Overexpression of gamma-glutamylcysteine synthetase in human malignant mesothelioma.
Mesothelioma is a fatal tumor resistant to all treatment modalities for reasons that are still unresolved. Glutathione (GSH)-associated pathways are induced by oxidants and cytotoxic drugs, and they are also involved in the progression and resistance of some tumor cells in vitro. The rate-limiting enzyme in GSH biosynthesis is gamma-glutamylcysteine synthetase (gamma GCS). However, the expression of this enzyme has not been systematically investigated in malignant tumors, and there are no studies of gamma GCS in biopsy specimens of malignant mesothelioma. We investigated the immunohistochemical distribution and expression of both subunits of gamma GCS in healthy pleural mesothelium, pleural mesothelioma tumor biopsy samples (34 cases), and mesothelioma cells in culture (7 cell lines). Nonmalignant mesothelium showed no immunoreactivity for either subunit in any of the cases. The heavy (catalytic) subunit of gamma GCS was highly immunostained in 29 and weakly positive in 5 cases. High-moderate and weak immunoreactivity of the light (regulatory) subunit of gamma GCS was found in 15 and 7 tumors, respectively, whereas 12 cases showed no reactivity. There was no correlation with either catalytic or regulatory subunit expression and patient survival. There was, however, a significant correlation between the heavy chain and multidrug resistance protein (MRP) 2 (P =.048), whereas no correlation was observed between the light chain and MRP1 or MRP2. Treatment of cultured mesothelioma cells with buthionine sulfoximine (BSO), to inhibit gamma GCS, significantly potentiated cisplatin-induced cytotoxicity mainly by nonapoptotic mechanism when assessed by counting the living cells, TUNEL (terminal deoxytransferase-mediated dUTP nick-end labeling) assay, and caspase-3 cleavage. In conclusion, gamma GCS is highly positive in most cases of malignant mesothelioma and may play an important role in the primary drug resistance of this tumor in vivo.
Department of Internal Medicine, University of Oulu, Helsinki, Finland.
Kristiina
K
Järvinen
Ylermi
Y
Soini
Katriina
K
Kahlos
Vuokko L
VL
Kinnula
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002455:Cell Division; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology; D004151:Dipeptides / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D007124:Immunoenzyme Techniques; D020287:In Situ Nick-End Labeling; D008297:Male; D026901:Membrane Transport Proteins; D008654:Mesothelioma / Q000201:enzymology* / Q000473:pathology; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism; D010994:Pleura / Q000201:enzymology; D010997:Pleural Neoplasms / Q000201:enzymology* / Q000473:pathology; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D019328:Buthionine Sulfoximine; D002945:Cisplatin; D004151:Dipeptides; D004791:Enzyme Inhibitors; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C000715087:ABCC2 protein, human; C017341:gamma-glutamylcysteine; C421109:multidrug resistance-associated protein 1