Inhibition of the MEK1/ERK pathway reduces arachidonic acid release independently of cPLA2 phosphorylation and translocation.
BACKGROUND
The 85-kDa cytosolic phospholipase A2 (cPLA2) mediates arachidonic acid (AA) release in MDCK cells. Although calcium and mitogen-activated protein kinases regulate cPLA2, the correlation of cPLA2 translocation and phosphorylation with MAPK activation and AA release is unclear.


RESULTS
MEK1 inhibition by U0126 inhibited AA release in response to ATP and ionomycin. This directly correlated with inhibition of ERK activation but not with phosphorylation of cPLA2 on Ser505, which was only partially inhibited by ERK inhibition. Inhibition of AA release by U0126 was still observed when stoichiometric phosphorylation of cPLA2 on Ser505 was maintained by activating p38 with anisomycin. Translocation kinetics of wild-type cPLA2 and cPLA2 containing S505A or S727A mutations to Golgi were similar in response to ATP and ionomycin and were not affected by U0126.


CONCLUSIONS
These results suggest that the ability of cPLA2 to hydrolyze membrane phospholipid is reduced by inhibition of the MEK1/ERK pathway and that the reduction in activity is independent of cPLA2 phosphorylation and translocation to membrane. The results also demonstrate that cPLA2 mutated at the phosphorylation sites Ser505 and Ser727 translocated with similar kinetic as wild-type cPLA2.
Evans
John H
JH
Program in Cell Biology, Department of Pediatrics, National Jewish Medical and Research Center, 1400 Jackson Street, Denver, Colorado 80206, USA. evansj@njc.org
Fergus
Daniel J
DJ
Leslie
Christina C
CC
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D001692:Biological Transport / Q000187:drug effects; D002070:Butadienes / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D003600:Cytosol / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D049452:Green Fluorescent Proteins; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008856:Microscopy, Fluorescence; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009154:Mutation; D009570:Nitriles / Q000494:pharmacology*; D010741:Phospholipases A / Q000235:genetics / Q000378:metabolism*; D054467:Phospholipases A2; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
D002070:Butadienes; D004791:Enzyme Inhibitors; D008164:Luminescent Proteins; D009570:Nitriles; C113580:U 0126; D049452:Green Fluorescent Proteins; D016718:Arachidonic Acid; D015759:Ionomycin; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium