Reversible activation of secretory phospholipase A2 by sulfhydryl reagents.
Secretory phospholipase A(2)s (sPLA(2)s) have been implicated in physiological and pathological events, but the regulatory mechanism(s) of their activities in cells remains to be solved. Previously, we reported that phenylarsine oxide (PAO), a sulfhydryl reagent, stimulated arachidonic acid (AA) release in rat pheochromocytoma PC12 cells. In this study, we examined the effects of thimerosal, another sulfhydryl reagent, to clarify the sulfhydryl modification and activation of sPLA(2) molecules in cells. Like PAO, thimerosal-stimulated AA release in an irreversible manner and the responses were not additive. Dithiol compounds such as dithiothreitol inhibited AA release from both the thimerosal- and the PAO-treated cells, and monothiol compounds (l-Cys and glutathione) decreased the thimerosal response. Both sulfhydryl reagents stimulated AA release from the HEK293T cells expressing human sPLA(2)X, and stimulated the sPLA(2) activities of bee venom sPLA(2) and the soluble fraction of sPLA(2)X-expressing cells. Our results suggest that the sPLA(2)s in cells are inactive and modification of disulfide bonds in the molecules can be a trigger of sPLA(2) activation in cells. Sulfhydryl reagents are useful tools for studying the regulatory mechanism(s) of sPLA(2) activity in cells.
Nabemoto
Maiko
M
Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba 260-8675, Japan.
Ohsawa
Keiko
K
Nakamura
Hiroyuki
H
Hirabayashi
Tetsuya
T
Saito
Takeshi
T
Okuma
Yasunobu
Y
Nomura
Yasuyuki
Y
Murayama
Toshihiko
T
D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D003545:Cysteine / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005978:Glutathione / Q000494:pharmacology; D054501:Group II Phospholipases A2; D006801:Humans; D016716:PC12 Cells; D010741:Phospholipases A / Q000187:drug effects / Q000378:metabolism*; D054467:Phospholipases A2; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D013439:Sulfhydryl Reagents / Q000494:pharmacology*; D013849:Thimerosal / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D001152:Arsenicals; D004791:Enzyme Inhibitors; D011956:Receptors, Cell Surface; D013439:Sulfhydryl Reagents; C029341:oxophenylarsine; D013849:Thimerosal; D010741:Phospholipases A; D054501:Group II Phospholipases A2; D054467:Phospholipases A2; D005978:Glutathione; D003545:Cysteine; D002118:Calcium; D004229:Dithiothreitol