title: STARD4 knockdown in HepG2 cells disrupts cholesterol trafficking associated with the plasma membrane, ER, and ERC.
abstract: STARD4, a member of the evolutionarily conserved START gene family, has been implicated in the nonvesicular intracellular transport of cholesterol. However, the direction of transport and the membranes with which this protein interacts are not clear. We present studies of STARD4 function using small hairpin RNA knockdown technology to reduce STARD4 expression in HepG2 cells. In a cholesterol-poor environment, we found that a reduction in STARD4 expression leads to retention of cholesterol at the plasma membrane, reduction of endoplasmic reticulum-associated cholesterol, and decreased ACAT synthesized cholesteryl esters. Furthermore, D4 KD cells exhibited a reduced rate of sterol transport to the endocytic recycling compartment after cholesterol repletion. Although these cells displayed normal endocytic trafficking in cholesterol-poor and replete conditions, cell surface low density lipoprotein receptor (LDLR) levels were increased and decreased, respectively. We also observed a decrease in NPC1 protein expression, suggesting the induction of compensatory pathways to maintain cholesterol balance. These data indicate a role for STARD4 in nonvesicular transport of cholesterol from the plasma membrane and the endocytic recycling compartment to the endoplasmic reticulum and perhaps other intracellular compartments as well.
authors.affiliation: The Laboratory of Biochemical Genetics and Metabolism, The Rockefeller University, New York, NY 10065, USA.
authors.forename: Jeanne
authors.initials: J
authors.lastname: Garbarino
authors.forename: Meihui
authors.initials: M
authors.lastname: Pan
authors.forename: Harvey F
authors.initials: HF
authors.lastname: Chin
authors.forename: Frederik W
authors.initials: FW
authors.lastname: Lund
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Maxfield
authors.forename: Jan L
authors.initials: JL
authors.lastname: Breslow
mesh_terms: D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D004705:Endocytosis; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism*; D056945:Hep G2 Cells; D006801:Humans; D026901:Membrane Transport Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D026901:Membrane Transport Proteins; D034741:RNA, Small Interfering; C456544:STARD4 protein, human; D002784:Cholesterol