Analysis of TALE homeobox genes in neuroblastic tumors: ganglioneuroblastoma and ganglioneuroma

A large proportion of patients suffering from the malignant pediatric tumor neuroblastoma die of progressive disease despite intensive therapy. Neuroblastomas belong to the group of neuroblastic tumors, together with the more benign, differentiated ganglioneuroblastomas and ganglioneuromas. Little is known of the genes driving the differentiation processes in these tumor types. A search for the transcription factors differentially expressed between ganglioneuromas, ganglioneuroblastomas, and neuroblastomas in a series of 110 neuroblastic tumors (NB110) identified a large number of HOX- and TALE (Three Amino acid Loop Extension)-class homeobox transcription factor genes. The MEIS1-3, PBX1 and -3, and PKNOX1 TALE genes showed highest expression in neuroblastomas and lowest in ganglioneuromas and ganglioneuroblastomas. The PKNOX2 and TGIF1-2 genes showed the opposite expression pattern. This suggests an involvement of TALE genes in neuroblastoma differentiation. Expression of MEIS1, a known oncogene in haematopoietic tumors, was high in all neuroblastomas, and strongly correlated with undifferentiated histology. Consequently, we generated IMR-32 neuroblastoma cells capable of inducible shRNA-mediated MEIS1 knockdown. We observed differentiation, growth arrest and induction of apoptosis upon MEIS1 down-regulation. Affymetrix profiling of time-course experiments using these cells allowed the identification of MEIS1 target genes. Analysis of the target genes in the NB110 series showed that 323 of these were also significantly correlated to MEIS1 expression and to tumor differentiation in neuroblastic tumors. Genes involved in the cell cycle and in developmental pathways were over-represented in this gene set. We conclude that MEIS1 governs several of the signal transduction routes important for neuroblastoma survival and differentiation.

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