Heterogeneity of protein kinase C isoform expression in chemically induced HL60 cells

Nuclear Receptors as Potential Therapeutic Targets for Myeloid Leukemia

The nuclear receptor (NR) superfamily has been studied extensively in many solid tumors and some receptors have been targeted to develop therapies. However, their roles in leukemia are less clear and vary considerably among different types of leukemia. Some NRs participate in mediating the differentiation of myeloid cells, making them attractive therapeutic targets for myeloid leukemia. To date, the success of all-trans retinoic acid (ATRA) in treating acute promyelocytic leukemia (APL) remains a classical and unsurpassable example of cancer differentiation therapy. ATRA targets retinoic acid receptor (RAR) and forces differentiation and/or apoptosis of leukemic cells. In addition, ligands/agonists of vitamin D receptor (VDR) and peroxisome proliferator-activated receptor (PPAR) have also been shown to inhibit proliferation, induce differentiation, and promote apoptosis of leukemic cells. Encouragingly, combining different NR agonists or the addition of NR agonists to chemotherapies have shown some synergistic anti-leukemic effects. This review will summarize recent research findings and discuss the therapeutic potential of selected NRs in acute and chronic myeloid leukemia, focusing on RAR, VDR, PPAR, and retinoid X receptor (RXR). We believe that more mechanistic studies in this field will not only shed new lights on the roles of NRs in leukemia, but also further expand the clinical applications of existing therapeutic agents targeting NRs.

Vitamin D3-driven signals for myeloid cell differentiation--implications for differentiation therapy

Primitive myeloid leukemic cell lines can be driven to differentiate to monocyte-like cells by 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), and, therefore, 1,25(OH)(2)D(3) may be useful in differentiation therapy of myeloid leukemia and myelodysplastic syndromes (MDS). Recent studies have provided important insights into the mechanism of 1,25(OH)(2)D(3)-stimulated differentiation. For myeloid progenitors to complete monocytic differentiation a complex network of intracellular signals has to be activated and/or inactivated in a precise temporal and spatial pattern. 1,25(OH)(2)D(3) achieves this change to the 'signaling landscape' by (i) direct genomic modulation of the level of expression of key regulators of cell signaling and differentiation pathways, and (ii) activation of intracellular signaling pathways. An improved understanding of the mode of action of 1,25(OH)(2)D(3) is facilitating the development of new therapeutic regimens.

Characterization and quantitation of membrane proteomes using multidimensional MS-based proteomic technologies

A major goal of proteomics is to develop methods that enable the systematic characterization of every protein within the cell or particular subcellular proteome using a single analytical platform. Although the equivalent has already been achieved in genomics, reaching this goal in proteomics represents a much greater challenge due to the wide dynamic range of protein expression, numerous post-translational modifications and remarkable physicochemical heterogeneity of proteins. A major analytical challenge has involved developing more effective means for proteome-scale investigations of membrane proteins, whose solubility differs drastically from that of cytoplasmic proteins. Fortunately, rapid progress has increased the ability to characterize this critically important class of proteins on a scale analogous to that of aqueous soluble proteins.

Secretions of MMP-9 by soluble glucocorticoid-induced tumor necrosis factor receptor (sGITR) mediated by protein kinase C (PKC)? and phospholipase D (PLD) in murine macrophage

The secretion of matrix metalloproteinase (MMP-9) is stimulated by the glucocorticoid-induced tumor necrosis factor receptor (GITR), a new tumor necrosis factor receptor (TNFR) family, in murine macrophages via an activation of protein kinase C (PKC)delta and phospholipase D (PLD). Secretions of MMP-9 are stimulated by the phosphatidic acid (PA), a product of PLD activity and an inhibition of PA production by a 1-propanol inhibited secretion of MMP-9 by soluble GITR (sGITR). MMP-9 is not secreted by diacylglycerol (DAG) and an inhibitor of PA phosphatase has no effect on the secretion induced by sGITR, indicating that PA is responsible for MMP-9 secretion in murine macrophages. Our data indicates that sGITR-induced activation of PKCdelta and PLD increases MMP-9 secretions in macrophages.

Ciprofloxacin transport by chemoattractant-activated polymorphonuclear leukocytes: regulation by priming and protein kinase C

At infection sites, polymorphonuclear leukocyte (PMN) function is enhanced ("primed") by granulocyte-macrophage colony-stimulating factor (GM-CSF) or lipopolysaccharide (LPS) and activated by formyl peptides. In this study, GM-CSF or LPS alone had no significant effects on PMN ciprofloxacin transport. Through a mechanism involving protein kinase C, activation by formyl-Met-Leu-Phe (fMLP) significantly decreased the K(m) of ciprofloxacin transport and enhanced ciprofloxacin accumulation. This effect was dramatically enhanced when PMNs were primed with GM-CSF or LPS prior to activation by fMLP.

Protein kinase C isoforms in normal and leukemic neutrophils: altered levels in leukemic neutrophils and changes during myeloid maturation in chronic myeloid leukemia

Protein kinase C (PKC) is reported to play a role in maturation of the myeloid cell and functions of the mature neutrophil. The neutrophils in chronic myeloid leukemia (CML) exhibit defects in several functions. As a step towards understanding the role of PKC in the defects in function of the leukemic cells, this study investigates the expression of PKC isoforms, their subcellular distribution, levels and kinase activity in the normal and leukemic neutrophils. It also investigates changes in representative PKC isoforms during myeloid maturation. This study confirms the presence of PKC alpha, beta and delta and shows, for the first time, the presence of non conventional PKC isoform theta, atypical PKC isoform lambda/iota and PKC isoform mu in normal human neutrophils. In unstimulated cells all the detected PKC isoforms showed a predominantly cytosolic localisation in normal and CML neutrophils. Cytosol-membrane distribution of PKC alpha and delta were significantly altered in leukemic neutrophils as compared to normal cells. Cytosolic levels of all PKC isoforms were reduced in CML neutrophils with PKC alpha, beta, iota, theta, and mu showing a significant decrease. Cytosolic levels of PKC delta contrary to the trend observed for other PKC isoforms showed a slight increase in CML cells, while its membrane levels were significantly reduced in CML neutrophils. Total PKC kinase activity in CML neutrophil cytosol was significantly reduced, while specific kinase activity of two representative isoforms, PKC alpha and delta, from normal and CML neutrophils were similar, thereby increasing the significance of the altered levels of PKC isoforms in CML, and highlighting their role in the defects in function exhibited by the leukemic neutrophils. The levels of PKC delta and iota increased and decreased respectively as the leukemic myeloid cell matured from the blast to the neutrophil, while the levels of PKC alpha and beta were not altered. This suggests a role for PKC delta and iota in the maturation of the leukemic myeloid cell.

Quantitative profiling of differentiation-induced microsomal proteins using isotope-coded affinity tags and mass spectrometry

An approach to the systematic identification and quantification of the proteins contained in the microsomal fraction of cells is described. It consists of three steps: (1) preparation of microsomal fractions from cells or tissues representing different states; (2) covalent tagging of the proteins with isotope-coded affinity tag (ICAT) reagents followed by proteolysis of the combined labeled protein samples; and (3) isolation, identification, and quantification of the tagged peptides by multidimensional chromatography, automated tandem mass spectrometry, and computational analysis of the obtained data. The method was used to identify and determine the ratios of abundance of each of 491 proteins contained in the microsomal fractions of naïve and in vitro- differentiated human myeloid leukemia (HL-60) cells. The method and the new software tools to support it are well suited to the large-scale, quantitative analysis of membrane proteins and other classes of proteins that have been refractory to standard proteomics technology.

Protein phosphatase 2A activates the HIV-2 promoter through enhancer elements that include the pets site

Human immunodeficiency virus type 2 (HIV-2) gene expression is regulated by upstream promoter elements, including the peri-Ets (pets) site, which mediate enhancer stimulation following treatment with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). We previously showed that the oncoprotein DEK binds to the pets site in a site-specific manner. In this report, we show that binding to the HIV-2 pets site is modulated by treatment of U937 monocytic cells with TPA, an activator of protein kinase C. TPA treatment resulted in a reduction in the levels of DEK and the formation of a faster migrating pets complex in gel shift assays. We show further that the actions of TPA on pets binding can be duplicated by phosphatase treatment of nuclear proteins and is blocked with okadaic acid, a protein phospatase-2A (PP2A) inhibitor. Finally, we demonstrate that ectopic expression of the catalytic domain of PP2A can activate the HIV-2 enhancer/promoter alone or in synergy with TPA, an effect mediated in part through the pets site. These results suggest that, through an interaction with the protein kinase C pathway, PP2A is strongly involved in regulating HIV-2 enhancer-mediated transcription. This is a consequence of its effects on DEK expression and binding to the pets site, as well as its effects on other promoter elements. These findings have implications not only for HIV-2 transcription but also for multiple cellular processes involving DEK or PP2A.

Monocytic differentiation of HL-60 cells is characterized by the nuclear translocation of phosphatidylinositol 3-kinase and of definite phosphatidylinositol-specific phospholipase C isoforms

Immunochemical and immunocytochemical data indicate that nuclei of HL-60 cells contain different enzymes involved in the phosphoinositide cycle, such as PI 3-K and the phosphatidylinositol-specific PLC isoforms beta3, gamma1 and gamma2. These enzymes translocate differently to the nuclear fraction when HL-60 cells are treated with differentiating doses of vitamin D3: PI 3-K translocated progressively to the nucleus in parallel with full differentiation until 96 hours. PLC beta3 increased until 72 hours of treatment and then lowered its intranuclear amount and PLC gamma1 was unchanged at all the examined times. PLC gamma2 nuclear translocation increased progressively until 96 hours of vitamin D3 administration. A fourth PLC isozyme, beta2, present in the cytoplasm of untreated cells, translocates to the cytoplasm after vitamin D3 addition and reaches the highest concentration at the end of monocytic differentiation. Terminal monocytic differentiation was characterized at the nuclear level by high levels of PI 3-K and PLC gamma2 and by the novel expression of PLC beta2. We then observed that the xi isoform of PKC, constitutively present in nuclei of HL-60 cells, translocated to the nucleus when cells were induced to differentiate along the monocytic lineage, but the nuclear translocation of PKC xi was blocked as a consequence of PI 3-K inhibition by Wortmannin. These findings indicate that the main components of the noncanonical and canonical inositol lipid signal transduction pathways, including PI 3-K, PLC beta2 and beta3, PLC gamma2, undergo nuclear translocation and may therefore play a relevant role during monocytic differentiation at the nuclear level. Furthermore, PKC xi nuclear translocation appears to be related to PI 3-K activity.

Lineage-Restricted Expression of Protein Kinase C Isoforms in Hematopoiesis

The pattern of expression of several protein kinase C (PKC) isoforms (, βΙ, δ, ɛ, η, and ζ) during the course of hematopoietic development was investigated using primary human CD34+ hematopoietic cells and stable cell lines subcloned from the growth factor-dependent 32D murine hematopoietic cell line. Each 32D cell clone shows the phenotype and growth factor dependence characteristics of the corresponding hematopoietic lineage. Clear-cut differences were noticed between erythroid and nonerythroid lineages. (1) The functional inhibition of PKC-ɛ in primary human CD34+ hematopoietic cells resulted in a twofold increase in the number of erythroid colonies. (2) Erythroid 32D Epo1 cells showed a lower level of bulk PKC catalytic activity, lacked the expression of ɛ and η PKC isoforms, and showed a weak or absent upregulation of the remaining isoforms, except βΙ, upon readdition of Epo to growth factor-starved cells. (3) 32D, 32D GM1, and 32D G1 cell lines with mast cell, granulo-macrophagic, and granulocytic phenotype, respectively, expressed all the PKC isoforms investigated, but showed distinct responses to growth factor readdition. (4) 32D Epo 1.1, a clone selected for interleukin-3 (IL-3) responsiveness from 32D Epo1, expressed the ɛ isoform only when cultured with IL-3. On the other hand, when cultured in Epo, 32D Epo1.1 cells lacked the expression of both ɛ and η PKC isoforms, similarly to 32D Epo1. (5) All 32D cell lines expressed the mRNA for PKC-ɛ, indicating that the downmodulation of the ɛ isoform occurred at a posttranscriptional level. In conclusion, the PKC isoform expression during hematopoiesis appears to be lineage-specific and, at least partially, related to the growth factor response.

Lineage-Restricted Expression of Protein Kinase C Isoforms in Hematopoiesis

The pattern of expression of several protein kinase C (PKC) isoforms (, βΙ, δ, ɛ, η, and ζ) during the course of hematopoietic development was investigated using primary human CD34+ hematopoietic cells and stable cell lines subcloned from the growth factor-dependent 32D murine hematopoietic cell line. Each 32D cell clone shows the phenotype and growth factor dependence characteristics of the corresponding hematopoietic lineage. Clear-cut differences were noticed between erythroid and nonerythroid lineages. (1) The functional inhibition of PKC-ɛ in primary human CD34+ hematopoietic cells resulted in a twofold increase in the number of erythroid colonies. (2) Erythroid 32D Epo1 cells showed a lower level of bulk PKC catalytic activity, lacked the expression of ɛ and η PKC isoforms, and showed a weak or absent upregulation of the remaining isoforms, except βΙ, upon readdition of Epo to growth factor-starved cells. (3) 32D, 32D GM1, and 32D G1 cell lines with mast cell, granulo-macrophagic, and granulocytic phenotype, respectively, expressed all the PKC isoforms investigated, but showed distinct responses to growth factor readdition. (4) 32D Epo 1.1, a clone selected for interleukin-3 (IL-3) responsiveness from 32D Epo1, expressed the ɛ isoform only when cultured with IL-3. On the other hand, when cultured in Epo, 32D Epo1.1 cells lacked the expression of both ɛ and η PKC isoforms, similarly to 32D Epo1. (5) All 32D cell lines expressed the mRNA for PKC-ɛ, indicating that the downmodulation of the ɛ isoform occurred at a posttranscriptional level. In conclusion, the PKC isoform expression during hematopoiesis appears to be lineage-specific and, at least partially, related to the growth factor response.

A lineage-specific protein kinase crucial for myeloid maturation

To identify genes involved in macrophage development, we used the differential display technique and compared the gene expression profiles for human myeloid HL-60 leukemia cell lines susceptible and resistant to macrophage maturation. We identified a gene coding for a protein kinase, protein kinase X (PRKX), which was expressed in the maturation-susceptible, but not in the resistant, cell line. The expression of the PRKX gene was found to be induced during monocyte, macrophage, and granulocyte maturation of HL-60 cells. We also studied the expression of the PRKX gene in 12 different human tissues and transformed cell lines and found that, among these tissues and cell types, the PRKX gene is expressed only in blood. Among the blood cell lineages, the PRKX gene is specifically expressed in macrophages and granulocytes. Antisense inhibition of PRKX expression blocked terminal development in both the leukemic HL-60 cells and normal peripheral blood monocytes, implying that PRKX is a key mediator of macrophage and granulocyte maturation. Using the HL-60 cell variant deficient in protein kinase C-beta (PKC-beta) and several stable PKC-beta transfectants, we found that PRKX gene expression is under control of PKC-beta; hence PRKX is likely to act downstream of this PKC isozyme in the same signal transduction pathway leading to macrophage maturation.

Isolation and Characterization of a Variant HL60 Cell Line Defective in the Activation of the NADPH Oxidase by Phorbol Myristate Acetate

Promyelocytic human leukemia HL60 cells can be differentiated into neutrophil-like cells that exhibit an NADPH oxidase activity through direct stimulation of protein kinase C (PKC) with PMA or through formyl peptide receptor activation. We have isolated a variant HL60 clone that exhibited a conditional PMA-induced oxidative response depending on the agent used for the differentiation. While cells differentiated with DMSO responded to either PMA or N-formyl peptide (N-formyl-Met-Leu-Phe-Lys or fMLFK), cells differentiated with dibutyryl-cAMP (Bt2cAMP) responded to fMLFK but very poorly to PMA. However, in Bt2cAMP-differentiated cells, the expression of the different PKC isoforms was similar to that observed in DMSO-differentiated cells. Moreover, PMA was able to induce a normal phosphorylation of the cytosolic factor p47phox and to fully activate extracellular signal-regulated kinases (Erk1/2). Interestingly, Bt2cAMP-differentiated cells exhibited a strong and sustained O2− production when costimulated with PMA and suboptimal concentrations of fMLFK which were, per se, ineffective. This sustained response was only slightly reduced by the conjunction of the mitogen-activated protein (MAP) kinase kinase (MEK) inhibitor PD98059 and wortmannin, a phosphatidylinositol-3 kinase (PI3K) inhibitor. Variant HL60 cells that were stably transfected with a constitutively active form of Rac1 were able, when differentiated with Bt2cAMP, to secrete oxidant following PMA stimulation. Altogether, the results suggest that, in addition to the phosphorylation of p47phox, the activation of NADPH oxidase requires the activation of a Rac protein through a pathway that diverges at a point upstream of MEK and that is independent of the activation of wortmannin sensitive PI3K.

Protein kinase C isoforms in normal and chronic myeloid leukemic neutrophils. Distinct signal for PKC alpha by immunodetection on PVDF membrane, decreased expression of PKC alpha and increased expression of PKC delta in leukemic neutrophils

Neutrophils from patients with Chronic Myeloid Leukemia (CML) exhibit defects in several functions. They also show altered phosphorylation-dephosphorylation patterns of several proteins on stimulation with phorbol myristate acetate--a direct activator of protein kinase C (PKC). Since PKC mediates several functions of the neutrophil, in this study we investigate the PKC isoform profile and subcellular distribution in normal and CML neutrophils in an attempt to elucidate their role in CML signalling. Our results show the presence of PKC alpha, betaI, betaII and delta in both the cell types. A distinct and clear signal was obtained for PKC alpha, the isoform reported to be absent or present in very low amounts in normal neutrophils. In addition, PKC alpha was present in significantly lower levels in CML neutrophils while the PKC delta isoform was found in significantly higher amounts in the CML cytosol as compared to that in normal cells. PKC alpha, betaI, betaII and delta isoforms could not be detected in the nucleus of unstimulated normal and CML neutrophils. The altered levels of PKC alpha and delta may be one of the causes for the defects in function exhibited by the leukemic cells.

Accumulation of catalytically active PKC-zeta into the nucleus of HL-60 cell line plays a key role in the induction of granulocytic differentiation mediated by all-trans retinoic acid

The effect of differentiating doses of all-trans retinoic acid (ATRA, 10(-6) M) and vitamin D3 (10(-7) M) was investigated on the nuclear levels of endogenous ceramide and protein kinase C-zeta (PKC-zeta) catalytic activity in HL-60 myeloid cells. ATRA induced a parallel increase of ceramide and catalytically active PKC-zeta into the nuclear compartment of HL-60 cells (peak at 72 h). On the other hand, vitamin D3 increased the levels of nuclear ceramide and PKC-zeta activity to a lesser extent and with a delayed kinetics compared to ATRA (peak at 96 h). Pretreatment of HL-60 cells with high pharmacological concentrations of exogenously-added C2-ceramide (10(-6) M) completely blocked the ATRA-mediated activation of nuclear PKC-zeta. Exogenous C2-ceramide (10(-6) M) also inhibited the granulocytic differentiation induced by ATRA, whereas it did not affect monocytic differentiation mediated by vitamin D3. Transient transfection experiments performed with a plasmid construct containing a constitutively active mutated form of the PKC-zeta cDNA fused in 3' to a fluorescent tag protein (pEGFP-PKC-zeta) demonstrated that the overexpression of catalytically active PKC-zeta was not accompanied by the appearance of a differentiated morphology. These findings suggest that nuclear PKC-zeta is necessary but not sufficient to induce granulocytic differentiation of HL-60 myeloid malignant cells.

An apparently novel protein of human leukocytes, reactive with an antibody to protein kinase C-gamma, is rapidly modified upon cell activation: initial characterization in neutrophils and their cytoplasts

On immunoblots of human neutrophil cytoplasts (U-CYT), a previously undescribed 97 kDa protein was revealed by intense and selective reaction with an antibody that was initially raised to recognize PKC-gamma. Denoted "gamma-rp" for gamma-related protein, this acidic cytosolic protein somewhat resembled the classic forms of PKC in several biochemical respects. Appearing as a doublet on low-percentage SDS-PAGE gels, both its mobility and staining pattern were rapidly altered by treatment of U-CYT with either phorbol ester or chemotactic peptide. Whole neutrophil gamma-rp was detectable only after TCA precipitation of intact cells. It was also detectable in human platelets, lymphocytes, and neutrophil-like differentiated HL60 cells, but not in fibroblasts, erythrocytes, monocytes, or monocyte-like differentiated HL60 cells. Our data suggest that gamma-rp merits further study as a potential participant in cellular activation, and as a possible structural or functional relative of PKC.

Stimulation of osteopontin mRNA expression in HL-60 cells is independent of differentiation

12-O-Tetradecanoylphorbol 13-acetate (TPA) induces HL-60 cells to differentiate along the monocyte/macrophage pathway and stimulates expression of the extracellular adhesion protein osteopontin (OPN). In this study, the mechanism of TPA-mediated OPN mRNA expression and its relationship to differentiation were investigated. The induction of OPN mRNA by TPA was dose dependently inhibited by staurosporine (0.4-10.0 nM) and chelerythrine (0.1-5.0 microM), indicating that OPN expression requires PKC activation. Furthermore, the mitogen-activated protein kinase kinase (MAPKK) inhibitor, PD 098059 (1.0-10.0 microM), inhibited the effect of TPA in a dose-dependent fashion. Cycloheximide (10 microg/ml) ablated the induction of OPN mRNA by TPA. To determine if OPN mRNA expression was associated with a particular differentiational pathway, HL-60 cells were treated with RA, 9-cis-RA, calcitriol, or sodium butyrate. None of these agents stimulated OPN mRNA. Treatment with TPA subsequent to a 120-h pretreatment with retinoic acid (RA), 9-cis-RA, or calcitriol resulted in a potentiation of the induction of OPN mRNA. These results support a role for protein kinase C (PKC) in promoting OPN expression because each of these agents increased PKC levels. An hOPN promoter/reporter construct was responsive to TPA, indicating that this effect is at the level of transcription. Thus, TPA-stimulated transcription of the OPN gene apparently occurs via a PKC/MAPK-dependent mechanism that is independent of that associated with differentiation and is not dependent on the maturational state of these cells.

Intranuclear translocation of phospholipase C beta2 during HL-60 myeloid differentiation

Phospholipases C (PLC) beta3, gamma1, and gamma2 were detected in nuclei of HL-60 promyelocitic leukaemia cells. When HL-60 cells undergo terminal myeloid differentiation in the presence of ATRA, the beta2 isoform appeared inside nuclei and was up-regulated until 72 hours of ATRA treatment. The beta3 isozyme was also increased until 72 hours and both isoforms lowered their intranuclear amount at 96 hours and following days of treatment. By contrast PLC gamma1 and gamma2 progressively increased in the nucleus during granulocytic differentiation even after 72 hours of treatment. Terminal differentiation was characterised by the expression of high levels of PLC gamma1 and gamma2 and by low levels of PLC beta2 and beta3 in the nucleus. PIP2 and PIP hydrolysis paralleled the prevalence of the beta or gamma subfamily, respectively. Moreover, at all the examined times no changes of PLCs in the whole cell were detectable, indicating a de novo nuclear translocation of the beta2 and an increased accumulation of beta3, gamma1, and gamma2 isoforms. Thus, the intranuclear presence, expression, and activity of PLC isozymes, which are modulated during differentiation of HL-60 cells, implicate a role for nuclear phosphoinositide signalling in the process of cell maturation. In particular the nuclear translocation of PLC beta2 candidates this PLC as a key enzyme in the granulocytic differentiative commitment of HL-60 cells.

Differential expression of protein kinase C isozymes and small GTP-binding proteins during HL60 cell differentiation by retinoic acid and cyclic AMP: relation with phospholipase D (PLD) activation

The differential expression of protein kinase C (PKC) isozymes and small GTP-binding proteins, and their relation to O2 generation and phospholipase D (PLD) activation were analyzed during the differentiation of human promyelocytic HL60 cells to neutrophil-like cells induced by either retinoic acid (RA) or dibutyryl cyclic AMP (dbcAMP). In response to either one of the inducers, nitroblue tetrazolium (NBT) reduction activity time-dependently increased. Although PLD activity was upregulated by dbcAMP-treatment, only a slight increase was observed in RA-treated cells. Small GTP-binding proteins Rac1, Rap1, and RhoA, which are reported to be implicated in O2- generation or PLD activation, were already expressed in undifferentiated HL60 cells and their significant changes were not detected during differentiation. The mRNAs of the cytosolic components of NADPH oxidase system, p47phox and p67phox, were present in trace amounts in undifferentiated cells. However, they rapidly increased in response to RA or dbcAMP. In response to either RA or dbcAMP, the increases were observed in cPKC isozymes (alpha, beta I, beta II) but not in other subtypes (delta, epsilon, theta, zeta) by both RT-PCR and Western blot analyses. In dbcAMP-treated cells PKC alpha increased remarkably, whereas PKC beta I and beta II mainly elevated in RA-treated cells. These results suggest the possibility that cPKCs are closely related to cell differentiation and that PKC alpha is involved in PLD activation.

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.

Inhibition of proliferation and induction of monocytic differentiation on HL60 human promyelocytic leukemia cells treated with bile acids in vitro

We have tested the effect of several bile acids on the proliferation and differentiation of the HL60 human promyelocytic leukemia cell line in vitro. Deoxycholate, chenodeoxycholate and lithocholic acid caused dose-dependent inhibition of cell proliferation and induction of differentiation along the monocyte/macrophage pathway as determined by morphology, NBT test, non-specific esterase, and staining by monoclonal antibodies against specific cell-surface antigens. Optimal effects were obtained at 100, 75, and 60 microM of the 3 bile acids respectively. Cell-cycle flow-cytometric analysis showed that a substantial fraction of HL60 cells accumulated at the G0/G1 transition. Protein-kinase-C inhibitors such as sphinganine and H-7 inhibited the differentiation-inducing effect of bile acids, suggesting a possible role for PKC in this regulation. When bile acids were combined with non-effective concentrations of all-trans retinoic acid, enhancement of the monocytic differentiation of THP-1 human leukemia cells was observed. Our findings demonstrate induction of tumor-cell differentiation by bile acids, compounds that present minimal undesirable effects in humans.

Differential phosphorylation in normal and leukemic granulocytes in response to phorbol 12-myristate 13-acetate

Granulocytes from the peripheral blood of patients with chronic myeloid leukemia (CML) exhibit a number of functional defects. To explore the relationship of these aberrations to signal transduction, granulocytes from normal subjects and CML patients were labelled with 32Pi, stimulated with phorbol myristate acetate (PMA) and the phosphoproteins (Pps) in the unstimulated and stimulated cells analyzed by 2D-SDS-PAGE followed by autoradiography. Results show that there are six distinct reproducibly phosphorylated proteins referred to as Pp1-Pp6 identifiable in the basal patterns of the resting granulocytes. Amongst these, Pp1 and Pp5 are more intensely phosphorylated and Pp3 is very faint or absent in unstimulated CML cells, relative to the normal granulocytes. On stimulation of normal cells with PMA, Pp1, Pp3, Pp4 and Pp6 exhibit distinct patterns of phosphorylation-dephosphorylation. In the CML cells, however, Pp1 and Pp4 are unresponsive to PMA. We conclude that PKC-mediated functions involving Pp1, Pp3 and Pp4 are most probably defective in CML cells.