title: Syndecan-1 expression is regulated in an isoform-specific manner by the farnesoid-X receptor.
abstract: Syndecan-1 (SDC1), a transmembrane heparan sulfate proteoglycan that participates in the binding and internalization of extracellular ligands, was identified in a screen designed to isolate genes that are regulated by the farnesoid X-receptor (FXR, NR1H4). Treatment of human hepatocytes with either naturally occurring (chenodeoxycholic acid) or synthetic (GW4064) FXR ligands resulted in both induction of SDC1 mRNA and enhanced binding, internalization, and degradation of low density lipoprotein. Transient transfection assays, using wild-type and mutant SDC1 promoter-luciferase genes, led to the identification of a nuclear hormone receptor-binding hexad arranged as a direct repeat separated by one nucleotide (DR-1) in the proximal promoter that was necessary and sufficient for activation by FXR. The wild-type, but not a mutated DR-1 element, conferred FXR responsiveness to a heterologous thymidine kinase promoter-reporter gene. Four murine FXR isoforms have been identified recently that differ either at their amino terminus and/or by the presence or absence of four amino acids in the hinge region. Interestingly, the activities of the human SDC1 promoter-reporter constructs were highly induced by the two FXR isoforms that do not contain the four-amino acid insert and were unresponsive to the isoforms containing the four amino acids. Thus, current studies demonstrate that hepatic SDC1 is induced in an FXR isoform-specific manner. Increased expression of SDC1 may account in part for the hypotriglyceridemic effect that can result from the administration of chenodeoxycholic acid to humans.
authors.affiliation: Department of Biological Chemistry and Medicine, UCLA, Los Angeles, California 90095, USA.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Anisfeld
authors.forename: Heidi R
authors.initials: HR
authors.lastname: Kast-Woelbern
authors.forename: Marie E
authors.initials: ME
authors.lastname: Meyer
authors.forename: Stacey A
authors.initials: SA
authors.lastname: Jones
authors.forename: Yanqiao
authors.initials: Y
authors.lastname: Zhang
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Williams
authors.forename: Timothy
authors.initials: T
authors.lastname: Willson
authors.forename: Peter A
authors.initials: PA
authors.lastname: Edwards
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004268:DNA-Binding Proteins; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D008156:Luciferases / Q000235:genetics; D008562:Membrane Glycoproteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics*; D011509:Proteoglycans / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D053668:Syndecan-1; D053667:Syndecans; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D008156:Luciferases; D008562:Membrane Glycoproteins; D020033:Protein Isoforms; D011509:Proteoglycans; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D053668:Syndecan-1; D053667:Syndecans; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated; C508241:SDC1 protein, human