Characterization of nicotinamide methyltransferase in livers of mice bearing Ehrlich ascites tumors: preferential increase of activity

Methylosystem for Cancer Sieging Strategy

As cancer is a genetic disease, methylation defines a biologically malignant phenotype of cancer in the association of one-carbon metabolism-dependent S-adenosylmethionine (SAM) as a methyl donor in each cell. Methylated substances are involved in intracellular metabolism, but via intercellular communication, some of these can also be secreted to affect other substances. Although metabolic analysis at the single-cell level remains challenging, studying the "methylosystem" (i.e., the intercellular and intracellular communications of upstream regulatory factors and/or downstream effectors that affect the epigenetic mechanism involving the transfer of a methyl group from SAM onto the specific positions of nucleotides or other metabolites in the tumor microenvironment) and tracking these metabolic products are important research tasks for understanding spatial heterogeneity. Here, we discuss and highlight the involvement of RNA and nicotinamide, recently emerged targets, in SAM-producing one-carbon metabolism in cancer cells, cancer-associated fibroblasts, and immune cells. Their significance and implications will contribute to the discovery of efficient methods for the diagnosis of and therapeutic approaches to human cancer.

Expression of nicotinamide N-methyltransferase in hepatocellular carcinoma is associated with poor prognosis

BACKGROUND

Hepatocellular carcinoma (HCC) is the most common tumor in the adult liver, with high relapse and mortality rates despite diverse treatment modalities. In this study, nicotinamide N-methyltransferase (NNMT), a key enzyme in drug metabolism, was investigated as a potential prognostic factor.

METHODS

Frozen tumors and non-cancerous surrounding tissues from 120 patients with primary HCC were studied. Expressions of NNMT and internal control genes were measured by real-time reverse-transcription PCR (RT-PCR). The relationship of NNMT mRNA level with clinicopathologic parameters and clinical outcome was evaluated.

RESULTS

NNMT mRNA level is markedly reduced in HCCs compared to non-cancerous surrounding tissues (P < 0.0001), and NNMT expression in tumors was significantly correlated with tumor stage (P = 0.010). Moreover, stratification of patients based on tumor NNMT mRNA levels revealed that the patients who expressed higher NNMT mRNA levels tended to have a shorter overall survival (OS) time (P = 0.053) and a significantly shorter disease-free survival (DFS) time (P = 0.016). Both NNMT expression (P = 0.0096) and tumor stage (P = 0.0017) were found to be significant prognostic factors for DFS in a multivariate analysis.

CONCLUSION

The results of this study indicated that NNMT gene expression is associated with tumor stage and DFS time in HCC cases. Because of the broad substrate specificity of NNMT, which could alter the efficacy and adverse effects of chemotherapy, NNMT merits further investigation regarding its role as a prognostic factor with a larger cohort of HCC patients.

Histone deacetylase inhibitor depsipeptide represses nicotinamide N-methyltransferase and hepatocyte nuclear factor-1beta gene expression in human papillary thyroid cancer cells

Nicotinamide N-methyltransferase (NNMT) catalyzes N-methylation of nicotinamide and other structural analogues. NNMT gene expression is enhanced in many papillary thyroid cancer cells and activated by hepatocyte nuclear factor (HNF)-1beta. In this work, we studied the effects of depsipeptide, a histone deacetylase inhibitor, on NNMT gene expression in BHP 18-21 papillary thyroid cancer cells. Depsipeptide reduced NNMT mRNA level in a dose-dependent and time-dependent manner as determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In contrast, expression of the sodium iodide symporter (NIS), a gene with differentiated function, waas enhanced in the treated cells. NNMT protein level determined by Western blot analysis and NNMT catalytic activity was also reduced significantly in the depsipeptide-treated cells. To study the mechanism of NNMT gene repression by depsipeptide, effects of depsipeptide on NNMT promoter activity were determined by luciferase reporter gene assay. NNMT promoter activity was significantly reduced in the HNF-1beta-positive BHP 18-21 cells but not in the HNF-1beta-negative BHP 14-9 papillary cancer cells. A mutant reporter construct with mutations in a HNF-1 site in the NNMT basal promoter region did not respond to depsipeptide in both HNF-1beta protein levels, and abolished activity of DNA binding to the HNF-1 site in the NNMT promoter region. Protein synthesis inhibitor cycloheximide and proteasome inhibitor MG-132 enhanced HNF-1beta stability in the depsipeptide-treated cells. In summary, depsipeptide represses NNMT and HNF-1beta gene expression in some papillary thyroid cancer cells. the repression of NNMT by depsipeptide is at the transcription level through downregulation of transcription activator HNF-1beta.

Activation of nicotinamide N-methyltransferase gene promoter by hepatocyte nuclear factor-1beta in human papillary thyroid cancer cells

We previously demonstrated that the human nicotinamide N-methytransferase (NNMT) gene was highly expressed in many papillary thyroid cancers and cell lines. The expression in other papillary and follicular cancers or cell lines and normal thyroid cells was low or undetectable. To gain an understanding of the molecular mechanism of this cell-specific expression, the NNMT promoter was cloned and studied by luciferase reporter gene assay. The promoter construct was expressed highly in papillary cancer cell lines, including those with higher (e.g. BHP 2-7) and lower (e.g. BHP 14-9) NNMT gene expression, and expressed weakly in follicular thyroid cancer cell lines. Further study with 5'-deletion promoter construct suggested that the NNMT promoter was regulated differently in BHP 2-7 and BHP 14-9 cells. In BHP 2-7 cells, promoter activity was dependent on an upstream sequence. In BHP 14-9 cells, sequence in the basal promoter region contributed notably to the overall promoter activity. RT-PCR or Western blot analysis indicated that hepatocyte nuclear factor-1beta (HNF-1beta) was expressed in only papillary cancer cell lines with high NNMT gene expression. HNF-1beta was not expressed or expressed very weakly in other papillary, follicular, and Hurthle cancer cell lines and primary cultures of normal thyroid cells and benign thyroid conditions. A HNF-1 binding site was identified in the NNMT basal promoter region. Mutations in this site decreased NNMT promoter activity in the HNF-1beta-positive BHP 2-7 cells, but not in the HNF-1beta-negative BHP 14-9 cells. HNF-1beta bound to the HNF-1 site specifically as a homodimer as determined by gel retardation assays with HNF-1beta-specific antibody. Cotransfection of a HNF-1beta expression plasmid increased NNMT promoter activity significantly in both HNF-1beta-positive and -negative thyroid cancer cell lines and Hep G2 liver cancer cells. Furthermore, transient expression of HNF-1beta in BHP 14-9 cells increased endogenous NNMT protein levels. In summary, HNF-1beta functions as a transcription activator for NNMT gene expression in some papillary thyroid cancer cells.

Expression of nicotinamide N-methyltransferase (E.C. 2.1.1.1) in the Parkinsonian brain

Nicotinamide N-methyltransferase (NNMT) has been proposed as a link between the environmental and genetic factors of Parkinson disease (PD). Therefore, we explored the hypothesis that high levels of NNMT expression may predispose to the development of PD. Regions of high mRNA expression were shown in the spinal cord, medulla, and temporal lobe, with lowest expression in the cerebellum, subthalamic nucleus, and caudate nucleus. Using 2 NNMT antibodies, the protein was shown to be expressed in multipolar neurons in the temporal lobe, caudate nucleus, and spinal cord, granular neurons of the cerebellum, dopaminergic neurons in the substantia nigra, and in the axons of the third nerve. Expression of NNMT was compared in PD and non-PD control cerebella and caudate nucleus. PD tissue exhibited significantly increased levels of NNMT protein and activity. PD disease duration was inversely correlated with the level of expression in cerebellum. This is the first demonstration that patients with PD have higher levels of NNMT activity and protein in brain tissue than those without PD and that NNMT expression is associated with neurons that degenerate in PD.

Increased hepatic nicotinamide N-methyltransferase activity as a marker of cancer cachexia in mice bearing colon 26 adenocarcinoma

When a cachexigenic subclone (clone 20) of murine colon 26 adenocarcinoma was transplanted into female BALB/c mice, hepatic NNMT activity continued to increase until death in proportion to progressive carcass weight loss, a marker of cancer cachexia. On the other hand, noncachexigenic subclone (clone 5)-transplanted mice showed neither increase of NNMT activity nor carcass weight loss. Among cytostatic fluorinated pyrimidines, 5'-dFUrd could inhibit the increase of NNMT activity and prevent weight loss in mice bearing clone 20. On the other hand, 2'-dFUrd did not show these effects. 5-FUra and Tegafur inhibited the increase of NNMT activity at higher concentrations. These findings suggest that the levels of hepatic NNMT activity are closely associated with the degree of weight loss, and they appear to be a useful marker of cancer cachexia.

Nicotinamide methylation and hepatic energy reserve: a study by liver perfusion in vitro

BACKGROUND/AIMS

The synthesis of pyridine nucleotides from nicotinamide requires adenosine triphosphate. In man when exogenous nicotinamide is poorly utilized in this synthesis, the excess follows a dissipative metabolic pathway and is excreted in urine as N-methylnicotinamide. In human cirrhosis N-methylnicotinamide serum levels are higher than normal, in basal condition and after nicotinamide oral load. The aim of this study was to verify N-methylnicotinamide production in relation to hepatic content of adenosine triphosphate during in vitro perfusion of rat liver, in normal conditions and after adenosine triphosphate depletion by metabolic stress.

METHODS

"Stress" was obtained by pre-washing with saline for 15 min before the perfusion with nutritive medium.

RESULTS

The adenosine triphosphate decrease in the stressed liver was 38% after pre-washing with saline and 80% at the end of nutritive perfusion. In control liver the corresponding decreases were 1% after pre-washing with nutritive medium and 65% at the end of perfusion with the same medium. The total nicotinamide adenine dinucleotide decreases were 44% and 56% in the stressed liver, and 19% and 52% in the control liver. The output levels of N-methylnicotinamide at 90 min of rat liver nutritive perfusion were 31.50 +/- 4.72 nmol/g for normal liver and 66.40 +/- 13.17 for stressed liver (p<0.001). Liver adenosine triphosphate was inversely related to N-methylnicotinamide production (r=0.93; p<0.001).

CONCLUSIONS

These data suggest that nicotinamide methylation may be enhanced when there is hepatic adenosine triphosphate decrease and energy failure induced by hypoxia or metabolic stress, similar to that obtained in vitro by saline washing before perfusion with nutritive medium. This study shows that the evaluation of N-methylnicotinamide production in man (before and after nicotinamide load) might be useful to explore the energy state of diseased liver.