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Submitted on December 2, 2008
Accepted on June 26, 2009
Department of Physiology, Department of Cell Biology and Morphology, and Center for Integrative Genomics, Lausanne University, 1005 Lausanne, Switzerland; Department of Internal Medicine, University Hospital Center, and University of Lausanne, Switzerland; GlaxoSmithKline R&D Drug Discovery, Research Triangle Park NC and King of Prussia, PA 19406; Division of Endocrinology and Diabetes, University Hospital Zurich, Zurich, Switzerland
* To whom correspondence should be addressed. E-mail: Christian.Widmann{at}unil.ch.
High-density lipoproteins (HDLs) protect pancreatic
cells against apoptosis. This property might relate to the increased risk to develop diabetes in patients with low HDL blood levels. The mechanisms by which HDLs protect
cells are poorly characterized however. Here we used a transcriptomic approach to identify genes differentially modulated by HDLs in
cells subjected to apoptotic stimuli. The transcript encoding 4E-BP1 was up-regulated by serum starvation and HDLs blocked this increase. 4E-BP1 inhibits cap-dependent translation in its non- or hypo-phosphorylated state but it looses this ability when hyper-phosphorylated. At the protein level, 4E-BP1 was also up-regulated in response to starvation and IL1
and this was blunted by HDLs. While an ectopic increase of 4E-BP1 expression induced
cell death, silencing 4E-BP1 increase with shRNAs inhibited the apoptotic-inducing capacities of starvation. HDLs can therefore protect
cells by blocking 4E-BP1 protein expression but this is not the sole protective mechanism activated by HDLs. Indeed, HDLs blocked apoptosis induced by ER stress with no associated decrease in total 4E-BP1 induction. Although, HDLs favored the phosphorylation, and hence the inactivation of 4E-BP1 in these conditions, this appeared not to be required for HDL protection. Our results indicate that HDLs can protect
cells through modulation of 4E-BP1 depending on the type of stress stimuli.
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