ABSTRACT: The RNA-binding protein Hdlbp/Vigilin is increased in hepatic steatosis and regulates VLDL secretion through modulation of Apob mRNA translation
Project description:The liver exerts a wide range of essential functions including the synthesis of plasma proteins and the integration of glucose and lipid homeostasis. While the role of transcriptional networks in the tight regulation of these processes has been extensively studied in healthy and disease states, much less is known about post-transcriptional control of gene expression through RNA-binding proteins (RBP). Here, we report that the highly expressed and conserved RBP Hdlbp/Vigilin is upregulated in patients with non-alcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) and in livers of insulin resistant obese mice. Gain and loss of function studies revealed that Vigilin regulates VLDL secretion through the modulation of ApoB mRNA translation. Photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP) analysis in primary hepatocytes demonstrated that Vigilin predominantly binds to CU-rich regions in coding sequences of transcripts of further metabolically relevant secretory proteins such as Apob/apoliproteinB, Ahsg/fetuin-A, Apoc3/apolipoproteinC-III, Fn1/fibronectin, Orm1/orosomucoid and Serpina1/alpha-1-antitrypsin. While mRNA levels of these targets did not change, protein levels were substantially decreased upon knockdown of Vigilin. Hepatic long-term knockdown via GalNAc-conjugated siRNAs ameliorated elevated VLDL/LDL levels and the formation of atherosclerotic plaques in Ldlr–/– mice. These studies uncover a role for Vigilin as a key regulator of hepatic Apob translation and secretion through binding to its mRNA and demonstrate the therapeutic potential of inhibiting Vigilin for cardiovascular diseases.
Project description:Background: Non-alcoholic fatty liver disease (NAFLD) affects nearly 25% of the global population. Cardiovascular disease (CVD) is the most common cause of death among patients with NAFLD, in line with highly prevalent dyslipidemia in this population. Increased plasma triglyceride (TG)-rich lipoprotein (TRL) concentrations, an important risk factor for CVD, are closely linked with hepatic TG content. Therefore, it is of great interest to identify regulatory mechanisms of hepatic TRL production and remnant uptake in the setting of hepatic steatosis. Approach and results: To identify liver-regulated pathways linking intra-hepatic and plasma TG metabolism, we performed transcriptomic analysis of liver biopsies from two independent cohorts of obese patients. Hepatic APOF (encoding apolipoprotein F) expression showed the 4th strongest negatively correlation with hepatic steatosis and the strongest negative correlation with plasma TG levels. The effects of adenoviral-mediated human ApoF (hApoF) overexpression on plasma and hepatic TG were assessed in C57BL6/J mice. Surprisingly, hApoF overexpression increased both hepatic VLDL-TG secretion and hepatic lipoprotein remnant clearance, associated a ~25% reduction in plasma TG levels. Conversely, reducing endogenous ApoF expression reduced VLDL secretion in vivo, and reduced hepatocyte VLDL uptake by ~15% in vitro. Transcriptomic analysis of APOF-overexpressing mouse livers revealed a gene signature related to enhanced ApoB-lipoprotein clearance, including increased expression of Ldlr and Lrp1, among others. Conclusion: These data reveal a previously undescribed role for ApoF in the control of plasma and hepatic lipoprotein metabolism by favoring VLDL-TG secretion and hepatic lipoprotein remnant particle clearance.
Project description:Genetic polymorphisms that impair VLDL secretion are linked to hepatic steatosis, fibrosis and hepatocellular cancer (HCC). Liver-specific deletion of microsomal triglyceride transfer protein (Mttp-LKO) impairs VLDL assembly, promoting hepatic steatosis and fibrosis, which are attenuated in Mttp-LKO mice with germline Fabp1 deletion (Fabp1/Mttp DKO) mice. Here we examine the impact of impaired VLDL secretion in Mttp-LKO mice on HCC incidence and progression in comparison to Fabp1/Mttp DKO mice. DEN treated Mttp-LKO mice exhibited steatosis with increased tumor burden compared to flox controls, while diethylnitrosamine (DEN)- treated Fabp1/Mttp DKO mice exhibited a paradoxical increase in tumor burden and >50% mortality by 50 weeks. Lipidomic surveys revealed progressive enrichment in distinct triglyceride species in livers from Mttp-LKO mice with further enrichment in Fabp1/Mttp DKO mice. RNAseq analysis performed on liver tissue at 6 months revealed mRNA changes suggesting altered monocarboxylic acid utilization and increased aerobic glycolysis, while hepatocytes from Fabp1/Mttp DKO mice exhibited increased capacity to utilize glucose and glutamine. Taken together, these findings demonstrate that hepatic tumorigenesis is increased in mice with impaired VLDL secretion and further accelerated via pathways including altered fatty acid compartmentalization and shifts in hepatic energy utilization.
Project description:The biological role of RNA-binding proteins (RBPs) in the secretory pathway and their contribution to the recognition and co-translational targeting of ER-localized mRNAs is not well established. In this work we used biochemical, transcriptomic and proteomic approaches to delineate the role of human HDLBP/vigilin. PAR-CLIP analysis revealed that HDLBP directly and specifically interacted with more than 80% of all expressed ER-localized mRNAs. Interestingly, the binding to the coding sequence was most prominent for ER-localized mRNAs, while cytosolic mRNAs showed higher binding in the 3’UTR. HDLBP crosslinked strongly to long CU-rich motifs that resided more frequently in coding sequences of ER-localized but not in cytosolic mRNAs. This indicated that the primary sequence composition determines the basis for HDLBP binding specificity and its multivalent interactions with ER-bound mRNAs. PAR-CLIP analysis also revealed direct interactions of HDLBP with the RNA components of the translational apparatus, while in vivo proximity proteomics detected proteins involved in translation and components of the signal recognition particle (SRP). Functional studies using CRISPR-Cas9 HDLBP knockout cell lines in combination with ribosome profiling, pSILAC, and luciferase assays showed decreased translation efficiency of HDLBP target mRNAs, impaired protein synthesis and secretion in the knockout conditions. Finally, HDLBP absence resulted in decrease of in vivo lung tumor formation. These results highlight a general function for HDLBP in the translation of ER -localized mRNAs via the secretory pathway and discover its relevance for cell proliferation and tumor progression.
Project description:The biological role of RNA-binding proteins (RBPs) in the secretory pathway and their contribution to the recognition and co-translational targeting of ER-localized mRNAs is not well established. In this work we used biochemical, transcriptomic and proteomic approaches to delineate the role of human HDLBP/vigilin. PAR-CLIP analysis revealed that HDLBP directly and specifically interacted with more than 80% of all expressed ER-localized mRNAs. Interestingly, the binding to the coding sequence was most prominent for ER-localized mRNAs, while cytosolic mRNAs showed higher binding in the 3’UTR. HDLBP crosslinked strongly to long CU-rich motifs that resided more frequently in coding sequences of ER-localized but not in cytosolic mRNAs. This indicated that the primary sequence composition determines the basis for HDLBP binding specificity and its multivalent interactions with ER-bound mRNAs. PAR-CLIP analysis also revealed direct interactions of HDLBP with the RNA components of the translational apparatus, while in vivo proximity proteomics detected proteins involved in translation and components of the signal recognition particle (SRP). Functional studies using CRISPR-Cas9 HDLBP knockout cell lines in combination with ribosome profiling, pSILAC, and luciferase assays showed decreased translation efficiency of HDLBP target mRNAs, impaired protein synthesis and secretion in the knockout conditions. Finally, HDLBP absence resulted in decrease of in vivo lung tumor formation. These results highlight a general function for HDLBP in the translation of ER -localized mRNAs via the secretory pathway and discover its relevance for cell proliferation and tumor progression.
Project description:The biological role of RNA-binding proteins (RBPs) in the secretory pathway and their contribution to the recognition and co-translational targeting of ER-localized mRNAs is not well established. In this work we used biochemical, transcriptomic and proteomic approaches to delineate the role of human HDLBP/vigilin. PAR-CLIP analysis revealed that HDLBP directly and specifically interacted with more than 80% of all expressed ER-localized mRNAs. Interestingly, the binding to the coding sequence was most prominent for ER-localized mRNAs, while cytosolic mRNAs showed higher binding in the 3’UTR. HDLBP crosslinked strongly to long CU-rich motifs that resided more frequently in coding sequences of ER-localized but not in cytosolic mRNAs. This indicated that the primary sequence composition determines the basis for HDLBP binding specificity and its multivalent interactions with ER-bound mRNAs. PAR-CLIP analysis also revealed direct interactions of HDLBP with the RNA components of the translational apparatus, while in vivo proximity proteomics detected proteins involved in translation and components of the signal recognition particle (SRP). Functional studies using CRISPR-Cas9 HDLBP knockout cell lines in combination with ribosome profiling, pSILAC, and luciferase assays showed decreased translation efficiency of HDLBP target mRNAs, impaired protein synthesis and secretion in the knockout conditions. Finally, HDLBP absence resulted in decrease of in vivo lung tumor formation. These results highlight a general function for HDLBP in the translation of ER -localized mRNAs via the secretory pathway and discover its relevance for cell proliferation and tumor progression.
Project description:The biological role of RNA-binding proteins (RBPs) in the secretory pathway and their contribution to the recognition and co-translational targeting of ER-localized mRNAs is not well established. In this work we used biochemical, transcriptomic and proteomic approaches to delineate the role of human HDLBP/vigilin. PAR-CLIP analysis revealed that HDLBP directly and specifically interacted with more than 80% of all expressed ER-localized mRNAs. Interestingly, the binding to the coding sequence was most prominent for ER-localized mRNAs, while cytosolic mRNAs showed higher binding in the 3’UTR. HDLBP crosslinked strongly to long CU-rich motifs that resided more frequently in coding sequences of ER-localized but not in cytosolic mRNAs. This indicated that the primary sequence composition determines the basis for HDLBP binding specificity and its multivalent interactions with ER-bound mRNAs. PAR-CLIP analysis also revealed direct interactions of HDLBP with the RNA components of the translational apparatus, while in vivo proximity proteomics detected proteins involved in translation and components of the signal recognition particle (SRP). Functional studies using CRISPR-Cas9 HDLBP knockout cell lines in combination with ribosome profiling, pSILAC, and luciferase assays showed decreased translation efficiency of HDLBP target mRNAs, impaired protein synthesis and secretion in the knockout conditions. Finally, HDLBP absence resulted in decrease of in vivo lung tumor formation. These results highlight a general function for HDLBP in the translation of ER -localized mRNAs via the secretory pathway and discover its relevance for cell proliferation and tumor progression.
Project description:The biological role of RNA-binding proteins (RBPs) in the secretory pathway and their contribution to the recognition and co-translational targeting of ER-localized mRNAs is not well established. In this work we used biochemical, transcriptomic and proteomic approaches to delineate the role of human HDLBP/vigilin. PAR-CLIP analysis revealed that HDLBP directly and specifically interacted with more than 80% of all expressed ER-localized mRNAs. Interestingly, the binding to the coding sequence was most prominent for ER-localized mRNAs, while cytosolic mRNAs showed higher binding in the 3’UTR. HDLBP crosslinked strongly to long CU-rich motifs that resided more frequently in coding sequences of ER-localized but not in cytosolic mRNAs. This indicated that the primary sequence composition determines the basis for HDLBP binding specificity and its multivalent interactions with ER-bound mRNAs. PAR-CLIP analysis also revealed direct interactions of HDLBP with the RNA components of the translational apparatus, while in vivo proximity proteomics detected proteins involved in translation and components of the signal recognition particle (SRP). Functional studies using CRISPR-Cas9 HDLBP knockout cell lines in combination with ribosome profiling, pSILAC, and luciferase assays showed decreased translation efficiency of HDLBP target mRNAs, impaired protein synthesis and secretion in the knockout conditions. Finally, HDLBP absence resulted in decrease of in vivo lung tumor formation. These results highlight a general function for HDLBP in the translation of ER -localized mRNAs via the secretory pathway and discover its relevance for cell proliferation and tumor progression.
Project description:At 2 months of age, liver-specific insulin receptor knockout (LIRKO) mice present hyperglycemia and hyperinsulinemia. Furthermore, LIRKO mice have increased levels of hepatic cholesterol. Indeed, many changes seen in cholesterol metabolism in LIRKO mice are also observed in humans with metabolic syndrome. For example, both show decreased levels of HDL and increased secretion of apoB and VLDL. These findings make the LIRKO mouse a unique non-dietary model of insulin resistant, hyperglycemia, dyslipidemia and atherosclerosis that resembles several clinical features of the human metabolic syndrome. By hepatic transcriptomic analysis of the wild-type (WT) offspring of LIRKO mice, we identify that members of the TGF-β family are differentially expressed in the offspring, including the NREP and GDF15.