IDENTIFICATION OF GLUTATHIONE-S-TRANSFERASE P-1 AS THE CLASS-PI FORM DOMINANTLY EXPRESSED IN MOUSE HEPATIC ADENOMAS

To clarify which of the two genes for pi class glutathione S-transfera ses (GSTs) (p-1 and p-2) is dominantly expressed in mouse hepatic aden omas, the relative mRNA levels were examined by means of the reverse t ranscription-polymerase chain reaction (RT-PCR), Hepatic adenomas were induced in male and female B6C3F1 mice by diethylnitrosamine treatmen t. Northern blot analysis revealed that pi class mRNA levels were decr eased in adenomas of male mice, but increased in those of females, wit h reference to the respective surrounding non-adenoma tissues, In cont rast to the marked sex difference in surrounding tissues, pi class GST mRNA levels in adenomas were almost the same in both males and female s. To evaluate p-1 and p-2 mRNA levels separately, the products of RT- PCR employing primers common for both cDNAs were digested with the end onuclease BnnI (specific for p-2) and then resolved by electrophoresis . The p-1 mRNA was thus found to be dominant in adenomas of both femal e and male mice. The p-2 mRNA levels were increased in the lesions as compared with those in the surrounding non-adenoma tissues. Recombinan t p-1 and p-2 proteins were expressed in Escherichia coli, Unlike p-1, the p-2 protein did not show any significant activity towards 1-chlor o-2,4-dinitrobenzene and did not bind to S-hexylglutathione-Sepharose despite immunological cross-reactivity, The dominant pi class form in adenomas could also be identified as p-1 by its binding to S-hexylglut athione-Sepharose. Single radial immunodiffusion analyses confirmed th at the p-1 protein levels were in line with the mRNA findings, i,e,, 1 .9+/-0.3 mg/g adenoma as compared to 6,5+/-1.2 mg/g non-adenoma tissue for males and 2.2+/-0.6 mg/g as compared to 0.7+/-0.2 mg/g for female s. The results thus indicated that the change of pi class forms in ade nomas is caused mainly by alteration in the p-1 level and the contribu tion of p-2 is minimal.