Transduction of Apaf-1 or caspase-9 induces apoptosis in A-172 cells that are resistant to p53-mediated apoptosis

Apoptosome Formation through Disruption of the K192-D616 Salt Bridge in the Apaf-1 Closed Form

The molecular mechanism of apoptosome activation through conformational changes of Apaf-1 auto-inhibited form remains largely enigmatic. The crystal structure of Apaf-1 suggests that some ionic bonds, including the bond between K192 and D616, are critical for the preservation of the inactive "closed" form of Apaf-1. Here, a split luciferase complementation assay was used to monitor the effect of disrupting this ionic bond on apoptosome activation and caspase-3 activity in cells. The K192E mutation, predicted to disrupt the ionic interaction with D616, increased apoptosome formation and caspase activity, suggesting that this mutation favors the "open"/active form of Apaf-1. However, mutation of D616 to alanine or lysine had different effects. While both mutants favored apoptosome formation such as K192E, D616K cannot activate caspases and D616A activates caspases poorly, and not as well as wild-type Apaf-1. Thus, our data show that the ionic bond between K192 and D616 is critical for maintaining the closed form of Apaf-1 and that disrupting the interaction enhances apoptosome formation. However, our data also reveal that after apoptosome formation, D616 and K192 play a previously unsuspected role in caspase activation. The molecular explanation for this observation is yet to be elucidated.

Upregulation of CASP9 through NF-κB and Its Target MiR-1276 Contributed to TNFα-promoted Apoptosis of Cancer Cells Induced by Doxorubicin

Under some conditions, nuclear factor-κB (NF-κB) has a pro-apoptotic role, but the mechanisms underlying this function remain unclear. This study demonstrated that NF-κB directly binds to CASP9 and miR1276 in tumor necrosis factor α (TNFα)-treated HeLa and HepG2 cells. NF-κB upregulated CASP9 expression, whereas downregulated miR1276 expression in the TNFα-treated cells. The miR1276 repressed CASP9 expression in both cells. As a result, a typical NF-κB-mediated coherent feed-forward loop was formed in the TNFα-treated cells. It was proposed that the NF-κB-mediated loop may contribute to cell apoptosis under certain conditions. This opinion was supported by the following evidence: TNFα promoted the apoptosis of HeLa and HepG2 cells induced by doxorubicin (DOX). CASP9 was significantly upregulated and activated by TNFα in the DOX-induced cells. Moreover, a known inhibitor of CASP9 activation significantly repressed the TNFα promotion of apoptosis induced by DOX. These findings indicate that CASP9 is a new mediator of the NF-κB pro-apoptotic pathway, at least in such conditions. This study therefore provides new insights into the pro-apoptotic role of NF-κB. The results also shed new light on the molecular mechanism underlying TNFα-promotion of cancer cells apoptosis induced by some anticancer drugs such as DOX.

Between death and survival: retinoic acid in regulation of apoptosis

The vitamin A metabolite all-trans-retinoic acid (RA) regulates multiple biological processes by virtue of its ability to regulate gene expression. It thus plays critical roles in embryonic development and is involved in regulating growth, remodeling, and metabolic responses in adult tissues. RA can also suppress carcinoma cell growth and is currently used in treatment of some cancers. Growth inhibition by RA may be exerted by induction of differentiation, cell cycle arrest, or apoptosis, or by a combination of these activities. Paradoxically, in the context of some cells, RA not only fails to inhibit growth but, instead, enhances proliferation and survival. This review focuses on the involvement of RA in regulating apoptotic responses. It includes brief overviews of transcriptional signaling by RA and of apoptotic pathways, and then addresses available information on the mechanisms by which RA induces apoptosis or, conversely, inhibits cell death and enhances survival.

miR-21: a small multi-faceted RNA

More than 1000 microRNAs (miRNAs) are expressed in human cells, some tissue or cell type specific, others considered as house-keeping molecules. Functions and direct mRNA targets for some miRNAs have been relatively well studied over the last years. Every miRNA potentially regulates the expression of numerous protein-coding genes (tens to hundreds), but it has become increasingly clear that not all miRNAs are equally important; diverse high-throughput screenings of various systems have identified a limited number of key functional miRNAs over and over again. Particular miRNAs emerge as principal regulators that control major cell functions in various physiological and pathophysiological settings. Since its identification 3 years ago as the miRNA most commonly and strongly up-regulated in human brain tumour glioblastoma [1], miR-21 has attracted the attention of researchers in various fields, such as development, oncology, stem cell biology and aging, becoming one of the most studied miRNAs, along with let-7, miR-17-92 cluster ('oncomir-1'), miR-155 and a few others. However, an miR-21 knockout mouse has not yet been generated, and the data about miR-21 functions in normal cells are still very limited. In this review, we summarise the current knowledge of miR-21 functions in human disease, with an emphasis on its regulation, oncogenic role, targets in human cancers, potential as a disease biomarker and novel therapeutic target in oncology.

Expression-targeted gene therapy for the treatment of transitional cell carcinoma

Targeted gene delivery for induced apoptosis of transitional cell carcinomas was carried out in vivo in mice via utilization of the murine cyclooxygenase type 2 (Cox-2) promoter (Tis10). MB49 cells, which constitutively overexpress Cox-2 like numerous other carcinomas, selectively expressed delivered genes that utilized this transcriptional control element. The products of the delivered genes were artificially inducible forms of caspases 3 and 9, which remained inactive until a chemical inducer of dimerization was later injected intraperitoneally. The genes were delivered intravesically as plasmids complexed with poly(ethylenimine). Significant improvements, in the form of reduced bladder mass, reduced tumor volume, anti-angiogenesis and inhibition of tumor growth were seen versus untreated or unactivated controls. In some instances, tumors were seen to go into complete remission. There were no apparent bystander effects associated with the treatments. This targeted gene therapy regimen could have wide applicability to numerous cancers due to constitutive overexpression of Cox-2.

Marker genes to predict sensitivity to FK228, a histone deacetylase inhibitor

In this study, we detected genes sensitive to an histone deacetylase inhibitor, FK228 [(E)-(1S,4S,10S,21R)-7-[(Z)-ethylidene]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo-[8,7,6]-tricos-16-ene-3,6,9,19,22-pentanone; FR901228, depsipeptide] in vitro and identified marker genes to predict sensitivity to FK228 in vivo using Affymetrix GeneChip. Three percent of genes (205/7070) were sensitive to FK228 in vitro, 105 and 100 genes, were up- and down-regulated, respectively, by FK228. Commonly up-regulated genes included p21(WAF1/Cip1), interleukin-8 (IL-8), histone family, JunB, caspase 9, mitogen-activated protein kinase phosphatase 1 (MKP-1) and mitogen-activated protein kinase (MAPK) family, and commonly down-regulated genes included cyclin A and MAPK family. One percent of genes (76/7070) showed native differences in patterns of expression, when FK228-sensitive (PC-3 prostate and SC-6-JCK (SC-6) stomach) and FK228-resistant (ACHN and A-498 renal) tumors implanted in BALB/c nu/nu mice were compared. Twenty-seven and forty nine of those genes were expressed at high or low levels, respectively, in FK228-sensitive tumors. Caspase 9 and MKP-1 genes showed distinct differences in patterns of expression between FK228-sensitive and resistant tumors and have been known to have roles in apoptosis and chromatin remodeling. The expression of caspase 9 gene was higher in FK228-sensitive tumors and the expression of MKP-1 gene was higher in FK228-resistant tumors. Caspase 9 and MKP-1 genes in the other FK228-sensitive tumors had the same patterns of expression as they did in PC-3 and SC-6 tumors. Our results present profiles of gene expression related to FK228 and marker genes to predict sensitivity to FK228, such as caspase 9 and MKP-1 genes.

A new challenge for successful immunotherapy by tumors that are resistant to apoptosis: two complementary signals to overcome cross-resistance

Tumor resistance to conventional therapies is a major problem in cancer treatment. While tumors initially respond to radiation or chemotherapies, subsequent treatments with these conventional modalities are ineffective against relapsed tumors. The problem of tumor resistance to chemotherapy and radiation has led to the development of immunotherapy and gene-based therapies. These alternative therapeutic approaches are intensely explored because they are supposed to be more tumor specific and better tolerated than the conventional therapies. Recent advances in apoptosis have revealed that resistance to apoptosis is one of the major mechanisms of tumor resistance to conventional therapies. Resistance to apoptosis is a naturally acquired characteristic during oncogenesis and is selected for after successive rounds of conventional therapies. Resistance to apoptosis involves dysregulation and/or mutation of apoptotic signaling molecules that render tumor cells unresponsive to apoptotic stimuli. Since both immunotherapy and chemotherapy kill tumors by apoptosis and the killings are signaled through a central core apoptotic program, dysregulation of this central program and development of resistance to apoptosis in chemoresistant cells could render them cross-resistant to immunotherapy. Therefore, in order to establish an effective antitumor response and to complement immunotherapy and gene-based therapies, cross-resistance due to resistance to apoptosis must be overcome. In this review, based on prior findings and recent evidence, we put forth a model, verified experimentally, in which chemoresistant tumor cells can be sensitized to immune-mediated killing by subtoxic concentrations of chemotherapeutic drugs/factors. The model involves two complementary signals. The first signal is a sensitizing signal that regulates pro/antiapoptotic targets, thus facilitating the apoptotic signal. The second apoptotic signal initiates a partial activation of the apoptotic signaling pathway, and activation is completed by complementation with signal one. Thus, effective killing of immunoresistant cells is achieved by both signals. The two-signal approach provides a new strategy to overcome cancer cross-resistance to immunotherapy and opens new avenues for the development of more effective and selective immunosensitizing agents.

5-Fluorouracil efficiently enhanced apoptosis induced by adenovirus-mediated transfer of caspase-8 in DLD-1 colon cancer cells

BACKGROUND

In order to develop a safe and effective gene therapy for cancer, more powerful therapeutic genes must be selected and a gene transduction methodology needs to be devised that minimizes the total dose of vector required. We investigated the combination effect of 5-fluorouracil (5-FU), a first-choice drug for the treatment of colorectal cancer and adenovirus-mediated transfer of caspase-8 in DLD-1 colon cancer cells.

METHODS

The degree of cell death was assessed by determining the percentage of cells which had died, and the degree of DNA fragmentation. The protein expression levels and degree of activation of caspase-8 were analyzed by Western blot analysis. The degree of transgene expression was assessed using adenoviral vectors expressing lacZ and GFP.

RESULTS

Combination treatment led to a significant induction of apoptosis, whereas treatment with either approach alone resulted in only minimal cytotoxicity. Caspase-8 was only activated in cells that received the combined treatment. Exposure to 5-FU increased the quantity of transgene expression per cell, 48 h post-infection. A potentiating effect of adenoviral treatment was also seen when 5-FU treatment was substituted by the overexpression of cyclin-dependent kinase inhibitors, p21(WAF1/CIP1) and p27(KIP1), suggesting that the cytostatic effect of 5-FU augmented apoptosis induced by caspase-8 gene transduction by inhibiting the dilution of gene products associated with cell division.

CONCLUSIONS

This combination strategy may be very useful in the treatment of 5-FU-resistant colorectal cancers and may also be more generally helpful in minimizing the dose of therapeutic vectors used in cancer gene therapy.

Caspase-8 gene transduction augments radiation-induced apoptosis in DLD-1 cells

Caspase-8 is a member of the cysteine protease family that plays a critical role in death receptor-mediated apoptosis. We previously demonstrated that adenovirally transduced caspase-8 efficiently induced apoptosis in tumor cells (Shinoura et al. (2000) Hum. Gene Ther. 11, 1123-1137). However, to ensure safety in clinical applications some devise for minimization of the dose of adenoviral vector required for sufficient antitumor effect is needed. In this study, we evaluated the proapoptotic effect in DLD-1 colon cancer cells of a combination of low-dose infection with an adenoviral vector expressing caspase-8 and X-ray irradiation. Under these conditions, X-ray irradiation strongly induced apoptosis whereas irradiation without transduction only had a trace proapoptotic effect. Overexpression of bcl-xL strongly blocked the activation of caspase-8 and induction of apoptosis, suggesting that adenovirally transduced caspase-8 was activated at a point downstream of mitochondria. This combination strategy may be a useful modality for gene therapy of colorectal cancer.

Co-transduction of Apaf-1 and caspase-9 highly enhances p53-mediated apoptosis in gliomas

Mutation of the p53 gene plays a critical role in the development of cancer and response to cancer therapy. To analyze the mechanism of cancer development and to improve cancer therapy, it is important to assess which genes are downstream components of p53 in cancers, and whether the expression levels of these genes affect p53-mediated apoptosis. In this study, we transduced the wild type p53 gene along with the Apaf-1 and caspase-9 genes via adenovirus vectors into U251 and U-373MG glioma cells harbouring a mutated p53, and evaluated the degree of apoptosis. Co-induction of Apaf-1 and caspase-9 genes highly enhanced p53-mediated apoptosis in glioma cells. Induction of wild type p53 enhanced the expression levels of Bax, p21/WAF1, and Fas protein. To determine which gene is activated by wild type p53 induction and, in turn, activates Apaf-1 and caspase-9, we transduced the Bax, p21/WAF1 or Fas gene via adenovirus vector to U251 cells to achieve a similar expression level as that induced by the Adv for p53 in U251 cells. U251 cells transduced with Fas concomitant with the Apaf-1 and caspase-9 genes underwent drastic apoptosis. This suggests that induction of wild type p53 upregulates Fas, which in turn may play a role in the activation of Apaf-1 and caspase-9. These results are important for analyzing the mechanism of tumour development and for predicting the therapeutic effect of p53 replacement gene therapy in a particular patient.

Over-expression of APAF-1 and caspase-9 augments radiation-induced apoptosis in U-373MG glioma cells

The p53 tumor-suppressor gene plays a critical role in radiation-induced apoptosis. Several genes, including Bax and Fas, are involved in p53-mediated apoptosis, and their over-expression enhances the degree of radiation-induced apoptosis. Apaf-1 and caspase-9 have been reported to be downstream components of p53-mediated apoptosis, suggesting that these genes play a role in radiation-induced apoptosis. In this study, we transduced U-373MG cells harboring mutant p53 with the Apaf-1 and/or caspase-9 genes via adenoviral (Adv) vectors concomitant with X-ray irradiation and evaluated the degree of apoptosis. The percentage of apoptotic cells in U-373MG cells co-infected with the Adv for Apaf-1 (Adv-APAF-1) and that for caspase-9 (Adv-Casp9) and treated with irradiation (24%) was much higher than that in cells co-infected with Adv-APAF-1 and Adv-Casp9 and not treated with irradiation (0.86%) and that in cells infected with either Adv-APAF-1 or Adv-Casp9 and treated with irradiation (2.0% or 2.6%, respectively). The apoptosis induced by co-transduction of Apaf-1 and caspase-9 and irradiation was repressed in cells that were co-infected with the Adv for Bcl-X(L) but not in cells co-infected with the Adv for Bcl-2. These results indicate that Apaf-1 and caspase-9 play a role in radiation-induced apoptosis in cancer cells harboring mutant p53. Bcl-X(L) may be critically involved in the radioresistance of cancer cells by repressing Apaf-1- and caspase-9-mediated apoptosis. Expression of Apaf-1 and caspase-9 in tumors may be an important determinant of the therapeutic effect of irradiation in cancer treatment.

Caspase-9 transduction overrides the resistance mechanism against p53-mediated apoptosis in U-87MG glioma cells

OBJECTIVE

Conflicting reports have been published with regard to the relationship between the efficacy of p53 gene therapy and the p53 status of gliomas. In this study, we evaluated whether U-87MG glioma cells harboring wild-type p53 and U251 and U-373MG glioma cells harboring mutated p53 demonstrate different sensitivities to p53-induced apoptosis. In addition, we tested whether transduction of Bax or caspase-9, which are downstream components of p53-induced apoptosis, can override the resistance mechanism of U-87MG cells to apoptosis.

METHODS

We transduced U-87MG, U251, and U-373MG glioma cells with p53, Bax, or caspase-9 genes via adenovirus (Adv) vectors, to induce the same level of respective proteins, and evaluated the degree of apoptosis.

RESULTS

U-87MG cells were highly resistant to Adv for p53 (Adv-p53)-mediated apoptosis, whereas U251 and U-373 cells underwent extensive apoptosis after Adv-p53 infection. In U-87MG cells, the elevation of Bax and Fas was not as marked as that observed in U251 and U-373MG cells after Adv-p53 infection. Endogenous expression of Bcl-XL and Bcl-2 in U-87MG cells was greater than that in U251 and U-373MG cells. U-87MG cells were more resistant to Bax-mediated apoptosis than were U251 or U-373MG cells. In contrast, U-87MG cells were more sensitive to caspase-9-mediated apoptosis than were U251 or U-373MG cells, suggesting that transduction of caspase-9 may override the resistance mechanism of U-87MG to p53-mediated apoptosis.

CONCLUSION

These results demonstrate that proapoptotic function induced by p53 transduction in U-87MG cells was repressed at several steps and that induction of caspase-9 may circumvent this resistance mechanism.