In addition to suppressing cholesterol synthesis and uptake, oxysterols also activate glycerophospholipid and SM (sphingomyelin) synthesis, possibly to buffer cells from excess sterol accumulation. In the present study, we investigated the effects of oxysterols on the CDP-choline pathway for PtdCho (phosphatidylcholine) synthesis using wild-type and sterol-resistant CHO (Chinese-hamster ovary) cells expressing a mutant of SCAP [SREBP (sterol-regulatory-element-binding protein) cleavage-activating protein] (CHO-SCAP D443N). [3H]Choline-labelling experiments showed that 25OH (25-hydroxycholesterol), 22OH (22-hydroxycholesterol) and 27OH (27-hydroxycholesterol) increased PtdCho synthesis in CHO cells as a result of CCTα (CTP:phosphocholine cytidylyltransferase α) translocation and activation at the NE (nuclear envelope). These oxysterols also activate PtdCho synthesis in J774 macrophages. in vitro, CCTα activity was stimulated 2- to 2.5-fold by liposomes containing 5 mol% 25OH, 22OH or 27OH. Inclusion of up to 5 mol% cholesterol did not further activate CCTα. 25OH activated CCTα in CHO-SCAP D443N cells leading to a transient increase in PtdCho synthesis and accumulation of CDP-choline. CCTα translocation to the NE and intranuclear tubules in CHO-SCAP D443N cells was complete after 1 h exposure to 25OH compared with only partial translocation by 4–6 h in CHO-Mock cells. These enhanced responses in CHO-D443N cells were sterol-dependent since depletion with cyclodextrin or lovastatin resulted in reduced sensitivity to 25OH. However, the lack of effect of cholesterol on in vitro CCT activity indicates an indirect relationship or involvement of other sterols or oxysterol. We conclude that translocation and activation of CCTα at nuclear membranes by side-chain hydroxylated sterols are regulated by the cholesterol status of the cell.
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February 2009
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Research Article|
January 28 2009
Oxysterol activation of phosphatidylcholine synthesis involves CTP:phosphocholine cytidylyltransferase α translocation to the nuclear envelope
Karsten Gehrig;
Karsten Gehrig
*The Atlantic Research Center, Department of Pediatrics, Dalhousie University, 5849 University Ave., Halifax, NS, Canada B3H 4H7
†Department of Biochemistry and Molecular Biology, Dalhousie University, 5849 University Ave., Halifax, NS, Canada B3H 4H7
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Thomas A. Lagace;
Thomas A. Lagace
1
*The Atlantic Research Center, Department of Pediatrics, Dalhousie University, 5849 University Ave., Halifax, NS, Canada B3H 4H7
†Department of Biochemistry and Molecular Biology, Dalhousie University, 5849 University Ave., Halifax, NS, Canada B3H 4H7
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Neale D. Ridgway
Neale D. Ridgway
2
*The Atlantic Research Center, Department of Pediatrics, Dalhousie University, 5849 University Ave., Halifax, NS, Canada B3H 4H7
†Department of Biochemistry and Molecular Biology, Dalhousie University, 5849 University Ave., Halifax, NS, Canada B3H 4H7
2To whom correspondence should be addressed (email nridgway@dal.ca).
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Publisher: Portland Press Ltd
Received:
September 22 2008
Revision Received:
October 28 2008
Accepted:
November 04 2008
Accepted Manuscript online:
November 04 2008
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2009 Biochemical Society
2009
Biochem J (2009) 418 (1): 209–217.
Article history
Received:
September 22 2008
Revision Received:
October 28 2008
Accepted:
November 04 2008
Accepted Manuscript online:
November 04 2008
Citation
Karsten Gehrig, Thomas A. Lagace, Neale D. Ridgway; Oxysterol activation of phosphatidylcholine synthesis involves CTP:phosphocholine cytidylyltransferase α translocation to the nuclear envelope. Biochem J 15 February 2009; 418 (1): 209–217. doi: https://doi.org/10.1042/BJ20081923
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