scholarly journals Clathrin and AP2 are required for PtdIns(4,5)P2-mediated formation of LRP6 signalosomes

2013 ◽  
Vol 200 (4) ◽  
pp. 419-428 ◽  
Author(s):  
Ingyu Kim ◽  
Weijun Pan ◽  
Sara A. Jones ◽  
Youxin Zhang ◽  
Xiaowei Zhuang ◽  
...  
Keyword(s):  
Wnt Signaling ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Super Resolution ◽  
Adaptor Protein ◽  
Related Protein ◽  
Cell Surfaces ◽  
Wnt Proteins ◽  
Canonical Wnt ◽  
Wnt3a Stimulation

Canonical Wnt signaling is initiated by the binding of Wnt proteins to their receptors, low-density lipoprotein-related protein 5 and 6 (LRP5/6) and frizzled proteins, leading to phosphatidylinositol (4,5)bisphosphate (PtdIns(4,5)P2) production, signalosome formation, and LRP phosphorylation. However, the mechanism by which PtdIns(4,5)P2 regulates the signalosome formation remains unclear. Here we show that clathrin and adaptor protein 2 (AP2) were part of the LRP6 signalosomes. The presence of clathrin and AP2 in the LRP6 signalosomes depended on PtdIns(4,5)P2, and both clathrin and AP2 were required for the formation of LRP6 signalosomes. In addition, WNT3A-induced LRP6 signalosomes were primarily localized at cell surfaces, and WNT3A did not induce marked LRP6 internalization. However, rapid PtdIns(4,5)P2 hydrolysis induced artificially after WNT3A stimulation could lead to marked LRP6 internalization. Moreover, we observed WNT3A-induced LRP6 and clathrin clustering at cell surfaces using super-resolution fluorescence microscopy. Therefore, we conclude that PtdIns(4,5)P2 promotes the assembly of LRP6 signalosomes via the recruitment of AP2 and clathrin and that LRP6 internalization may not be a prerequisite for Wnt signaling to β-catenin stabilization.

scholarly journals The low-density lipoprotein receptor-related protein 1 (LRP1) mediates the endocytosis of the cellular prion protein

2007 ◽  
Vol 402 (1) ◽  
pp. 17-23 ◽  
Author(s):  
David R. Taylor ◽  
Nigel M. Hooper
Keyword(s):  
Prion Protein ◽  
Low Density Lipoprotein ◽  
Neuronal Cells ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Adaptor Protein ◽  
Cellular Prion Protein ◽  
Low Density ◽  
Related Protein ◽  
Density Lipoprotein Receptor

PrPC (cellular prion protein) is located at the surface of neuronal cells in detergent-insoluble lipid rafts, yet is internalized by clathrin-dependent endocytosis. As PrPC is glycosyl-phosphatidylinositol-anchored, it requires a transmembrane adaptor protein to connect it to the clathrin endocytosis machinery. Using receptor-associated protein and small interfering RNA against particular LDL (low-density lipoprotein) family members, in combination with immunofluorescence microscopy and surface biotinylation assays, we show that the transmembrane LRP1 (LDL receptor-related protein 1) is required for the Cu2+-mediated endocytosis of PrPC in neuronal cells. We show also that another LRP1 ligand that can cause neurodegenerative disease, the Alzheimer's amyloid precursor protein, does not modulate the endocytosis of PrPC.

scholarly journals Canonical Wnt Signaling Inhibition in Renal Cell Carcinoma Bone Metastasis: Immunohistochemical Study of DKK1 and LRP5 Expression

2021 ◽  
Author(s):  
Zixiong Huang ◽  
Yiqing Du ◽  
Huaqi Yin ◽  
Gongwei Wang ◽  
Tao Xu
Keyword(s):  
Bone Metastasis ◽  
Wnt Signaling ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Renal Tissue ◽  
Primary Lesion ◽  
Canonical Wnt Signaling ◽  
Metastatic Lesions ◽  
Dkk1 Expression ◽  
Canonical Wnt

Abstract Introduction & Objectives: Canonical Wnt signaling (Wnt/β-catenin signaling) maintains the bone homeostasis by promoting the osteoblastic activities. The inhibitory factor, Dickkopf (DKK)1, enhances the bone resorption, especially in malignancies. The low density lipoprotein related protein (LRP) 5 is a component of membranous co-receptor of Wnt/β-catenin signaling and is also involved in serum low density lipoprotein cholestrol (LDL-C) level regulation. The clear cell renal cell carcinoma bone metastasis (ccRCC-BM) is characterized by osteolytic bone resorption. Whether and how Wnt/β-catenin signaling plays roles in regulating the invasion, metastasis and osteolytic process of ccRCC to bone remain unclear. This study investigated the expression of DKK1, LRP5 proteins in primary and metastatic lesions of RCC-BM. The therapeutic potential of Wnt/β-catenin signaling target medication was also evaluated.Materials & Methods: ccRCC-BM patients with paired samples of primary and metastatic lesions were selected. ccRCC patients without any metastasis (ccRCC-only) were set as control. Slides of paraffin-embedded tissue underwent immunohistochemical staining with monoclonalanti-DKK1 antibody and polyclonal anti-LRP5 antibody. Semi-quantitatively scoring according to staining intensity was performed. The staining results in the renal tissue adjacent to RCC, the primary RCC lesions (with BM or without BM), and the RCC-BM lesions were recorded. The expression difference was analyzed by univariate analysis of variance (ANOVA).Results: The expression of DKK1 was significantly different amid renal tissue adjacent to RCC, primary RCC and RCC-BM tissues (p< 0.001). The expression of DKK1 in primary RCC was significantly lower than that in renal tissue adjacent to RCC (p<0.001). No difference was found between ccRCC-BM group and ccRCC-only group. DKK1 expression in bone metastasis was significantly higher than that in primary tumor (p < 0.001). The expression of LRP5 in the primary tumor of ccRCC-BM group was significantly lower than that of adjacent renal tissue (p<0.01). Tendency of decreasing expression was found between primary lesion of ccRCC-BM group and primary lesion of ccRCC-only group (p=0.073). In bone metastasis, the expression of LRP5 protein was not significantly different from that in adjacent renal tissue and RCC primary lesion.Conclusions: A "rebound" of DKK1 expression was found in bone metastasis lesions. Along with the decreasing LRP5 expression in primary lesions of RCC-BM patients, this suggests that the canonical Wnt signaling (Wnt/β-catenin signaling) is inhibited during the bone metastasis process in ccRCC. The overexpression of DKK1 and the down-regulation of LRP5 receptor are involved.

scholarly journals The Genetics of Low-Density Lipoprotein Receptor-Related Protein 5 in Bone: A Story of Extremes

Endocrinology ◽  
2007 ◽  
Vol 148 (6) ◽  
pp. 2622-2629 ◽  
Author(s):  
Wendy Balemans ◽  
Wim Van Hul
Keyword(s):  
Bone Density ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Lipoprotein Receptor ◽  
Bone Homeostasis ◽  
Related Protein ◽  
Genetic Studies ◽  
Density Lipoprotein Receptor ◽  
Canonical Wnt ◽  
Lipoprotein Receptor Related Protein

A few years ago, human genetic studies provided compelling evidence that the low-density lipoprotein receptor-related protein 5 (LRP5) is involved in the regulation of bone homeostasis because pathogenic LRP5 mutations were found in monogenic conditions with abnormal bone density. On the one hand, the osteoporosis pseudoglioma syndrome results from loss of function of LRP5, whereas on the other hand, gain-of-function mutations in LRP5 cause conditions with an increased bone density. On the molecular level, these types of mutations result in disturbed (respectively, decreased and increased) canonical Wnt signaling, an important metabolic pathway in osteoblasts during embryonic and postnatal osteogenesis. This signaling cascade is activated by binding of Wnt ligand to the Frizzled/LRP5 receptor complex. In addition to the involvement of LRP5 in conditions with extreme bone phenotypes, the genetic profile of this gene has also been shown to contribute to the determination of bone density in the general population. Quite a number of studies already demonstrated that common polymorphic variants in LRP5 are associated with bone mineral density and consequently osteoporosis, a multifactorial trait with low bone mass and porous bone structure. These genetic studies together with results obtained from in vitro and in vivo studies emphasize the importance of LRP5 and canonical Wnt signaling in the regulation of bone homeostasis. Therefore, unraveling the exact mechanisms of this signaling cascade has become an important area in bone research. This review focuses on the genetics of LRP5 and summarizes the findings on monogenic bone conditions as well as the current knowledge of its involvement in the pathogenesis of osteoporosis.

scholarly journals Low-density Lipoprotein Receptor-related Protein 5 (LRP5)-deficient Rats Have Reduced Bone Mass and Abnormal Development of the Retinal Vasculature

2020 ◽  
Author(s):  
John L. Ubels ◽  
Cassandra R. Diegel ◽  
Gabrielle E. Foxa ◽  
Nicole J. Ethen ◽  
Jonathan N. Lensing ◽  
...  
Keyword(s):  
Bone Mass ◽  
Wnt Signaling ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Retinal Vasculature ◽  
Low Density ◽  
Lipoprotein Receptor ◽  
Related Protein ◽  
Density Lipoprotein Receptor ◽  
Lipoprotein Receptor Related Protein

AbstractHumans carrying homozygous loss-of-function mutations in the Wnt co-receptor LRP5 (low-density lipoprotein receptor–related protein 5) develop osteoporosis and a defective retinal vasculature known as familial exudative vitreoretinopathy (FEVR) due to disruption of the Wnt signaling pathway. The purpose of this study was to use CRISPR/Cas9-mediated gene editing to create strains of Lrp5-deficient rats and to determine whether knockout of Lrp5 resulted in phenotypes that model the bone and retina pathology in LRP5-deficient humans. Knockout of Lrp5 in rats produced low bone mass, decreased bone mineral density, and decreased bone size. The superficial retinal vasculature of Lrp5-deficient rats was sparse and disorganized, with extensive exudates and decreases in vascularized area, vessel length, and branch point density. This study showed that Lrp5 could be predictably knocked out in rats using CRISPR/Cas9, causing the expression of bone and retinal phenotypes that will be useful for studying the role of Wnt signaling in bone and retina development and for research on the treatment of osteoporosis and FEVR.

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