Transcriptional activation of the glutathione S-transferase pi gene in human ureteric and bladder carcinomas

Glutathione S-transferase activity and subunit composition in transitional cell cancer and mucosa of the human bladder

OBJECTIVES

Clinical data indicate that drug resistance to chemotherapy may occur in all stages of transitional cell cancer (TCC). Glutathione S-transferases (GSTs) are a family of detoxification enzymes composed of four different classes, denoted alpha (GSTA), mu (GSTM), pi (GSTP), and theta (GSTT), each containing one or more homo- or heterodimeric isoforms (GSTA1-1, GSTA1-2, and so forth), GSTs play a prominent role in drug detoxification and have been associated with resistance of tumor cells to anticancer agents. GST activity and isoenzyme levels were studied in TCC and normal bladder mucosa.

METHODS

Enzyme activity was studied in samples of TCC (n = 37), adjacent normal bladder mucosa (n = 37), and in bladder mucosa of control patients without TCC (n = 46). GST isoenzyme composition was studied in mucosa and TCC of 14 patients and 11 controls.

RESULTS

The mucosa of patients with TCC showed GST activity (191 +/- 21 nmol/min/mg cytosolic protein), similar to the mucosa of controls (176 +/- 15 nmol/min/mg). GST activity was significantly increased in TCC (666 +/- 157 nmol/min/mg) in comparison with adjacent mucosa (P < 0.003). In mucosa samples, the levels of GSTA (A1-1, A1-2, and A2-2) were below the detection limit in 92% of the samples. GSTM (GSTM1-1) was found in 9 controls and in 7 patients with TCC but not in the other 7 patients, whereas GSTP (GSTP1-1) could be detected in all samples. The levels of GSTM1-1 and GSTP1-1 were similar in mucosa of patients and controls. The mean relative increase of GSTP1-1 levels in TCC was 4.6-fold (P < 0.002). In the 7 patients with GSTM1-1-detectable expression in adjacent normal mucosa, mean GSTM1-1 levels in TCC were increased 2.8-fold compared with mean levels in normal adjacent mucosa (P < 0.02). GSTA was measured in five samples of TCC at relatively low levels.

CONCLUSIONS

Overexpression of GSTP1-1 and GSTM1-1 may suggest that in the process of TCC carcinogenesis, a selection pressure occurs, resulting in a tumor with enhanced detoxification properties, including that of therapeutic drugs.

Glutathione S-transferases in human testicular germ cell tumors: changes of expression and activity

Glutathione S-transferases are involved in the detoxification of carcinogens and xenobiotics and are potentially associated with the development of drug-resistance. Forty-six testicular germ cell tumors and 33 adjacent normal testicular tissue specimens were analyzed at the RNA level for the expression of glutathione S-transferase alpha and pi. Glutathione S-transferase alpha was expressed in 31 of the 33 normal testicular tissues (94%) but in only three of the 46 germ cell tumors (7%). Glutathione S-transferase pi mRNA was detected in all normal and malignant testicular tissue samples. Thirteen testicular germ cell tumors and eight normal testicular tissue samples were analyzed at the protein level. The mean specific activity of total cytosolic glutathione S-transferase in tumor tissue was decreased by about 80% as compared to normal testicular tissue. Protein analysis of the glutathione S-transferase subunits of normal testicular tissue demonstrated the presence of the glutathione S-transferase classes alpha, mu and pi, with a predominance of the mu class. In testicular germ cell tumors the glutathione S-transferase subunit pattern showed a predominance of glutathione S-transferase pi representing 88% +/- 3% of total glutathione S-transferase. Since all three glutathione S-transferase isoenzyme classes contribute to the resistance to antineoplastic drugs, the altered glutathione S-transferase isoenzyme pattern and the decrease of glutathione S-transferase activity may play a role in the high inherent drug sensitivity of human testicular germ cell tumors.

Glutathione S-transferases in normal and malignant human colon tissue

This study focuses on the GST composition of a tissue intrinsically resistant to chemotherapy, the human colon. GSTs were purified from matched pairs of colon tissue (normal and tumor) using glutathione affinity chromatography. The mean GST activity of colon tumors was 1.5-fold higher than that of normal tissue, with tumors of the sigmoid colon showing the greatest increase (2.3-fold). Two-dimensional gel electrophoresis and Western blot analysis of purified enzymes demonstrated the presence of all three GST classes (alpha, mu and pi) in colon, with GST pi being both the predominant isozyme in normal and malignant tissues. The level of alpha class subunits was the same in normal and tumor tissues, while the mu class subunits were decreased in tumors. A protein copurifying with GSTs from both normal and tumor tissue did not crossreact with GST antibodies, but instead reacted with a polyclonal antibody to glyoxylase I. This enzyme existed as a dimer in its native state. Upon boiling, monomeric subunits were produced with a molecular mass of 22.6 kDa and an isoelectric point more acidic than GST pi. Increased amounts of glyoxylase I were also found in tumor vs. normal colon. The apparent elevated levels of these glutathione-associated detoxifying enzymes in colon tumors may contribute to their intrinsic drug resistance.

Observations on the transcriptional activity of the glutathione S-transferase pi gene in human haematological malignancies and in the peripheral leucocytes of cancer patients under chemotherapy

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