ΔN-p73α accumulates in human neuroblastic tumors

Neuroblastic tumors (NTs), occurring in early childhood, display a wide spectrum of differentiation. Recurrent deletions involving the p73 locus are frequently observed in undifferentiated NTs. To address the question of the possible implication of p73 in neuroblastic differentiation, we investigated the status of the expression of this gene in a panel of differentiated and undifferentiated tumors. Although mutations were not found, p73 transcript profiles differed between undifferentiated and differentiated tumors. The frequency of the transcripts lacking exon 2 (species 1-3) appeared to be higher in undifferentiated than in differentiating and differentiated NTs. In contrast, products from using an alternate promoter (ΔN-p73) were present in all NTs. In addition, only ΔN-p73, but not full-length proteins, were detected by immunoblotting, suggesting a greater stability of N-truncated isoforms. Importantly, as in the adrenal medulla, most NTs showed p73-positive immunohistological staining with a cellular distribution and intensity varying according to the neuronal differentiation. Surprisingly, we observed redistribution of p73 from the nucleus to the cytoplasm during neuroblastic differentiation. Our data suggest that, in undifferentiated NTs, a link may exist between the accumulation of ΔN-p73α variants and the "nuclear exclusion" of p53.