Short‐term delay of Fas‐stimulated apoptosis by GM‐CSF as a result of temporary suppression of FADD recruitment in neutrophils: evidence implicating phosphatidylinositol 3‐kinase and MEK1‐ERK1/2 pathways downstream of classical protein kinase C

Granulocyte/macrophage colony‐stimulating factor (GM‐CSF) inhibits Fas‐induced apoptosis of neutrophils. However, the exact step in the apoptotic pathway blocked by GM‐CSF remained unclear. Here, we found that pretreatment of neutrophils with GM‐CSF inhibits the recruitment of Fas‐associated protein with death domain (FADD) to Fas, abolishing the formation of the death‐inducing signaling complex required for Fas‐induced apoptosis. Two‐dimensional electrophoresis revealed that GM‐CSF modifies the ratio of FADD subspecies. These GM‐CSF‐triggered changes were abrogated, and Fas‐induced apoptosis was restored by an inhibitor of classical protein kinase C (PKC), Gö6976, and by the combination of a phosphatidylinositol 3‐kinase (PI‐3K) inhibitor, LY294002, and an inhibitor of mitogen‐activated protein kinase kinase (MEK)1, PD98059. Gö6976 blocked GM‐CSF‐elicited phosphorylation of Akt/PKB and extracellular signal‐regulated kinase (ERK)1/2. These results indicated that GM‐CSF suppresses Fas‐induced neutrophil apoptosis by inhibiting FADD binding to Fas, through redundant actions of PI‐3K and MEK1‐ERK1/2 pathways downstream of classical PKC.