NNMT
Description
The NNMT (nicotinamide N-methyltransferase) is a protein-coding gene located on chromosome 11.
Nicotinamide N-methyltransferase (NNMT) is an enzyme that in humans is encoded by the NNMT gene. NNMT catalyzes the methylation of nicotinamide and similar compounds using the methyl donor S-adenosyl methionine (SAM-e) to produce S-adenosyl-L-homocysteine (SAH) and 1-methylnicotinamide.
== Function == Methylation of nicotinamide by NNMT and SAM-e is the major pathway for degradation of nicotinamide leading to excretion in the urine.
== Clinical significance == NNMT is highly expressed in the human liver. N-methylation is one method by which drug and other xenobiotic compounds are metabolized by the liver. NNMT expression in adipose tissue is associated with obesity and insulin resistance. Contrary to the negative effects of increased NNMT in adipose tissue, increased NNMT in liver is associated with a better metabolic profile, namely reduced serum triglycerides and free fatty acids. In adipose tissue, NNMT can lead to methylation depletion, whereas because of the many methylation enzymes in the liver NNMT has a negligible effect on liver methylation. But in the liver, the 1-methylnicotinamide produced by NNMT degradation of nicotinamide increases sirtuin 1 (SIRT1) by inhibiting degradation of that protein. Overexpression of SIRT1 in mice has been shown to reduce insulin and fasting glucose, as well as increased metabolism and physical function.
Catalyzes the N-methylation of nicotinamide using the universal methyl donor S-adenosyl-L-methionine to form N1-methylnicotinamide and S-adenosyl-L-homocysteine, a predominant nicotinamide/vitamin B3 clearance pathway (PubMed:8182091, PubMed:21823666, PubMed:23455543). Plays a central role in regulating cellular methylation potential, by consuming S-adenosyl-L-methionine and limiting its availability for other methyltransferases. Actively mediates genome-wide epigenetic and transcriptional changes through hypomethylation of repressive chromatin marks, such as H3K27me3 (PubMed:26571212, PubMed:23455543, PubMed:31043742). In a developmental context, contributes to low levels of the repressive histone marks that characterize pluripotent embryonic stem cell pre-implantation state (PubMed:26571212). Acts as a metabolic regulator primarily on white adipose tissue energy expenditure as well as hepatic gluconeogenesis and cholesterol biosynthesis. In white adipocytes, regulates polyamine flux by consuming S-adenosyl-L-methionine which provides for propylamine group in polyamine biosynthesis, whereas by consuming nicotinamide controls NAD(+) levels through the salvage pathway (By similarity). Via its product N1-methylnicotinamide regulates protein acetylation in hepatocytes, by repressing the ubiquitination and increasing the stability of SIRT1 deacetylase (By similarity). Can also N-methylate other pyridines structurally related to nicotinamide and play a role in xenobiotic detoxification (PubMed:30044909). {ECO:0000250|UniProtKB:O55239, ECO:0000269|PubMed:21823666, ECO:0000269|PubMed:23455543, ECO:0000269|PubMed:26571212, ECO:0000269|PubMed:30044909, ECO:0000269|PubMed:31043742, ECO:0000269|PubMed:8182091}
NNMT is also known as -.
