The LDL receptor-related protein (LRP) family: an old family of proteins with new physiological functions.

The low-density lipoprotein (LDL) receptor is the founding member of a family of seven structurally closely related transmembrane proteins (LRP1, LRP1b, megalin/LRP2, LDL receptor, very low-density lipoprotein receptor, MEGF7/LRP4, LRP8/apolipoprotein E receptor2). These proteins participate in a wide range of physiological processes, including the regulation of lipid metabolism, protection against atherosclerosis, neurodevelopment, and transport of nutrients and vitamins. While currently available data suggest that the role of the LDL receptor is limited to the regulation of cholesterol homeostasis by receptor-mediated endocytosis of lipoprotein particles, there is growing experimental evidence that the other members of the gene family have additional physiological functions as signal transducers. In this review, we focus on the latest discovered functions of two major members of this family, LRP1 and megalin/LRP2, and on the newly elucidated physiological role of a third member of the family, MEGF7/LRP4, which can also function as a modulator of diverse signaling pathways during development.