RESUMO
We aimed to directly align a chromosomal CGH (cCGH) pattern with the gene mapping data by taking advantage of the clustering of the GGCC motif at certain positions in the human genome. The alignment of chromosomal with sequence data was achieved by superimposition of (i) the fluorescence intensity of the sequence specific fluorochrome, Chromomycin A3 (CMA3), (ii) the cCGH fluorescence intensity profile of individual chromosomes and (iii) the GGCC density profile extracted from the Ensembl genome sequence database. The superimposition of these three pieces of information allowed us to precisely localize regions of amplification in the neuroblastoma cell line STA-NB-15. Two prominent cCGH peaks were noted, one at 2p24.3, the position 15.4 mega base (Mb), and the other at 2p23.2, 29.51 Mb. FISH and high resolution array CGH (aCGH) experiments disclosed an amplification of MYCN (16 Mb) and ALK (29.2-29.9 Mb), thus confirming the cCGH data. The combined visualization of sequence information and cCGH data drastically improves the resolution of the method to less than 2 Mb.
Assuntos
Mapeamento Cromossômico/métodos , Hibridização de Ácido Nucleico/métodos , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Quinase do Linfoma Anaplásico , Sequência de Bases , Linhagem Celular Tumoral , Cromomicina A3 , Citogenética/métodos , DNA/genética , DNA de Neoplasias/genética , Corantes Fluorescentes , Genoma Humano , Humanos , Hibridização in Situ Fluorescente/métodos , Proteína Proto-Oncogênica N-Myc , Proteínas Nucleares/genética , Proteínas Oncogênicas/genética , Proteínas Tirosina Quinases/genética , Receptores Proteína Tirosina QuinasesRESUMO
Recently, it was shown that MYCN amplified cells spontaneously expulse extrachromosomally amplified gene copies by micronuclei formation. Furthermore, it was shown that these cells lose their malignant phenotype and start to age. We tested whether it is possible to encourage neuroblastoma tumor cells to enter the senescence pathway by low concentrations of the micronuclei-inducing drug hydroxyurea (HU). We studied the effect of HU on 12 neuroblastoma cell lines with extra- or intrachromosomally amplified MYCN copies and without amplification. Two extrachromosomally amplified neuroblastoma cell lines (with double minutes) were investigated in detail. Already after 3 weeks of HU treatment, the BrdU uptake dropped to 25% of the starting cells. After 4 weeks, enlarged and flattened cells (F-cells) and increased granularity in the majority of cells were observed. A drastic reduction of the MYCN copy number-down to one copy per cell-associated with CD44 and MHCI upregulation in up to 100% of the HU treated neuroblastoma cells was found after 5-8 weeks. Telomere length was reduced to half the length within 8 weeks of HU treatment, and telomerase activity was not detectable at this time, while being strongly expressed at the beginning. All these features and the expression of senescence-associated-beta-galactosidase (SA-beta-GAL) in up to 100% of the cells support the hypothesis that these cells entered the senescence pathway. Thus, low-dose HU is a potent senescence elicitor for tumor cells with gene amplification, possibly representing an attractive additional strategy for treatment of this subset of tumors.
