Riboflavin deficiency impairs oxidative folding and secretion of apolipoprotein B-100 in HepG2 cells, triggering stress response systems

Karoline C. Manthey, Ching Chew Yap, Janos Zempleni

Research output: Contribution to journalArticle

56 Citations (Scopus)

Abstract

Secretory proteins such as apolipoprotein B-100 (apoB) undergo oxidative folding (formation of disulfide bonds) in the endoplasmic reticulum (ER) before secretion. Oxidative folding depends on flavoproteins in eukaryotes. Here, human liver (HepG2) cells were used to model effects of riboflavin concentrations in culture media on folding and secretion of apoB. Cells were cultured in media containing 3.1, 12.6, and 300 nmol/L of riboflavin, representing moderately deficient, physiological, and pharmacological plasma concentrations in humans, respectively. When cells were cultured in riboflavin-deficient medium, secretion of apoB decreased by >80% compared with controls cultured in physiological medium. The nuclear translocation of the transcription factor ATF-6 increased by >180% in riboflavin-deficient cells compared with physiological controls; this is consistent with ER stress. Nuclear translocation of ATF-6 was associated with activation of the unfolded protein response. Expression of stress-response genes coding for ubiquitin-activating enzyme 1, growth arrest and DNA damage inducible gene, and glucose regulated protein of 78 kDa was greater in riboflavin-deficient cells compared with other treatment groups. Finally, phosphorylation of the eukaryotic initiation factor (eukaryotic initiation factor 2α) increased in riboflavin-deficient cells, consistent with decreased translational activity. We conclude 1) that riboflavin deficiency causes ER stress and activation of unfolded protein response in HepG2 cells, and 2) that riboflavin deficiency decreases protein secretion in HepG2 cells. Decreased secretion of apoB in riboflavin-deficient cells might interfere with lipid homeostasis in vivo.

Original languageEnglish (US)
Pages (from-to)978-982
Number of pages5
JournalJournal of Nutrition
Volume135
Issue number5
StatePublished - May 1 2005

Fingerprint

Riboflavin Deficiency
apolipoprotein B-100
Apolipoprotein B-100
Riboflavin
Hep G2 Cells
riboflavin
stress response
secretion
Unfolded Protein Response
cells
Endoplasmic Reticulum Stress
endoplasmic reticulum
unfolded protein response
Cultured Cells
Ubiquitin-Activating Enzymes
Eukaryotic Initiation Factor-2
Activating Transcription Factors
Eukaryotic Initiation Factors
Flavoproteins
flavoproteins

Keywords

  • Apolipoprotein B-100
  • Human
  • Oxidative folding
  • Riboflavin
  • Unfolded protein response

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Food Science

Cite this

Riboflavin deficiency impairs oxidative folding and secretion of apolipoprotein B-100 in HepG2 cells, triggering stress response systems. / Manthey, Karoline C.; Yap, Ching Chew; Zempleni, Janos.

In: Journal of Nutrition, Vol. 135, No. 5, 01.05.2005, p. 978-982.

Research output: Contribution to journalArticle

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abstract = "Secretory proteins such as apolipoprotein B-100 (apoB) undergo oxidative folding (formation of disulfide bonds) in the endoplasmic reticulum (ER) before secretion. Oxidative folding depends on flavoproteins in eukaryotes. Here, human liver (HepG2) cells were used to model effects of riboflavin concentrations in culture media on folding and secretion of apoB. Cells were cultured in media containing 3.1, 12.6, and 300 nmol/L of riboflavin, representing moderately deficient, physiological, and pharmacological plasma concentrations in humans, respectively. When cells were cultured in riboflavin-deficient medium, secretion of apoB decreased by >80{\%} compared with controls cultured in physiological medium. The nuclear translocation of the transcription factor ATF-6 increased by >180{\%} in riboflavin-deficient cells compared with physiological controls; this is consistent with ER stress. Nuclear translocation of ATF-6 was associated with activation of the unfolded protein response. Expression of stress-response genes coding for ubiquitin-activating enzyme 1, growth arrest and DNA damage inducible gene, and glucose regulated protein of 78 kDa was greater in riboflavin-deficient cells compared with other treatment groups. Finally, phosphorylation of the eukaryotic initiation factor (eukaryotic initiation factor 2α) increased in riboflavin-deficient cells, consistent with decreased translational activity. We conclude 1) that riboflavin deficiency causes ER stress and activation of unfolded protein response in HepG2 cells, and 2) that riboflavin deficiency decreases protein secretion in HepG2 cells. Decreased secretion of apoB in riboflavin-deficient cells might interfere with lipid homeostasis in vivo.",
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