Loss of p53 expression is accompanied by upregulation of beta-catenin in meningiomas: a concomitant reciprocal expression

Abstract

Crosstalk between Wnt and p53 signalling pathways in cancer has long been suggested. Therefore in this study we have investigated the involvement of these pathways in meningiomas by analysing their main effector molecules, beta-catenin and p53. Cellular expression of p53 and beta-catenin proteins and genetic changes in TP53 were analysed by immunohistochemistry, PCR/RFLP and direct sequencing of TP53 exon 4. All the findings were analysed statistically. Our analysis showed that 47.5% of the 59 meningiomas demonstrated loss of expression of p53 protein. Moderate and strong p53 expression in the nuclei was observed in 8.5% and 6.8% of meningiomas respectively. Gross deletion of TP53 gene was observed in one meningioma, but nucleotide alterations were observed in 35.7% of meningiomas. In contrast, beta-catenin, the main Wnt signalling molecule, was upregulated in 71.2%, while strong expression was observed in 28.8% of meningiomas. The concomitant expressions of p53 and beta-catenin were investigated in the same patients. In the analysed meningiomas, the levels of the two proteins were significantly negatively correlated (P = 0.002). This indicates that meningiomas with lost p53 upregulate beta-catenin and activate Wnt signalling. Besides showing the reciprocal relationship between proteins, we also showed that the expression of p53 was significantly (P = 0.021) associated with higher meningioma grades (II and III), while beta-catenin upregulation was not associated with malignancy grades. Additionally, women exhibited significantly higher values of p53 loss when compared to males (P = 0.005). Our findings provide novel information about p53 involvement in meningeal brain tumours and reveal the complex relationship between Wnt and p53 signalling, they suggest an important role for beta-catenin in these tumours.

Keywords: Wnt and p53 signalling; beta-catenin; meningioma; p53; protein expression.

Figure 1

An AccII restriction site in the exon 4 and an MspI restriction site in the intron 6 of the TP53 gene were used as polymorphic gene markers in meningioma samples and analysed on Spreadex gels (Elchrom Scientific) stained with SYBR Gold (Molecular Probes). a) Polymorphic marker MspI is shown. Lane M – 100 bp molecular standard; lane 1 – corresponding blood sample; lane 2 – LOH of the p53 gene in a meningioma sample. b) Polymorphic marker AccII is shown. Lanes 1, 2 – uninformative homozygous sample and corresponding blood; lanes 3, 4 – heterozygous meningioma sample and corresponding blood sample; lane M – 100 bp molecular standard.

Figure 2

Sequence analysis of nucleotide alterations at codon 72 in wild‐type and tumour DNA (a) and at codon 70 in wild‐type and tumour DNA (b) observed in meningiomas.

Figure 3

Meningioma samples immunohistochemically stained for the expression of p53 and beta‐catenin proteins demonstrating a) loss of p53 expression; b) strong nuclear p53 expression; c) positive control for p53 – urothelial carcinoma of the bladder; d) moderate membranous and cytoplasmic beta‐catenin expression; e) strong cytoplasmic and nuclear beta‐catenin expression; f) negative control staining. Original magnification 200x, scale bar 50 μm.

Figure 4

Graph illustrating the levels of expression of beta‐catenin and p53 proteins in our total tumour sample showing that meningiomas with lost p53 upregulate beta‐catenin.