Bcl-2 oncoprotein expression and apoptosis in neuroblastoma

Destined to Die: Apoptosis and Pediatric Cancers

Apoptosis (programmed cell death) is a systematic and coordinated cellular process that occurs in physiological and pathophysiological conditions. Sidestepping or resisting apoptosis is a distinct characteristic of human cancers including childhood malignancies. This review dissects the apoptosis pathways implicated in pediatric tumors. Understanding these pathways not only unraveled key molecules that may serve as potential targets for drug discovery, but also molecular nodes that integrate with other signaling networks involved in processes such as development. This review presents current knowledge of the complex regulatory system that governs apoptosis with respect to other processes in pediatric cancers, so that fresh insights may be derived regarding treatment resistance or for more effective treatment options.

In Vitro Characterization of a Potent p53-MDM2 Inhibitor, RG7112 in Neuroblastoma Cancer Cell Lines

Background: Neuroblastoma (NB) is one of the most aggressive and common solid tumors in pediatrics. Development of effective new therapeutics for NB is in progress to help reduce mortality and morbidity of the disease, particularly in relapsed patients. The tumor suppressor protein p53 plays a critical role in multiple signaling pathways to maintain cellular hemostasis. Dysregulation of p53 protein and/or molecular aberrations have been associated with multiple human malignancies. p53 stability and protein activity is negatively regulated by the E3 ubiquitin ligase (MDM2). Thus, targeting p53-MDM2 protein-protein interaction is a feasible and promising therapeutic strategy to restore the physiological function of p53 in cancer cells. RG7112 is a highly potent and selective small molecule inhibitor, which target a unique structure located within p53 binding motif of MDM2. Methods: The efficacy of RG7112 in vitro using NB cell lines was examined. Two wild-type (WT)-p53 NB cell lines IMR5 and LAN-5, a mutant p53 cell line SK-N-BE(2), and a WT-p53/p14 deleted cell line SH-EP were employed. Results: Data showed that RG7112 significantly reduced cellular viability of IMR5 (IC₅₀, 562 nM) and LAN-5 (IC₅₀, 430 nM), but not SK-N-BE(2) and SH-EP cells. Further, RG7112 restores p53 and p21 protein levels in IMR5 and LAN-5 in a dose-dependent manner. RG7112 induces cell cycle arresting (60% G1 arresting) in WT-p53 cells (IMR5), but no pronounced effect observed in SK-N-BE(2). In this study, 15 different drugs in combination with RG7112 in IMR5 cell line and identified venetoclax (Bcl-2/Bcl-xL inhibitor) as a promising candidate were evaluated. Conclusions: Taken together, these findings provide initial proof-of-concept data for further investigations of RG7112 in selected subgroups of NB patients.

Proteomics-based identification of spontaneous regression-associated proteins in neuroblastoma

BACKGROUND

Spontaneous regression is usually found in stage 4s neuroblastoma, whereas the elucidation of the underlying molecular mechanism(s) is still limited.

PURPOSE

Our study aims to investigate the pathogenesis of spontaneous regression at the protein level.

METHODS AND MATERIALS

Differential expression of proteins in stage 4s neuroblastoma tissue, in stage 4 neuroblastoma tissue, and in normal adrenal tissue was investigated by use of 2-dimensional difference gel electrophoresis (2D-DIGE).

RESULTS

Twenty-four protein spots were found to have significant changes among the different tissues, in which 16 proteins were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Among these proteins, 7 proteins (RhoGDP-dissociation inhibitor 1, phosphatidylethanolamine-binding protein, prohibitin, etc) were up-regulated and 2 proteins (F-actin capping protein 1 subunit and aldose reductase) were down-regulated in stage 4s neuroblastoma compared with stage 4 neuroblastoma. The differential expression of selected candidate protein (RhoGDP-dissociation inhibitor 1 and CAPZA1) was further validated by western blotting.

CONCLUSION

Some proteins are differentially expressed between stage 4s and stage 4 neuroblastoma tissue, including those associated with differentiation and proliferation as well as apoptosis. RhoGDP-dissociation inhibitor 1 is highly expressed in stage 4s neuroblastoma tissue, whereas CAPZA1 is down-regulated.

Lysosomal-associated protein multispanning transmembrane 5 gene (LAPTM5) is associated with spontaneous regression of neuroblastomas

Background

Neuroblastoma (NB) is the most frequently occurring solid tumor in children, and shows heterogeneous clinical behavior. Favorable tumors, which are usually detected by mass screening based on increased levels of catecholamines in urine, regress spontaneously via programmed cell death (PCD) or mature through differentiation into benign ganglioneuroma (GN). In contrast, advanced-type NB tumors often grow aggressively, despite intensive chemotherapy. Understanding the molecular mechanisms of PCD during spontaneous regression in favorable NB tumors, as well as identifying genes with a pro-death role, is a matter of urgency for developing novel approaches to the treatment of advanced-type NB tumors.

Principal Findings

We found that the expression of lysosomal associated protein multispanning transmembrane 5 (LAPTM5) was usually down-regulated due to DNA methylation in an NB cell-specific manner, but up-regulated in degenerating NB cells within locally regressing areas of favorable tumors detected by mass-screening. Experiments in vitro showed that not only a restoration of its expression but also the accumulation of LAPTM5 protein, was required to induce non-apoptotic cell death with autophagic vacuoles and lysosomal destabilization with lysosomal-membrane permeabilization (LMP) in a caspase-independent manner. While autophagy is a membrane-trafficking pathway to degrade the proteins in lysosomes, the LAPTM5-mediated lysosomal destabilization with LMP leads to an interruption of autophagic flux, resulting in the accumulation of immature autophagic vacuoles, p62/SQSTM1, and ubiqitinated proteins as substrates of autophagic degradation. In addition, ubiquitin-positive inclusion bodies appeared in degenerating NB cells.

Conclusions

We propose a novel molecular mechanism for PCD with the accumulation of autophagic vacuoles due to LAPTM5-mediated lysosomal destabilization. LAPTM5-induced cell death is lysosomal cell death with impaired autophagy, not cell death by autophagy, so-called autophagic cell death. Thus LAPTM5-mediated PCD is closely associated with the spontaneous regression of NBs and opens new avenues for exploring innovative clinical interventions for this tumor.

Bcl-2 inhibitor and apigenin worked synergistically in human malignant neuroblastoma cell lines and increased apoptosis with activation of extrinsic and intrinsic pathways

Neuroblastoma is the most common extracranial solid tumor in infants and young children. Current treatments are not always effective and new therapies are needed. We examined efficacy of combination of the small molecule Bcl-2 inhibitor HA14-1 (HA) and the dietary isoflavonoid apigenin (APG) in human malignant neuroblastoma cells. Dose-response studies indicated that treatment with HA and APG for 24 h synergistically reduced cell viability in human malignant neuroblastoma SK-N-DZ, SH-SY5Y, and IMR32 cells. For further studies, we selected SK-N-DZ cells that showed the highest sensitivity following treatment with 2.5 microM HA, 100 microM APG, or combination (2.5 microM HA+100 microM APG). Wright staining showed increase in morphological features of apoptosis. Cell cycle distribution and Annexin V assay showed that combination therapy caused more apoptosis than either treatment alone. Western blotting revealed that combination therapy downregulated angiogenic factors and also induced extrinsic pathway of apoptosis with activation of caspase-8 for Bid cleavage to tBid. Alterations in Bax and Bcl-2 levels resulted in an increase in Bax:Bcl-2 ratio to activate intrinsic pathway of apoptosis with mitochondrial release of cytochrome c into the cytosol and activation of proteases. Increases in calpain and caspase-3 activities generated 145 kD spectrin break down product (SBDP) and 120 kD SBDP, respectively. Results showed that combination of HA and APG could be used for downregulation of angiogenic factors and activation of extrinsic and intrinsic pathways of apoptosis in malignant neuroblastoma cells.

Bcl-2 inhibitor HA14-1 and genistein together adeptly down regulated survival factors and activated cysteine proteases for apoptosis in human malignant neuroblastoma SK-N-BE2 and SH-SY5Y cells

Neuroblastoma is a pediatric extracranial tumor and a major cause of death in children under age 2. Conventional therapy shows inefficacy in most cases and thus development of new therapeutic strategies is urgently needed. We explored the efficacy of combination of the small molecule Bcl-2 inhibitor HA14-1 (HA) and the isoflavonoid genistein (GST) in human malignant neuroblastoma SK-N-BE2 and SH-SY5Y cells. Combination of 10 microM HA and 250 microM GST was optimal for SK-N-BE2 cells and combination of 5 microM HA and 100 microM GST was optimal for SH-SY5Y cells for induction of apoptosis. Phase-contrast microscopy and Wright staining showed morphological features of apoptosis. Cell cycle analysis and Annexin V-FITC/PI binding assay showed that combination of HA and GST was more effective in inducing apoptosis in both cell lines than either HA or GST alone. Western blotting showed that combination of HA and GST caused upregulation of Bax and down regulation of Bcl-2 resulting in increased Bax:Bcl-2 ratio and mitochondrial release of cytochrome c, Smac, and AIF. Down regulation of survival factors such as NF-kappaB, N-Myc, and survivin promoted apoptosis. Activation of caspase-8, calpain, and caspase-3 occurred in course of apoptosis. Increased calpain and caspase-3 activities were confirmed in the degradation of alpha-spectrin to 145 kD spectrin break down product (SBDP) and 120 kD SBDP, respectively. Thus, combination of HA and GST could serve as a promising therapeutic strategy for increasing apoptosis in different human malignant neuroblastoma cells.

Morphological and molecular assessment of apoptotic mechanisms in peripheral neuroblastic tumours

Multiple defects in apoptotic pathways have been described in peripheral neuroblastic tumours (NTs). Mitosis–karyorrhexis index (MKI) is a reliable morphological marker identifying favourable and unfavourable NTs. The extent to which apoptotic processes contribute to determine the clinical significance of MKI is still undefined. Apoptosis was investigated in a series of 110 peripheral NTs by comparing MKI to immunohistochemical and molecular apoptotic features. High MKI was found in 55 out of 110 NTs (50%) and was associated with advanced stage (P=0.007), neuroblastoma (NB) histological category (P=0.024), MYCN amplification (P<0.001), and poor outcome (P=0.011). Overall survival probability was 45% in patients with high MKI compared to 73% in patients with low MKI. In the same 110 NTs, the expression of Bcl-2, Bcl-X_L, Bax and Mcl-1 was studied by immunohistochemistry, but no significant associations were found with clinicohistological features. Microarray analysis of apoptotic genes was performed in 40 out of 110 representative tumours. No significant association was found between the expression of apoptotic genes and MKI or clinicohistological features. Proliferative activity was assessed in 60 out of 110 representative tumours using Ki67 immunostaining, but no significant correlations with MKI or clinicobiological features were found. In NTs, the combination of apoptosis and proliferation as expressed by MKI is a significant prognostic parameter, although neither of them is per se indicative of the clinicobiological behaviour and outcome.

Adrenocortical Tumors in Brazilian Children: Immunohistochemical Markers and Prognostic Factors

Context.—The behavior of adrenocortical tumors (ACTs) is usually difficult to establish in childhood, and the role of immunomarkers in predicting outcome has not yet been elucidated.

Objective.—To investigate the relationship between clinical, pathologic, and immunohistochemical findings and prognosis in a series of children with ACTs.

Patients and Methods.—Clinical data were evaluated retrospectively in 33 children with ACTs, including age at diagnosis, sex, time between first symptoms and diagnosis, clinical signs and symptoms, tumor position, and follow-up. Histologic sections were reviewed, each tumor was classified, and staging was performed according to previously published criteria. Immunohistochemical analysis of p53, Ki-67, c-Erb-B2, and Bcl-2 was performed according to previously published techniques.

Results.—Sixty-four percent (n = 21) of the patients were female, and the age at diagnosis in the cohort ranged from 2 to 96 months. Virilization alone affected 70% (n = 23) of the patients, and 18 patients had stage 1 disease, 9 had stage 2 disease, and 3 each had stage 3 and stage 4 disease. Female sex and stage 1 and stage 2 disease were associated with good outcome. None of the histopathologic criteria evaluated correctly predicted outcome. Only tumors with a volume exceeding 200 mL were associated with malignant behavior. Because only a small number of tumors expressed the antigens, results of these immunohistochemical tests were considered inconclusive.

Conclusion.—In this sample of pediatric ACTs, the clinical and surgical parameters are the most important prognostic factors, while the immunohistochemical markers evaluated were not predictive of outcome.

Antisense bcl-2 transfection up-regulates anti-apoptotic and anti-oxidant thioredoxin in neuroblastoma cells

Antisense bcl-2 therapy combined with chemotherapy has been proved to be effective in various tumors. However, the role played by antisense bcl-2 therapy alone is not clear. In this study, we compared the apoptosis and the protein profiles of antisense bcl-2 transfected human neuroblastoma SK-N-MC cells to the control cells. Flow cytometric data indicated that antisense bcl-2 transfection did not lead to more extensive apoptosis in SK-N-MC cells (14.9 +/- 3.8%) than the control cells (10.3 +/- 2.3%). The above observation was confirmed by fluorescence microscopy using Hoechst 33258 staining. However, antisense bcl-2 induced changes in the expression of various proteins as shown by proteomic comparison, which included the up-regulation of the anti-apoptotic and anti-oxidant protein thioredoxin. By western blot validation, thioredoxin was found to be up-regulated by 2.9-folds with the corresponding down-regulation of Bcl-2 by 2.1-folds. The up-regulation of thioredoxin may be a compensating mechanism for cell survival in neuroblastoma when Bcl-2 expression is suppressed, and it may to some extent attenuate the effectiveness of antisense bcl-2 therapy.

Imbalance of the mitochondrial pro- and anti-apoptotic mediators in neuroblastoma tumours with unfavourable biology

It has been proposed that a lack of apoptosis plays an important role in neuroblastoma (NB) progression. We therefore screened cDNA array filters, including 198 apoptotic genes, in order to identify mRNA transcripts that are differentially expressed in tumours with unfavourable versus favourable biology. Twenty-one genes were analysed further using real-time reverse-transcriptase-polymerase chain reaction (RT-PCR). Significantly lower levels of DNCL1 (PIN; P(c)(corrected) = 0.0054) and NTRK1 (TrkA; P(c) = 0.039) were found in NB tumours with unfavourable biology. In addition, BID, BCL2, APAF1, CASP2, CASP3 and CASP9 were found to be preferentially expressed in tumours with favourable biology, whereas CDKN1A (p21), IL2RA, and MCL1, were found to be preferentially expressed in NB tumours with unfavourable biology. In conclusion, mRNA levels of transcripts encoding pro-apoptotic mediators of the mitochondrial apoptotic pathway were found to be expressed to a lower extent in tumours with unfavourable biology. Our data also suggest that the mitochondrial pathway is suppressed in advanced stages of NB tumours, due to an imbalance between anti-apoptotic and pro-apoptotic mediators which is a finding that may have therapeutic significance.

Pediatric neuroblastomas: genetic and epigenetic 'danse macabre'

Neuroblastomas are the most frequently occurring solid tumors in children under 5 years. Spontaneous regression is more common in neuroblastomas than in any other tumor type, especially in young patients under 12 months. Unfortunately, the full clinical spectrum of neuroblastomas also includes very aggressive tumors, unresponsive to multi-modality treatment and accounting for most of the pediatric cancer mortalities under 5 years of age. It is generally emphasized that more than one biological entity of neuroblastoma exists. Structural genetic defects such as amplification of MYCN, gain of chromosome 17q and LOH of 1p and several other chromosomal regions have proven to be valuable as prognostic factors and will be discussed in relation to their clinical relevance. Recent research is starting to uncover important molecular pathways involved in the pathogenesis of neuroblastomas. The aim of this review is to discuss several important aspects of the biology of the neuroblast, such as the role of overexpressed oncogenes like MYCN and cyclin D1, the mechanisms leading to decreased apoptosis, like overexpression of BCL-2, survivin, NM23, epigenetic silencing of caspase 8 and the role of tumor suppressor genes, like p53, p73 and RASSF1A. In addition, the role of specific proteins overexpressed in neuroblastomas, such as the neurotrophin receptors TrkA, B and C in relation to spontaneous regression and anti-angiogenesis will be discussed. Finally, we will try to relate these pathways to the embryonal origin of neuroblastomas and discuss possible new avenues in the therapeutic approach of future neuroblastoma patients.

N-Myc overexpression leads to decreased beta1 integrin expression and increased apoptosis in human neuroblastoma cells

Neuroblastoma is a childhood tumor thought to arise through improper differentiation of neural crest cells. Increased N-Myc expression in neuroblastoma indicates highly malignant disease and poor patient prognosis. N-myc enhances cell growth, insulin-like growth factor type I receptor (IGF-IR) expression, and tumorigenicity in combination with Bcl-2. Despite these effects, N-Myc overexpression in SHEP neuroblastoma cells (SHEP/N-Myc cells) increases serum-withdrawal and mannitol-induced apoptosis. Although we have previously shown a protective effect of IGF-I in SHEP cells, in SHEP/N-Myc cells IGF-I rescue from mannitol-induced apoptosis is prevented. N-Myc overexpression has little effect on IGF-IR signaling pathways, but results in increased Akt phosphorylation when Bcl-2 is coexpressed. A loss of integrin-mediated adhesion promotes apoptosis in many systems. SHEP/N-Myc cells have dramatically less beta1 integrin expression than control cells, consistent with previous reports. beta1 integrin expression is decreased in more tumorigenic neuroblastoma cells lines, including IMR32 and SH-SY5Y cells. Reintroduction of beta1 integrin into the N-Myc-overexpressing cells prevents mannitol-mediated apoptosis. We speculate that N-Myc repression of beta1 integrin expression leads to a less differentiated phenotype, resulting in increased growth and tumorigenesis if properly supported or apoptosis if deprived of growth sustaining molecules.

Neuroblastoma, Apoptosis, and Growth Factors

Neuroblastoma is the most common extracranial tumor of childhood. This tumor is associated with alterations in apoptosis and is affected by various growth factors and cytokines. In this short review we will discuss recent findings in our laboratory where we have been studying a cell culture model of neuroblastoma.

Analyses of apoptotic regulators CASP9 and DFFA at 1P36.2, reveal rare allele variants in human neuroblastoma tumours

The genes encoding Caspase-9 and DFF45 have both recently been mapped to chromosome region 1p36.2, that is a region alleged to involve one or several tumour suppressor genes in neuroblastoma tumours. This study presents an update contig of the 'Smallest Region of Overlap of deletions' in Scandinavian neuroblastoma tumours and suggests that DFF45 is localized in the region. The genomic organization of the human DFF45 gene, deduced by in-silico comparisons of DNA sequences, is described for the first time in this paper. In the present study 44 primary tumours were screened for mutation by analysis of the genomic sequences of the genes. In two out of the 44 tumours this detected in the DFFA gene one rare allele variant that caused a non-polar to a polar amino acid exchange in a preserved hydrophobic patch of DFF45. One case was hemizygous due to deletion of the more common allele of this polymorphism. Out of 194 normal control alleles only one was found to carry this variant allele, so in respect of it, no healthy control individual out of 97 was homozygous. Moreover, our RT-PCR expression studies showed that DFF45 is preferably expressed in low-stage neuroblastoma tumours and to a lesser degree in high-stage neuroblastomas. We conclude that although coding mutations of Caspase-9 and DFF45 are infrequent in neuroblastoma tumours, our discovery of a rare allele in two neuroblastoma cases should be taken to warrant further studies of the role of DFF45 in neuroblastoma genetics.

Bcl-2 and M-Myc coexpression increases IGF-IR and features of malignant growth in neuroblastoma cell lines

The bcl-2 and c-myc oncogenes cooperate to transform multiple cell types. In the pediatric malignancy NB(2), Bcl-2 is highly expressed. In tumors with a poor prognosis, N-Myc, a protein homologous to c-Myc, is overexpressed as a result of gene amplification. The present study was designed to determine whether Bcl-2 cooperates with N-Myc to bestow a tumorigenic phenotype to neuroblastoma (NB) cells. NB cell lines that at baseline express neither Bcl-2 nor N-Myc were stably transfected to express these gene products. In this model, we found Bcl-2 rescues N-Myc-expressing cells from apoptosis induced by serum withdrawal. Coexpression of Bcl-2 and N-Myc supports growth in low serum conditions and anchorage-independent growth in soft agar. Similarly, in vivo tumorigenic and angiogenic activity was dependent on coexpression. Our data further suggests that the mechanism underlying these changes involves the receptor for insulin growth factor type I (IGF-IR).

Neuroblastoma and hepatocyte coculture conditioned media alter apoptosis

BACKGROUND

Neuroblastoma is a childhood tumor that often displays unusual biological behavior. The tumor may present with widespread metastases that are unresponsive to aggressive treatment. At other times, both the metastases and the primary tumor may spontaneously regress without treatment. Apoptosis, or programmed cell death, is thought to play a role in the dichotomous behavior of neuroblastoma. We hypothesize that neuroblastoma cells will interact with host tissues to release mediators that affect apoptosis.

MATERIALS AND METHODS

Human neuroblastoma cells and human Chang hepatocytes are grown in a noncontact, coculture system. After incubation for 4 days, the medium from the coculture system is collected. Neuroblastoma cells and Chang hepatocytes are then plated separately with the conditioned medium and their own standard growth medium as controls. After 4 days, these cells are harvested and cytospins made for immunostaining. Tumor necrosis factor alpha (TNF-alpha), Fas ligand, and Bcl-2, are measured with immunohistochemistry. Apoptosis is detected with the TUNEL method. Immunostaining data are interpreted with computer image analysis and reported as stain index. TUNEL data are reported as percentage apoptotic cells. All data are reported as means +/- SEM. Statistical analysis is performed and P < 0.05 considered significant.

RESULTS

Chang hepatocytes grown in the coculture conditioned media have an increase in TNF-alpha and Fas ligand. The neuroblastoma cells have a significant decrease in Fas ligand. There is a significant increase in the number of apoptotic hepatocytes when they are cultured in the conditioned media. In contrast, the neuroblastoma cells grown in the coculture conditioned media show no increase in apoptosis. Finally, Bcl-2 is significantly increased in the neuroblastoma cells cultured in the conditioned media.

CONCLUSIONS

Neuroblastoma cells grown in coculture conditioned media show increased expression of Bcl-2 and decreased Fas ligand levels. These changes should diminish apoptosis activity in the tumor cells. In contrast, the conditioned media induce elevated levels of proapoptotic mediators in the Chang hepatocytes. A tumor's ability to successfully metastasize may be dependent on mediators generated in the tumor-host interaction, and may not be just an independent characteristic of the tumor itself.

Molecular biology of neuroblastoma

PURPOSE AND RESULTS: Neuroblastoma, the most common solid extracranial neoplasm in children, is remarkable for its clinical heterogeneity. Complex patterns of genetic abnormalities interact to determine the clinical phenotype. The molecular biology of neuroblastoma is characterized by somatically acquired genetic events that lead to gene overexpression (oncogenes), gene inactivation (tumor suppressor genes), or alterations in gene expression. Amplification of the MYCN proto-oncogene occurs in 20% to 25% of neuroblastomas and is a reliable marker of aggressive clinical behavior. No other oncogene has been shown to be consistently mutated or overexpressed in neuroblastoma, although unbalanced translocations resulting in gain of genetic material from chromosome bands 17q23-qter have been identified in more than 50% of primary tumors. Some children have an inherited predisposition to develop neuroblastoma, but a familial neuroblastoma susceptibility gene has not yet been localized. Consistent areas of chromosomal loss, including chromosome band 1p36 in 30% to 35% of primary tumors, 11q23 in 44%, and 14q23-qter in 22%, may identify the location of neuroblastoma suppressor genes. Alterations in the expression of the neurotrophins and their receptors correlate with clinical behavior and may reflect the degree of neuroblastic differentiation before malignant transformation. Alterations in the expression of genes that regulate apoptosis also correlate with neuroblastoma behavior and may help to explain the phenomenon of spontaneous regression observed in a well-defined subset of patients.

CONCLUSION

The molecular biology of neuroblastoma has led to a combined clinical and biologic risk stratification. Future advances may lead to more specific treatment strategies for children with neuroblastoma.

Escaping cell death: survival proteins in cancer

Defects in apoptosis signaling pathways are common in cancer cells. Such defects may play an important role in tumor initiation because apoptosis normally eliminates cells with damaged DNA or dysregulated cell cycle, i.e., cells with increased malignant potential. Moreover, impaired apoptosis may enhance tumor progression and promote metastasis by enabling tumor cells to survive the transit in the bloodstream and to grow in ectopic tissue sites lacking the otherwise required survival factors. Finally, raised apoptosis threshold may have deleterious consequences by rendering cancer cells resistant to various forms of therapy. The intensive apoptosis research during the past decade has resulted in the identification of several proteins which may promote tumorigenesis by inhibiting apoptosis. Of special relevance in human cancer are those commonly expressed in primary tumors and functioning at the common part of the signaling pathway leading to apoptosis. Proteins fulfilling these criteria include antiapoptotic members of the Bcl-2 protein family, heat shock proteins, Hsp70 and Hsp27, as well as survivin, the novel cancer-associated member of the inhibitor of apoptosis protein family. Understanding the molecular mechanisms of action of these proteins may offer novel modes of rationally and selectively manipulating the sensitivity of cancer cells to therapy.

Induction of apoptosis in a neuroblastoma and hepatocyte coculture model

BACKGROUND

The dysregulation of apoptosis may alter the progression of tumor growth and explain the clinical dichotomy observed in children with neuroblastoma (NB). An overexpression of the bcl-2 proto-oncogene induces resistance to apoptosis and has been observed in unfavorable NB. We hypothesized that alterations in apoptosis may be a result of the interactions between NB and the tissues surrounding it.

MATERIALS AND METHODS

Human Chang liver cells (HCL, 10(4) cells/cm2) were plated in two-chamber slides for 3 days. Human NB cells (10(5) cells/cm2) were added to one of the chambers and incubated for 3 more days. Control NB were plated under identical conditions in its own medium and in the HCL medium with growth curves measured. DNA fragmentation was detected via the TUNEL method (TdT-mediated nick end-labeling) and bcl-2 expression was determined by immunostaining.

RESULTS

NB growth was unaltered by the change in medium. NB stained mildly positive for bcl-2 when plated alone but became markedly positive in coculture. Histologically, HCL and NB appeared healthy when plated alone, but a halo of apoptotic HCL was seen around NB in the coculture. When plated alone, both NB and HCL demonstrated minimal apoptotic activity as detected via the TUNEL method. In the coculture, a halo of HCL surrounding the NB exhibited markedly increased DNA fragmentation and this intensity diminished in cells distant from the NB.

CONCLUSIONS

The regulation of apoptosis was altered in this coculture model of NB and HCL. HCL stimulated NB to overexpress bcl-2 and presumably become resistant to apoptosis. Conversely, NB induced the surrounding HCL to undergo apoptosis. The interaction between the local tissue and NB induced alterations in apoptosis in both cell types and resulted in a survival advantage for NB.

Interleukin-1 beta converting enzyme (ICE) is preferentially expressed in neuroblastomas with favourable prognosis

To determine whether interleukin-1 beta converting enzyme (ICE) plays a role in the programmed cell death of neuroblastoma, we studied ICE expression in primary tumours. In patients in stages I, II and IVS, ICE mRNA was detected in 22 of 32 (69%) tumours, while only 5 of 26 (19%) tumours expressed ICE in stages III and IV (P < 0.001). ICE mRNA was expressed in 27 of 47 (57%) tumours without MYCN amplification, but it was not detected in any tumours with MYCN amplification (P < 0.01). Immunohistochemically, the cytoplasm was stained in all 15 neuroblastomas examined. The nuclei were stained in 12 neuroblastomas without MYCN amplification, whereas only 1 of 3 tumours with MYCN amplification had positive staining in the nuclei. In ganglioneuromas, high levels of ICE mRNA were expressed, but immunostaining showed that the protease expression was confined to the cytoplasm. These observations suggest that ICE may be associated with the spontaneous regression often seen in favourable neuroblastomas and that localisation of ICE protease in the cell may be important for the cell death pathway. Double staining for ICE and TUNEL showed that they were co-localised in some nuclei, but the distribution of ICE protease expression was not necessarily the same as that of DNA fragmentation, suggesting that the protease expression probably preceded DNA fragmentation during the apoptotic process. ICE may play an important role in regulating the apoptotic process of neuroblastoma.

Quantitative evaluation of apoptosis and proliferation in renal cell carcinoma. Correlation to tumor subtype, cytological grade according to thoenes-classification and the occurrence of metastasis

To analyse growth characteristics of human renal cell tumors, 66 renal cell carcinomas and one oncocytoma were investigated concerning the proliferative activity by immunohistochemical demonstration of the Ki-67 antigen (clone MIB1) and the apoptotic rate using the terminal deoxynucleotidyl-transferase mediated dUTP-fluorescin nick end labelling (TUNEL) method. The TUNEL method indicates DNA double strand breaks considered as a hallmark of programmed cell death (apoptosis). Apoptotic cells were observed in 57 of 67 cases. The apoptotic rate (percentage of stained tumor cells) varied from 0% to 54.1%. GI carcinomas possessed a statistically significant higher apoptotic rate than GII/GIII carcinomas. The proliferation index (percentage of Ki-67 labelled cells) ranged from 0.09% to 22.3%. The well differentiated carcinomas (GI) showed statistically lower proliferative activity than moderate and poorly differentiated carcinomas (GII/GII). The clear cell variant of renal cell carcinoma expressed a higher apoptotic rate than the chromophilic variant. A statistical correlation between apoptosis/proliferation and occurrence of metastasis could not be established. In progression from well to less differentiated renal cell carcinoma the decrease of apoptotic rate, as well as the increase of the proliferative activity, contributes to a rapid tumor growth.

Massive apoptosis detected by in situ DNA nick end labeling in neuroblastoma

To seek evidence that tumor regression in neuroblastoma might result from massive apoptosis, we investigated tumor cell death in 39 neuroblastomas. Characteristic histologic features of apoptosis, condensed nuclear fragments and eosinophilic cytoplasm, were observed in all specimens. A ladder of DNA fragments induced by apoptosis was demonstrated by means of DNA agarose gel electrophoresis in 18 of the 19 tumors examined. In situ DNA nick end labeling (TUNEL) stained the nuclei with DNA fragmentation in 16 of 39 neuroblastomas. The TUNEL -positive cells were distributed in a scattered fashion in 10 tumors. In the remaining six tumors, they were densely located around nonviable areas of calcifications, where karyorrhectic or pyknotic cells were frequently observed. Five of six patients with such tumors were under 12 months of age, but there was no significant difference between the two groups in the patient age, origin of the primary lesion, or tumor stage. Biological features, including histology. DNA ploidy, and N-myc amplification, were not significantly different . Double fluorescent staining for bcl-2 oncoprotein and TUNEL showed that bcl-2 oncoprotein was expressed in the cytoplasm of tumor cells that were negative for TUNEL staining. This accumulated evidence suggests that massive apoptosis of tumor cells occurs in some neuroblastomas and may be related to tumor regression, whereas inhibition of apoptosis by bcl-2 oncoprotein expression might be associated with the tumorigenesis of neuroblastomas, as reported in our previous study.