Select human cancer mutants of NRMT1 alter its catalytic activity and decrease N-terminal trimethylation.

Area of Science:

• Biochemistry
• Molecular Biology
• Oncology

Background:

• Mutations in EZH2, a histone methyltransferase, drive B-cell lymphoma by altering H3K27 methylation.
• NRMT1 and NRMT2 are homologous N-terminal methyltransferases with distinct catalytic activities due to active site residue differences.

Purpose of the Study:

• To investigate whether key aromatic residues in NRMT1/2 active sites determine their distinct catalytic functions.
• To analyze the impact of naturally occurring NRMT1 mutations found in human cancers on its enzymatic activity and tumor suppressor function.

Main Methods:

• Comparative analysis of NRMT1 and NRZH2 enzyme kinetics.
• Site-directed mutagenesis of NRMT1 active site residues.
• Expression of wild-type and mutant NRMT1 in cancer cell lines to assess oncogenic phenotypes and DNA damage sensitivity.

Main Results:

• Directed mutations in NRMT1's aromatic residues had minimal impact on catalytic activity.
• NRMT1 mutants N209I (endometrial cancer) and P211S (lung cancer) showed reduced trimethylase and increased monomethylase/dimethylase activity.
• These mutants, located in the peptide-binding channel, indicate a second structural region influencing enzyme specificity and function.

Conclusions:

• NRMT1 mutations can alter its catalytic activity, affecting its tumor suppressor role.
• NRMT1 mutants may contribute to oncogenesis or serve as biomarkers for sensitivity to DNA-damaging agents.