SYNTHESIS AND PROPERTIES OF THE VERY-LOW-DENSITY-LIPOPROTEIN RECEPTORAND A COMPARISON WITH THE LOW-DENSITY-LIPOPROTEIN RECEPTOR

The properties of the very-low-density lipoprotein (VLDL) receptor hav e been studied in Chinese hamster ovary (CHO) cells stably transfected with human VLDL-receptor cDNA and compared with those of the low-dens ity lipoprotein (LDL) receptor expressed under the same conditions. Im munoblotting showed that the cells produced a mature VLDL receptor pro tein, of apparent M-r 123000 on non-reduced and 158000 on reduced gels , that was less extensively glycosylated than the LDL receptor. The VL DL receptor was more slowly processed than the LDL receptor, with only approx. 70 % of the precursor being converted into the mature protein . Nevertheless, the majority of the receptor in the cells was in the m ature form, and most of this was present on the cell surface. The huma n VLDL receptor bound rabbit very-low-density lipoprotein with beta el ectrophoretic mobility (beta VLDL), but not human LDL, and uptake thro ugh the receptor led to stimulation of oleate incorporation into chole steryl esters. At 37 degrees C, the characteristics of VLDL-receptor-m ediated uptake and degradation of beta VLDL were essentially the same as those mediated by the LDL receptor. However, the VLDL receptor appa rently did not show the increase in affinity and decrease in binding o f beta VLDL on cooling to 4 degrees C that was exhibited by the LDL re ceptor. Thus the overexpressed VLDL receptor in CHO cells appears to b ehave as a lipoprotein receptor with similar, but not identical, prope rties to the LDL receptor.