Low-density lipoprotein activates Jun N-terminal kinase (JNK) in human endothelial cells.
We have reported previously that native low-density lipoprotein (LDL) activates c-Jun and transcription factor AP-1 in human umbilical vein endothelial cells (HUVEC). The aim of this study was to elucidate the upstream signaling mechanisms mediating LDL activation of c-Jun/AP-1. Using a c-Jun NH2-terminal kinase (JNK) activity assay, we have detected an increase in JNK activity in LDL-exposed HUVEC, which started at 15 min and reached maximum activity after 1-2 h. This JNK activity, increased by LDL, occurred in a dose-dependent fashion starting at a concentration of 80 mg/dl of LDL and reaching maximum activation at a concentration of 160-240 mg/dl. Following cotransfection, the increase of AP-1 driven luciferase activity by LDL was attenuated 54% by a kinase-deficient JNK1. Furthermore, a specific trans-reporting system was utilized to confirm c-Jun activation by upstream signal mechanisms. The results show c-Jun activity increased by 3-fold after LDL exposure when compared with respective controls. In contrast, LDL exposure did not affect the activation of extracellular signal regulated kinase 1 and 2 (ERK1/2), even though phorbol 12-myristate 13-acetate treatment remarkably increased the activity of these kinases. Thus, this study demonstrates, for the first time, that JNK mediates LDL-induced endothelial cell activation.
Zhu
Y
Y
Division of Biomedical Sciences, University of California, Riverside 92521, USA. yi.zhu@ucr.edu
Liao
H L
HL
Wang
N
N
Friedli
O
O
Verna
L
L
Stemerman
M B
MB
D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008156:Luciferases / Q000235:genetics; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism; D014162:Transfection