Regulated expression of the trophoblast alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein. Differentiation and cAMP modulate protein and mRNA levels.

The alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR/LRP) has several ligands including activated alpha 2-macroglobulin, pregnancy zone protein, and very low density lipoproteins enriched with apolipoprotein E. The diversity of ligands suggests a role for the alpha 2MR/LRP in a variety of processes including tissue remodeling and lipoprotein metabolism. We examined alpha 2MR/LRP in placental trophoblasts, invasive cells that also function in lipid transport and cholesterol metabolism. alpha 2MR/LRP protein was localized by immunohistochemistry in the syncytiotrophoblast of term placenta. Cytotrophoblasts did not stain prominently. alpha 2MR/LRP (protein and message) in primary cultures of human trophoblast cells increased as cytotrophoblasts differentiated into syncytiotrophoblast. 8-Bromo-cAMP prevented this increase and suppressed alpha 2MR/LRP expression. The cyclic nucleotide had similar suppressive effects on alpha 2MR/LRP in BeWo choriocarcinoma cells. In contrast, low density lipoprotein receptor gene expression was increased. We conclude that: 1) there is a differentiation-dependent pattern of alpha 2MR/LRP expression in the human trophoblast; 2) cAMP negatively regulates alpha 2MR/LRP; 3) there is an inverse relationship between alpha 2MR/LRP and low density lipoprotein receptor gene expression in trophoblast cells.