Abstract 1135 Arginine methylation of the family of formin homology domain containing proteins (FHOD) by protein arginine methyltransferase 7 (PRMT7) is inhibited by serine phosphorylation

Protein post translational modifications (PTMs) aid in the regulation of biological processes by altering an amino acids bulkiness and charge. Commonly known modifications include phosphorylation, methylation, acetylation and ubiquitylation. Although the primary focus of PTMs have been involved in understanding the effects of a single amino acid modification on biological processes, adding subsequent modifications increases the complexity. However, substrate recognition motifs for arginine methyltransferases and some serine/threonine kinases overlap leading to potential enzymatic crosstalk. We utilized P81 phosphocellulose assays as well as mass spectrometry approaches to identify that the family of formin homology domain containing proteins (Fhod) contain a substrate recognition motif specific for protein arginine methyltransferase 7 (PRMT7). In particular, PRMT7 methylates R1388 and R1390 in the diaphanous autoinhibitory domain (DAD) of the family of Fhod proteins. Additionally, we confirmed that S1389 and S1395 in the DAD domain can be phosphorylated by Rho/ROCK1 kinase (ROKβ). Furthermore, we have determined that if phosphoserine 1389 is present then PRMT7 is fully inhibited and cannot subsequently methylate R1388 or R1390. However, if phosphoserine 1395 is present then PRMT7 is mildly inhibited but can still methylate R1388 and R1390. Interchangeably, methylarginine at amino acid positions 1388 or 1390 reduces ROCK1 activity but does not fully inhibit enzyme activity. Taken together these results have identified a novel PRMT7 specific substrate as well as an additional regulatory element that may play a role in Fhod enzymatic activity. This work was supported by the National Science Foundation grant MCB-1714569 (to S. G. C.) and by funds from the UCLA Academic Senate Faculty Research Program, and the Elizabeth and Thomas Plott Chair in Gerontology of the UCLA Longevity Center (to S. G. C.). T. L. L was supported by the NIH Ruth L. Kirschstein National Research Service Award GM007185.