Mouse liver nicotinamide N-methyltransferase: cDNA cloning, expression, and nucleotide sequence polymorphisms

Area of Science:

• Biochemistry
• Genetics
• Molecular Biology

Background:

• Nicotinamide N-methyltransferase (NNMT) is an enzyme involved in methylation.
• Significant variations in hepatic NNMT activity exist across different mouse strains.
• The hypothesis that these variations stem from NNMT amino acid sequence differences was investigated.

Purpose of the Study:

• To clone mouse liver NNMT cDNA.
• To analyze NNMT cDNA sequences in mouse strains with differing NNMT activity levels.
• To investigate the role of developmental expression in NNMT activity variations.

Main Methods:

• Cloning of mouse liver NNMT cDNA.
• Sequencing of NNMT cDNA open reading frames (ORFs) in five inbred mouse strains.
• Expression of NNMT cDNA in COS-1 cells.
• Biochemical characterization of expressed NNMT.
• Analysis of NNMT activity during mouse growth and development.

Main Results:

• Mouse liver NNMT cDNA shares high nucleotide identity with human NNMT.
• No amino acid changes were found in NNMT sequences across different mouse strains, despite nucleotide variations.
• Expressed NNMT from different strains showed comparable enzyme activity and biochemical properties.
• Hepatic NNMT activity differences between high-activity (C57BL/6J) and low-activity (C3H/HeJ) strains diminished with age.

Conclusions:

• Strain-dependent variations in hepatic NNMT activity are not caused by differences in the NNMT amino acid sequence.
• Developmental regulation of NNMT expression plays a crucial role in observed strain-dependent activity differences.
• Future research should focus on the regulatory mechanisms of NNMT during development.