Date of Graduation
Epigenetics and Molecular Carcinogenesis
Doctor of Philosophy (PhD)
Mark T. Bedford
Shawn B. Bratton
Rick A. Finch
A limited pool of proteins attains vast functional repertoire due to posttranslational modifications (PTMs). Arginine methylation is a common posttranslational modification, which is catalyzed by a family of nine protein arginine methyltransferases or PRMTs. These enzymes deposit one or two methyl groups to the nitrogen atoms of arginine side-chains. Elucidating the substrate specificity of each PRMT will promote a better understanding of which signaling networks these enzymes contribute to. Although many PRMT substrates have been identified, and their methylation sites mapped, the optimal target motif for each of the nine PRMTs has not been systematically addressed. Here we describe the use of Oriented Peptide Array Libraries (OPALs) to methodically dissect the preferred methylation motifs for three of these enzymes – PRMT1, Coactivator associated arginine methyltransferase 1 (CARM1) and PRMT9. The OPAL platform can also be used to gauge the subtle changes in substrate specificities due to mutations in the enzymes, which may be important in pathologies. In parallel, we show that an OPAL platform with a fixed methylarginine residue can be used to validate the methyl-specific and sequence-specific properties of antibodies that have been generated against different PRMT substrates, and can also be used to confirm the pan nature of some methylarginine-specific antibodies.
CARM1 or PRMT4 plays an important role in transcriptional regulation. It deposits asymmetric dimethylarginine (ADMA) marks on both histone and non-histone proteins. We performed a comparative proteomic screen with Pan-methylarginine (Rme2a) antibodies and identified that Nuclear Factor I-B (NFIB) is a major CARM1 substrate. Nfib and Carm1 knockout mice die perinatally due to almost identical hyper-proliferation defects during lung development, suggesting a genetic link between NFIB and CARM1. NFIB can both activate and repress transcription, but the mechanism is unknown. Here, we show that CARM1 functions as a transcriptional regulator for NFIB targets, suggesting that the activating and repressing functions of NFIB could be modulated by CARM1 mediated methylation of NFIB.
Arginine Methylation, CARM1, OPAL Arrays, Transcription, SCLC