Evidence of apoptosis in neuroblastoma at onset and relapse. An analysis of a large series of tumors

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.

Spontaneous regression of a breast carcinoma: a case report

Spontaneous regression of malignant tumors is a rare event. It is defined as partial or total disappearance of a proven malignant tumor without adequate medical treatment. The causes of this phenomenon are various. Nevertheless, malignant tumors do regress occasionally for no apparent reason, as evidenced by many clinical observations. We report a case of a 68-year-old woman, who was presented with a several-month history of a painless firm lump, initially of 1 cm in diameter and growing to a large solid regular tumor of 2.5 x 2.5 cm in size, in the upper outer quadrant of her right breast. Preoperative histopathological diagnosis revealed ductal invasive carcinoma. Later on, while awaiting surgical treatment, she suffered an arm injury requiring a 1-month delay of surgery. After recovery, on the date of surgery the tumor disappeared, and, in addition, it was not found in tissue specimens obtained from quadrantectomy. After 78 months of follow-up there was no evidence of relapse. In this report, we discuss clinical and histopathological findings, patient management and possible mechanisms of cancer regression.

Differential expression of Bcl-2 and Bax may enhance neuroblastoma survival

BACKGROUND/PURPOSE

Aggressive tumors may alter their expression of Bcl-2 proteins to decrease apoptosis and increase survival. The authors reported previously that neuroblastoma cells have diminished apoptosis when placed in coculture with hepatocytes to stimulate a metastatic environment. It was hypothesized that the expression of proapoptotic (Bax) and prosurvival (Bcl-2 and Mcl-1) proteins would be altered in neuroblastoma cells grown in a cell culture model of metastatic neuroblastoma.

METHODS

Human neuroblastoma cells (IMR-32) were grown alone or in coculture with human hepatocytes for 2, 3, or 4 days. Bcl-2, Mcl-1, and Bax mRNA were measured with reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

Bcl-2, an antiapoptotic protein, was significantly increased in cocultured neuroblastoma cells by day 4. Bax, a proapoptotic protein, was significantly diminished by day 3. No significant change in Mcl-1 occurred in this study.

CONCLUSIONS

When neuroblastoma cells placed in coculture, the prosurvival protein, Bcl-2, is upregulated whereas the proapoptotic protein, Bax, is downregulated. The combination of these changes can maximally enhance the survival rate of neuroblastoma cells in coculture. The propensity for neuroblastoma to either metastasize or regress may be associated with its ability to differentially regulate the expression of different members of the Bcl-2 protein family.

Initial characterization of the apoptosis-inducing receptor for natural human anti-neuroblastoma IgM

BACKGROUND

Human neuroblastoma (NB) cells contain a 260 kDa surface antigen (NB-p260), which serves as receptor for natural human IgM antibodies (anti-NB IgM). Upon binding to NB-p260, these antibodies induce apoptosis in human NB cells.

PROCEDURE AND RESULTS

In this study, we purified NB-p260 to homogeneity from human LA-N-1 NB cells by sequential ion exchange chromatography followed by preparative SDS gel electrophoresis. Purified NB-p260 exhibited rapid autodegradation despite the presence of various protease inhibitors. The autodegradation process precluded extensive N-terminal sequencing. However, from repeat N-terminal sequence analysis, a consensus sequence of seven amino acid residues emerged that exhibited significant homology to the subunit c of the human mitochondrial ATP synthase, a hydrophobic membrane protein of 7.6 kDa. Western blot analyses demonstrated that purified NB-p260 was recognized by polyclonal antibodies raised against both subunit c-containing storage bodies and a synthetic peptide consisting of amino acid residues 32-45 of subunit c. In addition to peptide sequences related to subunit c, NB-p260 also contained epitopes related to the human heat shock protein HSP90. In Western blots, a monoclonal anti-HSP90 antibody reacted with purified NB-p260 as well as with a predominant protein fragment of approximately 90 kDa that appeared during the process of NB-p260 autodegradation. The anti-HSP90 antibody was also capable of binding to the surface of LA-N-1 cells and inhibiting the binding of human anti-NB IgM in a dose-dependent manner.

CONCLUSIONS

Collectively, our data suggest that NB-p260, the apoptosis-mediating receptor for natural human anti-NB IgM, represents a novel surface protein of human NB cells containing polypeptide sequences related to the subunit c of the mitochondrial ATP synthase and the heat shock protein HSP90.

Spontaneous apoptosis and retinoic acid receptor incidence in neuroblastomas and peripheral neuroectodermal tumors

Twelve cases of neuroblastoma (NB) (7 boys and 5 girls) and 4 cases of primitive peripheral neuroectodermal tumor (PNET) (3 boys and 1 girl) were investigated for the presence of apoptosis and retinoic acid receptor (RAR) by immunhistochemical method. The apoptotic index in NB was zero or 1% in 8 children and relatively low (2-4.8%) in the other 4 cases, while it was higher (4.1-10.5%) in PNET. The RAR index determined by immunoperoxidase reaction in NB was zero or 3% in 5 cases and 9-34% in 7 children. RAR index in PNET was 16-68% in all the 4 cases. Good correlation (r = .47 according to Pearson-Bravis) was found between the number of RAR and spontaneous apoptosis. These results suggest that the RAR index in untreated NB and PNET shows great individual variation since its determination is necessary for the evaluation of the efficacy of retinoic acid treatment.

Apoptosis in favourable neuroblastomas is not dependent on Fas (CD95/APO-1) expression but on activated caspase 3 (CPP32)

The mechanisms of apoptosis in neuroblastomas have been investigated by examining the expression profiles of Fas, Fas ligand (FasL), and caspase 3 in 42 primary tumour tissues. Immunohistochemically, no or weak Fas expression was detected in 25 out of 29 neuroblastomas (86 per cent), whereas high levels of expression of FasL and pro-caspase 3 were noted in 30 and 29 of 42 tumours, respectively (approximately 70 per cent). Overexpression of pro-caspase 3, but not FasL, correlated significantly with a younger age and low tumour stage. Western blot analysis of ten neuroblastomas confirmed the lack of Fas expression and the presence of strong FasL expression in all samples and pro-caspase 3 expression in five tumours, of which four belonged to the favourable type. These favourable tumours also showed vigorous Asp-Glu-Val-Asp (DEVD) hydrolytic, or caspase 3-like activities, while the unfavourable tumour lacked such activity. Moreover, immunostaining for the p17 subunit of the caspase 3 heterodimer showed that active caspase 3 was mainly localized in apoptotic tumour cells. Combined together, our results suggest that caspase 3, activated via a Fas-independent pathway, may play important roles in apoptosis, suppression of growth, and, in some cases, regression of favourable neuroblastomas.

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.

Modeling insight into spontaneous regression of tumors

The phenomenon of spontaneous regression of benign and malignant tumors is well documented in the literature and is commonly attributed to the induction of apoptosis or activation of the immune system. We attempt at evaluating the role of random effects in this phenomenon. To this end, we consider a stochastic model of tumor growth which is descriptive of the fact that tumors are inherently prone to spontaneous regression due to the random nature of their development. The model describes a population of actively proliferating cells which may give rise to differentiated cells. The process of cell differentiation is irreversible and terminates in cell death. We formulate the model in terms of temporally inhomogeneous Markov branching processes with two types of cells so that the expected total number of neoplastic cells is consistent with the observed mean growth kinetics. Within the framework of this model, the extinction probability for proliferating cells tends to one as time tends to infinity. Given the event of nonextinction, the distribution of tumor size is asymptotically exponential. The limiting conditional distribution of tumor size is in good agreement with epidemiologic data on advanced lung cancer.