Identifying genes involved in regulating differentiation of neuroblastoma cells

SHP2 Inhibition with TNO155 Increases Efficacy and Overcomes Resistance of ALK Inhibitors in Neuroblastoma

Survival rates among patients with high-risk neuroblastoma remain low and novel therapies for recurrent neuroblastomas are required. ALK is commonly mutated in primary and relapsed neuroblastoma tumors and ALK tyrosine kinase inhibitors (TKI) are promising treatments for ALK-driven neuroblastoma; however, innate or adaptive resistance to single-agent ALK-TKIs remain a clinical challenge. Recently, SHP2 inhibitors have been shown to overcome ALK-TKI resistance in lung tumors harboring ALK rearrangements. Here, we have assessed the efficacy of the SHP2 inhibitor TNO155 alone and in combination with the ALK-TKIs crizotinib, ceritinib, or lorlatinib for the treatment of ALK-driven neuroblastoma using in vitro and in vivo models. In comparison to wild-type, ALK-mutant neuroblastoma cell lines were more sensitive to SHP2 inhibition with TNO155. Moreover, treatment with TNO155 and ALK-TKIs synergistically reduced cell growth and promoted inactivation of ALK and MAPK signaling in ALK-mutant neuroblastoma cells. ALK-mutant cells engrafted into larval zebrafish and treated with single agents or dual SHP2/ALK inhibitors showed reduced growth and invasion. In murine ALK-mutant xenografts, tumor growth was likewise reduced or delayed, and survival was prolonged upon combinatorial treatment of TNO155 and lorlatinib. Finally, we show that lorlatinib-resistant ALK-F1174L neuroblastoma cells harbor additional RAS-MAPK pathway alterations and can be resensitized to lorlatinib when combined with TNO155 in vitro and in vivo. Our results report the first evaluation of TNO155 in neuroblastoma and suggest that combinatorial inhibition of ALK and SHP2 could be a novel approach to treating ALK-driven neuroblastoma, potentially including the increasingly common tumors that have developed resistance to ALK-TKIs.

SIGNIFICANCE

These findings highlight the translatability between zebrafish and murine models, provide evidence of aberrant RAS-MAPK signaling as an adaptive mechanism of resistance to lorlatinib, and demonstrate the clinical potential for SHP2/ALK inhibitor combinations for the treatment of ALK-mutant neuroblastoma, including those with acquired tolerance or potentially resistance to ALK-TKIs.

Mouse Neuroblastoma CB1 Cannabinoid Receptor-Stimulated [35S]GTPɣS Binding: Total and Antibody-Targeted Gα Protein-Specific Scintillation Proximity Assays

G protein-coupled receptors (GPCRs) are important regulators of cellular signaling functions and therefore are a major target for drug discovery. The CB1 cannabinoid receptor is among the most highly expressed GPCRs in neurons, where it regulates many differentiated neuronal functions. One model system for studying the biochemistry of neuronal responses is the use of neuroblastoma cells originating from the C1300 tumor in the A/J mouse, including cloned cell lines NS20, N2A, N18TG2, N4TG1, and N1E-115, and various immortalized hybrids of neurons with N18TG2 cells. GPCR signal transduction is mediated through interaction with multiple types and subtypes of G proteins that transduce the receptor stimulus to effectors. The [35S]GTPɣS assay provides a valuable pharmacological method to evaluate efficacy and potency in the first step in GPCR signaling. Here, we present detailed protocols for the [35S]GTPɣS-binding assay to measure the total G protein binding and the antibody-targeted scintillation proximity assay to measure specific Gα proteins in neuroblastoma cell membrane preparations. This chapter presents step-by-step methods from cell culture, membrane preparation, assay procedures, and data analysis.

N-Myc knockdown and apigenin treatment controlled growth of malignant neuroblastoma cells having N-Myc amplification

Malignant neuroblastomas mostly occur in children and are frequently associated with N-Myc amplification. Oncogene amplification, which is selective increase in copy number of the oncogene, provides survival advantages in solid tumors including malignant neuroblastoma. We have decreased expression of N-Myc oncogene using short hairpin RNA (shRNA) plasmid to increase anti-tumor efficacy of the isoflavonoid apigenin (APG) in human malignant neuroblastoma SK-N-DZ and SK-N-BE2 cell lines that harbor N-Myc amplification. N-Myc knockdown induced morphological and biochemical features of neuronal differentiation. Combination of N-Myc knockdown and APG most effectively induced morphological and biochemical features of apoptotic death. This combination therapy also prevented cell migration and decreased N-Myc driven survival, angiogenic, and invasive factors. Collectively, N-Myc knockdown and APG treatment is a promising strategy for controlling the growth of human malignant neuroblastoma cell lines that harbor N-Myc amplification.

Induction of cell cycle arrest at G1 and S phases and cAMP-dependent differentiation in C6 glioma by low concentration of cycloheximide

Background

Differentiation therapy has been shown effective in treatment of several types of cancer cells and may prove to be effective in treatment of glioblastoma multiforme, the most common and most aggressive primary brain tumor. Although extensively used as a reagent to inhibit protein synthesis in mammalian cells, whether cycloheximide treatment leads to glioma cell differentiation has not been reported.

Methods

C6 glioma cell was treated with or without cycloheximide at low concentrations (0.5-1 μg/ml) for 1, 2 and 3 days. Cell proliferation rate was assessed by direct cell counting and colony formation assays. Apoptosis was assessed by Hoechst 33258 staining and FACS analysis. Changes in several cell cycle regulators such as Cyclins D1 and E, PCNA and Ki67, and several apoptosis-related regulators such as p53, p-JNK, p-AKT, and PARP were determined by Western blot analysis. C6 glioma differentiation was determined by morphological characterization, immunostaining and Western blot analysis on upregulation of GFAP and o p-STAT3 expression, and upregulation of intracellular cAMP.

Results

Treatment of C6 cell with low concentration of cycloheximide inhibited cell proliferation and depleted cells at both G2 and M phases, suggesting blockade at G1 and S phases. While no cell death was observed, cells underwent profound morphological transformation that indicated cell differentiation. Western blotting and immunostaining analyses further indicated that changes in expression of several cell cycle regulators and the differentiation marker GFAP were accompanied with cycloheximide-induced cell cycle arrest and cell differentiation. Increase in intracellular cAMP, a known promoter for C6 cell differentiation, was found to be elevated and required for cycloheximide-promoted C6 cell differentiation.

Conclusion

Our results suggest that partial inhibition of protein synthesis in C6 glioma by low concentration of cycloheximide induces cell cycle arrest at G1 and M phases and cAMP-dependent cell differentiation.

Optimal neural differentiation and extension of hybrid neuroblastoma cells (NDC) for nerve-target evaluations using a multifactorial approach

In vitro models of tissues, such as the cornea, represent systems for modeling cell-to-cell interactions and tissue function. The objective of this study was to develop an optimized nerve differentiation medium to incorporate into a 3D in vitro model to study innervation and cell targeting. A hybrid neuroblastoma cell line (NDC) was examined for its ability to differentiate into neurons, produce neurites, and functionally contact target cells. Neuronal differentiation of NDCs was optimized through a combinatorial approach which involved culturing cells in the presence of various extracellular matrices and soluble factors. A serum-free medium containing nerve growth factor (NGF), dimethyl sulfoxide (DMSO), or dexamethasone resulted in the greatest proportion of NDCs demonstrating a neuronal morphology. Similarly, with supplementation of cyclic AMP (cAMP) or NGF, neurite extension was optimized. Combining these factors generated an optimized differentiation and extension medium, relative to the individual components alone. In co-culture with epithelial cells, NDC neurites generated in the optimized medium formed contacts with epithelial targets and produced substance P. Similarly, NDCs seeded into a collagen matrix produced neurites that projected through the matrix to target epithelial cells, promoted epithelial stratification, and increased the rate of epithelial wound healing. As well, differentiated NDCs could target and alter acetylcholine receptor clustering in mouse C2C12 myotubes, demonstrating synaptic plasticity. Our data supports the use of NDCs, in combination with optimized medium, for generating an innervated in vitro model.

Identifying altered gene expression in neuroblastoma cells preceding apoptosis

PURPOSE

Concomitant differentiation and partial inhibition of proteasome trigger cell death in a neuroblastoma cell line (NBP2). Neither induction of differentiation nor partial inhibition of proteasome alone affects the viability of NBP2 cells. We wanted to identify genes whose expression alters under concomitant conditions and may account for cell death.

METHODS

We used gel electrophoresis to analyze total genomic DNA for the detection of DNA fragmentation. Affymetrix Murine Genome U74A version 2 microarray was used to screen for approximately 6,000 functionally characterized genes and approximately 6,000 expressed sequence tags (ESTs). Real time PCR (RT-PCR) was performed to provide an accurate assessment of changes in gene expression.

RESULTS

Concomitant differentiation and partial inhibition of proteasome trigger apoptosis, characterized by genomic DNA fragmentation in NBP2 cells. We found that the expression of 41 genes changed 2.5-fold or more primarily under concomitant conditions midway through apoptosis. Based on real time PCR, the expression of galectin-3, glycosylated 96, a leucine zipper protein (LRG-21), and endothelial cell activated protein C receptor (EPCR) increased between 50-500-fold, whereas the expression of Polo serine/threonine kinase, N-myc, and Histone H2A.1 decreased ranging from 8 to 37 fold. Altered expression of galectin-3, EPCR, and LRG-21 was detected as early as 2-8 h post simultaneous conditions.

CONCLUSION

We identified new genes that might be involved in apoptotic events in neuroblastoma cells.

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.

Classification of neuroblastoma patients by published gene-expression markers reveals a low sensitivity for unfavorable courses of MYCN non-amplified disease

Currently, Pubmed lists 385 marker genes for neuroblastoma outcome. Using a customized neuroblastoma-microarray, we evaluated the prognostic impact of the gene-expression pattern of 349 of these candidates (90.6%) in 127 neuroblastoma patients with divergent outcome. By significance analysis of microarrays (SAM) and both uncorrected and Bonferroni-corrected ANOVA, 166/349 (47.5%), 218/349 (62.5%) and 128/349 (36.4%) candidates showed significant differential expression between patients with contrasting outcome. By Prediction Analysis for Microarrays (PAM), a 38-gene-classifier was derived from all markers, which classified patients outcome with an overall accuracy of 78.5%. However, patients with unfavorable outcome of MYCN non-amplified disease were largely misclassified (accuracy: 35%), suggesting that these courses are not identified by current marker genes.

Selenomethionine prevents degeneration induced by overexpression of wild-type human alpha-synuclein during differentiation of neuroblastoma cells

OBJECTIVE

High levels of wild-type alpha-synuclein are found in autopsied brain samples of idiopathic Parkinson's disease (PD), some familial PD, some Alzheimer's disease (AD) and Down's syndrome with dementia. Therefore, we have investigated whether overexpression of wild-type alpha-synuclein causes degeneration during adenosine, 3',5'-cyclic monophosphate (cAMP)-induced differentiation of murine neuroblastoma (NB) cells in culture. We have also studied whether selenomethionine can modify the effect of overexpression of alpha-synuclein during differentiation of NB cells.

METHODS

To study these issues, we established a murine neuroblastoma (NB) clone (NBP2-PN54-C20) that expressed high levels of wild-type human alpha-synuclein as determined by real time PCR and Western blot. We have utilized RO20-1724, an inhibitor of cyclic nucleotide phosphodiesterase, and prostaglandin A1 (PGA1), a stimulator of adenylate cyclase, or RO20-1724 and dibutyryl cAMP to induce terminal differentiation in over 95% of the cell population by elevating the intracellular levels of cAMP in NB cells. The viability of cells was determined by MTT assay and LDH leakage assay, and the degeneration was documented by photomicrographs.

RESULTS

The results showed that overexpression of human wild-type alpha-synuclein decreased viability and increased degenerative changes in comparison to those observed in vector control cells, when differentiation was induced by treatment with RO20-1724 and PGA1, but not with RO20-1724 and dibutyryl cAMP. When selenomethionine was added to NB cells overexpressing alpha-synuclein immediately after the addition of RO20-1724 and PGA1, the viability and degenerative changes were markedly reduced, suggesting the involvement of increased oxidative stress in the mechanism of action of alpha-synuclein. This protective effect was not observed after treatment with sodium selenite or methionine.

CONCLUSIONS

Data suggested that Overexpression of wild-type human alpha-synuclein-decreased viability and increased the levels of degenerative changes during differentiation of NB cells were reduced by selenomethionine treatment. This suggest that one of mechanisms of action alpha-synuclein may involve increased oxidative stress.

Prostaglandin-induced neurodegeneration is associated with increased levels of oxidative markers and reduced by a mixture of antioxidants

Prostaglandin E2 (PGE2), one product of inflammatory reactions, and PGA1, which is formed during PGE2 extraction, induce degeneration in adenosine 3',5'-cyclic monophosphate (cAMP)-induced differentiated neuroblastoma (NB) cells in culture. The mechanisms of action of PGE2 on neurodegeneration are not well understood. To investigate this, we have utilized PGA(1), which mimics the effect of PGE2 and is very stable in solution. We have assayed selected markers of oxidative stress such as heme oxygenase-1 (HO-1), catalase, glutathione peroxidase (GPx1), mitochondrial superoxide dismutase (Mn-SOD-2) and cytosolic superoxide dismutase (Cu/Zn-SOD-1). The results showed that the treatment of differentiated NB cells with PGA1 for a period of 48 hr increased the expression of HO-1 and catalase, decreased the expression of GPx1 and Mn-SOD-2, and did not change the expression of Cu/Zn-SOD-1 as measured by gene array and confirmed by real-time PCR. The protein levels of HO-1 and GPx1 increased; however, the protein level of Mn-SOD-2 decreased and the levels of catalase and Cu/Zn-SOD-1 did not change as determined by Western blot. The increases in the levels of HO-1 and GPx1 reflected an adaptive response to increased oxidative stress, whereas decrease in the level of Mn-SOD-2 may make cells more sensitive to oxidative damage. These data suggest that one of the mechanisms of action of PGA1 on neurodegeneration may involve increased oxidative stress. This was supported further by the fact that a mixture of antioxidants (alpha-tocopherol, vitamin C, selenomethionine, and reduced glutathione), but not the individual antioxidants, reduced the level of PGA1-induced degeneration in differentiated NB cells. The addition of a single antioxidant at two or four times the concentration used in the mixture was toxic.

Regulated expression of VP16CREB in neuroblastoma cells: analysis of differentiation and apoptosis

Highly malignant neuroblastoma tumors generally have defects in differentiation and apoptotic pathways. For a better understanding of these events, we use a murine neuroblastoma cell line (NBP2) that terminally differentiates into mature neurons in response to elevated levels of cAMP. Because one of the main downstream effectors of the cAMP signaling pathway is cAMP-response element binding (CREB), we reasoned that it might affect the expression of genes associated with differentiation and apoptotic events in NBP2 cells. To investigate this, we established tetracycline-regulated expression (TetOff) of VP16CREB, which constitutively transactivates promoters containing the CRE sequence motif. Using this system, we found that inducible expression of VP16CREB in NBP2 cells results in 1) morphological differentiation that is characterized by the formation of neurites and growth cones, 2) reversible cell differentiation unlike cAMP-induced terminal differentiation, 3) cell cycle arrest at G1, 4) no apoptosis in the presence of partial inhibition of proteasome unlike an increase in cAMP levels, and 5) changes in the expression of many genes, including down-regulation of N-myc, cyclin B1, Dickkopf-1, and Mad-2 and up-regulation of tyrosine hydroxylase, c-fos, N10, and ICER genes. Although VP16CREB expression and activation of the cAMP pathway impart many similar effects in NBP2 cells, they also bear some distinct genetic and morphological differences. Our data suggest that increased levels of cAMP function through not only CREB but also other signaling pathways that account for the additional cAMP-induced effects, including irreversible differentiation and onset of apoptosis during partial inhibition of proteasome in NBP2 cells.

Overexpression of alpha-synuclein decreased viability and enhanced sensitivity to prostaglandin E(2), hydrogen peroxide, and a nitric oxide donor in differentiated neuroblastoma cells

Increased accumulation of alpha-synuclein is associated with certain neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease (AD). One mechanism of alpha-synuclein-induced toxicity involves increased oxidative stress. It was unknown whether neurons overexpressing alpha-synuclein would exhibit increased sensitivity to hydrogen peroxide (H(2)O(2)) or 3-morpholinosydnonimine (SIN-1; a nitrous oxide donor). To study this, we developed a murine neuroblastoma (NB) cell line that overexpresses wild-type human alpha-synuclein (NBP2-PN54) under the control of the cytomegalovirus (CMV) promoter using a retroviral vector. Human alpha-synuclein mRNA and protein were readily detectable in NBP2-PN54 cells. Results showed that differentiated NBP2-PN54 cells exhibited decreased viability in comparison to differentiated vector (NBP2-PN1) and parent (NBP2) control cells. These cells also exhibited increased sensitivity to PGE(2), H(2)O(2) and SIN-1. Because of involvement of proteasome inhibition in neurodegeneration, we also investigated whether treatment of differentiated NBP2-PN54 cells with PGE(2), H(2)O(2) or SIN-1 inhibits proteasome activity. Results showed that H(2)O(2) and SIN-1 inhibited proteasome activity, but PGE(2) did not. These results suggest that overexpression of alpha-synuclein not only participates directly in degeneration of neurons, but it also increases the vulnerability of neurons to other potential neurotoxins.

Overexpression of amyloid precursor protein is associated with degeneration, decreased viability, and increased damage caused by neurotoxins (prostaglandins A1 and E2, hydrogen peroxide, and nitric oxide) in differentiated neuroblastoma cells

Inflammatory reactions are considered one of the important etiologic factors in the pathogenesis of Alzheimer's disease (AD). Prostaglandins such as PGE2 and PGA1 and free radicals are some of the agents released during inflammatory reactions, and they are neurotoxic. The mechanisms of their action are not well understood. Increased levels of beta-amyloid fragments (Abeta40 and Abeta42), generated through cleavage of amyloid precursor protein (APP), oxidative stress, and proteasome inhibition, are also associated with neurodegeneration in AD brains. Therefore, we investigated the effect of PGs and oxidative stress on the degeneration and viability of cyclic AMP-induced differentiated NB cells overexpressing wild-type APP (NBP2-PN46) under the control of the CMV promotor in comparison with differentiated vector (NBP2-PN1) or parent (NBP2) control cells. Results showed that differentiated NBP2-PN46 cells exhibited enhanced spontaneous degeneration and decreased viability in comparison with differentiated control cells, without changing the level of Abeta40 and Abeta42. PGA1 or PGE2 treatment of differentiated cells caused increased degeneration and reduced viability in all three cell lines. These effects of PGs are not due to alterations in the levels of vector-derived APP mRNA or human APP holoprotein, secreted levels of Abeta40 and Abeta42, or proteasome activity. H2O2 or SIN-1 (an NO donor) treatment did not change vector-derived APP mRNA levels, but H2O2 reduced the level of human APP protein more than SIN-1. Furthermore, SIN-1 increased the secreted level of Abeta40, but not of Abeta42, whereas H2O2 had no effect on the level of secreted Abeta fragments. Both H2O2 and SIN-1 inhibited proteasome activity in the intact cells. The failure of neurotoxins to alter APP mRNA levels could be due to the fact that they do not affect CMV promoter activity. These results suggest that the mechanisms of action of PGs on neurodegeneration are different from those of H2O2 and SIN-1 and that the mechanisms of neurotoxicity of H2O2 and SIN-1 are, at least in part, different from each other.

Concomitant differentiation and partial proteasome inhibition trigger apoptosis in neuroblastoma cells

Proteasome activity is essential during cAMP-induced terminal differentiation of a murine neuroblastoma cell line (NBP2). However, the mechanisms through which proteasome affects NBP2 differentiation have not been characterized. We hypothesized that proteasome is required to implement the differentiation-mediated effects on cell cycle, and its partial inhibition during differentiation may have adverse consequences. Here we show that partial inhibition of proteasome during cAMP-induced differentiation of NBP2 cells causes apoptosis. Whereas differentiation induced growth arrest at G1 phase, partial proteasome inhibition during differentiation resulted in the accumulation of cells at G2M phase. Cell cycle data correlated with the level of cyclin-dependent kinase inhibitors p21WAF and p27Kip1, and cyclin A. While the level of p21 and p27 increased, the level of cyclin A decreased upon differentiation. In contrast, cells treated with proteasome inhibitor in the presence of cAMP-inducing agents showed increased levels of p21 and cyclin A early in the course of differentiation. However, the level of p21 and p27, but not cyclin A, decreased later during concomitant differentiation and partial proteasome inhibition when cells were undergoing apoptosis. Our data suggest that differentiation-mediated growth arrest is dependent on the temporal activity of cell cycle proteins. Partial inhibition of proteasome interferes with differentiation events partly by stabilizing cell cycle proteins and this triggers apoptosis. Thus, differentiating drugs combined with partial proteasome inhibition may impart higher therapeutic efficacy than differentiating agents alone for the treatment of neuroblastoma tumors.

Requirement of the coiled-coil domains of p92(c-Fes) for nuclear localization in myeloid cells upon induction of differentiation

The nonreceptor tyrosine kinase Fes is implicated in myeloid cells differentiation. It has been observed that its localization can be cytoplasmic, perinuclear, or nuclear. To further characterize this point, we studied Fes subcellular localization in myeloid cell lines (HL60 and K562) and in COS1 cells. Fes was observed in both the nucleus and the cytoplasm of HL60, K562 cells overexpressing Fes and only in the cytoplasm of COS1 cells, suggesting that nuclear localization is cell context dependent. Moreover, in myeloid cells, the treatment with differentiation-inducing agents such as retinoic acid, phorbol esters and vitamin D, is followed by an increase of the oligomeric form of Fes in the nucleus. In fact, oligomerization seems to be necessary for translocation to occur, since Fes mutants missing the coiled-coil domains are not able to form oligomers and fail to localize in the nucleus. The active form of Fes is tyrosine phosphorylated; however, phosphorylation is not required for Fes to localize in the nucleus, since tyrosine kinase inhibitors do not block the translocation process.

Isolation of diallyl trisulfide inducible differentially expressed genes in human gastric cancer cells by modified cDNA representational difference analysis

Extensive epidemiologic studies indicated protective effects of consumption of garlic on reducing human gastric cancer (HGC) incidence. Diallyl trisulfide (DATS), a critical organic allyl sulfur component of garlic, was reported to have chemopreventive effects in inhibiting tumor process. We used DATS to treat HGC cell line BGC823 cells, and showed that DATS induces G1/S arrest and apoptosis in BGC823 cells demonstrated by a flow cytometric analysis. To further isolate DATS inducible differentially expressed genes in BGC823 cells, we combined a highly specific subtractive hybridization of cDNA representational difference analysis (cDNA RDA) with a sensitive bidirectional radioactive detection of mRNA differential display (mRNA DD) to develop a subtractive hybridization differential display (SHDD) method. This modified method adopted a first round of bidirectional subtractive hybridization between two sample cDNAs and a second round of bidirectional subtractive hybridization between the two resultant first-round difference products. Bidirectional subtractive hybridizations magnified the differences between the two sample cDNAs and favored isolating mRNA species with very small expression differences. We employed the SHDD method to detect DATS inducible differentially expressed genes in BGC823 cells. A total of 14 cDNA fragments (11 upregulated and 3 downregulated by DATS treatment) were isolated and confirmed by reverse Northern blot analysis. Our data show that SHDD is a powerful technique for identifying differentially expressed mRNA species between two sample cDNAs and provide useful cellular and molecular information for understanding the effects of garlic against human gastric cancer.

Altered expression of genes regulating cell growth, proliferation, and apoptosis during adenosine 3',5'-cyclic monophosphate-induced differentiation of neuroblastoma cells in culture

An elevation of the intracellular levels of adenosine 3',5'-cyclic monophosphate (cAMP) induces terminal differentiation in neuroblastoma (NB) cells in culture; however, genetic alterations during differentiation have not been fully identified. To investigate this, we used Mouse Genome U74A microarray containing approximately 6000 functionally characterized genes to measure changes in gene expression in murine NB cells 30 min and 4, 24, and 72 h after treatment with cAMP-stimulating agents. Based on the time of increase in differentiated functions and their status (reversible versus irreversible) after treatment with cAMP-stimulating agents, the induction of differentiation in NB cells was divided into three distinct phases: initiation (about 4 h after treatment when no increase in differentiated functions is detectable), promotion (about 24 h after treatment when an increase in differentiated functions occurs, but they are reversible upon the removal of cAMP), and maintenance (about 72 h after treatment when differentiated functions are maximally expressed, but they are irreversible upon the removal of cAMP). Results showed that alterations in expression of genes regulating cell growth, proliferation, apoptosis, and necrosis occurred during cAMP-induced differentiation of NB cells. Genes that were upregulated during the initiation, promotion, or maintenance phase were called initiators, promoters, or maintainers of differentiation. Genes that were downregulated during the initiation, promotion, or maintenance phase were called suppressors of initiation, promotion, or maintenance phase. Genes regulating growth may act as initiators, promoters, maintainers, or suppressors of these phases. Genes regulating cell proliferation may primarily act as suppressors of promotion. Genes regulating cell cycle may behave as suppressors of initiation or promotion, whereas those regulating apoptosis and necrosis may act as initiators or suppressors of initiation or promotion. The fact that genetic signals for differentiation occurred 30 min after treatment with cAMP, whereas cell-cycle genes were downregulated at a later time, suggests that decision for NB cells to differentiate is made earlier and not at the cell-cycle stage, as commonly believed.

Transcript profiling of functionally related groups of genes during conditional differentiation of a mammalian cochlear hair cell line

We have used Affymetrix high-density gene arrays to generate a temporal profile of gene expression during differentiation of UB/OC-1, a conditionally immortal cell line derived from the mouse cochlea. Gene expression was assessed daily for 14 days under differentiating conditions. The experiment was replicated in two separate populations of cells. Profiles for selected genes were correlated with those obtained by RT-PCR, TaqMan analysis, immunoblotting, and immunofluorescence. The results suggest that UB/OC-1 is derived from a population of nonsensory epithelial cells in the greater epithelial ridge that have the potential to differentiate into a hair-cell-like phenotype, without the intervention of Math1. Elements of the Notch signaling cascade were identified, including the receptor Notch3, with a transient up-regulation that suggests a role in hair cell differentiation. Several genes showed a profile similar to Notch3, including the transcriptional co-repressor Groucho1. UB/OC-1 also expressed Me1, a putative partner of Math1 that may confer competence to differentiate into hair cells. Cluster analysis revealed expression profiles for neural guidance genes associated with Gata3. The temporal dimension of this analysis provides a powerful tool to study genetic mechanisms that underlie the conversion of nonsensory epithelial cells into hair cells.

Neuronal differentiation and synapse formation occur in space and time with fractal dimension

The analysis of a set of experimental data obtained by an independent team of researchers confirms that neuronal differentiation or synapse formation do occur in time and space with fractal dimension. The interacting cells create first a dynamic system with its own attractor, (i.e., a fragment of time and space where the dynamic processes occur and where no further evolution of the system is possible at all owing to the action of the intrasystemic forces unless some extrasystemic forces act upon it). This attractor is then modified in the active manner by the differentiating cells until the system attains a degenerated stationary state and differentiation ends. The fractal structure of the system is also lost in the course of tumor progression. Our data indicate that the cellular system can attain the degenerated stationary state, leaving the attractor with a fractal dimension directly or undergoing diversification into many attractors and going through the areas of deterministic chaos. Since evolution of the cellular system is driven by the cooperative dynamic processes, as reflected by the changes of the mean fractal dimension between the intervals of the Gompertzian curve, it is likely that cells differentiate into neurons and create synapses with a conjugated probability and non-Gaussian distribution rather than with the classical probability and the Gaussian distribution. These findings can help to optimize features of artificial neural networks. They also define a simple in vitro biological model for biophysical and biochemical studies on natural neural networks.

Differentiation genes: are they primary targets for human carcinogenesis?

In spite of extensive research in molecular carcinogenesis, genes that can be considered primary targets in human carcinogenesis remain to be identified. Mutated oncogenes or cellular growth regulatory genes, when incorporated into normal human epithelial cells, failed to immortalize or transform these cells. Therefore, they may be secondary events in human carcinogenesis. Based on some experimental studies we have proposed that downregulation of a differentiation gene may be the primary event in human carcinogenesis. Such a gene could be referred to as a tumor-initiating gene. Downregulation of a differentiation gene can be accomplished by a mutation in the differentiation gene, by activation of differentiation suppressor genes, and by inactivation of tumor suppressor genes. Downregulation of a differentiation gene can lead to immortalization of normal cells. Mutations in cellular proto-oncogenes, growth regulatory genes, and tumor suppressor genes in immortalized cells can lead to transformation. Such genes could be called tumor-promoting genes. This hypothesis can be documented by experiments published on differentiation of neuroblastoma (NB) cells in culture. The fact that terminal differentiation can be induced in NB cells by adenosine 3',5'-cyclic monophosphate (cAMP) suggests that the differentiation gene in these cells is not mutated, and thus can be activated by an appropriate agent. The fact that cAMP-resistant cells exist in NB cell populations suggests that a differentiation gene is mutated in these cancer cells, or that differentiation regulatory genes have become unresponsive to cAMP. In addition to cAMP, several other differentiating agents have been identified. Our proposed hypothesis of carcinogenesis can also be applied to other human tumors such as melanoma, pheochromocytoma, medulloblastoma, glioma, sarcoma, and colon cancer.

Proteasome activity is critical for the cAMP-induced differentiation of neuroblastoma cells

1. The ubiquitin-proteasome pathway is involved in a variety of cellular functions in mammalian cells. The role of proteasome, however, in the course of cell differentiation is not well characterized. We hypothesized that proteasome activity might be essential during neuronal cell differentiation. 2. To investigate the role of proteasome during neuronal differentiation, we made use of a murine neuroblastoma cell line (NBP2) that terminally differentiates into mature neurons upon elevation of the intracellular level of adenosine 3',5'-cyclic monophosphate (cAMP). To monitor proteasome activity in NBP2 cells, we integrated an expression cassette for a short-lived green fluorescent protein (d2EGFP) into these cells, which were designated as NBP2-PN25. When NBP2-PN25 cells were treated with a proteasome inhibitor, lactacystin or MG132, a dose-dependent increase in the constitutive levels of d2EGFP expression was detected. 3. We also found that proteasome inhibition by lactacystin during the cAMP-induced differentiation of NBP2-PN25 cells triggered cell death. Both lactacystin and cAMP induction reduced the expression of mRNA for the differentiation-associated genes, such as N-myc and cyclin B1. While cAMP-inducing agents decreased the level of N-myc and cyclin B1 proteins, lactacystin increased the level of these proteins. 4. Our data suggest that a reduced level of N-myc and cyclin B1 proteins is critical to commence differentiation, and this can be blocked by a proteasome inhibitor, leading to cell death. Concomitant induction of differentiation and proteasome inhibition, may, therefore, be potentially useful for the treatment of human neuroblastomas.