Suppression of RIZ in biologically unfavourable neuroblastomas

Neuroblastoma is a paediatric solid tumor characterized by recurrent genomic abnormalities of prognostic importance. One of the most commonly observed abnormalities is deletion of the short arm of chromosome 1 and reduced expression of cancer related genes in this chromosomal arm. The long isoform of the retinoblastoma protein-interacting zink finger gene (RIZ1) is a known tumor suppressor and a candidate neuroblastoma gene located at 1p36.2. The present study was undertaken to further assess the possible involvement of RIZ in neuroblastoma development. Expression of RIZ transcripts were quantified in a panel of neuroblastoma cell lines and tumors (33 neuroblastomas and 3 ganglioneuromas). Methylation status of promoter P1 driving RIZ1 expression was quantified by bisulfite Pyrosequencing. Only low mean levels of promoter methylation (<10%) were observed in all samples. However, RIZ1 and RIZ1+2 mRNA were significantly under-expressed in biologically unfavourable tumors characterized by 1p loss (p<0.005) or MYCN amplification (p<0.005). Suppression of RIZ1 is likely to contribute to the pathogenesis of biologically unfavourable neuroblastomas. In contrast to multiple other neoplasias, RIZ1 promoter methylation is not a common event in neuroblastoma.