Apaf-1 expression in malignant melanoma

Sub-lethal signals in the mitochondrial apoptosis apparatus: pernicious by-product or physiological event?

One of the tasks of mitochondria is the rule over life and death: when the outer membrane is permeabilized, the release of intermembrane space proteins causes cell death by apoptosis. For a long time, this mitochondrial outer membrane permeabilization (MOMP) has been accepted as the famous step from which no cell returns. Recent results have however shown that this quite plainly does not have to be the case. A cell can also undergo only a little MOMP, and it can efficiently repair damage it has incurred in the process. There is no doubt now that such low-scale permeabilization occurs. A major unclarified issue is the biological relevance. Is small-scale mitochondrial permeabilization an accident, a leakiness of the apoptosis apparatus, perhaps during restructuring of the mitochondrial network? Is it attempted suicide, where cell death by apoptosis is the real goal but the stimulus failed to reach the threshold? Or, more boldly, is there a true biological meaning behind the event of the release of low amounts of mitochondrial components? We will here explore this last possibility, which we believe is on one hand appealing, on the other hand plausible and supported by some evidence. Recent data are consistent with the view that sub-lethal signals in the mitochondrial apoptosis pathway can drive inflammation, the first step of an immune reaction. The apoptosis apparatus is almost notoriously easy to trigger. Sub-lethal signals may be even easier to set off. We suggest that the apoptosis apparatus is used in this way to sound the call when the first human cell is infected by a pathogen.

Brain Regeneration Resembles Brain Cancer at Its Early Wound Healing Stage and Diverges From Cancer Later at Its Proliferation and Differentiation Stages

Gliomas are the most frequent type of brain cancers and characterized by continuous proliferation, inflammation, angiogenesis, invasion and dedifferentiation, which are also among the initiator and sustaining factors of brain regeneration during restoration of tissue integrity and function. Thus, brain regeneration and brain cancer should share more molecular mechanisms at early stages of regeneration where cell proliferation dominates. However, the mechanisms could diverge later when the regenerative response terminates, while cancer cells sustain proliferation. To test this hypothesis, we exploited the adult zebrafish that, in contrast to the mammals, can efficiently regenerate the brain in response to injury. By comparing transcriptome profiles of the regenerating zebrafish telencephalon at its three different stages, i.e., 1 day post-lesion (dpl)-early wound healing stage, 3 dpl-early proliferative stage and 14 dpl-differentiation stage, to those of two brain cancers, i.e., low-grade glioma (LGG) and glioblastoma (GBM), we reveal the common and distinct molecular mechanisms of brain regeneration and brain cancer. While the transcriptomes of 1 dpl and 3 dpl harbor unique gene modules and gene expression profiles that are more divergent from the control, the transcriptome of 14 dpl converges to that of the control. Next, by functional analysis of the transcriptomes of brain regeneration stages to LGG and GBM, we reveal the common and distinct molecular pathways in regeneration and cancer. 1 dpl and LGG and GBM resemble with regard to signaling pathways related to metabolism and neurogenesis, while 3 dpl and LGG and GBM share pathways that control cell proliferation and differentiation. On the other hand, 14 dpl and LGG and GBM converge with respect to developmental and morphogenetic processes. Finally, our global comparison of gene expression profiles of three brain regeneration stages, LGG and GBM exhibit that 1 dpl is the most similar stage to LGG and GBM while 14 dpl is the most distant stage to both brain cancers. Therefore, early convergence and later divergence of brain regeneration and brain cancer constitutes a key starting point in comparative understanding of cellular and molecular events between the two phenomena and development of relevant targeted therapies for brain cancers.

CaDrA: A Computational Framework for Performing Candidate Driver Analyses Using Genomic Features

The identification of genetic alteration combinations as drivers of a given phenotypic outcome, such as drug sensitivity, gene or protein expression, and pathway activity, is a challenging task that is essential to gaining new biological insights and to discovering therapeutic targets. Existing methods designed to predict complementary drivers of such outcomes lack analytical flexibility, including the support for joint analyses of multiple genomic alteration types, such as somatic mutations and copy number alterations, multiple scoring functions, and rigorous significance and reproducibility testing procedures. To address these limitations, we developed Candidate Driver Analysis or CaDrA, an integrative framework that implements a step-wise heuristic search approach to identify functionally relevant subsets of genomic features that, together, are maximally associated with a specific outcome of interest. We show CaDrA's overall high sensitivity and specificity for typically sized multi-omic datasets using simulated data, and demonstrate CaDrA's ability to identify known mutations linked with sensitivity of cancer cells to drug treatment using data from the Cancer Cell Line Encyclopedia (CCLE). We further apply CaDrA to identify novel regulators of oncogenic activity mediated by Hippo signaling pathway effectors YAP and TAZ in primary breast cancer tumors using data from The Cancer Genome Atlas (TCGA), which we functionally validate in vitro. Finally, we use pan-cancer TCGA protein expression data to show the high reproducibility of CaDrA's search procedure. Collectively, this work demonstrates the utility of our framework for supporting the fast querying of large, publicly available multi-omics datasets, including but not limited to TCGA and CCLE, for potential drivers of a given target profile of interest.

Anti-proliferative and pro-apoptotic activity of GD2 ganglioside-specific monoclonal antibody 3F8 in human melanoma cells

The beneficial clinical effects of immunotherapy with GD2-specific monoclonal antibodies (mAbs) in melanoma and neuroblastoma patients have stimulated interest in characterizing the mechanisms underlying their antitumor effects. Previous studies have shown that GD2-specific mAbs mediate complement- and cell-dependent cytotoxicity and induce caspase-dependent apoptosis of tumor cells. In this study, we showed that GD2-specific mAb 3F8, which is undergoing clinical evaluation, inhibited the in vitro growth and induced apoptosis of melanoma cells. This effect was dose- and time-dependent, mediated by the interaction of mAb 3F8 combining site with GD2 ganglioside, associated with GD2 expression level on the cell surface, mAb internalization and increase of GD2 containing endosomes triggered by mAb 3F8. The induction of apoptosis by mAb 3F8 was mediated by caspase 3-, 7-, and 8-dependent pathways, downregulation of the anti-apoptotic molecules survivin and cytochrome c, and caspase 9 independent-AIF release from mitochondria. In addition, analyses of signaling pathway components demonstrated that mAb 3F8 strongly inhibited AKT and FAK activation and increased cleaved PARP expression. These results indicated that multiple mechanisms played a role in the antitumor activity of mAb 3F8 in melanoma cells. This information should provide a mechanistic basis for the optimization of the rational design of immunotherapeutic strategies in the mAb-based treatment of GD2 positive tumors.

BH3-mimetics- and cisplatin-induced cell death proceeds through different pathways depending on the availability of death-related cellular components

Background

Owing to their important function in regulating cell death, pharmacological inhibition of Bcl-2 proteins by dubbed BH3-mimetics is a promising strategy for apoptosis induction or sensitization to chemotherapy. However, the role of Apaf-1, the main protein constituent of the apoptosome, in the process has yet not been analyzed. Furthermore as new chemotherapeutics develop, the possible chemotherapy-induced toxicity to rapidly dividing normal cells, especially sensitive differentiated cells, has to be considered. Such undesirable effects would probably be ameliorated by selectively and locally inhibiting apoptosis in defined sensitive cells.

Methodology and Principal Findings

Mouse embryonic fibroblasts (MEFS) from Apaf-1 knock out mouse (MEFS KO Apaf-1) and Bax/Bak double KO (MEFS KO Bax/Bak), MEFS from wild-type mouse (MEFS wt) and human cervix adenocarcinoma (HeLa) cells were used to comparatively investigate the signaling cell death-induced pathways of BH3-mimetics, like ABT737 and GX15-070, with DNA damage-inducing agent cisplatin (cis-diammineplatinum(II) dichloride, CDDP). The study was performed in the absence or presence of apoptosis inhibitors namely, caspase inhibitors or apoptosome inhibitors. BH3-mimetic ABT737 required of Apaf-1 to exert its apoptosis-inducing effect. In contrast, BH3-mimetic GX15-070 and DNA damage-inducing CDDP induced cell death in the absence of both Bax/Bak and Apaf-1. GX15-070 induced autophagy-based cell death in all the cell lines analyzed. MEFS wt cells were protected from the cytotoxic effects of ABT737 and CDDP by chemical inhibition of the apoptosome through QM31, but not by using general caspase inhibitors.

Conclusions

BH3-mimetic ABT737 not only requires Bax/Bak to exert its apoptosis-inducing effect, but also Apaf-1, while GX15-070 and CDDP induce different modalities of cell death in the absence of Bax/Bak or Apaf-1. Inclusion of specific Apaf-1 inhibitors in topical and well-localized administrations, but not in systemic ones, to avoid interferences with chemotherapeutics would be of interest to prevent chemotherapeutic-induced unwanted cell death which could improve cancer patient care.

Hypermethylation of apoptotic genes as independent prognostic factor in neuroblastoma disease

Neuroblastoma (NB) is an embryonal tumour of neuroectodermal cells, and its prognosis is based on patient age at diagnosis, tumour stage and MYCN amplification, but it can also be classified according to their degree of methylation. Considering that epigenetic aberrations could influence patient survival, we studied the methylation status of a series of 17 genes functionally involved in different cellular pathways in patients with NB and their impact on survival. We studied 82 primary NB tumours and we used methylation-specific-PCR to perform the epigenetic analysis. We evaluated the putative association among the evidence of hypermethylation with the most important NB prognostic factors, as well as to determine the relationship among methylation, clinical classification and survival. CASP8 hypermethylation showed association with relapse susceptibility and, TMS1 and APAF1 hypermethylation are associated with bad prognosis and showed high influence on NB overall survival. Hypermethylation of apoptotic genes has been identified as a good candidate of prognostic factor. We propose the simultaneous analysis of hypermethylation of APAF1, TMS1 and CASP8 apoptotic genes on primary NB tumour as a good prognostic factor of disease progression.

Molecular pathogenesis of cutaneous melanocytic neoplasms

Melanoma is the deadliest form of skin cancer without an effective treatment. An understanding of the genetic basis of melanoma has recently shed light on some of the mechanisms of melanomagenesis. This review explores the major genes involved in familial and sporadic cutaneous melanoma with an emphasis on CDKN2A, CDK4, MC1R, and MAPK pathway targets (e.g., RAS and BRAF), apoptosis regulators (e.g., BCL-2, AKT, and APAF-1), and the tumor-suppressor genes TP53 and PTEN. New directions for therapeutics based on our current knowledge of the genes implicated in melanoma are also discussed.

Tris (dibenzylideneacetone) dipalladium, a N-myristoyltransferase-1 inhibitor, is effective against melanoma growth in vitro and in vivo

PURPOSE

Melanoma is a solid tumor that is notoriously resistant to chemotherapy, and its incidence is rapidly increasing. Recently, several signaling pathways have been shown to contribute to melanoma tumorigenesis, including constitutive activation of mitogen-activated protein kinase, Akt, and Stat-3. The activation of multiple pathways may account in part for the difficulty in treatment of melanoma. In a recent screen of compounds, we found that an organopalladium compound, Tris (dibenzylideneacetone) dipalladium (Tris DBA), showed significant antiproliferative activity against melanoma cells. Studies were carried out to determine the mechanism of action of Tris DBA.

EXPERIMENTAL DESIGN

Tris DBA was tested on efficacy on proliferation of human and murine melanoma cells. To find the mechanism of action of Tris DBA, we did Western blot and gene array analyses. The ability of Tris DBA to block tumor growth in vivo was assessed.

RESULTS

Tris DBA has activity against B16 murine and A375 human melanoma in vivo. Tris DBA inhibits several signaling pathways including activation of mitogen-activated protein kinase, Akt, Stat-3, and S6 kinase activation, suggesting an upstream target. Tris DBA was found to be a potent inhibitor of N-myristoyltransferase-1, which is required for optimal activity of membrane-based signaling molecules. Tris DBA showed potent antitumor activity in vivo against melanoma.

CONCLUSION

Tris DBA is thus a novel inhibitor of N-myristoyltransferase-1 with significant antitumor activity and is well tolerated in vivo. Further preclinical evaluation of Tris DBA and related complexes is warranted.

The apoptosome: emerging insights and new potential targets for drug design

Apoptosis plays a crucial role in tissue homeostasis, development and many diseases. The relevance of Apaf1, the molecular core of apoptosome, has been underlined in mitochondria-dependent apoptosis, which according to a growing body of evidence, is involved in various pathologies where the equilibrium of life-and-death is dysregulated, such as heart attack, stroke, liver failure, cancer and autoimmune diseases. Consequently, great interest has emerged in devising therapeutic strategies for regulating the key molecules involved in the life-and-death decision. Here we review recent progress in apoptosis-based pharmacological therapies and, in particular, we point out a possible role of the apoptosome as an emerging and promising pharmacological target.

The reactive oxygen-driven tumor: relevance to melanoma

In melanoma, at least four major signaling abnormalities have been described. They include beta-catenin deregulation (mutation/mislocalization), p16 loss, MAP kinase activation, and Akt activation. In this review, we discuss the role of the fourth pathway, known as the reactive oxygen driven tumor. The role of reactive oxygen in tumorigenesis is likely to relate to virtually all forms of cancer, and lends itself to specific therapies. These include blockade of reactive oxygen, resulting in decreased activation of NF-kappaB, which should sensitize tumors to chemotherapy and radiation. The phenotype of the reactive oxygen driven tumor can be monitored using available markers already in use in most hospital laboratories.

Shb Gene Knockdown Increases the Susceptibility of SVR Endothelial Tumor Cells to Apoptotic Stimuli In Vitro and In Vivo

The Shb adapter protein is an Src homology 2-domain containing signaling intermediate operating downstream of several tyrosine kinase receptors, including vascular endothelial growth factor receptor-2. Shb is multifunctional and apoptosis is one response that Shb regulates. Inhibition of angiogenesis can be used in cancer therapy, and one way to achieve this is by inducing endothelial cell apoptosis. The angiosarcoma cell line SVR is of endothelial origin and can be used as a tool for studying in vivo inhibition of angiogenesis, and we thus employed an Shb-knockdown strategy using an inducible lentiviral system to reduce Shb levels in SVR cells and to study their responses. Shb knockdown increases the susceptibility of SVR cells to the apoptotic agents, cisplatin and staurosporine. Simultaneously, Shb knockdown causes reduced focal adhesion kinase (FAK) activation, monitored as phosphorylation of the regulatory residues tyrosines 576/577. No detectable effects on Akt or extracellular signal-regulated kinase activity were noted. The altered FAK activity coincided with an elongated cell phenotype that was particularly noticeable in the presence of staurosporine. In order to relate the effects of Shb knockdown to in vivo tumorigenicity, cells were exposed to the angiogenesis inhibitor honokiol, and again the cells with reduced Shb content exhibited increased apoptosis. Tumor growth in vivo was strongly reduced in the Shb-knockdown cells upon honokiol treatment. It is concluded that Shb regulates apoptosis and cell shape in tumor endothelial cells via FAK, and that Shb is a potential target for inhibition of angiogenesis.

XIAP activity dictates Apaf-1 dependency for caspase 9 activation

The current model for the intrinsic apoptotic pathway holds that mitochondrial activation of caspases in response to cytotoxic drugs requires both Apaf-1-induced dimerization of procaspase 9 and Smac/Diablo-mediated sequestration of inhibitors of apoptosis proteins (IAPs). Here, we showed that either pathway can independently promote caspase 9 activation in response to apoptotic stimuli. In drug-treated Apaf-1(-/-) primary myoblasts, but not fibroblasts, Smac/Diablo accumulates in the cytosol and sequesters X-linked IAP (XIAP), which is expressed at lower levels in myoblasts than in fibroblasts. Consequently, caspase 9 activation proceeds in Apaf-1(-/-) myoblasts; concomitant ablation of Apaf-1 and Smac is required to prevent caspase 9 activation and the onset of apoptosis. Conversely, in stimulated Apaf-1(-/-) fibroblasts, the ratio of XIAP to Smac/Diablo is high compared to that for myoblasts and procaspase 9 is not activated. Suppressing XIAP with exogenous Smac/Diablo or a pharmacological inhibitor can still induce caspase 9 in drug-treated Apaf-1-null fibroblasts. Thus, caspase 9 activation in response to intrinsic apoptotic stimuli can be uncoupled from Apaf-1 in vivo by XIAP antagonists.

Selective induction of chemotherapy resistance of mammary tumors in a conditional mouse model for hereditary breast cancer

We have studied in vivo responses of "spontaneous" Brca1- and p53-deficient mammary tumors arising in conditional mouse mutants to treatment with doxorubicin, docetaxel, or cisplatin. Like human tumors, the response of individual mouse tumors varies, but eventually they all become resistant to the maximum tolerable dose of doxorubicin or docetaxel. The tumors also respond well to cisplatin but do not become resistant, even after multiple treatments in which tumors appear to regrow from a small fraction of surviving cells. Classical biochemical resistance mechanisms, such as up-regulated drug transporters, appear to be responsible for doxorubicin resistance, rather than alterations in drug-damage effector pathways. Our results underline the promise of these mouse tumors for the study of tumor-initiating cells and of drug therapy of human cancer.