Identification of the MLL2 Complex as a Coactivator for Estrogen Receptor α

Abstract

A novel estrogen receptor (ER)␣ coactivator complex, the MLL2 complex, which consists of MLL2, ASH2, RBQ3, and WDR5, was identified. ER␣ directly binds to the MLL2 complex through two LXXLL motifs in a region of MLL2 near the C terminus in a liganddependent manner. Disrupting the interaction between ER␣ and the MLL2 complex with small interfering RNAs specific against MLL2 or an MLL2 fragment representing the interacting region with ER␣ significantly inhibited the ER␣ transcription activity. The MLL2 complex was recruited on promoters of ER␣ target genes along with ER␣ upon estrogen stimulation. Inhibition of MLL2 expression decreased the estrogen-induced expression of ER␣ target genes cathepsin D and to a lesser extent pS2. In addition, MCF-7 cell growth was also inhibited by the depletion of MLL2. These results demonstrate that the ER␣ signaling pathway is critically dependent on its direct interaction with the MLL2 complex and suggest a central role for the MLL2 complex in the growth of ER␣-positive cancer cells.The biological effects of estrogen are mediated by estrogen receptors (ER) 2 in estrogen responsive tissues. There are two types of estrogen receptors, ER␣ and ER␤. The well studied ER␣ is involved in normal mammary gland development as well as breast cancer initiation and progress (1-4). ER␣ has two transcriptional activation domains, the N-terminal activation domain AF-1 and the C-terminal activation domain AF-2. Upon estrogen binding, ER␣ undergoes a conformational change and regulates the expression of its target genes (5, 6). ER␣, just as other nuclear receptors, requires coactivators and corepressors for its function. A large number of ER␣ coactivators, including the three members of the SRC-1 family (SRC-1, SRC-2/GRIP1/TIF2, and SRC-3/AIB1/ ACTR/pCID/RAC3/TRAM1) (7-9), CREB-binding protein (CBP/ p300), and TRAP220 (DRIP 205, PBP) (10, 11), have been identified to date. Most of the coactivators interact with the AF-2 domain of ER␣ in a ligand-dependent manner. Some of these cofactors are intrinsic enzymes with the activity of acetyltransferase or methyltransferase or are able to recruit such enzymes (12-14) that modify histone composition of chromatin to make transcription factors accessible to specific regions of the genome. The varying patterns of histone modification are now referred to as a histone code and are proposed to be epigenetic markers for determining gene activation status (15). Some nuclear receptor coactivators (corepressors) are presented as multiprotein complexes, and these steady-state protein complexes probably act as functional units of nuclear receptor coregulators (16). ER␣ coactivator TRAP220/PBP exists in the multiprotein TRAP complex, which has molecular mass of ϳ2 MD and is composed of more than 30 subunits (17). The TRAP complex facilitates ER␣ actions by synergizing basal transcription machineries. The ER␣ coactivator PRIP (TRBP, TRAP250, NRC, and AIB3) is also demonstrated to stay in a massive steady-state complex ASCOM (18), which consists of MLL4, PRIP (ASC2), MLL...

Whole-genome sequencing reveals oncogenic mutations in mycosis fungoides

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How genetically heterogeneous is Kabuki syndrome?: MLL2 testing in 116 patients, review and analyses of mutation and phenotypic spectrum

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

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