Epitope mapping of novel p73 isoform antibodies

The human TP73 gene is a member of the p53 family and produces N- and C-terminal protein isoforms through alternative promoters, alternative translation initiation and alternative splicing. Most notably, N-terminal p73 proteins either contain a p53-like transactivation domain (TAp73 isoforms) or lack this domain (?TAp73 isoforms) and have opposing or independent functional properties. To date, there is a lack of well-characterised isoform-specific p73 antibodies. Here, we produced polyclonal and monoclonal antibodies to N-terminal p73 variants and the C-terminal p73a isoform, the most common variant in human tissues. These reagents show that TAp73 is a marker of multiciliated epithelial cells, while ?TAp73 is a marker of non-proliferative basal/reserve cells in squamous epithelium. We were unable to detect ?Np73 variant proteins, in keeping with recent data that this is a minor form in human tissues. Most cervical squamous cell carcinomas (79%) express p73a, and the distribution of staining in basal cells correlated with lower tumour grade. TAp73 was found in 17% of squamous cell carcinomas, with a random distribution and no association with clinicopathological features. These data indicate roles for ?TAp73 in maintaining a non-proliferative state of undifferentiated squamous epithelial cells and for TAp73 in the terminal differentiation process of multiciliation.