Cytosolic adaptor protein Dab2 is an intracellular ligand of endocytic receptor gp600/megalin

• Published in: Biochemical journal 2000-05, Vol.347 Pt 3 (3), p.613-621
• Main Authors: Oleinikov, A V, Zhao, J, Makker, S P
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing; Adaptor Proteins, Vesicular Transport; Amino Acid Motifs; Amino Acid Sequence; Animals; Binding Sites; Cell Line; Genes, Tumor Suppressor; Heymann Nephritis Antigenic Complex; Humans; Kidney - cytology; Kidney - metabolism; Ligands; Membrane Glycoproteins - chemistry; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Molecular Sequence Data; Phosphoproteins - chemistry; Phosphoproteins - metabolism; Point Mutation - genetics; Precipitin Tests; Protein Binding; Protein Structure, Tertiary; Proteins; Rats; Receptors, LDL - chemistry; Receptors, LDL - genetics; Receptors, LDL - metabolism; Sequence Deletion - genetics; Signal Transduction; Tumor Cells, Cultured; Tumor Suppressor Proteins; Two-Hybrid System Techniques
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/0264-6021:3470613

gp600/megalin, an endocytic receptor, belongs to the low-density lipoprotein receptor family. It is most abundant in the renal proximal tubular cells, where it is implicated in the reabsorption of a number of molecules filtered through the glomerulus. The cytoplasmic tail (CT) of gp600/megalin contains a number of sequence similarities, which indicate that gp600/megalin might be involved in signal transduction. To find intracellular proteins that would interact with the gp600/megalin CT, a human kidney cDNA library was screened by using the yeast two-hybrid system. The phosphotyrosine interaction domain (PID) of the Disabled protein 2 (Dab2), a mammalian structural analogue of Drosophila Disabled, was found to bind to the gp600/megalin CT in this system. The interaction between these two proteins was confirmed by a binding assay in vitro and by the co-immunoprecipitation of both proteins from renal cell lysates. The gp600/megalin CT contains three PsiXNPXY motifs (in which Psi represents a hydrophobic residue) that are potentially able to interact with PID. Analysis of the CT deletion and point-mutation variants of gp600/megalin by the two-hybrid system revealed that the third PsiXNPXY motif is most probably involved in this interaction. Dab2 is a mitogen-responsive phosphoprotein thought to be an adaptor molecule involved in signal transduction, and a suggested negative regulator of cell growth. Dab2 is the first intracellular ligand identified for gp600/megalin; gp600/megalin is the first known transmembrane receptor that interacts with the cytosolic protein Dab2. We speculate that their interaction might involve gp600/megalin in signal transduction pathways or might mediate the intracellular trafficking of this receptor.