Phospholipase A2 mediates immediate early genes in cultured renal epithelial cells: possible role of lysophospholipid.
BACKGROUND
Exposure to high levels of oxalate induces oxidant stress in renal epithelial cells and produces diverse changes in cell function, ranging from cell death to cellular adaptation, as evidenced by increased DNA synthesis, cellular proliferation, and induction of genes associated with remodeling and repair. These studies focused on cellular adaptation to this oxidant stress, examining the manner by which oxalate exposure leads to increased expression of immediate early genes (IEGs). Specifically, our studies assessed the possibility that oxalate-induced changes in IEG expression are mediated by phospholipase A2 (PLA2), a common pathway in cellular stress responses.


METHODS
Madin-Darby canine kidney (MDCK) cells were exposed to oxalate in the presence or absence of PLA2 inhibitors: mepacrine and arachidonyl trifluoromethyl ketone (AACOCF3). Expression of IEG (c-jun, egr-1, and c-myc) mRNA was assessed by Northern blot analysis. PLA2 activity was determined by measuring the release of [3H]arachidonic acid (AA) from prelabeled cells.


RESULTS
Oxalate exposure (1 to 1.5 mmol/L) induced time- and concentration-dependent increases in IEG mRNA. Treatment with mepacrine resulted in a 75 to 113% reduction of oxalate-induced c-jun, egr-1, and c-myc mRNA, while AACOCF3 caused a 41 to 46% reduction of oxalate-induced c-jun and egr-1 mRNA. Of the two major byproducts of PLA2, only lysophosphatidylcholine (20 micromol/L) increased c-jun and egr-1 mRNA. In contrast, AA (25 micromol/L) attenuated the oxalate-induced increase in c-jun and egr-1 mRNA, presumably by inhibiting PLA2 activity.


CONCLUSIONS
These findings suggest that PLA2 plays a major role in oxalate-induced IEG expression in renal epithelial cells and that lysophospholipids might be a possible lipid mediator in this pathway.
Kohjimoto
Y
Y
Department of Physiology, University of Massachusetts Medical School, Worcester 01655-0127, USA.
Honeyman
T W
TW
Jonassen
J
J
Gravel
K
K
Kennington
L
L
Scheid
C R
CR
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D016718:Arachidonic Acid / Q000494:pharmacology; D001095:Arachidonic Acids / Q000494:pharmacology; D015152:Blotting, Northern; D000001:Calcimycin / Q000494:pharmacology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D017781:Genes, Immediate-Early / Q000502:physiology*; D007476:Ionophores / Q000494:pharmacology; D007668:Kidney / Q000166:cytology; D007669:Kidney Calculi / Q000201:enzymology; D008246:Lysophospholipids / Q000378:metabolism*; D010070:Oxalates / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D054467:Phospholipases A2; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D011796:Quinacrine / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D014157:Transcription Factors / Q000235:genetics; D014316:Tritium
D001095:Arachidonic Acids; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007476:Ionophores; D008246:Lysophospholipids; D010070:Oxalates; D016755:Proto-Oncogene Proteins c-jun; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D014157:Transcription Factors; C081565:arachidonyltrifluoromethane; D014316:Tritium; D016718:Arachidonic Acid; D000001:Calcimycin; D010741:Phospholipases A; D054467:Phospholipases A2; D011796:Quinacrine