Ring finger protein 5 activates sterol regulatory element–binding protein 2 (SREBP2) to promote cholesterol biosynthesis via inducing polyubiquitination of SREBP chaperone SCAP

Abstract

Sterol regulatory element–binding protein 2 (SREBP2) is the master transcription factor that regulates cholesterol metabolism. SREBP2 activation is regulated by SREBP chaperone SCAP. Here we show that ring finger protein 5 (RNF5), an endoplasmic reticulum-anchored E3 ubiquitin ligase, mediates the Lys-29–linked polyubiquitination of SCAP and thereby activates SREBP2. RNF5 knockdown inhibited SREBP2 activation and reduced cholesterol biosynthesis in human hepatoma cells, and RNF5 overexpression activated SREBP2. Mechanistic studies revealed that RNF5 binds to the transmembrane domain of SCAP and ubiquitinates the Lys-305 located in cytosolic loop 2 of SCAP. Moreover, the RNF5-mediated ubiquitination enhanced an interaction between SCAP luminal loop 1 and loop 7, a crucial event for SREBP2 activation. Notably, an overexpressed K305R SCAP variant failed to restore the SREBP2 pathway in SCAP-deficient cell lines. These findings define a new mechanism by which an ubiquitination-induced SCAP conformational change regulates cholesterol biosynthesis.

RNF5 Regulation of RBBP4 Defines Acute Myeloid Leukemia Growth and Susceptibility to Histone Deacetylase Inhibitors

“…Limited reports on K29-linked protein ubiquitination highlights proteasome-independent functions, including changes in Wnt signaling 37 , antiviral innate immune response 38 , or protein aggregation in Parkinson disease 39 . RNF5 was shown to affect cholesterol biosynthesis through induction of K29-linked polyubiquitination of the sterol regulatory element-binding protein 2 (SREBP2) chaperone SCAP 40 . Notably, the importance of RNF5 control of RBBP4 for altered expression of genes seen in AML was substantiated by finding an inverse correlation between gene expression associated with RNF5- vs. RBBP4-expression.…”

Insulin-induced genes INSIG1 and INSIG2 mediate oxysterol-dependent activation of the PERK–eIF2α–ATF4 axis

“…Primer sequences are listed in Table S1 . The expression plasmid for N-terminal Myc-tagged human SCAP was described in a previous report ( 48 ). Preannealed oligo duplex Insig1-gRNAs/Insig1-gRNAa, Insig2-gRNAups/Insig2-gRNAupa, and Insig2-gRNAdowns/Insig2-gRNAdowna were cloned into pSpCas9(BB)-2A-Puro (PX459) V2.0 vector using BbsI restriction enzyme site to construct PX459/Insig1, PX459/Insig2upstream, and PX459/Insig2downstream each.…”

Prostate Cancer—Focus on Cholesterol

“…SREs are located in promoters of genes involved in cholesterol biosynthesis, import, and also in INSIG1 gene. INSIG2 gene is not under SREBP2 control but under insulin [ 35 , 51 , 54 , 55 , 56 ].…”