Expression of the O6-methylguanine-DNA methyltransferase gene in eight human tumor cell lines.

O6-methylguanine-DNA methyltransferase (MGMT) gene expression in 6 Mer+ (HeLa S3, SMMC-7721, SGC-7901, B-239, AGZY83-a, and Cc801) and 2 Mer- (SHG-44, and HeLa MR) human tumor cell lines was examined. Southern blot analysis revealed no deletion, amplification, or rearrangement of the MGMT gene in these cell lines. However, approximately 1.0 kb transcripts were detected in the 6 Mer+ cell lines but not in the 2 Mer- cell lines by Northern blot analysis. Furthermore, a rough correlation between MGMT activity and mRNA level in these cell lines was observed. These results suggest that transcriptional regulation of the MGMT gene is the molecular basis of the absence of MGMT activity in Mer- cell lines.