Glycine N-methyltransferase is a mediator of cytochrome P4501A1 gene expression.
Cytochrome P4501A1, the isozyme most closely approximating aryl hydrocarbon hydroxylase activity under conditions of induction, is thought to be regulated by several trans-acting factors, including the 4S polycyclic aromatic hydrocarbon-binding protein; this protein has recently been identified as glycine N-methyltransferase (Raha et al. (1994) J. Biol. Chem. 269, 5750-5756). Previous studies had shown that partially purified liver preparations containing the 4S binding protein interacted with 5'-flanking regions of the cytochrome P4501A1 gene. Consequently, the ability of the 4S binding protein to serve as a mediator in the regulation of the cytochrome P4501A1 gene was investigated further. Introduction of an antisense 24-mer oligonucleotide to glycine N-methyltransferase cDNA into rat hepatoma H4IIE cells by lipofectin resulted in a 60% reduction in the benzo(a)pyrene-mediated induction of ethoxyresorufin-O-deethylase activity and protein over the sense and scrambled antisense oligonucleotide controls. In addition, the antisense oligonucleotide caused a marked reduction in the steady-state level of cytochrome P4501A1 mRNA; no such effect was observed with the sense oligonucleotide. Introduction of GNMT polyclonal antibodies into H4IIE cells by a streptolysin-O permeabilization technique markedly reduced both benzo(a)pyrene-binding and benzo(a)-pyrene-induced ethoxyresorufin-O-deethylase activities, but had no effect on 2,3,7,8-tetrachlorodibenzo-p-dioxin induction. Collectively, these findings suggest that, in addition to the Ah (dioxin) receptor, glycine N-methyltransferase appears to be both a polycyclic aromatic hydrocarbon-binding protein and a mediator of the induction of the cytochrome P4501A1 gene by polycyclic hydrocarbons such as benzo(a)pyrene.
Raha
A
A
Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755-3835, USA.
Joyce
T
T
Gusky
S
S
Bresnick
E
E
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001564:Benzo(a)pyrene / Q000494:pharmacology; D015152:Blotting, Northern; D015153:Blotting, Western; D019363:Cytochrome P-450 CYP1A1; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D050938:Glycine N-Methyltransferase; D008780:Methyltransferases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D014407:Tumor Cells, Cultured
D000906:Antibodies; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D001564:Benzo(a)pyrene; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D019363:Cytochrome P-450 CYP1A1; D008780:Methyltransferases; D050938:Glycine N-Methyltransferase; C494512:Gnmt protein, rat