Low-temperature effect on the sterol-dependent processing of SREBPs and transcription of related genes in HepG2 cells

J Lipid Res. 2003 Aug;44(8):1581-90. doi: 10.1194/jlr.M300105-JLR200. Epub 2003 May 16.

Abstract

Lowering the growth temperature of HepG2 cells from 37 degrees C to 20 degrees C results in a 73% reduction in human squalene synthase (HSS) protein, a 76% reduction in HSS mRNA, and a 96% reduction in promoter activity of a secreted alkaline phosphatase-HSS reporter gene. A similar decrease in either mRNA or protein levels is observed for 3-hydroxy-3-methylglutaryl CoA reductase, farnesyl diphosphate synthase, the LDL receptor, and fatty acid synthase. All these proteins and mRNAs show either a decrease or a complete loss of sterol-dependent regulation in cells grown at 20 degrees C. In contrast, sterol regulatory element binding proteins (SREBPs)-1 and -2 exhibit a 2- to 3-fold increase in mRNA levels at 20 degrees C. The membrane-bound form of the SREBPs is dramatically increased, but the proteolytic processing to the nuclear (N-SREBP) form is inhibited under these conditions. Overexpression of the N-SREBP or SREBP cleavage-activating protein (SCAP), but not site-1 or site-2 proteases, restores the activation of the HSS promoter at 20 degrees C, most likely by liberating the SCAP-SREBP complex so that it can move to the Golgi for processing. These results indicate that the cholesterol synthesizing machinery is down-regulated at low temperatures, and points to the transport of the SCAP-SREBP complex to the Golgi as the specific down-regulated step.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Blotting, Northern
  • Blotting, Western
  • CCAAT-Enhancer-Binding Proteins / genetics*
  • CCAAT-Enhancer-Binding Proteins / metabolism*
  • Cell Line, Tumor
  • Cholesterol / biosynthesis
  • Cold Temperature*
  • DNA-Binding Proteins / genetics*
  • DNA-Binding Proteins / metabolism*
  • Down-Regulation / drug effects
  • Farnesyl-Diphosphate Farnesyltransferase / genetics
  • Gene Expression Regulation / drug effects*
  • Genes, Reporter / genetics
  • Humans
  • Lipids / biosynthesis
  • Promoter Regions, Genetic
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Receptors, LDL / genetics
  • Sterol Regulatory Element Binding Protein 1
  • Sterols / pharmacology*
  • Transcription Factors*
  • Transcription, Genetic / drug effects*

Substances

  • CCAAT-Enhancer-Binding Proteins
  • DNA-Binding Proteins
  • Lipids
  • RNA, Messenger
  • Receptors, LDL
  • SREBF1 protein, human
  • Sterol Regulatory Element Binding Protein 1
  • Sterols
  • Transcription Factors
  • Cholesterol
  • Farnesyl-Diphosphate Farnesyltransferase