Genomische Charakterisierung der T-ALL mit Hilfe der Mikroarray-comparative genomic Hybridisierung (Array-CGH)
Zusammenfassung der Projektergebnisse
Using microarray-based comparative genomic hybridization to analyze DNAs from human T-cell acute lymphoblastic leukemia (T-ALL), we identified a gain of DMA from chromosome 6, where the MYB gene is located. Fluorescence in situ hybridization on stretched DMA fibers from five TALL cell lines showed that the increased number of MYB copies resulted from a small tandem duplication of the gene on one of the two chromosome 6. The human MYB locus is flanked by 257 bp Alu repeats and the duplication is caused by homologous recombination between the flanking Alu elements on sister chromatids. The duplication was associated with increased MYB expression and was detected in a relatively high proportion of newly diagnosed T- ALL cases (24%). Since MYB duplication was not detected in matching remission samples, we concluded that Alu-mediated tandem duplication with increased MYB expression occurs somatically during the molecular pathogenesis of human T-ALL. T-cell acute lymphoblastic leukemia (T-ALL) is mostly characterized by specific chromosomal abnormalities, some occurring in a mutually exclusive manner possibly delineating specific T-ALL subgroups. One subgroup, including MlLrearranged, CALM-AF10 or inv(7)(p15q34) cases, is characterized by increased expression of HOXA genes. Using a gene expression based clustering analysis of 67 T-ALL cases with recurrent molecular genetic abnormalities and 25 samples lacking apparent chromosomal aberrations, we identified 5 new cases with elevated HOXA levels. Array CGH performed in parallel to expression analysis revealed a cryptic and recurrent deletion, del(9)(q34.11q34.13) in 3 of these 5 cases. This deletion results in a conserved SET-NUP214 fusion product, that was also identified in the T-ALL cell line LOUCY. SET-NUP214 binds in the promoter region of specific HOXA genes, where it interacts with CMR1 and DOT1L leading to the transcriptional activation of HOXA genes. Targeted inhibition of SET-NUP214 by silencing RNA abolished expression of HOXA genes, inhibited proliferation and induced differentiation in LOUCY but not in other TALL lines. Therefore, we conclude that SET-NUP214 contributes to the pathogenesis of TALL by enforcing T-cell differentiation arrest.
