Abstract
Human neutrophils or HL60 cells express P2U receptors and respond to micromolar concentrations of ATP, adenosine 5'-O-(thiotriphosphate) (ATPgammaS), or UTP with immediate increases in intracellular Ca2+ through activation of phosphoinositide phospholipase C (Cowen, D. S., Lazarus, H. M., Shurin, S. B., Stoll, S. E., and Dubyak, G. R. (1989) J. Clin. Invest. 83, 1651-1660). P2U agonists reportedly induce limited enzyme secretion and enhance the respiratory burst in response to chemotactic factors. We demonstrate here that P2U agonists are chemotactic for neutrophils or differentiated HL60 cells. Rhodamine phalloidin staining indicates that ATPgammaS treatment induces actin polymerization and shape changes similar to those seen when these cells are treated with chemotactic peptide fMet-Leu-Phe. Although undifferentiated HL60 cells fail to mount a rise in Ca2+ when challenged with fMet-Leu-Phe, they increase Ca2+ in response to P2U agonists. However, functional expression of phospholipase C-coupled receptors is not sufficient for chemotaxis since HL60 cell migration in response to these agonists or to fMet-Leu-Phe occurs only after exposure to differentiating agents such as BT2cAMP. In addition to the well known G protein-linked receptors for lipid or peptide chemotactic factors, neutrophils apparently also can utilize G protein-linked purino/pyrimidino receptors to recognize nucleotides as chemoattractants. High concentrations of ATP and UTP generated at sites of platelet aggregation and tissue injury could thus be important mediators of inflammation.
Highlights
Human neutrophils or HL60 cells express P2U receptors and respond to micromolar concentrations of ATP, adenosine 5-O-(thiotriphosphate) (ATP␥S), or UTP with immediate increases in intracellular Ca2؉ through activation of phosphoinositide phospholipase C
By comparing the effects of fMet-Leu-Phe and P2U receptor agonists on differentiating HL60 cells, we show that Ca2ϩ mobilization is an insufficient signal for chemotaxis, since undifferentiated HL60 cells fail to migrate in response to ATP␥S in spite of a robust Ca2ϩ response
Our observations that ATP␥S and UTP caused a complete cross-desensitization of the Ca2ϩ mobilization response of human neutrophils support recent reports that P2U receptors recognize both of these agonists [4, 5]
Summary
Vol 271, No 26, Issue of June 28, pp. 15597–15601, 1996 Printed in U.S.A. P2U Agonists Induce Chemotaxis and Actin Polymerization in Human Neutrophils and Differentiated HL60 Cells*. Human neutrophils or promyelocytic HL60 cells in various stages of differentiation respond to ATP, ATP␥S, or UTP with an immediate increase in intracellular Ca2ϩ This response is mediated through the activation of a pertussis toxin-sensitive G protein, which in turn activates the phosphoinositide phospholipase C (PI-PLC) cascade [1, 8, 10, 11]. Our results demonstrate that activation of P2U receptors on human peripheral blood neutrophils induces a typical chemotactic response, accompanied by actin polymerization and changes in cell shape characteristic of those seen during chemotaxis in response to fMet-Leu-Phe. By comparing the effects of fMet-Leu-Phe and P2U receptor agonists on differentiating HL60 cells, we show that Ca2ϩ mobilization is an insufficient signal for chemotaxis, since undifferentiated HL60 cells fail to migrate in response to ATP␥S in spite of a robust Ca2ϩ response
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