DNA methylation and gene expression of COX7A1, SPINT1 and KRT81 in glioblastoma and brain tissue

Abstract

Glioblastoma (GBM) is the most common primary brain tumor of the adult. Despite existing multimodal aggressive treatment regiments the prognosis of patients with GBM remains very poor. Most patients die within two years after diagnosis. Changes in individual gene expressions frequently accompany malignant cell transformation. Therefore comparative gene expression analyses of tumorous and non-tumorous tissue may help identify genes of significance in gliomagenesis. Epigenetic silencing of tumor suppressor genes is one of important mechanisms of gene inactivation during tumorigenesis. This study attempted to detect genes potentially regulated by promoter methylation in glioblastoma. To this end we analyzed the expression of COX7A1, SPINT1 and KRT81 in glioblastomas and human brain tissue and investigated their relation to promoter methylation of these genes. We based candidate gene selection on bioinformatics, reverse transcription-polymerase chain reaction (RT–PCR) and bisulfite sequencing. COX7A1, SPINT1 and KRT81 mRNA expression was analyzed in glioblastomas (n = 22) and human brain tissue (n = 2). COX7A1, SPINT1 and KRT81 promoter methylation was analyzed in selected glioblastoma samples, human brain and human lymphocytes by bisulfite sequencing. We found a differential gene expression of COX7A1, SPINT1 and KRT81 in the glioblastoma samples. Normal fetal and adult brain featured a robust expression of these genes. Analysis of bisulfite-modified DNA of brain tissue confirmed that the SPINT1 promoter had only single scattered methylated CpG- dinucleotides while the CpG- islands of the COX7A1 and KRT81 promoters were abundantly methylated in brain tissue despite robust gene expression. COX7A1 and KRT81 gene expression is independent of promoter methylation in glioblastoma. The data suggest the possibility of epigenetic regulation of SPINT1 in glioblastoma. Future work should focus on SPINT1 gene function in glial cells to substantiate its potential tumor suppressor gene function in gliomas.