Objectives-This study examines the ABCG1-mediated cholesterol efflux and intracellular cholesterol transport by studying the ABCG1 localization and function in macrophages. Methods and Results-HEK 293 cell overexpressing ABCG1, RNA interference, or macrophages from ABCG1 or ABCG4 knockout mice were used. ABCG1 but not ABCG4 had a major role in the increased cholesterol mass efflux produced by treatment of macrophages with LXR activators. In 293 cells, ABCG1 was found in the plasma membrane, Golgi, and recycling endosomes. In contrast, in basal macrophages, ABCG1 was predominantly intracellular, and redistributed to the plasma membrane after LXR activation. LXR activation increased macrophage cholesterol efflux to high-density lipoprotein (HDL), low-density lipoprotein (LDL), and cyclodextrin in an ABCG1-dependent fashion. Suppression of ABCG1 expression increased cholesteryl ester formation and decreased SREBP2 target gene expression in macrophages, even in the absence of HDL acceptors. Conclusions-LXR

SUMMARYMicroRNAs (miRNAs) are regulators of global gene expression and function in a broad range of biological processes. Recent studies have suggested that miRNAs can function as tumor suppressors or oncogenes by modulating the activities of evolutionarily conserved signaling pathways that are commonly dysregulated in cancer. We report the identification of the miR-310 to miR-313 (miR-310/13) cluster as a novel antagonist of Wingless (Drosophila Wnt) pathway activity in a functional screen for Drosophila miRNAs. We demonstrate that miR-310/13 can modulate Armadillo (Arm; Drosophila β-catenin) expression and activity by directly targeting the 3ʹ-UTRs of arm and pangolin (Drosophila TCF) in vivo. Notably, the miR-310/13-deficient flies exhibit abnormal germ and somatic cell differentiation in the male gonad, which can be rescued by reducing Arm protein levels or activity. Our results implicate a previously unrecognized function for miR-310/13 in dampening the activity of Arm in early somatic and germline progenitor cells, whereby inappropriate/sustained activation of Arm-mediated signaling or cell adhesion may impact normal differentiation in the Drosophila male gonad. MATERIALS AND METHODS Cell culture and high-throughput screen (HTS)For the HTS, the Wg pathway was activated in Drosophila Clone 8 (Cl8) and S2R+ cells [grown as described by DasGupta et al. (DasGupta et al., 2005)] by introducing Axin double-stranded RNA (dsRNA), which resulted in a robust, ligand-independent activation of the Wg-responsive dTF12 reporter (DasGupta et al., 2005) (Fig. 1A). We screened a library of miRNA expression constructs [UAS-dsRED-pri-miR (Silver et al., 2007)] that consisted of 75 previously screened pri-miR constructs (Silver et al., 2007) plus 115 as yet unscreened pri-miR plasmids for their ability to suppress dTF12 activity downstream of the DC in this transcriptionally sensitized background. A total of 190 screen-ready plasmids were plated using a Janus MDT automated workstation (Perkin Elmer) in 5 µl aliquots as quadruplicates arranged in a quadrant on a set of three 384-well plates. Several quadrants of four replica wells were left empty for the addition of assay-specific controls. Axin dsRNA was generated using the Megascript kit (Applied Biosystems) using the following primers (5Ј-3Ј): forward TAATACGACTCACTATAGGGagaccaaacgccgcaccgctcgcc and reverse TAATACGACTCACTATAGGGagacaaaagccggtcgcccgtac (capital letters denote priming regions for T7 RNA polymerase).Cells were suspended at 20,000 cells/well for S2/S2R+ and 40,000 cells/well for Cl8. The dTF12-luciferase (TOP12-Ffl) reporter and Pol IIIRenilla luciferase (PolIII-RL) were utilized as described (DasGupta et al., 2005), with the addition of 0.01 µg actin-GAL4 and 0.1 µg Axin dsRNA, and transfected using the Effectene kit (Qiagen). Cells were incubated posttransfection for 5 days and luciferase levels assessed using the Promega Dual-Glo kit (Promega).For screen data analysis, Firefly luciferase activity values were normalized to those of Renilla luciferase for each...