Loss of CARM1 Results in Hypomethylation of Thymocyte Cyclic AMP-regulated Phosphoprotein and Deregulated Early T Cell Development

Abstract

The coactivator-associated arginine methyltransferase, CARM1, is a positive regulator of transcription. Using high density protein arrays, we have previously identified in vitro substrates for CARM1. One of these substrates, TARPP (thymocyte cyclic AMP-regulated phosphoprotein), is expressed specifically in immature thymocytes. Here, we have demonstrated that TARPP is arginine-methylated at a single residue, Arg 650 , both in vitro and in vivo. In addition, recombinant TARPP is not methylated by extracts from Carm1 ؊/؊ cells, indicating that there is no redundancy in this pathway. We show that thymi from Carm1 ؊/؊ embryos (E18.5) have a 5-10-fold reduction in cellularity compared with wild type littermates. Flow cytometric analysis of thymocytes revealed a decrease in the relative proportion of double negative thymocytes in Carm1 ؊/؊ embryos because of a partial developmental arrest in the earliest thymocyte progenitor subset. These results demonstrate that CARM1 plays a significant role in promoting the differentiation of early thymocyte progenitors, possibly through its direct action on TARPP.

Identification of a Novel Inhibitor of Coactivator-associated Arginine Methyltransferase 1 (CARM1)-mediated Methylation of Histone H3 Arg-17

“…The arginine methyltransferase, CARM1/PRMT4, has been shown to regulate important cellular processes such as pluripotency maintenance (16,32), differentiation (6,15,17), splicing (18), and transcriptional activation (10 -14), as well as tumor manifestation and progression (33,34). However, the methyltransferase activity of this coactivator has been linked with only a few cases of transcriptional activation, muscle and thymocyte differentiation, and tumor progression.…”

“…Furthermore, TBBD did not show any significant effect on the HMTase activity of lysine methyltransferase G9a, as well as on the HAT activity of p300/ CBP-associated factor (Fig. 1B, lanes [3][4][5][6]. Although, the activity of all the four enzymes (CARM1, p300, G9a, and p300/CBP-associated factor) were normalized with the histone substrate (Fig.…”

“…CARM1 also participates in various other cellular processes through its ability to methylate nonhistone substrates. Recently, CARM1 has been implicated in muscle (15) and T-cell development (6), stem cell differentiation (16), adipocyte differentiation (17), RNA processing (18), and tumorigenesis (19). Despite such broad functional significance, the exact molecular mechanisms of the enzyme function are not understood, in part due to the unavailability of specific modulators.…”

“…The class I enzyme CARM1 (coactivator-associated arginine methyltransferase 1, also known as PRMT4), was first identified as a p160 coactivator-interacting protein in a yeast two-hybrid screen, and later as a histone methyltransferase and transcriptional coactivator (5). All the PRMTs except CARM1 target a glycine arginine recognition motif, whereas CARM1 recognizes XXPRX or XXRPX, where X is any amino acid (6). CARM1 interacts with GRIP1 (glucocorticoid receptor-interacting protein) and is a secondary coactivator of several nuclear receptors (7)(8)(9).…”

Interplay between chromatin remodelers and protein arginine methyltransferases

“…Moreover, PRMT4 À/À MEFs are defective in activation of estrogen responsive genes (Yadav et al, 2003). PRMT4 has also been shown to be required for normal T cell development and muscle differentiation (Chen et al, 2002;Kim et al, 2004). Using a flag-tagged PRMT4 cell line, a multisubunit complex dubbed ''nucleosomal methylation activator complex'' (NUMAC) was purified and shown to contain subunits of the BRG1-based SWI/SNF complex, suggesting a functional interdependence between PRMT4 and human SWI/SNF (Fig.…”