[Relationship between proteoglycans and apoE on the HepG2 cell surface].

OBJECTIVE

To characterize the associations and functions of apoE with the HepG2 cell surface through the study of the relationship between proteoglycans and apoE on HepG2 cell surface.

METHODS

The specific binding of 7C9, a monoclonal antibody against the N-terminal domain of apoE was employed to demonstrate the effects of glycosaminoglycans, heparinase, chondroitinase, xyloside, and chlorate on the apoE of HepG2 cell surface.

RESULTS

Growth of cells in beta-D-xyloside decreased cell surface apoE by 45% with a concomitant increase in apoE secretion (4.3-fold), underlining the importance of glycosaminoglycan association of apo E. Incubations with heparinase (3 U/ml) and heparin (1 mg/ml) decreased apoE by 25.0% and 30.5% respectively indicating association through cell surface haparin sulfate proteoglycans. Incubations with chondroitinase ABC (1.5 U/ml) reduced cell surface apoE by 40.0%. Chondroitin sulfate A and chondroitin sulfate B reduced cell surface apoE by 23.6% and 15.3% respectively while incubations with chondrointin sulfate C not effective. Decreasing the levels of cell surface apoE with haparin or chondrointin sulfates A and B increased the subsequent binding of LDL to the HepG2 cell surface.

CONCLUSIONS

ApoE associates with the cell surface mainly through chondrointin sulfate proteoglycans and to a lesser extent through heparan sulfate proteoglycans, decreased levels of cell surface apoE increase the binding of LDL to the cell surface.