Nicotinamide N-Methyltransferase inhibits HBV replication by suppressing NR5A1 expression invitro

Chronic hepatitis B virus (HBV) infection can lead to fibrosis, liver cirrhosis, and primary hepatocellular carcinoma. Investigating host factors that regulate HBV replication helps to identify antiviral targets. In the current study, we identified Nicotinamide N-Methyltransferase gene (NNMT) as a novel factor that regulates HBV transcription. NNMT is up-regulated at both the mRNA and protein levels in HepG2.2.15 cells compared to HepG2 cells. Overexpression of NNMT reduces HBV replication in several cell models, while knockdown of NNMT enhances HBV DNA levels. Mechanistically, NNMT suppresses HBV DNA replication by inhibiting HBV RNA transcription. The region required for the inhibitory effect of NNMT was narrowed to nt 1672-1708 in enhancer II by luciferase assays. On the other hand, ChIP assays and EMSA results showed that NNMT does not bind to this region substantially, either directly or indirectly. Next, a collection of hepatic nuclear receptor transcription factors was screened to determine whether they were affected by NNMT overexpression. NR5A1, a positive regulator of HBV replication, decreased significantly after NNMT overexpression. Collectively, the findings of this study shed light on the regulation of HBV transcription.

Nicotinamide N-methyltransferase protects against deoxynivalenol-induced growth inhibition by suppressing pro-inflammatory cytokine expression

Deoxynivalenol (DON) is an inevitable contaminant in cereals for infants. Indeed, children's growth retardation caused by widespread DON pollution has become a global problem that cannot be ignored. Accumulating evidence has shown that DON stunts growth in children through pro-inflammatory cytokines. An exogenous increase of methylnicotinamide, a metabolite produced by nicotinamide N-methyltransferase (NNMT), has anti-inflammatory effects, but it is not clear whether NNMT has the same effect, and the role of NNMT in DON-induced inflammation and growth impairment remains indistinct. The present research reports that NNMT is an inflammatory self-protective factor in DON-exposed L02 cells. DON promoted the production of pro-inflammatory cytokines. Furthermore, DON increased NNMT to reduce pro-inflammatory cytokines, including interleukin (IL)-1β, IL-11 and IL-6, and thus increased IGF-1 and cell viability, alleviating the cell growth inhibition induced by DON. Interestingly, NNMT negatively regulated the expression of IL-1β through Sirtuin type 1 (SIRT1). Collectively, these findings provide new mechanistic insights into the toxicity of DON-induced growth retardation and inflammatory responses in children.

Development of fluorescence polarization-based competition assay for nicotinamide N-methyltransferase

Methylation-mediated pathways play important roles in the progression of various diseases. Thus, targeting methyltransferases has proven to be a promising strategy for developing novel therapies. Nicotinamide N-methyltransferase (NNMT) is a major metabolic enzyme involved in epigenetic regulation through catalysis of methyl transfer from the cofactor S-adenosyl-l-methionine onto nicotinamide and other pyridines. Accumulating evidence infers that NNMT is a novel therapeutic target for a variety of diseases such as cancer, diabetes, obesity, cardiovascular and neurodegenerative diseases. Therefore, there is an urgent need to discover potent and specific inhibitors for NNMT to assess its therapeutical potential. Herein, we reported the design and synthesis of a fluorescent probe II138, exhibiting a K_d value of 369 ± 14 nM for NNMT. We also established a fluorescence polarization (FP)-based competition assay for evaluation of NNMT inhibitors. Importantly, the unique feature of this FP competition assay is its capability to identify inhibitors that interfere with the interaction of the NNMT active site directly or allosterically. In addition, this assay performance is robust with a Z'factor of 0.76, indicating its applicability in high-throughput screening for NNMT inhibitors.