Interactions of the Low Density Lipoprotein Receptor Gene Family with Cytosolic Adaptor and Scaffold Proteins Suggest Diverse Biological Functions in Cellular Communication and Signal Transduction

Department of Molecular Genetics and Pathology, University of Texas Southwestern Medical Center, Dallas 75390-9046, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 09/2000; 275(33):25616-24. DOI: 10.1074/jbc.M000955200
Source: PubMed


The members of the low density lipoprotein (LDL) receptor gene family bind a broad spectrum of extracellular ligands. Traditionally, they had been regarded as mere cargo receptors that promote the endocytosis and lysosomal delivery of these ligands. However, recent genetic experiments in mice have revealed critical functions for two LDL receptor family members, the very low density lipoprotein receptor and the apoE receptor-2, in the transmission of extracellular signals and the activation of intracellular tyrosine kinases. This process regulates neuronal migration and is crucial for brain development. Signaling through these receptors requires the interaction of their cytoplasmic tails with the intracellular adaptor protein Disabled-1 (DAB1). Here, we identify an extended set of cytoplasmic proteins that might also participate in signal transmission by the LDL receptor gene family. Most of these novel proteins are adaptor or scaffold proteins that contain PID or PDZ domains and function in the regulation of mitogen-activated protein kinases, cell adhesion, vesicle trafficking, or neurotransmission. We show that binding of DAB1 interferes with receptor internalization suggesting a mechanism by which signaling through this class of receptors might be regulated. Taken together, these findings imply much broader physiological functions for the LDL receptor family than had previously been appreciated. They form the basis for the elucidation of the molecular pathways by which cells respond to the diversity of ligands that bind to these multifunctional receptors on the cell surface.

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    • "Our finding that interaction between GIPC and LPA1 leads to downregulation of Akt signaling has important pathophysiological implications, given 1) that LPA1 has been shown to promote the development of various carcinomas, 2) that mutations in the PDZ binding motif of LPA1 induces oncogenic transformation [1], [42]–[44], [46], [51], [52], and 3) that GIPC plays a tumor suppressor role in breast cancer progression [51], [53]. Whether and how the interaction of these two proteins is abrogated during cancer progression remains unknown. "
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    • "It has been suggested that these motifs may be associated with the rapid endocytotic rate of LRP1 (Deane et al., 2008). The cytoplasmic tail is phosphorylated on serine and/or tyrosine residues (van der Geer, 2002) and can interact with different adaptor proteins associated with cell signaling, such as disabled-1 (Dab1), FE65 (Klug et al., 2011) and postsynaptic density protein 95 (PSD95) (Trommsdorff et al., 1998; Gotthardt et al., 2000; Herz et al., 2009). Thus, LRP1 has a dual role as a receptor which internalizes its ligands acting like a rapid cargo endocytotic cellular transporter and also as transmembrane cell signaling receptor (Pflanzner et al., 2011). "
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