Phospholipase D1 is required for lipopolysaccharide-induced tumor necrosis factor-alpha expression and production through S6K1/JNK/c-Jun pathway in Raw 264.7 cells

Abstract

The purpose of this study was to identify the role of phospholipase D1 (PLD1) in lipopolysaccharide (LPS)induced tumor necrosis factor-a (TNF-alpha) expression and production. LPS-induced TNF-a expression and production were TLR4 (Toll-like receptor 4)/Myd88 dependent in Raw 264.7 cells. LPS enhanced PLD activation, which was attenuated by TLR4 inhibitor (Polymixin B) or knockdown of Myd88 with siRNA treatment. To investigate the role of PLD in LPS-induced TNF-a expression and production, we transfected PLD1 and PLD2 siRNAs to Raw 264.7 cells, respectively. Interestingly, only knockdown of PLD1 decreased TNF-a expression but not PLD2. Next, we investigated the S6K1-JNK-c-Jun signaling pathway in LPS-induced TNF-a expression mechanism. Knockdown of PLD1 also decreased phosphorylation of S6K1, JNK and c-Jun induced by LPS. Furthermore, we found that activated c-Jun63/73 bound to TNF-a promoter and turned on TNF-a expression. Taken together, our results demonstrate that PLD1 is activated by LPS/TLR4/Myd88 pathway and regulates TNF-a expression and production through S6K1/JNK/c-Jun in Raw 264.7 cells.