Προσδιορισμός γενετικών αλλοιώσεων και μελέτη της έκφρασης των ογκογονιδίων Kras, Hras και Nras, των γονιδίων Akt, καθώς επίσης και της πρωτεΐνης p53 σε κακοήθεις όγκους του εγκεφάλου

Abstract

Brain tumors are intracranial solid neoplasms of abnormal grown cells, which are created either in the brain itself e.g. from neurons and glial cells (primary brain tumors) or spread from cancers primarily located in other organs (metastatic tumors). The most common brain tumors are glioblastomas and meningiomas. Even though the etiology of the formation of malignant brain tumors is still unknown, a number of genes implicated in the formation and development of tumors, has been found. Some of these genes such as the Ras, Akt and p53 genes have been investigated in this study. The purpose of the present study is to evaluate the molecular mechanisms which are involved in brain carcinogenesis. Therefore, we evaluated the mRNA expression of Ras, Akt, SDF-1, CXCR4 and p53 genes by RT-PCR in gliomas and meningiomas tissue samples and in adjacent normal specimens, derived from the same patients. The results were then correlated with the clinicopathological characteristics and survival data of the patients. Furthermore we evaluated the protein levels of Ras-p21 and we examined the correlation with their mRNA expression levels. We also examined the presence of activating mutations of the three Ras genes and p53. Our goals were: a) to determine the expression profile of the genes of interest to specify their role in malignant transformation of brain cells, b) to examine the possibility of using the expression profile of these genes as a molecular marker for the diagnosis of these malignancies in early stages. Our results show increased Kras transcript levels in normal samples, compared to glioblastomas, anaplastic and fibrillary astrocytomas, while increased Hras mRNA levels were observed in normal specimens compared to glioblastomas samples. Western blot analysis did not result in detectable levels of Ras-p21 protein in our samples. The expression profile of these genes is characterized mainly by underexpression in the three sample groups. Sequencing analysis did not detect the GGT->GTT (Gly12Val) mutation in codon 12 of the three Ras genes, in any of our samples. In Akt family genes, increased Akt-3 mRNA expression in normal samples compared to glioblastomas was observed, while Akt-1 and Akt-2 transcript levels did not show statistical differences between normal and tumor samples. The expression profile of Akt-1 and Akt-3 was characterized mainly by normal expression and underexpression, respectively. SDF-1α and CXCR4 genes were mainly overexpressed in glioblastomas. P53 transcript levels did not show any statistical difference between the sample groups. Sequencing analysis did not detect the CGTTGT (Arg273Cys) of the p53 gene, in any of our samples. Kaplan-Meier survival analysis in glioblastomas revealed that patients who overexpressed p53 gene, had decreased survival compared to those that normally expressed it. In meningiomas, Kras, Nras, Akt-2 θαη p53 transcript levels were increased compared to normal tissues. The GGT→GTT (Gly12Val) mutation in Ras genes was not detected in any of our samples. In Akt family genes, meningiomas were found to have elevated Akt-2 mRNA levels compared to normal samples. The GGT→GTT (Gly12Val) mutation in Ras genes and the CGTTGT (Arg273Cys) mutation of the p53 gene were not detected in any of our samples. Our results in gliomas and meningiomas indicate that different activation mechanisms prevail in malignant transformation of brain cells in each type of cancer.