Constitutive and inducible profile of glutathione S-transferase subunits in biliary epithelial cells and hepatocytes isolated from rat liver

Abstract

The constitutive and inducible cytosolic glutathione S-transferase (EC 2.5.1.18) subunit compositions of parenchymal cells (hepatocytes) and biliary epithelial cells (BEC) from rat liver have been quantitatively analysed using reverse-phase h.p.l.c. Hepatocytes, analysed in the absence of non-parenchymal cells, expressed constitutively the following subunits, in order of their concentration: 3, 4, 2, 1a, 1b, 8, 6 and 10. BEC express constitutively only four of the GST subunits expressed by hepatocytes and these are, in order of their concentration: subunits 2, 7, 4 and 3. Notable differences from hepatocytes are that BEC completely lack the Alpha-class subunits 1a and 1b that are major subunits in hepatocytes, Mu-class subunits make up a very low proportion of the total, and the Pi-class subunit 7 is a major subunit in BEC, whereas it is essentially absent from hepatocytes. For the first time, the effects of the inducing agents phenobarbitone (PB), beta-naphthoflavone (beta-NF) and ethoxyquin (EQ) have been characterized in a comprehensive and quantitative manner in both cell types. PB, beta-NF and EQ increased total GST protein in hepatocytes by approx. 2-fold, 3-fold and 4-fold respectively. Subunits significantly induced in hepatocytes were (in order of fold-induction): by PB, 1b > 8 > 3 > 2 > 4; by beta-NF, 1b > 8 > 2 > 3 > 4; and by EQ, 7 > 1b > 10 > 8 > 3 > 2 > 1a > 4. In BEC, neither PB nor beta-NF had significant effects on the total amount of GST protein, although PB did significantly induce subunit 3 at the expense of other subunits. EQ increased total GST protein nearly 5-fold in BEC, subunits 7 and 3 being induced dramatically above constitutive levels.

Influence of glutathione S-transferase B (ligandin) on the intermembrane transfer of bilirubin. Implications for the intracellular transport of nonsubstrate ligands in hepatocytes.

“…Other investigators have shown that the presence of high intracellular concentrations of GST facilitates net uptake of nonsubstrate ligands into the hepatocyte by decreasing ligand efflux from the cell (1,12,59,60), although these observations have been challenged (61). It is notable that various xenobiotic compounds have been demonstrated to modulate GST gene expression in a host of tissues, including the liver (44,62,63). Specific evidence in support of the potential regulation of GST expression by bilirubin is derived from the finding that erythrocytes of infants with neonatal jaundice (unconjugated hyperbilirubinemia) exhibit markedly elevated GST activity as compared with nonjaundiced newborns (64).…”

HEPATIC AND EXTRAHEPATIC SYNTHESIS AND DISPOSITION OF DINITROPHENYL-S-GLUTATHIONE IN BILE DUCT-LIGATED RATS

“…GST (GST) was not detected in liver, irrespective of the treatment. Normally, only traces of this isoform are found in hepatic cytosol, mostly because of contamination with biliary epithelial cells (Parola et al, 1993). Intestinal content of the different GST classes was not …”

Intracellular balance of oxidative stress and cytoprotective molecules in damaged interlobular bile ducts in autoimmune hepatitis and primary biliary cirrhosis: In situ detection of 8‐hydroxydeoxyguanosine and glutathione‐S‐transferase‐pi

“…Among the reductive substances that protect cells from oxidative stress, glutathione is a representative endogenous cytoprotective molecule and may protect biliary epithelial cells (BECs) from ROS as part of an antioxidant system 20,21 . Glutathione‐S‐transferase (GST) generates intracellular glutathione, and GST‐pi is a major subunit of biliary epithelial GST 22 . Recently, it was reported that GST‐pi expression was markedly reduced in the damaged bile ducts of PBC patients, reflecting a reduction of intracellular glutathione 23 .…”

“…20,21 Glutathione-S-transferase (GST) generates intracellular glutathione, and GST-pi is a major subunit of biliary epithelial GST. 22 Recently, it was reported that GST-pi expression was markedly reduced in the damaged bile ducts of PBC patients, reflecting a reduction of intracellular glutathione. 23 This suggests that the intracellular imbalance of oxidative stress and the antioxidant system may lead to the bile duct damage seen in PBC patients.…”