CXXC5 is a negative-feedback regulator of the Wnt/β-catenin pathway involved in osteoblast differentiation

Abstract

The positive roles of the Wnt/β-catenin pathway in osteoblast differentiation and bone mineral density (BMD) maintenance have been clearly demonstrated in both animal experiments and clinical investigations. CXXC finger protein 5 (CXXC5), a recently identified negative regulator of the Wnt/β-catenin pathway, showed altered cellular localization and function, which were dependent on the cell type in previous studies. However, the in vivo function of CXXC5 has not been clearly investigated yet. Here, we characterized CXXC5 as a negative regulator of osteoblast differentiation and bone formation. Deficiency of CXXC5 resulted in elevated BMD in mice without any severe gross developmental abnormalities. CXXC5 exerted a negative-feedback effect on the Wnt/β-catenin pathway via Wnt-dependent binding to Dishevelled (Dvl) during osteoblast differentiation. Suppression of the Dvl-CXXC5 interaction using a competitor peptide resulted in the activation of the Wnt/β-catenin pathway and osteoblast differentiation, and accelerated thickness growth of ex vivo-cultured calvariae. Overall, CXXC5 is a negative-feedback regulator induced by Wnt/β-catenin signaling that inhibits osteoblast differentiation and bone formation via interaction with Dvl. Cell Death and Differentiation (2015) 22, 912-920; doi:10.1038/cdd.2014.238; published online 30 January 2015Bone is an extremely dynamic tissue at the microscopic level. A dynamic process, called bone remodeling, takes place seamlessly in the bone to repair microdamage and to replace old bone with new bone. 1 The resorption of old bone and the formation of new bone must be in balance to maintain homeostasis and a constant mass of bone. Osteoblasts have been identified as an essential factor in regulation of the bone remodeling process, which produce bone matrix and differentiate into osteocytes for bone formation, as well as regulate differentiation and activation of osteoclasts for bone resorption. 2 The Wnt/β-catenin pathway is receiving increased attention as a main regulatory pathway for osteoblast differentiation. [2][3][4] Wnt-dependent nuclear accumulation of an effector protein of the pathway, β-catenin, is a major trigger of osteoblast differentiation and bone formation. 2 Many other intracellular and extracellular components of the Wnt/β-catenin pathway are known to regulate osteoblast differentiation. 4 Especially two negative regulators of this pathway, Dickkopf 1 and sclerostin, have been highlighted as osteoblast and osteocytespecific negative regulators of bone formation. 5 CXXC finger protein 5 (CXXC5) is a member of a small protein family in which the members contain CXXC-type zincfinger domain. 6 However, unlike other members of this family, CXXC5 lacks a KFGG motif, which is essential for non-methylated CpG recognition that regulates chromatin remodeling. 7 CXXC5 localizes to the cytosol or nucleus depending on particular cell type in different tissues. Localization of CXXC5 in the nucleus was observed in promyelocytic leukemia cells. 7 CXXC5 has a role as a nuclear t...

Three-dimensional system enabling the maintenance and directed differentiation of pluripotent stem cells under defined conditions

“…These findings are relevant to studies involving late osteoblast functions ( 36 , 37 ). Additional investigations will aim to fully reproduce the bone cell microenvironment by combining our 3D culture system with osteoclast precursors also derived from mPSCs.…”

Estradiol-Estrogen Receptor α Mediates the Expression of the CXXC5 Gene through the Estrogen Response Element-Dependent Signaling Pathway

“…Apart from being a transcription factor, CXXC5 was shown to act as a negative-feedback regulator of Wnt/β-catenin signaling by interacting with the cytoplasmic scaffold Dishevelled (Dvl) proteins in osteoblast differentiation and bone formation33, cutaneous wound healing and collagen production34, neural stem cell differentiation and telencephalon development13. CXXC5 was also reported to interact with and require for DNA damage-induced ATM phosphorylation, subsequent activation of p53, cell cycle arrest and apoptosis35.…”

Small molecule inhibitors of the Dishevelled‐ CXXC 5 interaction are new drug candidates for bone anabolic osteoporosis therapy

“…In pre‐osteoblasts, Tcf/β‐catenin complex binds with Runx2 in their nucleus and regulates osteogenic genes specifically (Reinhold & Naski, ). Among the direct transcriptional target genes of Wnt/β‐catenin signaling, an osteogenic gene, Fgf18 (Reinhold & Naski, ), but not oncogenic genes ( c‐Myc and cyclin D1 ) (He et al , ; Shtutman et al , ), were induced by Wnt3a treatment in pre‐osteoblasts (Kim et al , ). We also did not observe any sign for cancer development in CXXC5 −/− mice, grown up to 1.5 years.…”

“…In a previous study, we suggested the Dvl–CXXC5 interaction as a negative feedback mechanism of the Wnt/β‐catenin pathway and as a potent target for bone anabolic agents (Kim et al , ). We confirmed this hypothesis using a newly synthesized competitor peptide of the Dvl–CXXC5 interaction, which induced osteoblast differentiation and enhanced bone formation of ex vivo ‐cultured calvariae (Kim et al , ). Here, we identified KY‐02061, a small‐molecule inhibitor of Dvl–CXXC5 interaction by establishing a new Dvl–CXXC5 in vitro binding assay system and verified the competitor peptide‐mimicking effects of this compound.…”