Rapamycin down-regulates LDL-receptor expression independently of SREBP-2

Biochem Biophys Res Commun. 2008 Sep 5;373(4):670-4. doi: 10.1016/j.bbrc.2008.06.108. Epub 2008 Jul 9.

Abstract

As a key regulator of cholesterol homeostasis, sterol-regulatory element binding protein-2 (SREBP-2) up-regulates expression of genes involved in cholesterol synthesis (e.g., 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) Reductase) and uptake (the low density lipoprotein (LDL)-receptor). Previously, we showed that Akt, a critical kinase in cell growth and proliferation, contributes to SREBP-2 activation. However, the specific Akt target involved is unknown. A potential candidate is the mammalian target of rapamycin, mTOR. Rapamycin can cause hyperlipidaemia clinically, and we hypothesised that this may be mediated via an effect of mTOR on SREBP-2. Herein, we found that SREBP-2 activation and HMG-CoA Reductase gene expression were unaffected by rapamycin treatment. However, LDL-receptor gene expression was decreased by rapamycin, suggesting that this may contribute to the hyperlipidaemia observed in rapamycin-treated patients. Rapamycin did not affect mRNA stability, so the decrease in LDL-receptor gene expression is likely to be occurring at the transcriptional level, although independently of SREBP-2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CHO Cells
  • Cholesterol / biosynthesis*
  • Cholesterol / genetics
  • Cricetinae
  • Cricetulus
  • Down-Regulation
  • Gene Expression / drug effects
  • Gene Expression Regulation
  • Golgi Apparatus / metabolism
  • Hydroxymethylglutaryl CoA Reductases / genetics
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Protein Kinases / metabolism
  • RNA Stability / drug effects
  • Receptors, LDL / genetics
  • Receptors, LDL / metabolism*
  • Sirolimus / pharmacology*
  • Sterol Regulatory Element Binding Protein 2 / metabolism*
  • TOR Serine-Threonine Kinases

Substances

  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Receptors, LDL
  • SREBP cleavage-activating protein
  • Sterol Regulatory Element Binding Protein 2
  • Cholesterol
  • Hydroxymethylglutaryl CoA Reductases
  • Protein Kinases
  • TOR Serine-Threonine Kinases
  • Sirolimus