Very low density lipoprotein receptor from mammary gland and mammary epithelial cell lines binds and mediates endocytosis of Mr, 40,000 receptor associated protein

AbstractWe here report that the Mr 40,000 receptor associated protein (RAP), previously found to bind to α2-macroglobulin receptor/low density lipoprotein receptor related protein (α2MR/LRP) and glycoprotein 330 (gp330), binds to an Mr, 105,000 membrane protein from bovine mammary gland, human mamma tumors and mammary epithelial cell lines. We have purified this protein from bovine and human sources. N-terminal amino acid sequencing and immunoblotting analyses showed that the protein was identical or closely related to very low density lipoprotein receptor (VLDL-R). Experiments with the human mamma carcinoma cell line MCF-7 showed that this receptor was able to mediate an efficient endocytosis of RAP. These novel findings strongly suggest that RAP functions as a modulator of ligand binding to VLDL-R, similarly to α2MR/LRP and gp330