Mitochondrial reactive oxygen species and nitric oxide-mediated cancer cell apoptosis in 2-butylamino-2-demethoxyhypocrellin B photodynamic treatment

Photodynamic therapy (PDT) is a novel and promising cancer treatment which employs a combination of a photosensitizing chemical and visible light to induce apoptosis in cancer cells. Singlet oxygen has been recognized as the main origin of oxidative stress in PDT. However, the precise mechanism of PDT-induced apoptosis is not well characterized, especially the dualistic role of nitric oxide (NO). To dissect the apoptosis pathways triggered by PDT, the intracellular free radicals in MCF-7 cells were investigated by examining a novel photosensitizer 2-butylamino-2-demethoxyhypocrellin B (2-BA-2-DMHB)-mediated PDT. It was found that exposure of the cells to 2-BA-2-DMHB and irradiation resulted in a significant increase of intracellular ROS in minutes, and then followed by cytoplasmic free calcium enhancement, mitochondrial nitric oxide synthase (mtNOS) activation, cytochrome c release, and apoptotic death. Scavengers of singlet oxygen or NO could attenuate PDT-induced cell viability loss, nucleus morphology changes, cytochrome c release, mitochondria swelling, and apo-apoptosis gene p53 and p21 mRNA levels. The results suggested that both ROS and NO played important roles in the apoptosis-induced by PDT.     

Phospholipase A2-activating protein (PLAA) enhances cisplatin-induced apoptosis in HeLa cells

Phospholipase A₂ (PLA₂)-activating protein (PLAA) is a novel signaling molecule that regulates eicosanoid production and participates in inflammatory responses. In our current study, we revealed that PLAA production was induced by the chemotherapeutic drug cisplatin in HeLa cervical carcinoma cells. To determine the potential pro-apoptotic effects of PLAA induction by cisplatin, we utilized HeLa (Tet-off) cells overexpressing the plaa gene (plaa ^high) and compared them with control (plaa ^low) cells, which produce endogenous plaa from the chromosome. Cisplatin-stimulated plaa ^high cells contained significantly higher levels of DNA fragmentation, caspase 3, 8 and 9 activities, PLA₂ enzyme activity, and cytochrome c leakage from mitochondria than did the cisplatin-stimulated plaa ^low cells. Importantly, siRNA against PLAA (siRNA–PLAA) reduced the levels of cisplatin-induced PLAA, DNA fragmentation, and PLA₂ activation, while promoting cell viability in both plaa ^high and plaa ^low cells. Cisplatin-induced-cytochrome c leakage in plaa ^high cells was reduced by siRNA–PLAA and restored by the addition of exogenous arachidonic acid (AA), suggesting to us that PLAA induction by cisplatin promoted cytochrome c leakage/mitochondrial damage partially by accumulating AA. In addition, cisplatin-stimulated plaa ^high cells produced less cytoprotective clusterin than did the cisplatin-stimulated plaa ^low cells, and siRNA–PLAA promoted clusterin production from both plaa ^high and plaa ^low cells. We showed that clusterin reduced DNA fragmentation in cisplatin-stimulated plaa ^high and plaa ^low cells, which is consistent with the notion that clusterin promotes cancer chemoresistance. Furthermore, cisplatin-stimulated plaa ^high cells produced more IL-32 (a pro-apoptotic protein) than did cisplatin-stimulated plaa ^low cells, and siRNA–PLAA reduced IL-32 production from both plaa ^high and plaa ^low cells. Finally, our proteomic analysis revealed that cisplatin-stimulated plaa ^high cells contained higher levels of phosphorylated JNK/c-Jun and FasL than did plaa ^low cells treated the same way. In summary, our data indicated that PLAA induction enhanced cisplatin-induced-apoptosis through four pathways, namely by: 1) accumulation of AA and mitochondrial damage, 2) downregulation of the cytoprotective clusterin, 3) upregulation of the pro-apoptotic IL-32, and 4) induction of JNK/c-Jun signaling and FasL expression.     

FAM129B/MINERVA, a novel adherens junction-associated protein, suppresses apoptosis in HeLa cells

A recent proteomics study identified FAM129B or MINERVA as a target of the MAP kinase (Erk1/2) signaling cascade in human melanoma cells. Phosphorylation of the protein was found to promote cell invasion and the dissociation of the protein from the cell-cell junctions. Suppression of apoptosis during metastasis is a prerequisite for the survival and spread of cancer cells. During apoptosis, the adherens junctions are disassembled as the dying cell retracts, and new contacts are formed between normal neighboring cells. In this study, we show that FAM129B was cytosolic in exponentially growing HeLa cells but was translocated to the adherens junctions where it colocalized with β-catenin whenever contact between two or more cells was established. Silencing the FAM129B gene expression by specific siRNAs did not induce apoptosis or inhibit the growth of HeLa cells. However, when apoptosis was induced by exposure to TNFα/cycloheximide or other apoptotic signaling molecules, the onset of apoptosis was accelerated 3-4-fold when FAM129B was depleted. Annexin V binding, the inactivation of the DNA repair enzyme, poly(ADP-ribose) polymerase, and the activation of the caspases occurred more rapidly in the cells lacking FAM129B. The rapid induction of apoptosis in FAM129B knockdown cells was reversed by co-transfection with recombinant FAM129B, indicating that its effect on apoptosis was specific. As apoptosis proceeded, FAM129B was degraded and disappeared from the plasma membrane. Thus, one crucial facet of the mechanism by which FAM129B promotes cancer cell invasion is likely to be the suppression of apoptosis.     

A pro-apoptotic effect of the CDK inhibitor p57(Kip2) on staurosporine-induced apoptosis in HeLa cells

Apoptosis, or programmed cell death, is involved in many biological events, including tumorigenesis. Recently, it has been reported that two members of the Cip/Kip family of CDK inhibitors, p21(Cip1) and p27(Kip1), are involved in the regulation of apoptosis. Here, we report that selective expression of the third member in this family, p57(Kip2), potentiated staurosporine-induced apoptosis in HeLa cells. This pro-apoptotic effect was associated with an increased caspase-3 activity. In contrast, glucocorticoid treatment, despite inducing p57(Kip2) expression in HeLa cells, was found to have an inhibitory effect on staurosporine-induced apoptosis. This anti-apoptotic effect of glucocorticoids could be explained by a concomitant increase in Bcl-x(L) expression. The results presented in this study show that p57(Kip2) has a stimulatory effect on apoptosis induced by staurosporine, suggesting a role for p57(Kip2) in the response of tumor cells to cytotoxic drugs.     

Tumor PO(2) changes during photodynamic therapy depend upon photosensitizer type and time after injection

In this study, the vascular and tissue oxygen changes induced by photodynamic therapy in the RIF-1 tumor were examined, using electron paramagnetic resonance (EPR) oximetry. Two photosensitizers, including verteporfin (BPD-MA in a lipid-based formulation) and aminolevulinic acid-induced protoporphyrin IX (ALA-PPIX), were investigated with optical irradiation, sufficient to induce sub-curative damage in the tumor tissue, and the transient changes in PO(2) and vascular perfusion were examined. A large increase in tissue oxygenation (from 3 up to 9.5 mmHg) was observed when treated with ALA-PPIX based photodynamic therapy, which lasted during the treatment and a small residual increase that returned back to baseline levels by 48 h after treatment. With verteporfin-based photodynamic therapy, one group of animals was irradiated 15 min after injection and exhibited a small decrease in oxygenation relative to pre-irradiation levels. The second group was irradiated at 3 h after injection and exhibited a large increase in the average PO(2), (from 3 to 15 mmHg) by the end of the treatment. These observations indicate that photodynamic therapy significantly increases tissue PO(2) under certain treatment conditions, with the potential cause being either increased local blood flow or decreased local oxygen metabolic consumption due to cellular damage.     

A novel yeast-binding lectin from hemolymph Cyclina sinensis (Gmelin) and its effects on yeast cells

A lectin, Cyclina sinensis (Gmelin) (CSL), was isolated from hemolymph C. sinensis by ion-exchange on Cellulose DE52 and purified by gel filtration on Sephadex G-100 and HPLC on TSK gel G4000PW_XL. SDS-PAGE showed that the CSL protein had a molecular mass of 72 kDa, had consisted of 40 and 18 kDa subunits. The lectin activity of CSL was Ca²⁺-denpendent. The total carbohydrate content of CSL was found to be 16.2%. According to the principle of β-elimination reaction, the oligosaccharide moiety and peptide moiety of CSL might belong to O-glucosidic linkage. CSL was found to agglutinate rabbit erythrocytes and yeast Saccharomyces cerevisiae. The hemagglutination activity was inhibited by GalNAc and Man. CSL was observed to promote the yeast cells growth and ethanol production by yeast cells. The number of yeast and ethanol production increased with increasing concentration of CSL. In addition, the nitric oxide (NO) production increased as CSL concentration increased. The results indicate that CSL can be a potential yeast stimulator in fermentation process.     

5-Hydroxy-2-(2-phenylethyl)chromone (5-HPEC): A novel non-nitrogenous ligand for 5-HT2B receptor

Chromones are a class of natural products found in almost every known terrestrial plant with over 4000 naturally occurring derivatives having been isolated and structurally elucidated. Recently, 5-hydroxy-2-(2-phenylethyl)chromone (5-HPEC), isolated from Imperata cylindrical, showed neuroprotective activity against glutamate induced excitotoxicity in primary cultures of rat cortical cells. In comparison to other naturally occurring neuroprotective chromones, 5-HPEC contains fewer hydroxyl groups. Here we report our most recent characterization on this interesting natural product against a number of CNS receptors for the purpose to identify the potential molecular targets that may be related to its biological activity. Based on our studies, including radiobinding assays, calcium flux functional assays and molecular modeling studies, 5-HPEC may represent a type of novel nonnitrogenous ligands to the 5-HT2B receptor.     

Discovery of a novel small molecule, 1-ethoxy-3-(3,4-methylenedioxyphenyl)-2-propanol, that induces apoptosis in A549 human lung cancer cells

A novel small molecule, 1-ethoxy-3-(3,4-methylenedioxyphenyl)-2-propanol (EOD), was synthesized in our laboratory. Previously, we reported pharmacological properties of EOD, triggering apoptosis in Human umbilical vein endothelial cells (HUVECs). Here, we further investigated the effects of EOD on the growth of A549 human lung cancer cells. EOD treatment induced apoptosis in A549 cells via up-regulating the expression of P53 protein, blocking cell cycle partly at G1 phase, and ultimately activating caspase-3. In contrast, caspase-8 might be irrelevant to EOD-triggered apoptosis. This study indicated that EOD might be a potential chemopreventive agent for lung cancer. The work would encourage us to add more novel compounds to our 'library' of small molecules derived through modern synthetic organic chemistry, and would drive us to determine the proteins that the compounds target.     

PFKFB3参与了11'-deoxyverticillin A(C42)诱导的HeLa细胞自噬和凋亡

摘要:【目的】明确糖酵解调节基因PFKFB3参与11-脱氧轮枝菌素A(11'-deoxyverticillin A,C42)诱导HeLa细胞自噬和凋亡中的作用。【方法】利用电镜、荧光显微镜、蛋白免疫杂交、转染、MTS 活性检测、siRNA干扰、定量RT-PCR等对C42处理的HeLa 细胞自噬和凋亡情况进行了检测。【结果】C42能够引起HeLa细胞不同的死亡。敲降自噬关键基因BECN1或LC3后,明显增加PARP-1的切割和促进C42引起的细胞活性丢失。尽管高浓度C42能更明显地抑制细胞增殖,但却不能增加细胞的自噬流;C42促进的自噬能被糖酵解调节基因PFKFB3的抑制剂所降低;而过量表达糖酵解调节基因PFKFB3能促进细胞自噬。【结论】糖酵解调节基因PFKFB3直接参与了C42诱导的HeLa细胞自噬,这种自噬的发生抑制了其诱导的细胞凋亡。     

Opposing effects of protein kinase C delta and protein kinase B alpha on H(2)O(2)-induced apoptosis in CHO cells.

H(2)O(2)-induced apoptosis was enhanced in the CHO cell line overproducing protein kinase C delta (PKCdelta) as judged by DNA fragmentation. In response to the H(2)O(2) treatment, PKCdelta was tyrosine phosphorylated and recovered as a constitutively active form, but its proteolytic fragment was not generated. In contrast, H(2)O(2)-induced apoptosis was suppressed in the CHO cell line overexpressing protein kinase B alpha (PKBalpha). Consistently, phosphorylation of BAD, a pro-apoptotic protein negatively regulated by PKBalpha, was sustained in the cells overproducing PKBalpha, but was not changed in the cells overexpressing PKCdelta. In the CHO cell line overproducing both PKCdelta and PKBalpha, H(2)O(2)-induced tyrosine phosphorylation of PKCdelta was suppressed, and DNA fragmentation was diminished concomitantly. These results suggest that PKCdelta contributes to H(2)O(2)-induced apoptosis by a mechanism independent of BAD and that PKCdelta is a target of PKB for the regulation of cell survival.     

Novel 9-(2-(1-arylethylidene)hydrazinyl)acridine derivatives: Target Topoisomerase 1 and growth inhibition of HeLa cancer cells

A series of 9-(2-(1-arylethylidene)hydrazinyl)acridine and its analogs were designed, synthesized and evaluated for biological activities. Various biochemical assays were performed to determine the free radical scavenging capacity of synthesized compounds (4a–4j). Anticancer activity of these compounds was assessed against two different human cancer cell lines viz cervical cancer cells (HeLa) and liver cancer cells (HepG2) as well as normal human embryonic kidney cell line (HEK 293). Compounds 4b, 4d and 4e showed potential anti-proliferative effects on HeLa cells. Based on results obtained from antioxidant and cytotoxicity studies, 4b, 4d and 4e were further studied in detail for different biological activities. 4b, 4d and 4e reduced the cell growth, inhibited metastatic activity and declined the potential of cell migration in HeLa cell lines. Topoisomerase1 (Top1) treated with compounds 4b, 4d and 4e exhibited inhibition of Top1 and prevented DNA replication. Molecular docking results validate that interaction of compounds 4b, 4d and 4e with Top1-DNA complex, which might be accountable for their inhibitory effects. Further it was concluded that compounds 4b, 4d and 4e arrests the cells at S phase and consequently induces cell death through DNA damage in HeLa cells.     

A novel human TPIP splice-variant (TPIP-C2) mRNA, expressed in human and mouse tissues, strongly inhibits cell growth in HeLa cells

Alternative splicing of mRNAs is known to involve a major regulation of gene expression at RNA level in mammalian cells. The PTEN (Phosphatase and TENsin homologue deleted from the human chromosome 10), TPTE (Transmembrane Phosphatase with TEnsin homology) and TPIP (TPTE and PTEN homologous Inositol lipid Phosphatase) belong to a family of dual-specific lipid and protein phosphatases. PTEN is a well characterized tumor suppressor, which plays crucial role in cell survival, cell cycle regulation, cell proliferation as well as adhesion, motility and migration of cells. The C2-domain of PTEN is essential for PTEN-functions. We have isolated a novel 1019 bp human TPIP cDNA (TPIP-C2) from a human testis cDNA library. In silico analysis of the cDNA revealed that it is produced from the TPIP-locus on the human chromosome 13 by alternative RNA-splicing. It has a unique 5'-Alu sequence, a LINE sequence followed by a 582 bp Open Reading Frame (ORF) encoding a 193 aa polypeptide with a partial phosphatase domain and a C2-domain. TPIP-C2 mRNA is expressed in human testis and in mouse tissues. Mouse testis and brain showed higher levels of TPIP-C2 mRNA in comparison to the heart, liver and kidney under normal physiological conditions. TPIP-C2 mRNAs from human and mouse testes show extensive sequence identity. Over-expression of TPIP-C2 cDNA in HeLa cells strongly (up to 85%) inhibited cell growth/proliferation and caused apoptosis in a caspase 3-dependent manner. These findings suggest for the first time that a TPIP splice-variant mRNA with a partial phosphatase domain and a C2-domain is expressed in cells and tissues of human and murine origins under normal physiological conditions. Inhibition of cell growth/proliferation and induction of apoptosis by overexpression of TPIP-C2 mRNA in HeLa cells suggest that it may be involved in negative regulation of cell growth/proliferation.     

DNA-damage, cell-cycle arrest and apoptosis induced in BEAS-2B cells by 2-hydroxyethyl methacrylate (HEMA)

The methacrylate monomer 2-hydroxyethyl methacrylate (HEMA) is commonly used in resin-based dental restorative materials. These materials are cured in situ and HEMA and other monomers have been identified in ambient air during dental surgery. In vitro studies have demonstrated a toxic potential of methacrylates, and concerns have been raised regarding possible health effects due to inhalation. In this study we have investigated the mechanisms of HEMA-induced toxicity in the human lung epithelial cell line BEAS-2B. Depletion of cellular glutathione (GSH) and an increased level of reactive oxygen species (ROS) were seen after 2h of exposure, but the levels were restored to control levels after 12h. After 24h, inhibited cell proliferation and apoptotic cell death were found. The results of the Comet assay and the observed phosphorylation of DNA-damage-associated signalling proteins including Chk2, H2AX, and p53 suggest that the toxicity of HEMA is mediated by DNA damage. Further, the antioxidant trolox did not counteract the HEMA-induced cell-cycle arrest, which indicates that the DNA damage is of non-oxidative origin.     

A novel benzodiazepine increases the sensitivity of B cells to receptor stimulation with synergistic effects on calcium signaling and apoptosis

Bz-423 is a 1,4-benzodiazepine with selective lymphotoxic properties and potent therapeutic activity against lupus-like disease in autoimmune mice. In NZB/W lupus-prone mice, Bz-423 specifically kills germinal center B cells, which are the cells that drive disease both in this model and in human systemic lupus erythematosus. In this report, the mechanistic basis for the selective action of Bz-423 is investigated. We show that Bz-423-induces superoxide as an immediate early response and that this reactive oxygen species is more effective as a second messenger death signal in B cells activated by B cell receptor stimulation compared with resting cells. As a result, low [Bz-423] that are not cytotoxic to non-stimulated cells kill stimulated cells in synergy with anti-immunoglobulin M antibodies. Subsequent experiments demonstrated that Bz-423 extends the rise in intracellular calcium that accompanies anti-immunoglobulin M stimulation, and this effect mediates the synergistic death response. Because B cell hyperactivation and altered calcium signaling is a distinguishing feature of autoreactive lymphocytes in lupus, the mechanism by which Bz-423 induces apoptosis preferentially targets disease-causing cells on the basis of their activation state. Thus, molecules like Bz-423 could form the basis for new and selective anti-lupus agents.     

3-(3-Methoxyphenyl)-6-(3-amino-4-methoxyphenyl)-7H-[1,2,4] triazolo [3,4-b][1,3,4] thiadiazine,a novel tubulin inhibitor,evokes G2/M cell cycle arrest and apoptosis in SGC-7901 and HeLa cells

Gastric cancer and cervical cancer are two major malignant tumors that threaten human health. The novel chemotherapeutic drugs are needed urgently to treat gastric cancer and cervical cancer with high anticancer activity and metabolic stability. Previously we have reported the synthesis, characterization and identification of a novel combretastatin A-4 analog, 3-(3-methoxyphenyl)-6-(3-amino-4- methoxyphenyl) -7H-[1,2,4]triazolo[3,4-b][1,3,4] thiadiazine (XSD-7). In this study, we sought to investigate its anticancer mechanisms in a human gastric cancer cell line (SGC-7901 cells) and human cervical carcinoma cell line (HeLa cells). The 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay showed that XSD-7 induced cytotoxicity in SGC-7901 and HeLa cells with inhibitory concentration 50 values of 0.11 ± 0.03 and 0.12 ± 0.05 µM, respectively. Immunofluorescence studies proved that XSD-7 inhibited microtubule polymerization during cell division in SGC-7901 and HeLa cells. Then, these cells were arrested at G2/M cell cycle and subsequently progressed into apoptosis. In further study, mitochondrial membrane potential analysis and Western blot analysis demonstrated that XSD-7 treatment-induced SGC-7901 cell apoptosis via both the mitochondria-mediated pathway and the death receptor-mediated pathway. In contrast, XSD-7 induced apoptosis in HeLa cells mainly via the mitochondria-mediated pathway. Hence, our data indicate that XSD-7 exerted antiproliferative activity by disrupting microtubule dynamics, leading to cell cycle arrest, and eventually inducing cell apoptosis. XSD-7 with novel structure has the potential to be developed for therapeutic treatment of gastric cancer and cervical cancer.     

Neuroprotective effects of (-)-epigallocatechin-3-gallate (EGCG) on paraquat-induced apoptosis in PC12 cells

Green tea, owing to its beneficial effect on health, is becoming more and more popular worldwide. (-)-Epigallocatechin-3-gallate (EGCG), the main ingredient of green tea polyphenols, is a known protective effect on injured neurons in neurodegenerative disease, such as Alzheimer's disease and Parkinson's disease. Paraquat (PQ) is a widely used herbicide that possesses a similar structure to MPP(+) and is toxic to mesencephalic dopaminergic neurons. In the present study, PQ-injured PC12 cells were chosen as an in vitro cell model of Parkinson's disease and the neuroprotective effects of EGCG were investigated. The results showed that EGCG attenuated apoptosis of PC12 cells induced by PQ. The possible mechanism may be associated with maintaining mitochondrial membrane potential, inhibiting caspase-3 activity and downregulating the expression of pro-apoptotic protein Smac in cytosol. The present study supports the notion that EGCG could be used as a neuroprotective agent for treatment of neurodegenerative diseases.     

2-(Cyclohexylamino)-1-(4-cyclopentylpiperazin-1-yl)-2-methylpropan-1-one, a novel compound with neuroprotective and neurotrophic effects in vitro

Focusing on development of novel drug candidates for the treatment of neurodegenerative diseases, we developed and synthesized a new compound, 2-(cyclohexylamino)-1-(4-cyclopentylpiperazin-1-yl)-2-methylpropan-1-one (amido-piperizine 1). The compound demonstrated robust neuroprotective properties after both glutamate excitotoxicity and peroxide induced oxidative stress in primary cortical cultures. Furthermore, amido-piperizine 1 was found to significantly induce neurite outgrowth in vitro which could suggest central reparative and regenerative potential of the compound.With these potential beneficial effects in CNS, the ability of the amido-piperizine 1 to penetrate the blood-brain barrier was tested using MDR1-MDCK cells. Amido-piperizine 1 was found not to be a P-gp substrate and to have a high blood-brain barrier penetration potential, indicating excellent availability to the CNS. Moreover, amido-piperizine 1 had a fast metabolic clearance rate in vitro, suggesting that parenteral in vivo administration seems preferable.As an attempt to elucidate a possible mechanism of action, we found that amido-piperizine 1 bound in nano-molar range to the sigma-1 receptor, which could explain the observed neuroprotective and neurotrophic properties, and with a 100-fold lower affinity to the sigma-2 receptor. These results propose that amido-piperizine 1 may hold promise as a drug candidate for the treatment of stroke/traumatic brain injury or other neurodegenerative diseases.     

A stable HeLa cell line that inducibly expresses poliovirus 2A(pro): effects on cellular and viral gene expression

A HeLa cell clone (2A7d) that inducibly expresses the gene for poliovirus protease 2A (2A(pro)) under the control of tetracycline has been obtained. Synthesis of 2A(pro) induces severe morphological changes in 2A7d cells. One day after tetracycline removal, cells round up and a few hours later die. Poliovirus 2A(pro) cleaves both forms of initiation factor eIF4G, causing extensive inhibition of capped-mRNA translation a few hours after protease induction. Methoxysuccinyl-Ala-Ala-Pro-Val-chloromethylketone, a selective inhibitor of 2A(pro), prevents both eIF4G cleavage and inhibition of translation but not cellular death. Expression of 2A(pro) still allows both the replication of poliovirus and the translation of mRNAs containing a picornavirus leader sequence, while vaccinia virus replication is drastically inhibited. Translation of transfected capped mRNA is blocked in 2A7d-On cells, while luciferase synthesis from a mRNA bearing a picornavirus internal ribosome entry site (IRES) sequence is enhanced by the presence of 2A(pro). Moreover, synthesis of 2A(pro) in 2A7d cells complements the translational defect of a poliovirus 2A(pro)-defective variant. These results show that poliovirus 2A(pro) expression mimics some phenotypical characteristics of poliovirus-infected cells, such as cell rounding, inhibition of protein synthesis and enhancement of IRES-driven translation. This cell line constitutes a useful tool to further analyze 2A(pro) functions, to complement poliovirus 2A(pro) mutants, and to test antiviral compounds.     

Study on induction of apoptosis on HeLa and Vero cells by recombinant shiga toxin and its subunits

Verotoxin (VT) or shiga toxin (Stx) produced by enterohemorrhagic Escherichia coli (EHEC) and Shigella dysenteriae is AB5 holotoxin with potent protein synthesis inhibitor. VT can induce both apoptosis and necrosis depending on the cell type, it has been shown that VT-induced apoptosis and cytotoxicity are distinct processes, and the A subunit can be necessary for apoptosis. In other words, the precise role of each subunit in apoptosis signaling has yet to be established. In this study, induction of apoptosis has been examined by using both recombinant A and B subunits, and recombinant Stx (rStx) with different doses in HeLa and Vero cells. For this purpose, the polymyxin B extract of constructs expressing A, B and AB5 recombinant proteins was used. Therefore, amounts greater than normally reported were used to induce desire effects on cell lines. The apoptotic effect of A and B subunits appear at higher doses than that of rStx. The highest apoptotic effect was observed for rStx at low concentration, compared to A and B subunits. A or B subunits separately cannot induce the signaling pathway stimulated by holotoxin though A subunit, does induce laddering pattern similar to holotoxin. We concluded that both subunits are important in complete death signaling pathway. Since different concentration of A and B subunits and rStx was required in different assay, therefore, it could be emphasized that cell death or even apoptosis caused by either of the subunits or holotoxin depends on sensitivity or specificity of the assay and cell types used.