Soy isoflavones affect sterol regulatory element binding proteins (SREBPs) and SREBP-regulated genes in HepG2 cells

Eimear Mullen, Rachel M. Brown, Timothy F. Osborne, Neil F. Shay

Research output: Contribution to journalArticle

Abstract

Soy intake reduces cholesterol levels. However, both the identity of the soy component or components that contribute to this reduction and the cellular mechanism producing this reduction are unknown. Soy consists of protein, lipids, fiber, and phytochemicals including isoflavones. We propose that the isoflavone component of soy mediates this effect, at least in part, by affecting cellular sterol homeostasis. We investigated the effects of an isoflavone-containing soy extract and the individual isoflavones on the maturation of the sterol regulatory element binding proteins (SREBP) and the expression of SRE-regulated genes controlling lipid metabolism. We found a corresponding increase in the mature form of SREBP-2 in both soy extract- and isoflavone-treated HepG2 cells, whereas there was no significant change in the levels of SREBP-1. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase protein and HMG CoA synthase mRNA levels also increased. When HepG2 cells were transiently transfected with HMG CoA synthase and LDL receptor reporter plasmids there was an increase in expression in response to soy extract or isoflavone treatment from both of these promoters, but this induction was blunted in the presence of sterols (P < 0.05). The mechanism responsible for this effect may be via a statin-like inhibition of HMG CoA reductase enzyme activity or by enhanced SREBP processing via the SREBP cleavage activating protein. We hypothesize that maturation of SREBP and induction of SRE-regulated genes produce an increase in surface LDL receptor expression that increases the clearance of plasma cholesterol, thus decreasing plasma cholesterol levels.

Original languageEnglish (US)
Pages (from-to)2942-2947
Number of pages6
JournalJournal of Nutrition
Volume134
Issue number11
DOIs
StatePublished - Nov 2004

Keywords

  • Cardiovascular disease
  • HMG CoA synthase
  • LDL receptor
  • SREBP
  • Soy isoflavones

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Nutrition and Dietetics

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