Smad Ubiquitylation Regulatory Factor 1/2 (Smurf1/2) Promotes p53 Degradation by Stabilizing the E3 Ligase MDM2

School of Life Sciences, Tsinghua University, Beijing 100842, China.
Journal of Biological Chemistry (Impact Factor: 4.57). 07/2010; 285(30):22818-30. DOI: 10.1074/jbc.M110.126920
Source: PubMed


The tumor suppressor p53 protein is tightly regulated by a ubiquitin-proteasomal degradation mechanism. Several E3 ubiquitin ligases, including MDM2 (mouse double minute 2), have been reported to play an essential role in the regulation of p53 stability. However, it remains unclear how the activity of these E3 ligases is regulated. Here, we show that the HECT-type E3 ligase Smurf1/2 (Smad ubiquitylation regulatory factor 1/2) promotes p53 degradation by enhancing the activity of the E3 ligase MDM2. We provide evidence that the role of Smurf1/2 on the p53 stability is not dependent on the E3 activity of Smurf1/2 but rather is dependent on the activity of MDM2. We find that Smurf1/2 stabilizes MDM2 by enhancing the heterodimerization of MDM2 with MDMX, during which Smurf1/2 interacts with MDM2 and MDMX. We finally provide evidence that Smurf1/2 regulates apoptosis through p53. To our knowledge, this is the first report to demonstrate that Smurf1/2 functions as a factor to stabilize MDM2 protein rather than as a direct E3 ligase in regulation of p53 degradation.

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    • "The experimental procedures of western Blot (WB), GST-pull down (GPD) and co-immunoprecipitation (Co-IP) were performed as described before4445. For the in vivo ubiquitination (IVU) assays, cells were treated with MG132 (20 μM) together with the selective compounds or vehicle to avoid the proteasome-mediated protein degradation. "
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    • "Besides the TGF-β signaling components, Smurf2 interacts with a diverse array of proteins, some of which affect tumorigenesis. For example, Smurf2 interacts with MDM2/HDM2 and enhances its ability to ubiquitinate and degrade the tumor suppressor p53 [28], implying that Smurf2 could promote tumorigenesis in some context. On the other hand, Smurf2 targets the helix-loop-helix transcription regulator Id1 (inhibitor of differentiation or DNA binding) for proteasomal degradation [29]. "
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    • "The lysed protein extracts were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), transferred onto nitrocellulose membranes, then blotted, as reported previously [24]. Anti-Smad4 antibody was purchased from Cell Signaling Technology. "
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    ABSTRACT: Transforming growth factor (TGF)-β/Smad signaling plays an important role in colon cancer development, progression and metastasis. In this study we demonstrated that the microRNA-130a/301a/454 family is up-regulated in colon cancer tissues compared to paired adjacent normal mucosa, which share the same 3'-untranslational region (3'-UTR) binding seed sequence and are predicated to target Smad4. In colorectal cancer HCT116 and SW480 cells, overexpression of miRNA-130a/301a/454 mimics enhances cell proliferation and migration, while inhibitors of these miRNAs affect cell survival. The biological function of miRNA-130a/301a/454 on colon cancer cells is likely mediated by suppression of Smad4, and the up-regulation of the miRNAs is correlated with Smad4 down-regulation in human colon cancers. Collectively, these results suggest that miRNA-130a/301a/454 are novel oncogenic miRNAs contributing to colon tumorigenesis by regulating TGF-β/Smad signaling, which may have potential application in cancer therapy.
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