Extracellular LDLR repeats modulate Wnt signaling activity by promoting LRP6 receptor endocytosis mediated by the Itch E3 ubiquitin ligase
Sapna Vijayakumar1,4, Guizhong Liu1,5, Huei-Chi Wen1,6, Yaa Abu2,7, Robert Chong1, Horacio Nastri3,8, Gadi G. Bornstein3,9, Zhen-Qiang Pan1 and Stuart A. Aaronson1
1 Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
2 Princeton University, Princeton, New Jersey, USA
3 Centers for Therapeutic Innovation, Pfizer Inc. New York, NY, USA
4 Present address: Pfizer, San Diego, CA, USA
5 Present address: China Suzhou Industrial Park, China
6 Present address: Dermatology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
7 Present address: Ragon Institute of MIT, MGH, and Harvard, Cambridge, MA, USA
8 Present address: Antibody Biotherapeutics, Incyte Corporation, Wilmington, DE, USA
9 Present address: TESARO, Waltham, MA, USA
Correspondence:
Sapna Vijayakumar, email:
Correspondence:
Stuart A. Aaronson, email:
Keywords: Wnt, LRP6, LDLRR, sarcoma, Itch E3 ubiquitin ligase, internalization
Received: June 02, 2017 Accepted: June 21, 2017 Published: July 12, 2017
Abstract
The low-density lipoprotein related protein 6 (LRP6) receptor is an important effector of canonical Wnt signaling, a developmental pathway, whose dysregulation has been implicated in various diseases including cancer. The membrane proximal low- density lipoprotein (LDL) receptor repeats in LRP6 exhibit homology to ligand binding repeats in the LDL receptor (LDLR), but lack known function. We generated single amino acid substitutions of LRP6-LDLR repeat residues, which are highly conserved in the human LDLR and mutated in patients with Familial Hypercholesteremia (FH). These substitutions negatively impacted LRP6 internalization and activation of Wnt signaling. By mass spectrometry, we observed that the Itch E3 ubiquitin ligase associated with and ubiquitinated wild type LRP6 but not the LDLR repeat mutants. These findings establish the involvement of LRP6-LDLR repeats in the regulation of canonical Wnt signaling.
