Phospholipase D is required in the signaling pathway leading to p38 MAPK activation in neutrophil-like HL-60 cells, stimulated by N-formyl-methionyl-leucyl-phenylalanine.

Human acute myelogenous leukemia cells (HL-60 cells) can be induced to differentiate to neutrophils by exposure to dibutyryl-cyclic AMP. The differentiation of HL-60 cells allowed the mitogen-activated protein kinases p38 and p44/p42 to be rapidly and transiently activated upon stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP). Western blot analysis using phosphospecific p38 and p44/p42 mitogen-activated protein kinase antibodies showed that increasing concentrations of ethanol or 1-butanol but not 2-butanol (0.05-0.5%) inhibited fMLP-induced p38 activation but did not inhibit p44/p42 activation. These data indicated that activation of phospholipase D (PLD) was required for activation of p38 but not p44/p42. We compared the effect of fMLP with those of tumor necrosis factor alpha (TNF alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF). We found that ethanol did not inhibit p38 phosphorylation upon stimulation with either GM-CSF or TNF alpha. These results suggested that in cells stimulated with fMLP, PLD was upstream of p38. To further test the involvement of PLD, we used antisense inhibition of human PLD1 expression. Treatment with antisense oligonucleotides inhibited p38 but not p44/p42 phosphorylation. These data supported a role for human PLD1 in fMLP-induced p38 activation in neutrophil-like HL-60 cells. In addition, the results obtained with TNF alpha and GM-CSF demonstrated that p38 activation occurred independently of PLD activation.