出版社：American Society for Biochemistry and Molecular Biology
摘要：We have previously shown that lecithin:cholesterol acyltransferase (LCAT) can transform ultracentrifugally isolated HepG2 lipoproteins (d 1.235 g/ml fraction (lipid-poor apoA-I); hence we investigated whether inclusion of d > 1.235 g/ml fraction in LCAT incubations altered HDL subpopulations. After 18 h incubation of CM (containing lipoproteins and d > 1.235 g/ml fraction) with purified LCAT, the major transformation product on GGE was a large 9.7-nm particle (HDL2b pattern); a minor component appeared at 7.4 nm (HDL3c). Differences in particle size distribution between CM and isolated lipoprotein incubations were not the result of differences in LCAT activity; mass ratios of unesterified cholesterol:cholesteryl ester and phospholipid:cholesteryl ester were similar. Removal of apoA-I from the d > 1.235 g/ml fraction by immunoaffinity chromatography prior to incubation with the d 1.235 g/ml fraction; therefore, lipid-poor apoA-I does not influence nascent HDL transformation. Cholesteryl ester was transferred from HepG2 HDL to LDL in CM incubations; however, cholesteryl ester transfer protein was not immunochemically identified. Removal of HepG2 LDL from CM prior to incubation with LCAT still resulted in the HDL2b pattern. We conclude that HepG2 cells secrete a factor(s) that modifies nascent HDL transformation products into a predominantly HDL2b subpopulation.
