[Show abstract][Hide abstract] ABSTRACT: Activating signal cointegrator-2 (ASC-2), a coactivator of multiple transcription factors that include retinoic acid receptor (RAR), associates with histone H3-K4 methyltranferases (H3K4MTs) MLL3 and MLL4 in mixed-lineage leukemia. Here, we show that mice expressing a SET domain mutant of MLL3 share phenotypes with isogenic ASC2+/- mice and that expression and H3-K4 trimethylation of RAR target gene RAR-beta2 are impaired in ASC-2-null mouse embryo fibroblasts (MEFs) or in MEFs expressing siRNAs against both MLL3 and MLL4. We also show that MLL3 and MLL4 are found in distinct ASC-2-containing complexes rather than in a common ASC-2 complex, and they are recruited to RAR-beta2 by ASC-2. In contrast, RAR-beta2 expression is intact in MEFs devoid of menin, a component of MLL1 and MLL2 H3K4MT complexes. These results suggest that ASC-2 confers target gene specificity to MLL3 and MLL4 H3K4MT complexes and that recruitment of H3K4MTs to their target genes generally involves interactions between integral components of H3K4MT complexes and transcription factors.
Proceedings of the National Academy of Sciences 11/2006; 103(42):15392-7. DOI:10.1073/pnas.0607313103 · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Activating signal cointegrator 2 (ASC-2), a cancer-amplified transcriptional coactivator of nuclear receptors and many other transcription factors, contains two LXXLL-type nuclear receptor interaction domains. Interestingly, the second LXXLL motif is highly specific to the liver X receptors (LXRs). In cotransfection, DN2, an ASC-2 fragment encompassing this motif, exerts a potent dominant-negative effect on transactivation by LXRs, which is rescued by ectopic coexpression of the full-length ASC-2 but not by other LXXLL-type coactivators, such as SRC-1 and TRAP220. In contrast, DN2/m, in which the LXXLL motif is mutated to LXXAA to abolish the interactions with LXRs, is without any effect. Accordingly, expression of DN2, but not DN2/m, in transgenic mice results in phenotypes that are highly homologous to those previously observed with LXRalpha(-/-) mice, including a rapid accumulation of large amounts of cholesterol and down-regulation of the known lipid-metabolizing target genes of LXRalpha in the liver upon being fed a high-cholesterol diet. These results identify ASC-2 as a physiologically important transcriptional coactivator of LXRs and demonstrate its pivotal role in the liver lipid metabolism.
[Show abstract][Hide abstract] ABSTRACT: Many transcription coactivators interact with nuclear receptors in a ligand- and C-terminal transactivation function (AF2)-dependent manner. These include activating signal cointegrator 2 (ASC-2), a recently isolated transcriptional coactivator molecule, which is amplified in human cancers and stimulates transactivation by nuclear receptors and numerous other transcription factors. In this report, we show that ASC-2 belongs to a steady-state complex of approximately 2 MDa (ASC-2 complex [ASCOM]) in HeLa nuclei. ASCOM contains retinoblastoma-binding protein RBQ-3, alpha/beta-tubulins, and trithorax group proteins ALR-1, ALR-2, HALR, and ASH2. In particular, ALR-1/2 and HALR contain a highly conserved 130- to 140-amino-acid motif termed the SET domain, which was recently implicated in histone H3 lysine-specific methylation activities. Indeed, recombinant ALR-1, HALR, and immunopurified ASCOM exhibit very weak but specific H3-lysine 4 methylation activities in vitro, and transactivation by retinoic acid receptor appears to involve ligand-dependent recruitment of ASCOM and subsequent transient H3-lysine 4 methylation of the promoter region in vivo. Thus, ASCOM may represent a distinct coactivator complex of nuclear receptors. Further characterization of ASCOM will lead to a better understanding of how nuclear receptors and other transcription factors mediate transcriptional activation.
[Show abstract][Hide abstract] ABSTRACT: The methylation of lysine residues of histones plays a pivotal role in the regulation of chromatin structure and gene expression. Here, we report two crystal structures of SET7/9, a histone methyltransferase (HMTase) that transfers methyl groups to Lys4 of histone H3, in complex with S-adenosyl-L-methionine (AdoMet) determined at 1.7 and 2.3 A resolution. The structures reveal an active site consisting of: (i) a binding pocket between the SET domain and a c-SET helix where an AdoMet molecule in an unusual conformation binds; (ii) a narrow substrate-specific channel that only unmethylated lysine residues can access; and (iii) a catalytic tyrosine residue. The methyl group of AdoMet is directed to the narrow channel where a substrate lysine enters from the opposite side. We demonstrate that SET7/9 can transfer two but not three methyl groups to unmodified Lys4 of H3 without substrate dissociation. The unusual features of the SET domain-containing HMTase discriminate between the un- and methylated lysine substrate, and the methylation sites for the histone H3 tail.
The EMBO Journal 02/2003; 22(2):292-303. DOI:10.1093/emboj/cdg025 · 10.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: For the orphan nuclear receptor subfamily that includes Nur77 (NGFI-B), Nurr1, and NOR-1, no transcriptional coregulators have been identified thus far. In this report, we found that Ca(2+)/calmodulin-dependent protein kinase IV enhances Nur77 transactivation in cotransfections either alone or in synergy with AF2dependent coactivator ASC-2, whereas corepressor silencing mediator for retinoid and thyroid hormone receptors (SMRT) is repressive. Interestingly, Nur77 interacted with SMRT but did not directly bind ASC-2, and accordingly, the putative AF2 core domain of Nur77 did not affect the Nur77 transactivation. SMRT harbors transferable repression domains that associate with various histone deacetylases. Surprisingly, histone deacetylase inhibitor trichostatin A was unable to block the repressive effect of SMRT while dramatically stimulating the Nur77 transactivation. These results suggest that SMRT and ASC-2 are specific coregulators of Nur77 and that SMRT may dynamically compete with a putative adaptor molecule, which links ASC-2 to Nur77, for the identical binding sites within Nur77 in vivo.
[Show abstract][Hide abstract] ABSTRACT: Background Sensorineural hearing loss, one of the most common diseases, has historically been regarded as an incurable and irreversible condition. The number of people with hearing loss has grown rapidly in recent years, because of the prevalence of environmental noise and the increase in the elderly population. Although hearing aids are provided as an alternative device to help hearing impaired people, no fundamental treatment is currently available. Several studies have shown that noise-induced hearing loss can be prevented by prior exposure to low-levels of acoustic stimuli, a procedure known as sound conditioning. However, to our knowledge, this is the first clinical study to evaluate the effects of sound conditioning on hearing restoration. Methods Nine patients with high-tone hearing loss were subjected to modified sound conditioning for 2 weeks. In all, 63 samples (i.e., frequency regions) were obtained from the patients. Acoustic stimuli consisted of frequency-modulated tone and amplitude-modulated narrow band noise. Behavioral hearing thresholds were compared before and after treatment to investigate the effects of modified sound conditioning. Findings Our findings demonstrate that modified sound conditioning improves hearing ability. On average, the behavioral hearing threshold decreased by 8·91 dB (i.e., approximately 15%) after sound conditioning for 2 weeks, followed by a 2 week break (p = 0·001, Wilcoxon's signed-rank test with Bonferroni's correction). Twelve of the 63 samples exhibited hearing improvements in excess of 15 dB, whereas 27 samples showed hearing improvements of 5 to 15 dB. Interpretation Modified sound conditioning may improve the hearing abilities of patients with sensorineural hearing loss. Funding Earlogic Korea Inc.