Bcl-2 blocks cisplatin-induced apoptosis by suppression of ERK-mediated p53 accumulation in B104 cells

The functional roles of competitive endogenous RNA (ceRNA) networks in apoptosis in human cancers: The circRNA/miRNA/mRNA regulatory axis and cell signaling pathways

Circular RNAs are noncoding RNAs with circular conformation mainly due to backsplicing event. CircRNAs can potentially impact cell biological processes by interacting with cell signaling pathways. Numerous circRNAs have been found to be aberrantly expressed in a variety of cancers. These RNAs can act as ceRNA (competitive endogenous RNA) by sponging certain miRNAs to form circRNA/miRNA/mRNA networks. Dysregulation of ceRNA networks may lead to dysfunctions in various cell pathways, which modulate apoptosis-associated genes and ultimately result in cancer progression. Since disruption of apoptosis is one of the leading causes of cancer development, one approach for cancer treatment is to drive cells toward apoptosis. In this review, we present a summary of studies on the role of ceRNA networks in cellular signaling pathways that regulate apoptosis; these networks are suggested to be potential biomarkers for cancer treatment.

Time dependent cisplatin dosing differences on hypoalgesia focusing on oxidative stress

Although cisplatin is a key drug in cancer chemotherapy, it often causes sensory peripheral neuropathy, presenting as allodynia in the early stage and hypoalgesia in the serious stage. Chronotherapy has previously been shown to ameliorate cisplatin-induced peripheral neuropathy that was severe enough to cause hypoalgesia in rats. It also has adverse effects such as renal dysfunction and ototoxicity, which are induced by oxidative stress. Here, we show that oxidative stress causes severe cisplatin-induced peripheral neuropathy, and that differences in oxidative stress occur depending on the dosing time of cisplatin. Cisplatin was administered to rats at 5:00 or 17:00 every seven days for four weeks. The antioxidant agent, 1,3-Dimethylthiourea (DMTU), was administered before and after the administration of cisplatin. The hot plate test was used to assess hypoalgesia. Oxidative stress in the sciatic nerve was assessed from thiobarbituric acid reactive substances (TBARs) and superoxide dismutase (SOD) activity. Nerve apoptosis was analysed with qRT-PCR. We observed an increase in TBARs and a decrease in SOD activity with the development of cisplatin-induced hypoalgesia, which was ameliorated by DMTU treatment. Furthermore, differences in the dosing time of cisplatin caused differences in oxidative stress which were correlated with cisplatin-induced hypoalgesia. Severe oxidative stress caused cisplatin-induced hypoalgesia, and chronotherapy with cisplatin ameliorated hypoalgesia by reducing oxidative stress. In the future, chronotherapy with cisplatin may contribute to the treatment of cancer in humans.

Low-intensity low-frequency pulsed ultrasound ameliorates sciatic nerve dysfunction in a rat model of cisplatin-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy is a neurological complication that frequently occurs during chemotherapeutic intervention, resulting in damaged myelin sheath, motor weakness and/or sensory impairment. This study aims to investigate the therapeutic efficiency of low-intensity pulsed low-frequency ultrasound on cisplatin-induced peripheral neuropathy. Rats were randomly divided into five experimental groups as control, cisplatin administration, 10 mg/kg melatonin treatment after cisplatin administration, 1 MHz frequency 0.5 W/cm² pulsed ultrasound treatment after cisplatin administration and 1 MHz frequency 1.5 W/cm² pulsed ultrasound treatment after cisplatin administration. Chemical neuropathy was induced by the injection of 3 mg/kg/week of cisplatin (i.p.) for 5 weeks. Afterwards, melatonin and pulsed ultrasound treatments were applied for 15 consecutive days. Cisplatin administration resulted in a decrease in nociceptive pain perception and nerve conduction velocities together with a decrease in myelin thickness and diameters of axons and myelinated fibers, indicating a dysfunction and degeneration in sciatic nerves. In addition, cisplatin administration led to a decrease, in superoxide dismutase activity, and an increase in malondialdehyde and IL-1β levels together with an increase in caspase-3 protein expression levels and a decrease in Bcl-2 and Parkin levels. The ultrasound treatments resulted in an increase in nociceptive pain perception and sciatic nerve conduction; led to a decrease in oxidative stress and inflammation, restored nerve degeneration and regulated apoptosis and mitophagy. Taken together, low-intensity pulsed low-frequency ultrasound was efficient in restoring the alterations attributable to cisplatin-induced peripheral neuropathy, and warrants further investigations.

ERK: A Double-Edged Sword in Cancer. ERK-Dependent Apoptosis as a Potential Therapeutic Strategy for Cancer

The RAF/MEK/ERK signaling pathway regulates diverse cellular processes as exemplified by cell proliferation, differentiation, motility, and survival. Activation of ERK1/2 generally promotes cell proliferation, and its deregulated activity is a hallmark of many cancers. Therefore, components and regulators of the ERK pathway are considered potential therapeutic targets for cancer, and inhibitors of this pathway, including some MEK and BRAF inhibitors, are already being used in the clinic. Notably, ERK1/2 kinases also have pro-apoptotic functions under certain conditions and enhanced ERK1/2 signaling can cause tumor cell death. Although the repertoire of the compounds which mediate ERK activation and apoptosis is expanding, and various anti-cancer compounds induce ERK activation while exerting their anti-proliferative effects, the mechanisms underlying ERK1/2-mediated cell death are still vague. Recent studies highlight the importance of dual-specificity phosphatases (DUSPs) in determining the pro- versus anti-apoptotic function of ERK in cancer. In this review, we will summarize the recent major findings in understanding the role of ERK in apoptosis, focusing on the major compounds mediating ERK-dependent apoptosis. Studies that further define the molecular targets of these compounds relevant to cell death will be essential to harnessing these compounds for developing effective cancer treatments.

Pathogenesis of platinum-induced peripheral neurotoxicity: Insights from preclinical studies

One of the most relevant dose-limiting adverse effects of platinum drugs is the development of a sensory peripheral neuropathy that highly impairs the patients' quality of life. Nowadays there are no available efficacy strategies for the treatment of platinum-induced peripheral neurotoxicity (PIPN), and the only way to prevent its development and progression is by reducing the dose of the cytostatic drug or even withdrawing the chemotherapy regimen. This clinical issue has been the main focus of hundreds of preclinical research works during recent decades. As a consequence, dozens of in vitro and in vivo models of PIPN have been developed to elucidate the molecular mechanisms involved in its development and to find neuroprotective targets. The apoptosis of peripheral neurons has been identified as the main mechanism involved in PIPN pathogenesis. This mechanism of DRG sensory neurons cell death is triggered by the nuclear and mitochondrial DNA platination together with the increase of the oxidative cellular status induced by the depletion of cytoplasmic antioxidant mechanisms. However, since there has been no successful transfer of preclinical results to clinical practise in terms of therapeutic approaches, some mechanisms of PIPN pathogenesis still remain to be elucidated. This review is focused on the pathogenic mechanisms underlying PIPN described up to now, provided by the critical analysis of in vitro and in vivo models.

Diepoxybutane-induced apoptosis is mediated through the ERK1/2 pathway

Diepoxybutane (DEB) is the most potent active metabolite of butadiene, a regulated air pollutant. We previously reported the occurrence of DEB-induced, p53-dependent, mitochondrial-mediated apoptosis in human lymphoblasts. The present study investigated the role of the extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) pathway in DEB-induced apoptotic signaling in exposed human lymphoblasts. Activated ERK1/2 and mitogen-activated protein (MAP) kinase/ERK1/2 kinase (MEK) levels were significantly upregulated in DEB-exposed human lymphoblasts. The MEK inhibitor PD98059 and ERK1/2 siRNA significantly inhibited apoptosis, ERK1/2 activation, as well as p53 and phospho-p53 (serine-15) levels in human lymphoblasts undergoing DEB-induced apoptosis. Collectively, these results demonstrate that DEB induces apoptotic signaling through the MEK-ERK1/2-p53 pathway in human lymphoblasts. This is the first report implicating the activation of the ERK1/2 pathway and its subsequent role in mediating DEB-induced apoptotic signaling in human lymphoblasts. These findings contribute towards the understanding of DEB toxicity, as well as the signaling pathways mediating DEB-induced apoptosis in human lymphoblasts.

Ouabain-induced apoptosis in cochlear hair cells and spiral ganglion neurons in vitro

Ouabain is a common tool to explore the pathophysiological changes in adult mammalian cochlea in vivo. In prior studies, locally administering ouabain via round window membrane demonstrated that the ototoxic effects of ouabain in vivo varied among mammalian species. Little is known about the ototoxic effects in vitro. Thus, we prepared cochlear organotypic cultures from postnatal day-3 rats and treated these cultures with ouabain at 50, 500, and 1000 μM for different time to elucidate the ototoxic effects of ouabain in vitro and to provide insights that could explain the comparative ototoxic effects of ouabain in vivo. Degeneration of cochlear hair cells and spiral ganglion neurons was evaluated by hair-cell staining and neurofilament labeling, respectively. Annexin V staining was used to detect apoptotic cells. A quantitative RT-PCR apoptosis-focused gene array determined changes in apoptosis-related genes. The results showed that ouabain-induced damage in vitro was dose and time dependent. 500 μM ouabain and 1000 μM ouabain were destructively traumatic to both spiral ganglion neurons and cochlear hair cells in an apoptotic signal-dependent pathway. The major apoptotic pathways in ouabain-induced spiral ganglion neuron apoptosis culminated in the stimulation of the p53 pathway and triggering of apoptosis by a network of proapoptotic signaling pathways.

Cisplatin toxicity reduced in human cultured renal tubular cells by oxygen pretreatment

Cisplatin is an effective and widely used chemotherapy agent and its side effects, particularly nephrotoxicity, limit its usage and related platinum-based drugs. Cisplatin nephrotoxicity is mainly due to extremely increase in reactive oxygen species (ROS) generation leading to kidney tubular cell death. Preconditioning with oxidative stress has been demonstrated to stimulate the cellular adaptation to subsequent severe oxidative stress. Short term oxygen pre-exposure as a mild oxidative stress may enhance some endogenous defense mechanisms, so its effect on Cisplatin induced cell death was investigated in present research. We studied the effects of hyperoxic environment pre-exposure on Cisplatin toxicity in an in-vitro model of cultured human embryonic tubular epithelial cells (AD293). Viability of AD293 cells, as evaluated by MTT-assay, was affected by Cisplatin in a time (1-4 h) dependent model. Biochemical markers of cell apoptosis were evaluated using immunoblotting. Pretreatment with nearly pure oxygen (≥90%) for 2 h significantly reduced the level of cell damage. Activated caspase 3 and Bax/Bcl-2 ratio were significantly increased in Cisplatin-treated cells. Oxygen pretreatment inhibited caspase 3 activation and decreased Bax/Bcl-2 ratio. Oxygen pre-treatment itself not showed any cytotoxicity in exposure times up to 3 h. Our data indicate that hyperoxic preconditioning reduces Cisplatin toxicity in cultured human tubular epithelial cells. The exact mechanism of protection is unclear, though enhancement of some endogenous defense mechanisms and subsequently scavenging of free oxygen radicals may play an important role.

OTOTOXIC EFFECTS OF CARBOPLATIN IN ORGANOTYPIC CULTURES IN CHINCHILLAS AND RATS

Carboplatin, a second-generation platinum chemotherapeutic drug, is considerably less ototoxic than cisplatin. While common laboratory species such as mice, guinea pigs and rats are highly resistant to carboplatin ototoxicity, the chinchilla stands out as highly susceptible. Moreover, carboplatin causes an unusual gradient of cell death in chinchillas. Moderate doses selectively damage type I spiral ganglion neurons (SGN) and inner hair cells (IHC) and the lesion tends to be relatively uniform along the length of the cochlea. Higher doses eventually damage outer hair cells (OHC), but the lesion follows the traditional gradient in which damage is more severe in the base than the apex. While carboplatin ototoxicity has been well documented in adult animals in vivo, little is known about its in vitro toxicity. To elucidate the ototoxic effects of carboplatin in vitro, we prepared cochlear and vestibular organotypic cultures from postnatal day 3 rats and adult chinchillas. Chinchilla cochlear and vestibular cultures were treated with carboplatin concentrations ranging from 50 µM to 10 mM for 48 h. Consistent with in vivo data, carboplatin selectively damaged IHC at low concentrations (50-100 µM). Surprisingly, IHC loss decreased at higher doses and IHC were intact at doses exceeding 500 µM. The mechanisms underlying this nonlinear response are unclear but could be related to a decrease in carboplatin uptake via active transport mechanisms (e.g., copper). Unlike the cochlea, the carboplatin dose-response function increased with dose with the highest dose destroying all chinchilla vestibular hair cells. Cochlear hair cells and auditory nerve fibers in rat cochlear organotypic cultures were unaffected by carboplatin concentrations <10 µM; however, the damage in OHC were more severe than IHC once the dose reached 100 µM. A dose at 500 µM destroyed all the cochlear hair cells, but hair cell loss decreased at high concentrations and nearly all the cochlear hair cells were present at the highest dose, 5 mM. Unlike the nonlinear dose-response seen with cochlear hair cells, rat auditory nerve fiber and spiral ganglion losses increased with doses above 50 µM with the highest dose destroying virtually all SGN. The remarkable species differences seen in vitro suggest that chinchilla IHC and type I SGN posse some unique biological mechanism that makes them especially vulnerable to carboplatin toxicity.

Antimicrobial cyclic decapeptides with anticancer activity

Antimicrobial peptides have been considered as potential candidates for cancer therapy. We report here the cytotoxicity of a library of 66 antibacterial cyclodecapeptides on human carcinoma cell lines, and their effects on apoptosis [as assessed by cleavage of poly(ADP-ribose) polymerase (PARP)] and cell signaling proteins (p53 and ERK1/2) in cultured human cervical carcinoma cells. A design of experiments approach permitted to analyze the results of a subset of 16 peptides and define rules for high anticancer activity against MDA-MB-231 breast carcinoma cells. Eight peptides were identified with IC(50) values ranging from 18.5 to 57.5 μM against the five cell lines tested, being HeLa cells the most sensitive. Among these sequences, BPC88, BPC96, BPC98, and BPC194 displayed specificity and high cytotoxicity against HeLa cells (IC(50) of 22.5-38.5 μM), showed low hemolytic activity and low cytotoxicity to non-malignant fibroblasts, and were stable to proteases in human serum. Induction of apoptosis by these peptides was observed and the apoptotic effect of BPC88 and BPC96 caused a marked decrease on the activated form of ERK1/2 kinase and an induction of p53. We further showed that BPC96 at low doses synergized the cytotoxic effect of cisplatin. These findings suggest that cyclic decapeptides may represent novel anticancer agents providing a new strategy in cancer therapy.

Emerging MEK inhibitors

IMPORTANCE OF THE FIELD

The Ras/Raf/MEK/ERK pathway is often activated by genetic alterations in upstream signaling molecules. Integral components of this pathway such as Ras and B-Raf are also activated by mutation. The Ras/Raf/MEK/ERK pathway has profound effects on proliferative, apoptotic and differentiation pathways. This pathway can often be effectively silenced by MEK inhibitors. AREAS COVERED BY THIS REVIEW: This review will discuss targeting of MEK which could lead to novel methods to control abnormal proliferation which arises in cancer and other proliferative diseases. This review will cover the scientific literature from 1980 to present and is a follow on from a review which focused on Emerging Raf Inhibitors published in this same review series.

WHAT THE READER WILL GAIN

By reading this review the reader will understand the important roles that genetics play in the response of patients to MEK inhibitors, the potential of combining MEK inhibitors with other types of therapy, the prevention of cellular aging and the development of cancer stem cells.

TAKE HOME MESSAGE

Targeting MEK has been shown to be effective in suppressing many important pathways involved in cell growth and the prevention of apoptosis. MEK inhibitors have many potential therapeutic uses in the suppression of cancer, proliferative diseases and aging.

Cellular responses to Cisplatin-induced DNA damage

Cisplatin is one of the most effective anticancer agents widely used in the treatment of solid tumors. It is generally considered as a cytotoxic drug which kills cancer cells by damaging DNA and inhibiting DNA synthesis. How cells respond to cisplatin-induced DNA damage plays a critical role in deciding cisplatin sensitivity. Cisplatin-induced DNA damage activates various signaling pathways to prevent or promote cell death. This paper summarizes our current understandings regarding the mechanisms by which cisplatin induces cell death and the bases of cisplatin resistance. We have discussed various steps, including the entry of cisplatin inside cells, DNA repair, drug detoxification, DNA damage response, and regulation of cisplatin-induced apoptosis by protein kinases. An understanding of how various signaling pathways regulate cisplatin-induced cell death should aid in the development of more effective therapeutic strategies for the treatment of cancer.

Carvedilol protects against the renal mitochondrial toxicity induced by cisplatin in rats

The clinical use of cisplatin is highly limited by its nephrotoxicity, which has been associated with mitochondrial dysfunction. We investigated the protective effect of carvedilol, an antihypertensive with strong antioxidant properties, against the nephrotoxicity induced by cisplatin in rats. Carvedilol was able to counteract the renal damage by preventing the mitochondrial dysfunction induced by cisplatin. The mitochondrial eletrochemical potential, calcium uptake, respiration and the phosphorylative capacity were preserved by the co-administration of carvedilol. The mechanism of protection probably does not involve alterations in the cellular and sub-cellular distribution of cisplatin. The study suggests that carvedilol is a potential drug for the adjuvant nephroprotective therapy during cisplatin chemotherapy.

Enhancement of antitumor activity of cisplatin in human lung cancer cells by tumor suppressor FUS1

FUS1 is a novel tumor suppressor gene located in the human chromosome 3p21.3 region. We previously showed that restoration of FUS1 function in 3p21.3-deficient human non-small-cell lung cancer (NSCLC) cells significantly inhibited tumor cell growth in vitro and in vivo. In this study, we evaluated the combined effects of the tumor suppressor FUS1 and the chemotherapeutic drug cisplatin on tumor cell growth and apoptosis induction in NSCLC cells, and explored the molecular mechanism of their mutual action. Exogenous expression of FUS1 by nanoparticle-mediated gene transfer sensitized the response of NSCLC cells to cisplatin, resulting in a 4- to 6-fold increase in tumor-suppressing activity. A systemic treatment with a combination of FUS1-nanoparticles and cisplatin in a human H322 lung cancer orthotopic xenograft mouse model dramatically enhanced the therapeutic efficacy of cisplatin. We also found that the FUS1-enhanced chemosensitivity is associated with the downregulation of MDM2, accumulation of p53 and activation of the Apaf-1-dependent apoptosis pathway. Our results demonstrated an important role of FUS1 in modulating chemosensitivity of lung cancer cells, and suggested that a proper combination of molecular therapeutics such as the proapoptotic tumor suppressor FUS1 and the conventional chemotherapeutic drugs such as cisplatin may be an efficient treatment strategy for human lung cancer.

Anticancer and chemosensitizing effects of 2,3-DCPE in ovarian carcinoma cell lines: link with ERK activation and modulation of p21WAF1/CIP1, Bcl-2 and Bcl-xL expression

OBJECTIVE

Emergence of chemoresistance in the course of treatments with platinum drugs remains a major hurdle to ovarian carcinoma therapy. We have previously shown that acquisition of cisplatin resistance by OAW42-R ovarian carcinoma cells was associated with the loss of ERK activation in response to cisplatin. To try to sensitize this cell line by restoring ERK activation, we tested a new synthetic compound, 2[[3-(2,3-dichlorophenoxy)propyl]amino]ethanol (2,3-DCPE), which was described to induce ERK activation and to display anticancer properties.

METHODS

We treated four ovarian carcinoma cell lines with 2,3-DCPE, alone or combined with cisplatin. We characterized its effects on apoptosis induction and proliferation and correlated them with molecular modulations.

RESULTS

We showed that 2,3-DCPE induced cell death and ERK phosphorylation in a time- and concentration-dependent manner in OAW42-R cells. 2,3-DCPE-triggered apoptosis was also associated with the inhibition of Bcl-2 expression and, to a less extent, with that of Bcl-xL. Treatment with 2,3-DCPE also elicited a strong G0/G1 cell cycle arrest, accompanied with p21WAF1/CIP1 up-regulation. All of these effects revealed to be irreversible. Moreover, 2,3-DCPE exerted a cytostatic effect on OAW42, IGROV1-R10 and SKOV3 ovarian carcinoma cells, the sensitivity to 2,3-DCPE appearing in particular linked with a low basal level of P-ERK. Finally, we showed that 2,3-DCPE increased the cytotoxic effect of cisplatin in OAW42-R resistant cells.

CONCLUSION

Our results emphasized the potential interest of 2,3-DCPE, used alone or combined with cisplatin, for ovarian carcinoma treatment. The absence of basal P-ERK may constitute a predictive marker of response to this novel therapy.

Cisplatin-induced nephrotoxicity is associated with oxidative stress, redox state unbalance, impairment of energetic metabolism and apoptosis in rat kidney mitochondria

The clinical use of cisplatin (cis-diamminedichloroplatinum II) is highly limited by its nephrotoxicity. The precise mechanisms involved in cisplatin-induced mitochondrial dysfunction in kidney have not been completely clarified. Therefore, we investigated in vivo the effects of cisplatin on mitochondrial bioenergetics, redox state, and oxidative stress as well as the occurrence of cell death by apoptosis in cisplatin-treated rat kidney. Adult male Wistar rats weighing 200-220 g were divided into two groups. The control group (n = 8) was treated only with an intraperitoneal (i.p.) injection of saline solution (1 ml per 100 g body weight), and the cisplatin group (n = 8) was given a single injection of cisplatin (10 mg/kg body weight, i.p.). Animals were sacrificed 72 h after the treatment. The cisplatin group presented acute renal failure characterized by increased plasmatic creatinine and urea levels. Mitochondrial dysfunction was evidenced by the decline in membrane electrochemical potential and the substantial decrease in mitochondrial calcium uptake. The mitochondrial antioxidant defense system was depleted, as shown by decreased GSH and NADPH levels, GSH/GSSG ratio, and increased GSSG level. Moreover, cisplatin induced oxidative damage to mitochondrial lipids, including cardiolipin, and oxidation of mitochondrial proteins, as demonstrated by the significant decrease of sulfhydryl protein concentrations and increased levels of carbonylated proteins. Additionally, aconitase activity, which is essential for mitochondrial function, was also found to be lower in the cisplatin group. Renal cell death via apoptosis was evidenced by the increased caspase-3 activity. Results show the central role of mitochondria and the intensification of apoptosis in cisplatin-induced acute renal failure, highlighting a number of steps that might be targeted to minimize cisplatin-induced nephrotoxicity.

Cisplatin cytotoxicity in organ of corti-derived immortalized cells

Cisplatin is an anticancer drug currently used in the treatment of genital and head and neck tumors. Its use in these and other types of tumors is narrowed by onset of chemoresistance and severe undesired side effects, like as nephro- and ototoxicity, whose mechanisms of action are only partially understood. In the present study we investigated the effects of cisplatin (cis-dichlorodiaminoplatin, CDDP) on a cell line (OC-k3) developed from organs of Corti of transgenic mice. We observed at 48 h that cell death due to cisplatin was time and concentration-dependent. The cell death displayed some morphological hallmarks of apoptosis, including nuclear fragmentation into several large nuclear fragments, surrounded by a rearranged and thickened actin cytoskeleton. No DNA laddering was detected, suggesting absence of endonuclease activity, nor annexin V positivity, suggesting absence of phosphatidylserine externalization. Several molecules protected the cells against CDDP induced cytotoxicity, including methionine, suramin and PD98059. Methionine reduced CDDP-uptake, while suramin, a polycathionic compound a specifically binding external proteins, did not. This finding suggested that suramin could exert its protective effect by acting on an intracellular transduction pathway. We tested this hypothesis by studying the effect of suramin and PD98059, a MEK inhibitor, on the mitogen activated protein kinase (MAPK) cascade. After CDDP treatment, we found an increase of phosphorylation of extracellular regulated kinases (ERK)1/2, that could be inhibited by PD98059 and suramin. These data suggest that ERK pathways can play a role in mediating the cell death induction in presence of a CDDP challenge.

ERK1/2 activation attenuates TRAIL-induced apoptosis through the regulation of mitochondria-dependent pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) functions as an extracellular signal, which triggers apoptosis in tumor cells. In order to characterize the molecular events involved in TRAIL cytotoxic signaling, we attempted to determine the role of extracellular signal-regulated kinase 1/2 (ERK1/2), as well as its downstream targets in TRAIL-treated HeLa cells. Here we demonstrate that TRAIL exposure resulted in the activation of ERK1/2, and the elevation of anti-apoptotic Bcl-2 protein levels. ERK1/2 inhibition with PD98059 promoted cell death via the down-regulation of Bcl-2 protein levels, together with increasing mitochondrial damage, including the collapse of mitochondrial membrane potential, the release of cytochrome c from mitochondria to cytoplasm and caspase activity. These results suggest that the ERK1/2 activation is a kind of survival mechanism to struggle against TRAIL-induced stress condition in early stage, via activating cellular defense mechanisms like as the up-regulation of the Bcl-2/Bax ratio, as well as several mitochondrial events.

Bcl-2 overexpression disrupts the morphology of PC12 cells through reduced ERK activation

Bcl-2 has been hypothesized to regulate many cellular functions in addition to its well-characterized role in the prevention of programmed cell death. To understand the role of Bcl-2 in regulating cell morphology and to explore the mechanism of this effect, we examined the effects of Bcl-2 overexpression on the morphology of PC12 cells in culture. We demonstrate that the overexpression of Bcl-2 in PC12 cells results in altered cell morphology and reduced actin expression. Analysis of extracellular signal-regulated kinase (ERK) 1/2 phosphorylation reveals that the morphological changes seen after bcl-2 transfection are associated with reduced ERK activation. Treatment of control (mock-transfected) PC12 cells with the mitogen-activated ERK-activating kinase (MEK) inhibitor PD98059 converts their flat, process-bearing morphology into the rounded, process-free morphology of bcl-2-transfected cells, further confirming the association of ERK activation with altered cell shape. In conclusion, the present study describes a novel function of Bcl-2 in regulating cell shape through reduced ERK activation.

Ginkgo biloba extract regulates differentially the cell death induced by hydrogen peroxide and simvastatin

Several human diseases have been associated with the overproduction of reactive oxygen species (ROS) and subsequently various antioxidants emerged as potential therapeutic agents that scavenge ROS. As an oxidative stress model of human disease, we used hydrogen peroxide (H2O2) to study effect of ROS on C6 glioma cells as a surrogate for astrocytes. H2O2 induced dose- and time-dependent apoptotic cell death which was preceded by growth arrest, and transiently activated the signalling proteins ATF-2, ERK1/2 and AKT in C6 glioma cells. While several antioxidants failed to block H2O2-induced apoptosis of these cells, Ginkgo biloba extract (EGb) totally prevented the cell death and growth inhibition induced by H2O2. Interestingly, EGb did not prevent the activation of ATF-2, ERK1/2 and AKT induced by H2O2 excluding the role of these factors in the pro-apoptotic effect of H2O2. We have previously shown that the lipid-lowering drug, simvastatin, causes apoptotic cell death in C6 glioma cells [Koyuturk M, Ersoz M, Altiok N. Simvastatin induces proliferation inhibition and apoptosis in C6 glioma cells via c-jun N-terminal kinase. Neurosci Lett 2004;370(2-3):212-7]. However, in parallel experiments with H2O2, EGb was unable to prevent cell death induced by simvastatin suggesting the involvement of separate signalling pathways between H2O2 and simvastatin. Thus, EGb and other plant flavonoids might have potential as protective agents against apoptosis through scavenging ROS upon cerebral or myocardial diseases associated with free radical generation.

Activation of ERK1/2 and p38 kinases by polycyclic aromatic hydrocarbons in rat liver epithelial cells is associated with induction of apoptosis

Deregulation of various signaling pathways, linked either to induction of cell proliferation or to modulation of cellular differentiation and apoptosis, has been proposed to contribute to carcinogenicity of polycyclic aromatic hydrocarbons (PAHs). In the present study, we investigated effects of the PAHs previously shown to induce cell proliferation and/or apoptosis in contact-inhibited rat liver epithelial WB-F344 cells, with an aim to define the role of mitogen-activated protein kinases in both events. We found that only strong genotoxin dibenzo[a,l]pyrene (DBalP) activated extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 kinase, but not c-Jun N-terminal kinases (JNKs), at concentrations inducing both apoptosis and phosphorylation of p53 tumor suppressor at serine 15 residue. In contrast, the PAHs stimulating cell proliferation in WB-F344 cell line had no effect on activation of ERK1/2, p38 or JNKs. Synthetic inhibitors of ERK1/2 activation (U0126) or p38 kinase activity (SB203580) prevented both apoptosis and induction of p53 phosphorylation by DBalP. Pifithrin-alpha, inhibitor of p53 transcriptional activity, prevented induction of apoptosis and activation of ERK1/2 and p38. Taken together, our data suggest that both ERK1/2 and p38 are activated in response to DBalP and that they might be involved in regulation of cellular response to DNA damage induced by DBalP, while neither kinase is involved in the release from contact inhibition induced by PAHs.

The activation of ERK1/2 via a tyrosine kinase pathway attenuates trail-induced apoptosis in HeLa cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) serves as an extracellular signal that triggers apoptosis in tumor cells. To characterize the molecular events involved in TRAIL-induced apoptotic signaling, we investigated the role of extracellular signal-regulated kinase 1/2 (ERK1/2) in HeLa cell death. Here we show that TRAIL-activated ERK1/2 through a tyrosine kinase-dependent pathway, subsequently elevated anti-apoptotic Bcl-2 protein levels. ERK1/2 inhibition with PD98059 promoted apoptotic cell death through the downregulation of ERK1/2 activity and Bcl-2 protein levels. Moreover, tyrosine kinase inhibition with Genistein in TRAIL-induced apoptosis effectively attenuated ERK1/2 activity and enhanced apoptotic cell death. Taken together, our results indicate that ERK1/2 activation via tyrosine kinase pathway plays a protective role as the cellular defense mechanism through the upregulation of Bcl-2 protein levels in TRAIL-induced apoptosis.

Adrenomedullin prevents apoptosis in prostate cancer cells

The 52-aminoacid peptide adrenomedullin (AM) is expressed in the normal and malignant prostate. We have previously shown that prostate cancer cells produce and secrete AM, which acts as an autocrine growth inhibitory factor. We have evaluated in the present study the role of AM in prostate cancer cell apoptosis, induced either by serum deprivation or treatment with the chemotherapeutic agent etoposide (which acts as an inhibitor of topoisomerase II). For this purpose we over-expressed AM in PC-3, DU 145 and LNCaP cells, which were transfected with an expression vector carrying AM. We also treated the parental cell lines with synthetic AM in normal culture conditions and in conditions of induced-apoptosis. After serum removal, AM prevented apoptosis in DU 145 and PC-3 cells, but not in LNCaP cells. When treated with etoposide, AM prevented apoptosis in PC-3 and LNCaP cells, but not in DU 145 cells. Cell cycle analysis demonstrated a significant decrease in the percentage of AM-overexpressing PC-3 cells in the subG0/G1 phase after treatment with etoposide, as compared to the percentage of mock-transfected PC-3 treated cells. Western blot showed that protein levels of phosphorylated ERK1/2 increased in parental PC-3 cells after treatment with etoposide. In PC-3 cells overexpressing AM, phosphorylated ERK1/2 basal levels were lower than basal levels of parental PC-3 cells, and treatment with etoposide did not result in such an increase. Etoposide produced a significant increase in cleaved PARP in parental PC-3 cells. However, PC-3 clones overexpressing AM that were treated with etoposide only showed a mild increase in fragmented PARP. The ratio Bcl-2/Bax was reduced in parental or mock-transfected PC-3 cells after treatment with etoposide. On the contrary, this ratio was not reduced in PC-3 clones with AM overexpression that were treated with etoposide. All these data demonstrate that AM plays a protective role against induced apoptosis in prostate cancer cells. These results may have important implications in prostate cancer resistance to chemotherapeutic agents.

Antisense bcl-2 transfection up-regulates anti-apoptotic and anti-oxidant thioredoxin in neuroblastoma cells

Antisense bcl-2 therapy combined with chemotherapy has been proved to be effective in various tumors. However, the role played by antisense bcl-2 therapy alone is not clear. In this study, we compared the apoptosis and the protein profiles of antisense bcl-2 transfected human neuroblastoma SK-N-MC cells to the control cells. Flow cytometric data indicated that antisense bcl-2 transfection did not lead to more extensive apoptosis in SK-N-MC cells (14.9 +/- 3.8%) than the control cells (10.3 +/- 2.3%). The above observation was confirmed by fluorescence microscopy using Hoechst 33258 staining. However, antisense bcl-2 induced changes in the expression of various proteins as shown by proteomic comparison, which included the up-regulation of the anti-apoptotic and anti-oxidant protein thioredoxin. By western blot validation, thioredoxin was found to be up-regulated by 2.9-folds with the corresponding down-regulation of Bcl-2 by 2.1-folds. The up-regulation of thioredoxin may be a compensating mechanism for cell survival in neuroblastoma when Bcl-2 expression is suppressed, and it may to some extent attenuate the effectiveness of antisense bcl-2 therapy.

Expression of kinase suppressor of Ras1 enhances cisplatin-induced extracellular signal-regulated kinase activation and cisplatin sensitivity

Kinase suppressor of Ras1 (KSR1) interacts with several mitogen-activated protein (MAP) kinase pathway components, including Raf, MAP/extracellular signal-regulated kinase (ERK) kinase (MEK), and ERK, and acts as a positive regulator of the Ras signaling cascade. Previous studies have shown that exposure of cells to the anticancer agent cisplatin (cis-diamminedichloroplatinum, CDDP) is associated with changes in multiple signal transduction pathways, including c-Jun-NH2-kinase, ERK, and p38 pathways. Moreover, ERK activation has been linked to changes in cell survival following CDDP treatment. In this report, we have examined the effects of KSR1 expression on the sensitivity of cells to CDDP-induced apoptosis. Loss of KSR1 expression in mouse embryo fibroblasts (MEFs) derived from KSR1 knockout mice (KSR-/- MEF) is associated with decreased CDDP-induced ERK activation and increased resistance to CDDP-induced apoptosis compared with wild-type MEFs (KSR+/+ MEF). Furthermore, transduction of KSR-/- MEFs and MCF-7 breast cancer cells with wild-type KSR1 resulted in enhanced ERK activation following CDDP exposure and increased sensitivity to CDDP. In addition, inhibition of ERK activation by exposing MEFs to the MEK1/2-specific inhibitors PD98059 and U0126 protected both KSR+/+ and KSR-/- MEFs cells from CDDP-induced apoptosis. These results indicate that KSR1-mediated regulation of ERK activity represents a novel determinant of CDDP sensitivity of cancer cells.

Extracellular signal-regulated kinase activation and Bcl-2 downregulation mediate apoptosis after gemcitabine treatment partly via a p53-independent pathway

Gemcitabine is a promising compound for the treatment of human lung cancer. Although apoptosis has been shown to play a role in certain cell types with gemcitabine, the steps leading to cell death after the drug-target interaction are not well understood. We studied the molecular mechanisms of gemcitabine-induced apoptosis and determined the role of p53 function on the cytotoxic effects of gemcitabine in human nonsmall cell lung cancer (NSCLC) H1299 and H1299/p53 cells. Here, we found that gemcitabine induced an apoptotic cell death via a Bcl-2-dependent caspase-9 activation pathway. Moreover, phosphorylated activation of extracellular signal-regulated kinase (ERK) was observed upon gemcitabine treatment. Genetical or pharmacological inhibition of ERK activation markedly blocked gemcitabine-induced cell death. Furthermore, inactivation of Akt was also involved in this event. Taken together, our observations indicate that ERK activation and Akt inactivation mediated gemcitabine-induced apoptosis independently of p53 in human NSCLC H1299 cells.

Novel platinum(IV) complexes induce rapid tumor cell deathin vitro

The anticancer activity of platinum complexes has been known since the discovery of classical Pt(II)-based drug cisplatin. However, Pt(IV) complexes have greater inertness than corresponding Pt(II) complexes, thus allowing the oral administration and reducing the toxicity associated with platinum-based chemotherapy. Here, we describe the in vitro antitumor activity of some novel Pt(IV)-based agents against mouse fibrosarcoma L929 cells and human astrocytoma U251 cells. The cytotoxicity of 2 Pt(IV) complexes with bidentate ethylenediamine-N,N'-di-3-propanoato esters was found to be markedly higher than that of their Pt(II) counterparts and comparable to the antitumor action of cisplatin. In contrast to cisplatin, which caused oxidative stress-independent apoptotic cell death of tumor cells, these Pt(IV) complexes induced oxygen radical-mediated tumor cell necrosis. Importantly, the cytotoxic action of novel Pt(IV) complexes was markedly more rapid than that of cisplatin, indicating their potential usefulness in anticancer therapy.

Xanthoangelol, a Major Chalcone Constituent of Angelica keiskei, Induces Apoptosis in Neuroblastoma and Leukemia Cells

Xanthoangelol, a major chalcone constituent of the stem exudates of Angelica keiskei, was evaluated for cell toxicity and apoptosis-inducing activity in human neuroblastoma (IMR-32) and leukemia (Jurkat) cells. Xanthoangelol concentration-dependently reduced the survival rates of both cell lines as revealed by the trypan blue exclusion test. Early apoptosis induced by 4 h incubation with xanthoangelol was detected using flow cytometry after double-staining with annexin V and propidium iodide (PI). Western blot analysis showed that xanthoangelol markedly reduced the level of precursor caspase-3 and increased the level of cleaved caspase-3, but Bax and Bcl-2 proteins were not affected. These results suggest that xanthoangelol induces apoptotic cell death by activatation of caspase-3 in neuroblastoma and leukemia cells through a mechanism that does not involve Bax/Bcl-2 signal transduction. Therefore, xanthoangelol may be applicable as an effective drug for treatment of neuroblastoma and leukemia.

Requirement for ERK activation in sinomenine-induced apoptosis of macrophages

Sinomenine (SN), an immunnosuppressive compound derived from the Chinese medicinal plant Sinomenium acutum, has been used to treat autoimmune diseases effectively. Previous studies show SN can inhibit lymphocytes proliferation and macrophage production of pro-inflammatory factors. However, little is known about the mechanisms by which SN inhibits macrophage functions. In this study, we demonstrated that SN could inhibit the proliferation of murine macrophages RAW264.7 by inducing apoptosis in a dose- and time-dependent manner. We found activation of extracellular signal-regulated protein kinase (ERK) in SN-treated macrophages, and requirement for ERK activation in SN-induced apoptosis of macrophages. Contemporarily, the expression of p27/KIP1, proapoptotic factor Bax increased, and expression of Bcl-2 decreased, which might cooperate to induce apoptosis. Inhibiting ERK activation reduced the increased expression of p27 and Bax, but had no effect on the decreased expression of Bcl-2, suggesting the involvement of ERK activation in the SN-induced increased expression of p27 and Bax. These results demonstrated that SN could induce apoptosis of macrophages through activation of ERK, and ERK activation might partially involve in the increased expression of p27 and Bax in apoptotic macrophages. Therefore, induction of macrophage apoptosis through ERK activation may be one of mechanisms by which SN exhibits its immunosuppressive function.

Early single cell bifurcation of pro- and antiapoptotic states during oxidative stress

In a population of cells undergoing oxidative stress, an individual cell either succumbs to apoptotic cell death or maintains homeostasis and survives. Exposure of PC-12-D(2)R cells to 200 microm hydrogen peroxide (H(2)O(2)) induces apoptosis in about half of cells after 24 h. After 1-h exposure to 200 microm H(2)O(2), both antiapoptotic extracellular regulated kinase (ERK) phosphorylation and pro-apoptotic Ser-15-p53 phosphorylation are observed. Microarray and real-time PCR assays of gene expression after H(2)O(2) exposure identified several transcripts, including egr1, that are rapidly induced downstream of ERK. Single cell analysis of egr1 induction and of phospho-ERK and phospho-p53 formation revealed the presence of two distinct cellular programs. Whereas the proportion of cells activating ERK versus p53 at 1 h depended on H(2)O(2) concentration, individual cells showed exclusively either phospho-p53 formation or activation of ERK and egr1 induction. Exposure to H(2)O(2) for 1 h also elicited these two non-overlapping cellular responses in both dopaminergic SN4741 cells and differentiated postmitotic PC-12-D(2)R cells. Repressing p53 with pifithrin-alpha or small interfering RNA increased ERK phosphorylation by H(2)O(2), indicating that p53-dependent suppression of ERK activity may contribute to the bi-stable single cell responses observed. By 24 h, the subset of cells in which ERK activity was suppressed exhibit caspase 3 activation and the nuclear condensation characteristic of apoptosis. These studies suggest that the individual cell rapidly and stochastically processes the oxidative stress stimulus, leading to an all-or-none cytoprotective or pro-apoptotic signaling response.

Effect of haemopoietic growth factors on cancer cell lines and their role in chemosensitivity

The recombinant growth factors (GFs) erythropoietin (Epo) and granulocyte-macrophage colony stimulating factor (GM-CSF) have important roles in the management of cancer patients. However, the effects of these GFs at a cellular level are not well understood. We examined the effect of GFs alone, and in combination with cytotoxic chemotherapy, in a panel of seven cell lines. Flow cytometric analysis showed varying levels of receptor expression, which correlated with phosphorylated MAPK expression. Additionally, there were also concomitant increases in BCL-2 protein levels in those cells with high levels of MAPK activation. Although culturing cells with Epo or GM-CSF did not alter cell viability by themselves, GF pretreatment in cell lines expressing higher receptor levels resulted in a reduced magnitude of cell kill following exposure to cytotoxic IC50 concentrations of cisplatin. Subsequent co-culture with either the MEK inhibitor U0126 or the GM-CSF antagonist E21R negated this induced resistance to cytotoxic chemotherapy, confirming the importance of the GF receptor as well as MAPK in mediating these effects. These results suggest that the use of GFs during chemotherapy may be detrimental in those cancers expressing higher levels of the specific receptor. Conversely, our results also suggest that GFs are safe to use in chemotherapeutic regimens if the cancer cells do not overexpress the particular receptor.

Caveolin-induced activation of the phosphatidylinositol 3-kinase/Akt pathway increases arsenite cytotoxicity

The inhibitory effect of caveolin on the cellular response to growth factor stimulation is well established. Given the significant overlap in signaling pathways involved in regulating cell proliferation and stress responsiveness, we hypothesized that caveolin would also affect a cell's ability to respond to environmental stress. Here we investigated the ability of caveolin-1 to modulate the cellular response to sodium arsenite and thereby alter survival of the human cell lines 293 and HeLa. Cells stably transfected with caveolin-1 were found to be much more sensitive to the toxic effects of sodium arsenite than either untransfected parental cells or parental cells transfected with an empty vector. Unexpectedly, the caveolin-overexpressing cells also exhibited a significant activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, which additional studies suggested was likely due to decreased neutral sphingomyelinase activity and ceramide synthesis. In contrast to its extensively documented antiapoptotic influence, the elevated activity of Akt appears to be important in sensitizing caveolin-expressing cells to arsenite-induced toxicity, as both pretreatment of cells with the PI3K inhibitor wortmannin and overexpression of a dominant-negative Akt mutant markedly improved the survival of arsenite-treated cells. This death-promoting influence of the PI3K/Akt pathway in caveolin-overexpressing cells appeared not to be unique to sodium arsenite, as wortmannin pretreatment also resulted in increased survival in the presence of H(2)O(2). In summary, our results indicate that caveolin-induced upregulation of the PI3K/Akt signaling pathway, which appears to be a death signal in the presence of arsenite and H(2)O(2), sensitizes cells to environmental stress.

Inhibition of aldose reductase enhances HeLa cell sensitivity to chemotherapeutic drugs and involves activation of extracellular signal-regulated kinases

Changes in glucose metabolism during diabetes are linked to an increased risk for the development of cancer. Increased activity of aldose reductase, the rate-limiting polyol pathway enzyme that converts glucose into sorbitol, mediates pathologies associated with diabetes and is thought to be involved in increased resistance to chemotherapeutic drugs. Thus, increased intracellular sorbitol levels may serve a protective function in cancer cells. In these studies we determined whether an inhibitor of aldose reductase could enhance the effectiveness of anticancer agents. Our findings indicate that treatment with the aldose reductase inhibitor, ethyl 1-benzyl-3-hydroxy-2(5H)-oxopyrrole-4-carboxylate (EBPC), enhances the cytotoxic effects of the anticancer agents doxorubicin and cisplatin in HeLa cervical carcinoma cells. To establish a mechanistic basis for the increased cytotoxicity by EBPC, we examined the activity of the extracellular signal-regulated kinase (ERK) pathway, which is an important regulator of cell growth. Interestingly, treatment with EBPC in combination with the chemotherapeutic drugs increased ERK activity as compared to treatment with the chemotherapeutic drugs, suggesting a possible role for the ERK pathway in mediating doxorubicin- or cisplatin-induced cell death. Consistent with this possibility, inhibition of ERK activation by the MEK inhibitor, U0126, reversed the EBPC-mediated enhancement of cell death. In summary, these data provide evidence that adjuvant therapy with aldose reductase inhibitors improves the effectiveness of chemotherapeutic drugs, possibly through an ERK pathway-mediated mechanism.