SYNTHESIS AND SECRETION OF LIPOPROTEIN-LIPASE IN HEPARAN SULFATE-DEFICIENT CHINESE-HAMSTER OVARY CELLS

Synthesis and secretion of lipoprotein lipase was studied in two mutan ts of Chinese hamster ovary (CHO) cells which, due to a lack of xylosy l transferase (pgsA-745) or galactosyl transferase (pgsB-761), respect ively, were deficient in heparan sulfate and chondroitin sulfate. One of the mutants (pgsB-761) was two- to threefold more active in synthes is and secretion of catalytically active lipoprotein lipase than the o ther mutant, which was about as active as the wild-type (K1) cells. A similar relation was found when lipoprotein lipase was metabolically l abelled with S-35-methionine and then immunoprecipitated. Heparin stim ulated secretion from all three cell types to a similar extent labour twofold). Heparin-releasable binding of I-125-labelled lipoprotein lip ase was lower to either of the mutant cells than to the wild-type cell s. Binding to the wild-type cells was reduced by heparitinase, while t he low binding to the mutants was not affected. By immunogold labellin g of cryosections, lipoprotein lipase was detected on the plasma membr anes and on the inside of secretory vesicles of both wild-type and mut ant cells, suggesting that some carrier could be involved. Inhibition of vesicular transport by monensin caused accumulation of lipoprotein lipase in the cells. In wild-type cells the lipase was mainly on the i nside of vesicular structures, while in the mutants the main part was associated with membranous bodies that formed within the vesicles duri ng a chase period. These results suggest that if lipoprotein lipase ne eds a carrier during intracellular assembly and transport, this functi on can be Fulfilled by some structure other than heparan sulfate.