PI3K limits TNF-α production in CD16-activated monocytes

IgG complexes bind to Fc receptor family members Fc gamma RI (CD64), Fc gamma RII (CD32) and Fc gamma RIII (CD16), activating cell MAPK and PI3K resulting in increased cytokine production from particular leukocytes. The signaling molecules involved in cytokine production after cross-linking CD16 have not been determined in monocytes. To address this question, TNF-alpha, IL-1 beta and IL-6 were measured in activated monocytes after inhibiting MEK1/2, PI3K and glycogen synthase kinase-beta (GSK-3 beta). The roles of GSK-3 beta and NF-kappa B were then determined using reporter assays and siRNA treatment. The data suggested that an MAPK pathway stimulated TNF-alpha release but that active PI3K limited TNF-alpha, IL-1 beta and IL-6 cytokine production after cross-linking CD16. PI3K was also shown to limit nuclear translocation of NF-kappa B. The limiting effect of PI3K on TNF-alpha production from activated monocytes depended on the decrease of GSK-3 beta activity, which significantly reduced the transactivation of NF-kappa B. Moreover, the TNF-alpha production induced by CD16 cross-linking was reduced in monocytes after treatment with siRNA against NF-kappa B, implying that this transcription factor functioned in TNF-alpha production. The results suggest that CD16 cross-linking activated PI3K and that active PI3K limited TNF-alpha production by inhibiting GSK-3 beta activity, that blocked the action of NF-kappa B.