G-Protein-coupled receptors in HL-60 human leukemia cells

Abstract

1. 1. HL-60 human leukemia cells are a widely employed model system for the analysis of signal transduction processes mediated via regulatory heterotrimeric guanine nucleotide-binding proteins (G-proteins). HL-60 promyelocytes are pluripotent and can be differentiated into neutrophilic or monocytic cells. 2. 2. HL-60 cells express formyl peptide-, complement C5a-, leukotriene B 4 (LTB 4)- and platelet-activating factor receptors, receptors for purine and pyrimidine nucleotides, histamine H 1- and H 2-receptors, β 2-adrenoceptors and prostaglandin receptors. 3. 3. The major G-proteins in HL-60 cells are pertussis toxin (PTX)-sensitive G i-proteins (G i2 > G i3). G s-proteins and G-proteins of the G q-family (e.g., G 16) are expressed, too. 4. 4. G-protein-regulated effector systems in HL-60 cells are adenylyl cyclase and phospholipase C-β 2 (PLC-β 2) and, possibly, phospholipase D (PLD), nonselective cation (NSC) channels and NADPH oxidase. 5. 5. The expression of signal transduction pathways in HL-60 cells strongly depends on the differentiation state of cells. 6. 6. Formyl peptides, via G i-proteins, mediate activation of PLC, PLD, NSC channels, NADPH oxidase and azurophilic granule release and are referred to as full secretagogues. In dibutyryl cAMP (Bt 2cAMP)-differentiated HL-60 cells, C5a and LTB 4 are partial and incomplete secretagogues, respectively. There are substantial differences in the G i-protein activations induced by formyl peptides, C5a and LTB 4. 7. 7. In HL-60 promyelocytes, purine and pyrimidine nucleotides mediate activation of PLC and NSC channels largely via PTX-insensitive G-proteins and induce functional differentiation. In Bt 2cAMP-differentiated HL-60 cells, they additionally activate PLD, NADPH oxidase and granule release via PTX-sensitive and -insensitive pathways. ATP and UTP are partial secretagogues. Multiple types of receptors (i.e., P 2Y- and P 2U-receptors and pyrimidinocyeptors) may mediate the effects of nucleotides in HL-60 cells. 8. 8. Bt 2cAMP- and 1α,25-dihydroxycholecalciferol-differentiated HL-60 cells express H l-receptors coupled to G i-proteins and PTX-insensitive G-proteins. In the former cells, histamine mediates activation of PLC and NSC channels, and in the latter, activation of NSC channels. Histamine is an incomplete secretagogue in these cells. 9. 9. HL-60 promyelocytes express H 2-receptors coupled to adenylyl cyclase, PLC, and NSC channels. There are substantial differences in the agonist/antagonist profiles of H 2-receptor-mediated cAMP formation and rises in cytosolic Ca 2+ concentration, indicative of the involvement of different H 2-receptor subtypes. H 2-receptors mediate functional differentiation of HL-60 cells. 10. 10. Certain cationic-amphiphilic histamine receptor ligands (i.e., 2-substituted histamines, lipophilic guanidines, and a histamine trifluoromethyl-toluidide derivative) show stimulatory effects in HL-60 cells that are attributable to receptor-independent activation of G i-proteins.