Involvement of caspase-3 activation in squamocin-induced apoptosis in leukemia cell line HL-60

Annonaceous acetogenins have potent antitumor effect in vitro and in vivo. Squamocin is one of the annonaceous acetogenins and has been reported to have antiproliferative effect on cancer cells. Our results from this study showed that squamocin inhibited proliferation of HL-60 cells with IC50 value of 0.17 microg/ml and induced apoptosis of HL-60 cells. Investigation of the mechanism of squamocin-induced apoptosis revealed that treatment of HL-60 cells with squamocin resulted in extensive nuclear condensation. DNA fragmentation, cleavage of the death substrate poly (ADP-ribose) polymerase (PARP) and induction of caspase-3 activity. Pretreatment of HL-60 cells with caspase-3 specific inhibitor DEVD-CHO prevented squamocin-induced DNA fragmentation, PARP cleavage and cell death. The expression levels of protein bcl-2, bax have no change in response to squamocin treatment in HL-60 cells, whereas stress-activated protein kinase (SAPK/JNK) was activated after treatment with squamocin in HL-60 cells. These results suggest that apoptosis of HL-60 cells induced by squamocin requires caspase-3 activation and is related to SAPK activation.     

Reversible inhibition of caspase-3 activity by iron(III): potential role in physiological control of apoptosis

Desferoxamine is known to induce apoptosis in cancer cells, but the mechanisms are still not fully understood. We have shown that iron(III) is a potent caspase-3 inhibitor, and the inhibition is reversible by the iron chelating agent desferoxamine. Also, protein disulfide isomerase (PDI) is capable of activating caspase-3 inhibited by iron(III), likely by formation of iron-sulfur complex through its active site thiols. Data presented here suggests that iron(III) could be a potential inhibitor of apoptosis in vivo, by caspase-3-dependent inhibition with a possibility of recovery through PDI overexpression.     

Nitric oxide induces thymocyte apoptosis via a caspase-1-dependent mechanism

We previously showed that NO induces apoptosis in thymocytes via a p53-dependent pathway. In the present study, we investigated the role of caspases in this process. The pan-caspase inhibitor, ZVAD-fmk, and the caspase-1 inhibitor, Ac-YVAD-cho, both inhibited NO-induced thymocyte apoptosis in a dose-dependent manner, whereas the caspase-3 inhibitor, Ac-DEVD-cho, had little effect even at concentrations up to 500 microM. ZVAD-fmk and Ac-YVAD-cho were able to inhibit apoptosis when added up to 12 h, but not 16 h, after treatment with the NO donor S-nitroso-N-acetyl penicillamine (SNAP). Caspase-1 activity was up-regulated at 4 h and 8 h and returned to baseline by 24 h; caspase-3 activity was not detected. Cytosolic fractions from SNAP-treated thymocytes cleaved the inhibitor of caspase-activated deoxyribonuclease. Such cleavage was completely blocked by Ac-YVAD-cho, but not by Ac-DEVD-cho or DEVD-fmk. Poly(ADP-ribose) polymerase (PARP) was also cleaved in thymocytes 8 h and 12 h after SNAP treatment; addition of Ac-YVAD-cho to the cultures blocked PARP cleavage. Furthermore, SNAP induced apoptosis in 44% of thymocytes from wild-type mice; thymocytes from caspase-1 knockout mice were more resistant to NO-induced apoptosis. These data suggest that NO induces apoptosis in thymocytes via a caspase-1-dependent but not caspase-3-dependent pathway. Caspase-1 alone can cleave inhibitor of caspase-activated deoxyribonuclease and lead to DNA fragmentation, thus providing a novel pathway for NO-induced thymocyte apoptosis.     

Intranasal Delivery of a Caspase-1 Inhibitor in the Treatment of Global Cerebral Ischemia

Caspase-1 is an enzyme implicated in neuroinflammation, a critical component of many diseases that affect neuronal degeneration. However, it is unknown whether a caspase-1 inhibitor can modify apoptotic neuronal damage incurred during transient global cerebral ischemia (GCI) and whether intranasal administration of a caspase-1 inhibitor is an effective treatment following GCI. The present study was conducted to examine the potential efficiency of post-ischemic intranasal administration of the caspase-1 inhibitor Boc-D-CMK in a 4-vessel occlusion model of GCI in the rat. Herein, we show that intranasal Boc-D-CMK readily penetrated the central nervous system, subsequently inhibiting caspase-1 activity, decreasing mitochondrial dysfunction, and attenuating caspase-3-dependent apoptotic pathway in ischemia-vulnerable hippocampal CA1 region. Further investigation regarding the mechanisms underlying Boc-D-CMK’s neuroprotective effects revealed marked inhibition of reactive gliosis, as well as reduction of the neuroinflammatory response via inhibition of the downstream pro-inflammatory cytokine production. Intranasal Boc-D-CMK post-treatment also significantly enhanced the numbers of NeuN-positive cells while simultaneously decreasing the numbers of TUNEL-positive and PARP1-positive cells in hippocampal CA1. Correspondingly, behavioral tests showed that deteriorations in spatial learning and memory performance, and long-term recognition memory following GCI were significantly improved in the Boc-D-CMK post-treated animals. In summary, the current study demonstrates that the caspase-1 inhibitor Boc-D-CMK coordinates anti-inflammatory and anti-apoptotic actions to attenuate neuronal death in the hippocampal CA1 region following GCI. Furthermore, our data suggest that pharmacological inhibition of caspase-1 is a promising neuroprotective strategy to target ischemic neuronal injury and functional deficits following transient GCI.     

Taurine reduces caspase-8 and caspase-9 expression induced by ischemia in the mouse hypothalamic nuclei

Summary. Taurine is a sulphur-containing amino acid abundant in the nervous system. It protects cells from ischemia-induced apoptosis, but the mechanism underlying this is not well established. The aim of our study was to explore the effects of taurine on two main pathways of apoptosis induced by ischemia: receptor-mediated and mitochondrial cell death. Brain slices containing the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus were incubated in vitro under control and simulated ischemic (oxygen-glucose deprivation for 30 min) conditions in the absence and presence of 20 mM taurine. Brain slices were harvested after the 180-min “postischemic” period and fixed in 4% paraformaldehyde. To estimate apoptosis, immunostaining was done for caspase-8 and caspase-9 in paraffin-embedded sections. Immunoreactive caspase-8 and caspase-9 cells were observed in SON and PVN in all experimental groups, but in the “ischemic” group the expression of caspase-8 and caspase-9 and the number of immunoreactive cells was significantly increased in both hypothalamic nuclei. Addition of taurine (20 mM) to the incubation medium induced a marked decrease in caspase-8 and caspase-9 immunoreactivity after ischemia in SON and PVN when compared with the taurine-untreated “ischemic” group. Taurine reduces ischemia-induced caspase-8 and caspase-9 expression, the key inductors of apoptosis in SON and PVN. Authors’ address: Dr. Andrey Taranukhin, Tampere Brain Research Center, Medical School, University of Tampere, FI-33014 Finland     

Hydrogen peroxide inhibits activation, not activity, of cellular caspase-3 in vivo

Oxidants such as H(2)O(2) can induce a low level of apoptosis at low concentrations but at higher concentrations cause necrosis. Higher concentrations of H(2)O(2) also inhibit the induction of apoptosis by chemotherapy drugs. One theory is that, at higher concentrations, H(2)O(2) causes direct oxidative inactivation of caspase-3 activity, thus preventing the apoptotic pathway from being used. We find that treatment of recombinant caspase-3 with H(2)O(2) can partially reduce its enzymatic activity: However, the following findings show that this does not occur in the cell. (1) The inhibition by H(2)O(2) of VP-16-induced apoptosis and cellular caspase-3 activity can be overcome by adding inhibitors of poly(ADP-ribose) polymerase (PARP) at sub-stoichiometric concentrations. (2) Delayed addition of H(2)O(2) to VP-16-treated cells prevents additional caspase induction but does not inhibit the caspase activity that has already been generated. (3) H(2)O(2) is a poor inhibitor of caspase-3 activity in cell lysates. (4) Addition of H(2)O(2) to cells inhibits activation of caspase-9, which is required for activation of caspase-3. We conclude that inhibition of caspase-3 activity in the cell occurs indirectly at a step located upstream of caspase-3 activation. H(2)O(2) acts in part by inducing DNA strand breaks and activating PARP, thus depleting the cells of ATP. When this pathway is blocked, even high concentrations of H(2)O(2) can induce caspase-9 and -3 activation and cause apoptosis.     

Involvement of caspase-3-like protease in the mechanism of cell death following focally evoked limbic seizures

The cysteine protease caspase-3 may be involved in the mechanism of cell death following seizures. Using a rat model of focally evoked limbic epilepsy with continuous electroencephalography monitoring, we investigated seizure-induced changes in caspase-3 protein expression and processing, enzyme activity, and the in vivo effect of caspase-3 inhibition. Seizures were induced by intraamygdaloid injection of kainic acid (0.1 microg) and were terminated after 45 min by diazepam (30 mg/kg) administration. Animals were killed 0-72 h following diazepam administration. Levels of the 32-kDa proenzyme form of caspase-3 were unaffected by seizures. Levels of the 17-kDa cleaved (active) fragment of caspase-3 were almost undetectable in control brain, but were increased significantly at 4 and 24 h within ipsilateral hippocampus and cortex in seizure animals. Caspase-3-like protease activity was increased within the ipsilateral hippocampus at 8 and 24 h following seizures. Caspase-3 immunoreactivity was increased within the vulnerable ipsilateral CA3/CA4 subfield at 24 and 72 h following seizures and was associated predominantly, but not exclusively, with neurons exhibiting DNA fragmentation. The putatively selective caspase-3 inhibitor N-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-fluoromethyl ketone significantly improved neuronal survival bilaterally within the hippocampal CA3/CA4 subfields following seizures. Collectively, these data suggest that caspase-3 may play a significant role in the mechanism by which neurons die following seizures.     

Sequential caspase-2 and caspase-8 activation is essential for saikosaponin a-induced apoptosis of human colon carcinoma cell lines

In this study, we investigated the signaling pathways implicated in SSa-induced apoptosis of human colon carcinoma (HCC) cell lines. SSa-induced apoptosis of HCC cells was associated with proteolytic activation of caspase-9, caspase-3, and PARP cleavages and decreased levels of IAP family members, such as XIAP and c-IAP-2, but not of survivin. The fluorescence intensity of DiOC6 was significantly reduced after SSa treatment. CsA significantly inhibited SSa-induced loss of mitochondrial transmembrane potential and moderately inhibited SSa-induced cell death. SSa treatment also enhanced the activities of caspase-2 and caspase-8, Bid cleavage, and the conformational activation of Bax. Additionally, SSa-induced apoptosis was inhibited by both the selective caspase-2 inhibitor z-VDVAD-fmk and the selective caspase-8 inhibitor z-IETD-fmk and also by si-RNAs against caspase-2 and caspase-8. The selective caspase-9 inhibitor, z-LEHD-fmk, also inhibited SSa-induced apoptosis, albeit to a lesser extent compared to z-VDVAD-fmk and z-IETD-fmk, indicating that both mitochondria-dependent and mitochondria-independent pathways are associated with SSa-induced apoptosis. Both z-VDVAD-fmk and z-IETD-fmk significantly attenuated the colony-inhibiting effect of SSa. Moreover, inhibition of caspase-2 activation by the pharmacological inhibitor z-VDVAD-fmk, or by knockdown of protein levels using a si-RNA, suppressed SSa-induced caspase-8 activation, Bid cleavage, and the conformational activation of Bax. Although caspase-8 is an initiator caspase like caspase-2, the inhibition of caspase-8 activation by knockdown using a si-RNA did not suppress SSa-induced caspase-2 activation. Altogether, our results suggest that sequential activation of caspase-2 and caspase-8 is a critical step in SSa-induced apoptosis.     

Mild hypothermia protects hippocampal neurons from oxygen-glucose deprivation injury through inhibiting caspase-3 activation

Mild hypothermia (MH) is thought to be one of the most effective therapeutic methods to treat hypoxic-ischemic encephalopathy (HIE) after cardiac arrest (CA). However, its precise mechanisms remain unclear. In this research, hippocampal neurons were cultured and treated with mild hypothermia and Ac-DEVD-CHO after oxygen-glucose deprivation (OGD). The activity of caspase-3 was detected, in order to find the precise concentration of Ac-DEVD-CHO with the same protective role in OGD injury as MH treatment. Western blot and immunofluorescence staining were conducted to analyze the effects of MH and Ac-DEVD-CHO on the expressions of caspase-3, caspase-8, and PARP. The neuronal morphology was observed with an optical microscope. The lactic acid dehydrogenase (LDH) release rate, neuronal viability, and apoptotic rate were also detected. We found that MH (32 °C) and Ac-DEVD-CHO (5.96 μMol/L) had equal effects on blocking the activation of caspase-3 and the OGD-induced cleavage of PARP, but neither had any effect on the activation of caspase-8, which goes on to activate caspase-3 in the apoptotic pathway. Meanwhile, both MH and Ac-DEVD-CHO had similar effects in protecting cell morphology, reducing LDH release, and inhibiting OGD-induced apoptosis in neurons. They also similarly improved neuronal viability after OGD. In conclusion, caspase-3 serves as a key intervention point of the key modulation site or regulatory region in MH treatment that protects neuronal apoptosis against OGD injury. Inhibiting the expression of caspase-3 had a protective effect against OGD injury in MH treatment, and caspase-3 activation could be applied to evaluate the neuroprotective effectiveness of MH on HIE.     

Overexpression of microRNA-378 attenuates ischemia-induced apoptosis by inhibiting caspase-3 expression in cardiac myocytes

MicroRNAs (miRNAs) are a novel class of powerful, endogenous regulators of gene expression. In an intact rat model of myocardial ischemia caused by coronary artery ligation, this study identified 17 miRNAs that changed more than 1.5-fold in the myocardium subjected to 4-h ischemia. Using miRNA microarray analysis, most of these aberrantly expressed miRNAs were confirmed by quantitative RT-PCR. MiR-378, a significantly down-regulated miRNA, was selected for further function study. In serum deprived rat H9c2 cardiomyocytes exposed to hypoxia (1% O₂), miR-378 expression was down-regulated as well. The overexpression of miR-378 resulting from miR-378 mimic transfection significantly enhanced cell viability, reduced lactate dehydrogenase release, and inhibited apoptosis and necrosis. By contrast, miR-378 deficiency resulting from miR-378 inhibitor transfection aggravated the hypoxia-induced apoptosis and cell injury. In accordance, miR-378 inhibitor caused significant apoptosis and cell injury to cardiomyocytes cultured under normoxia. Using bioinformatic algorithms, caspase-3, a key apoptosis executioner, was predicted as a putative target of miR-378. The quantitative RT-PCR showed no effects of miR-378 mimic or inhibitor on caspase-3 mRNA level. However, the amount of caspase-3 proteins was reduced by miR-378 mimic, whereas increased by miR-378 inhibitor. Furthermore, the luciferase reporter assay confirmed caspase-3 to be a target of miR-378, and the apoptosis and cell injury caused by miR-378 inhibitor in both normoxic and hypoxic cells were abolished by a caspase-3 inhibitor. This study first showed that miR-378 inhibited caspase-3 expression and attenuated ischemic injury in cardiomyocytes. It may represent a potential novel treatment for apoptosis and ischemic heart disease.     

Mechanism of UV-Induced Apoptosis in Human Leukemia Cells: Roles of Ca/Mg-Dependent Endonuclease, Caspase-3, and Stress-Activated Protein Kinases

Ultraviolet light (UV) induced rapid apoptosis of U937 leukemia cells, concurrent with DNA fragmentation and cleavage of poly(ADP-ribose)polymerase (PARP) by activated caspase-3. Thein vitroreconstitution of intact HeLa S3 nuclei and apoptotic U937 cytosolic extract (CE) revealed that (i) Ca²⁺/Mg²⁺-dependent, Zn²⁺-sensitive endonuclease activated in the apoptotic CE induced DNA ladder in HeLa nuclei at pH 6.8–7.4, (ii) activated caspase-3 cleaved PARP in HeLa nuclei, and (iii) when the apoptotic CE was treated with the caspase-3 inhibitor (1 μM Ac-DEVD-CHO) or the caspase-1 inhibitor (10 μM Ac-YVAD-CHO), the former, but not the latter, caused a 50% inhibition of DNA fragmentation and the complete inhibition of PARP cleavage in HeLa nuclei. Similarly, Ac-DEVD-CHO (100 μM) inhibited apoptosis and DNA ladder by 50% and PARP cleavage completely in UV-irradiated U937 cells, but Ac-YVAD-CHO (100 μM) did not. Thus, UV-induced apoptosis of U937 cells involves the Ca²⁺/Mg²⁺-dependent endonuclease pathway and the caspase-3–PARP cleavage–Ca²⁺/Mg²⁺-dependent endonuclease pathway. The former pathway produced directly 50% of apoptotic DNA ladder, and the latter involved activated caspase-3 and PARP cleavage, followed by formation of the remaining 50% DNA ladder by the activated endonuclease. In UV-irradiated B-cell lines, further, p53-dependent increase of Bax resulted in a greater caspase-3 activation compared to its absence. However, UV-induced activation of JNK1 and p38 was not affected by the caspase-1 and -3 inhibitors in U937 cells, so that caspases-1 and -3 do not function upstream of JNK1 and p38.     

Protein kinase C inhibition induces DNA fragmentation in COLO 205 cells which is blocked by cysteine protease inhibition but not mediated through caspase-3

Enhancing apoptosis to remove abnormal cells has potential in reversing cancerous processes. Caspase-3 activation generally accompanies apoptosis and its substrates include enzymes responsible for DNA fragmentation and isozymes of protein kinase C (PKC). Recent data, however, question its obligatory role in apoptosis. We have examined whether modulation of PKC activity induces apoptosis in COLO 205 cells and the role of caspase-3. Proliferation ([3H]thymidine) and apoptosis (DNA fragmentation and FACS) of COLO 205 cells were measured in response to PKC activation and inhibition. Caspase-3 activity was assayed and the effects of its inhibition with Ac-DEVD-cmk, and the effect of other protease inhibitors, on apoptosis were determined. PKC activation and inhibition both reduced DNA synthesis and induced DNA fragmentation. As PKC inhibitors induced DNA fragmentation more rapidly than PKC activators and failed to block activator effects, we conclude that it is PKC down-regulation (i.e., inhibition) after activator exposure that mediates apoptosis. Increases in caspase-3 activity occurred during apoptosis but apoptosis was not blocked by caspase inhibition. By contrast, the cysteine protease inhibitor, E-64d, blocked apoptosis. Cysteine proteases not of the caspase family may either act more closely to the apoptotic process than caspases or lie on an alternative, more active pathway.     

Combined mechanical trauma and metabolic impairment in vitro induces NMDA receptor-dependent neuronal cell death and caspase-3-dependent apoptosis.

Neuronal necrosis and apoptosis occur after traumatic brain injury (TBI) in animals and contribute to subsequent neurological deficits. In contrast, relatively little apoptosis is found after mechanical injury in vitro. Because in vivo trauma models and clinical head injury have associated cerebral ischemia and/or metabolic impairment, we transiently impaired cellular metabolism after mechanical trauma of neuronal-glial cultures by combining 3-nitropropionic acid treatment with concurrent glucose deprivation. This produced greater neuronal cell death than mechanical trauma alone. Such injury was attenuated by the NMDA receptor antagonist dizocilpine (MK801). In addition, this injury significantly increased the number of apoptotic cells over that accruing from mechanical injury alone. This apoptotic cell death was accompanied by DNA fragmentation, attenuated by cycloheximide, and associated with an increase in caspase-3-like but not caspase-1-like activity. Cell death was reduced by the pan-caspase inhibitor BAF or the caspase-3 selective inhibitor z-DEVD-fmk, whereas the caspase-1 selective inhibitor z-YVAD-fmk had no effect; z-DEVD-fmk also reduced the number of apoptotic cells after combined injury. Moreover, cotreatment with MK801 and BAF resulted in greater neuroprotection than either drug alone. Thus, in vitro trauma with concurrent metabolic inhibition parallels in vivo TBI, showing both NMDA-sensitive necrosis and caspase-3-dependent apoptosis.     

Titanium dioxide nanoparticles induce apoptosis through the JNK/p38-caspase-8-Bid pathway in phytohemagglutinin-stimulated human lymphocytes

We investigated the signaling pathways underlying nano-TiO₂-induced apoptosis in cultured human lymphocytes. Nano-TiO₂ increased the proportion of sub-G1 cells, activated caspase-9 and caspase-3, and induced caspase-3-mediated PARP cleavage. Nano-TiO₂ also induced loss of mitochondrial membrane potential, which suggests that nano-TiO₂ induces apoptosis via a mitochondrial pathway. A time-sequence analysis of the induction of apoptosis by nano-TiO₂ revealed that nano-TiO₂ triggered apoptosis through caspase-8/Bid activation. We also observed that inhibition of caspase-8 by z-IETD-fmk suppressed the caspase-8/Bid activation, caspase-3-mediated PARP cleavage, and apoptosis. Nano-TiO₂ activated two MAPKs, p38 and JNK. In addition, the selective p38 inhibitor SB203580 and selective JNK inhibitor SP600125 suppressed nano-TiO₂-induced apoptosis and caspase-8 activation to moderate and significant extents, respectively. Knockdown of protein levels of JNK1 and p38 using an RNA interference technique also suppressed caspase-8 activation. Our results suggest that nano-TiO₂-induced apoptosis is mediated by the p38/JNK pathway and the caspase-8-dependent Bid pathway in human lymphocytes.     

Inhibition of nitric oxide and caspase-3 mediated apoptosis by a tetrapeptide derivative (PEP1261) in cultured synovial fibroblasts from collagen-induced arthritis

In this study, the effect of (Boc-Lys (Boc)-Arg-Asp-Ser (tBu)-OtBu), a tetrapeptide derivative (PEP1261) was examined for antiproliferative potency and apoptotic induction. Synovial fibroblasts were isolated from collagen-induced arthritic (CIA) rats and exposed to peptides viz., PEP1261, and parental peptides (KRDS and RGDS). Viability of the cells decreased in the presence of PEP1261 at a lower concentration (0.1 mM) when compared to RGDS and KRDS (1 mM). The treatment of cells with peptides showed induction of apoptosis, resulting in the cleavage of caspase-3 as well as its substrate poly-(ADP-ribose) polymerase (PARP). Pretreatment of cells with caspase-3 inhibitor prevented inhibition of [³H] thymidine incorporation, DNA fragmentation, and cleavage of caspase-3 and PARP as confirmed by western blotting as well as annexin-V/PI-staining using flow cytometry. However, caspase-1 and caspase-2 inhibitors did not prevent the peptides from inducing apoptosis indicating that caspase-3 might have a role in the process of apoptosis induced by peptides. Treatment of synovial fibroblasts with nitric oxide donor, S-nitroso-N-acetyl-dl-penicillamine (SNAP) (500 μM) showed significant elevation of nitric oxide levels and resulted in absence of apoptosis by preventing the inhibition of [³H] thymidine incorporation. This was further evidenced by annexin V/propidium iodide (PI) staining and absence of DNA fragmentation, intra cellular caspase-3 activity and PARP cleavage. In contrast, SNAP followed by PEP1261 and parental peptides-induced apoptosis by lowering the levels of nitric oxide. These results suggested that PEP1261 suppressed the proliferation and induced apoptosis in cultured synovial fibroblasts from CIA rats. This study also confirmed that PEP1261 inhibited nitric oxide level in cultured synovial fibroblasts.     

Involvement of caspase-3 in apoptosis induced by Viscum album var. coloratum agglutinin in HL-60 cells

A cytotoxic lectin (Viscum album L. coloratum agglutinin, VCA) from Korean mistletoe was isolated by affinity chromatography on Sepharose 4B immobilized with asialofetuin. In HL-60 cells, addition of VCA resulted in a dose- and time-dependent growth suppression, morphological changes of apoptotic nuclei, and DNA fragmentation characteristics of apoptosis. To investigate how caspase-3 activation during VCA-induced apoptosis induces cleavages of PARP, the expression of PARP and the pattern of caspase-3 activation in HL-60 cells were investigated. The native and processed PARP forms typically seen in apoptotic cells were observed, and a decrease in expression of the 32-kDa form of caspase-3 in a dose-dependent manner was observed. The VCA-induced apoptosis was significantly inhibited by a caspase-3 specific inhibitor, z-DEVD-FMK, and the PARP processing and caspase-3 activation were also inhibited by the inhibitor. A possible involvement of cell cycle arrest in VCA-induced apoptosis was investigated by flow cytometry and the results suggested that the apoptotic effect of VCA is not involved in the induction of cell cycle arrest.     

Involvement of caspase-3 in epigallocatechin-3-gallate-mediated apoptosis of human chondrosarcoma cells

Green tea polyphenol-(-)epigallocatechin-3-gallate (EGCG)-is a potent chemopreventive agent in many test systems and has been shown to inhibit tumor promotion and induce apoptosis. In this study we describe a novel observation that EGCG displayed strong inhibitory effects on the proliferation and viability of HTB-94 human chondrosarcoma cells in a dose-dependent manner and induced apoptosis. Investigation of the mechanism of EGCG-induced apoptosis revealed that treatment with EGCG resulted in DNA fragmentation, induction of caspase-3/CPP32 activity, and cleavage of the death substrate poly(ADP-ribose)polymerase (PARP). Pretreatment of cells with a synthetic pan-caspase inhibitor (Z-VAD-FMK) and a caspase-3-specific inhibitor (DEVD-CHO) prevented EGCG-induced PARP cleavage. The induction of apoptosis by EGCG via activation of caspase-3/CPP32-like proteases may provide a mechanistic explanation for its antitumor effects.     

Molecular mechanism of apoptosis: prediction of three-dimensional structure of caspase-6 and its interactions by homology modeling

Caspases, the intracellular cysteine proteinases, play a central role in the process of programmed cell death. Caspases induce apoptosis through a highly integrated and regulated biological, biochemical, and genetic mechanism. Although proper execution of apoptosis is fundamental for cell growth artificial caspase inhibition can be considered in certain degenerative diseases. This realization has attracted attention towards caspases as likely targets for pharmaceutical intervention. Here we analyze the structure of caspase-6 and also predict the possible glycosylation, phosphorylation, and myristoylation sites as very little is known about the functional role of these post translational modifications in the caspase family. These studies are expected to improve our understanding of associations of caspases with other molecules and the possible role played in apoptosis. The predicted tertiary structure of caspase-6 as well as the enzyme complexed with its inhibitor (tetra-peptide aldehyde Ac-IETD-CHO) shows similar binding feature as seen in other caspases. Cys/His catalytic dyad for caspase-6 and -8 show possible involvement of a third component, i.e., Pro29 and Arg258 in caspase-6 and caspase-8, respectively. Changes in the length and nature of loop between alpha5 and beta9, involved in defining the S4 subsite, result in modification of P4 (Ile) site. These interactions provide detail of inhibitor binding on structural level and also help in designing mutants for structure-function studies of these enzymes.     

The large subunit of replication factor C is a substrate for caspase-3 in vitro and is cleaved by a caspase-3-like protease during Fas-mediated apoptosis.

Caspase-3 is an ICE-like protease activated during apoptosis induced by different stimuli. Poly(ADP-ribose) polymerase (PARP), the first characterized substrate of caspase-3, shares a region of homology with the large subunit of Replication Factor C (RF-C), a five-subunit complex that is part of the processive eukaryotic DNA polymerase holoenzymes. Caspase-3 cleaves PARP at a DEVD-G motif present in the 140 kDa subunit of RF-C (RFC140) and evolutionarily conserved. We show that cleavage of RFC140 during Fas-mediated apoptosis in Jurkat cells and lymphocytes results in generation of multiple fragments. Cleavage is inhibited by the caspase-3-like protease inhibitor Ac-DEVD-CHO but not the caspase-1/ICE-type protease inhibitor Ac-YVAD-CHO. In addition, recombinant caspase-3 cleaves RFC140 in vitro at least at three different sites in the C-terminal half of the protein. Using amino-terminal microsequencing of radioactive fragments, we identified three sites: DEVD723G, DLVD922S and IETD1117A. We did not detect cleavage of small subunits of RF-C of 36, 37, 38 and 40 kDa by recombinant caspase-3 or by apoptotic Jurkat cell lysates. Cleavage of RFC140 during apoptosis inactivates its function in DNA replication and generates truncated forms that further inhibit DNA replication. These results identify RFC140 as a critical target for caspase-3-like proteases and suggest that caspases could mediate cell cycle arrest.