Diverse responses to retinoid in morphological differentiation, tumorigenesis and N-myc expression in human neuroblastoma sublines

Concurrent targeting of MAP3K3 and BRD4 by miR-3140-3p overcomes acquired resistance to BET inhibitors in neuroblastoma cells

Neuroblastoma (NB) harboring MYCN amplification is a refractory disease with a poor prognosis. As BRD4, an epigenetic reader belonging to the bromodomain and extra terminal domain (BET) family, drives transcription of MYCN in NB cells, BET inhibitors (BETis) are considered useful for NB therapy. However, clinical trials of BETis suggested that early acquired resistance to BETis limits their therapeutic benefit. MicroRNAs are small non-coding RNAs that mediate post-transcriptional silencing of target genes. We previously identified miR-3140-3p as a potent candidate for nucleic acid therapeutics for cancer, which directly targets BRD4. We demonstrated that miR-3140-3p suppresses tumor cell growth in MYCN-amplified NB by downregulating MYCN and MYC through BRD4 suppression. We established BETi-acquired resistant NB cells to evaluate the mechanism of resistance to BETi in NB cells. We revealed that activated ERK1/2 stabilizes MYCN protein by preventing ubiquitin-mediated proteolysis via phosphorylation of MYCN at Ser62 in BETi-acquired resistant NB cells, thereby attenuating the effects of BETi in these cells. miR-3140-3p efficiently downregulated MYCN expression by directly targeting the MAP3K3-ERK1/2 pathway in addition to BRD4 suppression, inhibiting tumor cell growth in BETi-acquired resistant NB cells. This study suggests that miR-3140-3p has the potential to overcome resistance to BETi in NB.

A MYCN-amplified cell line derived from a long-term event-free survivor among our sixteen established neuroblastoma cell lines

Although more than 110 neuroblastoma (NB) cell lines have been established, there have been neither reports on the rate of success to establish NB cell lines, nor well-documented NB cell lines from long-term-survivors. We attempted to establish NB cell lines from 114 patients. Sixteen NB cell lines were established from 12 patients. The success rates to establish cell lines were 1.4% (1/70) from patients in early stages, 25.0% (11/44) from those in advanced stages, and 10.5% (12/114) from those in all stages respectively. Eleven of these 12 patients eventually died. The surviving patient, who was in stage 4 with MYCN-amplification, has been event-free for 19 years after completing therapy. The serum MYCN DNA level in patient TK was very high before therapy, decreased after chemotherapy, and has remained at the normal levels until now. The gene expression profiling of the primary tumor and the K-N-TK cell line was analyzed with an NB-specific cDNA microarray, and indicated that the probability of 5-year survival was extremely low. Microarray-based comparative genomic hybridization (CGH) analysis indicated that genomic aberration profiles of the cell line were uncommon, with MYCN amplification, 17q gain and 11q loss. A unique KP-N-TK cell line, established from an event-free survivor, will be a useful tool for investigating how a patient can survive a tumor with an extremely poor prognosis.

Alteration of midkine expression associated with chemically-induced differentiation in human neuroblastoma cells

Midkine (MK), a neurotrophic polypeptide of which expression is developmentally regulated in embryogenesis, is expressed in malignant tumor tissues including neuroblastoma (NB). A retinoic acid analogue, E5166, and dibutyryl cyclic AMP (dbcAMP) are known to induce differentiation in NB cells. This study showed that MK mRNA expression increased in association with differentiation by E5166, but not by dbcAMP in SK-N-SH and KP-N-RTBM1 human NB cell lines. We concluded that MK could be an important factor in differentiation of NB cells, and further, that there could be at least two pathways in differentiation of NB cells at molecular mechanism.

Requirement of b-myb function for survival and differentiative potential of human neuroblastoma cells

The B-myb gene belongs to a family of transcription factors that also includes A-myb and c-myb. B-myb is expressed in many cell types including human neuroblastoma cells. Here we demonstrate that B-myb expression is down-regulated during retinoic acid-induced neural and glial differentiation of neuroblastoma cells. This modulation is an early event, is maintained at late times of induction, and is in part regulated at the transcriptional level. Constitutive expression of B-myb prevents retinoic acid-induced neural differentiation as reflected by morphological features and the expression of (or lack of) biochemical markers associated with the undifferentiated phenotype. Furthermore, the expression of antisense B-myb transcripts does not allow the rescue of viable cells, suggesting an important role for B-myb in the survival of neuroblastoma cells. These results indicate that B-myb plays a functional role in the differentiative potential of neuroblastoma cells, raising the possibility that this gene is one of the nuclear regulators in the cascade of events leading to cellular differentiation.

Inhibition by retinoic acid of hepatocarcinogenesis induced by N-nitrosomorpholine and of expression of myc oncogene protein in Sprague-Dawley rats

The effects of all-trans-retinoic acid (RA) on hepato-carcinogenesis induced by N-nitrosomorpholine (NNM) and on the expression of myc p110 proteins were investigated in male Sprague-Dawley rats. Rats received i.m. injections of RA twice a week and, from the beginning of the experiment, were given drinking water containing NNM for 8 weeks. Pre-neoplastic and neoplastic lesions staining positively for gamma-glutamyl transpeptidase (GGT), glutathione-S-transferase placental type (GST-P) or myc p110 protein were examined histochemically. At week 18, quantitative histological analysis showed that prolonged administration of RA resulted in a significant reduction in the number, size and volume of GGT-positive and GST-P-positive hepatic lesions. Administration of RA also caused a significant increase in the proportion of myc p110-negative lesions to the total pre-neoplastic lesions observed. Myc p110-negative lesions had a significantly lower mitotic index than myc p110-positive lesions. These findings indicate that RA inhibits hepatocarcinogenesis and suggest that this effect may be related to its influence in reducing the expression of myc gene proteins and its subsequent inhibition of cell proliferation in pre-neoplastic lesions.

Immunohistochemical analysis of N-myc protein expression in neuroblastoma: correlation with prognosis of patients

We have analyzed N-myc gene amplification and N-myc protein expression in 41 primary neuroblastomas. In this series, 22 patients are currently alive and disease-free, whereas 19 patients have died or are alive with progressive disease. All tumor samples were obtained at operation. N-myc gene amplification was detected by Southern blot analysis, and N-myc protein expression was detected using Bouin-fixed, paraffin-embedded tissue sections and immunohistochemical staining with anti-N-myc gene products serum. N-myc protein expression was detected in all 9 tumors with N-myc gene amplification (greater than or equal to 10 N-myc gene copies). Among 19 patients with poor prognosis, N-myc gene amplification was detected in 8 (42%) and N-myc protein expression in 18 (95%); neither was detected in 20 of the 22 patients who survived free of disease. We conclude that the immunohistochemical detection of N-myc protein expression is one of the most unfavorable prognostic factors in neuroblastoma patients.