Conserved Double Translation Initiation Site for Δ160p53 Protein Hints at Isoform's Key Role in Mammalian Physiology

p53 is the most commonly mutated gene in human cancers. Two fundamental reasons for this are its long protein isoforms protect from cancer, while its shorter C-terminal isoforms can support cancer and metastasis. Previously, we have shown that the & UDelta;160p53 protein isoform enhances survival and the invasive character of cancer cells. Here, we identified a translation initiation site nine codons downstream of codon 160-the known initiation codon for the translation of delta 160p53-that is recognized by the translation machinery. When translation failed to initiate from AUG160 due to mutation, it initiated from AUG169 instead, producing similar levels of a similar protein, delta 169p53, which promoted cell survival as efficiently as delta 160p53 following DNA damage. Interestingly, almost all mammalian species with an orthologue to human AUG160 also possess one for AUG169, while none of the non-mammalian species lacking AUG160 have AUG169, even if that region of the p53 gene is well conserved. In view of our findings, we do not believe that & UDelta;169p53 acts as a different p53 protein isoform; instead, we propose that the double translation initiation site strengthens the translation of these products with a critical role in cell homeostasis. Future studies will help verify if this is a more general mechanism for the expression of essential proteins in mammals.

Automated summary

p53 is the most commonly mutated gene in human cancers. It has been found that the long protein isoforms of p53 can protect against cancer, while the shorter C-terminal isoforms can support cancer and metastasis. The Δ160p53 protein isoform has been shown to enhance survival and invasive characteristics of cancer cells. In this study, a translation initiation site was identified downstream of codon 160, and when translation failed to initiate from AUG160 due to mutation, it initiated from AUG169 instead, producing a similar protein, Δ169p53, which promotes cell survival following DNA damage. The presence of both initiation sites is more common in mammalian species, suggesting a potential role in essential protein expression.