title: High-affinity Dkk1 receptor Kremen1 is internalized by clathrin-mediated endocytosis.
abstract: Kremens are high-affinity receptors for Dickkopf 1 (Dkk1) and regulate the Wnt/β-catenin signaling pathway by down-regulating the low-density lipoprotein receptor-related protein 6 (LRP6). Dkk1 competes with Wnt for binding to LRP6; binding of Dkk1 inhibits canonical signaling through formation of a ternary complex with Kremen. The majority of down-regulated clathrin-mediated endocytic receptors contain short conserved regions that recognize tyrosine or dileucine sorting motifs. In this study, we found that Kremen1 is internalized from the cell surface in a clathrin-dependent manner. Kremen1 contains an atypical dileucine motif with the sequence DXXXLV. Mutation of LV to AA in this motif blocked Kremen1 internalization; as reported previously for other proteins, the aspartic acid residue in Kremen1 is not critical. Inhibition of expression of the adaptor protein 2 (AP-2) or inhibition of clathrin by pitstop 2 also blocked Kremen1 internalization. The novel amino acid sequence identified in Kremen1 is similar to the motif previously identified in hydra, yeast, and other organisms known to signal from the trans-Golgi network to the endosomal compartment.
authors.affiliation: Department of Pediatric Surgery, Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania, USA. skm25@pitt.edu
authors.forename: Sanjay K
authors.initials: SK
authors.lastname: Mishra
authors.forename: Lacey
authors.initials: L
authors.lastname: Funair
authors.forename: Alex
authors.initials: A
authors.lastname: Cressley
authors.forename: George K
authors.initials: GK
authors.lastname: Gittes
authors.forename: R Cartland
authors.initials: RC
authors.lastname: Burns
mesh_terms: D033962:Adaptor Protein Complex 2 / Q000235:genetics / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002966:Clathrin / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D021381:Protein Transport; D016415:Sequence Alignment
chemical_list: D033962:Adaptor Protein Complex 2; D002966:Clathrin; C501127:Dkk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins