The Homodimeric Form of Glycine N-Methyltransferase Acts as a Polycyclic Aromatic Hydrocarbon-Binding Receptor

Abstract

In the rat, cytochrome P4501A1 gene expression is thought to be regulated by several trans-acting factors including the 4S polycyclic aromatic hydrocarbon (PAH)-binding protein, which was recently identified as glycine N-methyltransferase [Raha, A., Wagner, C., MacDonald, R. G., and Bresnick, E. (1994) J. Biol. Chem. 268, 5750-5756]. Glycine N-methyltransferase (GNMT) is one of those unique proteins which exhibit diversity in function. Different subunit configurations are involved in its enzymatic role as a methyltransferase and as PAH-binding receptor. Here we report a systematic study of the oligomeric state of GNMT in the presence of benzo[a]pyrene (B[a]P) in vivo and in vitro. We have used chemical cross-linking and denaturing polyacrylamide gel electrophoresis to show that the B[a]P-binding unit of GNMT is a homodimer. We recently reported that phosphorylation is involved in the interaction of B[a]P with the 4S PAH-binding protein [Bhat, R., Weaver, J. A., Wagner, C., Bodwell, J. E., and Bresnick, E. (1996) J. Biol. Chem. 271, 32551-32556]. In the present study, this observation has been amplified by using bacterially expressed GNMT, which was post-translationally modified by a reticulocyte lysate and ATP-generating system. This modification was also accompanied by the formation of homodimers in the presence of B[a]P. These results indicate that post-translational modification is involved in determining the final configuration, i.e., dimeric form, of GNMT which then acts as a PAH-binding receptor.

Functional Characterization of Glycine N-Methyltransferase and Its Interactive Protein DEPDC6/DEPTOR in Hepatocellular Carcinoma

“…It regulates the ratio of S-adenosylmethionine to S-adenosylhomocysteine and serves as a folate binding protein (12,13). In addition, GNMT binds carcinogens such as polyaromatic hydrocarbons and aflatoxins and prevents the deoxyribonucleic acid (DNA) adduct formation and cytotoxicity induced by these carcinogens (14)(15)(16). Diminished levels of GNMT were observed in both human HCC cell lines and tumor tissues (17,18).…”

Haplotypes, Loss of Heterozygosity, and Expression Levels of Glycine N-Methyltransferase in Prostate Cancer

“…GNMT, which is primarily expressed in cell cytoplasm (6,9,20), is a polycyclic aromatic hydrocarbon-binding protein (27). Previously, we and other groups showed that if the cells were treated with benzo(a)pyrene, GNMT will be translocated into the nuclei (8,28,29). Because cigarette smoking has been identified as a possible prostate cancer risk factor and GNMT inhibits benzo(a)pyrene-7,8-diol-9,10-epoxide-DNA adduct formation (8), the GNMT expression in the prostate may exert a protective effect for individuals exposed to benzo(a)pyrene and its down-regulation may be an early sign for prostate cancer carcinogenesis.…”

Glycine N -Methyltransferase Tumor Susceptibility Gene in the Benzo( a )pyrene-Detoxification Pathway

“…Preliminary data from our real-time PCR analysis showed that after BaP treatment, CYP1A1 gene expression was reduced by approximately 20% in SCG2-1-1 cells compared with HepG2 cells. 5 Previous research has shown that the tetrameric form of rat GNMT acts as an enzyme and that the dimeric form of rat GNMT is capable of binding with polycyclic aromatic hydrocarbons (39). In this study, we used LGA and a scoring function for estimating binding-related free energy change to locate possible sites for interactions between BaP and various forms of GNMT; we used X-ray crystallography data for rat GNMT for this purpose.…”