Schnurri-3 regulates ERK downstream of WNT signaling in osteoblasts
Jae-Hyuck Shim, … , Laurie H. Glimcher, Dallas C. Jones
Jae-Hyuck Shim, … , Laurie H. Glimcher, Dallas C. Jones
Published August 15, 2013
Citation Information: J Clin Invest. 2013;123(9):4010-4022. https://doi.org/10.1172/JCI69443.
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Research Article Bone biology

Schnurri-3 regulates ERK downstream of WNT signaling in osteoblasts

Abstract

Mice deficient in Schnurri-3 (SHN3; also known as HIVEP3) display increased bone formation, but harnessing this observation for therapeutic benefit requires an improved understanding of how SHN3 functions in osteoblasts. Here we identified SHN3 as a dampener of ERK activity that functions in part downstream of WNT signaling in osteoblasts. A D-domain motif within SHN3 mediated the interaction with and inhibition of ERK activity and osteoblast differentiation, and knockin of a mutation in Shn3 that abolishes this interaction resulted in aberrant ERK activation and consequent osteoblast hyperactivity in vivo. Additionally, in vivo genetic interaction studies demonstrated that crossing to Lrp5–/– mice partially rescued the osteosclerotic phenotype of Shn3–/– mice; mechanistically, this corresponded to the ability of SHN3 to inhibit ERK-mediated suppression of GSK3β. Inducible knockdown of Shn3 in adult mice resulted in a high–bone mass phenotype, providing evidence that transient blockade of these pathways in adults holds promise as a therapy for osteoporosis.

Authors

Jae-Hyuck Shim, Matthew B. Greenblatt, Weiguo Zou, Zhiwei Huang, Marc N. Wein, Nicholas Brady, Dorothy Hu, Jean Charron, Heather R. Brodkin, Gregory A. Petsko, Dennis Zaller, Bo Zhai, Steven Gygi, Laurie H. Glimcher, Dallas C. Jones

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Figure 2

In vivo function of the 3-lysine motif of SHN3 in bone formation.

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In vivo function of the 3-lysine motif of SHN3 in bone formation. (A) Th...
(A) The 3 lysine-to-alanine alleles knocked in to the endogenous Shn3 locus. Arrowheads denote position of primers (S5 and S3) used for PCR genotyping. (B) Primary Shn3+/+ and Shn3KI/KI BMSCs were lysed and immunoblotted with anti-SHN3 antibody. (C) μCT of 8-week-old Shn3+/+ and Shn3KI/KI mouse proximal femurs. (D) Histomorphometric and μCT analysis of 8-week-old Shn3+/+ and Shn3KI/KI mouse tibias. BV/TV, bone volume fraction; Ob.N/BPM, osteoblast number per bone perimeter; Ob.S/BS, osteoblast surface relative to bone surface; BFR, bone formation rate; Tb.N, trabecular number; Tb.Th, trabecular thickness; Tb.Sp, trabecular space; C.Th, cortical thickness. (E) Serum CTX levels in 8-week-old Shn3+/+ and Shn3KI/KI mice were determined by ELISA. (F–H) Shn3+/+ and Shn3KI/KI BMSCs were cultured in differentiation medium, and mineralization was analyzed by Von Kossa staining (F) and quantization of mineralized nodules (G). Alternatively, total RNA was extracted for RT-PCR analysis (H), and values normalized to Hprt. Results are presented as mean + SD. *P < 0.05, **P < 0.005, Student’s t test.