Utilizing proteomic approach to identify nuclear translocation related serine kinase phosphorylation site of GNMT as downstream effector for benzo[a]pyrene

Utilizing proteomic approach to identify nuclear translocation related serine kinase phosphorylation site of GNMT as downstream effector for benzo[a]pyrene

Glycine N-methyltransferase (GNMT) protein is highly expressed in certain tissues, such asliver, pancreas, and prostate. GNMT serves multiple roles which include a methyl grouptransfer enzyme and a liver tumor suppressor. Benzo(a)pyrene (BaP), a family member ofpolycyclic aromatic hydrocarbon (PAH), is a known environmental carcinogen found incoal tar, tobacco smoke, barbecued food and incomplete combustion of auto fuel. BaP recruitscytochrome P450 to transform itself into benzo(a)pyrene-7,8-diol-9,10-epoxide (B(a)PDE), which covalently interacts with DNA causing tumorigenesis. BaP can be detoxifiedthrough GNMT and induces GNMT translocation into the cellular nucleus. GNMT translocationis accompanied by phosphorylation, but the role of phosphorylation in GNMTremains to be explored. Using liquid chromatography coupled with tandem mass spectrometry,this study identified serine 9 of GNMT as the phosphorylation site upon BaPtreatment. When serine 9 was mutated and lost the capability to be phosphorylated, theoccurrence of BaP-induced GNMT nuclear translocation was dramatically decreased. Also,this mutant from of GNMT lost the ability of phosphorylation and increased cytochromeP450 1A1 (Cyp1a) expression upon BaP treatment. In addition, protein kinase C (PKC) and c- Jun NH2-terminal kinase (JNK) may be required for such phosphorylation. Further characterizationof phosphorylated GNMT for its link to BaP may bring new insights intochemical detoxification.