Victoria J. South

A novel endothelial-derived lipase that modulates HDL metabolism.

High-density lipoprotein (HDL) cholesterol levels are inversely associated with risk of atherosclerotic cardiovascular disease. At least 50% of the variation in HDL cholesterol levels is genetically determined, but the genes responsible for variation in HDL levels have not been fully elucidated. Lipoprotein lipase (LPL) and hepatic lipase (HL), two members of the triacylglyerol (TG) lipase family, both influence HDL metabolism and the HL (LIPC) locus has been associated with variation in HDL cholesterol levels in humans. We describe here the cloning and in vivo functional analysis of a new member of the TG lipase family. In contrast to other family members, this new lipase is synthesized by endothelial cells in vitro and thus has been termed endothelial lipase (encoded by the LIPG gene). EL is expressed in vivo in organs including liver, lung, kidney and placenta, but not in skeletal muscle. In contrast to LPL and HL, EL has a lid of only 19 residues. EL has substantial phospholipase activity, but less triglyceride lipase activity. Overexpression of EL in mice reduced plasma concentrations of HDL cholesterol and its major protein apolipoprotein A-I. The endothelial expression, enzymatic profile and in vivo effects of EL suggest that it may have a role in lipoprotein metabolism and vascular biology.

Cloning, expression of the human substance K receptor, and analysis of its role in mitogenesis.

The primary strudure of the human substance K receptor was established from the sequences of complementary DNA clones isolated from a human jejunal complementary DNA library. It consists of 398 amino acids, including seven putative transmembrane regions. The gene for the human substance K receptor was localized to chromosome region 10p13-10q23, a region with frequent chromosomal abnormalities. The human substance K receptor was expressed in transfeded NIH-3T3 cells lacking endogenous substance K receptors, and Scatchard analysis of 125I labeled substance K binding indicates approximately 100,000 receptors/cell with a single dissociation constant of 12 nM. Covalent cross-linking experiments utilizing 125I-substanceK and three different chemical cross-linking reagents (disuccinimidyl suberate, disuccinimidyl tartrate, or 1-ethyl-3-(3dimethylaminopropyl)carbodiimide-HCI) demonstrate an apparent molecular weight of 45,000, consistent with little or no N-linked glycosylation. The binding of substance K to its receptor on transfeded cells led to a rapid increase in the produdion of total inositol phosphates and the release of Ca2� from internal stores. Growth of the cells transfeded with the human substance K receptor is stimulated by the addition of substance K to the medium to a level similar to 10% serum. Therefore, the human substance K receptor can function as a growth fador receptor when expressed in mouse 3T3 cells.