Abstract
Tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta are potent activators of the transcription factor NF-kappaB, induced during inflammatory conditions. We have previously shown that both secretory and cytosolic phospholipase A(2) (PLA(2)) are involved in TNF-alpha- and IL-1beta-induced NF-kappaB activation. In this study, we have addressed the mechanism of PLA(2) involvement with respect to downstream arachidonic acid (AA) metabolites and the functional coupling between PLA(2)s mediating NF-kappaB activation. We show that in addition to inhibitors of secretory and cytosolic PLA(2)s, 5-lipoxygenase inhibitors attenuate TNF-alpha- and IL-1beta-stimulated NF-kappaB activation. Exogenous addition of leukotriene B(4) (LTB(4)) restored NF-kappaB activation reduced by 5-lipoxygenase inhibitors or an LTB(4) receptor antagonist, thus identifying LTB(4) as a mediator in signaling to NF-kappaB. TNF-alpha- and IL-1beta-induced AA release from cellular membranes was accompanied by phosphorylation of cytosolic PLA(2). Inhibitors of secretory PLA(2) and of 5-lipoxygenase/LTB(4) functionality markedly reduced AA release and nearly completely abolished cytosolic PLA(2) phosphorylation. This demonstrates that secretory PLA(2), through 5-lipoxygenase metabolites, is an essential upstream regulator of cytosolic PLA(2) and AA release. Our results therefore suggest the existence of a functional link between secretory and cytosolic PLA(2) in cytokine-activated keratinocytes, providing a molecular explanation for the participation of both secretory and cytosolic PLA(2) in arachidonic acid signaling and NF-kappaB activation in response to proinflammatory cytokines.
Highlights
Tumor necrosis factor (TNF)-␣ and interleukin (IL)-1 are potent activators of the transcription factor Nuclear factor B (NF-B), induced during inflammatory conditions
Added arachidonic acid (AA) Reverses the Effect of SB203347 on NF-B Activation—To elucidate if the NF-B inhibition observed with phospholipase A2 (PLA2) inhibitors was due to reduced AA levels and, if AA is the effective NF-B signaling component produced by PLA2 activity, we examined the effect of the exogenous addition of AA on NF-B activation in the presence of SB203347
The present study suggests the existence of a functional link between snpPLA2 and cPLA2, conveyed by 5-LO metabolites, modulating TNF-␣- and IL-1-stimulated NF-B activation
Summary
Tumor necrosis factor (TNF)-␣ and interleukin (IL)-1 are potent activators of the transcription factor NF-B, induced during inflammatory conditions. Inhibitors of secretory PLA2 and of 5-lipoxygenase/LTB4 functionality markedly reduced AA release and nearly completely abolished cytosolic PLA2 phosphorylation. Several distinct snpPLA2s (groups IIa [12], IID [13], V [14], and X [4]) have been identified They require millimolar concentrations of calcium for catalytic activity and act on membrane phospholipids containing a variety of fatty acids, including AA, in the sn-2-position. Proinflammatory cytokines such as TNF-␣ and IL-1 regulate the expression of snpPLA2s of group IIa [12] and group V [15], and of cPLA2 group IV, in vitro [16, 17]. The TNF-␣-induced transduction pathway leading to activation of NF-B has been proposed to involve phosphatidylcholine-specific phospholipase C [37], sphingomyelinase [38, 39], and protein kinase C activated by ceramide [40]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
