Involvement of N-terminally truncated variants of p73, Delta TAp73, in head and neck squamous cell cancer

p73, a p53-related gene, encodes two classes of isoforms with opposing functions: (1) a full-length transactivation- competent p73 protein (TAp73) with tumour suppressor activity; and (2) a group of NH2-terminally truncated, transactivation- deficient p73 proteins, Delta Ex2p73, Delta Ex2- 3p73, Delta Np73 and Delta N'p73 (collectively named Delta TAp73) with oncogenic activity. In this study, for the first time, we analyse the deregulations of TAp73 and Delta TAp73 in head and neck squamous cell cancer (HNSCC) and compare them to p53 status. We found that all the p73 isoforms in HNSCC tissue were upregulated with respect to those in normal adjacent tissue. Concomitant upregulations of p73 transcripts were often found in cancer tissue but not in normal tissue. p53 mutations and p73 transcript alterations are not mutually exclusive. All the HNSCC specimens studied had at least one p53 mutation and/or one Delta TAp73 transcript alteration. Although both the Delta Np73 and the TAp73 transcripts were found to be upregulated in head and neck cancers, the predominant protein in the cancers analysed was Delta Np73. TAp73, in contrast, was only weakly expressed. This finding is highly relevant and sheds light on the puzzling question of the biological significance of TAp73 upregulation in cancers. Delta Np73 protein levels were significantly overexpressed in HNSCC tissue compared to matched normal tissue (p = 0.003). Furthermore, a trend was found for better overall survival in patients with a low expression of Delta Np73. Our results show that the deregulation of both the p53 and the p73 pathways plays an important role in inducing head and neck cancers.