TNF-α induces cytosolic phospholipase A₂expression via Jak2/PDGFR-dependent Elk-1/p300 activation in human lung epithelial cells

Abstract

Cytosolic phospholipase A2 (cPLA2) plays a pivotal role in mediating agonist-induced arachidonic acid release for prostaglandin (PG) synthesis during inflammation triggered by tumor necrosis factor-α (TNF-α). However, the mechanisms underlying TNF-α-induced cPLA2 expression in human lung epithelial cells (HPAEpiCs) were not completely understood. Here, we demonstrated that TNF-α induced cPLA2 mRNA and protein expression, promoter activity, and PGE2 secretion in HPAEpiCs. These responses induced by TNF-α were inhibited by pretreatment with the inhibitor of Jak2 (AG490), platelet-derived growth factor receptor (PDGFR) (AG1296), phosphoinositide 3 kinase (PI3K) (LY294002), or MEK1/2 (PD98059) and transfection with siRNA of Jak2, PDGFR, Akt, or p42. We showed that TNF-α markedly stimulated Jak2, PDGFR, Akt, and p42/p44 MAPK phosphorylation, which were attenuated by their respective inhibitors. Moreover, TNF-α stimulated Akt activation via a Jak2/PDGFR pathway in HPAEpiCs. In addition, TNF-α-induced p42/p44 MAPK phosphorylation was reduced by AG1296 or LY294002. On the other hand, TNF-α could induce Akt and p42/p44 MAPK translocation from the cytosol into the nucleus, which was inhibited by AG490, AG1296, or LY294002. Finally, we showed that TNF-α stimulated Elk-1 phosphorylation, which was reduced by LY294002 or PD98059. We also observed that TNF-α time dependently induced p300/Elk-1 and p300/Akt complex formation in HPAEpiCs, which was reduced by AG490, AG1296, or LY294002. The activity of cPLA2 protein upregulated by TNF-α was reflected on the PGE2 release, which was reduced by AG490, AG1296, LY294002, or PD98059. Taken together, these results demonstrated that TNF-α-induced cPLA2 expression and PGE2 release were mediated through a Jak2/PDGFR/PI3K/Akt/p42/p44 MAPK/Elk-1 pathway in HPAEpiCs.

TNF-α-Induced cPLA2 Expression via NADPH Oxidase/Reactive Oxygen Species-Dependent NF-κB Cascade on Human Pulmonary Alveolar Epithelial Cells

“…Several reports also demonstrate that TNF-α triggers several signal transduction pathways to activate the NOX activity and enhances intracellular ROS generation leading to expression of inflammatory genes (Rahman et al, 1998; Hashimoto et al, 2001; Li et al, 2005; Lee et al, 2013; Yang et al, 2014). Therefore, we investigated whether TNF-α-induced cPLA 2 expression is due to activation of NADPH oxidase and ROS generation.…”

“…5x Laemmli buffer was added and subjected to electrophoresis on SDS-PAGE, and then blotted using an anti-phospho-tyrosine, anti-phospho-serine, anti-p47 phox , anti-TRAF2, anti-TNFR1, or anti-ASK1 antibody, as previously described (Yang et al, 2014). …”

Myc Expression Drives Aberrant Lipid Metabolism in Lung Cancer

“…Following MYC deactivation, these transcripts decreased with time, suggesting their amplification at the gene expression level is linked to MYC. Finally, we examined the gene expression for proinflammatory cytokines TNF-a and IL-1b, that may play a role in regulating cPLA2 and eicosanoid synthesis (30)(31)(32)(33). We found a modest increase in Tnf-a with MYC activation, whereas Il-1b gene expression was closely correlated to MYC activity (Fig.…”

Cytosolic Phospholipase A2α Promotes Pulmonary Inflammation and Systemic Disease during Streptococcus pneumoniae Infection

“…The bulk of AA in mammalian cells is generated from the fatty acyl chains of glycerophospholipids present in cell membranes (34)(35)(36). AA availability is a ratelimiting factor in the production of eicosanoids, because AA release from membrane phospholipids due to enhanced activity of phospholipase A 2 (PLA 2 ) results in the increased production of eicosanoids (14,37).…”

“…Numerous inflammatory stimuli, such as interleukin 1␤ (IL-1␤), gamma interferon (IFN-␥), and TNF-␣, trigger the release of eicosanoids from human lung epithelial cells in a manner dependent on cPLA 2 activation (45,50,51). cPLA 2 has been implicated in PMN recruitment in vitro and promotes sepsis-induced acute lung injury (36,52,53), but its role in S. pneumoniae-induced lung inflammation and subsequent systemic spread of the pathogen has yet to be defined. Here we show that cPLA 2 ␣ plays a critical role in S. pneumoniae-induced AA release from cultured human airway epithelial cells and subsequent PMN transepithelial migration and is required for pulmonary inflammation, bacteremia, and lethality upon pneumococcal lung infection of mice.…”