Kinases: positive and negative regulators of apoptosis

Apoptosis and eryptosis: similarities and differences

Eryptosis is a regulated cell death (RCD) of mature erythrocytes initially described as a counterpart of apoptosis for enucleated cells. However, over the recent years, a growing number of studies have emphasized certain differences between both cell death modalities. In this review paper, we underline the hallmarks of eryptosis and apoptosis and highlight resemblances and dissimilarities between both RCDs. We summarize and critically discuss differences in the impact of caspase-3, Ca2+ signaling, ROS signaling pathways, opposing roles of casein kinase 1α, protein kinase C, Janus kinase 3, cyclin-dependent kinase 4, and AMP-activated protein kinase to highlight a certain degree of divergence between apoptosis and eryptosis. This review emphasizes the crucial importance of further studies that focus on deepening our knowledge of cell death machinery and identifying novel differences between cell death of nucleated and enucleated cells. This might provide evidence that erythrocytes can be defined as viable entities capable of programmed cell destruction. Additionally, the revealed cell type-specific patterns in cell death can facilitate the development of cell death-modulating therapeutic agents.

Oxidative Stress and ROS-Mediated Signaling in Leukemia: Novel Promising Perspectives to Eradicate Chemoresistant Cells in Myeloid Leukemia

Myeloid leukemic cells are intrinsically under oxidative stress due to impaired reactive oxygen species (ROS) homeostasis, a common signature of several hematological malignancies. The present review focuses on the molecular mechanisms of aberrant ROS production in myeloid leukemia cells as well as on the redox-dependent signaling pathways involved in the leukemogenic process. Finally, the relevance of new chemotherapy options that specifically exert their pharmacological activity by altering the cellular redox imbalance will be discussed as an effective strategy to eradicate chemoresistant cells.

Novel pyrrolopyrimidine derivatives induce p53-independent apoptosis via the mitochondrial pathway in colon cancer cells

A series of novel pyrrolopyrimidine urea derivatives were synthesized and evaluated for their anticancer activity against colon cancer cell lines. Compounds showed the remarkable cytotoxic activity on HCT-116 wt cell line. The most potent compound 4c (IC₅₀ = 0.14 μM) induced apoptosis in HCT-116 wt and HCT-116 p53-/- cell lines. Otherwise, treatment of HCT-116 BAX-/-BAK-/- cells with compound 4c didn't lead to activation of apoptosis, suggesting that compound 4c induces apoptotic cell death by activating BAX/BAK-dependent pathway. Moreover, while the compound 4c increase the activation of caspase-3 and caspase-9 levels in HCT-116 wt and HCT-116 p53-/- cells, caspase-3 or caspase-9 activation was not observed in HCT-116 BAX-/-BAK-/- cells. In addition, compound 4c induced mitochondrial apoptosis in cells grown as oncospheroids, which better mimic the in vivo milieu of tumors. 4c treatment also activated JNK along with inhibition of prosurvival kinases such as Akt and ERK 1/2 in HCT-116 wt and HCT-116 p53 -/- cells as well as in HCT-116 BAX-/-BAK-/- cells. Notably, our results indicated that compound 4c induced mitochondrial apoptosis through activation p53-independent apoptotic signaling pathways.

Systemic analysis of tyrosine kinase signaling reveals a common adaptive response program in a HER2-positive breast cancer

Drug-induced compensatory signaling and subsequent rewiring of the signaling pathways that support cell proliferation and survival promote the development of acquired drug resistance in tumors. Here, we sought to analyze the adaptive kinase response in cancer cells after distinct treatment with agents targeting human epidermal growth factor receptor 2 (HER2), specifically those that induce either only temporary cell cycle arrest or, alternatively, apoptosis in HER2-overexpressing cancers. We compared trastuzumab, ARRY380, the combination thereof, and a biparatopic, HER2-targeted designed ankyrin repeat protein (DARPin; specifically, 6L1G) and quantified the phosphoproteome by isobaric tagging using tandem mass tag liquid chromatography/tandem mass spectrometry (TMT LC-MS/MS). We found a specific signature of persistently phosphorylated tyrosine peptides after the nonapoptotic treatments, which we used to distinguish between different treatment-induced cancer cell fates. Next, we analyzed the activation of serine/threonine and tyrosine kinases after treatment using a bait peptide chip array and predicted the corresponding active kinases. Through a combined system-wide analysis, we identified a common adaptive kinase response program that involved the activation of focal adhesion kinase 1 (FAK1), protein kinase C-δ (PRKCD), and Ephrin (EPH) family receptors. These findings reveal potential targets to prevent adaptive resistance to HER2-targeted therapies.

Intraocular miR-211 exacerbates pressure-induced cell death in retinal ganglion cells via direct repression of FRS2 signaling

MicroRNAs (miRNAs) are emerging as important regulators of neurodegenerative diseases. However, research into ocular intracellular miRNAs, though possessing great potential to uncover novel and valuable therapeutic targets for glaucoma, is only at an early stage. Here we show that expression levels of miR-211 were significantly induced in aqueous humor (AH) samples from patients with glaucoma when compared to normal AH samples. Notably, oxidative stress-elicited miR-211 potentiated high pressure-induced retinal ganglion cells (RGCs) death by impairing ERK activation but enhancing P38 activation, an effect mediated by direct downregulation of fibroblast growth factor receptor substrate 2 (Frs2) signaling pathway in a sequence complementarity-dependent fashion. In support of the concept of a fundamental connection between miR-211 upregulation and augmented pressure-induced cell death in RGCs, we showed that ectopic expression of the exogenous FRS2 was sufficient to neutralize the miR-211-induced decrease in the cell viability and significantly improved miR-211-inhibited cell survival, in high pressure-challenged RGC-5 cells. Together, our findings show that miR-211 negatively modulates cell survival programs upon high pressure challenge by regulating Frs2 signaling, and they define roles for miR-211/Frs2 cascade in a regulatory feedback loop that mediates the pathogenesis of glaucoma.

Phosphorylation by protein kinase A disassembles the caspase-9 core

Caspases, the cysteine proteases which facilitate the faithful execution of apoptosis, are tightly regulated by a number of mechanisms including phosphorylation. In response to cAMP, PKA phosphorylates caspase-9 at three sites preventing caspase-9 activation, and suppressing apoptosis progression. Phosphorylation of caspase-9 by PKA at the functionally relevant site Ser-183 acts as an upstream block of the apoptotic cascade, directly inactivating caspase-9 by a two-stage mechanism. First, Ser-183 phosphorylation prevents caspase-9 self-processing and directly blocks substrate binding. In addition, Ser-183 phosphorylation breaks the fundamental interactions within the caspase-9 core, promoting disassembly of the large and small subunits. This occurs despite Ser-183 being a surface residue distal from the interface between the large and small subunits. This phosphorylation-induced disassembly promotes the formation of ordered aggregates around 20 nm in diameter. Similar aggregates of caspase-9 have not been previously reported. This two-stage regulatory mechanism for caspase-9 has likewise not been reported previously but may be conserved across the caspases.

Active site-adjacent phosphorylation at Tyr-397 by c-Abl kinase inactivates caspase-9

Caspase-9 (casp-9) is an initiator caspase and plays a central role in activating apoptotic cell death. Control of all caspases is tightly regulated by a series of phosphorylation events enacted by several different kinases. Caspase-9 is the most heavily phosphorylated of all caspases, with phosphorylation of at least 11 distinct residues in all three caspase-9 domains by nine kinases. Caspase-9 phosphorylation by the non-receptor tyrosine kinase c-Abl at Tyr-153 reportedly leads to caspase-9 activation. All other phosphorylation events on caspases have been shown to block proteolytic function by a number of mechanisms, so we sought to unravel the molecular mechanism of the putative caspase-9 activation by phosphorylation. Surprisingly, we observed no evidence for Tyr-153 phosphorylation of caspase-9 in vitro or in cells, suggesting that Tyr-153 is not phosphorylated by c-Abl. Instead, we identified a new site for c-Abl-mediated phosphorylation, Tyr-397. This residue is adjacent to the caspase-9 active site but, as a member of the second shell, not a residue that directly contacts substrate. Our results further indicate that Tyr-397 is the dominant site of c-Abl phosphorylation both in vitro and upon c-Abl activation in cells. Of note, phosphorylation at this site inhibits caspase-9 activity, and the bulk of the added phosphate moiety appeared to directly block substrate binding. c-Abl plays both proapoptotic and prosurvival roles, and our findings suggest that c-Abl's effects on caspase-9 activity promote the prosurvival mode.

Activation of c-Jun N-terminal kinase by Akabane virus is required for apoptosis

Akabane virus (AKAV) belongs to the Simbu serogroup of the genus Orthobunyavirus in the family Bunyaviridae. It has been shown that AKAV induces apoptosis in mammalian cells. It is necessary to understand the signaling pathways involved in AKAV-induced apoptosis to further elucidate the molecular virology of AKAV. c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) are mediators of apoptosis; therefore, we investigated the roles of JNK and p38 MAPK cascades in AKAV-infected cells. We found that JNK and p38 MAPK as well as their downstream substrates, c-Jun and heat shock protein 27 (HSP27), were phosphorylated in response to AKAV infection. A JNK inhibitor (SP600125) inhibited AKAV-mediated apoptosis whereas a p38 MAPK inhibitor (SB203580) did not. We conclude that AKAV infection activates the JNK and p38 MAPK signaling pathways, and the JNK cascade plays a crucial role in AKAV-induced apoptosis in vitro.

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JNK and p38 MAPK were phosphorylated in response to Akabane virus infection.

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Downstream substrates, c-Jun and heat shock protein 27, were also phosphorylated by viral infection.

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JNK inhibitor (SP600125) inhibited AKAV-mediated apoptosis whereas a p38 MAPK inhibitor (SB203580) did not.

Cell death induced by mechanical compression on engineered muscle results from a gradual physiological mechanism

Deep tissue injury (DTI), a type of pressure ulcer, arises in the muscle layers adjacent to bony prominences due to sustained mechanical loading. DTI presents a serious problem in the clinic, as it is often not visible until reaching an advanced stage. One of the causes can be direct mechanical deformation of the muscle tissue and cell. The mechanism of cell death induced by mechanical compression was studied using bio-artificial skeletal muscle tissues. Compression was applied by placing weights on top of the constructs. The morphological changes of the cytoskeleton and the phosphorylation of mitogen-activated protein kinases (MAPK) under compression were investigated. Moreover, inhibitors for each of the three major MAPK groups, p38, ERK, and JNK, were applied separately to look at their roles in the compression caused apoptosis and necrosis. The present study for the first time showed that direct mechanical compression activates MAPK phosphorylation. Compression also leads to a gradual destruction of the cytoskeleton. The percentage apoptosis is strongly reduced by p38 and JNK inhibitors down to the level of the unloaded group. This phenomenon could be observed up to 24h after initiation of compression. Therefore, cell death in bio-artificial muscle tissue caused by mechanical compression is primarily caused by a physiological mechanism, rather than through a physical mechanism which kills the cell directly. These findings reveal insight of muscle cell death under mechanical compression. Moreover, the result indicates a potential clinical solution to prevent DTI by pre-treating with p38 or/and JNK inhibitors.

Enrichment of Leishmania donovani ATP-binding proteins using a staurosporine capture compound

Trypanosomatid parasites of the genus Leishmania cause severe human diseases collectively termed leishmaniasis. Parasite ATP-binding proteins have emerged as potent targets for chemotherapeutic intervention. However, many parasite-specific ATP-binding proteins may escape current efforts in drug target identification, validation and deconvolution due to the lack of sequence conservation and functional annotation of these proteins in early branching eukaryotic trypanosomatids. Here, we selectively enriched for ATP-binding proteins from Leishmania donovani axenic promastigote and amastigote total protein extracts utilizing a Capture Compound™ (CC) linked to the ATP-competitive inhibitor staurosporine. As judged by in-gel kinase activity assay and competitive inhibition with free staurosporine, the CC specifically enriched for parasite phosphotransferases. Comparative nanoLC-MS(n) analysis identified 70 captured proteins, including 24 conserved protein kinases, and 32 hypothetical proteins with potential ATP-binding function. We identified conserved signature sequence motifs characteristic for staurosporine-binding protein kinases, and identified the hypothetical proteins LinJ.20.0280 and LinJ.09.1630 as novel ATP-binding proteins. Thus, functional enrichment procedures such as described here, combined with bio-informatics analyses and activity assays, provide powerful tools for the discovery of parasite-specific ATP-binding proteins that escape homology-based identification, which can be subsequently targeted for pharmacological intervention.

BIOLOGICAL SIGNIFICANCE

Functional enrichment using a Capture Compound™ linked to the ATP-competitive inhibitor staurosporine provides a powerful new tool for the discovery of parasite-specific ATP-binding proteins that escape homology-based identification, which can be subsequently targeted for pharmacological intervention.

Maslinic acid-enriched diet decreases intestinal tumorigenesis in Apc(Min/+) mice through transcriptomic and metabolomic reprogramming

Chemoprevention is a pragmatic approach to reduce the risk of colorectal cancer, one of the leading causes of cancer-related death in western countries. In this regard, maslinic acid (MA), a pentacyclic triterpene extracted from wax-like coatings of olives, is known to inhibit proliferation and induce apoptosis in colon cancer cell lines without affecting normal intestinal cells. The present study evaluated the chemopreventive efficacy and associated mechanisms of maslinic acid treatment on spontaneous intestinal tumorigenesis in Apc^Min/+ mice. Twenty-two mice were randomized into 2 groups: control group and MA group, fed with a maslinic acid–supplemented diet for six weeks. MA treatment reduced total intestinal polyp formation by 45% (P<0.01). Putative molecular mechanisms associated with suppressing intestinal polyposis in Apc^Min/+ mice were investigated by comparing microarray expression profiles of MA-treated and control mice and by analyzing the serum metabolic profile using NMR techniques. The different expression phenotype induced by MA suggested that it exerts its chemopreventive action mainly by inhibiting cell-survival signaling and inflammation. These changes eventually induce G1-phase cell cycle arrest and apoptosis. Moreover, the metabolic changes induced by MA treatment were associated with a protective profile against intestinal tumorigenesis. These results show the efficacy and underlying mechanisms of MA against intestinal tumor development in the Apc^Min/+ mice model, suggesting its chemopreventive potential against colorectal cancer.

Daunorubicin induces cell death via activation of apoptotic signalling pathway and inactivation of survival pathway in muscle-derived stem cells

Daunorubicin (as well as other anthracyclines) is known to be toxic to heart cells and other cells in organism thus limiting its applicability in human cancer therapy. To investigate possible mechanisms of daunorubicin cytotoxicity, we used stem cell lines derived from adult rabbit skeletal muscle. Recently, we have shown that daunorubicin induces apoptotic cell death in our cell model system and distinctly influences the activity of MAP kinases. Here, we demonstrate that two widely accepted antagonistic signalling pathways namely proapoptotic JNK and prosurvival PI3K/AKT participate in apoptosis. Using the Western blot method, we observed the activation of JNK and phosphorylation of its direct target c-Jun along with inactivation of AKT and its direct target GSK in the course of programmed cell death. By means of small-molecule kinase inhibitors and transfection of cells with the genes of the components of these pathways, c-Jun and AKT, we confirm that JNK signalling pathway is proapoptotic, whereas AKT is antiapoptotic in daunorubicin-induced muscle cells. These findings could contribute to new approaches which will result in less toxicity and fewer side effects that are currently associated with the use of daunorubicin in cancer therapies.

Lidocaine-induced apoptosis of gingival fibroblasts: participation of cAMP and PKC activity

Local anaesthetics are drugs that prevent or relieve pain by interrupting nervous conduction and are the most commonly used drugs in dentistry. Their main targets of action are voltage-dependent Na+ channels. The Na+ channel is modulated by phosphorylation of two enzymes: PKA (protein kinase A) and PKC (protein kinase C). We studied the ability of lidocaine to modulate programmed cell death of human gingival fibroblasts and the mechanisms involved in this process. Lidocaine (10-5 to 10-7 M) stimulated apoptosis in primary cultures and the caspase-3 activity in a concentration-dependent manner. The stimulatory effect of lidocaine on apoptosis was attenuated in the presence of HA 1004 (PKA inhibitor) and stimulated by staurosporine and Go 6976 (PKC inhibitors). Lidocaine-induced apoptotic nuclei correlated positively with cAMP accumulation and negatively with PKC activity. These results show that lidocaine promotes apoptosis in human gingival fibroblasts at concentrations used for local anaesthesia. The mechanism involves PKA stimulation and PKC inhibition, which in turn stimulates caspase-3 and leads to programmed cell death.

ICER evokes Dusp1-p38 pathway enhancing chemotherapy sensitivity in myeloid leukemia

PURPOSE

The inducible cyclic adenosine monophosphate (cAMP) early repressor (ICER) is found downregulated in acute myeloid leukemia (AML), failing to control cAMP response element binding protein (CREB) transcriptional activity, recently demonstrated to mediate AML progression. We aimed to characterize ICER's role in drug sensitivity by treating myeloid cell lines and primary AML with chemotherapics.

EXPERIMENTAL DESIGN

The effects on CREB target genes induced by ICER restoration and drug treatment were studied by quantitative real-time PCR (qRT-PCR) and western blot. Cell cycle and apoptosis analysis were performed. Possible ICER-evoked pathways were investigated in vitro. The mechanism involved in enhanced drug sensitivity was described in primary AML cultures by silencing ICER main target genes.

RESULTS

AML cell lines reduced cell growth and enhanced apoptotic behavior after chemotherapy treatment if ICER was expressed. A significantly lowered expression of CREB target genes involved in cell cycle control (CyA1, B1, D1), and in the mitogen-activated protein kinase signaling pathway (ERK, AKT, DUSP1/4), was found after Etoposide treatment. The dual-specificity phosphatases DUSP1 and DUSP4, directly repressed by ICER, activated the p38 pathway, which triggered enhanced caspase-dependent apoptosis. The silencing of DUSP1/4 in HL60 confirmed the same enhanced drug sensitivity induced by ICER. Primary AML cultures, silenced for DUSP1 as well as restored of ICER expression, showed DUSP1 downregulation and p38 activation.

CONCLUSION

ICER mediates chemotherapy anticancer activity through DUSP1-p38 pathway activation and drives the cell program from survival to apoptosis. ICER restoration or DUSP1 inhibition might be possible strategies to sensitize AML cancer cells to conventional chemotherapy and to inhibit tumor growth.

CD40-mediated cell death requires TRAF6 recruitment

CD40 has an important role in T cell-B cell interaction which rescues B lymphocytes from undergoing apoptosis. However, various studies have demonstrated that CD40 can also play a direct role in the induction of specific cell death and thus in the inhibition of tumour cell proliferation. Our previous studies showed that CD40-mediated cell death was independent of caspases and required no de novo protein synthesis. Knowing that CD40 signaling is mediated by its association with several intracellular effectors, including members of TNFR-associated factors (TRAFs) family, the goal of the present study is to investigate the mechanisms involved in the induction of cell death by CD40. Our data reveals that CD40-mediated cell death required lysosomal membrane permeabilization and the subsequent cathepsin B release. In addition, CD40 homodimer formation, a phenomenon known to be necessary for some CD40-mediated signals, was shown to negatively regulate cell death induced by CD40. Moreover, using HEK293 cells ectopically expressing CD40 deficient in TRAF binding, we showed that CD40-mediated apoptosis occurred in the absence of TRAF2 and TRAF3 association, but was significantly reduced when CD40 was deficient in its TRAF6 binding. Therefore, by outlining the role of lysosomal pathways and intracellular effectors, namely TRAF6 in CD40-mediated cell death, our study identifies new targets for anti-cancer therapy.

A peptide-based target screen implicates the protein kinase CK2 in the global regulation of caspase signaling

The convergence of caspase and protein kinase signaling pathways has become increasingly evident, as illustrated by the protection of caspase substrates from cleavage upon undergoing phosphorylation at or near to their caspase recognition motifs. To investigate the global role of phosphorylation in the regulation of caspase signaling, we designed a peptide match program to identify sequences from the human proteome that contained overlapping recognition motifs for caspases and kinases. We identified the protein kinase CK2 as the most prominent kinase with a consensus site for phosphorylation that overlapped with caspase recognition motifs. We then evaluated potential targets of CK2 and caspases by combining peptide array target screens with identification of caspase substrates. We identified numerous shared candidate targets of CK2 and caspases, including procaspase-3, which functions at a level at which both intrinsic and extrinsic apoptotic signals converge. Together, these data support a role for CK2-dependent phosphorylation as a global mechanism for inhibiting caspase signaling pathways.

High glucose induces apoptosis in embryonic neural progenitor cells by a pathway involving protein PKCδ

Diabetic-induced neural tube defects in embryos are caused by apoptosis of neural progenitor cells (NPCs); however, the underlying mechanisms are poorly understood. The present study is aimed to investigate the specific cellular proteins that may be involved in apoptosis of NPCs. We show here that hyperglycemia-induced apoptosis of NPCs was through a PKCδ-dependent mechanism. Tyrosine phosphorylation of PKCδ was required for PKCδ binding to c-Abl in the cytoplasm, and inhibition of c-Abl by STI571 or knock-down of c-Abl by RNAi decreased the phosphorylation of PKCδ. Moreover, translocation of PKCδ and c-Abl complex from the cytoplasm to the nucleus, was blocked by down-regulation of PKCδ or c-Abl. Furthermore, we found that interaction of PKCδ and c-Abl played a crucial role in p53 accumulation in the nucleus, which was linked to the apoptosis of NPCs in response to high glucose.

Bluetongue virus infection: activation of the MAP kinase-dependent pathway is required for apoptosis

Bluetongue virus (BTV) is a double-stranded RNA virus that induces apoptosis both in mammalian cell cultures and in target tissues. Based on information that members of the mitogen-activated protein kinase family (MAPKs) are mediators of apoptosis, we have examined in detail the MAPK-dependent apoptosis in BTV infection. Previously, we have shown that apoptosis in BTV infection requires the participation of mitochondrial apoptotic pathways. In addition, we demonstrated that NF-κB is activated and that its inhibition substantially reduces cellular apoptosis. For the first time, here we demonstrated the activation of MAPKs after BTV infection. Moreover, by pre-treatment with MAPK inhibitors, c-Jun N-terminal kinases (JNKs) and p38 MAPK, but not extracellular signal-related kinase (ERK), significantly decreased the induction of apoptosis. JNK and p38 activation regulated the cytochrome c released from mitochondria and caspase 3 activation. These results strengthen the understanding of BTV infection and contribute to our previous data confirming that BTV infection induces robust apoptosis in mammalian cells and is likely to play a primary role in BTV pathophysiology.

In vivo programmed cell death of Entamoeba histolytica trophozoites in a hamster model of amoebic liver abscess

Entamoeba histolytica trophozoites can induce host cell apoptosis, which correlates with the virulence of the parasite. This phenomenon has been seen during the resolution of an inflammatory response and the survival of the parasites. Other studies have shown that E. histolytica trophozoites undergo programmed cell death (PCD) in vitro, but how this process occurs within the mammalian host cell remains unclear. Here, we studied the PCD of E. histolytica trophozoites as part of an in vivo event related to the inflammatory reaction and the host-parasite interaction. Morphological study of amoebic liver abscesses showed only a few E. histolytica trophozoites with peroxidase-positive nuclei identified by terminal deoxynucleotidyltransferase enzyme-mediated dUTP nick end labelling (TUNEL). To better understand PCD following the interaction between amoebae and inflammatory cells, we designed a novel in vivo model using a dialysis bag containing E. histolytica trophozoites, which was surgically placed inside the peritoneal cavity of a hamster and left to interact with the host's exudate components. Amoebae collected from bags were then examined by TUNEL assay, fluorescence-activated cell sorting (FACS) and transmission electron microscopy. Nuclear condensation and DNA fragmentation of E. histolytica trophozoites were observed after exposure to peritoneal exudates, which were mainly composed of neutrophils and macrophages. Our results suggest that production of nitric oxide by inflammatory cells could be involved in PCD of trophozoites. In this modified in vivo system, PCD appears to play a prominent role in the host-parasite interaction and parasite cell death.

Phosphorylation of α-synuclein upregulates tyrosine hydroxylase activity in MN9D cells

Hyperphosphorylated α-synuclein is considered an important event in the pathogenesis of Parkinson's disease but its function remains elusive. In this study we provide evidence that tyrosine hydroxylase (TH) expression was unaffected by overexpression of wild-type and phospho-mimic mutant α-synuclein (S129D) in dopaminergic MN9D cells. However, α-synuclein overexpression evidently inhibited TH phosphorylation at Ser40 and dopamine synthesis, while α-synuclein (S129D) mutant enhanced TH phosphorylation and dopamine synthesis. This phospho-mimic mutant prevented wild-type α-synuclein cytotoxicity to MN9D cells, which might be due to aggregation of mutant α-synuclein in the cytoplasm and nuclei. These results demonstrated that phosphorylation at Ser129 was involved in the regulation of TH activity, as well as in eliminating the neurotoxicity of wild-type α-synuclein overexpression in MN9D cells.

Contrast expression patterns of JNK1 during sex reversal of the rice-field eel

The c-Jun N-terminal kinases (JNKs) are members of the mitogen-activated protein kinase family. Their functions in regulating animal development have been well studied in both invertebrates and vertebrates. However, it remains to be determined whether they play a role in sex determination. Here we present first evidence to show that expression of JNK1 displays distinct patterns during sex reversal of rice-field eel. Molecular cloning reveals that JNK1 is well conserved among rice-field eel and other vertebrates. Both quantitative real-time polymerase chain reaction and Western blot analysis demonstrate that JNK1 is highly expressed in the ovary of the female individual and reduced to a substantial degree at the later stage of the intersex. However, when the intersex individual develops into the stage of male, expression of the JNK1 in the testis of the male individual is distinctly downregulated. Associated with the contrast JNK1 expression pattern in female and male gonads, several stem cell marker genes including Nanog, Oct-3/4, and Sox-2 were also differentially expressed in female and male germinal stem cells. Together, these results suggest it is possible that JNK1 plays an important role in sexual reversal of the rice-field eel.

Phorbol ester–induced PKCϵ down-modulation sensitizes AML cells to TRAIL-induced apoptosis and cell differentiation

Despite the relevant therapeutic progresses made in these last 2 decades, the prognosis of acute myeloid leukemia (AML) remains poor. Phorbol esters are used at very low concentrations as differentiating agents in the therapy of myeloid leukemias. Tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), in turn, is a death ligand that spares normal cells and is therefore currently under clinical trials for cancer therapy. Emerging evidence, however, suggests that TRAIL is also involved in nonapoptotic functions, like cell differentiation. PKCϵ is differentially modulated along normal hematopoiesis, and its levels modulate the response of hematopoietic precursors to TRAIL. Here, we investigated the effects of the combination of phorbol esters (phorbol ester 4-β-phorbol-12,13-dibutyrate [PDBu]) and TRAIL in the survival/differentiation of AML cells. We demonstrate here that PDBu sensitizes primary AML cells to both the apoptogenic and the differentiative effects of TRAIL via PKCϵ down-modulation, without affecting TRAIL receptor surface expression. We believe that the use of TRAIL in combination with phorbol esters (or possibly more specific PKCϵ down-modulators) might represent a significative improvement of our therapeutic arsenal against AML.

Cytoprotective effects of phenolic acids on methylglyoxal-induced apoptosis in Neuro-2A cells

In the process of glycation, methylglyoxal is a reactive dicarbonyl compound physiologically generated as an intermediate of glycolysis, and is found in high levels in blood or tissue of diabetic models. Biological glycation has been commonly implicated in the development of diabetic microvascular complications of neuropathy. Increasing evidence suggests that neuronal cell cycle regulatory failure followed by apoptosis is an important mechanism in the development of diabetic neuropathy complication. Naturally occurring antioxidants, especially phenolic acids have been recommended as the major bioactive compounds to prevent chronic diseases and promote health benefits. The objective of this study was to investigate the inhibitory abilities of phenolic acids (chlorogenic acid, syringic acid and vanillic acid) on methylglyoxal-induced mouse Neuro-2A neuroblastoma (Neuro-2A) cell apoptosis in the progression of diabetic neuropathy. The data indicated that methylglyoxal induced mouse Neuro-2A neuroblastoma (Neuro-2A) cell apoptosis via alternation of mitochondria membrane potential and Bax/Bcl-2 ratio, activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase. Furthermore, the results demonstrated that activation of mitogen-activated protein kinase signal pathways (JNK and p38) participated in the methylglyoxal-induced Neuro-2A cell apoptosis process. Treatment of Neuro-2A cells with phenolic acids markedly suppresses cell apoptosis induced by methylglyoxal, suggesting that phenolic acids possess cytoprotective ability in the prevention of diabetic neuropathy complication.

PKCdelta signaling: mechanisms of DNA damage response and apoptosis

The cellular response to genotoxic stress that damages DNA includes cell cycle arrest, activation of DNA repair, and in the event of irreparable damage, induction of apoptosis. However, the signals that determine cell fate, that is, survival or apoptosis, are largely unknown. The delta isoform of protein kinase C (PKCdelta) has been implicated in many important cellular processes, including regulation of apoptotic cell death. The available information supports a model in which certain sensors of DNA lesions activate PKCdelta. This activation is triggered in part by tyrosine phosphorylation of PKCdelta by c-Abl tyrosine kinase. PKCdelta is further proteolytically activated by caspase-3. The cleaved catalytic fragment of PKCdelta translocates to the nucleus and induces apoptosis. Importantly, accumulating data have revealed the nuclear targets for PKCdelta in the induction of apoptosis. A pro-apoptotic function of activated PKCdelta is mediated by at least several downstream effectors known to be associated with the elicitation of apoptosis. Recent findings also demonstrated that PKCdelta is involved in cell cycle-specific activation and induction of apoptotic cell death. Moreover, previous studies have shown that PKCdelta regulates transcription by phosphorylating various transcription factors, including the p53 tumor suppressor that is critical for cell cycle arrest and apoptosis in response to DNA damage. These findings collectively support a pivotal role for PKCdelta in the induction of apoptosis with significant impact. This review is focused on the current views regarding the regulation of cell fate by PKCdelta signaling in response to DNA damage.

Estradiol prevents the injury-induced decrease of 90 ribosomal S6 kinase (p90RSK) and Bad phosphorylation

Estradiol prevents neuronal cell death through the activation of cell survival signals and the inhibition of apoptotic signals. This study investigated whether estradiol modulates the anti-apoptotic signal through the activation of Raf-MEK-ERK and its downstream targets, including 90 ribosomal S6 kinase (p90RSK) and Bad. Adult female rats were ovariectomied and treated with estradiol prior to middle cerebral artery occlusion (MCAO). Brains were collected 24h after MCAO and infarct volumes were analyzed. We confirmed that estradiol significantly reduces infarct volume and decreases the positive cells of TUNEL staining in the cerebral cortex. Estradiol prevents the injury-induced decrease of Raf-1, MEK1/2, and ERK1/2 phosphorylation. Also, it inhibits the injury-induced decrease of p90RSK and Bad phosphorylation. Further, in the presence of estradiol, the interaction of phospho-Bad and 14-3-3 increased, compared with that of oil-treated animals. Our findings suggest that estradiol prevents cell death due to brain injury and that Raf-MEK-ERK cascade activation and its downstream targets, p90RSK, Bad phosphorylation by estradiol mediated these protective effects.

Signaling and regulation of endothelial cell survival by angiopoietin-2

Angiopoietins are ligands for endothelial cell-specific Tie-2 receptors. Whereas angiopoietin-1 (Ang-1) activates these receptors and promotes cell survival, migration, and sprouting, little information is available regarding how Ang-2 influences these cells. In this study, we evaluated signaling pathways and biological effects of physiological concentrations of Ang-2 in cultured human umbilical vein endothelial cells. Ang-2 at 150 and 300 ng/ml elicited a transient (reaching peak values within 15 min of exposure) increase in the phosphorylation of Tie-2 receptors, protein kinase B (Akt), ERK1/2, and p38 members of the mitogen-activated protein kinases. However, unlike Ang-1, Ang-2 significantly inhibited JNK/SAPK phosphorylation. When vascular endothelial growth factor (VEGF) was present along with Ang-2, ERK1/2 phosphorylation was inhibited, whereas augmentation of Ang-1-induced ERK1/2 phosphorylation was triggered by VEGF. Ang-2 treatment had no effect on cell migration and in vitro wound healing but significantly attenuated serum deprivation-induced apoptosis and promoted survival. These effects were completely reversed by phosphatidylinositol 3 (PI3)-kinase and ERK1/2 inhibitors but were augmented by an inhibitor of the p38 pathway. These results suggest that Ang-2 promotes endothelial cell survival through the ERK1/2 and PI3-kinase pathways and that this angiopoietin is not a strong promoter of endothelial cell migration. We also conclude that the nature of interactions in terms of ERK1/2 activation between Ang-2 and VEGF is different from that of Ang-1 and VEGF.

Molecular pathways leading to oxidative stress-induced phosphorylation of Akt

Oxidative stress can activate a variety of intracellular signaling pathways. The authors previously reported the CaM-K inhibitor KN-93 inhibited hydrogen peroxide-induced phosphorylation of Akt on threonine 308 (T308). In this report they demonstrate that phosphorylation of T308 in response to hydrogen peroxide treatment is not inhibited by LY294002, suggesting that phosphorylation of this residue in response to oxidative stress is largely PI3K independent. In contrast, hydrogen peroxide-induced phosphorylation of Akt on serine 473 (S473) was downregulated by both PI3K and CaM-K inhibition, indicating that hydrogen peroxideinduced phosphorylation of Akt on S473 was largely dependent on both PI3K and a CaM-K activity. Further, it is reported that p56(Lck) had a substantial role in hydrogen peroxide-induced phosphorylation of S473, but only a minimal role in hydrogen peroxide-induced phosphorylation of T308. These data suggest that in response to hydrogen peroxide, two pathways are activated in Jurkat T lymphocytes that converge to result in the phosphorylation of Akt on S473 and T308. One pathway involves the CaM-Ks that may directly phosphorylate Akt on T308. In this pathway, neither the Src kinases nor PI3K are required. The other pathway mediated by hydrogen peroxide results in the phosphorylation of Akt on S473 and requires CaM-K, PI3K, and Src activity.

Protein serine/threonine phosphatase-1 dephosphorylates p53 at Ser-15 and Ser-37 to modulate its transcriptional and apoptotic activities

We have previously demonstrated that the serine/threonine protein phosphatase-1 (PP-1) plays an important role in promoting cell survival. However, the molecular mechanisms by which PP-1 promotes survival remain largely unknown. In the present study, we provide evidence to show that PP-1 can directly dephosphorylate a master regulator of apoptosis, p53, to negatively modulate its transcriptional and apoptotic activities, and thus to promote cell survival. As a transcriptional factor, the function of p53 can be greatly regulated by phosphorylation and dephosphorylation. While the kinases responsible for phosphorylation of the 17 serine/threonine sites have been identified, the dephosphorylation of these sites remains largely unknown. In the present study, we demonstrate that PP-1 can dephosphorylate p53 at Ser-15 and Ser-37 through co-immunoprecipitation, in vitro and in vivo dephosphorylation assays, overexpression and silence of the gene encoding the catalytic subunit for PP-1. We further show that mutations mimicking constitutive dephosphorylation or phosphorylation of p53 at these sites attenuate or enhance its transcriptional activity, respectively. As a result of the changed p53 activity, expression of the downstream apoptosis-related genes such as bcl-2 and bax is accordingly altered and the apoptotic events are either largely abrogated or enhanced. Thus, our results demonstrate that PP-1 directly dephosphorylates p53, and dephosphorylation of p53 has as important impact on its functions as phosphorylation does. In addition, our results reveal that one of the molecular mechanisms by which PP-1 promotes cell survival is to dephosphorylate p53, and thus negatively regulate p53-dependent death pathway.

Regulation of radiation-induced protein kinase Cdelta activation in radiation-induced apoptosis differs between radiosensitive and radioresistant mouse thymic lymphoma cell lines

Protein kinase Cdelta (PKCdelta) has an important role in radiation-induced apoptosis. The expression and function of PKCdelta in radiation-induced apoptosis were assessed in a radiation-sensitive mouse thymic lymphoma cell line, 3SBH5, and its radioresistant variant, XR223. Rottlerin, a PKCdelta-specific inhibitor, completely abolished radiation-induced apoptosis in 3SBH5. Radiation-induced PKCdelta activation correlated with the degradation of PKCdelta, indicating that PKCdelta activation through degradation is involved in radiation-induced apoptosis in radiosensitive 3SBH5. In radioresistant XR223, radiation-induced PKCdelta activation was lower than that in radiosensitive 3SBH5. Cytosol PKCdelta levels in 3SBH5 decreased markedly after irradiation, while those in XR223 did not. There was no apparent change after irradiation in the membrane fractions of either cell type. In addition, basal cytosol PKCdelta levels in XR223 were higher than those in 3SBH5. These results suggest that the radioresistance in XR223 to radiation-induced apoptosis is due to a difference in the regulation of radiation-induced PKCdelta activation compared to that of 3SBH5. On the other hand, Atm(-/-) mouse thymic lymphoma cells were more radioresistant to radiation-induced apoptosis than wild-type mouse thymic lymphoma cells. Irradiated wild-type cells, but not Atm(-/-) cells, had decreased PKCdelta levels, indicating that the Atm protein is involved in radiation-induced apoptosis through the induction of PKCdelta degradation. The decreased Atm protein levels induced by treatment with Atm small interfering RNA had no effect on radiation-induced apoptosis in 3SBH5 cells. These results suggest that the regulation of radiation-induced PKCdelta activation, which is distinct from the Atm-mediated cascade, determines radiation sensitivity in radiosensitive 3SBH5 cells.

OSU-03012 in the treatment of glioblastoma

In an article presented in this issue of Molecular Pharmacology, Yacoub et al. (p. 589) examine the actions of 2-amino-N{4-5-(2-phenanthrenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]phenyl}-acetamide (OSU-03012) on both primary and glioblastoma cell lines. The authors found that OSU-03012 could induce tumor cell death by itself but also acted as a strong sensitizing agent to radiotherapy-induced cell death. Glioblastoma cells were also more sensitive to this compound than nontransformed astrocytes. Radiation-induced cell death was refractory to small interfering RNA-directed inhibition of PDK1 but not OSU-03012. These results indicate that OSU-03012, which has been thought to primarily mediate antitumor effects via the inhibition of PDK1, has actions independent of PDK1. Furthermore, the authors demonstrated that the effects of OSU-03012 were independent of ERB-B1-vIII and PTEN expression. These are important findings because they start to identify a new mechanism to sensitize glioblastoma cells and also suggest that OSU-03012 could be combined with existing inhibitors to further sensitize tumor cells. In glioblastoma cells, OSU-03012 seemed to induce apoptosis via endoplasmic reticulum stress-induced PERK-dependent signaling. OSU-03012-induced death of the glioblastoma was only weakly suppressed by the pan-caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp, suggesting that OSU-03012-induced cell death was largely caspase-independent. Overall, these are exciting results and suggest that new more effective treatment options may be obtainable for people suffering from these deadly tumors.

Constitutive Activation of Extracellular Signal-Regulated Kinase Predisposes Diffuse Large B-Cell Lymphoma Cell Lines to CD40-Mediated Cell Death

CD40 promotes survival, proliferation, and differentiation of normal B cells but can cause activation-induced cell death in malignant B lymphocytes. CD40 ligand and anti-CD40 antibodies have been used successfully to induce apoptosis in lymphoma lines both in vitro and in xenograft tumor models. Although this makes CD40 an attractive target for antitumor therapies, the response of malignant B cells to CD40 signaling is variable, and CD40 stimulation can enhance proliferation and can increase chemoresistance in some cell lines. It would therefore be useful to identify markers that predict whether a specific cell line or tumor will undergo apoptosis when stimulated with CD40 and to identify targets downstream of CD40 that affect only the apoptotic arm of CD40 signaling. We have analyzed gene expression patterns in CD40-sensitive and CD40-resistant diffuse large B-cell lymphoma (DLBCL) cell lines to identify signaling pathways that are involved in CD40-mediated apoptosis. CD40-resistant lines expressed pre-B-cell markers, including RAG and VPREB, whereas CD40-sensitive cells resembled mature B cells and expressed higher levels of transcripts encoding several members of the CD40 signaling pathway, including LCK and VAV. In addition, CD40-sensitive DLBCL cell lines also displayed constitutive activation of extracellular signal-regulated kinase (ERK) and failed to undergo apoptosis when ERK phosphorylation was inhibited. In contrast, CD40-resistant lines showed no constitutive activation of ERK and no increase in ERK activity in response to CD40 stimulation. Our results suggest that constitutive activation of ERK may be required for death signaling by CD40.

PKCdelta modulates p21WAF1/CIP1 ability to bind to Cdk2 during TNFalpha-induced apoptosis

Cyclin-dependent kinase 2 (Cdk2) activity is thought to be involved in cell death-associated chromatin condensation and other manifestations of apoptotic death. Here we show that during TNFalpha-induced apoptosis, PKCdelta is activated in a caspase-3-dependent manner and phosphorylates p21(WAF1/CIP1), a specific cyclin-dependent kinase inhibitor, on (146)Ser. This residue is located near a cyclin-binding motif (Cy2) that plays an important role in the interaction between p21(WAF1/CIP1) and Cdk2, and its phosphorylation modulates the ability of p21(WAF1/CIP1) to associate with Cdk2. The phosphorylation of p21(WAF1/CIP1) is temporally related to the activation kinetics of Cdk2 activity during the apoptosis. We propose that during TNFalpha-induced apoptosis, PKCdelta-mediated phosphorylation of p21(WAF1/CIP1) at (146)Ser attenuates the Cdk2 binding of p21(WAF1/CIP1) and thereby upregulates Cdk2 activity.

Raf kinase as a target for anticancer therapeutics

The Ras-Raf-MEK-ERK (ERK) pathway is a logical therapeutic target because it represents a common downstream pathway for several key growth factor tyrosine kinase receptors which are often mutated or overexpressed in human cancers. Although considered mainly growth-promoting, in certain contexts, this pathway also seems to be apoptosis-suppressing. Several novel agents targeting this pathway have now been developed and are in clinical trials. One of the most interesting new agents is BAY 43-9006. Although initially developed as a Raf kinase inhibitor, it can also target several other important tyrosine kinases including VEGFR-2, Flt-3, and c-Kit, which contributes to its antiproliferative and antiangiogenic properties. To date, encouraging results have been seen with BAY 43-9006, particularly in renal cell cancers which are highly vascular tumors. This review will provide an overview of the ERK signaling pathway in normal and neoplastic tissue, with a specific focus on novel therapies targeting the ERK pathway at the level of Raf kinase.

Selective induction of apoptosis with proton pump inhibitor in gastric cancer cells

PURPOSE

To survive in an ischemic microenvironment with a lower extracellular pH, ability to up-regulate proton extrusion is critical for cancer cell survival. Gastric H+/K(+)-ATPase exchanges luminal K+ for cytoplasmic H+ and is the enzyme primarily responsible for gastric acidification. On the basis of the fact that blocking the clearance of acidic metabolites are known to induce the cell death, we hypothesized that pantoprazole (PPZ), one of gastric H+/K(+)-ATPase inhibitors used frequently to treat acid-related diseases, could inhibit growth of tumor cells.

EXPERIMENTAL DESIGN

Genomic DNA fragmentation, terminal deoxynucleotidyl transferase (Tdt)-mediated nick end labeling assay, and annexin V staining were performed to detect PPZ-induced apoptosis. Mitogen-activated protein kinase activation and heat shock proteins expression were determined by immunoblot with specific antibodies. The antitumor effect of PPZ was evaluated in vivo by a xenograft model of nude mice.

RESULTS

After PPZ treatment, apoptotic cell death was seen selectively in cancer cells and was accompanied with extracellular signal-regulated kinase deactivation. By contrast, normal gastric mucosal cells showed the resistance to PPZ-induced apoptosis through the overexpression of antiapoptotic regulators including HSP70 and HSP27. In a xenograft model of nude mice, administration of PPZ significantly inhibited tumorigenesis and induced large-scale apoptosis of tumor cells.

CONCLUSIONS

PPZ selectively induced in vivo and in vitro apoptotic cell death in gastric cancer, suggesting that proton pump inhibitors could be used for selective anticancer effects.

Pramanicin induces apoptosis in Jurkat leukemia cells: a role for JNK, p38 and caspase activation

Pramanicin is a novel anti-fungal drug with a wide range of potential application against human diseases. It has been previously shown that pramanicin induces cell death and increases calcium levels in vascular endothelial cells. In the present study, we showed that pramanicin induced apoptosis in Jurkat T leukemia cells in a dose- and time-dependent manner. Our data reveal that pramanicin induced the release of cytochrome c and caspase-9 and caspase-3 activation, as evidenced by detection of active caspase fragments and fluorometric caspase assays. Pramanicin also activated c-jun N-terminal kinase (JNK), p38 and extracellular signal-regulated kinases (ERK 1/2) with different time and dose kinetics. Treatment of cells with specific MAP kinase and caspase inhibitors further confirmed the mechanistic involvement of these signalling cascades in pramanicin-induced apoptosis. JNK and p38 pathways acted as pro-apoptotic signalling pathways in pramanicin-induced apoptosis, in which they regulated release of cytochrome c and caspase activation. In contrast the ERK 1/2 pathway exerted a protective effect through inhibition of cytochrome c leakage from mitochondria and caspase activation, which were only observed when lower concentrations of pramanicin were used as apoptosis-inducing agent and which were masked by the intense apoptosis induction by higher concentrations of pramanicin. These results suggest pramanicin as a potential apoptosis-inducing small molecule, which acts through a well-defined JNK- and p38-dependent apoptosis signalling pathway in Jurkat T leukemia cells.

Calcium-activated RAF/MEK/ERK signaling pathway mediates p53-dependent apoptosis and is abrogated by alpha B-crystallin through inhibition of RAS activation

The ocular lens is the only organ that does not develop spontaneous tumor. The molecular mechanism for this phenomenon remains unknown. Through examination of the signaling pathways mediating stress-induced apoptosis, here we presented evidence to show that different from most other tissues in which the extracellular signal-regulated kinases (ERKs) pathway is generally implicated in mediation of survival signals activated by different factors, the RAF/MEK/ERK signaling pathway alone plays a key role in stress-activated apoptosis of lens epithelial cells. Treatment of N/N1003A cells with calcimycin, a calcium mobilizer, activates the RAF/MEK/ERK pathway through RAS, which is indispensable for the induced apoptosis because inhibition of this pathway by either pharmacological drug or dominant negative mutants greatly attenuates the induced apoptosis. Calcimycin also activates p38 kinase and JNK2, which are not involved in calcium-induced apoptosis. Downstream of ERK activation, p53 is essential. Activation of RAF/MEK/ERK pathway by calcimycin leads to distinct up-regulation of p53. Moreover, overexpression of p53 enhances calcimycin-induced apoptosis, whereas inhibition of p53 expression attenuates calcimycin-induced apoptosis. Up-regulation of p53 directly promotes Bax expression, which changes the integrity of mitochondria, leading to release of cytochrome c, activation of caspase-3 and eventually execution of apoptosis. Overexpression of alphaB-crystallin, a member of the small heat-shock protein family, blocks activation of RAS to inhibit ERK1/2 activation, and greatly attenuates calcimycin-induced apoptosis. Together, our results provide 1) a partial explanation for the lack of spontaneous tumor in the lens, 2) a novel signaling pathway for calcium-induced apoptosis, and 3) a novel antiapoptotic mechanism for alphaB-crystallin.

Protein kinase C delta induces apoptosis of vascular smooth muscle cells through induction of the tumor suppressor p53 by both p38-dependent and p38-independent mechanisms

Apoptotic death of vascular smooth muscle cells (SMCs) is a prominent feature of blood vessel remodeling. In the present study, we examined the novel PKC isoform protein kinase C delta (PKCdelta) and its role in vascular SMC apoptosis. In A10 SMCs, overexpression of PKCdelta was sufficient to induce apoptosis, whereas inhibition of PKCdelta diminished H2O2-induced apoptosis. Moreover, evidence is provided that the tumor suppressor p53 is an essential mediator of PKCdelta-induced apoptosis in SMCs. Activation of PKCdelta led to accumulation as well as phosphorylation of p53 in SMCs; this induction correlated with apoptosis. Furthermore, blocking p53 induction with small interference RNA or targeted gene deletion prevented PKCdelta-induced apoptosis, whereas restoring p53 expression rescued the ability of PKCdelta to induce apoptosis in p53 null SMCs. We also establish that PKCdelta regulates p53 at both transcriptional and post-translational levels. Specifically, the transcriptional regulation required p38 MAPK, whereas the post-translational modification, at least for serine 46, did not involve MAPK. Additionally, PKCdelta, p38 MAPK, and p53 co-associate in cells under conditions favoring apoptosis. Together, our data suggest that SMC apoptosis proceeds through a pathway that involves PKCdelta, the intermediary p38 MAPK, and the downstream target tumor suppressor p53.