Loss of glutathione S-transferase (GST) μ phenotype in colorectal adenocarcinomas from patients with a GSTM1 positive genotype

Glutathione S-transferase (GST) μ phenotype was assessed in colon tissue from patients with ulcerative colitis and colorectal neoplasms that were positive for GSTM1 genotype. GST μ protein (enzyme linked immunosorbent assay) was absent in 2/9 unaffected colon tissue (22.3%), 4/13 tissues with chronic ulcerative colitis (CUC) (30.7%), 4/11 adenomas (36.4%) and 7/14 adenocarcinomas (50.0%; P≤0.05). GST-3H-trans-stilbene oxide activity was detected in all tissues except 1/13 (7.6%) CUC tissues and 7/14 (50.0%, P≤0.05) colorectal adenocarcinomas. Immunoreactive GST μ was observed in colonic epithelial cells but not in adjacent neoplastic cells by immunohistochemistry. Two-dimensional electrophoresis revealed several μ class isoforms in cytosol from unaffected colon that were absent in matched tumor cytosol. These results indicate that GSTM1 genotype may not necessarily reflect GST μ phenotype in colorectal tumors.