Detection of TP53 mutation in ameloblastoma by the use of a yeast functional assay

Background:   Mutations in TP53 have been observed in a variety of tumors including oral lesions, though there are no reports in ameloblastomas. The purpose of the study was to examine the TP53 status of ameloblastomas using newly developed yeast functional assay whose accuracy and sensitivity has been proven to be higher than those of the previous DNA structure-based methods such as single strand conformation polymorphism (SSCP) analysis. Methods:  TP53 status was analyzed by yeast functional assay and DNA sequencing in 12 cases of ameloblastoma which were diagnosed histologically and represented the clinical features of a benign tumor. After the extraction of RNA from the frozen tissue samples without microdissection, reverse transcription (RT)–PCR was carried out and these samples were used. The assay can detect mutations of p53 mRNA between codons 67 and 347 by the DNA-binding activity of the protein and reveal them as red colonies. Results:   One case of 47-year-old male gave 17% red colonies of yeast and the other 11 cases gave 5.4% (mean; range, 3–8%). To confirm this result, we obtained other nine samples from the case of 17% red colonies, which contained or did not contain tumor tissues, and analyzed them by the assay. Seven samples that were histologically negative for tumor cells gave 4.7% red colonies (mean; range, 1–7%). Two samples that were histologically positive for tumor cells gave 20 or 46% of red colonies. The p53 plasmids were recovered from the red colonies of these three samples showing high red colony ratios and were subjected to sequencing analysis after purification. In all these samples, the same clonal mutation of TGT (Cys) 238 TAT (Tyr) was demonstrated. Conclusions:  These results suggest that TP53 mutation may be involved in molecular pathogenesis in a subset of ameloblastomas, though it is infrequent.