Tomislav Vladušić

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

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.

Loss of heterozygosity of CDKN2A (p16INK4a) and RB1 tumor suppressor genes in testicular germ cell tumors

Loss of heterozygosity of CDKN2A (p16INK4a) and RB1 tumor suppressor genes in testicular germ cell tumors Background. Testicular germ cell tumors (TGCTs) are the most frequent malignances in young adult men. The two main histological forms, seminomas and nonseminomas, differ biologically and clinically. pRB protein and its immediate upstream regulator p16INK4a are involved in the RB pathway which is deregulated in most TGCTs. The objective of this study was to evaluate the occurrence of loss of heterozygosity (LOH) of the CDKN2A (p16INK4a) and RB1 tumor suppressor genes in TGCTs. Materials and methods. Forty TGCTs (18 seminomas and 22 nonseminomas) were analyzed by polymerase chain reaction using the restriction fragment length polymorphism or the nucleotide repeat polymorphism method. Results. LOH of the CDKN2A was found in two (6%) out of 34 (85%) informative cases of our total TGCT sample. The observed changes were assigned to two (11%) nonseminomas out of 18 (82%) informative samples. Furthermore, LOH of the RB1 was detected in two (6%) out of 34 (85%) informative cases of our total TGCT sample. Once again, the observed changes were assigned to two (10.5%) nonseminomas out of 19 (86%) informative samples. Both LOHs of the CDKN2A were found in nonseminomas with a yolk sac tumor component, and both LOHs of the RB1 were found in nonseminomas with an embryonal carcinoma component. Conclusions. The higher incidence of observed LOH in nonseminomas may provide a clue to their invasive behavior.

Genetic changes of MLH1 and MSH2 genes could explain constant findings on microsatellite instability in intracranial meningioma.

Postreplicative mismatch repair safeguards the stability of our genome. The defects in its functioning will give rise to microsatellite instability. In this study, 50 meningiomas were investigated for microsatellite instability. Two major mismatch repair genes, MLH1 and MSH2, were analyzed using microsatellite markers D1S1611 and BAT26 amplified by polymerase chain reaction and visualized by gel electrophoresis on high-resolution gels. Furthermore, genes DVL3 (D3S1262), AXIN1 (D16S3399), and CDH1 (D16S752) were also investigated for microsatellite instability. Our study revealed constant presence of microsatellite instability in meningioma patients when compared to their autologous blood DNA. Altogether 38% of meningiomas showed microsatellite instability at one microsatellite locus, 16% on two, and 13.3% on three loci. The percent of detected microsatellite instability for MSH2 gene was 14%, and for MLH1, it was 26%, for DVL3 22.9%, for AXIN1 17.8%, and for CDH1 8.3%. Since markers also allowed for the detection of loss of heterozygosity, gross deletions of MLH1 gene were found in 24% of meningiomas. Genetic changes between MLH1 and MSH2 were significantly positively correlated (p = 0.032). We also noted a positive correlation between genetic changes of MSH2 and DVL3 genes (p = 0.034). No significant associations were observed when MLH1 or MSH2 was tested against specific histopathological meningioma subtype or World Health Organization grade. However, genetic changes in DVL3 were strongly associated with anaplastic histology of meningioma (χ2 = 9.14; p = 0.01). Our study contributes to better understanding of the genetic profile of human intracranial meningiomas and suggests that meningiomas harbor defective cellular DNA mismatch repair mechanisms.