The Non Catalytic Protein ERG28 has a Functional Role in Cholesterol Synthesis and is Coregulated Transcriptionally

The enzymatic pathway of cholesterol biosynthesis has been well characterized. However, there remain several potential interacting proteins that may play ancillary roles in the regulation of cholesterol production. Here, we identified ERG28 (chromosome 14 open reading frame 1 [C14orf1]), a homologue of the yeast protein Erg28p, as a player in mammalian cholesterol synthesis. ERG28 is conserved from yeast to humans but has been largely overlooked in mammals. Using quantitative RT-PCR, luciferase assays, and publicly available chromatin immunoprecipitation sequencing data, we found that transcription of this gene is driven by the transcription factor SREBP-2, akin to most cholesterol synthesis enzymes, as well as identifying sterolresponsive elements and cofactor binding sites in its proximal promoter. Based on a split luciferase system, ERG28 interacted with itself and two enzymes of cholesterol synthesis (NSDHL and SC4MOL). Huh7 ERG28-KO cell lines were generated, revealing reduced total cholesterol levels in sterol-depleted environments. In addition, radiolabeled metabolic flux assays showed a 60 -75% reduction in the rate of cholesterol synthesis in the KO versus wild-type cells, which could be rescued by expression of ectopic ERG28. Unexpectedly, KO of ERG28 also impaired the activation of SREBP-2 under sterol-replete conditions, by a yet-to-be defined mechanism. These results indicate that ERG28 is clearly involved in cholesterol synthesis, although the precise role this noncatalytic protein plays in this complex metabolic pathway remains to be fully elucidated. A deeper understanding of ERG28, and other ancillary proteins of cholesterol synthesis, may help inform therapeutic strategies for diseases associated with aberrant cholesterol metabolism.

Automated summary

In this study, researchers identified the noncatalytic protein ERG28 as a player in mammalian cholesterol synthesis. They found that ERG28 is transcriptionally regulated by the transcription factor SREBP-2 and interacts with enzymes involved in cholesterol synthesis. Knockout of ERG28 resulted in reduced cholesterol levels and impaired cholesterol synthesis. Additionally, ERG28 knockout also affected the activation of SREBP-2 under sterol-replete conditions. These findings highlight the importance of ERG28 in cholesterol synthesis and suggest that further understanding of this protein could contribute to therapeutic strategies for diseases associated with aberrant cholesterol metabolism.