Submitted September 18, 2007
Accepted March 4, 2008
ATF4-dependent transcription is a key mechanism in VEGF upregulation by oxidized phospholipids: critical role of oxidized sn-2 residues in activation of unfolded protein response
Olga V. Oskolkova, Taras Afonyushkin, Alexander Leitner, Elena von Schlieffen, Peter S. Gargalovic, Aldons J. Lusis, Bernd R. Binder, and Valery N. Bochkov*
Department of Vascular Biology and Thrombosis Research, Center for Biomolecular Medicine and Pharmacy, Medical University of Vienna, Vienna, Austria
Department of Analytical Chemistry and Food Chemistry, University of Vienna, Vienna, Austria
Department of Medicine, Division of Cardiology, University of California, Los Angeles, CA, United States
* Corresponding author; email: valery.bochkov{at}meduniwien.ac.at.
We have shown previously that oxidized phospholipids (OxPLs), known to accumulate in atherosclerotic vessels, stimulate angiogenesis via induction of autocrine mediators such as VEGF. We now address the pathways mediating upregulation of VEGF in human endothelial cells treated with OxPLs. Analysis of structure-function relationship using individual species of OxPLs demonstrated a close relation between induction of VEGF and activation of the unfolded protein response (UPR). Inducers of UPR upregulated VEGF, while inhibition of UPR by chemical chaperones or knock-down of co-chaperone HTJ-1 inhibited elevation of VEGF mRNA induced by OxPLs. OxPLs induced protein expression of transcription factor ATF4, an important effector of UPR. Expression levels of VEGF in OxPL-treated cells strongly correlated with induction of the ATF4 target genes ATF3 and TRB3. Knocking down ATF4 was paralleled by loss of VEGF induction by OxPLs. Chromatin immunoprecipitation demonstrated that OxPLs stimulated binding of ATF4 to a regulatory site in the VEGF gene. Taken together, these data characterize UPR and more specifically its ATF4 branch as an important mechanism mediating upregulation of VEGF by OxPLs, and allow hypothesizing that the UPR cascade might play a role in pathological angiogenesis in atherosclerotic plaques.
