Reduced Expression of Glutathione S–Transferase Yb2 During Progression of Chemically Induced Hepatocellular Carcinomas in Fischer 344 Rats

Abstract

We followed the expression of several glutathione S-transferase subunits in altered foci, liver neoplasms and metastases produced in male Fischer 344 rats by a modified Solt-Farber protocol, to determine whether components of the resistant phenotype are lost during neoplastic progression. At 6 mo after initiation, altered foci and persistent nodules displayed increased immunohistochemical expression of glutathione S-transferase subunits Yf (r-class), Ya (a-class) and Ybl (p-class) in comparison with normal or surrounding liver tissue. However, although most altered foci exhibited little change in glutathione S-transferase Yb2 (p-class) subunit expression, 5% of Yf-positive foci and nodules were partially or completely deficient in Yb2 expression. At 12 and 18 mo after initiation, most grossly visible hepatocellular tumors retained induced expression of glutathione S-transferase subunits Yf, Ya and Ybl, but 63% of the carcinomas, 88% of the primary metastatic carcinomas and 94% of the pulmonary metastases were deficient in Yb2 expression. These differences in glutathione S-transferase subunit expression were confirmed by quantitative analysis by reverse-phase HPLC of S-hexylglutathione affinitypurified glutathione S-transferases from advanced tumors. Cytosolic glutathione S-transferase activity for truns-4-phenyl-3-buten-2-one in advanced tumors ranged from 42% to 66% of the activity in matched surrounding liver, whereas glutathione S-transferase activities for l-chloro-2,4-dinitrobenzene were increased by 140% to 161%. These studies demonstrate that progression of hepatocellular carcinomas in the resistant hepatocyte model of carcinogenesis in which several glutathione S-transferase subunits are induced is associated with the loss of a major constitutive p-class hepatic glutathione S-transferase. Although the mechanism and role of the reduction or loss of glutathione S-transferase Yb2 during malignant progression are unknown, we propose that loss of glu-

Modulation of Glutathione S-Transferase Alpha by Hepatitis B Virus and the Chemopreventive Drug Oltipraz

“…Enzymatic Assays-Cytosolic extracts from the various cell lines were prepared by cell lysis and centrifugation of debris at 12,000 ϫ g for 1 h. Protein concentrations were determined according to the method of Lowry, using bovine serum albumin as the standard. Total GST activity was assayed using 2-chloro-1,3-dinitrobenzene as the substrate (43). Selenium-independent glutathione peroxidase activity was assayed using cumene hydroperoxide (44).…”

“…In malignant hepatocytes from clinical specimens, Alpha subunit expression is almost always dramatically decreased. The reduction in expression appears to parallel the cellular transformation process, because adenomas demonstrate intermediary levels of GST Alpha (42)(43)(44)(45)(46). This loss of GST protection could increase the susceptibility of preneoplastic populations of hepatocytes to further contribute to genotoxic injury by chemicals during malignant progression.…”