Porcine model elucidates function of p53 isoform in carcinogenesis

Background The pig has long been an important animal species for biomedical research. Recent years has also seen an increasing number of genetically engineered pig models of human diseases including cancer. We previously generated pigs with a modified TP53 allele which carries a Cre-removable transcriptional stop signal in intron 1, and an oncogenic mutation TP53 R167H (orthologous to human TP53 R175H and mouse Trp53 R172H ) in exon 5. Pigs with the unrecombined mutant allele (fl TP53 R167H ) develop osteosarcoma (OS) in aged heterozygous and young homozygous animals. In addition, some homozygous animals also developed nephroblastomas and lymphomas. This observation suggested that TP53 gene dysfunction is itself the key initiator of tumorigenesis, but raises the question which aspects of the TP53 regulation leads to the development of such a narrow tumour spectrum, mainly OS. Methods We performed a series of molecular and cellular analyses to study the regulation of TP53 and its family members in both healthy tissue and tumours (n= 48) from fl TP53 R167H pigs. Human OS cell lines were used to prove relevance to human patients. Results Molecular analyses of p53 revealed the presence of two internal TP53 promoters (Pint and P2) equivalent to those found in human. Consequently, both pigs and human express TP53 isoforms. Data presented here strongly suggest that P2-driven expression of the mutant R167H-Δ152p53 isoform (equivalent to the human R175H-Δ160p53 isoform) and its circular counterpart circTP53 determine the tumour spectrum and play a critical role in the malignant transformation of bones, kidney or spleen in fl TP53 R167H pigs. The detection of Δ152p53 isoform mRNA in serum is indicative of tumorigenesis. Furthermore, we showed a tissue-specific p53-dependent deregulation of the p63 and p73 isoforms in these tumours. Conclusions This study highlights important species-specific differences in the transcriptional regulation of TP53 . For the first time a circTP53 RNA was identified. Results indicate that the Δ152p53 isoform, its circular circTP53 and p53 family members, TAp63δ and TAp73δ, likely play a role in the malignant transformation of bone and other tumours. Considering the similarities of TP53 regulation between pig and human, these observations provide useful pointers for further investigation into isoform function including the novel circTP53 in both the pig model and human patients.