The role of apoproteins AI and AII in binding of high-density lipoprotein3 to membranes derived from bovine aortic endothelial cells

Abstract

Although binding of high-density lipoproteins (HDL) to a variety of cells in culture has been widely reported, the mechanism of this binding has yet to be fully elucidated. The aim of the current studies was to explore the roles of apoproteins (apo) AI and AII in HDL3 binding to membranes derived from bovine aortic endothelial cells. Binding studies showed that HDL3 (which contains both apo AI and apo AII) and AII-HDL3 (which contain only apo AII) bound to membranes with similar affinity (44 +/- 6 and 41 +/- 9 micrograms/ml respectively) and capacity (673 +/- 97 and 969 +/- 101 ng bound/mg of membrane protein respectively). In contrast with these results, HDL3 [AI w/o AII] (which contain apo AI, but not apo AII) bound to the membranes with a significantly higher capacity (2228 +/- 206 ng bound/mg of membrane protein) and lower affinity (65 +/- 3 micrograms/ml) as compared with HDL3 or AII-HDL3. Therefore, although both apo AI and apo AII appear capable of facilitating HDL3 binding, the mechanisms involved probably differ. A model which fits the data postulates that a common receptor exists which binds both apo AI and apo AII, and that a particle containing AII can occupy up to four receptors (partly owing to each AII molecule containing two binding domains), whereas an HDL3 [AI w/o AII] particle can occupy only one.

High density lipoproteins stimulate the production and secretion of endothelin-1 from cultured bovine aortic endothelial cells.

“…We found that this apoprotein potently stimulates ET-1 production and secretion -85% comparably with HDL and therefore could predominantly account for the increased concentration of ET-1 caused by this lipoprotein. It has recently been shown that apo A-I binds to membranes prepared from BAEC with high affinity and capacity (22). In fact, the calculated binding Kd in these studies (44 ,gg/ml) is comparable with the concentrations of HDL used in our study, concentrations which significantly augment ET-1 production.…”

Haptoglobin-related Protein Mediates Trypanosome Lytic Factor Binding to Trypanosomes

“…8C). This is consistent with localization to lysosomes and other endocytic compartments in trypanosomes (21). When cells were co-incubated with Alexa-488-conjugated TLF-1 and the Hpr monoclonal antibody, no intracellular fluorescence was visible (Fig.…”

“…1A). Since TLF-1 contains apolipoproteins AI and AII, known ligands for HDL receptors, it is likely that the low affinity/high capacity TLF binding is due to either apolipoprotein AI or AII (21). The procyclic form of T. b. brucei binds HDL via receptor-mediated endocytosis with similar binding characteristics (22).…”

High-density lipoprotein stimulates endothelial cell movement by a mechanism distinct from basic fibroblast growth factor.

“…40 Binding of HDLs to ECs may be facilitated by apolipoprotein AI and apolipoprotein All, which share a common receptor. 41 An alternate uptake mechanism has been advanced in which HDLs bind to ECs primarily through lipid-lipid interactions rather than a specific polypeptide receptor.42 HDL may also exert its promigratory activity without directly interacting with cells. As one possibility, HDL, acting as a "lipid sink," may remove from the cells an endogenous antimigratory molecule.…”