Investigation of loh and methylation profiles of the ARHI tumour supressor gene in glial tumours

Although the ARHI gene, which is localized in the 1p31 chromosomal region, shows 60% homology to the Ras protooncogene, it is the first tumor supressor gene defined in the Ras family. The maternally silenced ARHI gene that is expressed only from the paternal allele, is known to be constitutively expressed in primarily the normal breast and ovarian tissues, and in normal heart, liver, pancreas, and brain tissues also. Studies have revealed reduction in the ARHI gene expression in 70 to 80% of the breast and ovarian cancers. It is not known yet whether the ARHI gene plays a role in the development of the glial brain tumors or not. This study aimed detection of the role of ARHI gene, which is expressed in the normal brain tissue, in development of the glial brain tumors. In the study, tumor and peripheral blood samples of 21 cases with glial tumor, and normal brain tissue samples obtained from 7 autopsies were investigated. Evaluation of the ARHI gene expression levels by Real time RT-PCR revealed decrease in 7 (33.3%) of the 21 glial tumor samples. Analysis of loss of heterozygosity, which is one of the mechanisms that can lead to decrease in expression, was performed by fragment analysis using 5 labeled polymorphic markers localized in the 1p31 region, namely D1S207, D1S226, D1S430, D1S488, and D1S2638. LOH was detected in 2 (9.5%) of the 21 cases, who were included in the 7 cases who were found to reveal a decrease in the ARHI gene expression by real time RT-PCR. Methylation status, which is another mechanism that can lead to decrease in the ARHI expression, was investigated in the tumor DNA samples of the remaining 5 cases. Studies performed revealed 3 different CpG islands in the promotor region of the ARHI gene, where the CpG region II had the highest relation with the gene expression loss. Thus, the methylation profiles of the CpG region II in these 5 cases were investigated by COBRA technique and restriction enzyme analysis. Evaluation of the results revealed no methylation in the CpG island region II located in the promotor of the ARHI gene in any of the 5 cases studied. Our results revealed that decrease in the ARHI tumor supressor gene expression may play a role in the glial brain tumor development, and that loss of heterozygosity can be one of the mechanisms responsible for this reduction in the ARHI gene expression. Key Words: Glial brain tumors ARHI, LOH, methylation