Tissue- and Nuclear Receptor-Specific Function of the C-Terminal LXXLL Motif of Coactivator NCoA6/AIB3 in Mice

Abstract

Although the LXXLL motif of nuclear receptor (NR) coactivators is essential for interaction with NRs, its role has not been assessed in unbiased animal models. The nuclear receptor coactivator 6 (NCoA6; also AIB3, PRIP, ASC-2, TRBP, RAP250, or NRC) is a coactivator containing an N-terminal LXXLL-1 (L1) and a C-terminal L2. L1 interacts with many NRs, while L2 interacts with the liver X receptor ␣ (LXR␣) and the estrogen receptor ␣ (ER␣). We generated mice in which L2 was mutated into AXXAL (L2m) to disrupt its interaction with LXR␣ and ER␣. NCoA6L2m/L2m mice exhibited normal reproduction, mammary gland morphogenesis, and ER␣ target gene expression. In contrast, when treated with an LXR␣ agonist, lipogenesis and the LXR␣ target gene expression were significantly reduced in NCoA6L2m/L2m mice. The induction of Cyp7A1 expression by a high-cholesterol diet was impaired in NCoA6 L2m/L2m mice, which reduced bile acid synthesis in the liver and excretion in the feces and resulted in cholesterol accumulation in the liver and blood. These results demonstrate that L2 plays a tissue-and NR-specific role: it is required for NCoA6 to mediate LXR␣-regulated lipogenesis and cholesterol/bile acid homeostasis in the liver but not required for ER␣ function in the mammary gland.The nuclear receptor (NR) superfamily consists of hormoneinducible transcription factors. Through regulation of gene expression, NRs control numerous biological events in development, growth, sexual maturation, reproduction, and metabolic homeostasis. Recent studies have identified a number of transcriptional coactivators and corepressors that modulate NR transcriptional activities and determine the expression levels of their target genes (28,36,41). Multiple coactivators usually form functional protein complexes which facilitate chromatin remodeling, general transcription factor assembly, RNA polymerase II recruitment, and transcriptional initiation. Mechanistically, most coactivators do not bind to DNA, and their recruitment to a gene promoter/enhancer is dependent on their interaction with specific agonist-bound NRs. Most coactivators contain one or more LXXLL (L, leucine; X, any amino acid) ␣-helix motifs required for interaction with the ligand-binding domain of NRs (10,26,27,37). Although the molecular basis and requirement of the LXXLL motif for NR coactivator function have been investigated using biochemical and cell culture experiments (10,26,27,37), the physiological function and the tissue and NR specificities of the LXXLL motif of coactivators have not been carefully assessed in an animal model using an unbiased molecular genetic approach.The nuclear receptor coactivator 6 (NCoA-6; also AIB3, PRIP, ASC-2, TRBP, RAP250, or NRC) is an NR coactivator amplified and overexpressed in some breast, colon, and lung cancers (4,9,16,20,24,25,50). Biochemical and cell culturebased experiments have demonstrated that NCoA6 interacts with and coactivates many NRs, including estrogen receptor ␣ (ER␣) and liver X receptor ␣ (LXR␣) (15,24,25). NCoA6 may enhance NR...

Key roles for MED1 LxxLL motifs in pubertal mammary gland development and luminal-cell differentiation

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

“…The importance of ASC-2 as a key coactivator of multiple nuclear receptors has been reported from studies with various ASC-2 mouse models (9,17). In particular, ASC-2-null mice display at least 2 major phenotypes comparable with those described for mice with targeted inactivation of the peroxisome proliferator-activated receptor ␥ (PPAR␥) and its dimerization partner retinoid X receptor (18,19).…”

A tumor suppressive coactivator complex of p53 containing ASC-2 and histone H3-lysine-4 methyltransferase MLL3 or its paralogue MLL4

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