Hyperforin induces Ca(2+)-independent arachidonic acid release in human platelets by facilitating cytosolic phospholipase A(2) activation through select phospholipid interactions.
Here, we investigated the modulation of cytosolic phospholipase A(2) (cPLA(2))-mediated arachidonic acid (AA) release by the polyprenylated acylphloroglucinol hyperforin. Hyperforin increased AA release from human platelets up to 2.6 fold (maximal effect at 10microM) versus unstimulated cells, which was blocked by cPLA(2)alpha-inhibition, and induced translocation of cPLA(2) to a membrane compartment. Interestingly, these stimulatory effects of hyperforin were even more pronounced after depletion of intracellular Ca(2+) by EDTA plus BAPTA/AM. Hyperforin induced phosphorylation of cPLA(2) at Ser505 and activated p38 mitogen-activated protein kinase (MAPK), and inhibition of p38 MAPK by SB203580 prevented cPLA(2) phosphorylation. However, neither AA release nor translocation of cPLA(2) was abrogated by SB203580. In cell-free assays using liposomes prepared from different lipids, hyperforin failed to stimulate phospholipid hydrolysis by isolated cPLA(2) in the presence of Ca(2+). However, when Ca(2+) was omitted, hyperforin caused a prominent increase in cPLA(2) activity using liposomes composed of 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphoethanolamine but not of 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (PAPC) unless the PAPC liposomes were enriched in cholesterol (20 to 50%). Finally, two-dimensional (1)H-MAS-NMR analysis visualized the directed insertion of hyperforin into POPC liposomes. Together, hyperforin, through insertion into phospholipids, may facilitate cPLA(2) activation by enabling its access towards select lipid membranes independent of Ca(2+) ions. Such Ca(2+)- and phosphorylation-independent mechanism of cPLA(2) activation may apply also to other membrane-interfering molecules.
Hoffmann
Marika
M
Institute of Pharmaceutical Chemistry/ZAFES, Johann Wolfgang Goethe-University Frankfurt, Max-von-Laue-Str. 9, D-60438 Frankfurt, Germany.
Lopez
Jakob J
JJ
Pergola
Carlo
C
Feisst
Christian
C
Pawelczik
Sven
S
Jakobsson
Per-Johan
PJ
Sorg
Bernd L
BL
Glaubitz
Clemens
C
Steinhilber
Dieter
D
Werz
Oliver
O
D016718:Arachidonic Acid / Q000378:metabolism*; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D001643:Bridged Bicyclo Compounds / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D003600:Cytosol / Q000201:enzymology*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D010696:Phloroglucinol / Q000031:analogs & derivatives* / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000378:metabolism*; D054467:Phospholipases A2 / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D001643:Bridged Bicyclo Compounds; D004791:Enzyme Inhibitors; D007093:Imidazoles; D010713:Phosphatidylcholines; D011725:Pyridines; D013729:Terpenes; D016718:Arachidonic Acid; D010696:Phloroglucinol; D048051:p38 Mitogen-Activated Protein Kinases; D054467:Phospholipases A2; C093642:SB 203580; C001654:hyperforin; D002118:Calcium; C028694:1-palmitoyl-2-oleoylphosphatidylcholine