title: Glucocorticoid response and promoter occupancy of the mouse LXRalpha gene.
abstract: The liver X receptors alpha and beta (LXRalpha and LXRbeta) are members of the nuclear receptor superfamily of proteins which are highly expressed in metabolically active tissues. They regulate gene expression of critical genes involved in cholesterol catabolism and transport, lipid and triglyceride biosynthesis, and carbohydrate metabolism in response to distinct oxysterol intermediates in the cholesterol metabolic pathway. Several LXR target genes have been identified, but there is limited information on how expression of the LXRs themselves is controlled. In this study we have characterized the upstream flanking region of the mouse LXRalpha gene. Transient transfections show that the LXRalpha promoter is able to drive transcription of a luciferase reporter gene, however, the transcriptional potential of the promoter in the cell lines used was low. The -2143 to -1513 region of the promoter mediates repression of reporter gene activity in all cells analyzed and multiple DNA-protein interactions were detected in this region by DNase I footprinting. The Zta, Ets, and Hes1 transcription factors were all shown to mediate alterations in reporter gene activity driven by LXRalpha promoter deletion constructs. These factors have been linked to cell cycle and differentiation processes suggesting that expression of LXRalpha might be under control of signalling mechanisms regulating cell proliferation. Several putative binding sites of the glucocorticoid receptor (GR) were identified in the LXRalpha promoter and transient cotransfections of the GR and LXRalpha promoter deletion constructs induced reporter gene activity. Addition of dexamethasone, a GR agonist, abolished this effect suggesting cross talk between GR and LXR signalling.
authors.affiliation: Department of Biosciences, Karolinska Institutet at NOVUM, Huddinge, Sweden. knut.steffensen@biosci.ki.se
authors.forename: Knut R
authors.initials: KR
authors.lastname: Steffensen
authors.forename: Elin
authors.initials: E
authors.lastname: Holter
authors.forename: Nyosha
authors.initials: N
authors.lastname: Alikhani
authors.forename: Winnie
authors.initials: W
authors.lastname: Eskild
authors.forename: Jan-Ake
authors.initials: JA
authors.lastname: Gustafsson
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D018983:DNA Footprinting; D004268:DNA-Binding Proteins; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D008099:Liver / Q000378:metabolism; D000071518:Liver X Receptors; D051379:Mice; D008969:Molecular Sequence Data; D057093:Orphan Nuclear Receptors; D011401:Promoter Regions, Genetic / Q000235:genetics*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism*; D011965:Receptors, Glucocorticoid / Q000235:genetics* / Q000378:metabolism*; D017385:Sequence Homology; D013045:Species Specificity; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D000071518:Liver X Receptors; C000605213:NR1H3 protein, human; C000605214:Nr1h3 protein, mouse; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D011965:Receptors, Glucocorticoid; D014157:Transcription Factors