Arachidonic acid induces Fas and FasL upregulation in human leukemia U937 cells via Ca2+/ROS-mediated suppression of ERK/c-Fos pathway and activation of p38 MAPK/ATF-2 pathway.
Arachidonic acid (AA)-induced apoptotic death of human leukemia U937 cells was characteristic of increase in intracellular Ca(2+) concentration ([Ca(2+)]i), ROS generation, ERK inactivation, p38 MPAK activation, degradation of procaspase-8 and production of truncated Bid (tBid). Moreover, AA treatment upregulated Fas/FasL protein expression and transcription of Fas/FasL mRNA. Downregulation of FADD blocked AA-induced procaspase-8 degradation and rescued viability of AA-treated cells. BAPTA-AM (Ca(2+) chelator) pretreatment abolished AA-induced ROS generation, while N-acetylcysteine (NAC, ROS scavenger) was unable to alter AA-elicited [Ca(2+)]i increase. Pretreatment with BAPTA-AM or NAC abrogated p38 MAPK activation and restored ERK activation. Suppression of p38 MAPK or transfection of constitutively active MEK1 abolished AA-induced Fas and FasL upregulation. AA treatment repressed ERK-mediated c-Fos phosphorylation but evoked p38 MAPK-mediated ATF-2 phosphorylation. Knockdown of c-Fos and ATF-2 by siRNA reflected that c-Fos counteracted the effect of ATF-2 on Fas/FasL upregulation. Taken together, our data indicate that Fas/FasL upregulation in AA-treated U937 cells is elicited by Ca(2+)/ROS-mediated suppression of ERK/c-Fos pathway and activation of p38 MAPK/ATF-2, and suggest that autocrine Fas-mediated apoptotoic mechanism is involved in AA-induced cell death.
Liu
Wen-Hsin
WH
Institute of Biomedical Sciences, National Sun Yat-Sen University-Kaohsiung Medical University Joint Research Center, National Sun Yat-Sen University, Kaohsiung 804, Taiwan.
Chang
Long-Sen
LS
D051698:Activating Transcription Factor 2 / Q000235:genetics / Q000502:physiology*; D017209:Apoptosis / Q000187:drug effects; D016718:Arachidonic Acid / Q000494:pharmacology*; D015153:Blotting, Western; D020013:Calcium Signaling / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000096:biosynthesis; D053222:Fas Ligand Protein / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D008156:Luciferases / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects; D051336:Mitochondrial Membranes / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D034622:RNA Interference; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D013347:Subcellular Fractions / Q000187:drug effects; D014162:Transfection; D020298:U937 Cells; D015854:Up-Regulation; D019014:fas Receptor / Q000096:biosynthesis* / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000235:genetics / Q000502:physiology*
D051698:Activating Transcription Factor 2; D053222:Fas Ligand Protein; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D019014:fas Receptor; D016718:Arachidonic Acid; D008156:Luciferases; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases