The homeobox gene MEIS1 is amplified in IMR-32 and highly expressed in other neuroblastoma cell lines
Introduction
Neuroblastoma is one of the commonest solid tumours in young children, constituting 10% of all cancers in children under 15 years of age. It arises as an embryonal tumour of the sympathetic nervous system, but demonstrates clinical heterogeneity, with the clinical course ranging from spontaneous regression to extremely aggressive tumour behaviour. Low, intermediate and high-risk groups of patients are associated with distinct molecular genetic and biological features [1]. Favourable features include early stage (1, 2A, 2B or 4S), age at diagnosis less than 1 year, triploid karyotype, lack of 1p abnormalities and the absence of MYCN amplification. Unfavourable features are advanced stage (3 or 4), age over 1 year, pseudodiploid and tetraploid karyotypes, deletion of the short arm of chromosome 1, MYCN amplification and gain of the long arm of chromosome 17 [2]. Patients with these features frequently have poor prognosis, showing little response even to aggressive multi-agent chemotherapy.
The relative contributions to tumorigenesis of MYCN amplification and other genes affected by chromosome aberrations in neuroblastoma are currently unknown. Several genes may be co-amplified with MYCN in neuroblastoma, yet none are amplified in the absence of MYCN amplification. One of these, the DEAD box motif gene DDX1, is amplified in 60–70% of MYCN-amplified neuroblastomas [3]. DDX1 has been mapped to a position 340 kb 5′ and telomeric to MYCN in chromosome band 2p24 [4]. More recently, neuroblastoma amplified gene (NAG) was also shown to be co-amplified in 70% of MYCN-amplified neuroblastomas and to map telomeric to MYCN [5]. The gene ornithine decarboxylase (ODC1) in chromosome band 2p25, is occasionally co-amplified with MYCN and is thought to be at the border of the region of DNA which is usually co-amplified [6]. Since a correlation between MYCN and ODC1 expression has been noted in neuroblastoma cell lines, it has been suggested that MYCN may be the natural regulator of ODC1 expression in neuronal tumours [7].
In this study, we investigated the genomic regions which are co-amplified with MYCN in the neuroblastoma cell line IMR-32. The cell line was established from an abdominal mass in a 13-month-old Caucasian male [8], and contains two copies of a large sub-metacentric chromosome, der(1), resulting from a non-reciprocal translocation between chromosomes 1 and 17. This large marker chromosome contains a homogeneously staining region (HSR) carrying amplified MYCN, flanked by material from chromosome 17 [9].
We show here that the homeobox gene MEIS1 is present in multiple copies in this HSR in IMR-32, where it is highly expressed. The gene is also highly expressed in other neuroblastoma and medulloblastoma cell lines where it is not amplified. We discuss these findings in the context of homeobox genes in neural development and tumorigenesis.
Section snippets
Cell culture and chromosome preparation
The following cell lines were obtained from the American Type Culture Collection (ATCC, Manassas, USA) and cultured using recommended conditions: neuroblastoma cell lines IMR-32 (from an abdominal mass), SK-N-AS, SK-N-Be, SK-N-DZ, SK-N-FI (all from bone marrow metastases), CHP212, Kelly (both from brain), and SK-N-LI; medulloblastoma cell lines HTB186 (desmoplastic cerebellar medulloblastoma), D283 (metastatic medulloblastoma) and TE671 (sub-line No. 2); erythroleukaemia cell line HEL 92.1.7
CGH and FISH analysis
Genomic regions 2p24-p23, 2p16 and 2p14 were found by CGH to be amplified in IMR-32 cells (data not shown). The HSR contained within the derivative chromosome 1 was then microdissected, and shown by FISH to be derived from bands 2p24, 2p23, 2p16 and 2p14, confirming the CGH results. An initial screen by FISH using probes available for genes mapping to our regions of interest along chromosome arm 2p showed the following genes were not present in the HSR: VREL, CD8A, TGFA, FSH, hMSH2, GFAT and
Discussion
The aim of this study was to identify sequences which are co-amplified with MYCN in the neuroblastoma cell line IMR-32 and to determine whether the same sequences are amplified or highly expressed in other tumour cell lines. Our CGH results confirmed previous reports of amplification of sequences from several regions of chromosome 2 in IMR-32 20, 21. More recently, amplification of material from chromosome bands 2p13-p14 and 2p23 was found in primary neuroblastoma material suggesting that
Acknowledgements
This work was supported by the Imperial Cancer Research Fund. In addition, R.H.F and D.N. were partly supported by project grant SP2475/0101 from the Cancer Research Campaign, UK and Human Genome Mapping Project strategic grant G9422614 from the Medical Research Council, UK. We thank the HGMP resource centre for kindly providing reagents, and Jürgen Groet and Pedro Baptista for assistance with experiments.
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