Research Topics:

• Characterizing mutants of N-terminal methyltransferases, and their functional roles in oncogenesis.

Altered levels of histone methylation have recently been observed as drivers of oncogenesis.  A subset of B-cell lymphoma patients have mutations in the histone H3 lysine 27 (H3K27) methyltransferase EZH2, which change its catalytic specificity from a monomethylase to a trimethylase.  These mutations occur in aromatic resides surrounding the active site and result in increased growth rates and altered transcriptional profiles.  We work with the N-terminal methyltransferases NRMT1 and NRMT2.  NRMT1 is a trimethylase, and NRMT2 is a monomethylase.  Mutations of both NRMT1 and NRMT2 are found in human cancers, and we are interested in determining if any of these mutations reverse the catalytic specificities of NRMT1 and NRMT2, similar to the mutations seen in EZH2.  We have tested both naturally occurring NRMT1 and NRMT2 mutations, as well as, directed mutations in the conserved (as compared to EZH2) aromatic residues of the active site.  While minimal effects are seen with the directed aromatic cage mutations, one-hour methyltransferase assays show that the NRMT1 P211S and N209I mutants (found in lung cancer and endometrial cancer, respectively) display decreased trimethylase and increased monomethylase activity.  The NRMT2 V224L mutant (found in breast cancer) displays decreased monomethylase activity but lacks a corresponding increase in trimethylase activity.   Unexpectedly, these mutants are located in an unstructured loop covering the active site, and indicate a second structural mode for determining enzyme specificity.

Posters Presented:

• Characterizing N-terminal methyltransferase mutants found in human cancers.  Kaitlyn Shields, Christine Schaner Tooley.  Research!Louisville (Sep-2014).  University of Louisville, Louisville, KY.