ATP-dependent chromatin-remodeling complexes are known to facilitate transcriptional activation by opening chromatin structures. We report a novel human complex, named NURD, which contains not only ATP-dependent nucleosome disruption activity, but also histone deacetylase activity, which usually associates with transcriptional repression. The deacetylation is stimulated by ATP on nucleosomal templates, suggesting that nucleosome disruption aids the deacetylase to access its substrates. One subunit of NURD was identified as MTA1, a metastasis-associated protein with a region similar to the nuclear receptor core-pressor, N-CoR; and antibodies against NURD partially relieve transcriptional repression by thyroid hormone receptor. These results suggest that ATP-dependent chromatin remodeling can participate in transcriptional repression by assisting repressors in gaining access to chromatin.

Covalent modification of histones plays an important role in regulating chromatin dynamics and transcription. Histone methylation was thought to be an irreversible modification until recently. Using a biochemical assay coupled with chromatography, we have purified a JmjC domain-containing protein, JHDM2A, which specifically demethylates mono- and dimethyl-H3K9. Similar to JHDM1, JHDM2A-mediated histone demethylation requires cofactors Fe(II) and alpha-ketoglutarate. Mutational studies indicate that a JmjC domain and a zinc finger present in JHDM2A are required for its enzymatic activity. Overexpression of JHDM2A greatly reduced the H3K9 methylation level in vivo. Knockdown of JHDM2A results in an increase in the dimethyl-K9 levels at the promoter region of a subset of genes concomitant with decrease in their expression. Finally, JHDM2A exhibits hormone-dependent recruitment to androgen-receptor target genes, resulting in H3K9 demethylation and transcriptional activation. Thus, our work identifies a histone demethylase and links its function to hormone-dependent transcriptional activation.

Acetylation of core histone tails plays a fundamental role in transcription regulation. In addition to acetylation, other posttranslational modifications, such as phosphorylation and methylation, occur in core histone tails. Here, we report the purification, molecular identification, and functional characterization of a histone H4-specific methyltransferase PRMT1, a protein arginine methyltransferase. PRMT1 specifically methylates arginine 3 (Arg 3) of H4 in vitro and in vivo. Methylation of Arg 3 by PRMT1 facilitates subsequent acetylation of H4 tails by p300. However, acetylation of H4 inhibits its methylation by PRMT1. Most important, a mutation in the S-adenosyl-l-methionine-binding site of PRMT1 substantially crippled its nuclear receptor coactivator activity. Our finding reveals Arg 3 of H4 as a novel methylation site by PRMT1 and indicates that Arg 3 methylation plays an important role in transcriptional regulation.

Nuclear receptors play critical roles in the regulation of eukaryotic gene expression. We report the isolation and functional characterization of a novel transcriptional coactivator, termed steroid receptor RNA activator (SRA). SRA is selective for steroid hormone receptors and mediates transactivation via their amino-terminal activation function. We provide functional and mechanistic evidence that SRA acts as an RNA transcript; transfected SRA, unlike other steroid receptor coregulators, functions in the presence of cycloheximide, and SRA mutants containing multiple translational stop signals retain their ability to activate steroid receptor-dependent gene expression. Biochemical fractionation shows that SRA exists in distinct ribonucleoprotein complexes, one of which contains the nuclear receptor coactivator steroid receptor coactivator 1. We suggest that SRA may act to confer functional specificity upon multiprotein complexes recruited by liganded receptors during transcriptional activation.

The antitumor activity of tamoxifen in patients with breast cancer may be determined, in part, by tumor levels of AIB1 and HER-2. Thus, AIB1 may be an important diagnostic and therapeutic target.