Effect of lipoprotein lipase on binding of chylomicrons to LDL receptor-deficient Chinese hamster ovary cells

The authors investigated the binding of human plasma 125I-labelled chylomicrons to Chinese hamster ovary (CHO) cells, i.e. native CHO cells are mutant ldl-A7 cells lacking the low-density lipoproteins receptor, in the absence and presence of exogenous bovine milk lipoprotein lipase (LPL) in the culture medium. Only a small amount of binding to either cell was observed in the absence of added LPL. Exogenously added LPL increased the specific binding of chylomicrons to ldl-A7 cells, as well as to native CHO cells. The enhanced binding of chylomicrons to ldl-A7 cells or native CHO cells by LPL was inhibited by heparinase and a monoclonal antibody against LPL (5D2) which recognizes the carboxyl terminal of LPL. However, the enhanced binding was not inhibited by 1 M NaCl, which abolishes the enzymatic activity of LPL in either ldl-A7 cell or native CHO cells. These results suggest that LPL enhances the binding of chylomicrons to heparan sulphate proteoglycans of CHO cells, and that it is the carboxyl terminal of LPL but not the enzymatic activity of LPL that is essential for LPL to mediate the binding of chylomicrons to CHO cells.