Subcellular localization and regulation of StarD4 protein in macrophages and fibroblasts

• Published in: Biochimica et biophysica acta Vol. 1811; no. 10; pp. 597 - 606
• Main Authors: Rodriguez-Agudo, Daniel, Calderon-Dominguez, Maria, Ren, Shunlin, Marques, Dalila, Redford, Kaye, Medina-Torres, Miguel Angel, Hylemon, Phillip, Gil, Gregorio, Pandak, William M.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.10.2011
• Subjects: 3T3-L1 Cells; Acetyl-CoA C-Acetyltransferase - genetics; Acetyl-CoA C-Acetyltransferase - metabolism; Animals; Antigens, CD - genetics; Antigens, CD - metabolism; Antigens, Differentiation, Myelomonocytic - genetics; Antigens, Differentiation, Myelomonocytic - metabolism; bile acids; Cells, Cultured; Cholesterol; Cholesterol transporter; droplets; endoplasmic reticulum; fibroblasts; Fibroblasts - cytology; Fibroblasts - drug effects; Fibroblasts - metabolism; Fluorescent Antibody Technique; Gene Expression Regulation - drug effects; Gene Expression Regulation - genetics; hepatocytes; homeostasis; Humans; Immunoblotting; in vitro studies; In Vitro Techniques; Kupffer cells; liver; Liver - metabolism; Lovastatin - pharmacology; Macrophage; macrophages; Macrophages - cytology; Macrophages - drug effects; Macrophages - metabolism; Membrane Transport Proteins - genetics; Membrane Transport Proteins - metabolism; Metabolism; Mice; recombinant proteins; Reverse Transcriptase Polymerase Chain Reaction; START domain; Steroidogenic acute regulatory protein; Sterols - pharmacology; START domain; Steroidogenic acute regulatory protein; Metabolism; Cholesterol; Macrophage; Cholesterol transporter
• ISSN: 1388-1981; 0006-3002; 1879-2618
• DOI: 10.1016/j.bbalip.2011.06.028

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. ► StarD4 is a START domain protein with a cholesterol-specific lipid binding pocket. ► StarD4 is found in hepatocytes, macrophages and fibroblast in the cytoplasm and ER. ► StarD4 is regulated by sterols and upregulated during macrophage differentiation. ► The protein is able to increase ACAT activity in an in vitro assay. ► StarD4 is a highly regulated, non-vesicular, directional cholesterol transporter.