EXPRESSION OF ALPHA(2)-MACROGLOBULIN RECEPTOR-ASSOCIATED PROTEIN IN NORMAL HUMAN EPIDERMAL MELANOCYTES AND HUMAN-MELANOMA CELL-LINES

alpha(2)-Macroglobulin receptor/low-density lipoprotein receptor-relat ed protein is a multifunctional cell surface receptor known to bind an d internalize a large number of ligands. alpha(2)-Macroglobulin recept or-associated protein acts as an intracellular ''chaperone'' for th is receptor, and it has been shown to inhibit binding of all its known l igands. In this paper, we characterize the expression of the receptor- associated protein in both normal human epidermal melanocytes and in s ix different human melanoma cell lines, by the use of flow cytometry a nd Western blotting analysis. We show that ail the melanoma cell lines and the normal melanocytes express the receptor-associated protein at similar levels, with most located intracellularly. No receptor-associ ated protein was detected at the cell surface in the melanocytes or in three of the cell lines. However, in two of the melanoma cell lines, large amounts of receptor-associated protein were found on the cell su rface, these having the largest amounts of it reported to date; in a f urther melanoma cell line, there was a small amount at the cell surfac e. We have also shown that the melanocytes and all the melanoma cell l ines express the receptor itself at a wide range of levels, the highes t levels of both the cell surface receptor and the cell surface recept or-associated protein being found in one particular melanoma cell line . By growing the cell lines under controlled conditions, we have demon strated that, although the total cellular content of the receptor is m arkedly increased at high cell culture density, this treatment has no effect on the level of expression of the receptor-associated protein. J. Cell. Biochem. 71 :149-157, 1998. (C) 1998 Wiley-Liss, Inc.