title: Cytosolic adaptor protein Dab2 is an intracellular ligand of endocytic receptor gp600/megalin.
abstract: 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.
authors.affiliation: Department of Pediatrics, Division of Nephrology, School of Medicine, University of California, Davis, CA 95616, USA. avoleinikov@ucdavis.edu
authors.forename: A V
authors.initials: AV
authors.lastname: Oleinikov
authors.forename: J
authors.initials: J
authors.lastname: Zhao
authors.forename: S P
authors.initials: SP
authors.lastname: Makker
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D001665:Binding Sites; D002460:Cell Line; D016147:Genes, Tumor Suppressor; D026541:Heymann Nephritis Antigenic Complex; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008024:Ligands; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D017354:Point Mutation / Q000235:genetics; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins; D051381:Rats; D011973:Receptors, LDL / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins; D020798:Two-Hybrid System Techniques
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D051017:Apoptosis Regulatory Proteins; C102885:DAB2 protein, human; D026541:Heymann Nephritis Antigenic Complex; D008024:Ligands; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D011506:Proteins; D011973:Receptors, LDL; D025521:Tumor Suppressor Proteins