title: Subcellular localization and regulation of StarD4 protein in macrophages and fibroblasts.
abstract: StarD4 is a member of the StarD4 subfamily of START domain proteins with a characteristic lipid binding pocket specific for cholesterol. The objective of this study was to define StarD4 subcellular localization, regulation, and function. Immunobloting showed that StarD4 is highly expressed in the mouse fibroblast cell line 3T3-L1, in human THP-1 macrophages, Kupffer cells (liver macrophages), and hepatocytes. In 3T3-L1 cells and THP-1 macrophages, StarD4 protein appeared localized to the cytoplasm and the endoplasmic reticulum (ER). More specifically, in THP-1 macrophages StarD4 co-localized to areas of the ER enriched in Acyl-CoA:cholesterol acyltransferase-1 (ACAT-1), and was closely associated with budding lipid droplets. The addition of purified StarD4 recombinant protein to an in vitro assay increased ACAT activity 2-fold, indicating that StarD4 serves as a rate-limiting step in cholesteryl ester formation by delivering cholesterol to ACAT-1-enriched ER. In addition, StarD4 protein was found to be highly regulated and to redistribute in response to sterol levels. In summary, these observations, together with our previous findings demonstrating the ability of increased StarD4 expression to increase bile acid synthesis and cholesteryl ester formation, provide strong evidence for StarD4 as a highly regulated, non-vesicular, directional, intracellular transporter of cholesterol which plays a key role in the maintenance of intracellular cholesterol homeostasis.
authors.affiliation: Department of Medicine, Virginia Commonwealth University, Richmond, VA, USA. drodriguezag@vcu.edu
authors.forename: Daniel
authors.initials: D
authors.lastname: Rodriguez-Agudo
authors.forename: Maria
authors.initials: M
authors.lastname: Calderon-Dominguez
authors.forename: Shunlin
authors.initials: S
authors.lastname: Ren
authors.forename: Dalila
authors.initials: D
authors.lastname: Marques
authors.forename: Kaye
authors.initials: K
authors.lastname: Redford
authors.forename: Miguel Angel
authors.initials: MA
authors.lastname: Medina-Torres
authors.forename: Phillip
authors.initials: P
authors.lastname: Hylemon
authors.forename: Gregorio
authors.initials: G
authors.lastname: Gil
authors.forename: William M
authors.initials: WM
authors.lastname: Pandak
mesh_terms: D041721:3T3-L1 Cells; D000101:Acetyl-CoA C-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D006801:Humans; D015151:Immunoblotting; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism; D008148:Lovastatin / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013261:Sterols / Q000494:pharmacology; D000097382:CD68 Molecule
chemical_list: D000101:Acetyl-CoA C-Acetyltransferase; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D008148:Lovastatin; D026901:Membrane Transport Proteins; D013261:Sterols; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C456544:STARD4 protein, human; C506639:ACAT1 protein, human