Role of apolipoprotein A-I in HDL binding to a rat hepatoma cell in culture
The binding of HDL to rat Fu5AH hepatoma cells at 4/sup 0/, and uptake and degradation at 37/sup 0/, was investigated in monolayer cultures. HDL, free of apo E and apo A-IV, was obtained from the plasma of nephrotic rats (HDLne). /sup 125/I-labeled HDLne bound to the cells in a specific, saturable manner. By Scatchard analysis, two classes of binding sites were obtained: a high affinity binding site (Kd = 1.25 +/- 0.023 ..mu..g/ml, or 5 x 10/sup -9/ M), and a lower affinity site (Kd = 45 +/- 15 ..mu..g/ml, or 1.8 x 10/sup -7/ M). In competitive binding experiments, normal rat HDL was nearly as effective as HDLne, but rat VLDL and human lipoproteins were ineffective. Rat apo A-I/phospholipid complexes also did not complete effectively for HDLne binding, although they were capable of binding to the cells. However, LDL (1.02 < d < 1.063) from nephrotic rat plasma, containing 20% of apo A-I, was as effective as rat HDL in competing for HDLne binding when the competition was expressed as a function of apo A-I content. Control experiments indicated that labeled apo A-I from HDLne did not exchange appreciably with unlabeled apo A-I on the LDLne. When the hepatoma cells were allowed to internalize and degrade HDLne at 37/sup 0/, the acid-soluble products (iodotyrosine and iodide) were derived almost entirely from the breakdown of apo A-I. We conclude that the rat hepatoma cell (Fu5AH) has high affinity HDL binding sites which recognize apo A-I-lipid complexes in which apo A-I an appropriate conformation.
- Research Organization:
- Medical Coll. of Pennsylvania, Philadelphia (USA)
- OSTI ID:
- 5620541
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
AFFINITY
ANIMAL CELLS
ANIMALS
APOLIPOPROTEINS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
CELL CULTURES
CHOLESTEROL
CPB
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
HYDROXY COMPOUNDS
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIPIDS
LIPOPROTEINS
LIVER CELLS
MAMMALS
MEMBRANE PROTEINS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
PROTEINS
RADIOISOTOPES
RATS
REACTION KINETICS
RECEPTORS
RODENTS
SOMATIC CELLS
STEROIDS
STEROLS
TRACER TECHNIQUES
UPTAKE
VERTEBRATES