PKC‐α controls MYD88‐dependent TLR/IL‐1R signaling and cytokine production in mouse and human dendritic cells

Conventional PKC (cPKC)‐α regulates TRIF‐dependent IFN response factor 3 (IRF3)‐mediated gene transcription, but its role in MyD88‐dependent TLR signaling remains unknown. Herein, we demonstrate that PKC‐α is induced by several MyD88‐dependent TLR/IL‐1R ligands and regulates cytokine expression in human and murine DC. First, inhibition of cPKC activity in human DC by cPKC‐specific inhibitors, Gö6976 or HBDDe, downregulated the production of classical inflammatory/immunomodulatory cytokines induced by TLR2, TLR5 or IL‐1R but not by TLR3 stimulation. Similarly, dominant negative PKC‐α repressed Pam3CSK4 induced NF‐κB‐ and AP‐1‐driven promoter activities in TLR2‐expressing human embryonic kidney 293 T cells. Dominant negative PKC‐α inhibited NF‐κB reporter activity mediated by overexpression of MyD88 but not TRIF. Unexpectedly, BM‐derived DC from PKC‐α−/− mice exhibited decreased TNF‐α and IL‐12p40 production induced by both MyD88‐ and TRIF‐dependent ligands. Furthermore, PKC‐α is coupled to TLR2 signaling proximal to MyD88 since MAPK and IκB kinase‐α/β phosphorylations and IκBα degradation were inhibited in PKC‐α−/− BM‐derived DC. Finally, co‐immunoprecipitation assays revealed that PKC‐α physically interacts with Pam3CSK4 activated TLR2 in WT but not in MyD88−/− DC. Collectively this study identifies a species‐specific role of PKC‐α as a key component that controls MyD88‐dependent cytokine gene expression in human and mouse but differentially regulates production of TRIF‐dependent cytokines.