Transfection of a human glioblastoma cell line with liver-type glutaminase (LGA) down-regulates the expression of DNA-repair gene MGMT and sensitizes the cells to alkylating agents

O6-methylguanine-DNA methyltransferase (MGMT) is a DNA-repair protein promoting resistance of tumor cells to alkylating chemotherapeutic agents. Glioma cells are particularly resistant to this class of drugs which include temozolomide (TMZ) and carmustine (BCNU). A previous study using the RNA microarray technique showed that decrease of MGMT mRNA stands out among the alterations in gene expression caused by the cell growth-depressing transfection of a T98G glioma cell line with liver-type glutaminase (LGA) [Szeliga et al. (2009) Glia, 57, 1014]. Here, we show that stably LGA-transfected cells (TLGA) exhibit decreased MGMT protein expression and activity as compared with non-transfected or mock transfected cells (controls). However, the decrease of expression occurs in the absence of changes in the methylation of the promoter region, indicating that LGA circumvents, by an as yet unknown route, the most common mechanism of MGMT silencing. TLGA turned out to be significantly more sensitive to treatment with 1001000 mu M of TMZ and BCNU in the acute cell growth inhibition assay (MTT). In the clonogenic survival assay, TLGA cells displayed increased sensitivity even to 10 mu M TMZ and BCNU. Our results indicate that enrichment with LGA, in addition to inhibiting glioma growth, may facilitate chemotherapeutic intervention.