The Ubiquitin Ligase SMURF1 Catalyzes the Polyubiquitination of ADAR1 / 中国生物化学与分子生物学报

It is known that SMAD specific E3 ubiquitin protein ligase 1 (SMURF1) mediates autophagy through its E3 ubiquitin ligase activity, but the ubiquitinated substrates of SMURF1 need to be further explored. In this paper, the interacting proteins of SMURF1 in THP-1 cells were captured and identified by co-immunoprecipitation (Co-IP) combined with mass spectrometry. It was found that SMURF1 could physically bind to 222 proteins in THP-1 cells, and Adenosine deaminase acting on RNA 1 (ADAR1) had a higher peptide binding score. SMURF1 overexpression vectors were constructed and transfected into HEK-293T cells, then Co-IP and Western blotting assays verified the interaction between exogenous SMURF1 and endogenous ADAR1. qRT-PCR and Western blotting assays were carried out after transfecting SMURF1 overexpression vectors in HEK-293T cells, which identified that overexpression of SMURF1 attenuated the protein levels of ADAR1 (P<0. 05). However, there was no significant difference in the mRNA level of ADAR1. HEK-293T cells with normal and overexpressing SMURF1 were treated with cycloheximide (CHX), respectively, and Western blotting assays showed a shortened half-life of ADAR1 after overexpression of SMURF1 (P < 0. 05). Furthermore, overexpression of SMURF1 increased the polyubiquitination level of ADAR1 as detected by Co-IP and Western blot (P<0. 05). After the proteasome inhibitor (MG132) treatment, the Western blotting assay was performed to demonstrate that the negative regulatory effect of SMURF1 on ADAR1 was weakened after the proteasome degradation pathway was attenuated (P<0. 05). This study shows that SMURF1 interacts with ADAR1, catalyzes the polyubiquitination of ADAR1 and mediates its degradation through the proteasome pathway, which provides a theoretical basis for exploring the various biological functions of SMURF1 by affecting the stability of ADAR1.

Beta-Catenin Downregulation Contributes to Epidermal Growth Factor-induced Migration and Invasion of MDAMB231 Cells

We previously demonstrated that epidermal growth factor (EGF) enhances cell migration and invasion of breast cancer cells in a SMAD ubiquitination regulatory factor 1 (SMURF1)-dependent manner and that SMURF1 induces degradation of β-catenin in C2C12 cells. However, the relationship between EGF-induced SMURF1 and β-catenin expression in breast cancer cells remains unclear. So, we investigated if EGF and SMURF1 regulate β-catenin expression in MDAMB231 human breast cancer cells. When MDAMB231 cells were incubated with EGF for 24, 48, and 72 hours, EGF significantly increased expression levels of SMURF1 mRNA and protein while suppressing expression levels of β-catenin mRNA and protein. Overexpression of SMURF1 downregulated β-catenin mRNA and protein, whereas knockdown of SMURF1 increased β-catenin expression and blocked EGF-induced β-catenin downregulation. Knockdown of β-catenin enhanced cell migration and invasion of MDAMB231 cells, while β-catenin overexpression suppressed EGF-induced cell migration and invasion. Furthermore, knockdown of β-catenin enhanced vimentin expression and decreased cytokeratin expression, whereas β-catenin overexpression decreased vimentin expression and increased cytokeratin expression. These results suggest that EGF downregulates β-catenin in a SMURF1-dependent manner and that β-catenin downregulation contributes to EGF-induced cell migration and invasion in MDAMB breast cancer cells.

Ubiquitin ligase Smurf1 promotes Smurf2 neddylation modification / 军事医学

Objective To investigate the mechanism of Smad ubiquitination-related factor 2 (Smurf2)neddylation. Methods The Smurf2 protein level was tested by overexpression of Nedd8,while the method of immunoprecipitation(IP) and Western blotting were used to analyz Smurf2-Nedd8 modification.The GST-pulldown experiment was conducted to prove protein interactions.The protein was obtained by grinding mouse tissue and Western blotting was used to test the protein expression level.Results Over expression of Nedd8 could lead to the down regulation of the Smurf2′s protein level.Smurf1 and Smurf2 could interact in the GST-pulldown experiment. Smurf1 could enhance Smurf2-Nedd8 modification.The Smurf2′s protein level was up-regulated in mouse tissue of Smurf1 C426A.Conclusion There is some relationship and also difference between Smurf1 and Smurf2.Smurf1 can enhance Smurf2-Nedd8 modification.

Establishment of two human tumor cell lines with lentivirus-mediated stably Smurf1 silencing and their effect on cell migration / 中国比较医学杂志

Objective To establish lentiviral expression vectors for Smurf1 silencing and assess the effects of Smurf1 silencing on cell migration.Methods HeLa and A549 cells were infected with lentiviral expression vectors for Smurf1 silencing respectively.After 7 days,the stable cell lines with Smurf1 silencing were obtained after puromycin-resistance screening,enrichment and expansion.The intracellular gene and protein levels of Smurf1 were detected by qPCR and western blot.Transwell assay was used to assess the effect of Smurf1 silencing on cell migration.Results The stable cell lines with Smurf1 silencing are constructed successfully.Silencing of Smurf1 down-regulated cell migration rate detected by Transwell assay.Conclusion Smurf1 promotes cell migration.

Ubiquitin ligase Smurf1 promotes poly-ubiquitination of PDK1 / 军事医学

Objective To investigate the mechanism of 3-phosphoinositide-dependent protein kinase 1(PDK1)poly-ubiquitination.Methods Co-immunoprecipitation(Co-IP)and Western blot(WB)were used to analyze poly-ubiquitination of PDK1.It was confirmed that ubiquitin ligase smad ubiquitylation regulatory factor 1(Smurf1)inprove PDK1 poly-ubiquitination within MEF cells,site-directed mutagenesis and WB before PDK1 poly-ubiquitination sites were determined.Results We found that PDK1 could undergoes poly-ubiquitination,ubiquitin ligase Smurf1 was found to be a direct E3 ligase for PDK1 poly-ubiquitination and might rely on the ubiquitin ligase Smurf 1 K699 site activity.K304 was PDK1 poly-ubiquitination modification site point.Conclusion The ubiquitin ligase Smurf1 can promate poly-ubiquitination of PDK1.

Role of Smurf1 in bone morphogenetic protein-induced osteogenesis / 第二军医大学学报

Bone morphogenetic proteins (BMPs) are confirmed growth factors that can induce osteogenesis. They can bind to the surface receptors of target cells and activate a series of intracellular Smad proteins, which then transduct the signal into cell nuclear; and with the assistance of a series of cofactors, the osteogenic gene expression can be triggered. Endogenous Smurfl plays an inhibitory effect on the above process. This paper reviews the role of Smurf1 in bone morphogenetic protein-induced bone formation.

Expression of Smad 7,Smurf 1 and Smurf 2 in basal cen carcinoma and squamous cell carcinoma / 中华皮肤科杂志

Objective To investigate the expression and significance of Smad 7,Smurf 1 and Smurf 2 in basal cell carcinoma and squamous cell carcinoma.Methods Biopsy specimens were resected from 14 patients with basal cell carcinoma,19 patients with squamous cell carcinoma and 30 normal controls.Quanti- tative real-time PCR and immunohistochemical techniques were utilized to assess the expression of Smad 7, Smurf 1 and Smurf 2 in these specimens.Results The gray scale for staining of Smad 7,Smurf 1 and Smurf 2 was 166.61?7.11,166.08?8.71,and 166.25?8.15 respectively in basal cell carcinoma,161.66?5.52,166.84?9.27,and 169.98?9.48 respectively in squamous cell carcinoma.The expression levels of Smad 7,Smurf 1 and Smurf 2 were all significantly increased in basal cell carcinoma and squamous cell car- cinoma in comparison with normal controls.Conclusions The over-expression of Smad 7,Smurf 1 and Smurf 2 may interfere with transforming growth factor?signaling transduction pathway through several links,therefore prevent the inhibitory effect of transforming growth factor?on epidermal proliferation,and accelerate the abnormal proliferation in above epidermal tumors.