Characterization of apoA-I-containing lipoprotein subpopulations secreted by HepG2 cells.
Recent immunoaffinity studies demonstrate two populations of high density lipoprotein (HDL) particles: one contains both apolipoprotein (apo) A-I and A-II [Lp(A-I w A-II)], and the other contains apoA-I but no A-II [Lp(A-I w/o A-II)]. To investigate whether these two populations are derived from different precursors, we applied sequential immunoaffinity chromatography to study the lipoprotein complexes in HepG2 conditioned serum-free medium. The apparent secretion rates of apoA-I, A-II, E, D, A-IV, and lecithin:cholesterol acyltransferase (LCAT) were 4013 +/- 1368, 851 +/- 217, 414 +/- 64, 171 +/- 51, 32 +/- 14, and 2.9 +/- 0.7 ng/mg cell protein per 24 h, respectively (n = 3-5). Anti-A-II removed all apoA-II but only 39 +/- 5% (n = 5) apoA-I from the medium. These HepG2 Lp(A-I w A-II) also contained 31 +/- 1% (n = 5) of the apoD and 82 +/- 2% (n = 3) of the apoE in the medium. The apoE existed both as E and E-A-II complex. Lipoproteins isolated from the apoA-II-free medium by anti-A-I contained, besides apoA-I, 60 +/- 3% of the medium apoD and trace quantities of apoE. The majority of HepG2 apoA-IV (78 +/- 4%) (n = 3) and LCAT (85 +/- 6%) (n = 3) was not associated with either apoA-I or A-II. HepG2 Lp(A-I w A-II) contained relatively more lipids than Lp(A-I w/o A-II) (45 vs. 37%).(ABSTRACT TRUNCATED AT 250 WORDS)
Cheung
M C
MC
Department of Medicine, School of Medicine, University of Washington, Seattle 98104.
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D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001054:Apolipoproteins A / Q000378:metabolism* / Q000648:ultrastructure; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D006801:Humans; D008075:Lipoproteins, HDL / Q000145:classification / Q000378:metabolism* / Q000648:ultrastructure; D008113:Liver Neoplasms; D008854:Microscopy, Electron; D010316:Particle Size; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000378:metabolism*
D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D001054:Apolipoproteins A; D008075:Lipoproteins, HDL; D007862:Phosphatidylcholine-Sterol O-Acyltransferase