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BACKGROUND & AIMS: Endoplasmic reticulum (ER) stress of hepatocytes plays a causative role in non-alcoholic fatty liver disease (NAFLD). Reduced expression of hepatic nuclear factor 4α (HNF4α) is a critical event in the pathogenesis of NAFLD and other liver diseases. Whether ER stress regulates HNF4α expression remains unknown. The aim of this study was to delineate the machinery of HNF4α protein degradation and explore a therapeutic strategy based on protecting HNF4α stability during NAFLD progression. METHODS: Correlation of HNF4α and tribbles homologue 3 (TRIB3), an ER stress sensor, was evaluated in human and mouse NAFLD tissues. RNA-sequencing, mass spectrometry analysis, co-immunoprecipitation, in vivo and in vitro ubiquitination assays were used to elucidate the mechanisms of TRIB3-mediated HNF4α degradation. Molecular docking and co-immunoprecipitation analyses were performed to identify a cell-penetrating peptide that ablates the TRIB3-HNF4α interaction. RESULTS: TRIB3 directly interacts with HNF4α and mediates ER stress-induced HNF4α degradation. TRIB3 recruits tripartite motif containing 8 (TRIM8) to form an E3 ligase complex that catalyzes K48-linked polyubiquitination of HNF4α on lysine 470. Abrogating the degradation of HNF4α attenuated the effect of TRIB3 on a diet-induced NAFLD model. Moreover, the TRIB3 gain-of-function variant p.Q84R is associated with NAFLD progression in patients, and induces lower HNF4α levels and more severe hepatic steatosis in mice. Importantly, disrupting the TRIB3-HNF4α interaction using a cell-penetrating peptide restores HNF4α levels and ameliorates NAFLD progression in mice. CONCLUSIONS: Our findings unravel the machinery of HNF4α protein degradation and indicate that targeting TRIB3-TRIM8 E3 complex-mediated HNF4α polyubiquitination may be an ideal strategy for NAFLD therapy. IMPACT AND IMPLICATIONS: Reduced expression of hepatic nuclear factor 4α (HNF4α) is a critical event in the pathogenesis of NAFLD and other liver diseases. However, the mechanism of HNF4α protein degradation remains unknown. Herein, we reveal that TRIB3-TRIM8 E3 ligase complex is responsible for HNF4α degradation during NAFLD. Inhibiting the TRIB3-HNF4α interaction effectively stabilized HNF4α protein levels and transcription factor activity in the liver and ameliorated TRIB3-mediated NAFLD progression. Our findings demonstrate that disturbing the TRIM8-TRIB3-HNF4α interaction may provide a novel approach to treat NAFLD and even other liver diseases by stabilizing the HNF4α protein.
Assuntos
Peptídeos Penetradores de Células , Hepatopatia Gordurosa não Alcoólica , Proteínas Serina-Treonina Quinases , Animais , Humanos , Camundongos , Proteínas de Transporte/metabolismo , Proteínas de Ciclo Celular/metabolismo , Peptídeos Penetradores de Células/metabolismo , Fígado/patologia , Simulação de Acoplamento Molecular , Proteínas do Tecido Nervoso , Hepatopatia Gordurosa não Alcoólica/metabolismo , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Serina-Treonina Quinases/antagonistas & inibidores , Proteínas Repressoras , Ubiquitina-Proteína Ligases/metabolismoRESUMO
The aims of the present study were to elucidate the regulatory effect of exogenous Tribbles homologue 3 (TRB3) expression on the Wnt/ßcatenin signaling pathway and epithelialmesenchymal transition (EMT) in transforming growth factorß1 (TGFß1)induced mouse alveolar epithelial cells (MLE12) and investigate the underlying regulatory mechanisms. TRB3 expression was upregulated and downregulated using gene overexpression and RNA interference techniques, respectively. TGFß1stimulated MLE12 cells were examined for EMT and activation condition of the Wnt/ßcatenin signaling pathway using Cell Counting Kit8, flow cytometry, western blotting, reverse transcriptionquantitative PCR, ELISA and immunofluorescence techniques. During TGFß1induced EMT, TRB3 expression was found to be significantly upregulated (P<0.05). In the TRB3 overexpression group, upregulated expression of ßcatenin and EMTrelated genes and proteins was observed (P<0.05), and an increase in fibrosisrelated factors in the cell culture supernatant was detected (P<0.05); however, the results were the opposite in the TRB3 downregulated group (P<0.05). TRB3 may be involved in the regulation of EMT in TGFß1induced MLE12 cells through the Wnt/ßcatenin signaling pathway.
Assuntos
Células Epiteliais Alveolares/metabolismo , Proteínas de Ciclo Celular/metabolismo , Transição Epitelial-Mesenquimal , Fator de Crescimento Transformador beta1/farmacologia , Via de Sinalização Wnt , Actinas/metabolismo , Células Epiteliais Alveolares/efeitos dos fármacos , Animais , Apoptose/efeitos dos fármacos , Caderinas/metabolismo , Linhagem Celular , Proliferação de Células/efeitos dos fármacos , Colágeno/genética , Colágeno/metabolismo , Transição Epitelial-Mesenquimal/efeitos dos fármacos , Fibronectinas/metabolismo , Fluorescência , Camundongos , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Vimentina/metabolismo , Via de Sinalização Wnt/efeitos dos fármacos , beta Catenina/metabolismoRESUMO
Parkinson's disease (PD) is a degenerative disorder of the central nervous system, resulting in loss of dopamine neurons. Excessive endoplasmic reticulum (ER) stress and autophagy dysfunction play a crucial role on Parkinson's disease (PD) development. It has been showed that acidic fibroblast growth factor (aFGF) alleviates the development of PD by inhibiting ER stress. But the role of autophagy and its relationship with ER stress during aFGF treatment for PD has not been elucidated. We found that both aFGF and rapamycin (Rapa) improved 6-Hydroxy Dopamine (6-OHDA)-induced PD development as shown with histomorphology results in striatum and substantia nigra (SNpc). Additionally, aFGF promoted autophagy with increasing mTOR and decreasing p62 expressions, and then exerts its neuroprotective role in 6-OHDA-treated PC12 cells, which were abolished by chloroquine (CQ) treatment. Moreover, 4-phenylbutyric acid (4-PBA) administration inhibited the expressions of autophagy markers during 6-OHDA-treated PC12 cells, which was similar with aFGF treating PC12 cells under 6-OHDA condition. Furthermore, we had detected the expressions of CHOP and its downstream factor, tribbles homologue 3 (TRB3), a pro-apoptotic protein. We found that TRB3 and CHOP expressions were significantly downregulated after treating with aFGF and 4-PBA in 6-OHDA-treated PC12 cells and PD model. Taken together, this study has demonstrated that aFGF treatment ameliorates 6-OHDA-induced elevated ER stress and subsequently suppression of autophagy via inhibiting TRB3 activation, and consequently ameliorates 6-OHDA-induced neurotoxicity.
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Δ(9)-Tetrahydrocannabinol (THC), the major active ingredient of marijuana, and other cannabinoids inhibit tumor growth in animal models of cancer. This effect relies, at least in part, on the up-regulation of several endoplasmic reticulum stress-related proteins including the pseudokinase tribbles homologue-3 (TRIB3), which leads in turn to the inhibition of the AKT/mTORC1 axis and the subsequent stimulation of autophagy-mediated apoptosis in tumor cells. Here, we took advantage of the use of cells derived from Trib3-deficient mice to investigate the precise mechanisms by which TRIB3 regulates the anti-cancer action of THC. Our data show that RasV(12)/E1A-transformed embryonic fibroblasts derived from Trib3-deficient mice are resistant to THC-induced cell death. We also show that genetic inactivation of this protein abolishes the ability of THC to inhibit the phosphorylation of AKT and several of its downstream targets, including those involved in the regulation of the AKT/mammalian target of rapamycin complex 1 (mTORC1) axis. Our data support the idea that THC-induced TRIB3 up-regulation inhibits AKT phosphorylation by regulating the accessibility of AKT to its upstream activatory kinase (the mammalian target of rapamycin complex 2; mTORC2). Finally, we found that tumors generated by inoculation of Trib3-deficient cells in nude mice are resistant to THC anticancer action. Altogether, the observations presented here strongly support that TRIB3 plays a crucial role on THC anti-neoplastic activity. This article is part of a Special Issue entitled Lipid Metabolism in Cancer.