Increased Acetylation in the DNA-binding Domain of TR4 Nuclear Receptor by the Coregulator ARA55 Leads to Suppression of TR4 Transactivation

Abstract

The nuclear receptor TR4 is a key regulator for many physiological processes, including growth, development, and metabolism. However, how the transcriptional activity of TR4 is regulated in the absence of ligand(s) remains largely unknown. Here we found that an androgen receptor (AR) coactivator, ARA55, might function as a corepressor to suppress TR4 transactivation. Molecular mechanistic dissection with mutation analysis found that ARA55 could enhance TR4 acetylation at the conserved acetylation sites of lysine 175 and lysine 176 in the DNAbinding domain via recruiting proteins with histone acetyl transferase activity, which might then reduce significantly the TR4 DNA binding activity that resulted in the suppression of TR4 transactivation. These results are in contrast to the classic ARA55 coactivator function to enhance AR transactivation partially via increased AR acetylation in the hinge/ligand-binding domain. Together, these results not only provide a novel functional mechanism showing that acetylation of different nuclear receptors at different domains by coregulator may lead to differential receptor transactivation activity but also provide a new way for small molecules to control TR4 transactivation via altering TR4 acetylation levels, and such small molecules may have potential therapeutic applications in the future. The androgen receptor (AR)2 -associated protein ARA55 is a nuclear receptor coactivator (1, 2) that belongs to the group III LIM domain-containing protein family (3), which can function as molecular adaptors to stabilize protein complexes (4, 5). First identified as an AR coactivator (1, 2), ARA55 could also enhance the transactivation of other nuclear receptors, such as glucocorticoid receptor (6) and peroxisome proliferator-activated receptor ␥ (7). ARA55 lacks histone acetyltransferase (HAT) or methyltransferase activity (5). However, ARA55, with four LIM domains within its amino terminus, could still be able to influence acetylation on nuclear receptors via recruitment of histone acetyltransferase-containing coactivators, such as CBP and p300 (5). ARA55 also recruits corepressor complexes to glucocorticoid-responsive promoters in the absence of ligands (7), suggesting that ARA55 may be able to coordinate corepressor release, as well as coactivator recruitment upon glucocorticoid ligand stimulation.An important mechanism by which ARA55 enhances AR transactivation is that ARA55 serves as a bridge protein to recruit HATs, such as CBP/p300 (8). Acetylation of the histones by HATs promotes chromatin structural changes that result in the promotion of gene transactivation (9). CBP/p300 can also acetylate AR on conserved lysines located in the hinge/ligandbinding domain (LBD). A recent genomic study identified 3600 lysine acetylation sites on 1750 proteins (10), suggesting that protein acetylation could be as common as protein phosphorylation to alter or influence protein function (11). Indeed, almost all of the enzymes involved in human or yeast metabolic processes are acetylated (12, 13). Th...

Recent advances in the study of testicular nuclear receptor 4

“…TR4 was also found to interact with some receptors or be modulated by some genes having roles in many physiological functions (Chen Y.T. et al, 2008;Huang et al, 2010;Liu et al, 2011a;Xie et al, 2011;Zhou et al, 2011). However, there are still many questions that need to be answered regarding the detailed mechanisms and the cross-talk between TR4 effects in different tissues.…”

Differential roles of PPARγ vs TR4 in prostate cancer and metabolic diseases

“…This involves dynamic partitioning of TR2 into Pml-containing and Pml-free pools (Park et al 2007, Gupta et al 2008. Acetylation TR4 can be acetylated at K175 and K176, which attenuates its DNA binding ability to TR4 response elements (TR4REs) on its target genes (Xie et al 2011). The coregulator ARA55 increased TR4 acetylation levels via modulation of HAT enzymes bound to the ARA55-TR4 complex.…”

“…The coregulator ARA55 increased TR4 acetylation levels via modulation of HAT enzymes bound to the ARA55-TR4 complex. However, the physiological function of acetylated TR4 remains unclear (Xie et al 2011).…”

“…Interestingly, expression of AR target genes was also repressed by the dimerization with TR4 (Lee et al 1999). ARA55 is one of the coregulators that AR and TR4 share (Xie et al 2011). ARA55 enhances AR transcriptional activity but inhibits TR4 activity.…”

VDR Activity Is Differentially Affected by Hic-5 in Prostate Cancer and Stromal Cells

“…In prostate stromal cells, for example, Hic-5 is necessary for full transactivation of the androgen receptor (AR) target gene KGF (keratinocyte growth factor), influencing the recruitment of various transactivators (42). Alternatively, in the absence of steroid ligands, Hic-5 functions in transcriptional repression through the gene-specific recruitment of the nuclear receptor co-repressor (NCoR) complex (45, 46). In addition to binding to nuclear receptors, Hic-5 also binds to other transcription factors, feeding back onto TGF-β signaling through interaction with Smad3.…”