Metabolism of high-density lipoproteins in cultured rat luteal cells.
The uptake of cholesterol from high-density lipoproteins (HDL) labeled with 125I and [3H]cholesterol was examined in cultured rat luteal cells. Luteal cells were incubated with labeled HDL, following which the metabolic fate of the apolipoproteins and cholesterol moieties of the receptor-bound HDL were examined. About 50% of the originally bound HDL apolipoproteins were released into the medium in 24 h by a temperature-dependent process while only 5% of the HDL cholesterol was released unmetabolized. Inclusion of unlabeled HDL in the chase incubation resulted in increased release of apolipoprotein-derived radioactive products without significant change in the release of unmetabolized cholesterol. 60% of the apolipoprotein-derived radioactivity could be precipitated with trichloroacetic acid; the remaining trichloroacetic acid-soluble radioactive fraction was identified as [125I]iodotyrosine. Gel filtration chromatography of the chase-released material showed that the trichloroacetic acid-precipitable products, which contained no detectable amounts of cholesterol, eluted over a range of molecular sizes (9-80 kDa). No intact HDL was retroendocytosed. About 80% of trichloroacetic acid-precipitable products could be immunoadsorbed on anti-apolipoprotein A-I antibody immobilized on CNBr-activated Sepharose, suggesting the presence of fragments containing apolipoprotein A-I. This material was also capable of reassociating with native HDL. Lysosomal inhibitors were partially effective in inhibiting the amount of trichloroacetic acid-soluble products formed. The lysosomal degradation appeared to have no role in the uptake of HDL-derived cholesterol. These studies demonstrate preferential and total uptake of HDL cholesterol by luteal cells, with concomitant degradation of the lipoprotein.
D000818:Animals; D001053:Apolipoproteins / Q000378:metabolism; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D008076:Cholesterol, HDL / Q000378:metabolism; D003080:Cold Temperature; D003338:Corpus Luteum / Q000378:metabolism*; D005260:Female; D008075:Lipoproteins, HDL / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D001053:Apolipoproteins; D008076:Cholesterol, HDL; D008075:Lipoproteins, HDL; D002784:Cholesterol; C008542:monodansylcadaverine; D002103:Cadaverine