Aberrant CYP1A1 induction: discrepancy of CYP1A1 mRNA and aryl hydrocarbon hydroxylase activity in mutant cells of mouse hepatoma line, Hepa-1.
We have isolated new benzo[a]pyrene-resistant clones, cl-21 and cl-32, of the mouse hepatoma line, Hepa-1. CYP1A1-dependent aryl hydrocarbon hydroxylase activity is not inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin or 3-methylcholanthrene in these two cell lines. However, mRNA of CYP1A1 is inducible in cl-21 and cl-32 cells, as in the wild-type cells, in spite of an undetectable level of cytosolic Ah receptor. The cl-21 cDNA of Cyp1a-1 was found to have a single mutation leading to an amino acid substitution from Leu (118) to Arg (118). However, the CYP1A1 protein band was not detected on Western immunoblots. The cDNA of cl-32 was found to have a single mutation leading to an amino acid change from Arg (359) to Trp (359). The presence of the mature protein in cl-32 was confirmed by Western blot analysis. Somatic cell hybridization experiments demonstrated that the phenotype of cl-21 and cl-32 is recessive and that these clones belong to the same complementation group. These data suggest that there may be a non-Ah receptor-mediated mechanism of CYP1A1 induction.
Kikuchi
H
H
Department of Molecular Genetics, Tohoku University, Sendai.
Usuda
M
M
Sagami
I
I
Ikawa
S
S
Watanabe
M
M
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D001483:Base Sequence; D001564:Benzo(a)pyrene / Q000494:pharmacology; D015152:Blotting, Northern; D015153:Blotting, Western; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D018076:DNA, Complementary / Q000737:chemistry; D004351:Drug Resistance; D006822:Hybrid Cells; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; D012333:RNA, Messenger; D001564:Benzo(a)pyrene; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases