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  • 标题:Recombinant human serum amyloid A (apoSAAp) binds cholesterol and modulates cholesterol flux.
  • 本地全文:下载
  • 作者:J S Liang ; J D Sipe
  • 期刊名称:JLR Papers In Press
  • 印刷版ISSN:0022-2275
  • 电子版ISSN:1539-7262
  • 出版年度:1995
  • 卷号:36
  • 期号:1
  • 页码:37-46
  • 语种:English
  • 出版社:American Society for Biochemistry and Molecular Biology
  • 摘要:During acute inflammation, the serum amyloid A (apoSAA) proteins apoSAA1 and apoSAA2 are transiently associated with high density lipoproteins (HDL) in concentrations of as much as 1000-fold more than their concentrations during homeostasis; however, their effect on HDL function is unclear. Recombinant apoSAAp, a hybrid of the closely related human apoSAA1 and apoSAA2 isoforms, was found to exhibit a high affinity for cholesterol. The adsorption of apoSAAp to polystyrene microtiter wells at physiological pH, temperature, and salt concentration was inhibited and reversed by cholesterol. ApoSAAp, to a greater extent than apoA-I, albumin, or fetal bovine serum, enhanced diffusion of cholesterol from HDL across a membrane that retained molecules > 3.5 kDa. Cholesterol from 25 nM to 125 microM inhibited binding of [3H]cholesterol to 167 nM apoSAAp. A cholesterol binding assay was developed to determine the dissociation constant for binding of [3H]cholesterol to apoSAAp; Kd = 1.7 +/- 0.3 x 10(-7) M and the maximum binding capacity (Bmax) is 1.1 +/- 0.1 mol/mol. After binding cholesterol, the apparent size of apoSAAp as determined by gel filtration on Sephacryl S-100 was increased from 12 to 23 kDa. ApoSAAp enhanced free [14C]cholesterol uptake from tissue culture medium by HepG2 cells, an effect that was dose dependent and blocked by polyclonal antibodies to human apoSAA1 and apoSAA2. ApoSAAp, unlike apoA-I, was taken up from serum-free medium by HepG2 cells and appeared to be degraded by cell-associated enzymes. Unlike peritoneal exudate cells, human HepG2 hepatoma cells do not secrete an enzyme that degrades apoSAAp. These results suggest that apoSAA can potentially serve as a transient cholesterol-binding protein.
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