Granulocyte/macrophage colony-stimulating factor affects myo-inositol metabolism in a novel manner. Implications for its priming action on human neutrophils

Abstract

Little is known about the signal transduction processes involved in the priming action of granulocyte/macrophage colonystimulating factor (GM-CSF) on neutrophils. This study has used myo-[3H]inositol-labelled human neutrophils to determine whether preincubation with GM-CSF influences myo-inositol (Ins) metabolism in control cells, or in cells stimulated with the bacterial chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMetLeuPhe). GM-CSF pretreatment did not influence the total cellular 3H radioactivity content, demonstrating that the cytokine had no effect on Ins uptake. However, neutrophils pretreated with GM-CSF showed a dramatic 25-40 % fall in the free [3H]Ins content of the cell, which was almost quantitatively recovered in a 2-4-fold increase in radioactivity within Ptdlns. The remainder of the 3H radioactivity was found proportionately distributed throughout all other [3H]Ins-containing metabolites. Interestingly, in comparison with controls, the GM-CSF-stimulated increases in [3H]polyphosphoinositide (including 3-phosphorylated lipids) and [3H]Ins polyphosphate contents were consistently higher than that observed with Ptdlns. This observation suggests that GM-CSF influences the hormone-sensitive pool of Ptdlns, possibly through the activation of a Ptdlns synthase which is rate-limiting to subsequent metabolic pathways. This is the first report of an action of GM-CSF on Ins metabolism, and highlights the conversion of Ins to Ptdlns as a key regulatory metabolic step.

Priming of human neutrophil superoxide generation by tumour necrosis factor‐α is signalled by enhanced phosphatidylinositol 3,4,5‐trisphosphate but not inositol 1,4,5‐trisphosphate accumulation

“…Changes in intracellular calcium concentration ([Ca 2+ ] i ) have also been implicated in the priming process [12], but there have been no studies detailing the effects of priming agents on secretagogue‐induced Ins(1,4,5)P 3 generation. To date, only single time point measurements of the effects of GM‐CSF priming on fMLP‐stimulated Ins(1,4,5)P 3 have been reported, which show either enhanced [13]or unaltered [14]Ins(1,4,5)P 3 accumulation.…”

Thrombin Primes Responsiveness of Selective Chemoattractant Receptors at a Site Distal to G Protein Activation

“…For example, granulocytemacrophage colony-stimulating factor enhances Ca 2ϩ mobilization and superoxide generation stimulated by both peptide (fMLP and C5a) and lipid (PAF) chemoattractants as well as by direct activation of G proteins (6). It has been proposed that the priming effect of granulocyte-macrophage colony-stimulating factor may reside in its ability to cause de novo synthesis of cellular G proteins or activation of phosphoinositide kinase, which increases the availability of substrates for phospholipase C (7,34). In the studies presented here, the effect reached a maximum 3-5 min after thrombin addition, and thus de novo protein synthesis is unlikely to be involved.…”