Reappraisal of p53 mutations in human malignant astrocytic neoplasms by p53 functional assay: Comparison with conventional structural analyses

Abstract

We previously reported clonal expansion of p53 mutations in malignant astrocytic tumors detected with a yeast p53 functional assay that measures mutant p53 alleles quantitatively and loss of p53 transcriptional competence qualitatively (Tada et al., Int J Cancer 67:447-450, 1996). This method selectively detects inactivating mutations and is relatively insensitive to contamination of tumor samples with normal tissue. To determine whether the mutation frequency and spectrum detected in this way differ from those seen with conventional techniques, 54 malignant astrocytomas were tested with the yeast assay, and the abnormalities detected were characterized by DNA sequencing. Inactivating p53 mutations were found in 67% of anaplastic astrocytomas and 41% of glioblastomas. Overall, mutations were found in 48% of tumors, compared with only 29% in previous studies (P < 0.005), a difference that probably reflects the greater sensitivity of the yeast assay than of conventional techniques. The frequency of mutations in anaplastic astrocytomas (in our study plus published studies) was significantly higher than in glioblastomas (39% vs 29%; P < 0.05). This suggests that acquisition of p53 mutations is not rate limiting for progression to glioblastoma and that many glioblastomas develop by p53-independent pathways. Sequencing of mutant p53 cDNAs rescued from yeast showed that the mutation spectrum for functionally inactive mutants was nearly identical to the spectra from previous studies on structural mutants, indicating that transcriptional activity is the critical biological target of p53 mutation in malignant astrocytomas.

Molecular Cloning of p53 cDNA of Mongolian Gerbil and Establishment of Yeast p53 Functional Assay System

“…All samples showed less than 10% red colonies [ Table 2] and had no clonal mutations (data not shown). As previously reported, human and rat normal tissues typically give 5 -10% background red colonies with the same assay used here [19,22]. This background does not reflect genetic mutation and is due mainly to RT-PCR artifact [19,22].…”

Application of a Yeast Assay to Detect Functional p53 Mutations in Archival Prostate Cancer Tissue

“…[27][28][29] In this study, we also found yeast analysis of p53 genomic DNA from archival tumor tissue to be more sensitive than SSCP analysis. Additionally, we observed that careful dissection of the marked tumor-rich area allows us to detect the p53 mutations in small tumor foci.…”

“…Other investigators have shown that yeast analysis of p53 mRNA from fresh tumor tissue is more sensitive than other p53 mutation-detecting approaches including SSCP. [27][28][29] In this study, we also found yeast analysis of p53 genomic DNA from archival tumor tissue to be more sensitive than SSCP analysis. Additionally, we observed that careful dissection of the marked tumor-rich area allows us to detect the p53 mutations in small tumor foci.…”

Roles of the functional loss of <I>p53</I> and other genes in astrocytoma tumorigenesis and progression

“…In contrast, p53 mutations were detected in considerable fractions of higher-grade astrocytic tumors, indicating that loss of p53 function plays an important role in tumorigenesis of subsets of these tumors. It is particularly interesting that anaplastic astrocytomas showed the highest prevalence (67%) of p53 mutation (Tada et al, 1997). This is also apparent in the previously documented mutations in anaplastic astrocytomas (30%; Table 1).…”