Critical roles of the p110 beta subtype of phosphoinositide 3-kinase in lipopolysaccharide-induced Akt activation and negative regulation of nitrite production in RAW 264.7 cells

It has been suggested that PI3K participates in TLR signaling. However, identifying specific roles for individual PI3K subtypes in signaling has remained elusive. In macrophages from the p110gamma(-/-) mouse, LPS-induced phosphorylation of Akt occurred normally despite the fact that the action of anaphylatoxin C5a was impaired markedly. In RAW 264.7 cells expressing short hairpin RNA that targets p110beta, LPS-induced phosphorylation of Akt was significantly attenuated. In contrast, the LPS action was not impaired, but was rather augmented in the p110alpha-deficient cells. Previous pharmacologic studies have suggested that a PI3K-Akt pathway negatively regulates TLR-induced inducible NO synthase expression and cytokine production. In the p110beta-deficient cells, inducible NO synthase expression and IL-12 production upon stimulation by LPS were increased, whereas LPS-induced expression of COX-2 and activation of MAPKs were unaffected. Together, the results suggest a specific function of p110beta in the negative feedback regulation of TLR signaling.