Coactivator as a target gene specificity determinant for histone H3 lysine 4 methyltransferases

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-␤2 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-␤2 by ASC-2. In contrast, RAR-␤2 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.mixed-lineage leukemia (MLL) ͉ retinoic acid receptor ͉ transcription N uclear receptors (NRs) bind hormone response elements in target genes and regulate transcriptional initiation in a liganddependent manner (1). During ligand binding, the conserved C-terminal activation function 2 domain undergoes a structural change (1) that is recognized by an ␣-helical LXXLL motif (NR box) in transcriptional coactivators (2). Activating signal cointegrator-2 (ASC-2; also named AIB3, TRBP, TRAP250, NRC, and PRIP), a coactivator of many NRs and other transcription factors, contains two NR boxes (3). NR box 1 binds multiple NRs, including retinoic acid receptor (RAR), whereas NR box 2 interacts with liver X receptors. The physiological importance of ASC-2 as a key coactivator of these NRs and the pivotal roles of both NR boxes in this context have been proposed from recent studies with various ASC-2 mouse models (3).In HeLa nuclei, ASC-2 resides in a steady-state complex [ASC-2 complex (ASCOM)] (4) that contains retinoblastomabinding protein RbBP5, ␣͞␤-tubulins, and trithorax group proteins Ash2L, MLL4-1͞ALR-1, MLL4-2͞ALR-2, and MLL3͞ HALR (the paralog of MLL4͞ARL). † † MLL4-1 and MLL4-2 (collectively MLL4s) are encoded by the same gene, and they differ only at their N termini (4). The C termini of MLL3 and MLL4s contain a SET domain (5) with an intrinsic histone lysine-specific methyltransferase activity. Indeed, recombinant MLL3 and MLL4 SET domains and partially immunopurified ASCOM exhibit weak but specific histone H3-K4 methyltransferase (H3K4MT) activity in vitro (4).H3-K4 methylation, an evolutionarily conserved mark linked to transcriptionally active chromatin, has been proposed to counter the generally repressive chromatin environment imposed by H3-K9͞K27 methylation in higher eukaryotes (6). In particular, H3-K4 trimethylation is associated with promoters and early transcribed regions of active genes (7,8). H3K4MTs include yeast Set1 (ySet1), hSet1, MLL1, MLL2, and MLL3 and ...

Targeted inactivation of MLL3 histone H3–Lys-4 methyltransferase activity in the mouse reveals vital roles for MLL3 in adipogenesis

“…Importantly, ASC-2 is an integral and unique component of a Set1-like complex named ASCOM (for ASC-2 complex), which contains MLL3 or MLL4 (5,10). ASCOM indeed possesses H3K4MT activity (5,(10)(11)(12). More recent studies identified additional components of ASCOM, including UTX (11,12), a protein subsequently shown to be a H3K27-demethyase enzyme (13)(14)(15)(16).…”

“…In these mice, WT MLL3 is replaced by a mutant MLL3 that bears an in-frame deletion of a 61-aa catalytic core region in the MLL3 SET domain and is expressed and incorporated into ASCOM (10). Unlike ASC-2-null mice, which die at approximately embryonic day (E) 9.5-E13.5 (19)(20)(21)25), MLL3 ⌬/⌬ mice in C57BL/ 6-129S6 background show only a partial embryonic lethality (10).…”

“…Importantly, ASC-2 is an integral and unique component of a Set1-like complex named ASCOM (for ASC-2 complex), which contains MLL3 or MLL4 (5,10). ASCOM indeed possesses H3K4MT activity (5,(10)(11)(12).…”

“…In these mice, WT MLL3 is replaced by a mutant MLL3 that bears an in-frame deletion of a 61-aa catalytic core region in the MLL3 SET domain and is expressed and incorporated into ASCOM (10). Unlike ASC-2-null mice, which die at approximately embryonic day (E) 9.5-E13.5 (19)(20)(21)25), MLL3 ⌬/⌬ mice in C57BL/ 6-129S6 background show only a partial embryonic lethality (10). Interestingly, MLL3 ⌬/⌬ mice provide genetic evidence for complex formation between MLL3 and ASC-2, as these animals display at least 3 phenotypes that are shared with isogenic 129S6 ASC-2 ϩ/Ϫ mice (26), i.e., stunted growth, decreased cellular doubling rate, and lower fertility (10).…”

Regulation of vitamin D receptor function in MEN1-related parathyroid adenomas

“…MLL proteins possess methyltransferase activity specifically directed at lysine 4 of histone H3 (H3K4), and especially trimethylation of this residue (H3K4me3) (Ruthenburg et al, 2007). Menin is part of the MLL1 and MLL2, but not of the MLL3 or MLL4 complexes (Lee et al, 2006). The menin-MLL1 histone methyltransferase (HMT) complex was found to be important for -catenin regulated transcription of the c-Myc gene and is stabilised by the chromatin-associated protein lens epithelium-derived growth factor (LEDGF) (Sierra et al, 2006, Yokoyama andCleary, 2008).…”