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Parathyroid hormone-responsive Smad3-related factor, Tmem119, promotes osteoblast differentiation and interacts with the bone morphogenetic protein-Runx2 pathway.

ABSTRACT: The mechanisms whereby the parathyroid hormone (PTH) exerts its anabolic action on bone are incompletely understood. We previously showed that inhibition of ERK1/2 enhanced Smad3-induced bone anabolic action in osteoblasts. These findings suggested the hypothesis that changes in gene expression associated with the altered Smad3-induced signaling brought about by an ERK1/2 inhibitor would identify novel bone anabolic factors in osteoblasts. We therefore performed a comparative DNA microarray analysis between empty vector-transfected mouse osteoblastic MC3T3-E1 cells and PD98059-treated stable Smad3-overexpressing MC3T3-E1 cells. Among the novel factors, Tmem119 was selected on the basis of its rapid induction by PTH independent of later increases in endogenous TGF-?. The levels of Tmem119 increased with time in cultures of MC3T3-E1 cells and mouse mesenchymal ST-2 cells committed to the osteoblast lineage by BMP-2. PTH stimulated Tmem119 levels within 1 h as determined by Western blot analysis and immunocytochemistry in MC3T3-E1 cells. MC3T3-E1 cells stably overexpressing Tmem119 exhibited elevated levels of Runx2, osteocalcin, alkaline phosphatase, and ?-catenin, whereas Tmem119 augmented BMP-2-induced Runx2 levels in mesenchymal cells. Tmem119 interacted with Runx2, Smad1, and Smad5 in C2C12 cells. In conclusion, we identified a Smad3-related factor, Tmem119, that is induced by PTH and promotes differentiation in mouse osteoblastic cells. Tmem119 is an important molecule in the pathway downstream of PTH and Smad3 signaling in osteoblasts.

SUBMITTER: Hisa I

PROVIDER: S-EPMC3058974 | biostudies-literature | 2011 Mar

REPOSITORIES: biostudies-literature

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Parathyroid hormone-responsive Smad3-related factor, Tmem119, promotes osteoblast differentiation and interacts with the bone morphogenetic protein-Runx2 pathway.

Hisa Itoko I Inoue Yoshifumi Y Hendy Geoffrey N GN Canaff Lucie L Kitazawa Riko R Kitazawa Sohei S Komori Toshihisa T Sugimoto Toshitsugu T Seino Susumu S Kaji Hiroshi H

The Journal of biological chemistry 20110114 11

The mechanisms whereby the parathyroid hormone (PTH) exerts its anabolic action on bone are incompletely understood. We previously showed that inhibition of ERK1/2 enhanced Smad3-induced bone anabolic action in osteoblasts. These findings suggested the hypothesis that changes in gene expression associated with the altered Smad3-induced signaling brought about by an ERK1/2 inhibitor would identify novel bone anabolic factors in osteoblasts. We therefore performed a comparative DNA microarray anal ...[more]

PMID: 21239498

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Project description:Parathyroid hormone (PTH) stimulates bone remodeling and induces differentiation of bone marrow mesenchymal stromal/stem cells (MSCs) by orchestrating activities of local factors such as bone morphogenetic proteins (BMPs). The activity and specificity of different BMP ligands are controlled by various extracellular antagonists that prevent binding of BMPs to their receptors. Low-density lipoprotein receptor-related protein 6 (LRP6) has been shown to interact with both the PTH and BMP extracellular signaling pathways by forming a complex with parathyroid hormone 1 receptor (PTH1R) and sharing common antagonists with BMPs. We hypothesized that PTH-enhanced differentiation of MSCs into the osteoblast lineage through enhancement of BMP signaling occurs by modifying the extracellular antagonist network via LRP6. In vitro studies using multiple cell lines, including Sca-1(+) CD45(-) CD11b(-) MSCs, showed that a single injection of PTH enhanced phosphorylation of Smad1 and could also antagonize the inhibitory effect of noggin. PTH treatment induced endocytosis of a PTH1R/LRP6 complex and resulted in enhancement of phosphorylation of Smad1 that was abrogated by deletion of PTH1R, β-arrestin, or chlorpromazine. Deletion of LRP6 alone led to enhancement of pSmad1 levels that could not be further increased with PTH treatment. Finally, knockdown of LRP6 increased the exposure of endogenous cell-surface BMP receptor type II (BMPRII) significantly in C2C12 cells, and PTH treatment significantly enhanced cell-surface binding of (125) I-BMP2 in a dose- and time-dependent manner, implying that LRP6 organizes an extracellular network of BMP antagonists that prevent access of BMPs to BMP receptors. In vivo studies in C57BL/6J mice and of transplanted green fluorescent protein (GFP)-labeled Sca-1(+) CD45(-) CD11b(-) MSCs into the bone marrow cavity of Rag2(-/-) immunodeficient mice showed that PTH enhanced phosphorylation of Smad1 and increased commitment of MSCs to osteoblast lineage, respectively. These data demonstrate that PTH enhancement of MSC differentiation to the osteoblast lineage occurs through a PTH- and LRP6-dependent pathway by endocytosis of the PTH1R/LRp6 complex, allowing enhancement of BMP signaling.

Dataset Information

Parathyroid hormone-responsive Smad3-related factor, Tmem119, promotes osteoblast differentiation and interacts with the bone morphogenetic protein-Runx2 pathway.

Publications

Parathyroid hormone-responsive Smad3-related factor, Tmem119, promotes osteoblast differentiation and interacts with the bone morphogenetic protein-Runx2 pathway.

Similar Datasets

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