CHIP promotes Runx2 degradation and negatively regulates osteoblast differentiation

Department of Biological Sciences and Biotechnology, State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Medicine, Tsinghua University, Beijing 100084, China.
The Journal of Cell Biology (Impact Factor: 9.83). 07/2008; 181(6):959-72. DOI: 10.1083/jcb.200711044
Source: PubMed


Runx2, an essential transactivator for osteoblast differentiation, is tightly regulated at both the transcriptional and posttranslational levels. In this paper, we report that CHIP (C terminus of Hsc70-interacting protein)/STUB1 regulates Runx2 protein stability via a ubiquitination-degradation mechanism. CHIP interacts with Runx2 in vitro and in vivo. In the presence of increased Runx2 protein levels, CHIP expression decreases, whereas the expression of other E3 ligases involved in Runx2 degradation, such as Smurf1 or WWP1, remains constant or increases during osteoblast differentiation. Depletion of CHIP results in the stabilization of Runx2, enhances Runx2-mediated transcriptional activation, and promotes osteoblast differentiation in primary calvarial cells. In contrast, CHIP overexpression in preosteoblasts causes Runx2 degradation, inhibits osteoblast differentiation, and instead enhances adipogenesis. Our data suggest that negative regulation of the Runx2 protein by CHIP is critical in the commitment of precursor cells to differentiate into the osteoblast lineage.

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    • "Although it is known that Smurf1 captures RunX2 by WW-PY interacting, in this work, both selected compounds exerted notable effects on Runx2, but the effects are not pronounced as Smad1/5. The unexpected result may attribute to two reasons: one, Smurf1 mediated Runx2 degradation may be induced by other stimulus independent of BMP-22036; second, Runx2 has other ligases besides Smurf1, as even full abolishment of Smurf1 cannot entirely regulate Runx2 protein stability3738. "
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    ABSTRACT: The ubiquitin ligase Smad ubiquitination regulatory factor-1 (Smurf1) negatively regulates bone morphogenetic protein (BMP) pathway by ubiquitinating certain signal components for degradation. Thus, it can be an eligible pharmacological target for increasing BMP signal responsiveness. We established a strategy to discover small molecule compounds that block the WW1 domain of Smurf1 from interacting with Smad1/5 by structure based virtual screening, molecular experimental examination and cytological efficacy evaluation. Our selected hits could reserve the protein level of Smad1/5 from degradation by interrupting Smurf1-Smad1/5 interaction and inhibiting Smurf1 mediated ubiquitination of Smad1/5. Further, these compounds increased BMP-2 signal responsiveness and the expression of certain downstream genes, enhanced the osteoblastic activity of myoblasts and osteoblasts. Our work indicates targeting Smurf1 for inhibition could be an accessible strategy to discover BMP-sensitizers that might be applied in future clinical treatments of bone disorders such as osteopenia.
    Scientific Reports 05/2014; 4:4965. DOI:10.1038/srep04965 · 5.58 Impact Factor
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    • "Similarly, CHIP has been found to colocalize with ataxin-1 nuclear inclusions [102, 103]. Coimmunoprecipitation experiments using cytoplasmic and nuclear fractions of mammalian cells showed that CHIP interacted with p65 [104], RUNX1 [105], and RUNX2 [106] proteins only in the nuclear extracts but not from the cytoplasmic fractions. Furthermore, under heat-stress CHIP not only assisted p53 to regain its native and transcriptionally active form but also comigrated with it into the nucleus and was found tethered to p21 and p53 promoters along with p53, as revealed by chromatin immunoprecipitation [107]. "
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    ABSTRACT: The Carboxy-terminus of Hsc70 Interacting Protein (CHIP) is a co-chaperone E3 ligase containing three tandem repeats of tetratricopeptide (TPR) motifs and a C-terminal U-box domain separated by a central charged coiled-coil region. CHIP is known to function as a central quality-control E3 ligase and regulates several proteins involved in a myriad of physiological and pathological processes. Recent studies have highlighted varied regulatory mechanisms operating on the activity of CHIP which is crucial for cellular homeostasis. In this review article, we give a concise account of our current knowledge on the biochemistry and regulation of CHIP.
    BioMed Research International 04/2014; 2014(6). DOI:10.1155/2014/918183 · 3.17 Impact Factor
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    • "Our study showed a distinct reduction of Runx2 protein upon RA treatment, whereas Runx2 transcript levels were unchanged, consistent with several studies that have indicated that the Runx2 transcript levels are less clearly regulated [50]–[53]. It is not yet known how RA alters Runx2 protein levels, but one possible mechanism could be via RA-induced proteasomal degradation, in analogy to how RA induces degradation of phosphorylated Smad1 [54]. "
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    ABSTRACT: An excessive intake of vitamin A has been associated with an increased risk of fractures in humans. In animals, a high vitamin A intake leads to a reduction of long bone diameter and spontaneous fractures. Studies in rodents indicate that the bone thinning is due to increased periosteal bone resorption and reduced radial growth. Whether the latter is a consequence of direct effects on bone or indirect effects on appetite and general growth is unknown. In this study we therefore used pair-feeding and dynamic histomorphometry to investigate the direct effect of a high intake of vitamin A on bone formation in rats. Although there were no differences in body weight or femur length compared to controls, there was an approximately halved bone formation and mineral apposition rate at the femur diaphysis of rats fed vitamin A. To try to clarify the mechanism(s) behind this reduction, we treated primary human osteoblasts and a murine preosteoblastic cell line (MC3T3-E1) with the active metabolite of vitamin A; retinoic acid (RA), a retinoic acid receptor (RAR) antagonist (AGN194310), and a Cyp26 inhibitor (R115866) which blocks endogenous RA catabolism. We found that RA, via RARs, suppressed in vitro mineralization. This was independent of a negative effect on osteoblast proliferation. Alkaline phosphatase and bone gamma carboxyglutamate protein (Bglap, Osteocalcin) were drastically reduced in RA treated cells and RA also reduced the protein levels of Runx2 and Osterix, key transcription factors for progression to a mature osteoblast. Normal osteoblast differentiation involved up regulation of Cyp26b1, the major enzyme responsible for RA degradation, suggesting that a drop in RA signaling is required for osteogenesis analogous to what has been found for chondrogenesis. In addition, RA decreased Phex, an osteoblast/osteocyte protein necessary for mineralization. Taken together, our data indicate that vitamin A is a negative regulator of osteoblast mineralization.
    PLoS ONE 12/2013; 8(12):e82388. DOI:10.1371/journal.pone.0082388 · 3.23 Impact Factor
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