Ionizing radiation activates PERK/eIF2α/ATF4 signaling via ER stress-independent pathway in human vascular endothelial cells.
OBJECTIVE
Perturbations in protein folding induce endoplasmic reticulum (ER) stress, which elicits coordinated response, namely the unfolded protein response (UPR), to cope with the accumulation of misfolded proteins in ER. In this study, we characterized mechanisms underlying ionizing radiation (IR)-induced UPR signaling pathways.


METHODS
We analyzed alterations in UPR signaling pathways in human umbilical vein endothelial cells (HUVEC) and human coronary artery endothelial cells (HCAEC) irradiated with 15 Gy IR.


RESULTS
IR selectively activated the eIF2α/ATF4 branch of the UPR signaling pathway, with no alterations in the IRE1 and ATF6 branches in HUVEC and HCAEC. Phosphorylation of PERK was enhanced in response to IR, and the IR-induced activation of the eIF2α/ATF4 signaling pathway was completely inhibited by PERK knockdown with siRNA. Surprisingly, chemical chaperones, which inhibit the formation of misfolded proteins and sequential protein aggregates to reduce ER stress, failed to prevent the IR-induced phosphorylation of PERK and the subsequent activation of the eIF2α/ATF4 signaling pathway.


CONCLUSIONS
PERK mediates the IR-induced selective activation of the eIF2α/ATF4 signaling pathway, and the IR-induced activation of PERK/eIF2α/ATF4 signaling in human vascular endothelial cells is independent of alterations in protein-folding homeostasis in the ER.
Division of Radiation Effects, Korea Institute of Radiological and Medical Sciences , Seoul.
Eun Ju
EJ
Kim
Yoon-Jin
YJ
Lee
Seongman
S
Kang
Young-Bin
YB
Lim
D051701:Activating Transcription Factor 4 / Q000502:physiology*; D001217:Aspartate-Ammonia Ligase / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics; D002478:Cells, Cultured; D059865:Endoplasmic Reticulum Stress / Q000502:physiology*; D042783:Endothelial Cells / Q000378:metabolism / Q000528:radiation effects*; D015852:Eukaryotic Initiation Factor-2 / Q000502:physiology*; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics; D015398:Signal Transduction / Q000528:radiation effects*; D056811:Unfolded Protein Response / Q000528:radiation effects; D019892:eIF-2 Kinase / Q000502:physiology*
C497109:ATF4 protein, human; D018797:Cell Cycle Proteins; D015852:Eukaryotic Initiation Factor-2; D012097:Repressor Proteins; C474831:TRIB3 protein, human; D051701:Activating Transcription Factor 4; C460640:EIF2AK3 protein, human; D017346:Protein Serine-Threonine Kinases; D019892:eIF-2 Kinase; D001217:Aspartate-Ammonia Ligase