Phosphatidylinositol 3-Kinase in Interleukin 1 Signaling

The signaling mechanisms utilized by the proinflammatory cytokine interleukin-1 (IL-1) to activate the transcription factors NFkappaB and activator protein-1 (AP-1) are poorly defined. We present evidence here that IL-1 not only stimulates a dramatic increase in phosphatidylinositol 3-kinase (PI 3-kinase) activity but also induces the physical interaction of its type I receptor with the p85 regulatory subunit of PI 3-kinase. Furthermore, two PI 3-kinase-specific inhibitors, wortmannin and a dominant-negative mutant of the p85 subunit, inhibited IL-1-induced activation of both NFkappaB and AP-1. Transient transfection experiments indicated that whereas overexpression of PI 3-kinase may be sufficient to induce AP-1 and increase nuclear c-Fos protein levels, PI 3-kinase may need to cooperate with other IL-1-inducible signals to fully activate NFkappaB-dependent gene expression. In this regard, cotransfection studies suggested that PI 3-kinase may functionally interact with the recently-identified IL-1-receptor-associated kinase to activate NFkappaB. Our results thus indicate that PI 3-kinase is a novel signal transducer in IL-1 signaling and that it may differentially mediate the activation of NFkappaB and AP-1.