Selective Inhibition of Cholesterol Biosynthesis in Brain Cells by Squalestatin 1

Dean C. Crick, Julie Suders, Catherine M. Kluthe, Douglas A. Andres, Charles J. Waechter

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Abstract: The effect of squalestatin 1 (SQ) on squalene synthase and other enzymes utilizing farnesyl pyrophosphate (F‐P‐P) as substrate was evaluated by in vitro enzymological and in vivo metabolic labeling experiments to determine if the drug selectively inhibited cholesterol biosynthesis in brain cells. Direct in vitro enzyme studies with membrane fractions from primary cultures of embryonic rat brain (IC50 = 37 nM), pig brain (IC50 = 21 nM), and C6 glioma cells (IC50 = 35 nM) demonstrated that SQ potently inhibited squalene synthase activity but had no effect on the long‐chain cis‐isoprenyltransferase catalyzing the conversion of F‐P‐P to polyprenyl pyrophosphate (Poly‐P‐P), the precursor of dolichyl phosphate (Dol‐P). SQ also had no effect on F‐P‐P synthase; the conversion of [3H]F‐P‐P to geranylgeranyl pyrophosphate (GG‐P‐P) catalyzed by partially purified GG‐P‐P synthase from bovine brain; the enzymatic farnesylation of recombinant H‐p21ras by rat brain farnesyltransferase; or the enzymatic geranylgeranylation of recombinant Rab1A, catalyzed by rat brain geranylgeranyltransferase. Consistent with SQ selectively blocking the synthesis of squalene, when C6 glial cells were metabolically labeled with [3H]mevalonolactone, the drug inhibited the incorporation of the labeled precursor into squalene and cholesterol (IC50 = 3–5 µM) but either had no effect or slightly stimulated the labeling of Dol‐P, ubiquinone (CoQ), and isoprenylated proteins. These results indicate that SQ blocks cholesterol biosynthesis in brain cells by selectively inhibiting squalene synthase. Thus, SQ provides a useful tool for evaluating the obligatory requirement for de novo cholesterol biosynthesis in neurobiological processes without interfering with other critical reactions involving F‐P‐P.

Original languageEnglish
Pages (from-to)1365-1373
Number of pages9
JournalJournal of Neurochemistry
Volume65
Issue number3
DOIs
StatePublished - Sep 1995

Keywords

  • Farnesyl pyrophosphate
  • Isoprenoid biosynthesis
  • Squalene synthase
  • Squalestatin 1

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

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