title: Functional Differences of Very-Low-Density Lipoprotein Receptor Splice Variants in Regulating Wnt Signaling.
abstract: The very-low-density lipoprotein receptor (VLDLR) negatively regulates Wnt signaling. VLDLR has two major alternative splice variants, VLDLRI and VLDLRII, but their biological significance and distinction are unknown. Here we found that most tissues expressed both VLDLRI and VLDLRII, while the retina expressed only VLDLRII. The shed soluble VLDLR extracellular domain (sVLDLR-N) was detected in the conditioned medium of retinal pigment epithelial cells, interphotoreceptor matrix, and mouse plasma, indicating that ectodomain shedding of VLDLR occurs endogenously. VLDLRII displayed a higher ectodomain shedding rate and a more potent inhibitory effect on Wnt signaling than VLDLRI in vitro and in vivo O-glycosylation, which is present in VLDLRI but not VLDLRII, determined the differential ectodomain shedding rates. Moreover, the release of sVLDLR-N was inhibited by a metalloproteinase inhibitor, TAPI-1, while it was promoted by phorbol 12-myristate 13-acetate (PMA). In addition, sVLDLR-N shedding was suppressed under hypoxia. Further, plasma levels of sVLDLR-N were reduced in both type 1 and type 2 diabetic mouse models. We concluded that VLDLRI and VLDLRII had differential roles in regulating Wnt signaling and that decreased plasma levels of sVLDLR-N may contribute to Wnt signaling activation in diabetic complications. Our study reveals a novel mechanism for intercellular regulation of Wnt signaling through VLDLR ectodomain shedding.
authors.affiliation: Department of Physiology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA Harold Hamm Diabetes Center, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Department of Medicine, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA Harold Hamm Diabetes Center, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Oka
authors.affiliation: Department of Physiology, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA Harold Hamm Diabetes Center, The University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA jian-xing-ma@ouhsc.edu.
authors.forename: Jian-Xing
authors.initials: JX
authors.lastname: Ma
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000737:chemistry; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D004195:Disease Models, Animal; D015536:Down-Regulation; D006031:Glycosylation; D006801:Humans; D051379:Mice; D020033:Protein Isoforms / Q000378:metabolism*; D011973:Receptors, LDL / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000378:metabolism; D014018:Tissue Distribution; D060449:Wnt Signaling Pathway
chemical_list: D017077:Culture Media, Conditioned; D020033:Protein Isoforms; D011973:Receptors, LDL; C036053:VLDL receptor