Caspases and receptor cleavage

Antioxidant, cytotoxic and apoptotic activities of the rhizome of Zingiber zerumbet Linn. in Ehrlich ascites carcinoma bearing Swiss albino mice

Due to having a long history of traditional uses as a functional food, Zingiber zerumbet was selected here to explore the inherent antioxidant and antineoplastic activities of methanolic extract of its rhizome (MEZZR) against Ehrlich ascites carcinoma (EAC) cells. The rich polyphenol containing MEZZR showed a marked DPPH, ABTS, nitric oxide radicals and lipid peroxidation inhibition activity with an IC₅₀ of 3.43 ± 1.25, 11.38 ± 1.39, 23.12 ± 3.39 and 16.47 ± 1.47 µg/ml, respectively, when compared to the standard catechin. In vivo, MEZZR significantly inhibited EAC cell growth, decreased body weight gain, increased life span and restored the altered hematological characteristics of EAC-bearing mice. Moreover, MEZZR induced nuclear condensation and fragmentation, which are notable features of apoptosis as observed by fluorescence microscopy after staining EAC cells of MEZZR-treated mice with Hoechst 33342. Additionally, in vitro, the cell growth inhibition caused by the MEZZR in MTT assay, was remarkably decreased in the presence of caspase-3, -8 and -9 inhibitors. This study thus suggests that MEZZR may possess promising antiproliferative efficacy against EAC cells by inducing cell apoptosis.

The synergistic effect of eucalyptus oil and retinoic acid on human esophagus cancer cell line SK-GT-4

Background

In order to improve cancer patients' chances of survival, scientists have prioritized finding alternatives to chemotherapy, focusing their efforts on natural sources. The current study investigates the anti-cancer action of retinoic acid and Eucalyptus oil in esophageal cancer and studies their combined effect as well as the cellular pathways that each trigger as part of ongoing research in this field. As a model of esophageal cancer, the SK-GT-4 cancer cell line was treated with a series of concentrations of both materials.

Results

The concentrations of Eucalyptus oil (10, 100, 1000, and 1500 g/mL) and Retinoic acid (5, 100, 150, and 200 M/mL) were used for treatment of cells. The MTT test was used to assess the anti-cancer activity of Eucalyptus oil and Retinoic acid, and qPCR was used to determine cellular pathways. Our findings show that both Eucalyptus oil and Retinoic acid inhibit cancer cell growth significantly. Our findings revealed that the IC50 values for eucalyptus oil were 63 g/mL and 111.3 M l/mL for retinoic acid. Furthermore, the impact was at the level that causes apoptosis. The findings suggested that any herbal substance could act as an inducer of the caspase-9-dependent pathway. The caspase-8-dependent pathway, on the other hand, was restricted to retinoic acid.

Conclusion

Our research discovered that the two chemicals worked together to create a synergistic effect. This synergistic effect could be attributed to a close connection between external and internal apoptotic pathways, which inhibits SK-GT-4 cell growth.

Graphical Abstract

Unfolding the apoptotic mechanism of antioxidant enriched-leaves of Tabebuia pallida (lindl.) miers in EAC cells and mouse model

ETHNOPHARMACOLOGICAL RELEVANCE

Tabebuia pallida (Lindl.) Miers (T. pallida) is a well-known native Caribbean medicinal plant. The leaves and barks of T. pallida are used as traditional medicine in the form of herbal or medicinal tea to manage cancer, fever, and pain. Moreover, extracts from the leaves of T. pallida showed anticancer activity. However, the chemical profile and mechanism of anticancer activity of T. pallida leaves (TPL), stem bark (TPSB), root bark (TPRB) and flowers (TPF) remain unexplored.

AIM OF THE STUDY

The present study was designed to explore the regulation of apoptosis by T. pallida using Ehrlich Ascites Carcinoma (EAC) cultured cells and an EAC mouse model. LC-ESI-MS/MS was used for compositional analysis of T. pallida extracts.

MATERIALS AND METHODS

Dried and powdered TPL, TPSB, TPRB and TPF were extracted with 80% methanol. Using cultured EAC cells and EAC-bearing mice with and without these extracts, anticancer activities were studied by assessing cytotoxicity and tumor cell growth inhibition, changes in life span of mice, and hematological and biochemical parameters. Apoptosis was analyzed by microscopy and expression of selected apoptosis-related genes (Bcl-2, Bcl-xL, NFκ-B, PARP-1, p53, Bax, caspase-3 and -8) using RT-PCR. LC-ESI-MS analysis was performed to identify the major compounds from active extracts. Computer aided analyses was undertaken to sort out the best-fit phytoconstituent of total ten isolated compounds of this plant for antioxidant and anticancer activity.

RESULTS

In EAC mice compared with untreated controls, the TPL extract exhibited the highest cancer cell toxicity with significant tumor cell growth inhibition (p < 0.001), reduced ascites by body weight (p < 0.01), increased the life span (p < 0.001), normalized blood parameters (RBC/WBC counts), and increased the levels of superoxide dismutase and catalase. TPL-treated EAC cells showed increased apoptotic characteristics of membrane blebbing, chromatin condensation and nuclear fragmentation, and caspase-3 activation, compared with untreated EAC cells. Moreover, annexin V-FITC and propidium iodide signals were greatly enhanced in response to TPL treatment, indicating apoptosis induction. Pro- and anti-apoptotic signaling after TPL treatment demonstrated up-regulated p53, Bax and PARP-1, and down-regulated NFκ-B, Bcl-2 and Bcl-xL expression, suggesting that TPL shifts the balance of pro- and anti-apoptotic genes towards cell death. LC-ESI-MS data of TPL showed a mixture of glycosides, lapachol, and quercetin antioxidant and its derivatives that were significantly linked to cancer cell targets. The compound, pelargonidin-3-O-glucoside was found to be most effective in computer aided models.

CONCLUSIONS

In conclusion, the TPL extract of T. pallida possesses significant anticancer activity. The tumor suppressive mechanism is due to apoptosis induced by activation of antioxidant enzymes and caspases and mediated by a change in the balance of pro- and anti-apoptotic genes that promotes cell death.

Study of a common azo food dye in mice model: Toxicity reports and its relation to carcinogenicity

This study was conducted to evaluate the toxic effects of an azo dye carmoisine widely used in foods and to investigate its relation to carcinogenicity. Carmoisine administered into mice orally in four different doses as control, low, medium, and high equivalent to 0, 4, 200, and 400 mg/kg bw, respectively, for 120 days. The key toxicological endpoint was observed including animal body weight, organ weights, hematology, biochemistry, and molecular biology assessment. The body weights of medium- and high-dose carmoisine-treated mice group were significantly decreased as compared to the control mice group. Platelet, white blood cell and monocyte counts of treated group were considerably higher, while Hb and red blood cell counts were drastically lower than the control group. The biochemical parameters such as serum alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total protein, globulin, urea, and creatinine level were significantly increased, while serum cholesterol level was decreased after treatment as compared to the control. RT-PCR results showed that expression of Bcl-x and PARP gene was intensively increased, whereas expression of p53 gene was decreased in the mouse liver tissues treated with carmoisine. This study revealed that high-dose (400 mg/kg bw) treatment of carmoisine was attributable to renal failure and hepatotoxicity. It also would be suspected as a culprit for liver oncogenesis.

Synthesis and biological evaluation of alpha-bromoacryloylamido indolyl pyridinyl propenones as potent apoptotic inducers in human leukaemia cells

The combination of two pharmacophores into a single molecule represents one of the methods that can be adopted for the synthesis of new anticancer molecules. To investigate the influence of the position of the pyridine nitrogen on biological activity, two different series of α-bromoacryloylamido indolyl pyridinyl propenones 3a-h and 4a-d were designed and synthesized by a pharmacophore hybridization approach and evaluated for their antiproliferative activity against a panel of six human cancer cell lines. These hybrid molecules were prepared to combine the α-bromoacryloyl moiety with two series of indole-inspired chalcone analogues, possessing an indole derivative and a 3- or 4-pyridine ring, respectively, linked on either side of 2-propen-1-one system. The structure-activity relationship was also investigated by the insertion of alkyl or benzyl moieties at the N-1 position of the indole nucleus. We found that most of the newly synthesized displayed high antiproliferative activity against U-937, MOLT-3, K-562, and NALM-6 leukaemia cell lines, with one-digit to double-digit nanomolar IC50 values. The antiproliferative activities of 3-pyridinyl derivatives 3f-h revealed that N-benzyl indole analogues generally exhibited lower activity compared to N-H or N-alkyl derivatives 3a-b and 3c-e, respectively. Moreover, cellular mechanism studies elucidated that compound 4a induced apoptosis along with a decrease of mitochondrial membrane potential and activated caspase-3 in a concentration-dependent manner.

Ret function in muscle stem cells points to tyrosine kinase inhibitor therapy for facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) involves sporadic expression of DUX4, which inhibits myogenesis and is pro-apoptotic. To identify target genes, we over-expressed DUX4 in myoblasts and found that the receptor tyrosine kinase Ret was significantly up-regulated, suggesting a role in FSHD. RET is dynamically expressed during myogenic progression in mouse and human myoblasts. Constitutive expression of either RET9 or RET51 increased myoblast proliferation, whereas siRNA-mediated knockdown of Ret induced myogenic differentiation. Suppressing RET activity using Sunitinib, a clinically-approved tyrosine kinase inhibitor, rescued differentiation in both DUX4-expressing murine myoblasts and in FSHD patient-derived myoblasts. Importantly, Sunitinib also increased engraftment and differentiation of FSHD myoblasts in regenerating mouse muscle. Thus, DUX4-mediated activation of Ret prevents myogenic differentiation and could contribute to FSHD pathology by preventing satellite cell-mediated repair. Rescue of DUX4-induced pathology by Sunitinib highlights the therapeutic potential of tyrosine kinase inhibitors for treatment of FSHD.

DOI:http://dx.doi.org/10.7554/eLife.11405.001

Design, synthesis and antiproliferative activity of novel heterobivalent hybrids based on imidazo[2,1-b][1,3,4]thiadiazole and imidazo[2,1-b][1,3]thiazole scaffolds

Heterobivalent ligands constituted by two different pharmacophores that bind to different molecular targets or to two distinct sites on the same molecular target could be one of the methods used for the treatment of cancer. In view of the importance of imidazo[1,2-b][1,3]thiazole and imidazo[1,2-b][1,3,4]thiadiazole as privileged structures for the preparation of novel anticancer agents, we decided to explore the synthesis and biological evaluation of molecular conjugates comprising these fused bicyclic systems tethered at their C-6 position by a meta-(α-bromoacryloylamido)phenyl moiety. We found that most of the hybrid compounds displayed high antiproliferative activity toward a wide panel of cancer cell lines, with one-digit micromolar to submicromolar 50% inhibitory concentrations (IC50). We have observed that selected compounds 7d, 7e, 7n and 8c induced apoptosis, which was associated with the release of cytochrome c and cleavage of multiple caspases. Overexpression of the protective mitochondrial protein Bcl-2 did not confer protection to cell death induced by these compounds.

Pea lectin inhibits growth of Ehrlich ascites carcinoma cells by inducing apoptosis and G2/M cell cycle arrest in vivo in mice

Pea (Pisum sativum L.) lectin is known to have interesting pharmacological activities and of great interest on biomedical research. In the current research pea lectin was purified followed by ion exchange chromatography on DEAE column and affinity chromatography on glucose-sepharose column. The lectin shown 11.7-84% inhibitory effect against Ehrlich ascites carcinoma (EAC) cells at the concentration range of 8-120 μg/ml in RPMI 1640 medium as determined by MTT assay. Pea lectin was also shown 63% and 44% growth inhibition against EAC cells in vivo in mice when administered 2.8 mg/kg/day and 1.4 mg/kg/day (i.p.) respectively for five consequent days. When Pea lectin injected into the EAC bearing mice for 10 days its significantly increased the hemoglobin and RBC with the decreased of WBC levels toward the normal. Apoptotic cell morphological change of the treated EAC cells of mice was determined by fluorescence and optical microscope. Interestingly, cell growth inhibition of the lectin was significantly reduced in the presence of caspase inhibitors. Treatment with the lectin caused the cell cycle arrest at G2/M phase of EAC cells which was determined by flow cytometry. The expression of apoptosis-related genes, Bcl-2, Bcl-X and Bax was evaluated by reverse transcriptase polymerase chain reaction (RT-PCR). Intensive increase of Bax gene expression and totally despaired of Bcl-2 and Bcl-X gene expression were observed in the cells treated with Pea lectin for five consecutive days.

Down-regulation of neogenin accelerated glioma progression through promoter Methylation and its overexpression in SHG-44 Induced Apoptosis

Background

Dependence receptors have been proved to act as tumor suppressors in tumorigenesis. Neogenin, a DCC homologue, well known for its fundamental role in axon guidance and cellular differentiation, is also a dependence receptor functioning to control apoptosis. However, loss of neogenin has been reported in several kinds of cancers, but its role in glioma remains to be further investigated.

Methodology/Principal Findings

Western blot analysis showed that neogenin level was lower in glioma tissues than in their matching surrounding non-neoplastic tissues (n = 13, p<0.01). By immunohistochemical analysis of 69 primary and 16 paired initial and recurrent glioma sections, we found that the loss of neogenin did not only correlate negatively with glioma malignancy (n = 69, p<0.01), but also glioma recurrence (n = 16, p<0.05). Kaplan-Meier plot and Cox proportional hazards modelling showed that over-expressive neogenin could prolong the tumor latency (n = 69, p<0.001, 1187.6±162.6 days versus 687.4±254.2 days) and restrain high-grade glioma development (n = 69, p<0.01, HR: 0.264, 95% CI: 0.102 to 0.687). By Methylation specific polymerase chain reaction (MSP), we reported that neogenin promoter was methylated in 31.0% (9/29) gliomas, but absent in 3 kinds of glioma cell lines. Interestingly, the prevalence of methylation in high-grade gliomas was higher than low-grade gliomas and non-neoplastic brain tissues (n = 33, p<0.05) and overall methylation rate increased as glioma malignancy advanced. Furthermore, when cells were over-expressed by neogenin, the apoptotic rate in SHG-44 was increased to 39.7% compared with 8.1% in the blank control (p<0.01) and 9.3% in the negative control (p<0.01).

Conclusions/Significance

These observations recapitulated the proposed role of neogenin as a tumor suppressor in gliomas and we suggest its down-regulation owing to promoter methylation is a selective advantage for glioma genesis, progression and recurrence. Furthermore, the induction of apoptosis in SHG-44 cells after overexpression of neogenin, indicated that neogenin could be a novel target for glioma therapy.

Synthesis and antitumor molecular mechanism of agents based on amino 2-(3',4',5'-trimethoxybenzoyl)benzo[b]furan: inhibition of tubulin and induction of apoptosis

Induction of apoptosis is a promising strategy that could lead to the discovery of new molecules active in cancer chemotherapy. This property is generally observed when cells are treated with agents that target microtubules, dynamic structures that play a crucial role in cell division. Small molecules such as benzo[b]furans are attractive as inhibitors of tubulin polymerization. A new class of inhibitors of tubulin polymerization based on the 2-(3',4',5'-trimethoxybenzoyl)benzo[b]furan molecular skeleton, with the amino group placed at different positions on the benzene ring, were synthesized and evaluated for antiproliferative activity, inhibition of tubulin polymerization, and cell-cycle effects. The methoxy substitution pattern on the benzene portion of the benzo[b]furan moiety played an important role in affecting antiproliferative activity. In the series of 5-amino derivatives, the greatest inhibition of cell growth occurred if the methoxy substituent is placed at the C6 position, whereas C7 substitution decreases potency. The most promising compound in this series is 2-(3',4',5'-trimethoxybenzoyl)-3-methyl-5-amino-6-methoxybenzo[b]furan (3 h), which inhibits cancer cell growth at nanomolar concentrations (IC(50) =16-24 nM), and interacts strongly with tubulin by binding to the colchicine site. Sub-G(1) apoptotic cells in cultures of HL-60 and U937 cells were observed by flow cytometric analysis after treatment with 3 h in a concentration-dependent manner. We also show that compound 3 h induces apoptosis by activation of caspase-3, -8, and -9, and this is associated with cytochrome c release from mitochondria. The introduction of an α-bromoacryloyl group increased antiproliferative activity with respect to the parent amino derivatives.

Isoangustone A present in hexane/ethanol extract of Glycyrrhiza uralensis induces apoptosis in DU145 human prostate cancer cells via the activation of DR4 and intrinsic apoptosis pathway

Glycyrrhiza uralensis (licorice) is one of the most frequently prescribed ingredients in Oriental medicine, and licorice extract has been shown to exert anti-carcinogenic effects. However, its use as a cancer chemopreventive agent is rather limited, due to the fact that its principal component, glycyrrhizin, is known to induce hypertension. This study determined the effects of a hexane/ethanol extract of G. uralensis (HEGU), which contains undetectable amounts of glycyrrhizin, on the apoptosis of androgen-insensitive DU145 cells. HEGU induced apoptosis and increased the levels of cleaved caspase-9, caspase-7, caspase-3 and poly (ADP-ribose) polymerase (PARP). HEGU also induced mitochondrial membrane depolarization and cytochrome c release to the cytosol. HEGU increased the levels of Fas, death receptor 4 (DR4), cleaved caspase-8, Mcl-1S, and truncated Bid proteins. A caspase-8 inhibitor suppressed HEGU-induced apoptosis. An active fraction of HEGU was separated via column chromatography and the structure of the active compound isoangustone A was identified via 1H-NMR and 13C-NMR. Isoangustone A increased apoptotic cells, the cleavage of PARP and caspases, and the levels of DR4 and Mcl-1S. Transfection with DR4 small interfering RNA attenuated HEGU- and isoangustone A-induced apoptosis. These results demonstrate that the activation of DR4 contributes to HEGU- and isoangustone A-induced apoptosis of DU145 cells.

Polygonatum cyrtonema lectin induces murine fibrosarcoma L929 cell apoptosis via a caspase-dependent pathway as compared to Ophiopogon japonicus lectin

Galanthus nivalis agglutinin (GNA)-related lectin family, a superfamily of strictly mannose-binding specific lectins, has been well-known to possess several biological functions including apoptosis-inducing activities. However, the precise mechanisms of GNA-related lectins to induce apoptosis remains to be clarified. In this study, we showed that Polygonatum cyrtonema lectin (PCL) and Ophiopogon japonicus lectin (OJL), the two mannose-binding GNA-related lectins, could induce murine fibrosarcoma L929 cell apoptosis. In addition, we found that there was a close link between their sugar-binding and apoptosis-inducing activities. Interestingly, we further confirmed that the mechanism of lectin-induced apoptosis was a caspase-dependent pathway. Moreover, we found that the two lectins could amplify tumor necrosis factor α (TNFα)-induced apoptosis. Taken together, these findings would open a new perspective for GNA-related lectins as potential anti-tumor agents.

Granzymes in age-related cardiovascular and pulmonary diseases

Chronic inflammation is a hallmark of age-related cardiovascular and pulmonary diseases. Granzymes are a family of serine proteases that have been traditionally viewed as initiators of immune-mediated cell death. However, recent findings suggest that the pathophysiological role of granzymes is complex. Emerging functions for granzymes in extracellular matrix degradation, autoimmunity, and inflammation suggests a multifactorial mechanism by which these enzymes are capable of mediating tissue damage. Recent discoveries showing that granzymes can be produced and secreted by nonimmune cells during disease provide an additional layer of intricacy. This review examines the emerging biochemical and clinical evidence pertaining to intracellular and/or extracellular granzymes in the pathogenesis of aging and cardiopulmonary diseases.

Liver apoptosis is age dependent and is reduced by activation of peroxisome proliferator-activated receptor-gamma in hemorrhagic shock

A clinical observation in pediatric and adult intensive care units is that the incidence of multiple organ failure in pediatric trauma victims is lower than in adult patients. However, the molecular mechanisms are not yet defined. Recent experimental studies have shown that the nuclear peroxisome proliferator-activated receptor-gamma (PPARgamma) modulates the inflammatory process. In this study, we hypothesized that severity of liver injury may be age dependent and PPARgamma activation may provide beneficial effects. Hemorrhagic shock was induced in anesthetized young (3-5 mo old) and mature male Wistar rats (11-13 mo old) by withdrawing blood to a mean arterial blood pressure of 50 mmHg. After 3 h, rats were rapidly resuscitated with shed blood. Animals were euthanized 3 h after resuscitation. In mature rats, liver injury appeared more pronounced compared with young rats and was characterized by marked hepatocyte apoptosis, extravasation of erythrocytes, and accumulation of neutrophils. The ratio between the antiapoptotic protein Bcl-2 and the proapoptotic protein BAX was lower, whereas activity of caspase-3, the executioner of apoptosis, was higher in liver of mature rats compared with young rats. Plasma alanine aminotransferase levels were not different between the two age groups. This heightened liver apoptosis was associated with a significant downregulation of PPARgamma DNA binding in mature rats compared with young rats. Treatment with the PPARgamma ligand ciglitazone significantly reduced liver apoptosis in mature rats. Our data suggest that liver injury after severe hemorrhage is age dependent and PPARgamma activation is a novel hepatoprotective mechanism.

Inhibitory effect of PACAP on caspase activity in neuronal apoptosis: a better understanding towards therapeutic applications in neurodegenerative diseases

Programmed cell death, which is part of the normal development of the central nervous system, is also implicated in various neurodegenerative disorders. Cysteine-dependent aspartate-specific proteases (caspases) play a pivotal role in the cascade of events leading to apoptosis. Many factors that inhibit cell death have now been identified, but the underlying mechanisms are not fully understood. Pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to exert neurotrophic activities during development and to prevent neuronal apoptosis induced by various insults such as ischemia. Most of the neuroprotective effects of PACAP are mediated through the PAC1 receptor. This receptor activates a transduction cascade of second messengers to stimulate Bcl-2 expression, which inhibits cytochrome c release and blocks the activation of caspases. The inhibitory effect of PACAP on the apoptotic cascade suggests that selective, stable, and potent PACAP derivatives could potentially be of therapeutic value for the treatment of post-traumatic and/or chronic neurodegenerative processes.

Apoptosis-suppressing and autophagy-promoting effects of calpain on oridonin-induced L929 cell death

Calpain, calcium-dependent cysteine protease, is reported here to impose the crucial influence on oridonin-induced L929 cell apoptosis and autophagy. We found that inhibition of calpain increased oridonin-induced Bax activation, cytochrome c release and PARP cleavage, indicating that calpain plays an anti-apoptotic role in oridonin-induced L929 cell apoptosis. To explore this potential anti-apoptotic mechanism, we inhibited calpain and proteasome activity in oridonin-induced L929 cell apoptosis, and discovered that the inducible IkappaBalpha proteolysis was partially blocked by the inhibition of either calpain or proteasome, but completely blocked by the inhibition of both. It demonstrated that calpain and proteasome were two distinct pathways participating in IkappaBalpha degradation. To further study the role of calpain in oridonin-induced L929 cell autophagy, we discovered that calpain inhibitor decreased oridonin-induced autophagy, as well as Beclin 1 activation and the conversion from LC3-I to LC3-II. Moreover, Inhibition of autophagy by 3-MA increased oridonin-induced apoptosis. In conclusion, besides suppressing apoptosis, calpain promotes autophagy in oridonin-induced L929 cell death, and inhibition of autophagy might contribute to up-regulation of apoptosis.

The role of nitric oxide in intestinal epithelial injury and restitution in neonatal necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common life-threatening gastrointestinal disease encountered in the premature infant. Although the inciting events leading to NEC remain elusive, various risk factors, including prematurity, hypoxemia, formula feeding, and intestinal ischemia, have been implicated in the pathogenesis of NEC. Data from our laboratory and others suggest that NEC evolves from disruption of the intestinal epithelial barrier, as a result of a combination of local and systemic insults. We postulate that nitric oxide (NO), an important second messenger and inflammatory mediator, plays a key role in intestinal barrier failure seen in NEC. Nitric oxide and its reactive nitrogen derivative, peroxynitrite, may affect gut barrier permeability by inducing enterocyte apoptosis (programmed cell death) and necrosis, or by altering tight junctions or gap junctions that normally play a key role in maintaining epithelial monolayer integrity. Intrinsic mechanisms that serve to restore monolayer integrity following epithelial injury include enterocyte proliferation, epithelial restitution via enterocyte migration, and re-establishment of cell contacts. This review focuses on the biology of NO and the mechanisms by which it promotes epithelial injury while concurrently disrupting the intrinsic repair mechanisms.

A novel interaction between procaspase 8 and SPARC enhances apoptosis and potentiates chemotherapy sensitivity in colorectal cancers

Chemotherapy resistance accounts for the high mortality rates in patients with advanced cancers. We previously used a genomics approach to determine novel genes associated with this phenomenon and identified secreted protein acidic and rich in cysteine (SPARC) as a chemosensitizer capable of reversing therapy resistance in colorectal cancer cells by enhancing apoptosis in vitro and tumor regression in vivo. Here, we examined the mechanisms by which SPARC enhances apoptosis in the presence of chemotherapy. We show that SPARC potentiates apoptosis by augmenting the signaling cascade in a caspase-8-dependent manner, because apoptosis can be abolished by caspase 8 small interfering RNA in the presence of SPARC. This occurs independently of death receptor activation and leads to downstream involvement of Bid and subsequent apoptosis. Interestingly, this results from an interaction between SPARC and the N terminus of the procaspase-8 DED-containing domain. These exciting findings provide an initial map of the apoptosis signaling events mediated by SPARC and how this can ultimately result in the reversal of chemotherapy resistance and enhanced tumor regression. This signaling cascade can be exploited therapeutically and may have potential clinical implications for patients with advanced and therapy-refractory cancers.