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

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. Identification of a gene, SPRING (C12ORF49), as a novel regulator of the SREBP pathway and cholesterol homeostasis