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Hrd1-ERAD controls production of the hepatokine FGF21 through CREBH polyubiquitination

ABSTRACT: The endoplasmic reticulum-associated protein degradation (ERAD) is responsible for recognizing and retro-translocating protein substrates, misfolded or not, from the ER for cytosolic proteasomal degradation. HMG-CoA Reductase (HMGCR) Degradation protein - HRD1 - was initially identified as an E3 ligase critical for ERAD. However, its physiological functions remain largely undefined. Herein, we discovered that hepatic HRD1 expression is induced in the postprandial condition upon mouse refeeding. Mice with liver-specific HRD1 deletion failed to repress FGF21 production in serum and liver even in the refeeding condition and phenocopy the FGF21 gain-of-function mice showing growth retardation, female infertility and diurnal circadian behaviour disruption. HRD1-ERAD facilitates the degradation of the liver-specific ER-tethered transcription factor CREBH to downregulate FGF21 expression. HRD1-ERAD catalyzes poly-ubiquitin conjugation onto CREBH at lysine 294 for its proteasomal degradation, bridging a multi-organ crosstalk in regulating growth, circadian behaviour and female fertility through regulating the CREBH-FGF21 regulatory axis.

SUBMITTER: Dr. Deyu Fang

PROVIDER: S-SCDT-EMBOJ-2018-98942 | biostudies-other |

REPOSITORIES: biostudies-other

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Project description:Hepatitis C virus is a poor inducer of interferon (IFN), although its structured viral RNA can bind the RNA helicase RIG-I, and activate the IFN-induction pathway. Low IFN induction has been attributed to HCV NS3/4A protease-mediated cleavage of the mitochondria-adapter MAVS. Here, we have investigated the early events of IFN induction upon HCV infection, using the cell-cultured HCV JFH1 strain and the new HCV-permissive hepatoma-derived Huh7.25.CD81 cell subclone. These cells depend on ectopic expression of the RIG-I ubiquitinating enzyme TRIM25 to induce IFN through the RIG-I/MAVS pathway. We observed induction of IFN during the first 12 hrs of HCV infection, after which a decline occurred which was more abrupt at the protein than at the RNA level, revealing a novel HCV-mediated control of IFN induction at the level of translation. The cellular protein kinase PKR is an important regulator of translation, through the phosphorylation of its substrate the eIF2alpha initiation factor. A comparison of the expression of luciferase placed under the control of an eIF2alpha-dependent (IRES(EMCV)) or independent (IRES(HCV)) RNA showed a specific HCV-mediated inhibition of eIF2alpha-dependent translation. We demonstrated that HCV infection triggers the phosphorylation of both PKR and eIF2alpha at 12 and 15 hrs post-infection. PKR silencing, as well as treatment with PKR pharmacological inhibitors, restored IFN induction in JFH1-infected cells, at least until 18 hrs post-infection, at which time a decrease in IFN expression could be attributed to NS3/4A-mediated MAVS cleavage. Importantly, both PKR silencing and PKR inhibitors led to inhibition of HCV yields in cells that express functional RIG-I/MAVS. In conclusion, here we provide the first evidence that HCV uses PKR to restrain its ability to induce IFN through the RIG-I/MAVS pathway. This opens up new possibilities to assay PKR chemical inhibitors for their potential to boost innate immunity in HCV infection.

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Hrd1-ERAD controls production of the hepatokine FGF21 through CREBH polyubiquitination

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