: PKR-like ER kinase (PERK), activating transcription factor (ATF) 6 and inositol-requiring enzyme 1 (IRE1). These proteins sense the accumulation of unfolded proteins and their activation triggers specific adaptive responses to resolve the stress. Intriguingly, the very same receptors can initiate signalling pathways that lead to apoptosis when the attempts to resolve the ER stress fail. In this review, we describe the known pro-apoptotic signalling pathways emanating from activated PERK, ATF6 and IRE1 and discuss how their signalling switches from an adaptive to a pro-apoptotic response.

A new nonpeptidic inhibitor of 14-3-3 induces apoptotic cell death in chronic myeloid leukemia sensitive or resistant to imatinib

Resistance of chronic myeloid leukemia (CML) to tyrosine kinase inhibitor imatinib mesylate (IM) is most often due to point mutations in the Bcr-Abl fusion gene. T315I mutation (resulting in substitution of Ile for a Thr residue at the "gatekeeper" position 315) raises particular concern, because it also provides resistance to second-generation kinase inhibitors already approved for clinical use (nilotinib and dasatinib). Much effort is therefore focused on alternative molecular-based strategies. Previous studies proved that binding to 14-3-3 scaffolding proteins leads to cytoplasmic compartmentalization and suppression of proapoptotic and antiproliferative signals associated with Bcr-Abl protein kinase, hence contributing to leukemic clone expansion. Here we investigated the effect of 14-3-3 inhibition disruption on hematopoietic cells expressing the IM-sensitive wild type Bcr-Abl and the IM-resistant T315I mutation. Using a virtual screening protocol and docking simulations, we identified a nonpeptidic inhibitor of 14-3-3, named BV02, that exhibits a remarkable cytotoxicity against both cell types. c-Abl release from 14-3-3σ, promoting its relocation to nuclear compartment (where it triggers transcription of p73-dependent proapoptotic genes) and to mitochondrial membranes (where it induces the loss of mitochondrial transmembrane potential) combined with c-Abl enhanced association with caspase 9 (a critical step of sequential caspase activation further contributing to c-Abl pro-apoptotic function) has a prominent role in the effect of BV02 on Bcr-Abl-expressing cells. In conclusion, BV02 may be considered as a treatment option for CML and, in particular, for more advanced phases of the disease that developed IM resistance as a consequence of Bcr-Abl point mutations.

Assay development and high-throughput screening of small molecular c-Abl kinase activators

A 2-step kinase assay was developed and used in a high-throughput screen (HTS) of more than 1 million compounds in an effort to identify c-Abl tyrosine kinase activators. This assay employed a 2-step phosphorylation reaction: in the first step, purified recombinant c-Abl was activated by incubating with compound in the presence of adenosine triphosphate (ATP). In the second step, the TAMRA-labeled IMAP Abltide substrate was added to allow phosphorylation of the substrate to occur. The assay was calibrated such that inactive c-Abl protein was activated by ATP alone to a degree that it not only demonstrated a measurable c-Abl activity but also maintained a robust assay window for screening. The screen resulted in 8624 primary hits with >30% response. Further analysis showed that 1024 had EC(50) <10 µM with a max % response of >50%. These hits were structurally and chemically diverse with possibly different mechanisms for activating c-Abl. In addition, selective hits were shown to be cell permeable and were able to induce c-Abl activation as determined by In-Cell Western (ICW) analysis of HEK-MSRII cells transduced with BacMam virus expressing full-length c-Abl.

Phosphorylated proteins of the mammalian mitochondrial ribosome: implications in protein synthesis

Mitochondria, the powerhouse of eukaryotic cells, have their own translation machinery that is solely responsible for synthesis of 13 mitochondrially encoded protein subunits of oxidative phosphorylation complexes. Phosphorylation is a well-known post-translational modification in regulation of many processes in mammalian mitochondria including oxidative phosphorylation. However, there is still very limited knowledge on phosphorylation of mitochondrial ribosomal proteins and their role(s) in ribosome function. In this study, we have identified the mitochondrial ribosomal proteins that are phosphorylated at serine, threonine or tyrosine residues. Twenty-four phosphorylated proteins were visualized by phosphorylation-specific techniques including in vitro radiolabeling, residue specific antibodies for phosphorylated residues, or ProQ phospho dye and identified by tandem mass spectrometry. Translation assays with isolated ribosomes that were phosphorylated in vitro by kinases PKA, PKCdelta, or Abl Tyr showed up to 30% inhibition due to phosphorylation. Findings from this study should serve as the framework for future studies addressing the regulation mechanisms of mitochondrial translation machinery by phosphorylation and other post-translational modifications.

Overexpression of kinase-negative protein kinase Cdelta in pancreatic beta-cells protects mice from diet-induced glucose intolerance and beta-cell dysfunction

OBJECTIVE

In vitro models suggest that free fatty acid-induced apoptotic beta-cell death is mediated through protein kinase C (PKC)delta. To examine the role of PKCdelta signaling in vivo, transgenic mice overexpressing a kinase-negative PKCdelta (PKCdeltaKN) selectively in beta-cells were generated and analyzed for glucose homeostasis and beta-cell survival.

RESEARCH DESIGN AND METHODS

Mice were fed a standard or high-fat diet (HFD). Blood glucose and insulin levels were determined after glucose loads. Islet size, cleaved caspase-3, and PKCdelta expression were estimated by immunohistochemistry. In isolated islet cells apoptosis was assessed with TUNEL/TO-PRO3 DNA staining and the mitochondrial potential by rhodamine-123 staining. Changes in phosphorylation and subcellular distribution of forkhead box class O1 (FOXO1) were analyzed by Western blotting and immunohistochemistry.

RESULTS

PKCdeltaKN mice were protected from HFD-induced glucose intolerance. This was accompanied by increased insulin levels in vivo, by an increased islet size, and by a reduced staining of beta-cells for cleaved caspase-3 compared with wild-type littermates. In accordance, long-term treatment with palmitate increased apoptotic cell death of isolated islet cells from wild-type but not from PKCdeltaKN mice. PKCdeltaKN overexpression protected islet cells from palmitate-induced mitochondrial dysfunction and inhibited nuclear accumulation of FOXO1 in mouse islet and INS-1E cells. The inhibition of nuclear accumulation of FOXO1 by PKCdeltaKN was accompanied by an increased phosphorylation of FOXO1 at Ser256 and a significant reduction of FOXO1 protein.

CONCLUSIONS

Overexpression of PKCdeltaKN in beta-cells protects from HFD-induced beta-cell failure in vivo by a mechanism that involves inhibition of fatty acid-mediated apoptosis, inhibition of mitochondrial dysfunction, and inhibition of FOXO1 activation.

Potential utility of small tyrosine kinase inhibitors in the treatment of diabetes

Altered tyrosine kinase signalling has been implicated in several diseases, paving the way for the development of small-molecule TKIs (tyrosine kinase inhibitors). TKIs such as imatinib, sunitinib and dasatinib are clinically used for treating chronic myeloid leukaemia, gastrointestinal stromal tumours and other malignancies. In addition to their use as anti-cancer agents, increasing evidence points towards an anti-diabetic effect of these TKIs. Imatinib and other TKIs counteract diabetes not only in non-obese diabetic mice, but also in streptozotocin diabetic mice, db/db mice, high-fat-treated rats and humans with T2D (Type 2 diabetes). Although the mechanisms of protection need to be investigated further, the effects of imatinib and other TKIs in human T2D and the rapidly growing findings from animal models of T1D (Type 1 diabetes) and T2D are encouraging and give hope to improved treatment of human diabetes. In the present article, we review the anti-diabetic effects of TKIs which appear to involve both protection against beta-cell death and improved insulin sensitivity. Considering the relatively mild side effects of TKIs, we hypothesize that TKIs could be used to treat new-onset T1D, prevent T1D in individuals at high risk of developing the disease, treat the late stages of T2D and improve the outcome of islet transplantation.

N-myristoylated c-Abl tyrosine kinase localizes to the endoplasmic reticulum upon binding to an allosteric inhibitor

Allosteric kinase inhibitors hold promise for revealing unique features of kinases that may not be apparent using conventional ATP-competitive inhibitors. Here we explore the activity of a previously reported allosteric inhibitor of BCR-Abl kinase, GNF-2, against two cellular isoforms of Abl tyrosine kinase: one that carries a myristate in the N terminus and the other that is deficient in N-myristoylation. Our results show that GNF-2 inhibits the kinase activity of non-myristoylated c-Abl more potently than that of myristoylated c-Abl by binding to the myristate-binding pocket in the C-lobe of the kinase domain. Unexpectedly, indirect immunofluorescence reveals a translocation of myristoylated c-Abl to the endoplasmic reticulum in GNF-2-treated cells, whereas GNF-2 has no detectable effect on the localization of non-myristoylated c-Abl. These results indicate that GNF-2 competes with the NH(2)-terminal myristate for binding to the c-Abl kinase myristate-binding pocket and that the exposed myristoyl group accounts for the localization to the endoplasmic reticulum. We also demonstrate that GNF-2 can inhibit enzymatic and cellular kinase activity of Arg, a kinase highly homologous to c-Abl, which is also likely to be regulated through intramolecular binding of an NH(2)-terminal myristate lipid. These results suggest that non-ATP-competitive inhibitors, such as GNF-2, can serve as chemical tools that can discriminate between c-Abl isoform-specific behaviors.

c-Abl modulates AICD dependent cellular responses: transcriptional induction and apoptosis

APP intracellular domain (AICD) has been proposed as a transcriptional inductor that moves to the nucleus with the adaptor protein Fe65 and regulates transcription. The two proteins, APP and Fe65, can be phosphorylated by c-Abl kinase. Neprilysin has been proposed as a target gene for AICD. We found that AICD expression is decreased by treatment with STI-571, a c-Abl inhibitor, suggesting a modulation of AICD transcription by c-Abl kinase. We observed interaction between c-Abl kinase, the AICD fragment and the Fe65 adaptor protein. In addition, STI-571 reduces apoptosis in APPSw, and the apoptotic response induced by Fe65 over-expression was inhibited by with the expression of a kinase dead (KD) c-Abl and enhanced by over-expression of WT-c-Abl. However, in the APPSw cells, the ability of the KD-c-Abl to protect against Fe65 was reduced. Finally, in APPSw clone, we detected higher trans-activation of the pro-apoptotic p73 isoform, TAp73 promoter. Our results show that c-Abl modulates AICD dependent cellular responses, transcriptional induction as well as the apoptotic response, which could participate in the onset and progression of the neurodegenerative pathology, observed in Alzheimer's disease (AD).