Biomaterial Database

High density lipoprotein3 binding and biological action: high affinity binding is not necessary for stimulation of placental lactogen release from trophoblast cells. 1989

E V Jorgensen, and J T Gwynne, and S Handwerger

Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710.

High density lipoprotein (HDL3) binds with high affinity to many types of cells, but controversy exists concerning the nature and biological significance of the binding. We have recently demonstrated that HDL and apoproteins (apo)-AI, -AII, and -CI stimulate a specific and dose-dependent increase in placental lactogen (hPL) release from human trophoblast cells. To examine the possible relationship between HDL3 binding and stimulation of hPL release, we have characterized the binding of [125I]HDL3 to an enriched fraction of hPL-producing trophoblast cells. Binding studies were performed on trophoblast cells isolated by isopycnic centrifugation of collagenase/hyaluronidase-dispersed placental tissue and apo-E free-HDL3 (density, 1.125-1.215 g/ml). Scatchard analysis of binding studies performed at 37 C for 2 h revealed two classes of binding sites: 1) high affinity binding sites with a Kd of 9.7 +/- 2.2 micrograms/ml (1.3 x 10(-7) M) and 9.8 +/- 3.2 x 10(5) binding sites/trophoblast cell, and 2) low affinity binding sites with a Kd of 172.8 +/- 64.8 micrograms/ml (2.3 x 10(-6) M) and an estimated 3.2 x 10(6) sites/cell. As has been found in hepatocytes and other cells, the number of HDL3-binding sites per trophoblast cell (but not the binding affinity) decreased at lower incubation temperatures. In addition, HDL3 binding to trophoblasts cells did not require calcium and was not affected by prior treatment of the cells with pronase or trypsin. HDL3-binding sites on trophoblast cells, however, were not specific for HDL3. Low density lipoprotein (density, 1.063-1.055 g/ml), which does not stimulate hPL release, was nearly as potent on a molar basis as HDL3 in binding to the high and low affinity binding sites on trophoblast cells. Furthermore, nitrated HDL3, which does not compete for high affinity binding to trophoblast cells, stimulated hPL release. Although the characteristics of HDL3 binding to trophoblast cells are similar to those of other cells, these results strongly suggest that the binding of HDL3 to high affinity binding sites is not essential for HDL-mediated hPL release.

UI	MeSH Term	Description	Entries
D008075	Lipoproteins, HDL	A class of lipoproteins of small size (4-13 nm) and dense (greater than 1.063 g/ml) particles. HDL lipoproteins, synthesized in the liver without a lipid core, accumulate cholesterol esters from peripheral tissues and transport them to the liver for re-utilization or elimination from the body (the reverse cholesterol transport). Their major protein component is APOLIPOPROTEIN A-I. HDL also shuttle APOLIPOPROTEINS C and APOLIPOPROTEINS E to and from triglyceride-rich lipoproteins during their catabolism. HDL plasma level has been inversely correlated with the risk of cardiovascular diseases.	High Density Lipoprotein,High-Density Lipoprotein,High-Density Lipoproteins,alpha-Lipoprotein,alpha-Lipoproteins,Heavy Lipoproteins,alpha-1 Lipoprotein,Density Lipoprotein, High,HDL Lipoproteins,High Density Lipoproteins,Lipoprotein, High Density,Lipoprotein, High-Density,Lipoproteins, Heavy,Lipoproteins, High-Density,alpha Lipoprotein,alpha Lipoproteins
D008077	Lipoproteins, LDL	A class of lipoproteins of small size (18-25 nm) and light (1.019-1.063 g/ml) particles with a core composed mainly of CHOLESTEROL ESTERS and smaller amounts of TRIGLYCERIDES. The surface monolayer consists mostly of PHOSPHOLIPIDS, a single copy of APOLIPOPROTEIN B-100, and free cholesterol molecules. The main LDL function is to transport cholesterol and cholesterol esters to extrahepatic tissues.	Low-Density Lipoprotein,Low-Density Lipoproteins,beta-Lipoprotein,beta-Lipoproteins,LDL(1),LDL(2),LDL-1,LDL-2,LDL1,LDL2,Low-Density Lipoprotein 1,Low-Density Lipoprotein 2,LDL Lipoproteins,Lipoprotein, Low-Density,Lipoproteins, Low-Density,Low Density Lipoprotein,Low Density Lipoprotein 1,Low Density Lipoprotein 2,Low Density Lipoproteins,beta Lipoprotein,beta Lipoproteins
D010928	Placental Lactogen	A polypeptide hormone of approximately 25 kDa that is produced by the SYNCYTIOTROPHOBLASTS of the PLACENTA, also known as chorionic somatomammotropin. It has both GROWTH HORMONE and PROLACTIN activities on growth, lactation, and luteal steroid production. In women, placental lactogen secretion begins soon after implantation and increases to 1 g or more a day in late pregnancy. Placental lactogen is also an insulin antagonist.	Choriomammotropin,Chorionic Somatomammotropin, Human,Human Placental Lactogen,Lactogen Hormone, Placental,Mammotropic Hormone, Placental,Somatomammotropin, Chorionic,Choriomammotrophin,HCS (Human Chorionic Somatomammotropin),HPL (Human Placental Lactogen),PAPP-D,Placental Luteotropin,Pregnancy-Associated Plasma Protein D,Chorionic Somatomammotropin,Human Chorionic Somatomammotropin,Lactogen, Placental,Luteotropin, Placental,Placental Lactogen, Human,Placental Mammotropic Hormone,Pregnancy Associated Plasma Protein D
D002118	Calcium	A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.	Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D002500	Centrifugation, Isopycnic	A technique used to separate particles according to their densities in a continuous density gradient. The sample is usually mixed with a solution of known gradient materials and subjected to centrifugation. Each particle sediments to the position at which the gradient density is equal to its own. The range of the density gradient is usually greater than that of the sample particles. It is used in purifying biological materials such as proteins, nucleic acids, organelles, and cell types.	Isopycnic Centrifugation
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D001667	Binding, Competitive	The interaction of two or more substrates or ligands with the same binding site. The displacement of one by the other is used in quantitative and selective affinity measurements.	Competitive Binding
D014327	Trophoblasts	Cells lining the outside of the BLASTOCYST. After binding to the ENDOMETRIUM, trophoblasts develop into two distinct layers, an inner layer of mononuclear cytotrophoblasts and an outer layer of continuous multinuclear cytoplasm, the syncytiotrophoblasts, which form the early fetal-maternal interface (PLACENTA).	Cytotrophoblasts,Syncytiotrophoblasts,Trophoblast,Cytotrophoblast,Syncytiotrophoblast