Loss of heterozygosity of the p53 gene and deregulated expression of its mRNA and protein in human brain tumors

Tumor-specific alterations at the p53 gene locus were analyzed in 40 human brain tumor samples. Gliomas were more prevalent in young males and meningiomas in old females. Structural changes at the intron 1 region of the p53 gene were analyzed in these tumors by Southern blotting. Among the 40 tumors, 33 were informative and 21 of these (63.6%) informative cases showed loss of heterozygosity (LOH). This is the first report showing LOH at the intron 1 region of p53 gene in human brain tumors. The level of p53 mRNA, p53 protein and Ser 392 phosphorylated p53 protein were also analyzed in all tumor samples. Normal sized p53 mRNA and protein were present in all the tumor samples; however, their levels were 1.5- to 4-fold higher compared to the control suggesting deregulated p53 pathway in these tumors. No correlation was found between LOH status and the levels of p53 mRNA and protein. In all high-grade glioblastomas majority of the p53 protein existed as Ser 392 phosphorylated form as compared to low-grade gliomas. In addition, the percentage of Ser 392 phosphorylated form of p53 protein was lower in meningiomas and other brain tumor types irrespective of tumor grade. These results suggest involvement of Ser 392 phosphorylated form of p53 protein during the later stages of glioma development. These results also indicate that deregulation of p53 gene could occur at various steps in p53 pathway and suggest an overall deregulation of p53 gene in most brain tumor types.