Bid is not required for Bax translocation during UV-induced apoptosis

Modulation of Host Cell Processes by T3SS Effectors

Two of the enteric Escherichia coli pathotypes-enteropathogenic E. coli (EPEC) and enterohaemorrhagic E. coli (EHEC)-have a conserved type 3 secretion system which is essential for virulence. The T3SS is used to translocate between 25 and 50 bacterial proteins directly into the host cytosol where they manipulate a variety of host cell processes to establish a successful infection. In this chapter, we discuss effectors from EPEC/EHEC in the context of the host proteins and processes that they target-the actin cytoskeleton, small guanosine triphosphatases and innate immune signalling pathways that regulate inflammation and cell death. Many of these translocated proteins have been extensively characterised, which has helped obtain insights into the mechanisms of pathogenesis of these bacteria and also understand the host pathways they target in more detail. With increasing knowledge of the positive and negative regulation of host signalling pathways by different effectors, a future challenge is to investigate how the specific effector repertoire of each strain cooperates over the course of an infection.

Targeted therapy against EGFR and VEGFR using ZD6474 enhances the therapeutic potential of UV-B phototherapy in breast cancer cells

Background

The hypoxic environment of tumor region stimulated the up regulation of growth factors responsible for angiogenesis and tumor proliferation. Thus, targeting the tumor vasculature along with the proliferation by dual tyrosine kinase inhibitor may be the efficient way of treating advanced breast cancers, which can be further enhanced by combining with radiotherapy. However, the effectiveness of radiotherapy may be severely compromised by toxicities and tumor resistance due to radiation-induced adaptive response contributing to recurrence and metastases of breast cancer. The rational of using ZD6474 is to evaluate the feasibility and efficacy of combined VEGFR2 and EGFR targeting with concurrent targeted and localized UV-B phototherapy in vitro breast cancer cells with the anticipation to cure skin lesions infiltrated with breast cancer cells.

Materials and methods

Breast cancer cells were exposed to UV-B and ZD6474 and the cell viability, apoptosis, invasion and motility studies were conducted for the combinatorial effect. Graphs and statistical analyses were performed using Graph Pad Prism 5.0.

Results

ZD6474 and UV-B decreased cell viability in breast cancers in combinatorial manner without affecting the normal human mammary epithelial cells. ZD6474 inhibited cyclin E expression and induced p53 expression when combined with UV-B. It activated stress induced mitochondrial pathway by inducing translocation of bax and cytochrome-c. The combination of ZD6474 with UV-B vs. either agent alone also more potently down-regulated the anti-apoptotic bcl-2 protein, up-regulated pro-apoptotic signaling events involving expression of bax, activation of caspase-3 and caspase-7 proteins, and induced poly (ADP-ribose) polymerase resulting in apoptosis. ZD6474 combined with UV-B inhibited invasion of breast cancer cells in vitro as compared to either single agent, indicating a potential involvement of pro-angiogenic growth factors in regulating the altered expression and reorganization of cytoskeletal proteins in combinatorial treated breast cancer cells. Involvement of combination therapy in reducing the expression of matrix metalloprotease was also observed.

Conclusions

Collectively, our studies indicate that incorporating an anti-EGFR plus VEGFR strategy (ZD6474) with phototherapy (UV-B), an alternative approach to the ongoing conventional radiotherapy for the treatment of infiltrating metastatic breast cancer cells in the skin and for locally recurrence breast cancer than either approach alone.

Amplification activation loop between caspase-8 and -9 dominates artemisinin-induced apoptosis of ASTC-a-1 cells

Although caspases have been demonstrated to be involved in artemisinin (ARTE)-induced apoptosis, their exact functions are not well understood. The aim of this report is to explore the roles of caspase-8, -9 and -3 during ARTE-induced apoptosis in human lung adenocarcinoma (ASTC-a-1) cells. ARTE treatment induces a rapid generation of reactive oxygen species (ROS), and ROS-dependent apoptosis as well as the activation of caspase-8, -9 and -3 via time- and dose-dependent fashion. Of upmost importance, inhibition of caspase-8 or -9, but not caspase-3, almost completely blocks the ARTE-induced not only activation of the caspase-8, -9 and -3 but also apoptosis. In addition, the apoptotic process triggered by ARTE does not involve the Bid cleavage, tBid translocation, significant loss of mitochondrial membrane potential and cytochrome c release from mitochondria. Moreover, silencing Bax/Bak does not prevent the ATRE-induced cell death as well as the activation of caspase-8, -9 and -3. Collectively, our data firstly demonstrate that ARTE triggers a ROS-mediated positive feedback amplification activation loop between caspase-8 and -9 independent of mitochondria, which dominantly mediated the ARTE-induced apoptosis via a caspase-3-independent apoptotic pathway in ASTC-a-1 cells. Our findings imply a potential to develop new derivatives from artemisinin to effectively initiate the amplification activation loop of caspases.

Effects of Iron Oxide Nanoparticle Labeling on Human Endothelial Cells

Iron oxide nanoparticles (INOPS) are a potential contrast agent for magnetic resonance (MR) tracking of transplanted endothelial cells. The objective of this study was to examine the effect of INOPS labeling on endothelial cells. The mixture of INOPS and poly-l-lysine (PLL) was used to label human endothelial cells. Labeling efficiency was examined by Prussian blue staining, transmission electron microscopy, and atomic absorption spectrometry. The effect of iron oxide concentration on cell viability and proliferation were determined. The correlation of reactive oxygen species (ROS) and apoptosis was also examined. In vitro MRI scanning was carried out using a 1.5T MR system. INOPS-PLL could be readily taken up by endothelial cells and subsequently induce MRI signal intensity changes. However, higher labeling concentration (>50 μg/ml) and longer incubation (48 h) can affect cell viability and proliferation. Mitochondrial damage, apoptosis, and autolysosmes were observed under high INOPS-PLL concentrations, which were correlated to ROS production. INOPS-PLL nanoparticles can be used to label transplanted endothelial cells. However, high concentration of INOPS can impair cell viability, possibly through ROS-mediated apoptosis and autophagy.

Bax and calpain mediate excitotoxic oligodendrocyte death induced by activation of both AMPA and kainate receptors

Sustained activation of AMPA and kainate receptors in rat oligodendrocytes induces cytosolic calcium overload, mitochondrial depolarization, and an increase of reactive oxygen species, resulting in cell death. Here, we provide evidence that Bax, a proapoptotic member of the Bcl-2 protein family, is involved in excitotoxic apoptotic death of oligodendrocytes and that calpain mediates Bax activation. Cultured Bax(-/-) oligodendrocytes, obtained from the optic nerve of Bax knock-out mice, were resistant to AMPA and kainate receptor-mediated insults. In turn, both mitochondrial calcium uptake and mitochondrial alterations after excitotoxic insults were diminished in Bax-null oligodendrocytes. Moreover, pretreatment with furosemide, a blocker of Bax translocation to mitochondria, significantly protected rat and mouse oligodendrocytes from AMPA- and kainate-induced damage; in contrast, bongkrekic acid, a blocker of the mitochondrial permeability transition pore, had no effect. Finally, we analyzed the participation of calpain, which cleaves Bax and is activated by AMPA and kainate, in oligodendrocyte death. Pretreatment with 3-(4-iodophenyl)-2-mercapto-(Z)-2-propenoic acid (PD150606), a broad cell-permeable calpain inhibitor, and two additional calpain inhibitors diminished Bax activation, inhibited its translocation to mitochondria, and attenuated all apoptotic events resulting from excitotoxic insults to rat oligodendrocytes. Together, these results indicate that Bax and calpain are essential intermediaries of the mitochondria-dependent death pathway, triggered by AMPA and kainate receptor activation in oligodendrocytes.

Bufalin Induces Reactive Oxygen Species Dependent Bax Translocation and Apoptosis in ASTC-a-1 Cells

Bufalin has been shown to induce cancer cell death through apoptotic pathways. However, the molecular mechanisms are not well understood. In this study, we used the confocal fluorescence microscopy (CFM) to monitor the spatio-temporal dynamics of reactive oxygen species (ROS) production, Bax translocation and caspase-3 activation during bufalin-induced apoptosis in living human lung adenocarcinoma (ASTC-a-1) cells. Bufalin induced ROS production and apoptotic cell death, demonstrated by Hoechst 33258 staining as well as flow cytometry analysis. Bax redistributed from cytosol to mitochondria from 12 to 48 h after bufalin treatment in living cells expressed with green fluorescent protein Bax. Treatment with the antioxidant N-acetyl-cysteine (NAC), a ROS scavenger, inhibited ROS generation and Bax translocation and led to a significant protection against bufalin-induced apoptosis. Our results also revealed that bufalin induced a prominent increase of caspase-3 activation blocked potently by NAC. Taken together, bufalin induced ROS-mediated Bax translocation, mitochondrial permeability transition and caspase-3 activation, implying that bufalin induced apoptosis via ROS-dependent mitochondrial death pathway in ASTC-a-1 cells.

Caspase 3 is activated through caspase 8 instead of caspase 9 during H2O2-induced apoptosis in HeLa cells

Oxidative stress is known to be involved in a variety of pathological processes including atherosclerosis, diabetes, and neurodegenerative diseases. Understanding how intracellular signaling pathways respond to oxidative stress will have a significant implication in the therapy of these diseases. In this study, we applied hydrogen peroxide (H(2)O(2)) to trigger apoptosis and investigated the dynamic activation of various caspases using a FRET technique. We measured the activation dynamics of caspase 3 and caspase 9 based on two reporter systems, SCAT 3 and SCAT 9. We found that caspase 3 activation was earlier than that of caspase 9 following H(2)O(2) treatment. Caspase 3 was activated rapidly, reaching a maximum in 12±3 min, while the average duration of caspase 9 activation was 21±3 min. When cells were pretreated with Z-LEHD-fmk, a caspase 9 specific inhibitor, caspase 3 activation and apoptosis by H(2)O(2) treatment were little affected, although the caspase 9 activation was completely inhibited. When cells were pretreated with Z-DEVD-fmk, a caspase 3 specific inhibitor, the activation of both caspase 3 and caspase 9, as well as apoptosis, were inhibited. When cells were pretreated with Z-IETD-fmk, a caspase 8 specific inhibitor, the activation of caspase 3 and caspase 9 were significantly delayed. Finally, we found that Bax did not translocate from the cytosol to the mitochondrial membrane during H(2)O(2)-induced apoptosis. Our results suggest that, during H H(2)O(2)-induced apoptosis, caspase 3 is activated directly through caspase 8 and is not through the mitochondria-dependent caspase 9 activation.

Ascorbic acid enhances radiation-induced apoptosis in an HL60 human leukemia cell line

This study was conducted to examine the utility of the combined use of ascorbic acid (AsA) and radiation in clinical applications. We investigated cell survival, DNA fragmentation, and caspase activation after X-ray irradiation and AsA treatment of human leukemia HL60 cells. The number of living cells decreased after combined X-ray irradiation and AsA treatment (2 Gy + 5 mM) in comparison with that after X-ray irradiation (2 Gy) or AsA treatment (5 mM) alone. DNA fragmentation was more in the cells subjected to combined X-ray irradiation and AsA treatment than in those subjected to X-ray irradiation alone. Caspase-3, caspase-8, and caspase-9 were highly activated following combined X-ray irradiation and AsA treatment, but caspase-8 activity was not markedly increased after X-ray irradiation alone. Bax levels in the mitochondrial membrane fractions were increased after AsA treatment alone and after combined X-ray irradiation and AsA treatment. However, there was no apparent increase in the Bax levels after X-ray irradiation treatment alone. Thus, this study confirmed that supplementing X-ray irradiation with AsA treatment results in increased apoptosis in HL60 cells. With regard to the apoptosis-inducing factors, we hypothesized that Bax and caspase-8 were activated after combined X-ray irradiation and AsA treatment compared with either treatment alone.

Survivin mediates self-protection through ROS/cdc25c/CDK1 signaling pathway during tumor cell apoptosis induced by high fluence low-power laser irradiation

Survivin, an important member of inhibitor-of-apoptosis (IAP) family, can be up-regulated by various pro-apoptotic stimuli, such as UV, photodynamic therapy (PDT) and cisplatin. High fluence low-power laser irradiation (HF-LPLI) is a newly discovered pro-apoptotic stimulator. The anti-apoptotic mechanism of survivin during HF-LPLI-induced apoptosis is still not investigated. Here, we report that HF-LPLI up-regulates survivin activity through reactive oxygen species (ROS)/cdc25c protein phosphatase (cdc25c)/cyclin-dependent kinase (CDK1) signaling pathway in human lung adenocarcinoma cells (ASTC-a-1). The up-regulation of survivin activity can reduce HF-LPLI-induced apoptosis, while down-regulation of the activity can promote the apoptosis. In addition, activated survivin delays mitochondrial depolarization, cytochrome c release, caspase-9 and Bax activation, all of which are typical pro-apoptotic events of cell apoptosis induced by HF-LPLI. On the basis of the present studies, we conclude that survivin can mediate self-protection during tumor cell apoptosis caused by HF-LPLI.

RACK1 promotes Bax oligomerization and dissociates the interaction of Bax and Bcl-XL

Bax, a member of Bcl-2 family, plays an essential role in apoptotic pathways induced by a number of apoptotic stimulus. In a search for new potential binding partners of Bax, we identified the receptor for activated C-kinase 1 (RACK1) by a yeast two-hybrid assay. We demonstrated that RACK1 interacts with Bax through its BH3 domain both in vitro and in vivo. Using immunostaining and immunoprecipitation experiments, we found that RACK1 colocalizes with Bax oligomers and promotes Bax oligomerization both in vitro and in vivo. Furthermore, we observed that RACK1 also interacts with Bcl-XL, an anti-apoptotic protein associated with Bax. Interestingly, the Bcl-XL/Bax interaction is decreased when RACK1 is overexpressed, but is increased when RACK1 is depleted, suggesting RACK1 disrupts the association of Bax and Bcl-XL. In addition, we found that overexpression of RACK1 promotes UV-induced apoptosis, while knocking down RACK1 inhibits the effects. Together, these results indicate that RACK1 promotes apoptosis by promoting Bax oligomerization and dissociating the complex of Bax and Bcl-XL.

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.

Photobleaching-based quantitative analysis of fluorescence resonance energy transfer inside single living cell

The current advances of fluorescence microscopy and new fluorescent probes make fluorescence resonance energy transfer (FRET) a powerful technique for studying protein-protein interactions inside living cells. It is very hard to quantitatively analyze FRET efficiency using intensity-based FRET imaging microscopy due to the presence of autofluorescence and spectral crosstalks. In this study, we for the first time developed a novel photobleaching-based method to quantitatively detect FRET efficiency (Pb-FRET) by selectively photobleaching acceptor. The Pb-FRET method requires two fluorescence detection channels: a donor channel (CH ( 1 )) to selectively detect the fluorescence from donor, and a FRET channel (CH ( 2 )) which normally includes the fluorescence from both acceptor and donor due to emission spectral crosstalk. We used the Pb-FRET method to quantitatively measure the FRET efficiency of SCAT3, a caspase-3 indicator based on FRET, inside single living cells stably expressing SCAT3 during STS-induced apoptosis. At 0, 6 and 12 h after STS treatment, the FRET efficiency of SCAT3 obtained by Pb-FRET inside living cells was verified by two-photon excitation (TPE) fluorescence lifetime imaging microscopy (FLIM). The temporal resolution of Pb-FRET method is in second time-scale for ROI photobleaching, even in microsecond time-scale for spot photobleaching. Our results demonstrate that the Pb-FRET method is independent of photobleaching degree, and is very useful for quantitatively monitoring protein-protein interactions inside single living cell.

PUMA promotes Bax translocation by both directly interacting with Bax and by competitive binding to Bcl-X L during UV-induced apoptosis

Cell apoptosis induced by UV irradiation is a highly complex process in which different molecular signaling pathways are involved. p53 up-regulated modulator of apoptosis (PUMA) has been proposed as an important regulator in UV irradiation-induced apoptosis. However, the molecular mechanism through which PUMA regulates apoptosis, especially how PUMA activates Bcl-2-associated X protein (Bax) in response to UV irradiation is still controversial. In this study, by using real-time single-cell analysis and fluorescence resonance energy transfer, we investigated the tripartite nexus among PUMA, Bax, and Bcl-X(L) in living human lung adenocarcinoma cells (ASTC-a-1) to illustrate how PUMA promotes Bax translocation to initiate apoptosis. Our results show that the interaction between PUMA and Bax increased gradually, with Bax translocating to mitochondria and colocalizing with PUMA after UV irradiation, indicating PUMA promotes Bax translocation directly. Simultaneously, the interaction increased markedly between PUMA and Bcl-X(L) and decreased significantly between Bcl-X(L) and Bax after UV treatment, suggesting PUMA competitively binds to Bcl-X(L) to activate Bax indirectly. The above-mentioned results were further confirmed by coimmunoprecipitation experiments. In addition, pifithrin-alpha (a p53 inhibitor) and cycloheximide (a protein synthesis inhibitor) could inhibit PUMA-mediated Bax translocation and cell apoptosis. Together, these studies create an important conclusion that PUMA promotes Bax translocation by both by directly interacting with Bax and by competitive binding to Bcl-X(L) in UV-induced apoptosis.

BimL directly neutralizes Bcl-xL to promote Bax activation during UV-induced apoptosis

Bcl-2-interacting mediator of cell death (Bim) has been considered to initiate intrinsic apoptotic pathway through Bax activation. Previous studies indicated that BimL was involved in UV-induced apoptosis, but it remains unclear whether Bim activates Bax by directly engaging it or by releasing it from pro-survival relatives such as Bcl-xL. In this study, we attempt to determine the interactions between BimL and Bax/Bcl-xL during Ultraviolet (UV)-induced apoptosis. BimL activation appeared to be an important event in our experiments, as demonstrated by the significant inhibition of cell death, caspase-3 activity, and Bax translocation in cells with knockdown of endogenous BimL by RNAi approach. Both fluorescence resonance energy transfer (FRET) and Co-immunoprecipitation (CO-IP) assays indicated that Bcl-xL directly bound to Bax to inhibit its activation, while BimL directly neutralized Bcl-xL, followed by Bax release and activation upon UV irradiation. Not detected in our experiment was the interaction between BimL and Bax either using FRET approach in living cells or endogenous CO-IP assay. Thus, our findings provide strong evidence in living cells for the first time that BimL initiates apoptosis by abrogating Bcl-xL and promoting Bax activation under UV irradiation.

Regulation of Bax activation and apoptotic response to UV irradiation by p53 transcription-dependent and -independent pathways

The Trp53 tumor suppressor gene product (p53) functions in the nucleus to regulate proapoptotic genes, whereas cytoplasmic p53 directly activates proapoptotic Bcl-2 proteins to permeabilize mitochondria and initiate apoptosis. Here, we demonstrate that both p53 transcription-dependent and -independent pathways contribute to UV-induced apoptosis. First we show that Pifithrin-alpha, a small molecule inhibitor of p53 transcriptional activity, delays Bax translocation and cell death by UV irradiation. Then using CHX (cycloheximide) to prevent new protein expression in response to p53, we also find that Bax translocation and cell death by UV irradiation are delayed. Furthermore we find that overexpression of Bcl-x(L), an inhibitor of cytoplasmic p53 after UV irradiation, prevents cell death. Finally, we observe that Pifithrin-alpha and CHX effectively inhibit PUMA expression by UV irradiation. Taken together, these data indicate that the nuclear p53 promotes PUMA expression, which then displaces cytoplasmic p53 from Bcl-x(L), allowing p53 to induce mitochondrial permeabilization, thereby triggering apoptosis.

Bim(L) displacing Bcl-x(L) promotes Bax translocation during TNFalpha-induced apoptosis

Bcl-2 family proteins are implicated as essential regulators in tumor necrosis factor-alpha (TNFalpha)-induced apoptosis. Bim(L), a BH3-only member of Bcl-2 family, can directly or indirectly activate the proapoptotic Bax and the subsequent mitochondrial apoptotic pathway. However, the molecular mechanism of Bim(L) activating Bax activation during TNFalpha-induced apoptosis is not fully understood. In this study, the role of Bim(L) in Bax activation during TNFalpha-induced apoptosis was investigated in differentiated PC12 and MCF7 cells, with real-time single-cell analysis. The experimental results show that Bax translocated to mitochondria and cytochrome c (Cyt c) released from mitochondria after TNFalpha treatment. Furthermore, SP600125 (specific inhibitor of JNK) could inhibit the Cyt c release from mitochondria. Co-immunoprecipitation results show that, the interaction between Bcl-x(L) and Bax decreased after TNFalpha treatment, while that between Bcl-x(L) and Bim(L) increased. Bax did not co-immunoprecipitate with Bim(L) before or after the TNFalpha treatment. In addition, the increased interaction between Bim(L) and Bcl-x(L) was dynamically monitored by using fluorescence resonance energy transfer (FRET) technique. Most importantly, there was no evidence of Bim(L) redistribution to mitochondria until cell apoptosis. By comprehensively analyzing these data, it is concluded that Bim(L) displaces Bcl-x(L) in the mitochondria and promotes Bax translocation during TNFalpha-induced apoptosis.

Live morphological analysis of taxol-induced cytoplasmic vacuolization [corrected] in human lung adenocarcinoma cells

Taxol (paclitaxel), one of the most active cancer chemotherapeutic agents, can cause programmed cell death (PCD) and cytoplasmic vacuolization. The objective of this study was to analyze the morphological characteristics induced by taxol. Human lung adenocarcinoma (ASTC-a-1) cells were exposed to various concentration of taxol. CCK-8 was used to assay the cell viability. Atomic force microscopy (AFM), plasmid transfection and confocal fluorescence microscopy were performed to image the cells morphological change induced by taxol. Fluorescence resonance energy transfer (FRET) was used to monitor the caspase-3 activation in living cells during taxol-induced cell death. Cells treated with taxol exhibited significant swelling and cytoplasmic vacuolization which may be due to endoplasmic reticulum (ER) vacuolization. Caspase-3 was not activated during taxol-induced cytoplasmic vacuolization and cell death. These findings suggest that taxol induces caspase-3-independent cytoplasmic vacuolization, cell swelling and cell death through ER vacuolization.