The Very Low Density Lipoprotein Receptor Mediates the Cellular Catabolism of Lipoprotein Lipase and Urokinase-Plasminogen Activator Inhibitor Type I Complexes (*)
- Kelley M. Argraves(1),
- Frances D. Battey(1),
- Colin D. MacCalman(2),
- Keith R. McCrae(3),
- Mats Gåfvels(4),
- Karen F. Kozarsky(6),
- David A. Chappell(5),
- Jerome F. Strauss III(2) and
- Dudley K. Strickland(1)(§)
- From the (1) Holland Laboratory, Department of Biochemistry, American Red Cross, Rockville, Maryland 20855
- (2) Departments of Obstetrics and Gynecology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6142
- (3) Thrombosis Research Center, Temple University School of Medicine, Philadelphia, Pennsylvania 19140
- (4) Metabolism and Molecular Nutrition Units, Departments of Internal Medicine, Karolinska Institute and Huddinge University Hospital, Huddinge, S-14186 Sweden
- (5) Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa 52242, and the
- (6) Institute of Human Gene Therapy and Department of Molecular and Cellular Engineering, University of Pennsylvania, and the Wistar Institute, Philadelphia, Pennsylvania 19104
- § To whom correspondence should be addressed: American Red Cross, 15601 Crabbs Branch Way, Rockville, MD 20855. Tel.: 301-738-0726; Fax: 301-738-0794; strickla{at}hlsun.red-cross.org.
Abstract
The very low density lipoprotein (VLDL) receptor binds apolipoprotein E-rich lipoproteins as well as the 39-kDa receptor-associated
protein (RAP). Ligand blotting experiments using RAP and immunoblotting experiments using an anti-VLDL receptor IgG detected
the VLDL receptor in detergent extracts of human aortic endothelial cells, human umbilical vein endothelial cells, and human
aortic smooth muscle cells. To gain insight into the role of the VLDL receptor in the vascular endothelium, its ligand binding
properties were further characterized. In vitro binding experiments documented that lipoprotein lipase (LpL), a key enzyme in lipoprotein catabolism, binds with high affinity
to purified VLDL receptor. In addition, urokinase complexed with plasminogen activator-inhibitor type I (uPA•PAI-1) also bound
to the purified VLDL receptor with high affinity. To assess the capacity of the VLDL receptor to mediate the cellular internalization
of ligands, an adenoviral vector was used to introduce the VLDL receptor gene into a murine embryonic fibroblast cell line
deficient in the VLDL receptor and the LDL receptor-related protein, another endocytic receptor known to bind LpL and uPA•PAI-1
complexes. Infected fibroblasts that express the VLDL receptor mediate the cellular internalization of 
I-labeled LpL and uPA•PAI-1 complexes, leading to their degradation. Non-infected fibroblasts or fibroblasts infected with
the lacZ gene did not internalize these ligands. These studies confirm that the VLDL receptor binds to and mediates the catabolism
of LpL and uPA•PAI-1 complexes. Thus, the VLDL receptor may play a unique role on the vascular endothelium in lipoprotein
catabolism by regulating levels of LpL and in the regulation of fibrinolysis by facilitating the removal of urokinase complexed
with its inhibitor.
Footnotes
-
↵* This work was supported by Grants HL50787 and GM42581 (to D. K. S.), HL49264 (to D. A. C.), HL50827 (to K. R. M.), and HD29946 (to J. F. S.), a grant-in-aid from SEPA American Heart Association, and the W. W. Smith Charitable Trust. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵1 The abbreviations used are:
- LDL
-
low density lipoprotein
- LRP
-
low density lipoprotein receptor-related protein
- VLDL
-
very low density lipoprotein
- RAP
-
receptor-associated protein
- apo E
-
apolipoprotein E
- LpL
-
lipoprotein lipase
- LpLC
-
carboxyl-terminal domain (residues 313-448) of lipoprotein lipase
- uPA
-
urokinase
- pro-uPA
-
pro-urokinase
- PAI-1
-
plasminogen activator inhibitor type I
- Ad-lacZ
-
adenovirus containing lacZ cDNA
- Ad-VLDLR
-
adenovirus containing VLDL receptor cDNA
- GST
-
glutathione S-transferase
- PAGE
-
polyacrylamide gel electrophoresis
- BSA
-
bovine serum albumin
- uPAR
-
urokinase plasminogen activator receptor.
-
- Received April 14, 1995.
- Revision received August 10, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
