Effects of preincubation of primary monolayer cultures of rat hepatocytes with low- and high-density lipoproteins on the subsequent binding and metabolism of human low-density lipoprotein.
1. There are two distinct binding sites (Site 1 and Site 2) for human low-density lipoprotein (LDL) on rat hepatocytes in monolayer culture [Salter, Saxton & Brindley (1986) Biochem. J. 240, 549-557]. 2. Binding of 125I-LDL to Site 1, but not to Site 2, is up-regulated between 20 and 44 h in culture by preincubation of the cells with human high-density lipoprotein 3 (HDL3). 3. A similar preincubation with HDL2 had no significant effect on binding to either site. 4. Preincubation with human LDL led to a partial down-regulation of subsequent binding of 125I-LDL to Site 1. Since binding after incubation with LDL was measured at 37 degrees C, binding to Site 2 could not be distinguished from LDL that had been internalized by the cells. 5. Hepatocytes were shown to degrade 125I-LDL, resulting in the accumulation of [125I]iodotyrosine in the medium. Evidence was found that iodotyrosine may be further degraded by deiodinase produced by the cells. 6. Regulation of binding to Site 1 by preincubation with LDL or HDL3 was found to lead to a parallel regulation of LDL degradation. 7. It is concluded that rat hepatocytes not only bind but also metabolize human LDL and that these processes are under metabolic regulation.
Department of Biochemistry, University of Nottingham Medical School, Queen's Medical Centre, U.K.
A M
AM
Salter
M
M
Bugaut
J
J
Saxton
S C
SC
Fisher
D N
DN
Brindley
D000818:Animals; D002478:Cells, Cultured; D008074:Lipoproteins / Q000494:pharmacology*; D008075:Lipoproteins, HDL / Q000494:pharmacology; D008077:Lipoproteins, LDL / Q000378:metabolism* / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats
D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL