Endoplasmic reticulum stress causes the activation of sterol regulatory element binding protein-2.
BACKGROUND
Sterol regulatory element binding protein-2 (SREBP-2) is a membrane-bound transcription factor that upon proteolytic processing can activate the expression of genes involved in cholesterol biosynthesis and uptake. We as well as others have demonstrated that the accumulation of misfolded proteins within the endoplasmic reticulum (ER), a condition known as ER stress, can dysregulate lipid metabolism by activating the SREBPs. The purpose of this study was to determine the mechanism by which ER stress induces SREBP-2 activation.


RESULTS
HeLa and MCF7 cells were treated with ER stress-inducing agents to determine the effect of ER stress on SREBP-2 cleavage and subsequent cholesterol accumulation. Cells treated with thapsigargin (Tg) exhibit proteolytic cleavage of SREBP-2. Proteolytic cleavage of SREBP-2 induced by Tg occurred independently of caspase activation and was inhibited by the site-1 protease inhibitor AEBSF, suggesting that Tg-induced SREBP-2 cleavage occurs through the conventional site-1/-2 pathway. Treatment of HeLa cells with Tg also led to the accumulation of free cholesterol as measured by Filipin staining.


CONCLUSIONS
These results imply that ER stress-induced SREBP-2 activation occurs through the conventional pathway that normally regulates SREBP in accordance with intracellular sterol concentration.
Colgan
Stephen M
SM
Henderson Research Centre, McMaster University, 711 Concession Street, Hamilton, Ont., Canada L8V 1C3.
Tang
Damu
D
Werstuck
Geoff H
GH
Austin
Richard C
RC
D053148:Caspase 3 / Q000502:physiology; D002784:Cholesterol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D006367:HeLa Cells; D006801:Humans; D011499:Protein Processing, Post-Translational; D051782:Sterol Regulatory Element Binding Protein 2 / Q000235:genetics / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D051782:Sterol Regulatory Element Binding Protein 2; D013450:Sulfones; C002010:4-(2-aminoethyl)benzenesulfonylfluoride; D019284:Thapsigargin; D002784:Cholesterol; D053148:Caspase 3