EXPRESSION OF ALPHA(2) MACROGLOBULIN RECEPTOR LOW-DENSITY-LIPOPROTEINRECEPTOR-RELATED PROTEIN IS CELL-CULTURE DENSITY-DEPENDENT IN HUMAN BREAST-CANCER CELL-LINE BT-20

alpha(2)Macroglobulin receptor/low density lipoprotein receptor-relate d protein (alpha(2)MR/LRP) is a multifunctional cell plasma membrane r eceptor that binds and facilitates the endocytosis of a number of liga nds involved in protease regulation and lipoprotein metabolism. In the invasive breast cancer cell line BT-20 we show that the expression of alpha(2)MR/LRP can be strongly affected by cell culture density. By c omparing measurements of mRNA total cellular alpha(2)MR/LRP antigen, a nd cell surface alpha(2)MR/LRP expression Fee have demonstrated a mark ed cell density-dependent regulation of this receptor expression. Incr easing the cell density results in a 3.4-fold increase in cell surface alpha(2)MR/LRP expression. This corresponds to a marked increase in a lpha MR/LRP mRNA in Northern blots of total RNA from cells cultured at high density and to consistent increases in alpha(2)MR/LRP heavy chai n in Western blots of cell lysates from high density cultures. These s tudies together demonstrate the significant up-regulation of alpha(2)M R/LRP expression in BT-20 by increased cell density. (C) 1997 Academic Press.