A serine protease is involved in the initiation of DNA damage-induced apoptosis

A Novel Paclitaxel Derivative for Triple-Negative Breast Cancer Chemotherapy

Paclitaxel-triethylenetetramine hexaacetic acid conjugate (PTX-TTHA), a novel semi-synthetic taxane, is designed to improve the water solubility and cosolvent toxicity of paclitaxel in several aminopolycarboxylic acid groups. In this study, the in vitro and in vivo antitumor effects and mechanisms of PTX-TTHA against triple-negative breast cancer (TNBC) and its intravenous toxicity were evaluated. Results showed the water solubility of PTX-TTHA was greater than 5 mg/mL, which was about 7140-fold higher than that of paclitaxel (<0.7 µg/mL). PTX-TTHA (10-10⁵ nmol/L) could significantly inhibit breast cancer proliferation and induce apoptosis by stabilizing microtubules and arresting the cell cycle in the G2/M phase in vitro, with its therapeutic effect and mechanism similar to paclitaxel. However, when the MDA-MB-231 cell-derived xenograft (CDX) tumor model received PTX-TTHA (13.73 mg/kg) treatment once every 3 days for 21 days, the tumor inhibition rate was up to 77.32%. Furthermore, PTX-TTHA could inhibit tumor proliferation by downregulating Ki-67, and induce apoptosis by increasing pro-apoptotic proteins (Bax, cleaved caspase-3) and TdT-mediated dUTP nick end labeling (TUNEL) positive apoptotic cells, and reducing anti-apoptotic protein (Bcl-2). Moreover, PTX-TTHA demonstrated no sign of acute toxicity on vital organs, hematological, and biochemical parameters at the limit dose (138.6 mg/kg, i.v.). Our study indicated that PTX-TTHA showed better water solubility than paclitaxel, as well as comparable in vitro and in vivo antitumor activity in TNBC models. In addition, the antitumor mechanism of PTX-TTHA was related to microtubule regulation and apoptosis signaling pathway activation.

A serine protease inhibitor camostat mesilate prevents podocyte apoptosis and attenuates podocyte injury in metabolic syndrome model rats

Metabolic syndrome (MetS) is associated with chronic kidney disease and proteinuria. Previously, we reported that a synthetic serine protease inhibitor, camostat mesilate (CM), mitigated hypertension and proteinuria in rodent disease models. The present study evaluated the anti-hypertensive and anti-proteinuric effects of CM in MetS model rats (SHR/ND mcr-cp). Rats were divided into normal salt-fed (NS), high salt-fed (HS), HS and CM-treated (CM), and HS and hydralazine-treated (Hyd) groups. Rats were sacrificed after four weeks of treatment. Severe hypertension and proteinuria were observed in the HS group. Although CM and Hyd equally alleviated hypertension, CM suppressed proteinuria and glomerular sclerosis more efficiently than Hyd. The HS group revealed a decrease in podocyte number and podocyte-specific molecules, together with an increase in glomerular apoptotic cells and apoptosis-related proteins in the kidney. These changes were significantly attenuated by CM, but not by Hyd. Furthermore, CM ameliorated the apoptotic signals in murine cultured podocytes stimulated with the high glucose and aldosterone medium. In conclusion, CM could exert renoprotective effects in MetS model rats, together with the inhibition of podocyte apoptosis. Our study suggests that serine protease inhibition may become a new therapeutic strategy against MetS-related hypertension and renal injuries.

Synthesis and antitumor potential of new arylidene ursolic acid derivatives via caspase-8 activation

Continuing our studies on NO-donating ursolic acid-benzylidene derivatives as potential antitumor agents, we designed and synthesized a series of new arylidene derivatives containing NO-donating ursolic acid and aromatic heterocyclic units. Compounds 5c and 6c showed a significant broad-spectrum antitumor activity. Compound 5c exhibited nearly three- to nine-fold higher cytotoxicity as compared with the parent drug in A549, MCF-7, HepG-2, HT-29, and HeLa cells, and it was also found to be the most potent apoptosis inducer of MCF-7 cells. More importantly, compound 5c arrested the MCF-7 cell cycle in the G1 phase, which was associated with caspase activation and a decrease of the Bcl-2/Bax ratio. Meanwhile, compound 5c caused changes in morphological features, dissipation of the mitochondrial membrane potential, and accumulation of reactive oxygen species. A docking study revealed that the nitroxyethyl moiety of compound 5c may form hydrogen bonds with caspase-8 amino acid residues (SER256 and HIS255). Together, these data suggest that NO-donating ursolic acid-arylidene derivatives are potent apoptosis inducers in tumor cells.

Larrea tridentata Extract Mitigates Oxidative Stress-Induced Cytotoxicity in Human Neuroblastoma SH-SY5Y Cells

Creosote bush (Larrea tridentata; LT) leaves extracts were tested for their potential efficacy to mitigate cellular oxidative stress on human SH-SY5Y cells. Here, the differential nuclear staining assay, a bioimager system, and flow cytometric protocols, concurrently with several specific chemicals, were used to measure the percentage of cell viability and several facets implicated in the cytoprotective mechanism of LT extracts. Initially, three LT extracts, prepared with different solvents, ethanol, ethanol:water (e/w), and water, were tested for their capacity to rescue the viability of cells undergoing aggressive H₂O₂-induced oxidative stress. Results indicate that the LT extract prepared with a mixture of ethanol:water (LT-e/w; 60:40% v/v) displayed the most effective cytoprotection rescue activity. Interestingly, by investigating the LT-e/w mechanism of action, it was found that LT-e/w extract decreases the levels of H₂O₂-provoked reactive oxidative species (ROS) accumulation, mitochondrial depolarization, phosphatidylserine externalization, caspase-3/7 activation, and poly (ADP-ribose) polymerase (PARP) cleavage significantly, which are hallmarks of apoptosis. Thus, out of the three LT extracts tested, our findings highlight that the LT-e/w extract was the most effective protective reagent on SH-SY5Y cells undergoing oxidative stress in vitro, functioning as a natural anti-apoptotic extract. These findings warrant further LT-e/w extract examination in a holistic context.

Gene Co-expression Analysis Indicates Potential Pathways and Regulators of Beef Tenderness in Nellore Cattle

Beef tenderness, a complex trait affected by many factors, is economically important to beef quality, industry, and consumer’s palatability. In this study, RNA-Seq was used in network analysis to better understand the biological processes that lead to differences in beef tenderness. Skeletal muscle transcriptional profiles from 24 Nellore steers, selected by extreme estimated breeding values (EBVs) for shear force after 14 days of aging, were analyzed and 22 differentially expressed transcripts were identified. Among these were genes encoding ribosomal proteins, glutathione transporter ATP-binding cassette, sub-family C (CFTR/MRP), member 4 (ABCC4), and synaptotagmin IV (SYT4). Complementary co-expression analyses using Partial Correlation with Information Theory (PCIT), Phenotypic Impact Factor (PIF) and the Regulatory Impact Factor (RIF) methods identified candidate regulators and related pathways. The PCIT analysis identified ubiquitin specific peptidase 2 (USP2), growth factor receptor-bound protein 10 (GBR10), anoctamin 1 (ANO1), and transmembrane BAX inhibitor motif containing 4 (TMBIM4) as the most differentially hubbed (DH) transcripts. The transcripts that had a significant correlation with USP2, GBR10, ANO1, and TMBIM4 enriched for proteasome KEGG pathway. RIF analysis identified microRNAs as candidate regulators of variation in tenderness, including bta-mir-133a-2 and bta-mir-22. Both microRNAs have target genes present in the calcium signaling pathway and apoptosis. PIF analysis identified myoglobin (MB), enolase 3 (ENO3), and carbonic anhydrase 3 (CA3) as potentially having fundamental roles in tenderness. Pathways identified in our study impacted in beef tenderness included: calcium signaling, apoptosis, and proteolysis. These findings underscore some of the complex molecular mechanisms that control beef tenderness in Nellore cattle.

RNA-seq based transcriptional analysis reveals dynamic genes expression profiles and immune-associated regulation under heat stress in Apostichopus japonicus

In this study, we explored the gene expression profiles in Apostichopus japonicus under continuous heat stress (6 h, 48 h and 192 h) by applying RNA-seq technique. A total of 676, 1010 and 1083 differentially expressed genes were detected at three heat stress groups respectively, which suggested complex regulation of various biological processes. Then we focused on the changing of immune system under HS in sea cucumbers. Key immune-associated genes were involved in heat stress response, which were classified into six groups: heat shock proteins, transferrin superfamily members, effector genes, proteases, complement system, and pattern recognition receptors and signaling. Moreover, the mRNA expression of the immune-associated genes were validated by the real time PCR. Our results showed that an immunological strategy in this species was developed to confront abrupt elevated temperatures in the environment.

Cytotoxicity and genotoxicity of triethyleneglycol-dimethacrylate in macrophages involved in DNA damage and caspases activation

Triethyleneglycol-dimethacrylate (TEGDMA) is a monomer and widely used in dental composite resins. TEGDMA has been found to exhibit cytotoxicity and genotoxicity on many cells. However, little is known about the potential toxicological implications of TEGDMA on murine macrophage cell line RAW264.7. In this study, TEGDMA demonstrated a cytotoxic effect to RAW264.7 cells in a concentration- and time-dependent manner (p < 0.05). TEGDMA was found to induce two modes of cell death in a concentration-dependent manner (p < 0.05). TEGDMA-induced cell apoptosis was demonstrated by the increase in the portion of sub-G0/G1 phase and DNA ladder formation. In addition, TEGDMA exhibited genotoxicity via a dose-related increase in the numbers of micronucleus and DNA strand breaks (p < 0.05). Furthermore, the activation of caspase-3, -8, and -9 were generated by TEGDMA in a dose-dependent manner (p < 0.05). These results indicated that cytotoxicity and genotoxicity induced by TEGDMA in macrophages may be via DNA damage and caspase activation.

Heat-modified citrus pectin induces apoptosis-like cell death and autophagy in HepG2 and A549 cancer cells

Cancer is still one of the leading causes of death worldwide, and finding new treatments remains a major challenge. Previous studies showed that modified forms of pectin, a complex polysaccharide present in the primary plant cell wall, possess anticancer properties. Nevertheless, the mechanism of action of modified pectin and the pathways involved are unclear. Here, we show that citrus pectin modified by heat treatment induced cell death in HepG2 and A549 cells. The induced cell death differs from classical apoptosis because no DNA cleavage was observed. In addition, Z-VAD-fmk, a pan-caspase inhibitor, did not influence the observed cell death in HepG2 cells but appeared to be partly protective in A549 cells, indicating that heat-modified citrus pectin might induce caspase-independent cell death. An increase in the abundance of the phosphatidylethanolamine-conjugated Light Chain 3 (LC3) protein and a decrease in p62 protein abundance were observed in both cell types when incubated in the presence of heat-modified citrus pectin. These results indicate the activation of autophagy. To our knowledge, this is the first time that autophagy has been revealed in cells incubated in the presence of a modified form of pectin. This autophagy activation appears to be protective, at least for A549 cells, because its inhibition with 3-methyladenine increased the observed modified pectin-induced cytotoxicity. This study confirms the potential of modified pectin to improve chemotherapeutic cancer treatments.

Doubly chloro bridged dimeric copper(ii) complex: magneto-structural correlation and anticancer activity

A doubly chloro bridged dinuclear copper(ii) complex was synthesized and magneto-structural correlation was drawn.The complex exhibits promising anticancer activity in HepG2 cells.

CHK1 cleavage in programmed cell death is intricately regulated by both caspase and non-caspase family proteases

BACKGROUND

CHK1 is an important effector kinase that regulates the cell cycle checkpoint. Previously, we showed that CHK1 is cleaved in a caspase (CASP)-dependent manner during DNA damage-induced programmed cell death (PCD) and have examined its physiological roles.

METHODS AND RESULTS

In this study, we investigated the behavior of CHK1 in PCD. Firstly, we found that CHK1 is cleaved at three sites in PCD, and all cleavages were inhibited by the co-treatment of a pan-CASP inhibitor or serine protease inhibitors. We also showed that CHK1 is cleaved by CASP3 and/or CASP7 recognizing at (296)SNLD(299) and (348)TCPD(351), and that the cleavage results in the enhancement of CHK1 kinase activity. Furthermore, as a result of the characterization of cleavage sites by site-directed mutagenesis and an analysis performed using deletion mutants, we identified (320)EPRT(323) as an additional cleavage recognition sequence. Considering the consensus sequence cleaved by CASP, it is likely that CHK1 is cleaved by non-CASP family protease(s) recognizing at (320)EPRT(323). Additionally, the cleavage catalyzed by the (320)EPRT(323) protease(s) markedly and specifically increased when U2OS cells synchronized into G1 phase were induced to PCD by cisplatin treatment.

CONCLUSION

CHK1 cleavage is directly and indirectly regulated by CASP and non-CASP family proteases including serine protease(s) and the "(320)EPRT(323) protease(s)." Furthermore, (320)EPRT(323) cleavage of CHK1 occurs efficiently in PCD which is induced at the G1 phase by DNA damage.

GENERAL SIGNIFICANCE

CASP and non-CASP family proteases intricately regulate cleavage for up-regulation of CHK1 kinase activity during PCD.

Murine but not human basophil undergoes cell-specific proteolysis of a major endoplasmic reticulum chaperone

Introduction

Basophil has been implicated in anti-parasite defense, allergy and in polarizing T_H2 response. Mouse model has been commonly used to study basophil function although the difference between human and mouse basophils is underappreciated. As an essential chaperone for multiple Toll-like receptors and integrins in the endoplasmic reticulum, gp96 also participates in general protein homeostasis and in the ER unfolded protein response to ensure cell survival during stress. The roles of gp96 in basophil development are unknown.

Methods

We genetically delete gp96 in mice and examined the expression of gp96 in basophils by Western blot and flow cytometry. We compared the expression pattern of gp96 between human and mouse basophils.

Results

We found that gp96 was dispensable for murine basophil development. Moreover, gp96 was cleaved by serine protease(s) in murine but not human basophils leading to accumulation of a nun-functional N-terminal ∼50 kDa fragment and striking induction of the unfolded protein response. The alteration of gp96 was unique to basophils and was not observed in any other cell types including mast cells. We also demonstrated that the ectopic expression of a mouse-specific tryptase mMCP11 does not lead to gp96 cleavage in human basophils.

Conclusions

Our study revealed a remarkable biochemical event of gp96 silencing in murine but not human basophils, highlighting the need for caution in using mouse models to infer the function of basophils in human immune response. Our study also reveals a novel mechanism of shutting down gp96 post-translationally in regulating its function.

Cloning and characterization of a trypsin-like serine protease gene, a novel regeneration-related gene from Apostichopus japonicus

Trypsin-like serine protease (TLS) plays an important role in many physiological processes including wound healing, phlogosis reaction, blood clotting, regeneration etc. In this paper, a 1216 bp full-length cDNA sequence of TLS including 39 bp 5' UTR and 355 bp 3'UTR coding for a theoretical 273 amino acids protein was cloned from Apostichopus japonicus by means of the RACE technique for the first time. Bioinformatic analysis revealed that the gene with a 20 residues N-terminal signal peptide and a conserved C-terminal domain belongs to the trypsin-like serine protease superfamily. His78, Asp130 and Ser223 are the principal residues of the catalytic center. In-situ hybridization (ISH) analysis revealed that the TLS gene was widely distributed in different tissues. The expression patterns during different regeneration stages of the TLS gene in the body wall, intestine and respiratory trees were investigated using real-time quantitative PCR. The results show that there was a remarkable and temporary up-regulation of TLS gene expression in the body wall within 1h and subsequent down-regulation of TLS similar to intestine and respiratory trees. With the recovery of tissues, the expression level of the TLS gene was gradually up-regulated and finally reached normal levels. TLS was regulated during different regeneration stages suggesting that TLS is important in the regeneration process of A. japonicus.

Removal of uracil by uracil DNA glycosylase limits pemetrexed cytotoxicity: overriding the limit with methoxyamine to inhibit base excision repair

Uracil DNA glycosylase (UDG) specifically removes uracil bases from DNA, and its repair activity determines the sensitivity of the cell to anticancer agents that are capable of introducing uracil into DNA. In the present study, the participation of UDG in the response to pemetrexed-induced incorporation of uracil into DNA was studied using isogenic human tumor cell lines with or without UDG (UDG(+/+)/UDG(-/-)). UDG(-/-) cells were very sensitive to pemetrexed. Cell killing by pemetrexed was associated with genomic uracil accumulation, stalled DNA replication, and catastrophic DNA strand breaks. By contrast, UDG(+/+) cells were >10 times more resistant to pemetrexed due to the rapid removal of uracil from DNA by UDG and subsequent repair of the resultant AP sites (abasic sites) via the base excision repair (BER). The resistance to pemetrexed in UDG(+/+) cells could be reversed by the addition of methoxyamine (MX), which binds to AP sites and interrupts BER pathway. Furthermore, MX-bound AP sites induced cell death was related to their cytotoxic effect of dual inactivation of UDG and topoisomerase IIα, two genes that are highly expressed in lung cancer cells in comparison with normal cells. Thus, targeting BER-based therapy exhibits more selective cytotoxicity on cancer cells through a synthetic lethal mechanism.

The role of SPINK5 in asthma related physiological events in the airway epithelium

BACKGROUND

Genetic studies have shown that variants in SPINK5 may be associated with atopic diseases and asthma. However, the functional role of SPINK5 protein in asthma has not been elucidated.

OBJECTIVES

To determine the effects of SPINK5 on asthma related physiological events such as apoptosis, mucus and cytokine production by epithelial cells.

METHODS

A549 cells were transfected with SPINK5 expression vector and stimulated with increasing doses of hydrogen peroxide and neutrophil elastase (NE) for measurement of cell viability or apoptosis and analysis of mucus production. Cell viability was measured by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5- diphenyl-tetrazolium bromide) assay and apoptosis by Annexin V/PI staining. Levels of IL-4, IL-6, IL-8, IL-12, IL-13, IFNγ, IL-1β and RANTES were determined by ELISA in cell culture supernatants. Mucus production was determined by RT-PCR of the MUC5AC gene and PAS staining in NE treated cells.

RESULTS

Epithelial cells transfected with SPINK5 expression vector produced more IL-6, IL-8 and RANTES compared to non-transfected cells (p < 0.001, p = 0.003, p < 0.001, respectively). Even though cells transfected with SPINK5 vector displayed significantly higher cell death, we have not observed any clear effect of SPINK5 on apoptosis. PAS staining showed that SPINK5 slightly decreased the mucin production induced by neutrophil elastase in A549 cells. However, SPINK5 had no effect on MUC5AC transcription.

CONCLUSION

SPINK5 is an important molecule in asthma. Its role extends beyond its well known protease inhibitor properties.

Blockade of Caspase-2 Activity Inhibits Ischemia/Reperfusion-Induced Mitochondrial Reactive Oxygen Burst and Cell Death in Cardiomyocytes

We previously showed that initiator caspases-2 and −8 are prominently activated in ischemia/reperfusion (I/R)-induced injury in cardiomyocytes, but while blockade of caspase-2 activity enhanced cell survival, blockade of caspase-8 activity did not protect cardiomyocytes. Because apoptotic death in these cells is characterized by a burst of reactive oxygen species (ROS) at reperfusion and their survival by inhibition of this burst, we examined the effects of blocking caspase-2 and caspase-8 activities on ROS production. Caspase-2 inhibition blocked the reperfusion-induced ROS burst, while inhibition of caspase-8 did not. We also examined effects of caspase inhibition on mitochondrial membrane potential (ΔΨm) and mitochondrial function and found that blocking caspase-2, but not caspase-8, allowed recovery of ΔΨm and mitochondrial functionality. Furthermore, knockdown of caspase-2 by small-interfering (si)RNA confirmed caspase-2 participation in cytochrome c release, which correlates with loss of ΔΨm and cell death in these cardiomyocytes.

Effects of the Fas/Fas-L pathway on fluoride-induced apoptosis in SH-SY5Y cells

The mechanisms underlying fluoride-induced apoptosis in neurons still remain unknown. To investigate apoptosis, caspase-3 activity, and mRNA expression of Fas, Fas-L, and caspases (-3 and -8) induced by fluoride, human neuroblastoma (SH-SY5Y) cells were incubated with 0, 20, 40, and 80 mg/L sodium fluoride (NaF) for 24 h in vitro. The data show that cell viability in the 40 and 80 mg/L fluoride groups were significantly lower than that of the control group. The percentages of apoptosis in the 40 and 80 mg/L fluoride groups were markedly higher than those in the control group, and they increased with the increase in fluoride concentration. The activity of caspase-3 and mRNA expression levels for Fas, Fas-L, and caspases (-3 and -8) in the 40 and 80 mg/L fluoride groups were significantly higher than those in the control group. An agonistic anti-Fas monoclonal antibody (CH-11) significantly augmented apoptosis induction by fluoride, showing a synergistic effect, while a Fas-blocking antibody (ZB4) partly inhibited fluoride-induced apoptosis of SH-SY5Y cells. The results indicate that fluoride exposure could induce apoptosis in SH-SY5Y cells, and the Fas/Fas-L signaling pathway may play an important role in the process.

Non-caspase proteases: triggers or amplifiers of apoptosis?

Caspases are the most important effectors of apoptosis, the major form of programmed cell death (PCD) in multicellular organisms. This is best reflected by the appearance of serious development defects in mice deficient for caspase-8, -9, and -3. Meanwhile, caspase-independent PCD, mediated by other proteases or signaling components has been described in numerous publications. Although we do not doubt that such cell death exists, we propose that it has evolved later during evolution and is most likely not designed to execute, but to amplify and speed-up caspase-dependent cell death. This review shall provide evidence for such a concept.

Okadaic acid induces DNA fragmentation via caspase-3-dependent and caspase-3-independent pathways in Chinese hamster ovary (CHO)-K1 cells

DNA fragmentation is a hallmark of apoptosis that occurs in a variety of cell types; however, it remains unclear whether caspase-3 is required for its induction. To investigate this, we produced caspase-3 knockout Chinese hamster ovary (CHO)-K1 cells and examined the effects of gene knockout and treatment with caspase-3 inhibitors. Okadaic acid (OA) is a potent inhibitor of the serine/threonine protein phosphatases (PPs) PP1 and PP2A, which induce apoptotic cellular reactions. Treatment of caspase-3(-/-) cells with OA induced DNA fragmentation, indicating that caspase-3 is not an essential requirement. However, in the presence of benzyloxycarbonyl-Asp-Glu-Val-Asp (OMe) fluoromethylketone (z-DEVD-fmk), DNA fragmentation occurred in CHO-K1 cells but not in caspase-3(-/-) cells, suggesting that caspase-3 is involved in OA-induced DNA fragmentation that does not utilize DEVDase activity. In the absence of caspase-3, DEVDase activity may play an important role. In addition, OA-induced DNA fragmentation was reduced but not blocked in CHO-K1 cells, suggesting that caspase-3 is involved in caspase-independent OA-induced DNA fragmentation. Furthermore, OA-induced cleavage of caspase-3 and DNA fragmentation were blocked by pretreatment with the wide-ranging serine protease inhibitor 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride. These results suggest that serine proteases regulate DNA fragmentation upstream of caspase-3.

Hepatitis B and hepatitis C virus replication upregulates serine protease inhibitor Kazal, resulting in cellular resistance to serine protease-dependent apoptosis

Hepatitis B and C viruses (HBV and HCV, respectively) are different and distinct viruses, but there are striking similarities in their disease potential. Infection by either virus can cause chronic hepatitis, liver cirrhosis, and ultimately, liver cancer, despite the fact that no pathogenetic mechanisms are known which are shared by the two viruses. Our recent studies have suggested that replication of either of these viruses upregulates a cellular protein called serine protease inhibitor Kazal (SPIK). Furthermore, the data have shown that cells containing HBV and HCV are more resistant to serine protease-dependent apoptotic death. Since our previous studies have shown that SPIK is an inhibitor of serine protease-dependent apoptosis, it is hypothesized that the upregulation of SPIK caused by HBV and HCV replication leads to cell resistance to apoptosis. The evasion of apoptotic death by infected cells results in persistent viral replication and constant liver inflammation, which leads to gradual accumulation of genetic changes and eventual development of cancer. These findings suggest a possibility by which HBV and HCV, two very different viruses, can share a common mechanism in provoking liver disease and cancer.

Mechanistic insight into taxol-induced cell death

We analysed the involvement of proteases during taxol-mediated cell death of human A549 non-small-cell lung carcinoma cells using a proteomics approach that specifically targets protein N termini and further detects newly formed N termini that are the result of protein processing. Our analysis revealed 27 protease-mediated cleavages, which we divided in sites C-terminal to aspartic acid (Asp) and sites C-terminal to non-Asp residues, as the result of caspase and non-caspase protease activities, respectively. Remarkably, some of the former were insensitive to potent pancaspase inhibitors, and we therefore suggest that previous inhibitor-based studies that report on the caspase-independent nature of taxol-induced cell death should be judged with care. Furthermore, many of the sites C-terminal to non-Asp residues were also uniquely observed in a model of cytotoxic granule-mediated cell death and/or found by in vitro cataloging human mu-calpain substrates using a similar proteomics technique. This thus raises the hypothesis that killing tumor cells by chemotherapy or by immune cells holds similar non-Asp-specific proteolytic components with strong indications to calpain activity.

An endogenous calcium-dependent, caspase-independent intranuclear degradation pathway in thymocyte nuclei: antagonism by physiological concentrations of K(+) ions

Calcium ions have been implicated in apoptosis for many years, however the precise role of this ion in the cell death process remains incomplete. We have extensively examined the role of Ca(2+) on nuclear degradation in vitro using highly purified nuclei isolated from non-apoptotic rat thymocytes. We show that these nuclei are devoid of CAD (caspase-activated DNase), and DNA degradation occurs independent of caspase activity. Serine proteases rather than caspase-3 appear necessary for this Ca(2+) -dependent DNA degradation in nuclei. We analyzed nuclei treated with various concentrations of Ca(2+) in the presence of both a physiological (140 mM) and apoptotic (40 mM) concentration of KCl. Our results show that a 5-fold increase in Ca(2+) is required to induce DNA degradation at the physiological KCl concentration compared to the lower, apoptotic concentration of the cation. Ca(2+) -induced internucleosomal DNA degradation was also accompanied by the release of histones, however the apoptotic-specific phosphorylation of histone H2B does not occur in these isolated nuclei. Interestingly, physiological concentrations of K(+) inhibit both Ca(2+) -dependent DNA degradation and histone release suggesting that a reduction of intracellular K(+) is necessary for this apoptosis-associated nuclear degradation in cells. Together, these data define an inherent caspase-independent catabolic pathway in thymocyte nuclei that is sensitive to physiological concentrations of intracellular cations.

The AF4-mimetic peptide, PFWT, induces necrotic cell death in MV4-11 leukemia cells

Despite ongoing success in the treatment of childhood acute lymphoblastic leukemia, patients harboring translocations involving the MLL gene at chromosome 11q23 remain resistant to treatment. To improve outcomes, novel therapeutics designed to target the unusual biology of these leukemias need to be developed. Previously, we identified an interaction between the two most common MLL fusion proteins, AF4 and AF9, and designed a synthetic peptide (PFWT) capable of disrupting this interaction. PFWT induced cell death in leukemia cells expressing MLL-AF4 with little effect on the colony forming potential of hematopoietic progenitor cells, suggesting the AF4-AF9 complex is an important pharmacological target for leukemia therapy and PFWT is a promising chemotherapeutic prototype. In these studies, we demonstrate that PFWT induces death by necrosis in MV4-11 cells. Cell death is characterized by rapid loss of plasma membrane integrity with maintenance of nuclear membrane integrity, and is independent of caspase activation, DNA fragmentation, and mitochondrial membrane depolarization. PFWT-mediated necrosis is inhibited by the serine protease inhibitor TLCK, suggesting this death pathway is regulated. Given the resistance of t(4;11) leukemias to conventional chemotherapeutic agents that induce apoptosis, further identification of the molecular events mediating this death process should uncover new avenues for therapeutic intervention.

A single intrauterine injection of the serine protease inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride reversibly inhibits embryo implantation in mice

BACKGROUND

The study was conducted to investigate the inhibitory effect of 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF) on embryo implantation in mice with a view to identifying whether it might be a suitable agent for postcoital contraception.

STUDY DESIGN

The anti-implantation efficacy of AEBSF was determined by counting the number of visible implanted embryos on Day 8 of pregnancy following a single intrauterine injection of AEBSF at doses of 30, 300 and 3000 microg per mouse uterine horn on Day 3 of pregnancy. The reversibility of the inhibitory effect of AEBSF on implantation was further evaluated by observing the outcome of a subsequent pregnancy without AEBSF treatment.

RESULTS

A dose-dependent inhibitory effect of AEBSF on embryo implantation in vivo was observed. Morphological analysis revealed no significant cytotoxicity of AEBSF on the mouse uterine epithelia. Furthermore, the anti-implantation effect of AEBSF was reversible.

CONCLUSION

Intrauterine administration of AEBSF at an appropriate dose might provide a basis for the development of novel contraception.

Effects of fluoride on the expression of NCAM, oxidative stress, and apoptosis in primary cultured hippocampal neurons

The mechanisms underlying the neurotoxicity of endemic fluorosis still remain unknown. To investigate the expression level of neural cell adhesion molecules (NCAM), oxidative stress, and apoptosis induced by fluoride, the primary rat hippocampal neurons were incubated with 20, 40, and 80 mg/l sodium fluoride for 24 h in vitro. The results showed that the cell survival rate in the 80 mg/l fluoride-treated group was significantly lower than that of the control group. Forty and 80 mg/l of fluoride induced significantly increased lactate dehydrogenase release, intracellular reactive oxygen species, and the percentage of apoptosis. Compared with control group, the malondialdehyde levels were significantly elevated while glutathione levels and glutathione peroxidase activities were decreased in all fluoride-treated groups, accompanied by the markedly reduced superoxide dismutase activity in 80 mg/l fluoride-treated group. With respect to NCAM mRNA expression levels, a significant dose-dependent decrease was observed in 40 and 80 mg/l fluoride-treated groups against the control group. In addition, as compared to the control group, the protein expression levels of NCAM-180 in 40 and 80 mg/l fluoride-treated groups, NCAM-140 in all fluoride-treated groups, and NCAM-120 in the 80 mg/l fluoride-treated group were significantly decreased. Our study herein suggested that fluoride could cause oxidative stress, apoptosis, and decreased mRNA and protein expression levels of NCAM in rat hippocampal neurons, contributing to the neurotoxicity induced by fluoride.

Proapoptotic ability of oncogenic H-Ras to facilitate apoptosis induced by histone deacetylase inhibitors in human cancer cells

More than 35% of human urinary bladder cancers involve oncogenic H-Ras activation. In addition to tumorigenic ability, oncogenic H-Ras possesses a novel proapoptotic ability to facilitate the induction of apoptosis by histone deacetylase inhibitors (HDACI). HDACIs are a new class of anticancer agents and are highly cytotoxic to transformed cells. To understand the connection between the selectivity of HDACIs on transformed cells and the proapoptotic ability of oncogenic H-Ras to facilitate HDACI-induced apoptosis, we introduced oncogenic H-Ras into urinary bladder J82 cancer cells to mimic an acquisition of the H-ras gene activation in tumor development. Expression of oncogenic H-Ras promoted J82 cells to acquire tumorigenic ability. Meanwhile, oncogenic H-Ras increased susceptibility of J82 cells to HDACIs, including FR901228 and trichostatin A, for inducing apoptosis. The caspase pathways, the B-Raf and extracellular signal-regulated kinase pathway, p21(Cip1) and p27(Kip1), and core histone contents are regulated differently by FR901228 in oncogenic H-Ras-expressed J82 cells than their counterparts in parental J82 cells, contributing to the increased susceptibility to the induction of selective apoptosis. Our results lead us to a suggestion that HDACIs activate the proapoptotic ability of oncogenic H-Ras, indicating a potential therapeutic value of this new class of anticancer agents in the control of human urinary bladder cancer that has progressed to acquire oncogenic H-Ras.

Broad in vitro efficacy of plant-derived betulinic acid against cell lines derived from the most prevalent human cancer types

Betulinic acid (BA) is a widely available plant-derived triterpene with reported activity against cancer cells of neuroectodermal origin and leukaemias. Treatment with BA was shown to protect mice against transplanted human melanoma and led to tumor regression. In contrast, cells from healthy tissues were resistant to BA and toxic side-effects in animals were absent. These findings have raised interest in the chemotherapeutical anti-cancer potential of BA. A comprehensive assessment of the efficacy of BA against the clinically most important cancer types is currently lacking. Therefore, we tested the in vitro sensitivity of broad cell line panels derived from lung, colorectal, breast, prostate and cervical cancer, which are the prevalent cancer types characterized with highest mortalities in woman and men. Multiple assays were used in order to allow a reliable assessment of anti-cancer efficacy of BA. After 48 h of treatment with BA, cell viability as assessed with MTT and cell death as measured with propidium iodide exclusion showed clear differences in sensitivity between cell lines. However, in all cell lines tested colony formation was completely halted at remarkably equal BA concentrations that are likely attainable in vivo. Our results substantiate the possible application of BA as a chemotherapeutic agent for the most prevalent human cancer types.

A Bax/Bak-independent Mechanism of Cytochrome c Release

Bax and Bak are multidomain pro-apoptotic members of the Bcl-2 family of proteins that regulate mitochondria-mediated apoptosis by direct modulation of mitochondrial membrane permeability. Since double-knock-out mouse embryonic fibroblasts with deficiency of Bax and Bak are resistant to multiple apoptotic stimuli, Bax and Bak are considered to be an essential gateway for various apoptotic signals. Here we showed that the combination of calcium ionophore A23187 and arachidonic acid induced cytochrome c release and caspase-dependent death of double-knock-out mouse embryonic fibroblasts, indicating that other mechanisms of cytochrome c release exist. Furthermore, A23187/arachidonic acid (ArA)-induced caspase-dependent death was significantly suppressed by the treatment of several serine protease inhibitors including 4-(2-aminoethyl)benzenesulfonylfluoride and l-1-chloro-3-(4-tosylamido)-4-phenyl-2-butanone but not the overexpression of anti-apoptotic Bcl-2 family of proteins or the inhibition of mitochondrial membrane permeability transition. These results indicate that there are at least two mechanisms of cytochrome c release leading to caspase activation, a Bax/Bak-dependent mechanism and a Bax/Bak-independent, but serine protease(s)-dependent, mechanism.

Pro-apoptotic activity of oncogenic H-Ras for histone deacetylase inhibitor to induce apoptosis of human cancer HT29 cells

PURPOSE

To verify the pro-apoptotic activity of oncogenic H-Ras in the increased susceptibility of human cancer cells to histone deacetylase inhibitor (HDACI).

METHODS

The pro-apoptotic activity of oncogenic H-Ras(V12) was verified by its ability to increase susceptibility of human colorectal adenocarcinoma HT29 cells to HDACI for inducing apoptosis and growth inhibition, assayed by various methods. The mode of action of HDACI FR901228 was studied by its ability to modulate protein phosphorylation, acetylation, and expression levels in various signaling pathways, measured by Western blot analysis.

RESULTS

Activation of caspase-3, -7, and -8, and serine protease by FR901228 was facilitated by oncogenic H-Ras to induce apoptosis. Expression of H-Ras(V12) changed the intrinsic modulation of Raf in cells responding to FR901228 treatment. Both p21( Cip1 ) and p27( Kip1 ) were induced in FR901228-treated cells arrested in either the G0/G1 or G2/M phase of the cell cycle. Deacetylation of FR901228-induced acetylation of core histones was accelerated by H-Ras(V12) in cells undergoing apoptosis.

CONCLUSION

Expression of H-Ras(V12) increased susceptibility of HT29 cells to HDACI FR901228 and Trichostatin A for inducing apoptosis. The pro-apoptotic activity of H-Ras(V12) responding to HDACI indicates a potential value of this new class of anticancer agents in treating Ras-related human cancers.

A caspase-independent pathway mediates macrophage cell death in response to Mycobacterium tuberculosis infection

Macrophages can undergo apoptosis after infection with Mycobacterium tuberculosis. This macrophage response deprives the bacillus of its niche cell and supports the host response through better antigen presentation. The intracellular pathways of apoptosis that elaborate this macrophage response are not well understood. To address this issue, we investigated the contribution of various apoptosis pathways to M. tuberculosis-induced macrophage cell death. We found that macrophages die in a caspase-independent manner after infection with M. tuberculosis (at multiplicities of infection ranging from 1 to 20). There was evidence for the involvement of both the mitochondria (cleavage of Bid) and the lysosomes (cathepsin-mediated DNA fragmentation) in this cell death pathway. Dying macrophages displayed several features typical of apoptosis, including DNA fragmentation, nuclear condensation, and exposure of phosphatidylserine on the plasma membrane. However, nuclear fragmentation was not observed, which suggests that M. tuberculosis-induced cell death differs in some respects from classical apoptosis. This novel mechanism of cell death was blocked by serine protease inhibitors. A better understanding of this protective macrophage response may direct new vaccine and treatment options.

Inhibitory effect of 4-(2-aminoethyl)-benzenesulfonyl fluoride, a serine protease inhibitor, on PI3K inhibitor-induced CHOP expression

Endoplasmic reticulum stress contributes to several diseases such as neurodegenerative disorders and diabetes. In the previous report, we found that phosphatidylinositol 3-kinase (PI3K) down-regulation is important for inducing CHOP expression, an endoplasmic reticulum stress-induced transcription factor. In the present study, we investigated the effect of 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), a serine protease inhibitor, on PI3K inhibitor-induced CHOP expression. We found that AEBSF completely inhibited PI3K inhibitor-induced CHOP expression at both mRNA and protein levels. It is suggested that AEBSF is an important drug from a pharmacological point of view and the results may have important implications for understanding endoplasmic reticulum stress-related diseases.

Cleavage of misfolded nuclear receptor corepressor confers resistance to unfolded protein response-induced apoptosis

We have recently reported that accumulation of misfolded nuclear hormone receptor corepressor (N-CoR) as insoluble protein aggregates in acute promyelocytic leukemia (APL) cells induces endoplasmic reticulum (ER) stress and activates unfolded protein response (UPR). Although accumulation of misfolded proteins is known to trigger UPR-induced cytotoxic cell death in several neurodegenerative disorders, APL cells are notably resistant to UPR-induced apoptosis. The molecular basis for the paradoxical response of APL cells to UPR is not known. Here, we report that a glycoprotease, selectively expressed in APL cells, regulates the response of APL cells to UPR-induced apoptosis through processing of misfolded N-CoR protein. Results show that misfolded N-CoR is cleaved selectively in APL cells, and cellular extracts of APL cells and human primary APL cells contain activity that cleaves N-CoR protein. Purification and spectrometric analysis of N-CoR cleaving activity from an APL cell line reveals that it is a glycoprotein endopeptidase known as OSGEP. Furthermore, the cleavage of N-CoR in APL cells could be blocked by the broad-spectrum protease inhibitor AEBSF and by RNA interference-mediated down-regulation of OSGEP expression. AEBSF selectively inhibits growth and promotes apoptosis of APL cells possibly through a mechanism involving AEBSF-induced accumulation of insoluble N-CoR protein and by triggering ER stress. Taken together, these findings suggest that selective induction of protease activity in APL cells may represent a novel cytoprotective component of UPR, which could be exploited by tumor cells to survive the toxic insult of misfolded protein(s).

Gingipains from Porphyromonas gingivalis W83 synergistically disrupt endothelial cell adhesion and can induce caspase-independent apoptosis

We have shown previously that gingipains from Porphyromonas gingivalis W83 can induce cell detachment, cell adhesion molecule (CAM) cleavage, and apoptosis in endothelial cells; however, the specific roles of the individual gingipains are unclear. Using purified gingipains, we determined that each of the gingipains can cleave CAMs to varying degrees with differing kinetics. Kgp and HRgpA work together to quickly detach endothelial cells. Interestingly, in the absence of active caspases, both gingipain-active W83 extracts and purified HRgpA and RgpB induce apoptotic morphology, suggesting that the gingipains can induce both caspase-dependent and caspase-independent apoptosis. Using z-VAD-FMK to inhibit Kgp activity and leupeptin to inhibit Rgp activity in gingipain-active W83 extracts, we investigated the relative significance of the synergistic role of the gingipains. z-VAD-FMK or leupeptin delayed, but did not inhibit, cell detachment induced by gingipain-active W83 extracts or purified gingipains. There was partial cleavage of N-cadherin and cleavage of VE-cadherin was not inhibited. Degradation of integrin beta1 was inhibited only in the presence of z-VAD-FMK. These results further clarify the role P. gingivalis plays in tissue destruction occurring in the periodontal pocket.

c-Myc-dependent etoposide-induced apoptosis involves activation of Bax and caspases, and PKCdelta signaling

The c-Myc transcription factor is a key regulator of cell proliferation, differentiation, and apoptosis. While deregulation of myc induces programmed cell death, defects in the apoptotic program facilitate Myc-driven tumor development. We have treated c-Myc inducible mouse cells and rat fibroblasts with different c-myc status with cytotoxic drugs to explore the effect of c-Myc on drug-induced apoptosis. We found that c-Myc overexpression potentiated etoposide-, doxorubicin-, and cisplatin-induced cell death in mouse fibroblasts. In addition, these drugs provoked a strong apoptotic response in c-Myc-expressing cells, but a weak apoptosis in c-myc null Rat1 cells. In contrast, staurosporine-induced apoptosis was c-Myc-independent, confirming a functional apoptotic pathway in c-myc null cells. Apoptosis was paralleled by c-Myc-dependent Bax-activation after etoposide and doxorubicin treatment, but not after cisplatin administration. All three drugs induced higher caspase activation in c-Myc expressing cells than in c-myc null cells. Furthermore, etoposide treatment of c-Myc expressing cells resulted in PKCdelta cleavage, while inhibition of PKCdelta reduced etoposide-induced apoptosis and prevented Bax activation. Taken together, these findings suggest that Bax and caspase activation, together with PKCdelta signaling are involved in c-Myc-dependent etoposide-induced apoptosis.

Motexafin gadolinium induces mitochondriallymediated caspase-dependent apoptosis

Motexafin gadolinium (MGd, Xcytrin) is a tumor-localizing redox mediator that catalyzes the oxidation of intracellular reducing molecules including NADPH, ascorbate, protein and non-protein thiols, generating reactive oxygen species (ROS). MGd localizes to tumors and cooperates with radiation and chemotherapy to kill tumor cells in tissue culture and animal models. In this report, we demonstrate that MGd triggers the mitochondrial apoptotic pathway in the HF-1 lymphoma cell line as determined by loss of mitochondrial membrane potential, release of cytochrome c from mitochondria, activation of caspase-9 prior to caspase-8, cleavage of PARP and annexin V binding. There was minimal effect on MGd-induced apoptosis by the caspase inhibitor z-VAD-fmk, even though caspase-3 activity (as measured by DEVD-cleavage) was completely inhibited. However, MGd-induced apoptosis was reduced to baseline levels by the more potent caspase inhibitor Q-VD-OPh, demonstrating that MGd-induced apoptosis is indeed caspase-dependent. Apoptosis induced by dexamethasone, doxorubicin and etoposide (mediated through the mitochondrial pathway) was also more sensitive to inhibition by Q-VD-OPh than z-VAD-fmk. Our results demonstrating differential sensitivity of drug-induced apoptosis to caspase inhibitors suggest that the term "caspase-independent apoptosis" cannot be solely defined as apoptosis that is not inhibited by z-VAD-fmk as has been utilized in some published studies.

Expression and purification of the mitochondrial serine protease LACTB as an N-terminal GST fusion protein in Escherichia coli

LACTB is a mammalian mitochondrial protein sharing sequence similarity to the beta-lactamase/penicillin-binding protein family of serine proteases that are involved in bacterial cell wall metabolism. The physiological role of LACTB is unclear. In this study we have subcloned the cDNA of mouse LACTB (mLACTB) and produced recombinant mLACTB protein in Escherichia coli. When mLACTB was expressed as an N-terminal GST fusion protein (GST-mLACTB), full-length GST-mLACTB protein was recovered by glutathione-agarose affinity chromatography as determined by MALDI-TOF mass spectrometry and immunoblotting. Expression of mLACTB as a C-terminal GST fusion protein or with either an N- or C-terminal His6-tag resulted in proteolytic degradation of the protein and we were not able to detect full-length mLACTB. Analysis of GST-mLACTB by Fourier transform infrared spectrometry revealed the presence of alpha-helices, beta-sheets and turns, consistent with a well-defined secondary structure. These results show that mLACTB can be expressed as a GST fusion protein in E. coli and suggest that GST-mLACTB was properly folded.

The adaptor protein TRADD activates distinct mechanisms of apoptosis from the nucleus and the cytoplasm

TNFR1 associated death domain protein (TRADD) contains an N-terminal TRAF binding domain and a C-terminal death domain along with nuclear import and export sequences that cause shuttling between the cytoplasm and nucleus. The death domain of TRADD contains the nuclear import sequence and expression of the core death domain (nuclear TRADD) results in exclusive nuclear localization and activation of a distinct apoptotic pathway. Cytoplasmic TRADD activates apoptosis through Fas-associated death domain protein (FADD) and caspase-8 activation that was blocked by caspase inhibitors or dominant-negative FADD. These inhibitors did not inhibit death induced by nuclear TRADD, which could only be inhibited by combining caspase inhibitors and a serine protease inhibitor. The pathway activated by nuclear TRADD requires caspase-9 catalytic activity. However, apoptosis activating factor deficiency confers only partial protection from death. This pathway represents an alternate means by which TRADD can regulate cell death independently of FADD and caspase-8 that occurs from the nucleus rather than the cytoplasm.

Honokiol overcomes conventional drug resistance in human multiple myeloma by induction of caspase-dependent and -independent apoptosis

Honokiol (HNK) is an active component purified from magnolia, a plant used in traditional Chinese and Japanese medicine. Here we show that HNK significantly induces cytotoxicity in human multiple myeloma (MM) cell lines and tumor cells from patients with relapsed refractory MM. Neither coculture with bone marrow stromal cells nor cytokines (interleukin-6 and insulin-like growth factor-1) protect against HNK-induced cytotoxicity. Although activation of caspases 3, 7, 8, and 9 is triggered by HNK, the pan-caspase inhibitor z-VAD-fmk does not abrogate HNK-induced apoptosis. Importantly, release of an executioner of caspase-independent apoptosis, apoptosis-inducing factor (AIF), from mitochondria is induced by HNK treatment. HNK induces apoptosis in the SU-DHL4 cell line, which has low levels of caspase 3 and 8 associated with resistance to both conventional and novel drugs. These results suggest that HNK induces apoptosis via both caspase-dependent and -independent pathways. Furthermore, HNK enhances MM cell cytotoxicity and apoptosis induced by bortezomib. In addition to its direct cytotoxicity to MM cells, HNK also represses tube formation by endothelial cells, suggesting that HNK inhibits neovascurization in the bone marrow microenvironment. Taken together, our results provide the preclinical rationale for clinical protocols of HNK to improve patient outcome in MM.

Bax-dependent regulation of Bak by voltage-dependent anion channel 2

Many studies have demonstrated a critical role of Bax in mediating apoptosis, but the role of Bak in regulating cancer cell apoptotic sensitivities in the presence or absence of Bax remains incompletely understood. Using isogenic cells with defined genetic deficiencies, here we show that in response to intrinsic, extrinsic, and endoplasmic reticulum stress stimuli, HCT116 cells show clear-cut apoptotic sensitivities in the order of Bax+/Bak+ > Bax+/Bak- >> Bax-/Bak+ >> Bax-/Bak-. Small interference RNA-mediated knockdown of Bak in Bax-deficient cells renders HCT116 cells completely resistant to apoptosis induction. Surprisingly, however, Bak knockdown in Bax-expressing cells only slightly affects the apoptotic sensitivities. Bak, like Bax, undergoes the N terminus exposure upon apoptotic stimulation in both Bax-expressing and Bax-deficient cells. Gel filtration, chemical cross-linking, and co-immunoprecipitation experiments reveal that different from Bax, which normally exists as monomers in unstimulated cells and is oligomerized by apoptotic stimulation, most Bak in unstimulated HCT116 cells exists in two distinct protein complexes, one of which contains voltage-dependent anion channel (VDAC) 2. During apoptosis, Bak and Bax form both homo- and hetero-oligomeric complexes that still retain some VDAC-2. However, the oligomeric VDAC-2 complexes are diminished, and Bak does not interact with VDAC-2 in Bax-deficient HCT116 cells. These results highlight VDAC-2 as a critical inhibitor of Bak-mediated apoptotic responses.

Antimycin A-induced killing of HL-60 cells: Apoptosis initiated from within mitochondria does not necessarily proceed via caspase 9

BACKGROUND

Antimycin A (AMA) inhibits mitochondrial electron transport, collapses the mitochondrial membrane potential, and causes the production of reactive oxygen species. Previous work by me and my colleagues has demonstrated that AMA causes an array of typical apoptotic phenomena in HL-60 cells. The hypothesis that AMA causes HL-60 apoptosis by the intrinsic apoptotic pathway has now been tested.

METHODS

Z-LEHD-FMK and Z-IETD-FMK were used as specific inhibitors of the initiator caspases 9 and 8, respectively. Caspase 3 activation, DNA fragmentation, and cellular disintegration were measured by flow cytometry. Cytochrome c release, chromatin condensation, and nuclear fragmentation were measured by microscopy.

RESULTS

AMA caused mitochondrial cytochrome c release and neither Z-LEHD-FMK nor Z-IETD-FMK inhibited that. In the absence of caspase inhibition there was a very close correlation between cytochrome c release and caspase 3 activation. Z-LEHD-FMK blocked caspase 3 activation but enhanced DNA fragmentation and failed to stop nuclear or cellular disintegration. Z-IETD-FMK also blocked caspase 3 activation but, in contrast to Z-LEHD-FMK, delayed DNA fragmentation and disintegration of the nucleus and the cell.

CONCLUSIONS

The hypothesis to explain AMA-induced HL-60 apoptosis was clearly inadequate because: (a) caspase 9 inhibition did not prevent DNA fragmentation or cell death, (b) apoptosis proceeded in the absence of caspase-3 activation, (c) the main pathway leading to activation of the executioner caspases was by caspase-8 activation, but caspase 8 inhibition only delayed apoptosis, and (d) activation of caspases 8 and 9 may be necessary for caspase-3 activation. Thus, in this cell model, apoptosis triggered from within the mitochondria does not necessarily proceed by caspase 9, and caspase 3 is not critical to apoptosis. The results provide further evidence that, when parts of the apoptotic network are blocked, a cell is able to complete the program of cell death by alternate pathways.

Plakin proteins are coordinately cleaved during apoptosis but preferentially through the action of different caspases

In epithelial cells, cell-cell and cell-matrix junctions, desmosomes and hemidesmosomes, provide anchorage sites for the keratin-intermediate filaments. The plakin proteins desmoplakin (DP), plectin, and periplakin represent intracellular constituents of these adhesion junctions. In staurosporine-treated apoptotic HaCaT cells, DP, plectin, and periplakin became cleaved coordinately with the elimination of keratins 10 and 14, while involucrin, actin, and keratin 18 displayed considerable stability. The caspase inhibitor zVAD-fmk prevented both the cell detachment and protein cleavage, indicating the function of caspases in these events. Closer examination in vitro revealed that while caspases 2 and 4 most efficiently cleaved DP, and plectin served as a target for caspases 3 and 7, periplakin as well as keratins were cleaved by caspase 6. The involvement of multiple caspases in the destruction of epithelial cell integrity ensures the efficient elimination of cytoskeleton, but also provides specificity for selectively targeting individual adhesion molecules.

Cell death triggered by alpha-emitting 213Bi-immunoconjugates in HSC45-M2 gastric cancer cells is different from apoptotic cell death

PURPOSE

Radioimmunotherapy with alpha-particle-emitting nuclides, such as 213Bi, is a promising concept for the elimination of small tumour nodules or single disseminated tumour cells. The aim of this study was to investigate cellular damage and the mode of cell death triggered by 213Bi-immunoconjugates.

METHODS

Human gastric cancer cells (HSC45-M2) expressing d9-E-cadherin were incubated with different levels of activity of 213Bi-d9MAb targeting d9-E-cadherin and 213Bi-d8MAb, which does not bind to d9-E-cadherin. Micronucleated (M) cells, abnormal (A) cells and apoptotic (A) [(MAA)] cells were scored microscopically in the MAA assay following fluorescent staining of nuclei and cytoplasm. Chromosomal aberrations were analysed microscopically following Giemsa staining. The effect of z-VAD-fmk, known to inhibit apoptosis, on the prevention of cell death was investigated following treatment of HSC45-M2 cells with sorbitol as well as 213Bi-d9MAb. Activation of caspase 3 after incubation of HSC45-M2 cells with both sorbitol and 213Bi-d9MAb was analysed via Western blotting.

RESULTS

Following incubation of HSC45-M2 human gastric cancer cells expressing d9-E-cadherin with 213Bi-d9MAb the number of cells killed increased proportional to the applied activity concentration. Microscopically visible effects of alpha-irradiation of HSC45-M2 cells were formation of micronuclei and severe chromosomal aberrations. Preferential induction of these lesions with specific 213Bi-d9MAb compared with unspecific 213Bi-d8MAb (not targeting d9-E-cadherin) was not observed if the number of floating, i.e. unbound 213Bi-immunoconjugates per cell exceeded 2 x 10(4), most likely due to intense crossfire. In contrast to sorbitol-induced cell death, cell death triggered by 213Bi-immunoconjugates was independent of caspase 3 activation and could not be inhibited by z-VAD-fmk, known to suppress the apoptotic pathway.

CONCLUSION

213Bi-immunoconjugates seem to induce a mode of cell death different from apoptosis in HSC45-M2 cells.