Transcription factor AP2alpha (TFAP2a) regulates differentiation and proliferation of neuroblastoma cells

Neuroblastoma, the most common extracranial solid tumour of childhood, is derived from neural crest progenitor cells. The TFAP2a transcription factor regulates neural crest patterning. We analysed TFAP2a protein expression in 97 primary neuroblastic tumors and report that TFAP2a was strongly expressed in poorly differentiated neuroblastomas. TFAP2a expression in tumor cells of differentiated neuroblastic tumors was below detection. TFAP2a was strongly expressed in 4 of 6 neuroblastoma cell lines tested, and TFAP2a siRNA mediated knock down in SH-EP cells reduced proliferation and induced a more differentiated phenotype associated with an increase in the expression of the differentiation marker neurotensin.

Translating expression profiling into a clinically feasible test to predict neuroblastoma outcome

PURPOSE

To assess the feasibility of predicting neuroblastoma outcome using highly parallel quantitative real-time PCR data.

EXPERIMENTAL DESIGN

We generated expression profiles of 63 neuroblastoma patients, 47 of which were analyzed by both Affymetrix U95A microarrays and highly parallel real-time PCR on microfluidic cards (MFC; Applied Biosystems). Top-ranked genes discriminating patients with event-free survival or relapse according to high-level analysis of Affymetrix chip data, as well as known neuroblastoma marker genes (MYCN and NTRK1/TrkA), were quantified simultaneously by real-time PCR. Analysis of PCR data was accomplished using high-level bioinformatics methods including prediction analysis of microarray, significance analysis of microarray, and Computerized Affected Sibling Pair Analyzer and Reporter.

RESULTS

Internal validation of the MFC method proved it highly reproducible. Correlation of MFC and chip expression data varied markedly for some genes. Outcome prediction using prediction analysis of microarray on real-time PCR data resulted in 80% accuracy, which is comparable to results obtained using the Affymetrix platform. Real-time PCR data were useful for risk assessment of relapsing neuroblastoma (P = 0.0006, log-rank test) when Computerized Affected Sibling Pair Analyzer and Reporter analysis was applied.

CONCLUSIONS

These data suggest that multiplex real-time PCR might be a promising approach to reduce the complexity of information obtained from whole-genome array experiments. It could provide a more convenient and less expensive tool for routine application in a clinical setting.

Biological effects of TrkA and TrkB receptor signaling in neuroblastoma

The Trk family consists of three receptor tyrosine kinases, each of which can be activated by one or more of four neurotrophins-NGF, BDNF, NT3 and NT4. Neurotrophins mediate their multiple effects through a number of distinct intracellular signaling cascades regulating such diverse biological responses as cell survival, proliferation and differentiation in normal and neoplastic neuronal cells. Expression of Trk receptors also plays an important role in the biology and clinical behavior of neuroblastomas. High expression of TrkA is present in neuroblastomas with favorable biological features and highly correlated with patient survival, whereas TrkB is mainly expressed on unfavorable, aggressive neuroblastomas. This short review discusses recent data on the biological roles of TrkA and TrkB signaling in neuroblastoma.

Prediction of clinical outcome and biological characterization of neuroblastoma by expression profiling

Neuroblastoma is a common childhood tumor comprising cases with rapid disease progression as well as spontaneous regression. Although numerous prognostic factors have been identified, risk evaluation in individual patients remains difficult. To define a reliable prognostic predictor and gene signatures characteristic of biological subgroups, we performed mRNA expression profiling of 68 neuroblastomas of all stages. Expression data were analysed using support vector machines (SVM-rbf), prediction analysis of microarrays (PAM), k-nearest neighbors (k-NN) algorithms and multiple decision trees. SVM-rbf performed best of all methods, and predicted recurrence of neuroblastoma with an accuracy of 85% (sensitivity 77%, specificity 94%). PAM identified a classifier of 39 genes reliably predicting outcome with an accuracy of 80%. In comparison, conventional risk stratification based on stage, age and MYCN-status only reached a predictive accuracy of 64%. Kaplan-Meier analysis using the PAM classifier indicated a 5-year survival of 20 versus 78% for patients with unfavorably versus favorably predicted neuroblastomas, respectively (P = 0.0001). Significance analysis of microarrays (SAM) identified additional genes differentially expressed among subgroups. MYCN-amplification and high expression of NTRK1/TrkA demonstrated a strong association with specific gene expression patterns. Our data suggest that microarray-derived data in addition to traditional clinical factors will be useful for risk assessment and defining biological properties of neuroblastoma.

The neurotrophin receptor TrkB cooperates with c-Met in enhancing neuroblastoma invasiveness

Neuroblastoma is the most frequent extracranial solid malignancy of childhood with a high mortality in advanced tumour stages. The hallmark of neuroblastoma is its clinical and biological heterogeneity. The molecular mechanisms leading to favourable or unfavourable tumour behaviour are still speculative. However, amplification of the oncogene MYCN and expression of the neurotrophin receptor TrkB are known to contribute to a highly malignant phenotype. To define the mechanisms through which TrkB may mediate neuroblastoma progression, we stably expressed this receptor in the neuroblastoma cell lines SH-SY5Y and SK-N-AS. The transfectants, but not the controls, had an increased invasive potency both, in vitro and in vivo, as demonstrated by Matrigel-invasion and chorioallantoic membrane assays, respectively. The retinoic acid-induced TrkB expression in parental SH-SY5Y cells was also associated with enhanced cell invasiveness. The TrkB mediated invasiveness involved the upregulation of the hepatocyte growth factor (HGF) and its receptor c-Met, resulting in an autocrine loop. Inhibition of HGF activity by anti-HGF neutralizing antibodies or disabling the function of c-Met by small interfering RNA suppressed the TrkB-induced invasiveness. The enhanced TrkB expression was associated with a significant increase in the secretion of various matrix-degrading proteases. Immunostaining and real-time RT-PCR analysis of tumour specimens demonstrated coordinated expression of TrkB and HGF/c-Met in experimental and primary neuroblastomas. We conclude that TrkB expression in neuroblastoma cells results in an increase in their invasive capability via upregulated expression of HGF/c-Met and enhanced activity of proteolytic networks.

Microarray analysis reveals differential gene expression patterns and regulation of single target genes contributing to the opposing phenotype of TrkA- and TrkB-expressing neuroblastomas

Expression of neurotrophin receptors of the tyrosine kinase receptor (Trk) family is an important prognostic factor in solid tumors including neuroblastoma. High expression of TrkA (NTRK1) is associated with a favorable biology and outcome of neuroblastoma, whereas TrkB (NTRK2) is expressed on aggressive neuroblastomas with unfavorable outcome. To gain new insights into the global gene expression program resulting in these divergent biological phenotypes, we stably expressed either TrkA or TrkB in the human SH-SY5Y neuroblastoma cell line. Gene expression profiles were obtained from parental cells and transfectants activated by their ligands in a time course over 24 h using oligonucleotide microarrays. Basal activation of Trk receptors in the absence of exogenous ligand was sufficient to induce broad and divergent genetic changes. Global gene regulation following external ligand stimulation was surprisingly similar in SY5Y-TrkA and SY5Y-TrkB cells except for the differential expression of distinct novel target genes. Consistent with their divergent biological phenotype, SY5Y-TrkA cells were characterized by upregulation of proapoptotic genes and angiogenesis inhibitors, whereas SY5Y-TrkB cells demonstrated upregulation of genes involved in invasion or therapy resistance. We suggest that the transcriptional program of neuroblastoma cells is modulated by Trk-receptor expression and basal activation rather than by ligand-induced activation. Fine-tuning of the malignant phenotype may be achieved by additional ligand stimulation with subsequent activation of a few specific genes.

Functional genomics and target gene validation in experimental and human disease

In contrast to rare monogenic disorders related to mutations in distinct genes, frequent multifactorial diseases including complex neuronal disorders as well as neoplasms involve expression changes in a multitude of genes. The integration of data derived from human disease tissue and of animal models by data mining constitutes a recent approach to increase the pathogenetic significance of target genes. Functional validation by animal models represents a key step to develop new treatment pathways for common disorders.:

Microarray-Analysis: A New Approach to Study the Molecular Mechanisms of Thermo-Chemotherapy

BACKGROUND

Experimental studies for the treatment of relapsed neuroblastoma include the use of hyperthermia in combination with chemotherapeutic drugs. Cytotoxic effects of alkylants and platinum compounds on tumor cells can be enhanced by hyperthermia in various in vitro models. However, the underlying molecular mechanisms are still largely unknown.

METHOD

In this study, we used microarray-analysis as a new biological approach to gain insight into the pharmacogenomics and possible target genes of thermochemotherapy. As a model, LAN 1 neuroblastoma cells were treated for 1 h with low doses of cisplatin alone, with simultaneous heating to 42 degrees C or with hyperthermia alone. Gene expression was analyzed at five time points 0 to 24 h after treatment using U95Av2 oligonucleotide arrays (Affymetrix Inc). Significant changes of gene expression levels were calculated by similarity metrices and Pearson correlation.

RESULTS

Only a few genes (n = 23) demonstrated altered expression following treatment of LAN 1 cells with cisplatin alone. Hyperthermia alone resulted in significant expression changes of 136 genes in comparison to untreated control cells. Combination therapy of cisplatin and hyperthermia resulted in expression changes of 251 genes, interestingly including 131 genes with unchanged expression under treatment with either cisplatin or hyperthermia alone. Significant changes of expression levels could be annotated to genes involved in heat shock response, protein degradation and apoptosis. These results are now being validated on mRNA- and protein levels by RT-PCR and Western Blot analysis.

CONCLUSION

Microarray-Analysis is a suitable new approach for the identification of target genes, which might play an important role for the synergistic effect of hyperthermia and chemotherapy in tumor cells.

A monomeric three-coordinate magnesium bis(amide)

The metallation reaction between dibutylmagnesium and 2,6-diisopropyl-N-(trimethylsilyl)aniline gives the unusual monomeric three-coordinate complex (diethyl ether-kappa O)bis[2,6-diisopropyl-N-(trimethylsilyl)anilido-kappa N]magnesium(II), [Mg(C(15)H(26)NSi)(2)(C(4)H(10)O)] or [Mg[(Me(3)Si)(2,6-(i)Pr(2)C(6)H(3))N](2)(Et(2)O)]. This low-coordinate species has a distorted trigonal-planar coordination environment, with an additional short Mg-C(ipso) contact of 2.799 (2) A.