Interaction of guanine-nucleotide-binding regulatory proteins with chemotactic peptide receptors in differentiated human leukemic HL-60 cells

Signaling pathways downstream of P2 receptors in human neutrophils

Extracellular nucleotides stimulate human neutrophils by activating the purinergic P2Y(2) receptor. However, it is not completely understood which types of G proteins are activated downstream of this P2 receptor subtype. We investigated the G-protein coupling to P2Y(2) receptors and several subsequent signaling events. Treatment of neutrophils with pertussis toxin (PTX), a Gi protein inhibitor, caused only approximately 75% loss of nucleotide-induced Ca(2+) mobilization indicating that nucleotides cause Ca(2+) mobilization both through Gi-dependent and Gi-independent pathways. However, the PLC inhibitor U73122 almost completely inhibited Ca(2+) mobilization in both nucleotide- and fMLP-stimulated neutrophils, strongly supporting the view that both the PTX-sensitive and the PTX-insensitive mechanism of Ca(2+) increase require activation of PLC. We investigated the dependence of ERK phosphorylation on the Gi pathway. Treatment of neutrophils with PTX caused almost complete inhibition of ERK phosphorylation in nucleotide or fMLP activated neutrophils. U73122 caused inhibition of nucleotide- or fMLP-stimulated ERK phosphorylation, suggesting that although pertussis toxin-insensitive pathways cause measurable Ca(2+) mobilization, they are not sufficient for causing ERK phosphorylation. Since PLC activation leads to intracellular Ca(2+) increase and PKC activation, we investigated if these intracellular events are necessary for ERK phosphorylation. Exposure of cells to the Ca(2+) chelator BAPTA had no effect on nucleotide- or fMLP-induced ERK phosphorylation. However, the PKC inhibitor GF109203X was able to almost completely inhibit nucleotide- or fMLP-induced ERK phosphorylation. We conclude that the P2Y(2) receptor can cause Ca(2+) mobilization through a PTX-insensitive but PLC-dependent pathway and ERK phosphorylation is highly dependent on activation of the Gi proteins.

Structure and regulation of the mDot1 gene, a mouse histone H3 methyltransferase

The nucleotide sequence data reported have been deposited in the DDBJ, EMBL, GenBank(R) and GSDB Nucleotide Sequence Databases under accession numbers AY196089, AY196090, AY376663, AY377920 and AY376664. Recently, a new class of histone methyltransferases that plays an indirect role in chromatin silencing by targeting a conserved lysine residue in the nucleosome core was described, namely the Dot1 (disruptor of telomeric silencing) family [Feng, Wang, Ng, Erdjument-Bromage, Tempst, Struhl and Zhang (2002) Curr. Biol. 12, 1052-1058; van Leeuwen, Gafken and Gottschling (2002) Cell (Cambridge, Mass.) 109, 745-756; Ng, Feng, Wang, Erdjument-Bromage, Tempst, Zhang and Struhl (2002) Genes Dev. 16, 1518-1527]. In the present study, we report the isolation, genomic organization and in vivo expression of a mouse Dot1 homologue (mDot1). Expressed sequence tag analysis identified five mDot1 mRNAs (mDot1a-mDot1e) derived from alternative splicing. mDot1a and mDot1b encode 1540 and 1114 amino acids respectively, whereas mDot1c-mDot1e are incomplete at the 5'-end. mDot1a is closest to its human counterpart (hDot1L), sharing 84% amino acid identity. mDot1b is truncated at its N- and C-termini and contains an internal deletion. The five mDot1 isoforms are encoded by 28 exons on chromosome 10qC1, with exons 24 and 28 further divided into two and four sections respectively. Alternative splicing occurs in exons 3, 4, 12, 24, 27 and 28. Northern-blot analysis with probes corresponding to the methyltransferase domain or the mDot1a-coding region detected 7.6 and 9.5 kb transcripts in multiple tissues, but only the 7.6 kb transcript was evident in mIMCD3-collecting duct cells. Transfection of mDot1a-EGFP constructs (where EGFP stands for enhanced green fluorescent protein) into human embryonic kidney (HEK)-293T or mIMCD3 cells increased the methylation of H3-K79 but not H3-K4, -K9 or -K36. Furthermore, DMSO induced mDot1 gene expression and methylation specifically at H3-K79 in mIMCD3 cells in a time- and dose-dependent manner. Collectively, these results add new members to the Dot1 family and show that mDot1 is involved in a DMSO-mediated signal-transduction pathway in collecting duct cells.

G-protein-mediated signal transduction for meiosis reinitiation in starfish oocyte

Starfish oocyte maturation is induced by 1-methyladenine. There were apparently two forms of 1-methyladenine receptor affected by GTP gamma S. Pertussis toxin ADP-ribosylated the 39-kDa alpha subunit of a G protein and inhibited maturation. Also, the G protein was ADP-ribosylated by cholera toxin only when 1-methyladenine was added. The purified G protein had an heterotrimeric structure consisting of 39 kDa alpha, 37 kDa beta, and 8 kDa gamma subunits. The deduced amino acid sequence of the cDNA of starfish G alpha was 89% identical to mammalian Gi-1 alpha. The purified starfish beta gamma-subunits induced maturation when they were microinjected into oocytes.

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

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. HL-60 cells express formyl peptide-, complement C5a-, leukotriene B4 (LTB4)- and platelet-activating factor receptors, receptors for purine and pyrimidine nucleotides, histamine H1- and H2-receptors, beta 2-adrenoceptors and prostaglandin receptors. 3. The major G-proteins in HL-60 cells are pertussis toxin (PTX)-sensitive Gi-proteins (Gi2 > Gi3). Gs-proteins and G-proteins of the Gq-family (e.g., G16) are expressed, too. 4. G-protein-regulated effector systems in HL-60 cells are adenylyl cyclase and phospholipase C-beta 2 (PLC-beta 2) and, possibly, phospholipase D (PLD), nonselective cation (NSC) channels and NADPH oxidase. 5. The expression of signal transduction pathways in HL-60 cells strongly depends on the differentiation state of cells. 6. Formyl peptides, via Gi-proteins, mediate activation of PLC, PLD, NSC channels, NADPH oxidase and azurophilic granule release and are referred to as full secretagogues. In dibutyryl cAMP (Bt2cAMP)-differentiated HL-60 cells, C5a and LTB4 are partial and incomplete secretagogues, respectively. There are substantial differences in the Gi-protein activations induced by formyl peptides, C5a and LTB4. 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 Bt2cAMP-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., P2Y- and P2U-receptors and pyrimidinocyeptors) may mediate the effects of nucleotides in HL-60 cells. 8. Bt2cAMP- and 1 alpha,25-dihydroxycholecalciferol-differentiated HL-60 cells express H1-receptors coupled to Gi-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. HL-60 promyelocytes express H2-receptors coupled to adenylyl cyclase, PLC, and NSC channels. There are substantial differences in the agonist/antagonist profiles of H2-receptor-mediated cAMP formation and rises in cytosolic Ca2+ concentration, indicative of the involvement of different H2-receptor subtypes. H2-receptors mediate functional differentiation of HL-60 cells. 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 Gi-proteins.

Accumulation of cyclic ADP-ribose measured by a specific radioimmunoassay in differentiated human leukemic HL-60 cells with all-trans-retinoic acid

Cyclic adenosine diphosphoribose (cADPR) is a novel candidate for the mediator of Ca2+ release from intracellular Ca2+ stores. The formation of this cyclic nucleotide is catalyzed by not only Aplysia ADP-ribosyl cyclase but also an ecto-form enzyme of NAD+ glycohydrolase (NADase), which was previously identified as all-trans-retinoic acid (RA)-inducible CD38 in human leukemic HL-60 cells. In the present study, we developed a radioimmunoassay specific for cADPR, by which more than 100 fmol of cADPR could be detected without any interference by other nucleotides. The possible involvement of CD38 in the formation of cellular cADPR was investigated with the radioimmunoassay method. A marked increase in cellular cADPR was accompanied by all-trans-RA-induced differentiation of HL-60 cells. Moreover, a high level of cellular cADPR was observed in other leukemic cell lines, in which CD38 mRNA was expressed. Thus, CD38, which was initially identified as an NADase, appeared to be responsible for the formation of cellular cADPR.

Potentiation of Gi-mediated phospholipase C activation by retinoic acid in HL-60 cells. Possible role of G gamma 2

Differentiated HL-60 cells acquire responsiveness to fMet-Leu-Phe (fMLP), which activates phospholipase C and O2- generation in a pertussis toxin-sensitive manner. Addition of retinoic acid (RA) for the last 24 h during dimethyl sulfoxide (Me2SO)-induced differentiation enhanced fMLP-dependent signals and interaction between fMLP receptor and G(i). RA modifies both the function and subunit composition of G(i)2, the predominant G(i) of HL-60 membranes, as shown by comparing purified G(i)2 from membranes of Me2SO-treated cells (D-G(i)2) to G(i)2 from membranes of cells treated with both Me2SO and RA (DR-G(i)2). As compared to D-G(i)2, DR-G(i)2 induced more fMLP binding when added to membranes of pertussis toxin-treated HL-60 cells and, in the presence of GTP gamma S, stimulated beta gamma-sensitive phospholipase C in extracts of HL-60 cells to a much greater extent at a lower concentrations. Immunoblasts revealed that RA induced expression of the gamma 2 subunit, which was otherwise undetectable in G(i)2 purified from HL-60 cells or in HL-60 membranes. Possibly by inducing expression of gamma 2, RA alters two functions of the G(i) beta gamma subunit, modulation of fMLP receptor-G(i)2 coupling and activation of the effector, Phospholipase C.

Dimethyl sulphoxide: a review of its applications in cell biology

Dimethyl sulphoxide is a water miscible solvent that has wide applications in cell biology. It acts as a cryoprotective agent in a variety of cells and tissues allowing prolonged storage at subzero temperatures. The action of dimethyl sulphoxide on the stability of the liquid matrix of cell membranes appears to be responsible for its effects and this appears also to be true for related effects on membrane permeability and fusion. Dimethyl sulphoxide is also known to act as an inducer of cellular differentiation and as a free radical scavenger and radioprotectant. A review of the underlying molecular basis of all these effects of dimethyl sulphoxide is presented.

Histamine H1-receptors in HL-60 monocytes are coupled to Gi-proteins and pertussis toxin-insensitive G-proteins and mediate activation of Ca2+ influx without concomitant Ca2+ mobilization from intracellular stores

The results of binding studies suggest the presence of histamine H1-receptors in human monocytes, but it is not known whether these receptors are functionally active. This prompted us to study the effects of histamine (HA) on cytosolic Ca2+ concentration ([Ca2+]i) and superoxide anion (O2-) formation in HL-60 cells differentiated towards monocytes with 1 alpha,25-dihydroxycholecalciferol. In HL-60 monocytes, HA increased [Ca2+]i with a half-maximal effect at 8 microM and a maximum at 30-100 microM. Pertussis toxin (PTX) partially inhibited the stimulatory effects of HA on [Ca2+]i. Betahistine, a weak partial H1-receptor agonist, also increased [Ca2+]i, whereas H2- and H3-receptor agonists were ineffective. H1- but not H2- and H3-receptor antagonists inhibited HA-induced rises in [Ca2+]i. HA-induced rises in [Ca2+]i were desensitized in a homologous manner and were also inhibited by the activator of protein kinase C, 4 beta-phorbol 12-myristate 13-acetate. Various protein kinase C inhibitors did not interfere with homologous desensitization. The stimulatory effects of HA on [Ca2+]i were completely dependent on the presence of extracellular Ca2+ and were inhibited by the blocker of non-selective cation (NSC) channels, 1-(beta-[3-(4-methoxyphenyl)propoxyl]-4-methoxyphenethyl)-1 H-imidazole hydrochloride (SK & F 96365). HA was much less effective than the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), to induce rises in [Ca2+]i. Unlike fMLP, HA did not activate O2- formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulatory and inhibitory guanine-nucleotide-binding regulatory protein involvement in stimulation of arachidonic-acid release by N-formyl-methionyl-leucyl-phenylalanine and platelet-activating factor from guinea-pig alveolar macrophages. Differential receptor/G-protein interaction assessed by pertussis and cholera toxins

The involvement of guanine-nucleotide-binding regulatory proteins (G proteins) in the regulation of arachidonic-acid release induced by N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) or platelet-activating factor (PAF) was examined in guinea-pig alveolar macrophages. We report that maximal release of arachidonic acid in permeabilized cells requires the simultaneous addition of the agonist (fMet-Leu-Phe or PAF) and of GTP (or GTP[S]). Prior treatment of cells with increasing concentrations of pertussis toxin induces a parallel decrease of arachidonic-acid release and of the labeling of a 40-kDa protein in membranes incubated with [32P]NAD and pertussis toxin. fMet-Leu-Phe, but not PAF, allows the ADP-ribosylation of a 40-KDa protein by cholera toxin in the presence of Mg2+. This effect is prevented by guanyl nucleotides and by prior treatment with pertussis toxin. The 40-kDa protein ADP-ribosylated seems to be alpha i1 and/or alpha i2. Stimulation of GTPase activity by fMet-Leu-Phe and PAF has the same amplitude and is completely inhibited by pertussis toxin, but only in part by cholera toxin. Prior treatment of alveolar macrophages with cholera toxin, which ADP-ribosylates Gs, inhibits PAF-stimulated and fMet-Leu-Phe-stimulated arachidonic-acid release to the same extent, via a cAMP-protein-kinase-A cascade. The decreased responsiveness of alveolar macrophages previously treated with cholera toxin to fMet-Leu-Phe and PAF is associated with a strong increase of in-vitro [32P]NAD labeling of Gi proteins either by pertussis or by cholera toxin. This effect is mimicked by prior treatment of the cells with dibutyryl cAMP and okadaic acid, a protein-phosphatase inhibitor, suggesting the involvement of protein-kinase A in this process. In conclusion, our results demonstrate that fMet-Leu-Phe and PAF receptors interact differently with Gi1/2 proteins in guinea-pig alveolar macrophages. Gi1/2 proteins are a possible target of the cross-regulation of arachidonic-acid release by a Gs-mediated pathway.

Formyl peptides and ATP stimulate Ca2+ and Na+ inward currents through non-selective cation channels via G-proteins in dibutyryl cyclic AMP-differentiated HL-60 cells. Involvement of Ca2+ and Na+ in the activation of beta-glucuronidase release and superoxide production

In human neutrophils, the chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) induces increases in the intracellular free Ca2+ concentration ([Ca2+]i) with subsequent activation of beta-glucuronidase release and superoxide (O2-) production. Results from several laboratories suggest that the increase in [Ca2+]i is due to activation of non-selective cation (NSC) channels. We studied the biophysical characteristics, pharmacological modulation and functional role of NSC channels in dibutyryl cyclic AMP (Bt2cAMP)-differentiated HL-60 cells. fMLP increased [Ca2+]i by release of Ca2+ from intracellular stores and influx of Ca2+ from the extracellular space. fMLP also induced Mn2+ influx. Ca2+ and Mn2+ influxes were inhibited by 1-(beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl)-1H-imidazole hydrochloride (SK&F 96365). Under whole-cell voltage-clamp conditions, fMLP and ATP (a purinoceptor agonist) activated inward currents characterized by a linear current-voltage relationship and a reversal potential near 0 mV. NSC channels were substantially more permeable to Na+ than to Ca2+. SK&F 96365 inhibited fMLP- and ATP-stimulated currents with a half-maximal effect at about 3 microM. Pertussis toxin prevented stimulation by fMLP of NSC currents and reduced ATP-stimulated currents by about 80%. Intracellular application of the stable GDP analogue, guanosine 5'-O-[2-thio]diphosphate, completely blocked stimulation by agonists of NSC currents. In excised inside-out patches, single channel openings with an amplitude of 0.24 pA were observed in the presence of fMLP and the GTP analogue, guanosine 5'-O-[3-thio]triphosphate. The bath solution contained neither Ca2+ nor ATP. The current/voltage relationship was linear with a conductance of 4-5 pS and reversed at about 0 mV. fMLP-induced beta-glucuronidase release and O2- production were substantially reduced by replacement of extracellular CaCl2 or NaCl by ethylenebis(oxyethylenenitrilo)tetra-acetic acid and choline chloride respectively. In the absence of Ca2+ and Na+, fMLP was ineffective. SK&F 96365 inhibited fMLP-induced beta-glucuronidase release and O2- production in the presence of both Ca2+ and Na+, and in the presence of Ca2+ or Na+ alone. NaCl (25-50 mM) enhanced the basal and absolute extent of fMLP-stimulated GTP hydrolysis of heterotrimeric regulatory G-proteins in HL-60 membranes. The order of effectiveness of salts in enhancing GTP hydrolysis was LiCl > KCl > NaCl > choline chloride.(ABSTRACT TRUNCATED AT 400 WORDS)

Properties of 1-methyladenine receptors in starfish oocyte membranes: involvement of pertussis toxin-sensitive GTP-binding protein in the receptor-mediated signal transduction

In response to a meiosis-inducing hormone, 1-methyladenine (1-MA), starfish oocytes undergo reinitiation of meiosis with germinal vesicle breakdown. The 1-MA-initiated signal is, however, inhibited by prior microinjection of pertussis toxin into the oocytes, suggesting that a guanine nucleotide-binding protein (G protein) serving as the substrate of pertussis toxin is involved in the 1-MA receptor-mediated signal. We thus investigated properties of 1-MA receptors by means of binding of the radiolabeled ligand to the oocyte membranes. There were apparently two forms of 1-MA receptors with high and low affinities in the membranes. The high-affinity form was converted into the low-affinity one in the presence of a non-hydrolyzable analogue of GTP. A 39-kDa protein, which had been identified as the alpha-subunit of the major substrate G protein for pertussis toxin, was also ADP-ribosylated by cholera toxin only when 1-MA was added to the membranes. The ADP-ribosylated 39-kDa alpha-subunit could be immunoprecipitated with antibodies raised against the carboxy-terminal site of mammalian inhibitory G-alpha. These results indicate that 1-MA receptors are functionally coupled with the 39-kDa pertussis toxin-substrate G protein in starfish oocyte membranes.