title: Secretion of triacylglycerol-poor VLDL particles from McA-RH7777 cells expressing human hepatic lipase.
abstract: Hepatic lipase (HL) plays a role in the catabolism of apolipoprotein (apo)B-containing lipoproteins through its lipolytic and ligand-binding properties. We describe a potential intracellular role of HL in the assembly and secretion of VLDL. Transient or stable expression of HL in McA-RH7777 cells resulted in decreased (by 40%) incorporation of [(3)H]glycerol into cell-associated and secreted triacylglycerol (TAG) relative to control cells. However, incorporation of [(35)S]methionine/cysteine into cell and medium apoB-100 was not decreased by HL expression. The decreased (3)H-TAG synthesis/secretion in HL expressing cells was not attributable to decreased expression of genes involved in lipogenesis. Fractionation of medium revealed that the decreased [(3)H]TAG from HL expressing cells was mainly attributable to decreased VLDL. Expression of catalytically-inactive HL (HL(SG)) (Ser-145 at the catalytic site was substituted with Gly) in the cells also resulted in decreased secretion of VLDL-[(3)H]TAG. Examination of lumenal contents of microsomes showed a 40% decrease in [(3)H]TAG associated with lumenal lipid droplets in HL or HL(SG) expressing cells as compared with control. The microsomal membrane-associated [(3)H]TAG was decreased by 50% in HL expressing cells but not in HL(SG) expressing cells. Thus, expression of HL, irrespective of its lipolytic function, impairs formation of VLDL precursor [(3)H]TAG in the form of lumenal lipid droplets. These results suggest that HL expression in McA-RH7777 cells result in secretion of [(3)H]TAG-poor VLDL.
authors.affiliation: Department of Biochemistry, Microbiology & Immunology, Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, Canada, K1H 8M5.
authors.forename: Michelle
authors.initials: M
authors.lastname: Bamji-Mirza
authors.forename: Meenakshi
authors.initials: M
authors.lastname: Sundaram
authors.forename: Shumei
authors.initials: S
authors.lastname: Zhong
authors.forename: Erik F
authors.initials: EF
authors.lastname: Yao
authors.forename: Robin J
authors.initials: RJ
authors.lastname: Parks
authors.forename: Zemin
authors.initials: Z
authors.lastname: Yao
mesh_terms: D019943:Amino Acid Substitution; D055162:Biocatalysis; D002460:Cell Line; D015870:Gene Expression; D006801:Humans; D008049:Lipase / Q000235:genetics* / Q000378:metabolism; D050155:Lipogenesis / Q000235:genetics; D008079:Lipoproteins, VLDL / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D014162:Transfection; D014280:Triglycerides
chemical_list: C504173:LIPC protein, human; D008079:Lipoproteins, VLDL; D014280:Triglycerides; D008049:Lipase