Molecular dissection of TrkA signal transduction pathways mediating differentiation in human neuroblastoma cells

Small-molecule inhibition of the METTL3/METTL14 complex suppresses neuroblastoma tumor growth and promotes differentiation

The N6-methyladenosine (m6A) RNA modification is an important regulator of gene expression. m6A is deposited by a methyltransferase complex that includes methyltransferase-like 3 (METTL3) and methyltransferase-like 14 (METTL14). High levels of METTL3/METTL14 drive the growth of many types of adult cancer, and METTL3/METTL14 inhibitors are emerging as new anticancer agents. However, little is known about the m6A epitranscriptome or the role of the METTL3/METTL14 complex in neuroblastoma, a common pediatric cancer. Here, we show that METTL3 knockdown or pharmacologic inhibition with the small molecule STM2457 leads to reduced neuroblastoma cell proliferation and increased differentiation. These changes in neuroblastoma phenotype are associated with decreased m6A deposition on transcripts involved in nervous system development and neuronal differentiation, with increased stability of target mRNAs. In preclinical studies, STM2457 treatment suppresses the growth of neuroblastoma tumors in vivo. Together, these results support the potential of METTL3/METTL14 complex inhibition as a therapeutic strategy against neuroblastoma.

Identification of a novel gene signature for neuroblastoma differentiation using a Boolean implication network

Although induction of differentiation represents an effective strategy for neuroblastoma treatment, the mechanisms underlying neuroblastoma differentiation are poorly understood. We generated a computational model of neuroblastoma differentiation consisting of interconnected gene clusters identified based on symmetric and asymmetric gene expression relationships. We identified a differentiation signature consisting of series of gene clusters comprised of 1251 independent genes that predicted neuroblastoma differentiation in independent datasets and in neuroblastoma cell lines treated with agents known to induce differentiation. This differentiation signature was associated with patient outcomes in multiple independent patient cohorts and validated the role of MYCN expression as a marker of neuroblastoma differentiation. Our results further identified novel genes associated with MYCN via asymmetric Boolean implication relationships that would not have been identified using symmetric computational approaches and that were associated with both neuroblastoma differentiation and patient outcomes. Our differentiation signature included a cluster of genes involved in intracellular signaling and growth factor receptor trafficking pathways that is strongly associated with neuroblastoma differentiation, and we validated the associations of UBE4B, a gene within this cluster, with neuroblastoma cell and tumor differentiation. Our findings demonstrate that Boolean network analyses of symmetric and asymmetric gene expression relationships can identify novel genes and pathways relevant for neuroblastoma tumor differentiation that could represent potential therapeutic targets.

Regulation of nuclear actin levels and MRTF/SRF target gene expression during PC6.3 cell differentiation

Actin has important functions in both cytoplasm and nucleus of the cell, with active nuclear transport mechanisms maintaining the cellular actin balance. Nuclear actin levels are subject to regulation during many cellular processes from cell differentiation to cancer. Here we show that nuclear actin levels increase upon differentiation of PC6.3 cells towards neuron-like cells. Photobleaching experiments demonstrate that this increase is due to decreased nuclear export of actin during cell differentiation. Increased nuclear actin levels lead to decreased nuclear localization of MRTF-A, a well-established transcription cofactor of SRF. In line with MRTF-A localization, transcriptomics analysis reveals that MRTF/SRF target gene expression is first transiently activated, but then substantially downregulated during PC6.3 cell differentiation. This study therefore describes a novel cellular context, where regulation of nuclear actin is utilized to tune MRTF/SRF target gene expression during cell differentiation.

AC-265347 Inhibits Neuroblastoma Tumor Growth by Induction of Differentiation without Causing Hypocalcemia

Neuroblastoma is the most common extracranial solid tumor of childhood, with heterogeneous clinical manifestations ranging from spontaneous regression to aggressive metastatic disease. The calcium-sensing receptor (CaSR) is a G protein-coupled receptor (GPCR) that senses plasmatic fluctuation in the extracellular concentration of calcium and plays a key role in maintaining calcium homeostasis. We have previously reported that this receptor exhibits tumor suppressor properties in neuroblastoma. The activation of CaSR with cinacalcet, a positive allosteric modulator of CaSR, reduces neuroblastoma tumor growth by promoting differentiation, endoplasmic reticulum (ER) stress and apoptosis. However, cinacalcet treatment results in unmanageable hypocalcemia in patients. Based on the bias signaling shown by calcimimetics, we aimed to identify a new drug that might exert tumor-growth inhibition similar to cinacalcet, without affecting plasma calcium levels. We identified a structurally different calcimimetic, AC-265347, as a promising therapeutic agent for neuroblastoma, since it reduced tumor growth by induction of differentiation, without affecting plasma calcium levels. Microarray analysis suggested biased allosteric modulation of the CaSR signaling by AC-265347 and cinacalcet towards distinct intracellular pathways. No upregulation of genes involved in calcium signaling and ER stress were observed in patient-derived xenografts (PDX) models exposed to AC-265347. Moreover, the most significant upregulated biological pathways promoted by AC-265347 were linked to RHO GTPases signaling. AC-265347 upregulated cancer testis antigens (CTAs), providing new opportunities for CTA-based immunotherapies. Taken together, this study highlights the importance of the biased allosteric modulation when targeting GPCRs in cancer. More importantly, the capacity of AC-265347 to promote differentiation of malignant neuroblastoma cells provides new opportunities, alone or in combination with other drugs, to treat high-risk neuroblastoma patients.

TrkA Interacts with and Phosphorylates STAT3 to Enhance Gene Transcription and Promote Breast Cancer Stem Cells in Triple-Negative and HER2-Enriched Breast Cancers

Simple Summary

Breast cancer is the leading cancer in American women. Due to the inherent aggressiveness of triple-negative and HER2-enriched breast cancers, it is imperative to identify novel molecular targets for therapeutic intervention. Due to their abnormal activities in metastatic breast cancers, JAK2–STAT3 and TrkA pathways have been individually implicated in aggressive breast tumors. However, their co-activation and signaling interactions have not been thoroughly investigated. Therefore, our study aimed to elucidate the extent of crosstalk between JAK2–STAT3 and TrkA signaling pathways and its impact on breast cancer. Our data revealed a novel interaction between TrkA and STAT3, and that this interaction results in STAT3 phosphorylation and activation by TrkA, leading to enhanced stemness gene expression and stem cell renewal. We further found that the co-activation of JAK2–STAT3 and TrkA pathways is correlated with shorter time to develop overall and organ-specific metastasis, suggesting that this signaling crosstalk underlies the aggressiveness of triple-negative and HER2-enriched breast cancers.

Abstract

JAK2–STAT3 and TrkA signaling pathways have been separately implicated in aggressive breast cancers; however, whether they are co-activated or undergo functional interaction has not been thoroughly investigated. Herein we report, for the first time that STAT3 and TrkA are significantly co-overexpressed and co-activated in triple-negative breast cancer (TNBC) and HER2-enriched breast cancer, as shown by immunohistochemical staining and data mining. Through immunofluorescence staining–confocal microscopy and immunoprecipitation–Western blotting, we found that TrkA and STAT3 co-localize and physically interact in the cytoplasm, and the interaction is dependent on STAT3-Y705 phosphorylation. TrkA–STAT3 interaction leads to STAT3 phosphorylation at Y705 by TrkA in breast cancer cells and cell-free kinase assays, indicating that STAT3 is a novel substrate of TrkA. β-NGF-mediated TrkA activation induces TrkA–STAT3 interaction, STAT3 nuclear transport and transcriptional activity, and the expression of STAT3 target genes, SOX2 and MYC. The co-activation of both pathways promotes breast cancer stem cells. Finally, we found that TNBC and HER2-enriched breast cancer with JAK2–STAT3 and TrkA co-activation are positively associated with poor overall metastasis-free and organ-specific metastasis-free survival. Collectively, our study uncovered that TrkA is a novel activating kinase of STAT3, and their co-activation enhances gene transcription and promotes breast cancer stem cells in TNBC and HER2-enriched breast cancer.

Molecular mechanism of nur77 gene expression and downstream target genes in the early stage of forskolin-induced differentiation in PC12 cells

Forskolin promotes neuronal differentiation of PC12 cells via the PKA-CREB-dependent signaling pathway. Activation of PKA by forskolin phosphorylates CREB, which then binds to CRE sites in numerous gene promoters. However, it is unclear which gene contains the CRE sites responsible for forskolin-induced neuronal differentiation. In this study, we investigated how an immediate early gene, nur77, which has CRE sites in the promoter region, contributes to the early stage of differentiation of forskolin-treated PC12 cells. After treatment with forskolin, expression of Nur77 was upregulated within 1 hr. In addition, knockdown of nur77 inhibited neurite outgrowth induced by forskolin. We also revealed that the specific four CRE sites near the transcriptional start site (TSS) of nur77 were strongly associated with phosphorylated CREB within 1 hr after treatment with forskolin. To analyze the roles of these four sites, reporter assays using the nur77 promoter region were performed. The results showed that nur77 expression was mediated through three of the CRE sites, -242, -222, and -78, and that -78, the nearest of the three to the TSS of nur77, was particularly important. An analysis of neuronal markers controlled by Nur77 after A-CREB-Nur77-Synapsin1 signaling pathway plays a pivotal role in differentiation of forskolin-induced PC12 cells.

WNT Signaling in Neuroblastoma

The term WNT (wingless-type MMTV integration site family) signaling comprises a complex molecular pathway consisting of ligands, receptors, coreceptors, signal transducers and transcriptional modulators with crucial functions during embryonic development, including all aspects of proliferation, morphogenesis and differentiation. Its involvement in cancer biology is well documented. Even though WNT signaling has been divided into mainly three distinct branches in the past, increasing evidence shows that some molecular hubs can act in various branches by exchanging interaction partners. Here we discuss developmental and clinical aspects of WNT signaling in neuroblastoma (NB), an embryonic tumor with an extremely broad clinical spectrum, ranging from spontaneous differentiation to fatal outcome. We discuss implications of WNT molecules in NB onset, progression, and relapse due to chemoresistance. In the light of the still too high number of NB deaths, new pathways must be considered.

Insights into Current Tropomyosin Receptor Kinase (TRK) Inhibitors: Development and Clinical Application

The use of kinase-directed precision medicine has been heavily pursued since the discovery and development of imatinib. Annually, it is estimated that around ∼20 000 new cases of tropomyosin receptor kinase (TRK) cancers are diagnosed, with the majority of cases exhibiting a TRK genomic rearrangement. In this Perspective, we discuss current development and clinical applications for TRK precision medicine by providing the following: (1) the biological background and significance of the TRK kinase family, (2) a compilation of known TRK inhibitors and analysis of their cocrystal structures, (3) an overview of TRK clinical trials, and (4) future perspectives for drug discovery and development of TRK inhibitors.

Ulk1 Governs Nerve Growth Factor/TrkA Signaling by Mediating Rab5 GTPase Activation in Porcine Hemagglutinating Encephalomyelitis Virus-Induced Neurodegenerative Disorders

Porcine hemagglutinating encephalomyelitis virus (PHEV) is a highly neurovirulent coronavirus and causes neurological dysfunction in the central nervous system (CNS), but the neuropathological mechanism of PHEV remains poorly understood. We report that Unc51-like kinase 1 (Ulk1/Unc51.1) is a pivotal regulator of PHEV-induced neurological disorders and functions to selectively control the initiation of nerve growth factor (NGF)/TrkA endosome trafficking. We first identified the function of Ulk1 by histopathologic evaluation in a PHEV-infected mouse model in which neuronal loss was accompanied by the suppression of Ulk1 expression. Morphogenesis assessments in the primary cortical neurons revealed that overexpression or mutations of Ulk1 modulated neurite outgrowth, collateral sprouting, and endosomal transport. Likewise, Ulk1 expression was decreased following PHEV infection, suggesting that there was a correlation between the neurodegeneration and functional Ulk1 deficiency. We then showed that Ulk1 forms a multiprotein complex with TrkA and the early endosome marker Rab5 and that Ulk1 defects lead to either blocking of NGF/TrkA endocytosis or premature degradation of pTrkA via constitutive activation of the Rab5 GTPase. Further investigation determined that the ectopic expression of Rab5 mutants induces aberrant endosomal accumulation of activated pTrkA, proving that targeting of Ulk1-TrkA-NGF signaling to the retrograde transport route in the neurodegenerative process that underlies PHEV infection is dependent on Rab5 GTPase activity. Therefore, we described a long-distance signaling mechanism of PHEV-driven deficits in neurons and suggested that such Ulk1 repression may result in limited NGF/TrkA retrograde signaling within activated Rab5 endosomes, explaining the progressive failure of neurite outgrowth and survival.IMPORTANCE Porcine hemagglutinating encephalomyelitis virus (PHEV) is a neurotropic coronavirus and targets neurons in the nervous system for proliferation, frequently leaving behind grievous neurodegeneration. Structural plasticity disorders occur in the axons, dendrites, and dendritic spines of PHEV-infected neurons, and dysfunction of this neural process may contribute to neurologic pathologies, but the mechanisms remain undetermined. Further understanding of the neurological manifestations underlying PHEV infection in the CNS may provide insights into both neurodevelopmental and neurodegenerative diseases that may be conducive to targeted approaches for treatment. The significance of our research is in identifying an Ulk1-related neurodegenerative mechanism, focusing on the regulatory functions of Ulk1 in the transport of long-distance trophic signaling endosomes, thereby explaining the progressive failure of neurite outgrowth and survival associated with PHEV aggression. This is the first report to define a mechanistic link between alterations in signaling from endocytic pathways and the neuropathogenesis of PHEV-induced CNS disease.

WNT signaling, the development of the sympathoadrenal-paraganglionic system and neuroblastoma

Neuroblastoma (NB) is a tumor of the sympathoadrenal system arising in children under 15 years of age. In Germany, NB accounts for 7% of childhood cancer cases, but 11% of cancer deaths. It originates from highly migratory progenitor cells that leave the dorsal neural tube and contribute neurons and glial cells to sympathetic ganglia, and chromaffin and supportive cells to the adrenal medulla and paraganglia. Clinically, histologically and molecularly, NBs present as extremely heterogeneous, ranging from very good to very poor prognosis. The etiology of NB still remains unclear and needs to be elucidated, however, aberrant auto- and paracrine embryonic cell communications seem to be likely candidates to initiate or facilitate the emergence, progression and regression of NB. The wingless-type MMTV integration site (WNT) family of proteins represents an evolutionary highly conserved signaling system that orchestrates embryogenesis. At least 19 ligands in the human, numerous receptors and co-receptors are known, which control not only proliferation, but also cell polarity, migration and differentiation. Here we seek to interconnect aspects of WNT signaling with sympathoadrenal and paraganglionic development to define new WNT signaling cues in the etiology and progression of NB.

ESM1 mediates NGFR-induced invasion and metastasis in murine oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a highly invasive and metastatic malignancy. The nerve growth factor receptor (NGFR) has been observed to be expressed on a subset of cells in OSCC, and NGFR⁺ cells have greater tumor-initiating capacity in vivo. Further, inhibition of NGFR reduces tumor growth, indicating a functional role of this receptor; however, the mechanisms by which NGFR confers enhanced tumor formation are not known. Here, we used an established murine model of OSCC and gene expression array analysis to identify ESM1 as a downstream target gene of NGFR, critical for tumor invasion and metastasis. ESM1 encodes a protein called endocan, which has the property of regulating proliferation, differentiation, migration, and adhesion of different cell types. Incubation of NGFR⁺ murine OSCC cells with nerve growth factor resulted in increased expression of ESM1. Importantly, ESM1 overexpression conferred an enhanced migratory, invasive, and metastatic phenotype, similar to what has been correlated with NGFR expression. Conversely, shRNA knockdown of ESM1 in NGFR overexpressing OSCC cells abrogated the tumor growth kinetics and the invasive and metastatic properties associated with NGFR. Together, our data indicate that NGFR plays an important role in the pathogenesis and progression of OSCC via regulation of ESM1.

Cell death-based treatment of neuroblastoma

Neuroblastoma (NB) is the most common solid childhood tumor outside the brain and causes 15% of childhood cancer-related mortality. The main drivers of NB formation are neural crest cell-derived sympathoadrenal cells that undergo abnormal genetic arrangements. Moreover, NB is a complex disease that has high heterogeneity and is therefore difficult to target for successful therapy. Thus, a better understanding of NB development helps to improve treatment and increase the survival rate. One of the major causes of sporadic NB is known to be MYCN amplification and mutations in ALK (anaplastic lymphoma kinase) are responsible for familial NB. Many other genetic abnormalities can be found; however, they are not considered as driver mutations, rather they support tumor aggressiveness. Tumor cell elimination via cell death is widely accepted as a successful technique. Therefore, in this review, we provide a thorough overview of how different modes of cell death and treatment strategies, such as immunotherapy or spontaneous regression, are or can be applied for NB elimination. In addition, several currently used and innovative approaches and their suitability for clinical testing and usage will be discussed. Moreover, significant attention will be given to combined therapies that show more effective results with fewer side effects than drugs targeting only one specific protein or pathway.

Angiotensin II AT2 receptors regulate NGF-mediated neurite outgrowth via the NO-cGMP pathway

We investigated whether Angiotensin II type 2 (AT2) receptor activation was involved in NGF-induced nerve regeneration. NGF-mediated neurite outgrowth in cultured dorsal root ganglia (DRG) cells was significantly inhibited by AT2 receptor antagonist (PD123,319) treatment. AT2 receptor knockdown also inhibited NGF-mediated neurite outgrowth. To determine the mechanisms, we analyzed the NO-cGMP pathway. The cGMP analog increased NGF-mediated nerve elongation, which inhibited by PD123,319. Furthermore, soluble guanylate cyclase expression was significantly less in NGF and PD123,319 treatment DRG than in NGF treatment alone. These results suggest that NGF-mediated neurite outgrowth is suppressed by AT2 receptor signaling via the NO-cGMP-PKG pathway.

Neuroblastoma in dialog with its stroma: NTRK1 is a regulator of cellular cross-talk with Schwann cells

In neuroblastoma, the most common solid tumor of childhood, excellent prognosis is associated with extensive Schwann cell (SC) content and high-level expression of the neurotrophin receptor, NTRK1/TrkA, which is known to mediate neuroblastoma cell differentiation. We hypothesized that both stromal composition and neuroblastic differentiation are based on bidirectional neuroblastoma-SC interaction. Reanalysis of microarray data from human SY5Y neuroblastoma cells stably transfected with either NTRK1 or NTRK2 revealed upregulation of the mRNA for the SC growth factor, NRG1, in NTRK1-positive cells. Media conditioned by NTRK1-expressing neuroblastoma cells induced SC proliferation and migration, while antibody-based NRG1 neutralization significantly decreased these effects. Vice versa, NRG1-stimulated SC secreted the NTRK1-specific ligand, NGF. SC-conditioned medium activated the NTRK1 receptor in a neuroblastoma cell culture model conditionally expressing NTRK1 and induced differentiation markers in NTRK1-expressing cells. NTRK1 induction in neuroblastoma xenografts mixed with primary SC also significantly reduced tumor growth in vivo. We propose a model for NTRK1-mediated and NRG1-dependent attraction of adjacent SC, which in turn induce neuroblastic differentiation by secretion of the NTRK1-specific ligand, NGF. These findings have implications for understanding the mature and less malignant neuroblastoma phenotype associated with NTRK1 expression, and could assist the development of new therapeutic strategies for neuroblastoma differentiation.

Retinoic acid-induced CHD5 upregulation and neuronal differentiation of neuroblastoma

Background

Chromodomain-helicase DNA binding protein 5 (CHD5) is an important tumor suppressor gene deleted from 1p36.31 in neuroblastomas (NBs). High CHD5 expression is associated with a favorable prognosis, but deletion or low expression is frequent in high-risk tumors. We explored the role of CHD5 expression in the neuronal differentiation of NB cell lines.

Methods

NB cell lines SH-SY5Y (SY5Y), NGP, SK-N-DZ, IMR5, LAN5, SK-N-FI, NB69 and SH-EP were treated with 1–10 μM 13-cis-retinoic acid (13cRA) for 3–12 days. qRT-PCR and Western blot analyses were performed to measure mRNA and protein expression levels, respectively. Morphological differences were examined by both phase contrast and immunofluorescence studies.

Results

Treatment of SY5Y cells with 13cRA caused upregulation of CHD5 expression in a time- and dose-dependent manner (1, 5, or 10 μM for 7 or 12 days) and also induced neuronal differentiation. Furthermore, both NGP and SK-N-DZ cells showed CHD5 upregulation and neuronal differentiation after 13cRA treatment. In contrast, 13cRA treatment of IMR5, LAN5, or SK-N-FI induced neither CHD5 expression nor neuronal differentiation. NB69 cells showed two different morphologies (neuronal and substrate adherent) after 12 days treatment with 10 μM of 13cRA. CHD5 expression was high in the neuronal cells, but low/absent in the flat, substrate adherent cells. Finally, NGF treatment caused upregulation of CHD5 expression and neuronal differentiation in SY5Y cells transfected to express TrkA (SY5Y-TrkA) but not in TrkA-null parental SY5Y cells, and both changes were blocked by a pan-TRK inhibitor.

Conclusions

Treatment with 13cRA induces neuronal differentiation only in NB cells that upregulate CHD5. In addition, NGF induced CHD5 upregulation and neuronal differentiation only in TrkA expressing cells. Together, these results suggest that CHD5 is downstream of TrkA, and CHD5 expression may be crucial for neuronal differentiation induced by either 13cRA or TrkA/NGF signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0425-y) contains supplementary material, which is available to authorized users.

Temporal proteomics of NGF-TrkA signaling identifies an inhibitory role for the E3 ligase Cbl-b in neuroblastoma cell differentiation

SH-SY5Y neuroblastoma cells respond to nerve growth factor (NGF)-mediated activation of the tropomyosin-related kinase A (TrkA) with neurite outgrowth, thereby providing a model to study neuronal differentiation. We performed a time-resolved analysis of NGF-TrkA signaling in neuroblastoma cells using mass spectrometry-based quantitative proteomics. The combination of interactome, phosphoproteome, and proteome data provided temporal insights into the molecular events downstream of NGF binding to TrkA. We showed that upon NGF stimulation, TrkA recruits the E3 ubiquitin ligase Cbl-b, which then becomes phosphorylated and ubiquitylated and decreases in abundance. We also found that recruitment of Cbl-b promotes TrkA ubiquitylation and degradation. Furthermore, the amount of phosphorylation of the kinase ERK and neurite outgrowth increased upon Cbl-b depletion in several neuroblastoma cell lines. Our findings suggest that Cbl-b limits NGF-TrkA signaling to control the length of neurites.

Mutations in NTRK3 suggest a novel signaling pathway in human congenital heart disease

Congenital heart defects (CHDs) are the most common major birth defects and the leading cause of death from congenital malformations. The etiology remains largely unknown, though genetic variants clearly contribute. In a previous study, we identified a large copy-number variant (CNV) that deleted 46 genes in a patient with a malalignment type ventricular septal defect (VSD). The CNV included the gene NTRK3 encoding neurotrophic tyrosine kinase receptor C (TrkC), which is essential for normal cardiogenesis in animal models. To evaluate the role of NTRK3 in human CHDs, we studied 467 patients with related heart defects for NTRK3 mutations. We identified four missense mutations in four patients with VSDs that were not found in ethnically matched controls and were predicted to be functionally deleterious. Functional analysis using neuroblastoma cell lines expressing mutant TrkC demonstrated that one of the mutations (c.278C>T, p.T93M) significantly reduced autophosphorylation of TrkC in response to ligand binding, subsequently decreasing phosphorylation of downstream target proteins. In addition, compared with wild type, three of the four cell lines expressing mutant TrkC showed altered cell growth in low-serum conditions without supplemental neurotrophin 3. These findings suggest a novel pathophysiological mechanism involving NTRK3 in the development of VSDs.

The histone deacetylase inhibitor trichostatin A induces neurite outgrowth in PC12 cells via the epigenetically regulated expression of the nur77 gene

Histone deacetylase (HDAC) inhibitors induce histone acetylation and gene expression by changing local chromatin structures. They can thereby influence various cells to proliferate or differentiate. It has been reported that trichostatin A (TSA) or valproic acid (VPA) can induce the neuronal differentiation of mouse embryonic neural stem cells and rat cerebellar granule cells. It is unclear however which gene is responsible for the neuronal differentiation induced by HDAC inhibitors. In this study, we investigated the contribution of immediate early gene (IEG) nur77 to the neuronal differentiation induced by TSA. We report that TSA induces neurite outgrowth in PC12 cells, and C646, an inhibitor of HAT (histone acetyl transferase) (p300), prevents TSA-induced neurite formation. The acetylation of the Lys14 residue of histone H3, and mRNA and protein expression of nur77 gene were found to be stimulated after treatment with TSA, but not in the presence of C646. A knock-down of nur77 inhibits the neurite outgrowth induced by TSA. Furthermore, the ectopic expression of nur77 significantly elicits neurite formation in PC12 cells. These results suggest that the expression of nur77, which is up-regulated via the TSA-induced acetylation of Lys14 on histone H3, is essential for the neuronal differentiation in TSA-induced PC12 cells.

Neurotropic and neuroprotective activities of the earthworm peptide Lumbricusin

We recently isolated a polypeptide from the earthworm Lumbricus terrestris that is structurally similar to defensin, a well-known antibacterial peptide. An 11-mer antibacterial peptide (NH2-RNRRWCIDQQA), designated Lumbricusin, was synthesized based on the amino acid sequence of the isolated polypeptide. Since we previously reported that CopA3, a dung beetle peptide, enhanced neuronal cell proliferation, we here examined whether Lumbricusin exerted neurotropic and/or neuroprotective effects. Lumbricusin treatment induced a time-dependent increase (∼51%) in the proliferation of human neuroblastoma SH-SY5Y cells. Lumbricusin also significantly inhibited the apoptosis and decreased viability induced by treatment with 6-hydroxy dopamine, a Parkinson's disease-mimicking agent. Immunoblot analyses revealed that Lumbricusin treatment increased ubiquitination of p27(Kip1) protein, a negative regulator of cell-cycle progression, in SH-SY5Y cells, and markedly promoted its degradation. Notably, adenoviral-mediated over-expression of p27(Kip1) significantly blocked the antiapoptotic effect of Lumbricusin in 6-hydroxy dopamine-treated SH-SY5Y cells. These results suggest that promotion of p27(Kip1) degradation may be the main mechanism underlying the neuroprotective and neurotropic effects of Lumbricusin.

Rotary bioreactor culture can discern specific behavior phenotypes in Trk-null and Trk-expressing neuroblastoma cell lines

Neuroblastoma is characterized by biological and genetic heterogeneity that leads to diverse, often unpredictable, clinical behavior. Differential expression of the Trk family of neurotrophin receptors strongly correlates with clinical behavior; TrkA expression is associated with favorable outcome, whereas TrkB with unfavorable outcome. Neuroblastoma cells cultured in a microgravity rotary bioreactor spontaneously aggregate into tumor-like structures, called organoids. We wanted to determine if the clinical heterogeneity of TrkA- or TrkB-expressing neuroblastomas was reflected in aggregation kinetics and organoid morphology. Trk-null SY5Y cells were stably transfected to express either TrkA or TrkB. Short-term aggregation kinetics were determined by counting the number of single (non-aggregated) viable cells in the supernatant over time. Organoids were harvested after 8 d of bioreactor culture, stained, and analyzed morphometrically. SY5Y-TrkA cells aggregated significantly slower than SY5Y and SY5Y-TrkB cells, as quantified by several measures of aggregation. SY5Y and TrkB cell lines formed irregularly shaped organoids, featuring stellate projections. In contrast, TrkA cells formed smooth (non-stellate) organoids. SY5Y organoids were slightly smaller on average, but had significantly larger average perimeter than TrkA or TrkB organoids. TrkA expression alone is sufficient to dramatically alter the behavior of neuroblastoma cells in three-dimensional, in vitro rotary bioreactor culture. This pattern is consistent with both clinical behavior and in vivo tumorigenicity, in that SY5Y-TrkA represents a more differentiated, less aggressive phenotype. The microgravity bioreactor is a useful in vitro tool to rapidly investigate the biological characteristics of neuroblastoma and potentially to assess the effect of cytotoxic as well as biologically targeted drugs.

Discovery of a new bioactive molecule for neuroblastoma

Neuroblastoma, a common pediatric malignancy of neural crest origin, is unique in its wide spectrum of clinical and biological behavior, ranging from spontaneous regression or differentiation to rapid progression and metastasis. Overexpression of neurotrophin receptors of the tyrosine kinase (Trk) family has been identified as a major prognostic and biological factor for this disease. Novel molecules were selected using cheminformatics tools (structure-based virtual screening and ligand-based virtual screening) and screened in cell-based assays to modulate Trk receptor activity. One compound (C390-0031) had a potent antiproliferative activity in dose-response studies using neuroblastoma cell lines. The molecular effects of this molecule were further characterized by using cell cycle and Western blot analysis. Interestingly, despite the presence of the anchoring fragment to the Trk kinase domain composing its structure, this molecule does not inhibit TrkA like lestaurtinib, constituting a new chemical with a yet unknown mechanism of action.

Expression of NTRK1/TrkA affects immunogenicity of neuroblastoma cells

High levels of the NTRK1/TrkA receptor are expressed in low-stage neuroblastomas, which are characterized by a good patient prognosis and often undergo spontaneous regression. In addition to apoptosis, tumor-immune responses might contribute to this regression. We hypothesized that TrkA expression might enhance the immune response to neuroblastomas. Immunohistochemistry on neuroblastoma tissue microarrays confirmed significantly higher lymphocyte infiltration in low-stage compared with high-stage tumors. Flow cytometry of human SH-SY5Y cells stably transfected with NTRK1/TrkA cDNA revealed significant upregulation of major histocompatibility complex (MHC) class I complexes on TrkA-expressing cells. Corresponding to this upregulation, T cell activity and cytoxicity was enhanced in the presence of SY5Y-TrkA cells or by medium conditioned by them, suggesting the existence of additional soluble factors stimulating the T cell response. Activation of natural killer (NK) cells was only increased in the presence of SY5Y-TrkA conditioned medium (CM) and not in co-culture assays, suggesting a dominant inhibitory effect of upregulated MHC class I as the primary NK cell escape mechanism of TrkA-expressing neuroblastomas. We reanalyzed gene expression data obtained from the cell culture model to identify additional genes involved in the TrkA-mediated modulation of immune responses. Upregulation of selected target genes in SY5Y-TrkA cells was confirmed on transcript and protein levels. However, none of the proteins were detected in medium conditioned by SY5Y-TrkA cells, arguing against these factors as soluble mediators of the TrkA-induced immune response. We here provide evidence that TrkA expression in neuroblastoma leads to an increased immunogenicity that may contribute to a less malignant phenotype and/or spontaneous regression of neuroblastoma cells.

Clinical significance of SH2B1 adaptor protein expression in non-small cell lung cancer

The SH2B1 adaptor protein is recruited to multiple ligand-activated receptor tyrosine kinases that play important role in the physiologic and pathologic features of many cancers. The purpose of this study was to assess SH2B1 expression and to explore its contribution to the non-small cell lung cancer (NSCLC).

METHODS

SH2B1 expression in 114 primary NSCLC tissue specimens was analyzed by immunohistochemistry and correlated with clinicopathological parameters and patients' outcome. Additionally, 15 paired NSCLC background tissues, 5 NSCLC cell lines and a normal HBE cell line were evaluated for SH2B1 expression by RT-PCR and immunoblotting, immunofluorescence being applied for the cell lines.

RESULTS

SH2B1 was found to be overexpressed in NSCLC tissues and NSCLC cell lines. More importantly, high SH2B1 expression was significantly associated with tumor grade, tumor size, clinical stage, lymph node metastasis, and recurrence respectively. Survival analysis demonstrated that patients with high SH2B1 expression had both poorer disease- free survival and overall survival than other patients. Multivariate Cox regression analysis revealed that SH2B1 overexpression was an independent prognostic factor for patients with NSCLC.

CONCLUSIONS

Our findings suggest that the SH2B1 protein may contribute to the malignant progression of NSCLC and could offer a novel prognostic indicator for patients with NSCLC.

Network-based analysis of multivariate gene expression data

Multivariate microarray gene expression data are commonly collected to study the genomic responses under ordered conditions such as over increasing/decreasing dose levels or over time during biological processes, where the expression levels of a give gene are expected to be dependent. One important question from such multivariate gene expression experiments is to identify genes that show different expression patterns over treatment dosages or over time; these genes can also point to the pathways that are perturbed during a given biological process. Several empirical Bayes approaches have been developed for identifying the differentially expressed genes in order to account for the parallel structure of the data and to borrow information across all the genes. However, these methods assume that the genes are independent. In this paper, we introduce an alternative empirical Bayes approach for analysis of multivariate gene expression data by assuming a discrete Markov random field (MRF) prior, where the dependency of the differential expression patterns of genes on the networks are modeled by a Markov random field. Simulation studies indicated that the method is quite effective in identifying genes and the modified subnetworks and has higher sensitivity than the commonly used procedures that do not use the pathway information, with similar observed false discovery rates. We applied the proposed methods for analysis of a microarray time course gene expression study of TrkA- and TrkB-transfected neuroblastoma cell lines and identified genes and subnetworks on MAPK, focal adhesion, and prion disease pathways that may explain cell differentiation in TrkA-transfected cell lines.

Mitogen-activated protein kinase (MEK/ERK) inhibition sensitizes cancer cells to centromere-associated protein E inhibition

Inhibition of centromere-associated protein-E (CENP-E) has demonstrated preclinical anti-tumor activity in a number of tumor types including neuroblastoma. A potent small molecule inhibitor of the kinesin motor activity of CENP-E has recently been developed (GSK923295). To identify an effective drug combination strategy for GSK923295 in neuroblastoma, we performed a screen of siRNAs targeting a prioritized set of genes that function in therapeutically tractable signaling pathways. We found that siRNAs targeted to extracellular signal-related kinase 1 (ERK1) significantly sensitized neuroblastoma cells to GSK923295-induced growth inhibition (p = 0.01). Inhibition of ERK1 activity using pharmacologic inhibitors of mitogen-activated ERK kinase (MEK1/2) showed significant synergistic growth inhibitory activity when combined with GSK923295 in neuroblastoma, lung, pancreatic and colon carcinoma cell lines. Synergistic growth inhibitory activity of combined MEK/ERK and CENP-E inhibition was a result of increased mitotic arrest and apoptosis. There was a significant correlation between ERK1/2 phosphorylation status in neuroblastoma cell lines and GSK923295 growth inhibitory activity (r = 0.823, p = 0.0006). Consistent with this result we found that lung cancer cell lines harboring RAS mutations, which leads to oncogenic activation of MEK/ERK signaling, were significantly more resistant than cell lines with wild-type RAS to GSK923295-induced growth inhibition (p = 0.047). Here we have identified (MEK/ERK) activity as a potential biomarker of relative GSK923295 sensitivity and have shown the synergistic effect of combinatorial MEK/ERK pathway and CENP-E inhibition across different cancer cell types including neuroblastoma.

Characterization of critical domains within the tumor suppressor CASZ1 required for transcriptional regulation and growth suppression

CASZ1 is a zinc finger (ZF) transcription factor that is critical for controlling the normal differentiation of subtypes of neural and cardiac muscle cells. In neuroblastoma tumors, loss of CASZ1 is associated with poor prognosis and restoration of CASZ1 function suppresses neuroblastoma tumorigenicity. However, the key domains by which CASZ1 transcription controls developmental processes and neuroblastoma tumorigenicity have yet to be elucidated. In this study, we show that loss of any one of ZF1 to ZF4 resulted in a 58 to 79% loss in transcriptional activity, as measured by induction of tyrosine hydroxylase promoter-luciferase activity, compared to that of wild-type (WT) CASZ1b. Mutation of ZF5 or deletion of the C-terminal sequence of amino acids (aa) 728 to 1166 (a truncation of 38% of the protein) does not significantly alter transcriptional function. A series of N-terminal truncations reveals a critical transcriptional activation domain at aa 31 to 185 and a nuclear localization signal at aa 23 to 29. Soft agar colony formation assays and xenograft studies show that WT CASZ1b is more active in suppressing neuroblastoma growth than CASZ1b with a ZF4 mutation or a deletion of aa 31 to 185. This study identifies key domains needed for CASZ1b to regulate gene transcription. Furthermore, we establish a link between loss of CASZ1b transcriptional activity and attenuation of CASZ1b-mediated inhibition of neuroblastoma growth and tumorigenicity.

Gene expression of TRK neurotrophin receptors in advanced neuroblastomas in Singapore--a pilot study

The clinical hallmark of neuroblastoma is heterogeneity. Biologically, ploidy and N-Myc amplification are currently the only 2 features used to define risk group and to determine therapy. Tyrosine kinase neurotrophin receptors (Trks, including TrkA, TrkB, and TrkC) are important in the clinical and biological behavior of neuroblastomas. The authors aim to study Trks gene expression in their local population of advanced neuroblastoma patients. Multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) assay on the expression of TrkA, TrkB, TrkB-truncated, and TrkC was performed on a total of 19 advanced neuroblastoma archival tumors, diagnosed in KK Women's and Children's Hospital between 2003 and 2007. Of the 19 tumors investigated, Trks expression was present in 14 (73.6%) cases. Of these cases, 8 (42.1%), 10 (52.6%), 7 (36.8%), and 6 (31.6%) expressed TrkA, TrkB, TrkB-truncated, and TrkC receptor mRNAs, respectively. Subsequently, the authors compared Trks expression with N-Myc amplification status of the 19 patients. N-Myc was amplified in 5 (26.3%) of the cases. Within the non-N-Myc-amplified group, Trks expression was present in 9 (64%) of the 14 cases. The significant expression of Trk isoforms among advanced neuroblastoma cases as evident from this study support their role as possible risk assessment tools alongside N-Myc amplification status.

c.1810C>T polymorphism of NTRK1 gene is associated with reduced survival in neuroblastoma patients

Background

TrkA (encoded by NTRK1 gene), the high-affinity tyrosine kinase receptor for neurotrophins, is involved in neural crest cell differentiation. Its expression has been reported to be associated with a favourable prognosis in neuroblastoma. Therefore, the entire coding sequence of NTRK1 gene has been analysed in order to identify mutations and/or polymorphisms which may alter TrkA receptor expression.

Methods

DNA was extracted from neuroblastomas of 55 Polish and 114 Italian patients and from peripheral blood leukocytes of 158 healthy controls. Denaturing High-Performance Liquid Chromatography (DHPLC) and Single-Strand Conformation Polymorphism (SSCP) analysis were used to screen for sequence variants. Genetic changes were confirmed by direct sequencing and correlated with biological and clinical data.

Results

Three previously reported and nine new single nucleotide polymorphisms were detected. c.1810C>T polymorphism present in 8.7% of cases was found to be an independent marker of disease recurrence (OR = 13.3; p = 0.009) associated with lower survival rates (HR = 4.45 p = 0.041). c.1810C>T polymorphism's unfavourable prognostic value was most significant in patients under 18 months of age with no MYCN amplification (HR = 26; p = 0.008). In-silico analysis of the c.1810C>T polymorphism suggests that the substitution of the corresponding amino acid residue within the conservative region of the tyrosine kinase domain might theoretically interfere with the functioning of the TrkA protein.

Conclusions

NTRK1 c.1810C>T polymorphism appears to be a new independent prognostic factor of poor outcome in neuroblastoma, especially in children under 18 months of age with no MYCN amplification.

Interaction of Mint2 with TrkA is involved in regulation of nerve growth factor-induced neurite outgrowth

TrkA receptor signaling is essential for nerve growth factor (NGF)-induced survival and differentiation of sensory neurons. To identify possible effectors or regulators of TrkA signaling, yeast two-hybrid screening was performed using the intracellular domain of TrkA as bait. We identified muc18-1-interacting protein 2 (Mint2) as a novel TrkA-binding protein and found that the phosphotyrosine binding domain of Mint2 interacted with TrkA in a phosphorylation- and ligand-independent fashion. Coimmunoprecipitation assays showed that endogenous TrkA interacted with Mint2 in rat tissue homogenates, and immunohistochemical evidence revealed that Mint2 and TrkA colocalized in rat dorsal root ganglion neurons. Furthermore, Mint2 overexpression inhibited NGF-induced neurite outgrowth in both PC12 and cultured dorsal root ganglion neurons, whereas inhibition of Mint2 expression by RNA interference facilitated NGF-induced neurite outgrowth. Moreover, Mint2 was found to promote the retention of TrkA in the Golgi apparatus and inhibit its surface sorting. Taken together, our data provide evidence that Mint2 is a novel TrkA-regulating protein that affects NGF-induced neurite outgrowth, possibly through a mechanism involving retention of TrkA in the Golgi apparatus.

PSM/SH2B1 splice variants: critical role in src catalytic activation and the resulting STAT3s-mediated mitogenic response

A role of PSM/SH2B1 had been shown in mitogenesis and extending to phenotypic cell transformation, however, the underlying molecular mechanism remained to be established. Here, four alternative PSM splice variants and individual functional protein domains were compared for their role in the regulation of Src activity. We found that elevated cellular levels of PSM variants resulted in phenotypic cell transformation and potentiated cell proliferation and survival in response to serum withdrawal. PSM variant activity presented a consistent signature pattern for any tested response of highest activity observed for gamma, followed by delta, alpha, and beta with decreasing activity. PSM-potentiated cell proliferation was sensitive to Src inhibitor herbimycin and PSM and Src were found in the same immune complex. PSM variants were substrates of the Src Tyr kinase and potentiated Src catalytic activity by increasing the V(max) and decreasing the K(m) for ATP with the signature pattern of variant activity. Dominant-negative PSM peptide mimetics including the SH2 or PH domains inhibited Src catalytic activity as well as Src-mediated phenotypic cell transformation. Activation of major Src substrate STAT3 was similarly potentiated by the PSM variants in a Src-dependent fashion or inhibited by PSM domain-specific peptide mimetics. Expression of a dominant-negative STAT3 mutant blocked PSM variant-mediated phenotypic cell transformation. Our results implicate an essential role of the PSM variants in the activation of the Src kinase and the resulting mitogenic response--extending to phenotypic cell transformation and involving the established Src substrate STAT3.

All-trans retinoic acid arrests neuroblastoma cells in a dormant state. Subsequent nerve growth factor/brain-derived neurotrophic factor treatment adds modest benefit

BACKGROUND

Therapies aiming at inducing differentiation or apoptosis of neuroblastoma (NB) are an important research topic. Although retinoic acid showed promising antitumoral results, its effects against refractory disease are limited. Putative candidates for combination therapies are nerve growth factor (NGF; Tebu-Bio/Peprotech, Offenbach, Germany) and brain-derived neurotrophic factor (BDNF; Tebu-Bio/Peprotech, Offenbach, Germany) because their receptors are of prognostic clinical value in clinical neuroblastoma. Another clinical prognostic factor is the number of Schwann cells. Substances secreted by Schwann cells proved antitumoral capacities in vitro. The aim of the study was to analyze whether retinoic acid may offer an additional line of attack acting independent from Schwann cells and whether additive treatment with the neurotrophin-receptor ligands NGF/BDNF confers additional benefit.

METHODS

Human SHSY-5Y NB cells were cultured in vitro. After a 7-day all-trans retinoic acid (ATRA; Sigma-Aldrich Chemie, Taufkirchen, Germany) treatment (15 mumol/L of ATRA), NB proliferation was proportional to extinction in dimethyl-thiazol-diphenyltetrazoliumbromide (MTT) tests. Fluorescence-activated cell sorter (FACS) analysis for annexin and propidium iodide determined the degree of apoptosis and necrosis as well as the expression of the Schwann type cell marker S100. The S100 messenger RNA was assessed by reverse transcriptase polymerase chain reaction. In addition, the effect on NB proliferation was investigated when ATRA was combined with a 7-day treatment with NGF or BDNF (10, 50, 100 ng/mL) either before or after the 7-day ATRA treatment.

RESULTS

All-trans retinoic acid reduced proliferation (0.116 +/- 0.006 SEM vs 0.359 +/- 0.010 SEM in the untreated control group; P < .001). After ATRA treatment, 95% +/- 1.82% SEM were still viable, with only 2.61% +/- 1.17% SEM apoptotic and 2.38% +/- 0.69% SEM necrotic cells. All-trans retinoic acid induced a remarkable decrease in S100 expression in FACS (16.91% +/- 1.72% SEM vs 32.33% +/- 2.54% SEM in controls; P = .009). The S100 messenger RNA levels were not increased by ATRA (DeltaDeltaT values: 1.73, 2.77, and 1.43; n = 3). Both NGF and BDNF had only a modest synergistic effect when given after ATRA treatment. No effect was seen when they were administered before ATRA treatment.

CONCLUSIONS

All-trans retinoic proved to be a vigorous inhibitor of NB proliferation in vitro. However, because most NB cells remained viable combination therapies are required. Treatment with NGF and BDNF showed only a modest benefit and did not reflect the strong prognostic impact of tyrosine kinase receptors in clinical NB. The ATRA-induced proliferation arrest is not related to Schwann type subdifferentiation. This suggests that substances secreted by Schwann cells could be possible independent combination partners. We suggest studies using combinations of ATRA and substances secreted by Schwann cells.

Essential role of PSM/SH2-B variants in insulin receptor catalytic activation and the resulting cellular responses

The positive regulatory role of PSM/SH2-B downstream of various mitogenic receptor tyrosine kinases or gene disruption experiments in mice support a role of PSM in the regulation of insulin action. Here, four alternative PSM splice variants and individual functional domains were compared for their role in the regulation of specific metabolic insulin responses. We found that individual PSM variants in 3T3-L1 adipocytes potentiated insulin-mediated glucose and amino acid transport, glycogenesis, lipogenesis, and key components in the metabolic insulin response including p70 S6 kinase, glycogen synthase, glycogen synthase kinase 3 (GSK3), Akt, Cbl, and IRS-1. Highest activity was consistently observed for PSM alpha, followed by beta, delta, and gamma with decreasing activity. In contrast, dominant-negative peptide mimetics of the PSM Pro-rich, pleckstrin homology (PH), or src homology 2 (SH2) domains inhibited any tested insulin response. Potentiation of the insulin response originated at the insulin receptor (IR) kinase level by PSM variant-specific regulation of the Km (ATP) whereas the Vmax remained unaffected. IR catalytic activation was inhibited by peptide mimetics of the PSM SH2 or dimerization domain (DD). Either peptide should disrupt the complex of a PSM dimer linked to IR via SH2 domains as proposed for PSM activation of tyrosine kinase JAK2. Either peptide abolished downstream insulin responses indistinguishable from PSM siRNA knockdown. Our results implicate an essential role of the PSM variants in the activation of the IR kinase and the resulting metabolic insulin response. PSM variants act as internal IR ligands that in addition to potentiating the insulin response stimulate IR catalytic activation even in the absence of insulin.

Transglutaminase 2 and NF-kappaB interplay during NGF-induced differentiation of neuroblastoma cells

NGF treatment of neuroblastoma cells stimulates outgrowth of neurite processes associated with the expression of TrkA receptor and several differentiation markers. In this study, a 6 DIV exposure to NGF (50 ng/ml) increased immunostaining for alpha-tubulin, and expression of both alpha-tubulin and protein kinase C in the neuroblastoma cell line Neuro2a. Further, up-regulation of transglutaminase 1 and transglutaminase 2 expression, and reduction of transglutaminase 3 levels, were also observed in NGF-treated cells in comparison to untreated cells. Moreover, when Neuro2a cells were treated with the specific NF-kappaB inhibitor SN-50, the strong reduction of NF-kappaB activation was concomitant with a significant decrease of transglutaminase 2 expression, suggesting that NGF-evoked transglutaminase 2 induction could be related to NF-kappaB activation. To characterize the possible transglutaminase 2/NF-kappaB interplay, NGF treatment was carried out in Neuro2a cells which already over-expressed transglutaminase 2 after retinoic acid treatment. An additive effect of NGF was observed on the retinoic acid-induced transglutaminase 2 expression and enzyme activity, and NF-kappaB activation. However, a cystamine-mediated significant inhibition of transglutaminase activity (70%) was accompanied by a drastically reduced NF-kappaB activation only in cells exposed to NGF following retinoic acid treatment. We hypothesize that NF-kappaB activation was dependent on the transamidating activity related to high levels of TG2, and NGF enhanced NF-kappaB activation by a different, synergistically acting, pathway. These data suggest that the combined use of NGF and retinoic acid, or mimicking drugs, may provide the basics for the development of novel strategies in the therapeutic management of neuroblastomas.

Neurotrophin receptor expression in human primary retinoblastomas and retinoblastoma cell lines

BACKGROUND

Neurotrophin receptor signaling regulates proliferation, differentiation and death of neuronal cells. Expression of Trk receptors has been implicated in the pathogenesis and prognosis of embryonal tumors, including neuroblastoma, nephroblastoma, and medulloblastoma.

PROCEDURE

We analyzed TrkA, TrkB, TrkC, and p75 expression using semi-quantitative RT-PCR in 23 retinoblastomas and 8 retinoblastoma cell lines. Comparison of mRNA expression with clinical variables as well as the proliferation (PI) and apoptotic index (AI) of the tumor, was performed by Pearson correlation analysis and two-sample t-test.

RESULTS

Almost all tumor samples and cell lines demonstrated high expression of all Trk receptors. Expression of TrkB and its ligand, BDNF, was most pronounced, suggesting TrkB to be the major Trk receptor involved in retinoblastoma biology. In contrast, p75 expression was substantially reduced in a subset of tumors and cell lines, in particular compared to its expression in normal retina. Tumors with infiltrative growth demonstrated significantly lower relative levels of TrkC expression than localized tumors (P = 0.004). High expression of TrkA was associated with a higher AI (P = 0.04), and high expression of TrkC was associated with a younger age of the patients (P = 0.03). Inhibition of Trk signaling by K252a resulted in marked growth inhibition of retinoblastoma cells in vitro.

CONCLUSIONS

Our findings suggest a role for neurotrophin signaling in the biology of retinoblastoma. General Trk inhibitors are effective in decreasing growth rates of retinoblastoma cells in vitro, and should be evaluated in in vivo studies.

De novo identification of MIZ-1 (ZBTB17) encoding a MYC-interacting zinc-finger protein as a new favorable neuroblastoma gene

PURPOSE

Neuroblastoma is a childhood cancer that exhibits either a favorable or an unfavorable phenotype. Favorable neuroblastoma genes (EPHB6, EFNB2, EFNB3, NTRK1, and CD44) are genes whose high-level expression predicts favorable neuroblastoma disease outcome. Accordingly, the forced expression of these genes or their reactivation by gene silencing inhibitors in unfavorable neuroblastoma cells results in suppression of tumor growth and metastases. This study was undertaken to design an experimental strategy to identify additional favorable neuroblastoma genes.

EXPERIMENTAL DESIGN

Favorable neuroblastoma gene candidates were first identified by gene expression profiling analysis on IMR5 neuroblastoma cells treated with inhibitors of DNA methylation and histone deacetylase against the untreated control cells. Among the candidates, we focused on MIZ-1, which encodes a MYC-interacting zinc-finger protein, because it is known to enhance the expression of growth suppressive genes, such as CDKN1A.

RESULTS

High-level MIZ-1 expression was associated with favorable disease outcome of neuroblastoma (P = 0.0048). Forced MIZ-1 expression suppressed in vitro growth of neuroblastoma cell lines. High MIZ-1 expression was correlated with the small-size neuroblastoma xenografts treated with gene silencing inhibitors or a glucocorticoid. In addition, forced MIZ-1 expression enhanced the expression of CD44 and EFNB2 in neuroblastoma cell lines in vitro. Furthermore, MIZ-1 expression was positively correlated with the expression of favorable neuroblastoma genes (EFNB2, EFNB3, EPHB6, and NTRK1) in the human neuroblastoma xenograft therapeutic models.

CONCLUSION

MIZ-1 is a new favorable neuroblastoma gene, which may directly or indirectly regulate the expression of other favorable neuroblastoma genes.

Novel Brn3a cis-acting sequences mediate transcription of human trkA in neurons

TrkA, the receptor tropomyosin-related kinase for nerve growth factor, is critical not only for the correct spatial and temporal development of sensory neurons during embryogenesis but also for the survival of sensory neurons, the differentiation and apoptosis of neuronal tumors and suppression of latent herpes simplex virus genomes. While the regulation of the expression of trkA is a complex process, the transcription factor Brn3a is known to play an important role as an enhancer of trkA transcription during development in the mouse. Despite considerable information on the regulation of trkA during embryogenesis, the mechanisms by which the expression of trkA is regulated in differentiated neurons, or the factors that influence its expression in tumor cells, have not been identified. We initiated studies to determine whether Brn3a/trkA promoter interactions may be important in a model of differentiated neurons and in medulloblastoma cells. We constructed a plasmid that contains 1043 base pairs of genomic sequences that extend to 30 nucleotides upstream of trkA coding region. In contrast to previous data, a short 190 bp region that lies proximal to the trkA initiation codon was sufficient for Brn3a responsiveness in Vero cells. This region was also sufficient for Brn3a trans-activation in nerve growth factor-differentiated PC12 cells. At least two portions of the 190 bp fragment bind to Brn3a with an affinity high enough to be detected in electromobility shift assays. In addition, Brn3a increased levels of endogenous trkA transcripts in PC12 cells and initiated trkA expression in medulloblastoma cells, which normally do not express trkA.

Alternative TrkAIII splicing: a potential regulated tumor-promoting switch and therapeutic target in neuroblastoma

An association between elevated tyrosine kinase receptor (Trk)-A expression and better prognosis; the absence of mutation-activated TrkA oncogenes; the induction of apoptosis, growth arrest, morphological differentiation and inhibition of xenograft growth; and angiogenesis by TrkA gene transduction, provide the basis for the current concept of an exclusively tumor-suppressor role for TrkA in the aggressive pediatric tumor, neuroblastoma. This concept, however, has recently been challenged by the discovery of a novel hypoxia-regulated alternative TrkAIII splice variant, initial data for which suggest predominant expression in advanced-stage neuroblastoma. TrkAIII exhibits neuroblastoma xenograft tumor-promoting activity associated with the induction of a more angiogenic and stress-resistant neuroblastoma phenotype and antagonises nerve growth factor/TrkAI antioncogenic signaling. In this short review, the authors integrate this novel information into a modified concept that places alternative TrkA splicing as a potential pivotal regulator of neuroblastoma behavior and identifies the TrkAIII alternative splice variant as a potential biomarker of patient prognosis and novel therapeutic target.

PSM/SH2-B distributes selected mitogenic receptor signals to distinct components in the PI3-kinase and MAP kinase signaling pathways

The Pro-rich, PH, and SH2 domain containing mitogenic signaling adapter PSM/SH2-B has been implicated as a cellular partner of various mitogenic receptor tyrosine kinases and related signaling mechanisms. Here, we report in a direct comparison of three peptide hormones, that PSM participates in the assembly of distinct mitogenic signaling complexes in response to insulin or IGF-I when compared to PDGF in cultured normal fibroblasts. The complex formed in response to insulin or IGF-I involves the respective peptide hormone receptor and presumably the established components leading to MAP kinase activation. However, our data suggest an alternative link from the PDGF receptor via PSM directly to MEK1/2 and consequently also to p44/42 activation, possibly through a scaffold protein. At least two PSM domains participate, the SH2 domain anticipated to link PSM to the respective receptor and the Pro-rich region in an association with an unidentified downstream component resulting in direct MEK1/2 and p44/42 regulation. The PDGF receptor signaling complex formed in response to PDGF involves PI 3-kinase in addition to the same components and interactions as described for insulin or IGF-I. PSM associates with PI 3-kinase via p85 and in addition the PSM PH domain participates in the regulation of PI 3-kinase activity, presumably through membrane interaction. In contrast, the PSM Pro-rich region appears to participate only in the MAP kinase signal. Both pathways contribute to the mitogenic response as shown by cell proliferation, survival, and focus formation. PSM regulates p38 MAP kinase activity in a pathway unrelated to the mitogenic response.

DeltaNp73 modulates nerve growth factor-mediated neuronal differentiation through repression of TrkA

p73, a member of the p53 family, expresses two classes of proteins: the full-length TAp73 and the N-terminally truncated DeltaNp73. While TAp73 possesses many p53-like features, DeltaNp73 is dominant negative towards TAp73 and p53 and appears to have distinct functions in tumorigenesis and neuronal development. Given its biological importance, we investigated the role of DeltaNp73 in nerve growth factor (NGF)-mediated neuronal differentiation in PC12 cells. We show that overexpression of DeltaNp73alpha or DeltaNp73beta inhibits NGF-mediated neuronal differentiation in both p53-dependent and -independent manners. In line with this, we showed that the level of endogenous DeltaNp73 is progressively diminished in differentiating PC12 cells upon NGF treatment and knockdown of DeltaNp73 promotes NGF-mediated neuronal differentiation. Interestingly, we found that the ability of DeltaNp73 to suppress NGF-mediated neuronal differentiation is correlated with its ability to regulate the expression of TrkA, the high-affinity NGF receptor. Specifically, we found that DeltaNp73 directly binds to the TrkA promoter and transcriptionally represses TrkA expression, which in turn attenuates the NGF-mediated mitogen-activated protein kinase pathway. Conversely, the steady-state level of TrkA is increased upon knockdown of DeltaNp73. Furthermore, we found that histone deacetylase 1 (HDAC1) and HDAC2 are recruited by DeltaNp73 to the TrkA promoter and act as corepressors to suppress TrkA expression, which can be relieved by trichostatin A, an HDAC inhibitor. Taken together, we conclude that DeltaNp73 negatively regulates NGF-mediated neuronal differentiation by transrepressing TrkA.

A Novel Cyclophane Compound, CPPy, Facilitates NGF-Induced TrkA Signal Transduction and Induces Cell Differentiation in Neuroblastoma

Neuroblastoma (NB) often causes spontaneously regression, and can mature to ganglioneuroma. The form with the most favorable prognosis expresses high levels of TrkA, a high-affinity receptor for nerve growth factor (NGF), whereas advanced NB and associated cell lines have abnormalities in the NGF/TrkA signaling pathway. A novel cyclophane, cyclophane pyridine (CPPy), was designed to conserve the tyrosine phosphorylation of TrkA, thereby enhancing NGF/TrkA signal transduction. We investigated whether this compound improved NGF-induced tyrosine phosphorylation of the Y490 domain of TrkA and conserved the expression of an early gene (c-fos) in human NB cell lines (IMR-32 and NB-39). As determined by Western blotting, TrkA (Y490) phosphorylation was enhanced by the combination of CPPy (10(-8) M) and NGF (100 ng/ml) compared with NGF alone. CPPy also conserved NGF-induced c-fos mRNA expression. Moreover, CPPy induced the morphological differentiation of NB cells, leading to expression of the neuronal marker gene GAP-43. These data suggest that CPPy can induce the differentiation of NB cell lines by facilitating NGF-induced TrkA/Ras/MAPK signal transduction, and may therefore be an effective therapeutic agent for NB.

CyclinB2 and BIRC5 genes as surrogate biomarkers for neurite outgrowth in SH-SY5Y subclonal cells

Neurite outgrowth plays a key role in neuronal development and regeneration, and is the hallmark assay for the effects of neurotrophic factors such as nerve growth factor (NGF). However, measuring neurite outgrowth is a slow and resource-intensive process. We therefore wanted to identify surrogate biomarkers for neurite outgrowth activity by gene expression analysis in SH-O10 cells, a subclone of the human SH-SY5Y neuroblastoma cell line but with much higher NGF-induced neurite outgrowth activity. Microarray analysis identified seven genes where mRNA levels were changed. NGF-induced decreases in levels of two genes, CyclinB2 and BIRC5, were confirmed by quantitative real-time RT-PCR. Levels of NGF-induced decreases in CyclinB2 and BIRC5 mRNA in several SH-SY5Y subclones with different neurite outgrowth responses correlated with their neurite outgrowth activities. Decreases in CyclinB2 and BIRC5 mRNA induced by FK506 or retinoic acid, both of which exert potentiation of NGF-induced neurite outgrowth effects but with different mechanisms, also correlated with their neurite outgrowth activities. In conclusion, decreasing levels of CyclinB2 and BIRC5 mRNA strongly correlate with neurite outgrowth activities in terms of NGF-related effect in SH-SY5Y subclonal cells, and have potential to become quantitative surrogate biomarkers for measuring NGF-related neurite outgrowth.

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.

Differences in gene expression profile among SH-SY5Y neuroblastoma subclones with different neurite outgrowth responses to nerve growth factor

Nerve growth factor (NGF) plays a key role in the differentiation of neurons. In this study, we established three NGF-induced neurite-positive (NIN+) subclones that showed high responsiveness to NGF-induced neurite outgrowth and three NGF-induced neurite-negative (NIN-) subclones that abolished NGF-induced neurite outgrowth from parental SH-SY5Y cells, and analyzed differences in the NGF signaling cascade. The NIN+ subclones showed enhanced responsiveness to FK506-mediated neurite outgrowth as well. To clarify the mechanism behind the high frequency of NGF-induced neurite outgrowth, we investigated differences in NGF signaling cascade among subclones. Expression levels of the NGF receptor TrkA, and NGF-induced increases in mRNAs for the immediate-early genes (IEGs) c-fos and NGF inducible (NGFI) genes NGFI-A, NGFI-B and NGFI-C, were identical among subclones. Microarray analysis revealed that the NIN+ cell line showed a very different gene expression profile to the NIN- cell line, particularly in terms of axonal vesicle-related genes and growth cone guidance-related genes. Thus, the difference in NGF signaling cascade between the NIN+ and NIN- cell lines was demonstrated by the difference in gene expression profile. These differentially expressed genes might play a key role in neurite outgrowth of SH-SY5Y cells in a region downstream from the site of induction of IEGs, or in a novel NGF signaling cascade.

Differentiation of neuroblastoma cell line N1E-115 involves several signaling cascades

No systematic searches for differential expression of signaling proteins (SP) in undifferentiated vs. differentiated cell lineages were published and herein we used protein profiling for this purpose. The NIE-115 cell line was cultivated and an aliquot was differentiated with dimethylsulfoxide (DMSO), that is known to lead to a neuronal phenotype. Cell lysates were prepared, run on two-dimensional gel electrophoresis followed by MALDI-TOF-TOF identification of proteins and maps of identified SPs were generated. Seven SPs were comparable, 27 SPs: GTP-binding/Ras-related proteins, kinases, growth factors, calcium binding proteins, phosphatase-related proteins were observed in differentiated NIE-115 cells and eight SPs of the groups mentioned above were observed in undifferentiated cells only. Switching-on/off of several individual SPs from different signaling cascades during the differentiation process is a key to understand mechanisms involved. The findings reported herein are challenging in vitro and in vivo studies to confirm a functional role for deranged SPs.