© 1984 Oxford University Press
research-article |
Characterization, localization and regulation of a novel phenobarbital-inducible form of cytochrome P450, compared with three further P450-isoenzymes, NADPH P450-reductase, glutathione transferases and microsomal epoxide hydrolase
1Imperial Cancer Research Fund, Medical Oncology Unit Edinburgh, UK
2Institute of Toxicology, University of Mainz D-6500 Mainz, FRG
3Institute of Biochemistry, German Cancer Research Centre D-6500 Mainz, FRG
4Author to whom correspondence should be addressed.
Two cytochromes P450 (PB1 and PB2) have been isolated from the livers of rats treated with phenobarbital. PB2 (mol. wt. 53 500) is novel and is the first example of a phenobarbital-inducible enzyme with a Soret peak at 447 nm. Using an enzyme-linked immunosorbent assay, some immunochemical and structural similarities were observed between these cytochromes. PB1 and PB2 were induced by phenobarbital, Aroclor 1254, trans-stilbene oxide and to a lesser extent by isosafrole. Immunohistochemical localization of these proteins in the liver of untreated rats showed PB1 to be localized in a large area and PB2 in a narrow range of cells around the central vein. This demonstrates the heterogeneity of hepato-cytes even within the centrilobular area and indicates that the synthesis of these two proteins is regulated differently although both are induced by the same agent, phenobarbital. Two 3-methylcholanthrene inducible cytochromes MC1 (mol. wt. 54 500) and MC2 (mol. wt. 57 000) were present at very low levels, MC2 mostly in the periportal region but also diffusely distributed throughout the lobule including some centrilobular cells, MC1concentrated in the centrilobular region. The localization of two major groups of glutathione transferases (GST's) was also different. ‘C’ type proteins (Yb Yb') and microsomal epoxide hydrolase (EH), were concentrated around the central vein, whereas the ‘B’ type proteins (Ya Yc) and cytochrome P450 reductase were distributed in a larger area of this region. Thus, the localization was different for some members of the same enzyme family, whilst similarities in the localization existed across the border of the families: (1) PB2, MC1, EH and GST ‘C’ type proteins were concentrated in a narrow area around the central vein; (ii) PB1 and GST ‘B’ type proteins occupied a large centrilobular area; (iii) MC2 levels were very low, predominantly periportal but also diffusely distributed throughout the lobule. Treatment of the animals with inducers increased the staining intensity and in several cases extended the areas of cells containing these proteins over the adjacent zone without fundamentally altering their distributions. However, treatment with ß-naphthoflavone led to a shift of MC1 to the peri-portal area. This suggests that the expression of these proteins in certain cells is not an irreversible quality of differentiation but depends on the degree of suppression and derepression of regulatory components. The differences in the localization between the predominantly detoxifying enzymes EH and GST's and the cytochromes P450 which are frequently involved in the activation of carcinogens in all likelihood represent an important factor in the susceptibility of certain regions to chemical carcinogens, although it must be kept in mind that the method allows detection of immunoreactive protein but not that of enzyme activity.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  A. Braeuning, R. Sanna, J. Huelsken, and M. Schwarz Inducibility of Drug-Metabolizing Enzymes by Xenobiotics in Mice with Liver-Specific Knockout of Ctnnb1 Drug Metab. Dispos., May 1, 2009; 37(5): 1138 - 1145. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. J. Henderson, D. M. E. Otto, D. Carrie, M. A. Magnuson, A. W. McLaren, I. Rosewell, and C. R. Wolf Inactivation of the Hepatic Cytochrome P450 System by Conditional Deletion of Hepatic Cytochrome P450 Reductase J. Biol. Chem., April 4, 2003; 278(15): 13480 - 13486. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 O. Dohr, M. J. I. Paine, T. Friedberg, G. C. K. Roberts, and C. R. Wolf Engineering of a functional human NADH-dependent cytochrome P450 system PNAS, January 2, 2001; 98(1): 81 - 86. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Mino, J. Watanabe, and S. Kanamura Effect of 3-Methylcholanthrene Administration on Expression of Cytochrome P-450 Isoforms Induced by Phenobarbital in Rat Hepatocytes J. Histochem. Cytochem., October 1, 1998; 46(10): 1151 - 1160. [Abstract] [Full Text]
|
|
|
|
|
|
K. G. Mendelson, L.-R. Contois, S. G. Tevosian, R. J. Davis, and K. E. Paulson Independent regulation of JNK/p38 mitogen-activated protein kinases by metabolic oxidative stress in the liver PNAS, November 12, 1996; 93(23): 12908 - 12913. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Campbell, F Carlotti, P. Hall, A. Clark, and C. Wolf Regulation of the CYP1A1 promoter in transgenic mice: an exquisitely sensitive on-off system for cell specific gene regulation J. Cell Sci., January 11, 1996; 109(11): 2619 - 2625. [Abstract] [PDF]
|
|
|
|
 |
|
 H. Kraul, M. Pasanen, H. Sigusch, F. Stenback, S-S. Park, H. Gelboin, and O. Pelkonen Immunohistochemical properties of dipyrone-induced cytochromes P450 in rats Human and Experimental Toxicology, January 1, 1996; 15(1): 45 - 50. [Abstract] [PDF]
|
|