PI3K p110β Positively Regulates Lipopolysaccharide-Induced IL-12 Production in Human Macrophages and Dendritic Cells and JNK1 Plays a Novel Role

The PI3K family is thought to participate in TLR signaling, and it has been reported to be a negative regulator of TLR-mediated production of IL-12, a key inducer of Th1 responses. However, the role of individual PI3K subtypes in IL-12 production remains obscure. We defined the distinct regulation of LPS-mediated IL-12 production by p110 alpha and p110 beta catalytic subunits of PI3K in human APCs. We observed that knockdown of PI3K p110 beta by small interfering RNA (siRNA) suppressed both LPS-induced IL-12 protein production and mRNA expression in monocyte-derived macrophages and dendritic cells (DCs). Knockdown of PI3K p110 alpha by siRNA reduced LPS- induced IL-12 protein production in both cell types. Conversely, knockdown of PI3K p110 alpha suppressed LPS-induced IL-12 mRNA expression in monocyte-derived macrophages but minimally affected monocyte-derived DCs. PI3K p110 beta siRNA inhibited JNK activation, but not p38 MAPK or ERK activation, stimulated by LPS, while PI3K p110 alpha siRNA did not affect LPS-induced JNK, p38 MAPK, or ERK activation in both cell types. Transfection of siRNA against JNK1, JNK2, and both decreased LPS-induced IL-12 production. Furthermore, PI3K p110 beta ARNA attenuated LPS-induced JNK1 phosphorylation, while not affecting JNK2 phosphorylation. Our findings indicate that PI3K p110 beta positively controls LPS-induced IL-12 production through the JNK1-dependent pathway in human macrophages and DCs. The Journal of Immunology, 2009, 182: 5225-5231.