Allelic deletion at 11q23 is common in MYCN single copy neuroblastomas

Deletions of the long arm of chromosome 11 (11q) have been noted in primary neuroblastomas, but a comprehensive analysis has not been performed. Therefore, we analysed 331 neuroblastomas (295 sporadic, 15 familial and 21 tumor-derived cell lines) to determine the prevalence of 11q allelic deletions, to map the location of a putative tumor suppressor gene and to perform clinical correlative studies. Assays for loss of heterozygosity (LOH) were performed at 24 microsatellite loci spanning 11q. LOH was observed at multiple 11q loci in 129/295 (44%) sporadic neuroblastomas, 5/15 (33%) familial neuroblastomas, and 5/21 (24%) neuroblastoma cell lines. A single region of 2.1 cM within 11q23.3, flanked by markers D11S1340 and D11S1299, was deleted in all specimens with 11q LOH. Allelic loss at 11q23 was inversely related to MYCN amplification (P<0.001). Within the subset of cases with a single copy of MYCN, 11q LOH was associated with advanced stage disease (P=0.008), unfavorable histopathology (P=0.042), and decreased overall survival probability (P=0.008). However, 11q LOH was not independently prognostic in multivariate analyses. These data support the hypothesis that a tumor suppressor gene mapping within 11q23.3 is commonly inactivated during the malignant evolution of a large subset of neuroblastomas, especially those with unamplified MYCN.

High-level expression of EPHB6, EFNB2, and EFNB3 is associated with low tumor stage and high TrkA expression in human neuroblastomas

Neuroblastoma (NB) is a common pediatric tumor of neural crest origin that is biologically and clinically heterogeneous. EPH family receptor tyrosine kinases and ephrin ligands play fundamental roles in neurodevelopmental processes. Recently, we found that NB cell lines expressed several EPHB and EFNB transcripts, which encode EPHB subgroup receptors and ephrin-B subgroup ligands, respectively. To explore the role of EPHB receptors and ephrin-B ligands in the biology of NB, we examined the expression of EPHB and EFNB transcripts in 47 primary NB specimens. Multiple EPHB and EFNB transcripts were expressed in all of the NB tumors examined, suggesting the involvement of these transcripts in modulating the biological behavior of NB. Higher levels of EPHB6, EFNB2, and EFNB3 expression were found in low-stage tumors (stage 1, 2, and 4S) than in advanced-stage tumors (stage 3 and 4; P = 0.0013, P = 0.0048, and P = 0.027, respectively). Expression of TrkA, a well-established prognostic marker of favorable NB, was positively correlated with EPHB6, EFNB2, and EFNB3 expression (P < 0.0001, P = 0.0019, and P = 0.0001, respectively). MYCN-amplified tumors expressed lower levels of EPHB6, EFNB2, EFNB3, and TrkA transcripts compared to nonamplified tumors (P = 0.0006, P = 0.0023, P = 0.0048, and P = 0.0001, respectively). These data suggest that high-level expression of EPHB6, EFNB2, and EFNB3 is associated with favorable NB and that low-level expression of EPHB6, EFNB2, and EFNB3 correlates with aggressive MYCN-amplified NB. Thus, EPHB6, EFNB2, and EFNB3 may have biological relevance in NB. Further investigation on the biology of these genes may help provide insight into the treatment of NB.

Metastatic sites in stage IV and IVS neuroblastoma correlate with age, tumor biology, and survival

PURPOSE

The goal of this study was to determine the incidence of metastatic sites in neuroblastoma and the extent to which metastatic sites correlate with age, tumor biology, and survival.

PATIENTS AND METHODS

All 648 patients with stage IV and IVS neuroblastoma registered on Children's Cancer Group protocols 3881 and 3891 were analyzed. Metastatic site data were provided by treating institutions and reviewed in patients with central nervous system (CNS), intracranial, lung, or "other" metastases.

RESULTS

The incidence of metastatic sites at diagnosis was 70.5% in bone marrow, 55.7% in bone, 30.9% in lymph nodes, 29.6% in liver, 18.2% in intracranial and orbital sites, 3.3% in lung, and 0.6% in CNS. Event-free survival (EFS) was decreased in patients with bone, bone marrow, CNS, intracranial/ orbital, lung, and pleural metastases, and improved in those with liver and skin metastases. In infants, MYCN amplification and unfavorable Shimada histopathology correlated with increased frequencies of bone and intracranial or orbital metastases. In older patients, MYCN amplification correlated with increased frequencies of intracranial or orbital, liver, and lung metastases. Multivariate analysis revealed that metastatic site is not an independent prognostic factor.

CONCLUSIONS

Metastatic pattern in neuroblastoma differs with age and correlates with tumor biological features and EFS. These correlations could reflect changes in host or tumor biological features with age resulting in differences in metastatic capacity or tumor affinity for specific sites.

Lack of homozygously inactivated p73 in single-copy MYCN primary neuroblastomas and neuroblastoma cell lines

We examined 18 neuroblastoma cell lines and 32 primary single-copy MYCN tumor specimens to determine whether mutations of p73, a novel p53-related gene located in chromosome band 1p36.33, contribute to the genesis or progression of childhood neuroblastoma. By fluorescence in situ hybridization, 16 of the 18 cell lines, but only 3 of the 32 primary tumors, had evidence of a deleted p73 allele. Sequence analysis of the p73 coding region in the mRNAs expressed by these cell lines and tumors did not reveal inactivating mutations, suggesting that p73 is not homozygously inactivated in neuroblastoma. However, several novel splice forms of p73 mRNAs were identified, including one without exon 11 that predominated in multiple MYCN-amplified cell lines. Its encoded p73 protein differed from other splice forms in that the C-terminus was derived from an alternative reading frame. Further study of the functional properties of the protein encoded by this splice form of p73 will be needed to determine whether it contributes to the pathogenesis of childhood neuroblastoma with MYCN gene amplification.

Coexpression of transcripts encoding EPHB receptor protein tyrosine kinases and their ephrin-B ligands in human small cell lung carcinoma

The EPH family is the largest subfamily of receptor protein tyrosine kinases, consisting of the EPHA and EPHB subgroups. Ephrin-B1, ephrin-B2, and ephrin-B3 are ligands of the EPHB subgroup and are encoded by the EFNB1, EFNB2, and EFNB3 genes, respectively. We have shown previously that EPHB2 transcripts are expressed in six small cell lung carcinoma (SCLC) cell lines. In this study, we examined the expression of EPHB1, EPHB2, EPHB3, EPHB4, and EPHB6 in 4 SCLC tumor specimens and 14 cell lines including 3 cell lines derived from these tumor specimens. To investigate whether potential autocrine loops of EPHB receptors and ephrin-B ligands exist in SCLC, the expression of EFNB1, EFNB2, and EFNB3 was also examined. Our data show that transcripts encoding multiple members of the EPHB subgroup and the ephrin-B subgroup are coexpressed in SCLC cell lines and tumors. These results suggest that the EPHB subgroup receptor kinases may modulate the biological behavior of SCLC through autocrine and/or juxtacrine activation by ephrin-B ligands that are expressed in the same or neighboring cells.

Fluorescence in situ hybridization analysis of chromosome 1p36 deletions in human MYCN amplified neuroblastoma

BACKGROUND/PURPOSE

Deletion of the short arm of chromosome 1 (1p) is one of the poor prognostic factors in human neuroblastomas. Recent studies have suggested that one or more of the neuroblastoma tumor suppressor genes reside in this region and have identified the shortest region of overlap (SRO) on 1p36. The purpose of this study was to examine deletions of 1p in human neuroblastomas by fluorescence in situ hybridization (FISH).

METHODS

Two-color FISH analysis was performed to detect chromosome 1p36 abnormalities in 42 MYCN-amplified neuroblastomas. Four different probes from the 1p36 region, the E2F2, NPPA, D1S160, and CDC2L1 loci were used for detection of 1p abnormalities. A repeat sequence probe, which is specific for the heterochromatic region of chromosome 1 (pUC1.77), was used as a control.

RESULTS

Large deletions of 1p36 were observed in 31 (73.8%) of 42 tumors, whereas the remaining 11 (26.2%) showed no deletion. In these 11 tumors, a translocation of 1p was found in one and a duplication of 1p was detected in another.

CONCLUSIONS

A strong correlation between 1p abnormalities and MYCN amplification was found in this study. MYCN-amplified neuroblastomas were found to show large deletions of 1p encompassing the SRO. FISH provided a rapid and reliable method to detect hemizygous deletions of 1p.

Schwann cell-conditioned medium promotes neuroblastoma survival and differentiation

Neuroblastomas are histopathologically heterogeneous, ranging from immature malignant tumors to benign ganglioneuromas. The amount of Schwann cell stroma greatly increases with neuroblastoma differentiation, and these Schwann cells appear to be normal cells that infiltrate the tumor. To determine whether Schwann cells influence neuroblast differentiation, four human neuroblastoma cell lines were cultured in the presence or absence of human Schwann cell-conditioned medium for 7 days. Neuroblastoma cell survival, as determined by a colorimetric assay, more than doubled in three of the four neuroblastoma cell lines in the Schwann cell-conditioned medium. There was a corresponding reduction in apoptosis as measured by a nick-end labeling assay, with little change in mitotic rate. Schwann cell-conditioned medium induced extensive neurite outgrowth in all of the neuroblastoma cell lines, and these processes contained mature neurofilament in three of the cell lines. These results indicate that Schwann cells produce soluble substances capable of supporting survival and differentiation in neuroblastoma cell lines. This may represent a biological mechanism responsible for neuronal differentiation in stroma-rich neuroblastomas.

Mononucleotide repeat instability is infrequent in neuroblastoma

Neuroblastoma is a pediatric malignancy of the sympathetic nervous system and is frequently characterized by genetic aberrations (including aneuploidy, chromosomal deletions, translocations, and gene amplification) that suggest inherent genomic instability. Mutations in mismatch repair (MMR) genes have been associated with genomic instability in several human cancers, such as those of the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome. In these cases, replication errors at microsatellite repeats lead to microsatellite instability (MSI) and mutagenesis. In neuroblastoma, we and others have detected MSI infrequently when analyzed at di- or tetranucleotide repeat polymorphic markers. More recently, however, mutations in the MMR gene GTBP/hMSH6 have been associated with a limited phenotype of instability at mononucleotide repeats only (e.g., polyadenine tracts). Furthermore, mononucleotide repeats appear to be common downstream targets of MSI-related mutagenesis and are present in the transforming growth factor-beta receptor-II gene (TGF beta RII), the BAX proapoptosis gene, and the insulin-like growth factor II receptor gene (IGFIIR) frequently in tumors arising in HNPCC kindreds. Therefore, we analyzed 46 matched normal and tumor DNAs representing all clinical stages of neuroblastoma with the use of five polymorphic mononucleotide repeat markers to assess for MSI at mononucleotide repeats. Only one tumor (2%) demonstrated mononucleotide repeat instability, and the instability was at a single locus. We conclude that MSI, including mononucleotide repeat instability, is infrequent in human neuroblastoma, and therefore defects in DNA mismatch repair are not responsible for the genomic instability seen in this neoplasm.

RIZ1, but not the alternative RIZ2 product of the same gene, is underexpressed in breast cancer, and forced RIZ1 expression causes G2-M cell cycle arrest and/or apoptosis

The retinoblastoma protein-interacting zinc finger gene RIZ maps to the distal short arm of human chromosome 1 (1p36), a region thought to harbor tumor suppressor genes for a variety of human cancers including breast cancer. The RIZ gene normally produces two protein products of different length, RIZ1 and RIZ2. RIZ2 is generated by an internal promoter and lacks an NH2-terminal motif of RIZ1, the PR domain conserved in a subfamily of zinc finger genes that function as negative regulators of tumorigenesis. We have here studied whether the RIZ gene may play a role in human neoplasia. We found that expression of RIZ1 is commonly decreased or at undetectable levels in breast cancer tissues and cell lines. Decreased RIZ1 expression was also found in other tumor types including neuroblastoma and lung cancer. Remarkably, RIZ2 is normally expressed in all cases examined, suggesting that the abnormality observed for RIZ1 is specific. Forced RIZ1 expression in breast cancer cells caused cell cycle arrest in G2-M and/or programmed cell death. These observations suggest an exclusive negative selection for RIZ1 but not RIZ2 in breast cancer and a role for RIZ1 in tumor suppression.

MYCN is the only highly expressed gene from the core amplified domain in human neuroblastomas

MYCN amplification in neuroblastomas is strongly associated with advanced stages of disease and a poor prognosis. We have recently defined a 130 kb core region of the MYCN amplicon that is consistently amplified in neuroblastomas. However, it has been argued that other expressed sequences were coamplified with MYCN and, as a result, might contribute to the aggressive phenotype of MYCN-amplified neuroblastomas. Therefore, we have screened cosmids representing the core MYCN-amplified domain and surrounding DNA by using a differential hybridization approach to detect other amplified, highly expressed genes from this region. Our results suggest that MYCN is the only highly expressed gene consistently amplified in human neuroblastomas, and that the MYCN gene is likely to be the only selective marker for genomic amplification in these tumors.

Identification of a consistent region of allelic loss on 1p32 in meningiomas: correlation with increased morbidity

Meningioma is a common tumor of the central nervous system. Deletions of the short arm of chromosome 1 (1p) are the second most commonly observed chromosomal abnormality in these tumors. Here, we analyzed tumor and normal DNAs from 157 meningioma patients using PCR-based polymorphic loci. Loss of heterozygosity (LOH) for at least one informative marker on 1p was observed in 54 cases (34%), whereas LOH on 1q occurred in only 9 cases (8%). High-resolution deletion mapping defined a consensus region of deletion flanked distally by D1S2713 and proximally by D1S2134, which spans 1.5 cM within 1p32. LOH in this region has also been observed in several other malignancies, suggesting the presence of a tumor suppressor gene or genes that are important for several types of cancer. Statistical analysis revealed that 1p LOH was associated with chromosome 22 deletions and with abnormalities of the NF2 gene in meningioma. In addition, unlike other clinical and molecular characteristics, only 1p LOH was shown to be significantly associated with recurrence-free survival.

A variant transcript encoding an isoform of the human protein tyrosine kinase EPHB2 is generated by alternative splicing and alternative use of polyadenylation signals

We previously isolated and characterized cDNA clones of DRT (EPHB2), encoding a receptor protein-tyrosine kinase of the EPH family. Northern blot analysis showed that EPHB2 transcripts are expressed in three sizes of approximately 4, 5, and 11 kb, suggesting that these transcripts are generated by alternative splicing and/or alternative use of polyadenylation sites. To explore this possibility, we isolated additional EPHB2 cDNA clones, including clone 5K-1, by re-screening the human fetal brain cDNA library. Nucleotide sequence analysis of clone 5K-1 revealed that it represents a variant transcript of EPHB2 (EPHB2v). Relative to the EPHB2 cDNA sequence previously reported, clone 5K-1 has two coding region deletions of 3 and 93 nucleotides. Nucleotide sequence analyses of EPHB2 genomic DNA fragments corresponding to these deletions suggest that the EPHB2v transcript is generated by alternative splicing. The 3' end of clone 5K-1 contains a polyadenosine stretch preceded by a potential polyadenylation signal, which is not used to generate the EPHB2 transcript. Taken together, these data indicate that EPHB2v is generated by both alternative splicing and alternative use of polyadenylation sites. The EPHB2v protein lacks one arginine residue that resides immediately following the EPHB2 transmembrane domain. In contrast, as a result of the frame shift caused by the 93 nucleotide deletion, the C-terminus of the EPHB2v protein is longer by 70 amino acids than that of EPHB2. We also show that the human neuroblastoma cell line SY5Y and NTera-2N neurons express high levels of EPHB2 and lower levels of EPHB2v. These structural variations found between the EPHB2 and EPHB2v proteins may reflect functional heterogeneity of EPHB2.

Prognostic significance of age, MYCN oncogene amplification, tumor cell ploidy, and histology in 110 infants with stage D(S) neuroblastoma: the pediatric oncology group experience--a pediatric oncology group study

PURPOSE

Although a high rate of spontaneous regression is observed in infants with stage D(S) neuroblastoma (NB), survival is not uniform. To determine the prognostic relevance of age at diagnosis, therapy, and tumor biology in infants with stage D(S) NB, we reviewed the Pediatric Oncology Group (POG) experience.

PATIENTS AND METHODS

A review of patients diagnosed with stage D(S) NB registered on POG protocols was performed. Survival according to age at diagnosis, treatment, and tumor biology was determined.

RESULTS

Between 1987 and 1996, 110 infants with stage D(S) NB had an estimated 3-year survival rate of 85% +/- 4%; survival rate was 71% +/- 8% for infants 2 months of age or younger, and 68% +/- 12%, 44% +/- 33%, and 33% +/- 19% for patients with diploid, MYCN-amplified, and unfavorable histology tumors, respectively. Survival rates were similar for patients who received adjuvant chemotherapy versus those who did not (82% +/- 5% v 93% +/- 6%, respectively; P = .187). Furthermore, there was no statistical difference in survival rate for patients who underwent complete resection of their primary tumor compared with those who underwent partial resection or biopsy only (90% +/- 5% v 78% +/- 7%, respectively; P = .083).

CONCLUSION

Our review confirmed that the survival of infants with stage D(S) NB is excellent. However, subsets of patients with poor prognosis can be identified by young age and unfavorable biologic factors. More effective therapy is needed for the group of stage D(S) infants who show unfavorable clinical and biologic features.

Successful treatment of stage III neuroblastoma based on prospective biologic staging: a Children's Cancer Group study

PURPOSE

To identify a biologically favorable and unfavorable subset of patients with Evans stage III neuroblastoma and to determine whether treatment stratification would improve the event-free survival (EFS) for high-risk patients and maintain excellent EFS for the lower-risk patients.

PATIENTS AND METHODS

Risk stratification was performed by age, MYCN gene copy number, Shimada histopathologic classification, and serum ferritin level. Lower-risk patients were treated on the less intensive Children's Cancer Group (CCG)-3881, whereas high-risk patients were treated on CCG-3891, which included more intensive multimodality therapy and, in some cases, autologous bone marrow transplantation (ABMT).

RESULTS

Of 228 Evans stage III patients entered onto the study, 92% also met the definition of International Neuroblastoma Staging System (INSS) stage 3. One hundred forty-three patients met the lower-risk criteria, which included 89 patients less than 1 year of age and 54 patients 1 year of age or greater, and favorable biology, whereas 85 patients were 1 year of age or greater and biologically unfavorable. Biologically unfavorable patients 1 year of age or greater who underwent gross surgical resection had improved survival, whereas the outcome of infants or biologically favorable older patients did not change according to resection. The EFS rate at 4 years was 100% for the patients with favorable biology of any age, 90% for those less than 1 year of age but with at least one unfavorable characteristic, and 54% for Evans stage III patients 1 year of age or greater with unfavorable biology. Age, ferritin level, MYCN copy number, Shimada histopathology, primary site, and intraspinal extension were significant univariate prognostic factors for all patients, but only MYCN copy number and age were independent factors in multivariate analyses.

CONCLUSION

The excellent survival of the biologically favorable group and the historically improved EFS of the biologically unfavorable group suggest that biologic staging should be used to define the prognosis and treatment of stage III neuroblastoma.

Autoregulation of the human N-myc oncogene is disrupted in amplified but not single-copy neuroblastoma cell lines

Amplification of the N-myc gene is a significant adverse prognostic factor in neuroblastoma, a common childhood tumor. In non-transformed cells, myc expression is controlled through an autoregulatory circuit, through which elevated Myc protein levels lead to down-regulation of myc transcription. The precise mechanism of myc gene autoregulation is unknown. Loss of c-myc autoregulation has been documented in transformed cells from a number of different lineages, but N-myc autoregulation has not yet been investigated. In neuroblastoma, the increased N-Myc protein produced by amplified tumors would be expected to silence N-myc transcription if the autoregulatory loop were intact. To determine whether N-myc autoregulation is operative in human neuroblastoma, and to localize cis-acting elements which mediate N-myc autosuppression, we transfected a series of N-myc 5' promoter constructs into a panel of human neuroblastoma cell lines carrying one or multiple copies of N-myc. The transfected promoter was equally active in single-copy and amplified lines. Significant promoter activity in the presence of abundant Myc protein in amplified neuroblastoma lines indicates that autoregulation is disabled in this subset of tumors. To investigate whether single-copy lines produce insufficient N-Myc protein to trigger autosuppression yet retain an intact autoregulatory circuit, we transfected neuroblastoma lines with 5' promoter constructs in the presence of a c- or N-myc expression vector. Overexpression of c- or N-Myc resulted in diminution of activity of both the transfected promoter and the endogenous N-myc gene in single-copy, but not amplified lines. Using a series of 5' promoter-deletion minigenes, we localized a cis-acting element required for autoregulation close to the transcription start sites. While the precise mechanism of autosuppression remains unknown, we demonstrated that Myc is incapable of silencing the adenovirus major late promoter (AdMLP) in neuroblastoma cells, indicating that Myc suppression of its own promoter and the AdMLP involve distinct components. These studies provide the first systematic investigation of autoregulation in neuroblastoma, and indicate that single-copy neuroblastoma lines produce insufficient N-Myc protein to activate downstream effector(s) of autosuppression; the autoregulatory circuit is otherwise intact. Amplified lines, in contrast, have lost autoregulation.

Role of neurotrophins and their receptors in human neuroblastomas: a primary culture study

Expression of trk family genes are prognostic indicators of neuroblastoma. However, the functional role of neurotrophins and their receptors in neuroblastomas in vivo is still unclear. We studied the expression of neurotrophin receptors (trk-A, trk-B, trk-C) and their responsiveness to neurotrophins (NGF, BDNF, NT-3) in 25 human neuroblastomas using a primary culture system. The tumours in early stages and stage 4s responded to both NGF and NT-3, but not to BDNF, by surviving and differentiating terminally and the responsiveness was correlated with high levels of trk-A, especially the neuronal isoform. However, in many advanced stage tumours, the expression of trk-A was down-regulated and the response pattern to neurotrophins was diverse, without showing terminal differentiation. Interestingly, a stage 4 tumour with MYCN amplification which expressed high level of neuronal trk-A was dependent on nerve growth factor (NGF) for both survival and differentiation in primary culture. The results suggest that the NGF/trk-A signalling may be the main regulatory pathway for differentiation and survival of neuroblastoma in vivo and that trk-A overexpression may overcome aggressiveness, even of the tumour with MYCN amplification.

Screening for neuroblastoma is ineffective in reducing the incidence of unfavourable advanced stage disease in older children

Neuroblastoma exhibits many characteristics which would suggest that preclinical detection may improve outcome. The Quebec Neuroblastoma Screening Project was initiated to determine whether mass screening could reduce mortality in a large cohort of infants. All 476,603 children born in the province of Quebec during a 5-year period of time (1 May 1989 to 30 April 1994) were eligible for determinations of urinary catecholamine metabolites at 3 weeks and 6 months of age. Children with positive screening were referred to one of four paediatric cancer centres in Quebec for uniform evaluation and treatment. Standardised incidence ratios (SIRs) were calculated for neuroblastoma in Quebec and two comparable population-based controls during the same period of time using similar ascertainment procedures. Compliance with screening in Quebec was 91% at 3 weeks (n = 425,816) and 74% at 6 months (n = 349,706). Up to 31 July 1995 with a follow-up of the birth cohort of 15-75 months, 118 cases of neuroblastoma were diagnosed, 43 detected preclinically by screening, 20 detected clinically prior to screening at 3 weeks of age and 55 detected clinically after 3 weeks of age having normal screens (n = 52) or never screened (n = 3). Based on data from concurrent control populations, 54.5 cases of neuroblastoma would have been expected in Quebec during the study period for an SIR of 2.17 (95% CI 1.79-2.57, P < 0.0001). For the two control groups, the overall SIR was 1.00 (NS). SIRs for Quebec by age at diagnosis in yearly intervals show a marked increased incidence under 1 year of age (SIR = 2.85, 95% CI 2.26-3.50), with no reduction in incidence in subsequent years. We conclude that screening for neuroblastoma markedly increases the incidence in infants without decreasing the incidence of unfavourable advanced stage disease in older children. It is unlikely that screening for neuroblastoma in infants will reduce the mortality of this disease.

Human Krüppel-related 3 (HKR3): a candidate for the 1p36 neuroblastoma tumour suppressor gene?

Human Krüppel-related 3 (HKR3) is a zinc finger gene that maps within chromosome subbands 1p36.2-.3, a region postulated to contain a tumour suppressor gene associated with advanced neuroblastomas. Genomic clones of HKR3 were isolated from a P1 library and physically mapped to within 40 kb of D1S214 at 1p36.3. The gene is ubiquitously expressed in human tissues, but especially high levels are present in human fetal and adult nervous tissues. Hemizygous deletion of HKR3 in a lymphoblastoid cell line derived from a neuroblastoma patient with a constitutional 1p36 interstitial deletion and in the neuroblastoma cell line SK-N-AS, which also has a small interstitial 1p36 deletion, has been observed. Allelic loss at D1S214 in 15/15 informative primary neuroblastoma specimens with 1p36 deletions has also been observed. In a panel of 16 neuroblastoma cell lines, no gross genomic DNA rearrangements were noted, the gene was always expressed (albeit at variable levels) and there was no evidence for truncating mutations. Furthermore, there were no mutations detected in the zinc finger coding region in four neuroblastoma cell lines with 1p deletions analysed by direct sequence analysis. We conclude that HKR3 is a novel zinc finger gene that maps to a region of the genome commonly rearranged or deleted in neuroblastoma and other human cancers.

Expression and function of Trk-C in favourable human neuroblastomas

Human neuroblastomas express the neurotrophin receptors trk-A and trk-B. Favourable outcome is associated with expression of trk-A, while unfavourable, MYCN amplified tumours express trk-B. In this study we examined the expression of trk-C in primary neuroblastoma tumour-derived cell lines. We found by Northern blot analysis that trk-C mRNA is expressed in 14 of 55 (25%) primary tumours. Trk-C was expressed in significantly more lower stage tumours (stage 1, 2, 4S) than higher stage tumours (stage 3, 4, P < 0.04). The expression of trk-C was correlated positively with survival and negatively correlated with MYCN amplification. We also studied the function of trk-C in transfected cell lines and found that NT-3 promotes both cell survival and differentiation. Our results suggest that trk-C is involved in the biology of favourable neuroblastomas.

Molecular genetic analysis of familial neuroblastoma

Neuroblastoma has several clinical and molecular genetic parallels with the other paediatric embryonal tumours, such as retinoblastoma, including a hereditary form of the disease. We hypothesised that neuroblastoma susceptibility is due to germline mutations in a tumour suppressor gene and that this predisposition gene may be involved in sporadic neuroblastoma tumorigenesis as well. We therefore aimed to localise the familial neuroblastoma predisposition gene by linkage analysis in neuroblastoma kindreds. Eighteen families segregating for neuroblastoma were ascertained for candidate locus linkage analysis. Although many of the 49 affected individuals in these families were diagnosed as infants with multifocal primary tumours, there was marked clinical heterogeneity. We originally hypothesised that familial neuroblastoma predisposition would map to the telomeric portion of chromosome band 1p36, a genomic region likely to contain a sporadic neuroblastoma suppressor gene. However, neuroblastoma predisposition did not map to any of eight polymorphic markers spanning 1p36.2-.3 in three large kindreds. In addition, there was strong evidence against linkage to two Hirschsprung disease susceptibility genes (RET and EDNRB), a condition that can cosegregate with neuroblastoma as in one of the kindreds tested here. We conclude that the neuroblastoma susceptibility gene is distinct from the 1p36 neuroblastoma suppressor and two of the currently identified Hirschsprung disease susceptibility genes.

Molecular analysis of the region of distal 1p commonly deleted in neuroblastoma

Cellular, cytogenetic, and molecular evidence indicates that chromosome band 1p36 is often deleted in neuroblastoma cell lines and tumours, suggesting the presence of one or more tumour suppressor genes in this region. We used a multifaceted approach to analyse the commonly deleted region, 28 distal 1p-specific polymorphic loci were used to detect loss of heterozygosity (LOH) in a panel of primary neuroblastoma tumours. Thirty-two of 122 tumours (26%) demonstrated LOH at three or more loci. In addition, a patient with a constitutional deletion of 1p36.2-.3 and two neuroblastoma cell lines with 1p36 abnormalities were characterised by FISH. When combined with the LOH data, a single consensus region of deletion was defined proximally by PLOD and distally by D1S80, a region spanning approximately five megabases. Several proposed candidate tumour suppressor genes, including ID3, CDC2L1, DAN, PAX7, E2F2, TNFR2 and TCEB3, map outside of this region; however, the transcription factor HKR3 cannot be excluded. LOH for 1p is correlated with adverse clinical and biological features and a poor prognosis, but 1p LOH is not an independent predictor of overall survival. To identify additional candidate genes, an integrated physical map of 1p35-36 is being constructed. The current map includes 445 polymerase chain reaction (PCR)-formatted markers and 608 YACs. This map will help identify region-specific transcripts by direct selection and sequencing.