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

The authors investigated the binding of human plasma I-125-labelled chylomi crons to Chinese hamster ovary (CHO) cells, i.e, native CHO cells are mutan t ldl-A7 cells lacking the low-density lipoproteins receptor, in the absenc e and presence of exogenous bovine milk lipoprotein lipase (LPL) in the cul ture medium. Only a small amount of binding to either cell was observed in the absence of added LPL. Exogenously added LPL increased the specific bind ing of chylomicrons to Idl-A7 cells, as well as to native CHO cells. The en hanced binding of chylomicrons to ldl-A7 cells or native CHO cells by LPL w as inhibited by heparinase and a monoclonal antibody against LPL (5D2) whic h recognizes the carboxyl terminal of LPL. However, the enhanced binding we ts 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 enzymati c activity of LPL that is: essential for LPL to mediate the binding of chyl omicrons to CHO cells.