HEPARAN-SULFATE PROTEOGLYCANS ARE PRIMARILY RESPONSIBLE FOR THE MAINTENANCE OF ENZYME-ACTIVITY, BINDING, AND DEGRADATION OF LIPOPROTEIN-LIPASE IN CHINESE-HAMSTER OVARY CELLS

Various aspects of lipoprotein lipase (LPL) metabolism, including cell surface binding, degradation, and enzymatic activity, were compared between Chinese hamster ovary (CHO) cells and two distinct proteoglycan-deficient CHO cell lines. The contribution of low density lipoprotein receptor-related protein in binding LPL was also analyzed by the use of a 39-kDa receptor associated protein expressed as a glutathione S-transferase fusion protein (GST-RAP), Equilibrium binding data with I-125-LPL revealed the presence of a class of high affinity binding sites with a K-D of 7.8 nM in CHO cells, whereas no high affinity binding was observed for proteoglycan-deficient cells. The high affinity binding of LPL in CHO cells appeared to be concentrated in cell surface projections and was not effectively inhibited by GST-RAP. Moreover, degradation of endogenous and exogenous LPL was significantly greater in control CHO cells than in proteoglycan-deficient cells. Degradation of LPL in CHO cells was not affected by GST-RAP, suggesting that proteoglycans and not low density lipoprotein receptor-related protein are responsible for the majority of binding and degradation of LPL in these cells, Our data also show that proteoglycan binding is not essential for the assembly of active LPL homodimers, although proteoglycan binding controls the distribution of LPL activity, Furthermore, LPL produced by CHO cells was more stable than LPL produced by proteoglycan-deficient cells.