COMPARISON OF THE MESSENGER-RNA SEQUENCES FOR PI-CLASS GLUTATHIONE TRANSFERASES IN DIFFERENT HAMSTER SPECIES AND THE CORRESPONDING ENZYME-ACTIVITIES WITH ANTI-BENZO[A]PYRENE-7,8-DIHYDRODIOL 9,10-EPOXIDE

Glutathione S-transferase (GST) of class Pi (GST Pi) is known to detox ify the mutagenic and carcinogenic (+)-anti-benzo[a]pyrene-7,8-dihydro diol 9,10-epoxide [(+)-anti-BPDE] by conjugation glutathione. Previous ly, we have shown Chinese hamster V79 cells contain GST Pi, but seem t o lack the capacity to conjugate(+)-anti-BPDE, although these cells do conjugate other substrates with GSH [Romert, Dock, Jenssen and Jernst rom (1989) Carcinogenesis 10, 1701-1707; Swedmark, Romert, Morgenstern and Jenssen (1992) Carcinogenesis 13, 1719-1723; Swedmark and Jenssen (1994) Gene 139, 251-256]. In the present study we have compared four cell lines derived from different hamster species with respect to GST cDNA sequences and capacity to conjugate(+)- or (-)-anti-BPDE. The ce ll lines were V79 and Chinese hamster ovary cells (CHO), Armenian hams ter lung (AHL) cells and baby hamster kidney (BHK) cells. The sequenci ng revealed a complete homology between the V79 and CHO cDNA for GST P i, whereas the corresponding amino acid sequences predicted from the c orresponding AHL and BHK cDNAs differed by six and nine amino acids, r espectively, from the predicted V79 sequence. None of these changes al one was found to influence the xenobiotic substrate-binding site. The cytosolic fractions from BHK and AHL cells were found to catalyse conj ugation of (+)-anti-BPDE with GSH, whereas the corresponding activity in CHO cells was non-detectable. As shown previously, V79 cells were d evoid of activity towards (+)-anti-BPDE. All the cell lines studied de monstrated appreciable GST activity towards 1-chloro-2,4-dinitrobenzen e, but no activity with (-)-anti-BPDE. The latter result suggests that GST Pi is the sole or predominant GST in these cell lines, This was c onfirmed by HPLC analysis of purified enzymes obtained by affinity chr omatography, However, when the catalytic activities of the pure enzyme s were determined, all four different GST Pi enzymes were found to be highly capable of conjugating (+)-anti-BPDE with GSH. This observation indicates the existence of an intracellular factor that selectively i nhibits conjugation of (+)-anti-BPDE, but not of 1-chloro-2,4-dinitrob enzene in the V79 and CHO cell lines. This new phenomenon seems to be specific for Chinese hamster, since both these cell lines originate fr om this species.