Increased Bax expression is associated with cell death induced by ganciclovir in a herpes thymidine kinase gene-expressing glioma cell line

The herpes simplex virus thymidine kinase gene (HSV-tk) was stably transfec ted into rat C6 glioma cells (C6tk) in order to characterize the mechanisms underlying cell toxicity induced in vitro by the guanosine analog ganciclo vir (GCV), The results demonstrate the efficiency of the HSV-tk/GCV system in ablating most of the tumoral cells within 7 to 8 days of treatment with 20 mu M GCV; however, a few cells still survive. C6tk cells arrest in the S phase of the cell cycle after 2 days of drug treatment before undergoing c ell death, Microscopic analysis reveals dying cells with ultrastructural ch aracteristics consistent with apoptosis; we cannot rule out, however, that necrotic cell death may also be occurring. The cytotoxicity induced by GCV is not associated with changes in the expression of p53 protein, suggesting that cell cycle arrest and cell death may occur through a p53-independent pathway. C6tk cells constitutively express Bcl-xL and Bar proteins; when ex posed to GCV, Bcl-xL levels do not change but Bar accumulation is rapidly i nduced. These findings suggest that the balance between Bcl-xL and Bar prot eins may be of importance in determining the sensitivity of tumoral cells t o GCV.