Pla2g16 phospholipase mediates gain-of-function activities of mutant p53
Significance Mutations of p53 occur in approximately 50% of human cancer. p53 missense mutations exhibit gain-of-function activities. In this study, we discovered a previously unidentified mechanism of mutant p53 gain-of-function in osteosarcoma and mammary tumors. Our data indicate that mutant p53 binds to E26 transformation-specific motifs in the Pla2g16 phospholipase promoter to induce its expression, which leads to more aggressive and metastatic phenotypes. Thus, the study implicates mutant p53 regulation of lipid metabolism in cancer cells to confer its gain-of-function. The study suggests new therapeutic options for patients with mutant p53. p53R172H/+ mice inherit a p53 mutation found in Li-Fraumeni syndrome and develop metastatic tumors at much higher frequency than p53+/− mice. To explore the mutant p53 metastatic phenotype, we used expression arrays to compare primary osteosarcomas from p53R172H/+ mice with metastasis to osteosarcomas from p53+/− mice lacking metastasis. For this study, 213 genes were differentially expressed with a P value <0.05. Of particular interest, Pla2g16, which encodes a phospholipase that catalyzes phosphatidic acid into lysophosphatidic acid and free fatty acid (both implicated in metastasis), was increased in p53R172H/+ osteosarcomas. Functional analyses showed that Pla2g16 knockdown decreased migration and invasion in mutant p53-expressing cells, and vice versa: overexpression of Pla2g16 increased the invasion of p53-null cells. Furthermore, Pla2g16 levels were increased upon expression of mutant p53 in both mouse and human osteosarcoma cell lines, indicating that Pla2g16 is a downstream target of the mutant p53 protein. ChIP analysis revealed that several mutant p53 proteins bind the Pla2g16 promoter at E26 transformation-specific (ETS) binding motifs and knockdown of ETS2 suppressed mutant p53 induction of Pla2g16. Thus, our study identifies a phospholipase as a transcriptional target of mutant p53 that is required for metastasis.