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A suite of haploid genetic screens identifies SPRING as a novel determinant of SREBP signaling and cholesterol metabolism

ABSTRACT: The sterol-regulatory element binding protein (SREBP) transcription factors are central transcriptional regulators of sterol- and fatty acid metabolism. Using a suite of human haploid genetic screens, we identify the SREBP Regulating Gene (SPRING; C12ORF49) as a novel regulator of this pathway. SPRING is a glycosylated Golgi-resident membrane protein. Genetic ablation of SPRING in human Hap1 cells, murine Hepa1-6 hepatoma cells, and in primary murine hepatocytes leads to a marked reduction in SREBP signaling. In mice, deletion of Spring results in embryonic lethality. However, we show that adenoviral-mediated silencing of hepatic Spring expression also attenuates the SREBP response. Mechanistically, we demonstrate that attenuated SREBP signaling in SPRINGKO cells is a result of reduced SREBP cleavage-activating protein (SCAP) and its mislocalization. Whereas in control cells SCAP cycles between the ER and the Golgi in a sterol-dependent manner, in SPRINGKO cells SCAP is trapped in the Golgi irrespective of the cellular sterol status. Consistent with limited functional SCAP in SPRINGKO cells, reintroducing SCAP restores SREBP-dependent signaling, cholesterol biosynthesis, and lipoprotein uptake. Consistent with SREBP signaling being required for cell growth and proliferation, a wide range of human tumor cell lines display dependency on SPRING expression. In conclusion, we identify SPRING as a previously unrecognized determinant of the SREBP pathway that is essential for proper SCAP function.

ORGANISM(S): Homo sapiens

PROVIDER: GSE143530 | GEO | 2020/01/23

REPOSITORIES: GEO

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Project description:The sterol regulatory element binding proteins (SREBPs) are transcription factors that govern cholesterol and fatty acid metabolism. Owing to their central role in controlling hepatic lipid and lipoprotein metabolism their activity is tightly coordinated, and accordingly dysregulation of the SREBP pathway is associated with development of dyslipidemia and non-alcoholic fatty liver disease. Using a suite of genome-wide genetic screens we have recently identified SPRING (C12ORF49) as a novel post-transcriptional regulator of SREBP activation in vitro. Our previous work demonstrated that constitutive ablation of Spring in mice is embryonically lethal. Here we show that inducible global deletion of Spring is also untolerated, and therefore to interrogate the physiological role of SPRING in controlling hepatic lipid metabolism we developed liver-specific Spring knockout mice (LKO). Liver transcriptomics and proteomics analysis revealed severely attenuated SREBP signaling in livers and in hepatocytes of LKO mice, which was associated with marked effects on both plasma and hepatic lipid levels. In plasma, total cholesterol levels were dramatically reduced in both male and female LKO mice, apparent in both the LDL and HDL fractions, while triglyceride levels remained largely unaffected. In liver, loss of Spring diminished cholesterol and triglyceride biosynthesis resulting in decreased hepatic cholesterol and triglyceride content. This coincided with reduced secretion of VLDL into the circulation. Consistent with diminished hepatic de novo lipogenesis, LKO mice were protected from developing hepatosteatosis when challenged with a fructose-rich diet. Supporting the significance of our findings in mice, we identified common and rare SPRING genetic variants that are strongly associated with circulating HDL-c and ApoA1 levels in humans. Collectively, our study positions SPRING as a core component of hepatic SREBP signaling, and consequently of systemic lipid metabolism in mice and humans.

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A suite of haploid genetic screens identifies SPRING as a novel determinant of SREBP signaling and cholesterol metabolism

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