Epidermal growth factor triggers an original, caspase-independent pituitary cell death with heterogeneous phenotype

Analysis of Apoptosis by Thyroid Hormone Induction

Apoptosis is a type of programmed cell death which can be induced by thyroid hormone in pituitary and other cell models. This process is characterized by several biochemical changes, including modifications in plasma membrane lipid composition, mitochondrial membrane dysfunction, and DNA fragmentation, among others. These cellular alterations can be measured using western blotting and flow cytometry techniques. Here we describe the method to detect cleavage of poly-ADP ribose polymerase by western blotting, as well as different flow cytometry-based methods to quantify the sub-G1 hypodiploid cell population, the redistribution of phosphatidylserine to the outer leaflet of plasma membrane, and the loss of the mitochondrial inner membrane potential.

Polyploid cell dynamics and death before and after PEG-treatment of a NIH/3T3 derived culture: vinblastine effects on the regulation of cell subpopulations heterogeneity

BACKGROUND

Neoplastic subpopulations can include polyploid cells that can be involved in tumor evolution and recurrence. Their origin can be traced back to the tumor microenvironment or chemotherapeutic treatment, which can alter cell division or favor cell fusion, generating multinucleated cells. Their progeny, frequently genetically unstable, can result in new aggressive and more resistant to chemotherapy subpopulations. In our work, we used NIHs cells, previously derived from the NIH/3T3 line after serum deprivation, that induced a polyploidization increase with the appearance of cells with DNA content ranging from 4 to 24c. This study aimed to analyze the cellular dynamics of NIHs culture subpopulations before and after treatment with the fusogenic agent polyethylene glycol (PEG), which allowed us to obtain new giant polyploid cells. Successively, PEG-untreated and PEG-treated cultures were incubated with the antimicrotubular poison vinblastine. The dynamics of appearance, decrease and loss of cell subpopulations were evaluated by correlating cell DNA content to mono-multinuclearity resulting from cell fusion and division process alteration and to the peculiarities of cell death events.

RESULTS

DNA microfluorimetry and morphological techniques (phase contrast, fluorescence and TEM microscopies) indicated that PEG treatment induced a 4-24c cell increase and the appearance of new giant elements (64-140c DNA content). Ultrastructural analysis and autophagosomal-lysosomal compartment fluorochromization, which allowed us to correlate cytoplasmic changes to death events, indicated that cell depletion occurred through distinct mechanisms: apoptotic death involved 2c, 4c and 8c cells, while autophagic-like death involved intermediate 12-24c cells, showing nuclear (lobulation/micronucleation) and autophagic cytoplasm alterations. Death, spontaneously occurring, especially in intermediate-sized cells, was increased after vinblastine treatment. No evident cell loss by death events was detected in the 64-140c range.

CONCLUSIONS

PEG-treated NIHs cultures can represent a model of heterogeneous subpopulations originating from cell fusion and division process anomalies. Altogether, our results suggest that the different cell dynamics of NIHs subpopulations can affect the variability of responses to stimuli able to induce cell degeneration and death. Apoptptic, autophagic or hybrid forms of cell death can also depend on the DNA content and ability to progress through the cell cycle, which may influence the persistence and fate of polyploid cell descendants, also concerning chemotherapeutic agent action.

The emerging role of paraptosis in tumor cell biology: Perspectives for cancer prevention and therapy with natural compounds

Standard anti-cancer therapies promote tumor growth suppression mainly via induction of apoptosis. However, in most cases cancer cells acquire the ability to escape apoptotic cell death, thus becoming resistant to current treatments. In this setting, the interest in alternative cell death modes has recently increased. Paraptosis is a new form of programmed cell death displaying endoplasmic reticulum (ER) and/or mitochondria dilation, generally due to proteostasis disruption or redox and ion homeostasis alteration. Recent studies have highlighted that several natural compounds can trigger paraptosis in different tumor cell lines. Here, we review the molecular mechanisms underlying paraptotic cell death, as well as the natural products inducing this kind of cell death program. A better understanding of paraptosis should facilitate the development of new therapeutic strategies for cancer prevention and treatment.

RNAi Screening-based Identification of USP10 as a Novel Regulator of Paraptosis

Accumulating reports demonstrate that apoptosis does not explain all the effects of cancer therapy due to the innate and acquired apoptotic resistance of malignant cancer cells. Recently, paraptosis, a type of programmed cell death accompanied by dilation of mitochondria and/or the endoplasmic reticulum (ER), has garnered interest in cancer research as an alternative way to kill apoptosis-resistant cancers. We describe here the adaptation and validation of a high-content cell-based assay to screen and identify novel paraptotic regulators employing the malignant breast cancer cells undergoing curcumin-induced paraptosis. We used YFP-Mito cells, which express fluorescence selectively in mitochondria, to select paraptosis-related genes whose corresponding siRNAs appeared to modulate mitochondrial dilation, a morphological feature of paraptosis. From the selected 38 candidate genes, we chose ubiquitin specific peptidase 10 (USP10), a ubiquitin specific protease, as a strongly active candidate that warranted further evaluation of its involvement in paraptosis. We found that both siRNA-mediated knockdown of USP10 and treatment with the USP10 inhibitor, spautin-1, effectively attenuated curcumin-induced paraptosis. This systematic assay, in which a siRNA library is screened for the ability to ameliorate paraptotic changes in mitochondria, may enable researchers to identify potent regulators of paraptosis and new candidate genes/drugs to combat malignant breast cancer.

Lowering Etoposide Doses Shifts Cell Demise From Caspase-Dependent to Differentiation and Caspase-3-Independent Apoptosis via DNA Damage Response, Inducing AML Culture Extinction

Cytotoxic chemotherapy, still the most widely adopted anticancer treatment, aims at eliminating cancer cells inducing apoptosis with DNA damaging agents, exploiting the differential replication rate of cancer vs. normal cells; efficiency is evaluated in terms of extent of induced apoptosis, which depends on the individual cell sensitivity to a given drug, and on the dose. In this in vitro study, we report that the concentration of etoposide, a topoisomerase II poison widely used in clinics, determines both the kinetics of cell death, and the type of apoptosis induced. We observed that on a set of myeloid leukemia cell lines, etoposide at high (50 uM) dose promoted a rapid caspase-3-mediated apoptosis, whereas at low (0.5 uM) dose, it induced morphological and functional granulocytic differentiation and caspase-2-dependent, but caspase-3-independent, cell death, displaying features consistent with apoptosis. Both differentiation and caspase-2- (but not 3)-mediated apoptosis were contrasted by caffeine, a well-known inhibitor of the cellular DNA damage response (DDR), which maintained cell viability and cycling, indicating that the effects of low etoposide dose are not the immediate consequence of damage, but the result of a signaling pathway. DDR may be thus the mediator responsible for translating a mere dosage-effect into different signal transduction pathways, highlighting a strategic action in regulating timing and mode of cell death according to the severity of induced damage. The evidence of different molecular pathways induced by high vs. low drug doses may possibly contribute to explain the different effects of cytotoxic vs. metronomic therapy, the latter achieving durable clinical responses by treating cancer patients with stable, low doses of otherwise canonical cytotoxic drugs; intriguingly caspase-3, a major promoter of wounded tissue regeneration, is also a key factor of post-therapy cancer repopulation. All this suggests that cancer control in response to cytotoxic drugs arises from complex reprogramming mechanisms in tumor tissue, recently described as anakoinosis.

Cytoplasmic vacuolization in cell death and survival

Cytoplasmic vacuolization (also called cytoplasmic vacuolation) is a well-known morphological phenomenon observed in mammalian cells after exposure to bacterial or viral pathogens as well as to various natural and artificial low-molecular-weight compounds. Vacuolization often accompanies cell death; however, its role in cell death processes remains unclear. This can be attributed to studying vacuolization at the level of morphology for many years. At the same time, new data on the molecular mechanisms of the vacuole formation and structure have become available. In addition, numerous examples of the association between vacuolization and previously unknown cell death types have been reported. Here, we review these data to make a deeper insight into the role of cytoplasmic vacuolization in cell death and survival.

Leptin-dependent neurotoxicity via induction of apoptosis in adult rat neurogenic cells

Adipocyte-derived hormone leptin has been recently implicated in the control of neuronal plasticity. To explore whether modulation of adult neurogenesis may contribute to leptin control of neuronal plasticity, we used the neurosphere assay of neural stem cells derived from the adult rat subventricular zone (SVZ). Endogenous expression of specific leptin receptor (ObRb) transcripts, as revealed by RT-PCR, is associated with activation of both ERK and STAT-3 pathways via phosphorylation of the critical ERK/STAT-3 amino acid residues upon addition of leptin to neurospheres. Furthermore, leptin triggered withdrawal of neural stem cells from the cell cycle as monitored by Ki67 labeling. This effect was blocked by pharmacological inhibition of ERK activation thus demonstrating that ERK mediates leptin effects on neural stem cell expansion. Leptin-dependent withdrawal of neural stem cells from the cell cycle was associated with increased apoptosis, as detected by TUNEL, which was preceded by cyclin D1 induction. Cyclin D1 was indeed extensively colocalized with TUNEL-positive, apoptotic nuclei. Cyclin-D1 silencing by specific shRNA prevented leptin-induced decrease of the cell number per neurosphere thus pointing to the causal relationship between leptin actions on apoptosis and cyclin D1 induction. Leptin target cells in SVZ neurospheres were identified by double TUNEL/phenotypic marker immunocytofluorescence as differentiating neurons mostly. The inhibition of neural stem cell expansion via ERK/cyclin D1-triggered apoptosis defines novel biological action of leptin which may be involved in adiposity-dependent neurotoxicity.

The hsp70 inhibitor VER155008 induces paraptosis requiring de novo protein synthesis in anaplastic thyroid carcinoma cells

In this study, we evaluated the effect of the hsp70 inhibitor VER155008 on survival of anaplastic thyroid carcinoma (ATC) cells. In ATC cells, VER155008 increased the percentages of dead cells and vacuolated cells. VER155008 did not lead to the cleavage of caspase-3 protein regardless of pretreatment with z-VAD-fmk. VER155008 increased LC3-II protein levels but the protein levels were not changed by autophagy inhibitors. VER155008 caused the dilatation of endoplasmic reticulum (ER), and the increased mRNA levels of Bip and CHOP, suggesting paraptosis. VER155008-induced paraptosis was attenuated by pretreatment with cycloheximide. In conclusion, VER155008 induces paraptosis characterized by cytoplasmic vacuolation, independence of caspase, dilatation of ER and induction of ER stress markers in ATC cells. Moreover, VER155008-induced paraptosis requires de novo protein synthesis in ATC cells.

Mechanisms in photodynamic therapy: part two-cellular signaling, cell metabolism and modes of cell death

Photodynamic therapy (PDT) has been known for over a hundred years, but is only now becoming widely used. Originally developed as a tumor therapy, some of its most successful applications are for non-malignant disease. In the second of a series of three reviews, we will discuss the mechanisms that operate in PDT on a cellular level. In Part I [Castano AP, Demidova TN, Hamblin MR. Mechanism in photodynamic therapy: part one-photosensitizers, photochemistry and cellular localization. Photodiagn Photodyn Ther 2004;1:279-93] it was shown that one of the most important factors governing the outcome of PDT, is how the photosensitizer (PS) interacts with cells in the target tissue or tumor, and the key aspect of this interaction is the subcellular localization of the PS. PS can localize in mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus and plasma membranes. An explosion of investigation and explorations in the field of cell biology have elucidated many of the pathways that mammalian cells undergo when PS are delivered in tissue culture and subsequently illuminated. There is an acute stress response leading to changes in calcium and lipid metabolism and production of cytokines and stress proteins. Enzymes particularly, protein kinases, are activated and transcription factors are expressed. Many of the cellular responses are centered on mitochondria. These effects frequently lead to induction of apoptosis either by the mitochondrial pathway involving caspases and release of cytochrome c, or by pathways involving ceramide or death receptors. However, under certain circumstances cells subjected to PDT die by necrosis. Although there have been many reports of DNA damage caused by PDT, this is not thought to be an important cell-death pathway. This mechanistic research is expected to lead to optimization of PDT as a tumor treatment, and to rational selection of combination therapies that include PDT as a component.

High-dose glucocorticoid aggravates TBI-associated corticosteroid insufficiency by inducing hypothalamic neuronal apoptosis

Emerging experimental and clinical data suggest that severe illness, such as traumatic brain injury (TBI), can induce critical illness-related corticosteroid insufficiency (CIRCI). However, underlying mechanisms of this TBI-associated CIRCI remain poorly understood. We hypothesized that dexamethasone (DXM), a synthetic glucocorticoid, which was widely used to treat TBI, induces hypothalamic neuronal apoptosis to aggravate CIRCI. To test this hypothesis, we have evaluated the dose effect of DXM (1 or 10mg/kg) on the development of acute CIRCI in rats with fluid percussion injury-induced TBI and on cultured rat hypothalamic neurons in vitro (DXM, 10(-5)-10(-8)mol/L). Corticosterone Increase Index was recorded as the marker for CIRCI. In addition, MTT and TUNEL assays were used to measure the viability and apoptosis of hypothalamic neurons in primary culture. Moreover, high-resolution hopping probe ion conductance microscopy (HPICM) was used to monitor the DXM-induced morphological changes in neurons. The incidence of acute CIRCI was significantly higher in the high-dose DXM group on post-injury day 7. Cellular viability was significantly decreased from 12h to 24h after the treatment with a high-dose of DXM. A significantly increase in TUNEL positive cells were detected in cultured cells treated with a high-dose of DXM after 18h. Neurites of hypothalamic neuron were dramatically thinner and the numbers of dendritic beadings increased in neurons treated with the high dose of DXM for 12h. In conclusion, high-dose DXM induced hypothalamic neurons to undergo apoptosis in vivo and in vitro, which may aggravate TBI-associated CIRCI.

Antagonistic functional duality of cancer genes

Cancer evolution is a stochastic process both at the genome and gene levels. Most of tumors contain multiple genetic subclones, evolving in either succession or in parallel, either in a linear or branching manner, with heterogeneous genome and gene alterations, extensively rewired signaling networks, and addicted to multiple oncogenes easily switching with each other during cancer progression and medical intervention. Hundreds of discovered cancer genes are classified according to whether they function in a dominant (oncogenes) or recessive (tumor suppressor genes) manner in a cancer cell. However, there are many cancer "gene-chameleons", which behave distinctly in opposite way in the different experimental settings showing antagonistic duality. In contrast to the widely accepted view that mutant NADP(+)-dependent isocitrate dehydrogenases 1/2 (IDH1/2) and associated metabolite 2-hydroxyglutarate (R)-enantiomer are intrinsically "the drivers" of tumourigenesis, mutant IDH1/2 inhibited, promoted or had no effect on cell proliferation, growth and tumorigenicity in diverse experiments. Similar behavior was evidenced for dozens of cancer genes. Gene function is dependent on genetic network, which is defined by the genome context. The overall changes in karyotype can result in alterations of the role and function of the same genes and pathways. The diverse cell lines and tumor samples have been used in experiments for proving gene tumor promoting/suppressive activity. They all display heterogeneous individual karyotypes and disturbed signaling networks. Consequently, the effect and function of gene under investigation can be opposite and versatile in cells with different genomes that may explain antagonistic duality of cancer genes and the cell type- or the cellular genetic/context-dependent response to the same protein. Antagonistic duality of cancer genes might contribute to failure of chemotherapy. Instructive examples of unexpected activity of cancer genes and "paradoxical" effects of different anticancer drugs depending on the cellular genetic context/signaling network are discussed.

Ras and Rap1 govern spatiotemporal dynamic of activated ERK in pituitary living cells

The Ras/Raf/MEK/ERK is a conserved signalling pathway involved in the control of fundamental cellular processes. Despite extensive research, how this pathway can process a myriad of diverse extracellular inputs into substrate specificity to determine biological outcomes is not fully understood. It has been established that the ERK1/2 pathway is an integrative point in the control of the pituitary function exerted by various extracellular signals. In addition we previously established that the GTPases Ras and Rap1 play a key role in the regulation of ERK1/2-dependent prolactin transcription by EGF or the cAMP-dependent neuropeptide VIP. In this report, using the FRET-based biosensor of ERK activity (EKAR) in the pituitary GH4C1 cell line, we show that both EGF and VIP tightly control the spatiotemporal dynamic of activated ERK with different magnitude and duration. Importantly, we provide the first evidence of a differential control of cytoplasmic and nuclear pools of activated ERK by the GTPases Ras and Rap1. Ras is required for nuclear magnitude and duration of EGF-dependent ERK activation, whereas it is required for both VIP-activated cytoplasmic and nuclear ERK pools. Rap1 is exclusively involved in VIP-activated ERK nuclear pool. Moreover, consistent with the control of the nuclear pool of activated ERK by the GTPases, we observe the same differential role of Ras and Rap1 on ERK nuclear translocation triggered by EGF or VIP. Together these findings identify Ras and Rap1 as determinant partners in shaping nuclear and cytoplasmic ERK kinetics in response to EGF and VIP, which in turn should control pituitary secretion.

Methylprednisolone exacerbates acute critical illness-related corticosteroid insufficiency associated with traumatic brain injury in rats

Emerging evidence demonstrates that severe illness could induce critical illness-related corticosteroid insufficiency (CIRCI) and cause poor prognosis. The purpose of this study was to test the hypothesis that methylprednisolone (MP), a synthetic glucocorticoid, promotes post-traumatic apoptosis in both the hypothalamus and pituitary, resulting in acute CIRCI and increased mortality in the acute phase of traumatic brain injury (TBI). We tested this hypothesis by measuring acute CIRCI in rats subjected to fluid percussion injury (FPI) and treated with MP (5-30mg/kg). The corticosteroid response to TBI was evaluated using the corticosterone increase index (CII), where values less than 2.5 were considered indicative of acute CIRCI. The CII of MP treated rats was comparable to that of saline treated control rats before injury but was significantly decreased in injured rats receiving high-dose MP on post-injury day 7. Similarly, the incidence of acute CIRCI was significantly higher in the high-dose MP group on post-injury day 7. Furthermore, the CII of rats that did not survive post-injury was significantly lower compared to that of survival and was indicative of acute CIRCI. We also examined apoptosis in the paraventricular nucleus (PVN) of the hypothalamus and the adenohypophysis of the pituitary, using a TUNEL assay and transmission electron microscopy (TEM). The number of TUNEL-positive cells was significantly higher in injured rats treated with high-dose MP. No TUNEL-positive cells were detected in the adenohypophysis across experimental groups at either 7 or 14days after TBI. However, autopsies performed on rats that did not survive post-injury revealed obvious apoptotic cells in the adenohypophysis. Moreover, TEM revealed morphological changes characteristic of apoptosis in both the PVN and adenohypophysis of high-dose MP treated rats. These data suggest that MP therapy for TBI could increase neuronal apoptosis in both the hypothalamus and pituitary and consequently exacerbate acute CIRCI and mortality induced by TBI.

Taxol induces paraptosis independent of both protein synthesis and MAPK pathway

Our recent studies have shown that high concentration of taxol induced a caspase-independent paraptosis-like cell death and cytoplasmic vacuolization derived predominantly from endoplasmic reticulum (ER) swelling in human lung carcinoma cell lines (ASTC-a-1). In this report, we further explored the relationship between taxol-induced cell death and vacuolization, and the roles of protein synthesis, mitogen-activated protein kinase kinases (MEK), c-jun N-terminal kinase (JNK) and P38 in taxol-induced paraptosis. Enhanced green fluorescent protein (EGFP) was used to probe the cell morphological change, while ER-targeted red fluorescent protein (er-RFP) was used to probe ER spatial distribution. Real-time monitoring of the ER swelling dynamics during the formation of vacuolization inside single living cells co-expressing EGFP and er-RFP further demonstrated that taxol-induced cytoplasmic vacuolization was from the ER restructuring due to fusion and swelling. PI staining showed that taxol-induced vacuolization was not necrosis. These results further demonstrated that the taxol-induced cell death was neither apoptosis nor necrosis, and fitted the criteria of paraptosis characterized by cytoplasmic vacuolization, caspase-independence, lack of apoptotic morphology and insensitivity to broad caspase inhibitor. Our data further indicated that taxol-induced paraptosis required neither protein synthesis nor the participation of MEK, JNK, and P38, which was different from the insulin-like growth factor I receptor (IGFIR)-induced paraptosis. These results suggest that high concentration of taxol activates an alternative paraptotic cell death pathway.

S100B interaction with the receptor for advanced glycation end products (RAGE): a novel receptor-mediated mechanism for myocyte apoptosis postinfarction

RATIONALE

Post-myocardial infarction ventricular remodeling is associated with the expression of a variety of factors including S100B that can potentially modulate myocyte apoptosis.

OBJECTIVE

This study was undertaken to investigate the expression and function of S100B and its receptor, the receptor for advanced glycation end products (RAGE) in both postinfarction myocardium and in a rat neonatal myocyte culture model.

METHODS AND RESULTS

In a rat model of myocardial infarction following coronary artery ligation, we demonstrate in periinfarct myocytes, upregulation of RAGE, induction of S100B, and release into plasma with consequent myocyte apoptosis. Using a coimmunoprecipitation strategy, we demonstrate a direct interaction between S100B and RAGE. In rat neonatal cardiac myocyte cultures, S100B at concentrations > or = 50 nmol/L induced myocyte apoptosis, as evidenced by increased terminal DNA fragmentation, TUNEL, cytochrome c release from mitochondria to cytoplasm, phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p53, increased expression and activity of proapoptotic caspase-3, and decreased expression of antiapoptotic Bcl-2. Transfection of a full-length cDNA of RAGE or a dominant-negative mutant of RAGE resulted in increased or attenuated S100B-induced myocyte apoptosis, respectively. Inhibition of ERK1/2 by U0126/PD-98059 or overexpression of a dominant negative p53 comparably inhibited S100B-induced myocyte apoptosis.

CONCLUSIONS

These results suggest that interaction of RAGE and its ligand S100B after myocardial infarction may play a role in myocyte apoptosis by activating ERK1/2 and p53 signaling. This receptor-mediated mechanism is uniquely amenable to therapeutic intervention.

Epidermal growth factor competes with EGF receptor inhibitors to induce cell death in EGFR-overexpressing tumor cells

Epidermal growth factor receptor (EGFR) signaling plays an important role in cell growth and differentiation. Mutations in the EGFR gene and EGFR gene amplifications have been associated with increased responsiveness to selective EGFR tyrosine kinase inhibitors (EGFR-TKIs). By contrast, EGF may also stimulate apoptosis in tumor cells, depending on EGFR and Her2 (erbB-2) expression levels. In the present study, we investigated cellular responses after EGFR activation by EGF, or inhibition by cetuximab and gefitinib. EGF treatment induced a near-immediate increase in p38 MAPK phosphorylation together with inactivation of ERK1/2. In contrast, gefitinib- and cetuximab-induced phosphorylation of p38 MAPK was much delayed, and gefitinib also induced a delayed activation of ERK1/2. EGF induced progressive cell death of A431 cells with prolonged treatment, whereas cetuximab- or gefitinib-treated cells showed temporary growth arrest and subsequent re-growth. Moreover, in combination treatment experiments, cetuximab or gefitinib competitively inhibited EGF-induced cell death. Normal WI38-VA13 cells did not display any noticeable changes in cell proliferation in response to EGF, gefitinib or cetuximab. EGF-induced death signaling is apparently irreversible: EGF induced significant EGFR phosphorylation/internalization and activated caspase-3, -8 and -9, effects that were not observed in cetuximab- or gefitinib-treated cells. Collectively, these results indicate that EGF may be a more potent cytotoxic agent than EGFR blockers in EGFR-overexpressing cancer cells.

Dz13, a DNAzyme targeting c-jun, induces off-target cytotoxicity in endothelial cells with features of nonapoptotic programmed cell death

We have previously shown that Dz13, a catalytic DNA molecule (DNAzyme) designed against c-jun, is cytotoxic to nonquiescent cells by a mechanism independent of c-jun mRNA cleavage. In this report, we evaluated programmed cell death (PCD) pathways in order to gain further insight into the mechanism of action of Dz13. Using human dermal microvascular endothelial cells (HMEC-1), we found that Dz13-mediated cell death is characterized by mitochondrial depolarization, caspase-8 activation, lysosomal increase, and autophagosome formation. Classical DNA laddering and translocation of mitochondrial proteins were not observed. An array of inhibitors, including those targeting caspases, failed to abrogate cytotoxicity and mitochondrial depolarization. Cytotoxicity did not proceed from endoplasmic reticulum (ER) stress. The possible involvement of PARP-1 in Dz13-mediated cytotoxicity was indicated by its differential release as gauged by protein extraction data and its apparent binding to Dz13, as evidenced by protein pull-down experiments. This study on Dz13-mediated cytotoxicity presents a detailed investigation into the interplay of cell death effectors involved in apoptosis, autophagy, and necrosis, and demonstrates a novel form of oligonucleotide-mediated cytotoxicity with features of PCD.

Role of STAT3 as a negative regulator in Mac2- binding protein expression

BACKGROUND

Mac-2 binding protein (Mac-2BP) is a secreted glycoprotein from the culture fluid of several human cancer cells, especially breast, lung, and gastric cells. Mac-2BP plays a role in immune response and cell adhesion activity in patients with various cancer and infectious diseases. In this study, we attempted to identify the regulators of Mac-2BP expression at the transcriptional level.

METHODS

To determine the effect of epidermal growth factor (EGF) to Mac-2BP expression in gastric cancers, we constructed the different lengths of Mac-2BP promoter plasmids and measured the promoter activity and Mac-2BP expression. In addition to investigating the role of signal transducer and activator of transcription3 (STAT3) or human telomerase reverse transcriptase (hTERT) as a regulator of Mac-2BP, we transfected the small interfering RNA (siRNA) specific for STAT3 or hTERT, and Mac-2BP level was observed by a quantitative ELISA.

RESULTS

EGF treatment could suppress the Mac-2BP transcription in HEK293 or gastric cancer cell lines (SNU-638 or AGS). In 5'-deleted promoter experiment, pGL3-Mac Pro-2377 transfected cells showed a decreased luciferase activity compared to pGL3-Mac Pro-2277. We also identified that (-2,366/-2,356) on Mac-2BP promoter is a putative STAT3 binding site and suppression of STAT3 with STAT3 specific siRNA increased the Mac-2BP level, suggesting the role of STAT3 as a negative regulator, in contrast to hTERT, which is known as a positive regulator.

CONCLUSIONS

EGF signal is critical for the Mac-2BP expression, and more importantly, STAT3 could work as a negative regulator, while hTERT as a positive regulator in Mac-2BP transcription.

Thyroid hormone-mediated activation of the ERK/dual specificity phosphatase 1 pathway augments the apoptosis of GH4C1 cells by down-regulating nuclear factor-kappaB activity

Thyroid hormone (T3) plays a crucial role in processes such as cell proliferation and differentiation, whereas its implication on cellular apoptosis has not been well documented. Here we examined the effect of T3 on the apoptosis of GH4C1 pituitary cells and the mechanisms underlying this effect. We show that T3 produced a significant increase in apoptosis in serum-depleted conditions. This effect was accompanied by a decrease in nuclear factor-kappaB (NF-kappaB)-dependent transcription, IkappaBalpha phosphorylation, translocation of p65/NF-kappaB to the nucleus, phosphorylation, and transactivation. Moreover, these effects were correlated with a T3-induced decrease in the expression of antiapoptotic gene products, such as members of the inhibitor of apoptosis protein and Bcl-2 families. On the other hand, ERK but not c-Jun N-terminal kinase or MAPK p38, was activated upon exposure to T3, and inhibition of ERK alone abrogated T3-mediated apoptosis. In addition, T3 increased the expression of the MAPK phosphatase, dual specificity phosphatase 1 (DUSP1), in an ERK-dependent manner. Interestingly, the suppression of DUSP1 expression abrogated T3-induced inhibition of NF-kappaB-dependent transcription and p65/NF-kappaB translocation to the nucleus, as well as T3-mediated apoptosis. Overall, our results indicate that T3 induces apoptosis in rat pituitary tumor cells by down-regulating NF-kappaB activity through a mechanism dependent on the ERK/DUSP1 pathway.

Autophagic cell death induced by TrkA receptor activation in human glioblastoma cells

The neurotrophin receptor tropomyosin-related kinase A (TrkA) and its ligand nerve growth factor (NGF) are expressed in astrocytomas, and an inverse association of TrkA expression with malignancy grade was described. We hypothesized that TrkA expression might confer a growth disadvantage to glioblastoma cells. To analyze TrkA function and signaling, we transfected human TrkA cDNA into the human glioblastoma cell line G55. We obtained three stable clones, all of which responded with striking cytoplasmic vacuolation and subsequent cell death to NGF. Analyzing the mechanism of cell death, we could exclude apoptosis and cellular senescence. Instead, we identified several indications of autophagy: electron microscopy showed typical autophagic vacuoles; acridine orange staining revealed acidic vesicular organelles; acidification of acidic vesicular organelles was prevented using bafilomycin A1; cells displayed arrest in G2/M; increased processing of LC3 occurred; vacuolation was prevented by the autophagy inhibitor 3-methyladenine; no caspase activation was detected. We further found that both activation of ERK and c-Jun N-terminal kinase but not p38 were involved in autophagic vacuolation. To conclude, we identified autophagy as a novel mechanism of NGF-induced cell death. Our findings suggest that TrkA activation in human glioblastomas might be beneficial therapeutically, especially as several of the currently used chemotherapeutics also induce autophagic cell death.

Expression of cortical and hippocampal apoptosis-inducing factor (AIF) in aging and Alzheimer's disease

Apoptosis-inducing factor (AIF) is a mitochondrial oxidoreductase originally identified for its role in caspase-independent programmed cell death (PCD). In this study, we investigated AIF protein expression levels in frontal and temporal cortices of normal subjects of various ages, as well as in subjects with Alzheimer's disease (AD). AIF levels were also measured in the hippocampus of age-matched elderly and AD subjects. Amounts of all three AIF isoforms increased significantly with age in both cortical areas. Interestingly, AIF expression levels in the cortex (but not hippocampus) were consistently lower in AD compared to age-matched controls. The up-regulation of cortical AIF in normal aging is consistent with its previously hypothesized role as a free radical scavenger, and may thus represent an adaptive cellular response to compensate for the steady increase in oxidative stress occurring with age.

Epidermal growth factor can induce apoptosis in neuroblastoma

BACKGROUND/PURPOSE

In previous studies, incubation of doxorubicin-resistant neuroblastoma SK-N-SH (Dox-R) cells with epidermal growth factor (EGF) decreased extracellular signal-regulated kinase activation. Because extracellular signal-regulated kinase activation is associated with cell proliferation, we hypothesized that EGF could induce apoptosis and decrease the rate of cell growth in these cells.

METHODS

The growth of wild-type (WT) SK-N-SH and Dox-R cells after incubation with EGF concentrations ranging from 1 to 100 ng/mL was determined by a colorimetric assay. Apoptosis was assessed by Hoechst staining and DNA laddering in WT, Dox-R, and cisplatin-resistant cells treated with EGF (100 ng/mL). Cleaved caspase-3 and EGF receptor (human epidermal growth factor receptor [HER1-HER4]) expression were verified by Western blot and reverse transcriptase-polymerase chain reaction.

RESULTS

Epidermal growth factor decreased WT cell growth at concentrations between 50 and 100 ng/mL; Dox-R cell growth was attenuated at all EGF concentrations. Apoptosis was observed in WT and Dox-R cells incubated with EGF. Maximal cleaved caspase-3 expression occurred in WT cells treated with EGF 100 ng/mL and in Dox-R treated with EGF 5 to 10 ng/mL. Epidermal growth factor did not induce apoptosis in cisplatin-resistant cells. HER2 and HER3 transcription was maximal in WT and Dox-R cells, respectively.

CONCLUSIONS

Wild-type and Dox-R cells exhibited decreased cell growth after EGF treatment because of apoptosis. This involved caspase-3 activation and could work through HER2 and HER3 receptors.

Apoptosis-inducing factor: A matter of neuron life and death

The mitochondrial flavoprotein apoptosis-inducing factor (AIF) is the main mediator of caspase-independent apoptosis-like programmed cell death. Upon pathological permeabilization of the outer mitochondrial membrane, AIF is translocated to the nucleus, where it participates in chromatin condensation and is associated to large-scale DNA fragmentation. Heavy down-regulation of AIF expression in mutant mice or reduced AIF expression achieved with small interfering RNA (siRNA) provides neuroprotection against acute neurodegenerative insults. Paradoxically, in addition to its pro-apoptotic function, AIF likely plays an anti-apoptotic role by regulating the production of reactive oxygen species (ROS) via its putative oxidoreductase and peroxide scavenging activities. In this review, we discuss accumulating evidence linking AIF to both acute and chronic neurodegenerative processes by emphasising mechanisms underlying the dual roles apparently played by AIF in these processes.

A novel paraptosis pathway involving LEI/L-DNaseII for EGF-induced cell death in somato-lactotrope pituitary cells

We have recently reported that EGF triggers an original form of cell death in pituitary cell line (GH4C1) with a phenotype sharing some characteristics of both apoptosis (internucleosomal DNA fragmentation) and paraptosis (caspase-independence and cytoplasmic vacuolization). However, the endonuclease involved in EGF-induced DNA fragmentation has not been assessed so far. In the present work we therefore further explored the putative paraptosis involvement in EGF-induced cell death and asked whether L-DNaseII might be involved. Indeed, this endonuclease is known to mediate internucleosomal DNA fragmentation in caspase independent manner. Our Western blot, immunocytochemistry and enzymatic measurement assays show that EGF triggers a cleavage of Leukocyte Elastase Inhibitor (LEI) precursor into L-DNaseII, its subsequent enzymatic activation and nuclear translocation thus pointing to the involvement of this endonuclease pathway in caspase-independent DNA fragmentation. In addition, EGF-induced cell death can be blocked by paraptosis inhibitor AIP-1/Alix, but not with its anti-apoptotic C-terminal fragment (Alix-CT). Altogether these data suggest that EGF-induced cell death defines a novel, L-DNaseII-mediated form of paraptosis.

Novel permissive role of epidermal growth factor in transforming growth factor beta (TGF-beta) signaling and growth suppression. Mediation by stabilization of TGF-beta receptor type II

Transforming growth factor beta (TGF-beta) signals through TGF-beta receptor serine/threonine kinases (TbetaRI and TbetaRII) and Smads, regulating cell growth and apoptosis. Although loss of TGF-beta receptor levels is strongly selected for during the progression of most cancers, tumor cells frequently escape from complete loss of TGF-beta receptors through unknown mechanisms. Here, we provide the first evidence that epidermal growth factor (EGF) signaling, which is generally enhanced in cancer, is permissive for regulation of gene expression and growth suppression by TGF-beta in LNCaP prostate adenocarcinoma cells. Our results support that these permissive effects occur through enhanced stability of TbetaRII mRNA and reversal of TGF-beta-mediated TbetaRII mRNA loss. Changes in stability of TbetaRII mRNA occur soon after EGF or TGF-beta1 addition (optimal within 3 h) and are independent of de novo protein synthesis or transcription. Remarkably, such loss of TbetaRII by TGF-beta can be mediated by a kinase-dead TbetaRII (K277R), as well as by other forms of this receptor harboring mutations at prominent autophosphorylation sites. Moreover, Smad3 small interfering RNA, which blocks TGF-beta-induced AP-1 promoter activity, does not block changes in the expression of TbetaRII by EGF or TGF-beta. We have also shown that changes in TbetaRII levels by EGF are EGF receptor-kinase-dependent and are controlled by signals downstream of MEK1/2. Our findings provide invaluable insights on the role of the EGF receptor-kinase in enhancing TGF-beta responses during prostate carcinogenesis.

Bax activation and translocation to mitochondria mediate EGF-induced programmed cell death

The ErbB family of receptor tyrosine kinases is involved in the regulation of cell proliferation, differentiation and apoptosis. Previous studies indicate that cells expressing elevated levels of the EGFR and ErbB-2 undergo programmed cell death in response to EGF or other EGFR ligands. However, the detailed mechanisms of EGF-induced apoptosis are unclear. This report demonstrates that in the cells undergoing EGF-dependent apoptosis Bax changes its conformation and forms multimeric aggregates, which accumulate on the mitochondrial membrane. Bax activation and translocation to the mitochondria induces a loss of mitochondrial transmembrane potential and cell death. Also, during EGF-induced apoptosis there is downregulation of Bcl-xL, an anti-apoptotic protein. Expression of Bcl-xL in cells susceptible to EGF-dependent apoptosis prevents cell death. The data indicate that addition of EGF does not result in a significant release of cytochrome c from mitochondria and EGF-induced apoptosis is mainly caspase independent.