The ubiquitin ligase gp78 promotes sarcoma metastasis by targeting KAI1 for degradation. Nat Med
ABSTRACT Metastasis is the primary cause of mortality from cancer, but the mechanisms leading to metastasis are poorly understood. In particular, relatively little is known about metastasis in cancers of mesenchymal origins, which are known as sarcomas. Approximately ten proteins have been characterized as 'metastasis suppressors', but how these proteins function and are regulated is, in general, not well understood. Gp78 (also known as AMFR or RNF45) is a RING finger E3 ubiquitin ligase that is integral to the endoplasmic reticulum (ER) and involved in ER-associated degradation (ERAD) of diverse substrates. Here we report that expression of gp78 has a causal role in the metastasis of an aggressive human sarcoma and that this prometastatic activity requires the E3 activity of gp78. Further, gp78 associates with and targets the transmembrane metastasis suppressor, KAI1 (also known as CD82), for degradation. Suppression of gp78 increases KAI1 abundance and reduces the metastatic potential of tumor cells, an effect that is largely blocked by concomitant suppression of KAI1. An inverse relationship between these proteins was confirmed in a human sarcoma tissue microarray. Whereas most previous efforts have focused on genetic mechanisms for the loss of metastasis suppressor genes, our results provide new evidence for post-translational downregulation of a metastasis suppressor by its ubiquitin ligase, resulting in abrogation of its metastasis-suppressing effects.
- SourceAvailable from: Jin Chai
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- "Interestingly, substantially more ubiquitin conjugated MRP2 was detected in cells cotransfected with GFP-Ub K0 than with GFP-Ub WT , supporting that polyubiquitination of MRP2 leads to its degradation . As ubiquitin conjugation is the rate limiting step in target protein degradation  , we examined which ubiquitin ligase E3s was responsible for MRP2 ubiquitination in human cholestatic livers, i.e., GP78, TEB4 and HRD1. As shown in Figure 6C and D, only GP78 expression was significantly increased at both mRNA and protein levels (2.1-flod, p<0.05 and 4.2-fold, p<0.01 of control livers, respectively), whereas hepatic expression of TEB4 and HRD1 did not change. "
ABSTRACT: Multidrug resistance-associated protein 2 (MRP2) excretes conjugated organic anions including bilirubin and bile acids. Malfunction of MRP2 leads to jaundice in patients. Studies in rodents indicate that Radixin plays a critical role in determining Mrp2 canalicular membrane expression. However, it is not known how human hepatic MRP2 expression is regulated in cholestasis. We assessed liver MRP2 expression in patients with obstructive cholestasis caused by gallstone blockage of bile ducts, and investigated the regulatory mechanism in HepG2 cells. Western blot detected that liver MRP2 protein expression in obstructive cholestatic patients (n=30) was significantly reduced to 25% of the non-cholestatic controls (n=23). Immunoprecipitation identified Ezrin but not Radixin associating with MRP2 in human livers, and the increased amount of phospho-Ezrin Thr567 was positively correlated with the amount of co-precipitated MRP2 in cholestatic livers, whereas Ezrin and Radixin total protein levels were unchanged in cholestasis. Further detailed studies indicate that Ezrin Thr567 phosphorylation plays an important role in MRP2 internalization in HepG2 cells. Since increased expression of PKCα, δ and ε were detected in these cholestatic livers, we further confirmed that these PKCs stimulated Ezrin phosphorylation and reduced MRP2 membrane expression in HepG2 cells. Finally, we identified GP78 as the key ubiquitin ligase E3 involved in MRP2 proteasome degradation. Activation of liver PKCs during cholestasis leads to Ezrin Thr567 phosphorylation resulting in MRP2 internalization and degradation where ubiquitin ligase E3 GP78 is involved. This process provides a mechanistic explanation for jaundice seen in patients with obstructive cholestasis. Copyright © 2015. Published by Elsevier B.V.Journal of Hepatology 07/2015; DOI:10.1016/j.jhep.2015.07.016 · 10.40 Impact Factor
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- "As shown in Figure 3F, Amfr À/À MEFs showed an increased number of HSV-1-GFP-positive cells. AMFR Catalyzes K27-Linked Polyubiquitination of STING As an E3 ubiquitin ligase in ERAD (ER-associated protein degradation ), AMFR catalyzes the polyubiquitination of HMG-CoA reductase (HMGCR) and the metastasis suppressor KAI1, and promotes their proteasome-dependent degradation (Song et al., 2005; Tsai et al., 2007). Our in vitro ubiquitination assays confirmed that AMFR could catalyze the formation of polyubiquitin chains, whereas AMFR C2S could not (Figure 4B). "
ABSTRACT: Stimulator of interferon genes (STING, also known as MITA, ERIS, or MPYS) is essential for host immune responses triggered by microbial DNAs. However, the regulatory mechanisms underlying STING-mediated signaling are not fully understood. We report here that, upon cytoplasmic DNA stimulation, the endoplasmic reticulum (ER) protein AMFR was recruited to and interacted with STING in an insulin-induced gene 1 (INSIG1)-dependent manner. AMFR and INSIG1, an E3 ubiquitin ligase complex, then catalyzed the K27-linked polyubiquitination of STING. This modification served as an anchoring platform for recruiting TANK-binding kinase 1 (TBK1) and facilitating its translocation to the perinuclear microsomes. Depletion of AMFR or INSIG1 impaired STING-mediated antiviral gene induction. Consistently, myeloid-cell-specific Insig1(-/-) mice were more susceptible to herpes simplex virus 1 (HSV-1) infection than wild-type mice. This study uncovers an essential role of the ER proteins AMFR and INSIG1 in innate immunity, revealing an important missing link in the STING signaling pathway. Copyright © 2014 Elsevier Inc. All rights reserved.Immunity 12/2014; 41(6):919-933. DOI:10.1016/j.immuni.2014.11.011 · 19.75 Impact Factor
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- "Glycoprotein 78 (gp78) is a cell surface receptor that also functions as an E3 ubiquitin ligase in the endoplasmic reticulum-associated degradation pathway. A study by Tsai et al (15) reported that the expression of gp78 exhibits a causal role in the metastasis of an aggressive human sarcoma. Furthermore, gp78 is associated with, and targets, the transmembrane metastasis suppressor, KIA1, for degradation. "
ABSTRACT: The mechanisms eliciting colorectal adenocarcinoma are not well understood and the FBXL20 gene is problematic as it exhibits an abnormal expression in colorectal cancer cells. In the present study a recombinant plasmid, pReceiver-M03-FBL20 expression plasmid was constructed, which overexpressed FBXL20; this was transfected into Lovo cells to form Lovo-FBL20 cells. The FBXL20 expression level was examined by quantitative polymerase chain reaction (qPCR) and western blot analysis. The cell viability and invasion capacity were measured using cell counting kit 8, Transwell chamber and wound healing assays, respectively. The associated genes, including E-cadherin, β-catenin, c-Myc, SET nuclear oncogene, protein phosphatase-2A, Axin, p53 and caspase 3, were detected by qPCR and western blotting. It was demonstrated that the FBXL20 expression level was markedly upregulated in the Lovo-FBL20 cells transfected with pReceiver-M03-FBL20 expression plasmid, compared with that of the Lovo cells. In addition, the cell viability and invasion capacity of the Lovo-FBL20 cells were significantly increased. These increases correlated with a significant upregulation in the expression level of β-catenin and c-Myc, and a downregulated expression level of E-cadherin. The results of the present study indicate that FBXL20 may mediate the ubiquitin degradation of E-cadherin resulting in an increased invasive ability of malignant cells.Oncology letters 06/2014; 7(6):2185-2191. DOI:10.3892/ol.2014.2031 · 0.99 Impact Factor