Project description:During gene expression, ribosome stalling frequently occurs and can lead to detrimental effects on cellular homeostasis. Several quality control mechanisms, including RQC and NRD, have been identified to resolve these aberrant translation events. While the molecular mechanisms of each pathway have been extensively characterized, the mechanisms underlying the mutual regulation of these factors' expression remain to be elucidated. In this study, we employed a series of knockout mouse and human cell lines to investigate the crosstalk between translational quality control factors. Our findings revealed that LTN1 suppresses RNF10 expression in a manner dependent on the RING domain of LTN1. This discovery offers new insights into the coordination of translational surveillance pathways.
Project description:Protein arginine methyltransferase 5 (PRMT5) is an important member of the protein arginine methyltransferase family that regulates many cellular processes through epigenetic control of target gene expression. Because of its overexpression in a number of human cancers and its essential role in cell proliferation, transformation, and cell cycle progression, PRMT5 has been recently proposed to function as an oncoprotein in cancer cells. However, how its expression is regulated in cancer cells remains largely unknown. We have previously demonstrated that the transcription of PRMT5 can be negatively regulated by the PKC/c-Fos signaling pathway through modulating the transcription factor NF-Y in prostate cancer cells. In the present study, we demonstrated that PRMT5 undergoes polyubiquitination, possibly through multiple lysine residues. We also identified carboxyl terminus of heat shock cognate 70-interacting protein (CHIP), an important chaperone-dependent E3 ubiquitin ligase that couples protein folding/refolding to protein degradation, as an interacting protein of PRMT5 via mass spectrometry. Their interaction was further verified by co-immuoprecipitation, GST pull-down, and bimolecular fluorescence complementation (BiFC) assay. In addition, we provided evidence that the CHIP/chaperone system is essential for the negative regulation of PRMT5 expression via K48-linked ubiquitin-dependent proteasomal degradation. Given that down-regulation of CHIP and overexpression of PRMT5 have been observed in several human cancers, our finding suggests that down-regulation of CHIP may be one of the mechanisms underlying PRMT5 overexpression in these cancers.
Project description:Aberrant activation of inflammation signaling triggered by tumor necrosis factor α (TNF-α), interleukin-1 (IL-1), and interleukin-17 (IL-17) is associated with immunopathology. Here, we identify neural precursor cells expressed developmentally down-regulated gene 4-like (NEDD4L), a HECT type E3 ligase, as a common negative regulator of signaling induced by TNF-α, IL-1, and IL-17. NEDD4L modulates the degradation of mitogen-activated protein kinase kinase kinase 2 (MEKK2) via constitutively and directly binding to MEKK2 and promotes its poly-ubiquitination. In interleukin-17 receptor (IL-17R) signaling, Nedd4l knockdown or deficiency enhances IL-17-induced p38 and NF-κB activation and the production of proinflammatory cytokines and chemokines in a MEKK2-dependent manner. We further show that IL-17-induced MEKK2 Ser520 phosphorylation is required not only for downstream p38 and NF-κB activation but also for NEDD4L-mediated MEKK2 degradation and the subsequent shutdown of IL-17R signaling. Importantly, Nedd4l-deficient mice show increased susceptibility to IL-17-induced inflammation and aggravated symptoms of experimental autoimmune encephalomyelitis (EAE) in IL-17R signaling-dependent manner. These data suggest that NEDD4L acts as an inhibitor of IL-17R signaling, which ameliorates the pathogenesis of IL-17-mediated autoimmune diseases.
Project description:Aberrant activation of inflammation signaling triggered by tumor necrosis factor α (TNF-α), interleukin-1 (IL-1), and interleukin-17 (IL-17) is associated with immunopathology. Here we identify neural precursor cell expressed developmentally down-regulated gene 4-like (NEDD4L), a HECT type E3 ligase, as a common negative regulator of signaling induced by TNF-α, IL-1, and IL-17. NEDD4L modulates the degradation of mitogen-activated protein kinase kinase kinase 2 (MEKK2) via constitutively and directly binding to MEKK2 and promotes its poly-ubiquitination. In interleukin-17 receptor (IL-17R) signaling, Nedd4l knockdown or deficiency enhances IL-17-induced p38 and NF-κB activation and the production of proinflammatory cytokines and chemokines in a MEKK2-dependent manner. We further show that IL-17-induced MEKK2 Ser520 phosphorylation is required not only for downstream p38 and NF-κB activation but also for NEDD4L-mediated MEKK2 degradation and the subsequent shutdown of IL-17R signaling. Importantly, Nedd4l deficient mice show increased susceptibility to IL-17-induced inflammation and aggravated symptoms of experimental autoimmune encephalomyelitis (EAE) in IL-17R signaling-dependent manner. These data suggest that NEDD4L acts as an inhibitor of IL-17R signaling, which ameliorates the pathogenesis of IL-17-mediated autoimmune diseases.
Project description:Previously, we reported on a novel anti-apoptotic E3 ubiquitin ligase, apoptosis-resistant E3 ubiquitin protein ligase 1 (AREL1), that ubiquitinates inhibitors of apoptosis proteins antagonists. The present study demonstrated that AREL1 ubiquitinated Metaxin 2 (MTX2), which was involved in TNF-induced necroptosis. MTX2 has been identified as a protein that belongs to the Metaxin family. It interacts with another Metaxin protein, Metaxin 1 (MTX1), which is localized in the outer membrane of mitochondria, and is involved in TNF-induced necroptosis. This study found that AREL1 interacted with MTX2, but not MTX1, while the amino-terminal domain of MTX2 interacted with MTX1, AREL1 interacted with the carboxyl-terminal domain of MTX2. Furthermore, AREL1 expression led to a decrease in the protein expression of MTX2, but not MTX1. However, a mutant form of AREL1, AREL1C790A, which is deficient for E3 activity, did not cause MTX2 degradation. Moreover, the protein levels of MTX2 were increased by AREL1 knockdown. Therefore, these results implied that AREL1 ubiquitinates and promotes the degradation of MTX2. The expression of MTX2, together with MTX1, enhanced TNF-induced necroptosis. However, AREL1 inhibited necroptosis even in cells expressing Metaxin proteins. Therefore, these results suggested that the inhibition of AREL1-dependent ubiquitination of MTX2 could be beneficial to sensitize tumor cells to TNF-induced necroptosis.
Project description:Transforming growth factor β (TGFβ) pathway is a master regulator of cell proliferation, differentiation, and death. Deregulation of TGFβ signalling is well established in several human diseases including autoimmune disorders and cancer. Thus, understanding molecular pathways governing TGFβ signalling may help better understand the underlying causes of some of those conditions. Here, we show that a HECT domain E3 ubiquitin ligase TRIP12 controls TGFβ signalling in multiple models. Interestingly, TRIP12 control of TGFβ signalling is completely independent of its E3 ubiquitin ligase activity. Instead, TRIP12 recruits SMURF2 to SMAD4, which is most likely responsible for inhibitory monoubiquitination of SMAD4, since SMAD4 monoubiquitination and its interaction with SMURF2 were dramatically downregulated in TRIP12-/- cells. Additionally, genetic inhibition of TRIP12 in human and murine cells leads to robust activation of TGFβ signalling which was rescued by re-introducing wildtype TRIP12 or a catalytically inactive C1959A mutant. Importantly, TRIP12 control of TGFβ signalling is evolutionary conserved. Indeed, genetic inhibition of Drosophila TRIP12 orthologue, ctrip, in gut leads to a reduced number of intestinal stem cells which was compensated by the increase in differentiated enteroendocrine cells. These effects were completely normalised in Drosophila strain where ctrip was co-inhibited together with Drosophila SMAD4 orthologue, Medea. Similarly, in murine 3D intestinal organoids, CRISPR/Cas9 mediated genetic targeting of Trip12 enhances TGFβ mediated proliferation arrest and cell death. Finally, CRISPR/Cas9 mediated genetic targeting of TRIP12 in MDA-MB-231 breast cancer cells enhances the TGFβ induced migratory capacity of these cells which was rescued to the wildtype level by re-introducing wildtype TRIP12. Our work establishes TRIP12 as an evolutionary conserved modulator of TGFβ signalling in health and disease.
Project description:The histone deacetylase 6 (HDAC6) plays critical roles in human tumorigenesis and metastasis. As such, HDAC6-selective inhibitors have entered clinical trials for cancer therapy. However, the upstream regulator(s), especially ubiquitin E3 ligase(s), responsible for controlling the protein stability of HDAC6 remains largely undefined. Here, we report that Cullin 3SPOP earmarks HDAC6 for poly-ubiquitination and degradation. We found that the proteasome inhibitor MG132, or the Cullin-based E3 ligases inhibitor MLN4924, but not the autophagosome-lysosome inhibitor bafilomycin A1, stabilized endogenous HDAC6 protein in multiple cancer cell lines. Furthermore, we demonstrated that Cullin 3-based ubiquitin E3 ligase(s) primarily reduced the stability of HDAC6. Importantly, we identified SPOP, an adaptor protein of Cullin 3 family E3 ligases, specifically interacted with HDAC6, and promoted its poly-ubiquitination and subsequent degradation in cells. Notably, cancer-derived SPOP mutants disrupted their binding with HDAC6 and thereby failed to promote HDAC6 degradation. More importantly, increased cellular proliferation and migration in SPOP-depleted HCT116 colon cancer cells could be partly reversed by additional depletion of HDAC6, suggesting that HDAC6 is a key downstream effector for SPOP tumor suppressor function. Together, our data identify the tumor suppressor SPOP as an upstream negative regulator for HDAC6 stability, and SPOP loss-of-function mutations might lead to elevated levels of the HDAC6 oncoprotein to facilitate tumorigenesis and metastasis in various human cancers.
Project description:Viperin is a broadly conserved radical SAM enzyme that synthesizes the antiviral nucleotide ddhCTP. In higher animals, viperin expression also accelerates the degradation of various cellular and viral proteins necessary for viral replication; however, the details of this process remain largely unknown. Here, we show that viperin activates a component of the protein ubiquitination machinery, which plays an important role in both protein degradation and immune signaling pathways. We demonstrate that viperin binds the E3 ubiquitin ligase, TRAF6, which catalyzes K63-linked ubiquitination associated with immune signaling pathways. Viperin activates ubiquitin transfer by TRAF6-2.5-fold and causes a significant increase in polyubiquitinated forms of TRAF6 that are important for mediating signal transduction. Our observations both imply a role for viperin as an agonist of immune signaling and suggest that viperin may activate other K48-linked E3-ligases involved in targeting proteins for proteasomal degradation.
Project description:In the course of combating infectious agents, type I interferon (IFN) needs a timely downregulation mechanism to avoid detrimental overreaction. Here we showed a mechanism for restraining type I IFN responses, which relied on a HECT domain ubiquitin (Ub) E3 ligase, RAUL. RAUL limited type I IFN production by directly catalyzing lysine 48-linked polyubiquitination of both interferon regulatory factor 7 (IRF7) and IRF3 followed by proteasome-dependent degradation. Suppression of RAUL by dominant-negative RAUL or siRNA augmented both basal and virus-induced production of type I IFN, which resulted in reduced viral replication. The Kaposi's sarcoma-associated herpes virus immediate-early lytic cycle trigger protein RTA recruited this mechanism to augment its countermeasures against the host antiviral response. These results unveil a previously unrecognized "brake mechanism" for type I IFN that maintains proper low amounts of type I IFN under physiological conditions and restrains its magnitude when the antiviral response intensifies.
Project description:Apoptotic protease-activating factor 1 (Apaf-1) is a component of apoptosome, which regulates caspase-9 activity. In addition to apoptosis, Apaf-1 plays critical roles in the intra-S-phase checkpoint; therefore, impaired expression of Apaf-1 has been demonstrated in chemotherapy-resistant malignant melanoma and nuclear translocation of Apaf-1 has represented a favorable prognosis of patients with non-small cell lung cancer. In contrast, increased levels of Apaf-1 protein are observed in the brain in Huntington's disease. The regulation of Apaf-1 protein is not yet fully understood. In this study, we show that etoposide triggers the interaction of Apaf-1 with Cullin-4B, resulting in enhanced Apaf-1 ubiquitination. Ubiquitinated Apaf-1, which was degraded in healthy cells, binds p62 and forms aggregates in the cytosol. This complex of ubiquitinated Apaf-1 and p62 induces caspase-9 activation following MG132 treatment of HEK293T cells that stably express bcl-xl. These results show that ubiquitinated Apaf-1 may activate caspase-9 under conditions of proteasome impairment.