Synergistic Coactivator Function by Coactivator-associated Arginine Methyltransferase (CARM) 1 and β-Catenin with Two Different Classes of DNA-binding Transcriptional Activators

Abstract

The androgen receptor (AR) binds to and activates transcription of specific genes in response to its cognate steroid hormone, dihydrotestosterone. Transcriptional activation by the DNA-bound AR is accomplished with the help of a variety of coactivator proteins. For example, the p160 coactivators bind directly to AR and recruit additional coactivators such as the histone acetyltransferase p300 and the histone methyltransferase CARM1. The current study tested whether CARM1 can cooperate with other types of coactivator proteins. Recently it was shown that ␤-catenin can also bind directly to and serve as a coactivator for AR. Here it is shown that CARM1 binds to ␤-catenin and can function in synergy with ␤-catenin and p300 as coactivators for AR. The methyltransferase activity of CARM1 is important for its synergistic coactivator function with ␤-catenin. The synergistic coactivator function of ␤-catenin and CARM1 is not restricted to steroid receptors because these two coactivators can also act synergistically with another type of DNA binding transcriptional activator, LEF-1/TCF-4.␤-catenin is a critical component of at least two signaling pathways, one that regulates cell-cell adhesion and organization of the actin cytoskeleton, and another that mediates Wnt/ Wingless (Wg) 1 signaling (1-3). ␤-catenin protein levels are usually maintained at a low level through active degradation. The glycogen synthase kinase complex constitutively phosphorylates ␤-catenin, targeting it for ubiquitination and degradation by proteasomes. Activation of the Wnt/Wg pathway leads to inhibition of glycogen synthase kinase activity and thus stabilizes ␤-catenin protein. As its level increases some ␤-catenin accumulates in the nucleus, where it binds to and enhances transcriptional activation by at least two different classes of enhancer element-binding transcriptional activator proteins: the lymphoid enhancer factor/T-cell factor (LEF/TCF) proteins (4, 5) and nuclear receptors such as the androgen receptor (AR) and retinoic acid receptor (6, 7). Thus, at the distal end of the Wnt/Wg and nuclear receptor signaling pathways ␤-catenin can act as a transcriptional coactivator protein.Transcriptional coactivators are a diverse group of proteins that are recruited to a specific promoter by interaction with specific enhancer-binding proteins (2,8,9). Coactivators participate in chromatin remodeling and recruitment of RNA polymerase II to the promoter. Many coactivators function as complexes, in which one component (hereafter, a primary coactivator) anchors the complex to the enhancer-binding protein, while other components (hereafter, secondary coactivators) mediate the transcriptional activation process (10, 11). Binding of ␤-catenin to LEF/TCF causes displacement of corepressor complexes containing histone deacetylases (5). In addition, ␤-catenin also recruits and acts synergistically as a coactivator with p300 or CBP (2, 12-14). These two related proteins acetylate histones and interact with components of the basal transcription machinery, su...

Coactivator-associated arginine methyltransferase 1 (CARM1) is a positive regulator of the Cyclin E1 gene

“…Accordingly, reporter gene assays showed that CARM1 acts as a potent transcriptional coactivator of the CCNE1 gene and of other G 1 ͞S-regulated genes (DHFR, cdc6), together with E2F͞DP and by way of the E2F sites present in these promoters. This result is consistent with recent reports showing that the CARM1 transcriptional coactivating function is not restricted to nuclear receptors, but that it also associates and cooperates with p53, NF-B, and LEF1͞TCF4 (29)(30)(31). Thus, this ubiquitously expressed enzyme is likely to have a more pleiotropic function than was originally thought, notably in the control of the cell cycle and survival.…”

“…Consistent with this function, CARM1 recruitment at nuclear receptor-responsive genes was found to coincide with their activation (23,24,(26)(27)(28)(29) and with histone H3-R17-and H3-R26-specific methylations of their promoter region (23,24,(26)(27)(28)(29). More recently, CARM1 was also found to associate and cooperate with p53, NF-B and LEF1͞TCF4 (29,31,32), suggesting that this enzyme plays pleiotropic roles in cell proliferation and survival. Here, we show that CARM1 acts as a potent coactivator for the CCNE1 gene together with ACTR and through E2F sites.…”

“…Thus, although much of the previous evidence for the involvement of CARM1 in transcription has come from studies involving nuclear receptors and their p160 coactivators, our data suggest the existence of an E2F-dependent recruitment of enzymatically active CARM1 to the CCNE1 gene and to a subset of other E2F target genes (29,31,32).…”

Complex regulation of human androgen receptor expression by Wnt signaling in prostate cancer cells

“…b-Catenin binds to the activation function 2 region within the N-terminal domain of liganded hAR protein and augments liganddependent hAR transcriptional activity in PCa cells (Song et al, 2003). The coactivator function of b-catenin likely involves increased recruitment of p160 coactivator proteins as well as tertiary proteins, such as histone methyltransferase (Koh et al, 2002). b-Catenin also alters ligand specificity of hAR-mediated transcription, enhancing transcriptional activation by androstenedione and estradiol and diminishing antagonism by bicalutamide (Truica et al, 2000).…”

Specific protein methylation defects and gene expression perturbations in coactivator-associated arginine methyltransferase 1-deficient mice

“…The opposite observation has been made for H3 methylation, where prior acetylation of H3 by CREB-binding protein (CBP) facilitates its methylation by CARM1 (17). CARM1's coactivator activity is not dedicated to transactivated steroid receptors but also functions with the myogenic transcription factor mouse embryonic fibroblast (MEF) 2C (18) and ␤-catenin (19). Chromatin immunoprecipitation analysis has shown that histone H3 becomes methylated in vivo on Arg-17 at the estrogen receptor-regulated pS2 gene (20) and at a genome integrated mouse mammary tumor virus (MMTV) reporter (21), and this methylation coincides with the presence of CARM1.…”