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...

C. elegans and Drosophila generate distinct signaling and adhesive forms of β-catenin at the level of gene expression. Whether vertebrates, which rely on a single β-catenin gene, generate unique adhesive and signaling forms at the level of protein modification remains unresolved. We show that β-catenin unphosphorylated at serine 37 (S37) and threonine 41 (T41), commonly referred to as transcriptionally Active β-Catenin (ABC), is a minor nuclear-enriched monomeric form of β-catenin in SW480 cells, which express low levels of E-cadherin. Despite earlier indications, the superior signaling activity of ABC is not due to reduced cadherin binding, as ABC is readily incorporated into cadherin contacts in E-cadherin-restored cells. β-catenin phosphorylated at serine 45 (S45) or threonine 41 (T41) (T41/S45) or along the GSK3 regulatory cassette S33, S37 or T41 (S33/37/T41), however, is largely unable to associate with cadherins. β-catenin phosphorylated at T41/S45 and unphosphorylated at S37 and T41 is predominantly nuclear, while β-catenin phosphorylated at S33/37/T41 is mostly cytoplasmic, suggesting that β-catenin hypophosphorylated at S37 and T41 may be more active in transcription due to its enhanced nuclear accumulation. Evidence that phosphorylation at T41/S45 can be spatially separated from phosphorylations at S33/37/T41 suggests that these phosphorylations may not always be coupled, raising the possibility that phosphorylation at S45 serves a distinct nuclear function.

The cadherin–catenin complex mediates cell–cell adhesion at adherens junctions. Phosphorylation of E-cadherin in its β-catenin–binding domain promotes surface stability of E-cadherin and robust cell–cell adhesion.

The cadherin-catenin adhesion complex is a key contributor to epithelial tissue stability and dynamic cell movements during development and tissue renewal. How this complex is regulated to accomplish these functions is not fully understood. We identified several phosphorylation sites in mammalian aE-catenin (also known as catenin a-1) and Drosophila a-Catenin within a flexible linker located between the middle (M)-region and the carboxy-terminal actin-binding domain. We show that this phospho-linker (P-linker) is the main phosphorylated region of a-catenin in cells and is sequentially modified at casein kinase 2 and 1 consensus sites. In Drosophila, the P-linker is required for normal a-catenin function during development and collective cell migration, although no obvious defects were found in cadherin-catenin complex assembly or adherens junction formation. In mammalian cells, nonphosphorylatable forms of a-catenin showed defects in intercellular adhesion using a mechanical dispersion assay. Epithelial sheets expressing phosphomimetic forms of a-catenin showed faster and more coordinated migrations after scratch wounding. These findings suggest that phosphorylation and dephosphorylation of the a-catenin P-linker are required for normal cadherin-catenin complex function in Drosophila and mammalian cells.