Twin enzymes, divergent control: The cholesterogenic enzymes DHCR14 and LBR are differentially regulated transcriptionally and post‐translationally

Abstract

Cholesterol synthesis is a tightly regulated process, both transcriptionally and post‐translationally. Transcriptional control of cholesterol synthesis is relatively well understood. However, post‐translational regulation has only been examined for a few of the ~20 enzymes in cholesterol biosynthesis. Two of the four sterol reductases, DHCR14 and LBR, share evolutionary ties with a high level of sequence homology, and they uniquely share the same delta‐14 reductase activity in cholesterol biosynthesis. However, the post‐translational regulation of these twin enzymes is poorly understood. Using CHO‐7 cells stably expressing epitope tagged DHCR14 or LBR, we investigated the post‐translational regulation of these enzymes. We found that DHCR14 and LBR undergo differential post translational regulation, with DHCR14 being rapidly turned over, triggered by cholesterol and other sterol intermediates while LBR remained stable. DHCR14 is degraded via the ubiquitin‐proteasome system and via mass‐spectrometry we identified several E3 ligases that modulate basal DHCR14 levels. Significantly, we found that gene expression across an array of human tissues showed an inverse relationship between the C14‐sterol reductases; one enzyme or the other tends to be predominantly expressed in each tissue. Overall, our findings indicate that while LBR tends to be the constitutively active delta‐14 reductase, DHCR14 levels are tuneable, responding to the local cellular demands for cholesterol. Support or Funding Information This work was supported by Australian Research Council Grant DP170101178. PhD Candidates were funded by the Research Training Program from the Australian Government Department of Education.