p73 gene transcripts in human brain tumors: overexpression and altered splicing in ependymomas

The p73 gene encodes a protein that shares structural and functional homologies with the p53 tumor suppressor protein. The p73 gene is monoallelically expressed in normal tissue, maps to chromosome 1p36 and is deleted in human neuroblastoma cell lines. Alternative splicing of exon 13 in p73 transcripts generates two isoforms, p73alpha and p73beta, that differ in their carboxy-terminus and in their ability to form homotypic interactions. In this study, we investigated, in 129 human central nervous system tumors of various histological types, the levels of p73 transcripts and the splicing characteristics of p73 mRNA. Whereas p73 mRNA content was consistently low in most tumoral types, especially in meningiomas, some glioblastomas, medulloblastomas and metastases exhibited elevated p73 mRNA content. However, ependymomas expressed consistently high amounts of p73 mRNA, significantly different from the other tumoral types. Whereas the short (p73beta) isoform accounted for 20-25% of the total p73 mRNA in most of the tumors, these splicing characteristics were altered in ependymomas (only 9% of p73beta) and in neurinomas (up to 53% of p73beta). These observations suggest tissular or tumoral differences in the control of p73 gene transcription and alternative splicing, and raise the problem of the role of p73 isoforms in the control of tumor growth, particularly in ependymomas.