Terminal differentiation surface antigens of myelomonocytic cells are expressed in human promyelocytic leukemia cells (HL60) treated with chemical inducers

The expression of two surface antigens present on the cell membrane of both human granulocytes and monocytes was studied during the process of myelomonocytic differentiation using two monoclonal antibodies (B9.8.1 and B13.4.1). These surface antigens are not present on immature myeloid cells nor on nonmyeloid hematopoietic cells, but can be detected when the cells are terminally differentiated. Among the bone marrow cells, B13.4.1 binds to metamyelocytes and B9.8.1 to metamyelocytes and a fraction (30%) of myelocytes. HL60 human promyelocytic leukemia cells did not react with such monoclonal antibodies. However, when such cells were induced to differentiate in vitro into mature myeloid elements by treatment with retinoic acid or dimethyl sulfoxide, 70%--90% of the differentiated cells expressed both surface antigens. Cell sorting studies on these treated HL60 cells indicated that myelocytes and metamyelocytes were the most immature cells expressing such markers. Expression of the two surface antigens was also observed when HL60 cells were induced to differentiate into monocyte/macrophage cells by treatment with the tumor promoter 12-O- tetradecanoyl-phorbol-13-acetate. Thus, human promyelocytic leukemia cells induced to differentiate in vitro by treatment with specific chemical agents express membrane antigens in the same pattern as normal bone marrow myeloid cells at the corresponding stage of differentiation.     

Induction of gamma-interferon activity by elevated temperatures in human B-lymphoblastoid cell lines.

When the human B-lymphoblastoid cell lines GM3299 and GM4408 were heat shocked, elevated levels of antiviral activity were detected. This antiviral activity has been characterized as the result of de novo synthesis of interferon (IFN) gamma. Levels of antiviral activity as high as 20,000 units/ml per 10(6) cells were found after heat treatment. By using anti-IFN-alpha and anti-IFN-gamma sera, it was shown that the high antiviral activity in GM3299 after heat shock is due to a synergistic effect of constitutively produced IFN-alpha and induced IFN-gamma.     

Transcriptional and post-transcriptional regulation of granulocyte-macrophage colony-stimulating factor production in human growth factor dependent M-07e cells

Summary. Human myeloid leukaemia cell lines have been shown to differentiate into distinct cell lineages in vitro in response to several differentiation-inducing agents. A human eosinophilic leukaemia cell line, EoL-1, has been shown to differentiate into mature eosinophilic granulocytes by treatment with the culture supernatant of a human T-cell line, HIL-3. In this study we have studied whether the EoL-1 cell line has potential to differentiate into cell lineage other than eosinophils. We found that EoL-1 cells cultured in the presence of tumour necrosis factor (TNF)-α (10u/ml) and interferon (IFN)-γ (1000u/ml) for 2–4d differentiated into macrophage-like cells in morphology, and expressed CD14 antigen on their cell surface. It is possible that the small subpopulation of EoL-1 cells which contains non-specific esterase (NSE) activity may be preferentially differentiated by TNF-α and IFN-γ. To clarify this issue, we have cloned the EoL-1 cell line and obtained NSE negative and positive sublines. Both EoL-1 sublines differentiated into monocyte/ macrophage-like cells, because: (a) EoL-1 sublines were induced to express CD14 antigen, and (b) they attached firmly to the plastic wells; (c) after differentiation they became strongly positive for NSE staining, and secreted TNF-α in response to the stimulation with lipopolysaccharide; and (d) they exhibited potent phagocytic activity. Therefore, we found that the EoL-1 cell line has the ability to differentiate not only into mature eosinophilic cells but also into monocyte/macrophage cell lineage, suggesting that EoL-1 cells represent immature cells with ability to differentiate into multiple cell lineages.     

A Novel Interferon-Inducible Gene Expressed during Myeloid Differentiation

ABSTRACT: The acute promyelocytic leukemia cell line, NB4, can be induced to differentiate to mature granulocytes by retinoic acid treatment. A novel retinoic acid-inducible cDNA clone, designated RI58, was isolated from a cDNA library constructed from retinoic acid-treated NB4 cells by differential hybridization. RI58 cDNA encodes a protein of 58kDa which has a similarity in its amino acids sequence to interferon (IFN)-inducible proteins. In addition, RI58 was induced by recombinant human IFN-α (rhIFN-α) in NB4 cells. RI58 was detectable within 4 hours post-stimulation with rhIFN-α, while it took as long as 1day after retinoic acid stimulation. Culture supernatant from retinoic acid-treated NB4 cells also induced RI58 expression similarly as rhIFN-α. This activity in culture supernatant was inhibited by anti-leukocyte IFN antiserum which showed specific reactivity to rhIFN-α. These results indicate that RI58 is induced by retinoic acid stimulation through autocrinally secreted IFN-α from NB4 cells. In the retinoic acid-treated NB4 cells, the expression of RI58 was increased along the process of differentiation. On the other hand, it was expressed constitutively in untreated non-hematopoietic cell lines and mature hematopoietic cell lines.     

Combinations of recombinant human interferons and retinoic acid synergistically induce differentiation of the human promyelocytic leukemia cell line HL-60

The human acute promyelocytic leukemia cell line HL-60 is induced to differentiate into morphologically and functionally mature monocytelike cells by incubation with a combination of 10 nmol/L retinoic acid (RA) and various concentrations of recombinant immune interferon (rIFN- gamma). These induced cells show marked increases in antibody-dependent cellular cytotoxicity (ADCC), antibody-coated erythrocyte (EA) rosettes, nonspecific esterase, and 5'-nucleotidase activity. rIFN- gamma alone at concentrations of 10 to 1,000 U/mL has essentially no effect on morphological maturation, nitroblue tetrazolium reduction, and immunophagocytosis. However, rIFN-gamma at these concentrations increases EA rosetting in a concentration-dependent manner that is not affected by 10 nmol/L RA. At a concentration of 1,000 U/ml, rIFN-gamma induces moderate increases in nonspecific esterase, 5'-nucleotidase, and ADCC. These parameters are markedly increased by the addition of 10 nM RA, a concentration which alone has no effect on these markers. Based on units of antiviral activity, rIFN-gamma is tenfold more active than rIFN-alpha D in inducing EA rosettes and 40-fold more active in inducing nitroblue tetrazolium reduction and immunophagocytosis. These results, indicating that combinations of rIFN-gamma or rIFN-alpha and RA synergistically induce differentiation of HL-60, suggest that this combination may have clinical utility in the treatment of patients with certain leukemias.     

Induction of terminal differentiation in human promyelocytic leukemia cells by tumor-promoting agents.

Human promyelocytic leukemia cells (HL-60) were induced to differentiate into mature cells by the tumor-promoting agent phorbol-12-myristate-13-acetate and other related phorbol diesters. Differentiation was determined by an increase in the percent of myelocytes, metamyelocytes, and other mature myeloid cells as well as by an increase in the percent of phagocytizing cells. Induction of differentiation could be determined after 2 days of treatment with phorbol-12-myristate-13-acetate at a dose as low as 6 X 10(11) M. A correlation was found between reported tumor-promoting activity of a series of phorbol esters and their ability to induce myeloid differentiation and to inhibit cell growth. It is suggested that tumor-promoting agents like chemicals that induce terminal differentiation in these cells, at extremely low concentrations, may be used as a tool in the study of the control of cell growth, cell differentiation, and malignancy in human leukemic cells.     

Retinoic acid cooperates with tumor necrosis factor and immune interferon in inducing differentiation and growth inhibition of the human promyelocytic leukemic cell line HL-60

In this study, we analyzed the effect of tumor necrosis factor (TNF) on retinoic acid (RA)-induced myeloid differentiation of the promyelocytic HL-60 leukemia cell line. We show that low concentrations of the two substances, almost inactive in inducing differentiation when used separately, induce differentiation when added simultaneously to the cell cultures. Cells simultaneously expressing both monocyte/macrophage phenotype (typically induced by TNF) and granulocyte characteristics (typically induced by RA) are induced by a combination of the two factors, indicating that TNF and RA potentiate each other's activity. The results obtained using immune interferon (IFN-gamma) in combination with the two inducers suggest that the mechanism of action of TNF and IFN-gamma are possibly different. The inhibitory effect of RA on the expression of HLA class I antigens and of the high-affinity Fc receptor is potentiated by TNF but completely reversed by rIFN-gamma.     

Separate induction of MHC and thyroid microsomal antigen (McAg) expression on thyroid cell monolayers: enhancement of lectin-induced McAg expression by interferon-gamma

Interferon-gamma (IFN gamma) induced the expression of the MHC class II antigens HLA-DR and -DQ on 1- to 2-week-old thyrocytes from normal thyroid tissue and thyroid tissue from patients with autoimmune thyroid disease; it also enhanced the expression of B2-microglobulin, which is associated with MHC class I molecules. However, the expression of thyroglobulin and thyroid microsomal antigen (McAg) was not detected after IFN gamma stimulation. Autologous and allogeneic peripheral blood mononuclear cells had the same ability as IFN gamma to induce antigen expression when cocultured with thyrocytes. In contrast, leucoagglutinin (LAG) induced McAg as well as HLA-DR and B2-microglobulin expression on thyrocytes, but not thyroglobulin expression. Concanavalin A and pokeweed mitogen also induced McAg expression. The time course of LAG induction of McAg was not always correlated with that of HLA-DR. Anti-IFN gamma, antiinterleukin-2 receptor, and anti-HLA-DR monoclonal antibodies inhibited LAG or peripheral blood mononuclear cell induction of HLA-DR expression, but not LAG induction of McAg expression. Anti-HLA-DR reduced the IFN gamma induction of HLA-DR. INF gamma enhanced thyrocyte McAg expression induced by LAG, especially when thyrocytes were incubated with IFN gamma for 24 h before LAG stimulation. In contrast, in the absence of LAG stimulation, IFN gamma suppressed already present spontaneous McAg expression. TSH did not induce McAg and HLA-DR expression on DR-negative thyrocytes, but enhanced weak DR expression induced by other stimulants, e.g. IFN gamma or lectins. These data suggest that in vitro induction mechanisms of MHC class I and II antigens and McAg are different; MHC antigens are induced by IFN gamma, whereas McAg is induced by lectin, probably acting on thyrocytes directly; and IFN gamma has an enhancing effect on LAG-induced thyrocyte McAg expression.     

1,25-Dihydroxyvitamin D3 antagonizes interferon-gamma-induced expression of class II major histocompatibility antigens on thyroid follicular and testicular Leydig cells

Interferon-gamma (IFN gamma) induces production and expression of major histocompatibility complex class II molecules on both marrow-derived and nonbone marrow-derived cell types. 1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3], a seco-steroid derived from vitamin D3, has previously been reported to enhance such expression alone or together with IFN gamma on a number of monocyte/macrophage tumorigenic lines. In contrast, the present studies have found that 1,25-(OH)2D3 inhibited the ability of IFN gamma to induce class II antigen expression on nontransformed rat thyroid follicular epithelial cells (FRTL-5) and mouse testicular Leydig cells (TM3). Although 1,25-(OH)2D3 inhibited the induction of both IA and IE class II locus products, IFN gamma augmentation of class I major histocompatibility complex antigens was not affected. 1,24-(OH)2D3 and 24,25-(OH)2D3 also inhibited class II induction by IFN gamma. Notably, the relative inhibitory ability of these compounds paralleled the strength of their binding affinities for the 1,25-(OH)2D3 receptor, indicating that this antagonistic effect probably requires receptor-ligand interaction. Other steroid hormones, such as hydrocortisone or testosterone, had no inhibitory effect on IFN gamma-induced class II expression on Leydig cells. Additionally, the failure of indomethacin to reverse the effect of 1,25-(OH)2D3 and the finding that exogenous prostaglandin E2 did not inhibit class II induction in these cells indicated that prostaglandins are probably not responsible for this anti-IFN gamma activity. In total, these results suggest that an endocrinological mediator is capable of inhibiting class II induction on resident endocrine tissue populations and, therefore, could help to diminish local CD4+ T-cell recognition of these cells.     

T-leukemia cell lines CCRF-CEM,HPB-ALL,JM and MOLT-4: Changes in isoenzyme profiles during induction of differentiation

Summary Biochemical analysis has been used to monitor the induction of differentiation in cultured human T-leukemia cell lines (CCRF-CEM, HPB-ALL, JM and MOLT-4) by the phorbolester 12-O-tetradecanoylphorbol 13-acetate (TPA). The isoenzymes of carboxylic esterase, acid phosphatase, hexosaminidase and lactate dehydrogenase were separated by isoelectric focusing on horizontal thin-layer polyacrylamide gels and stained by histo-cytochemical methods. TPA inhibited the proliferative activity in all four cell lines and led to aggregation of cells seen as floating clusters. TPA induced an increase in number and staining intensity of isoenzymes of all four enzymes in the cell lines studied. This corresponds to an induced isoenzymatic maturation as the progressive increase in number and staining intensity of the isoenzymes parallels the differentiation along the T-cell pathway. However, regardless of the initial stage of arrested differentiation, the cell lines could be induced only to differentiate to a certain more mature stage, but could not be triggered to differentiate terminally with regard to expression of isoenzyme patterns.     

Interferon-gamma-induced expression of tissue factor activity during human monocyte to macrophage maturation.

The expression of tissue factor (TF) during differentiation of human monocytes (MO) to macrophages (MAC) in vitro is investigated in this study. In MO, TF activity can be induced by the addition of lipopolysaccharides (LPS) as detected by Northern blot analysis and measured functionally as procoagulant activity (PCA), while IFN gamma alone has only marginal stimulatory activity. During in vitro differentiation of MO into MAC, however, there is a steady increase in IFN gamma-induced PCA with a maximum on day 7. While MO during the first 2 days in culture are more responsive to LPS, IFN gamma becomes the prominent stimulus for mature MAC. The response to IFN gamma is rapid with a peak within 6-8 h and a subsequent downregulation to baseline activity within 24 h. Our results demonstrate that IFN gamma can effectively induce TF in human MAC and that its expression is developmentally regulated during MO to MAC maturation in vitro.     

Interferon gamma encapsulated into liposomes enhances the activity of monocytes and natural killer cells and has antiproliferative effects on tumor cells in vitro

Summary The effects of human interferon gamma (IFN gamma) encapsulated into liposomes were investigated in vitro. Monocytes were induced to release a cytotoxic factor with either IFN gamma encapsulated into liposomes, free IFN gamma or lipopolysaccharide (LPS). If IFN gamma was applied in the liposomal form, less IFN activity was required to stimulate monocytes. Most of the cytotoxic factor was secreted during the first 4 h of stimulation. The cytotoxic factor in supernatants from PMNLs was completely neutralized by a monospecific polyclonal antiserum to tumor necrosis factor (TNF). Combining subthreshold doses of IFN gamma liposomes or IFN gamma with lipopolysaccharide synergistically enhanced the release of TNF. In fluorescence analysis, altered expression of the class II HLA-DR antigen on LeuM3 positive monocytes was induced with IFN gamma liposomes as well as with IFN gamma. Not only monocytes but also natural killer (NK) cells were stimulated to higher cytotoxicity by IFN gamma liposomes in a dose-dependent manner. In comparison with IFN gamma, the same amount of activity was necessary for adequate stimulation of NK-cells against the K562 target cells. Furthermore, the antiproliferative effects of IFN gamma liposomes and free IFN gamma on several human tumor cell lines was compared. Among several cell lines tested, U937 and A549 turned out to be sensitive to IFN gamma, and both cell lines reacted with 50% growth inhibition at a lower amount of gamma presented by liposomes than in the free form. These data show production of IFN gamma liposomes which possess immunmodulatory and antiproliferative activity in vitro. In several of the test systems studied, liposome-encapsulated IFN gamma was more effective than free IFN gamma.     

The expression and modulation of human myeloid-specific antigens during differentiation of the HL-60 cell line

Antigenic changes detected by myeloid-specific monoclonal antibodies on HL-60 cells induced to differentiate by various chemical mediators were investigated using flow cytometry. Antigen levels detected by monocyte- granulocyte-specific monoclonal antibodies AML-2-23, 61D3, and 63D3 increased dramatically after differentiation of HL-60 cells along the granulocytic pathway by the addition of dimethyl formamide (DMF), dimethylsulfoxide (DMSO), or cis-retinoic acid. The expression of these same antigens also increased in conjunction with monocytoid differentiation when HL-60 cells were treated with supernatants from leukocytes stimulated with phytohemagglutinin (PHA-LCM) or with mixed lymphocyte conditioned medium (MLC). In contrast, treatment of HL-60 cells with phorbol 12-myristate 13-acetate (PMA), which also induced differentiation along the monocyte pathway, had no effect on the expression of these monocyte-associated antigens. The expression of antigens on HL-60 cells recognized by the granulocyte-specified monoclonal antibodies PMN 6 and PMN 29 decreased after treatment of HL- 60 cells with PMA, but remained constant after treatment with DMF, DMSO, cis-retinoic acid, PHA-LCM, or MLC. These results suggest that normal myeloid differentiation may be dependent on various signals and that morphological and cell surface marker maturity may, under some conditions, be separable. The utility of the HL-60 cell line as a model of myeloid differentiation and for evaluation of inductive signals is discussed.     

Induced differentiation of HL-60 promyelocytic leukemia cells to monocyte/macrophages is inhibited by hydroquinone, a hematotoxic metabolite of benzene.

Chronic exposure of humans to benzene has been shown to have a cytotoxic effect on hematopoietic progenitor cells in intermediate stages of differentiation, which can lead to aplastic anemia and acute myelogenous leukemia. We studied the effect of hydroquinone (HQ), a toxic metabolite of benzene found in the bone marrow, on the human promyelocytic leukemia cell line (HL-60), which can be induced to differentiate to both monocyte and myeloid cells, and thus has been used as a surrogate for a granulocyte/macrophage progenitor cell. Exposure of HL-60 cells to noncytotoxic concentrations of HQ for 3 hours before induction with phorbol myristate acetate (TPA) caused a dose-dependent inhibition of the acquisition of characteristics of monocytic differentiation, such as adherence, nonspecific esterase (NSE) activity, and phagocytosis, but had no effect on cell proliferation. HQ appeared to be affecting maturation beyond the monoblast/promonocyte stages. HQ also prevented differentiation induced by 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]; however, the block occurred after the acquisition of adherence. HQ at concentrations that inhibited monocytic differentiation had no effect on differentiation to granulocytes, suggesting that the block in the differentiation of these bipotential cells is a step unique to the monocytic pathway. HQ was unable to prevent differentiation induced by the macrophage-derived cytokine, interleukin (IL)-1, a differentiation factor for cells of the monocytic lineage.     

High FUS/TLS expression in acute myeloid leukaemia samples

Retinoic acid has the ability to induce differentiation in some myeloid leukaemia cell lines and has been used to induce remission in acute promyelocytic leukaemia patients. We have analysed changes in gene expression, by differential display, in HL60 cells exposed to all-trans retinoic acid (ATRA) for only 1 h. Only about 0.4% of the genes examined by this technique showed changes in expression level, and all four of the gene fragments identified were downregulated during the short 1 h exposure. Two of the fragments were novel, a third was MYC and the fourth was the FUS proto-oncogene. Northern analysis showed that FUS was downregulated within 1 h only during induced neutrophil differentiation but not at all during induced monocyte differentiation. Unlike the sensitive cell lines, ATRA-resistant cell lines did not show a downregulation of FUS over a 24 h period of exposure to ATRA. Using a semiquantitative PCR analysis, no difference in FUS levels was observed between ATRA-sensitive and -resistant cell lines. A similar analysis was carried out on primary acute myeloid leukaemia (AML), peripheral stem cell harvests (PBSC) and cord blood samples. The PBSC and cord blood samples had FUS levels that were similar or generally less than the cell lines. However, much higher levels were seen in 63% of the AML samples examined. The data presented are consistent with previous reports for a role for FUS in the promotion and maintenance of cellular proliferation.     

Essential amino acid deprivation induces monocytic differentiation of the human HL-60 myeloid leukemia cell line

In this study we examine the effects of amino acid deprivation on the growth and differentiation of the human HL-60 myeloid leukemia cell line. The HL-60 cell line was chosen for study because of its ability to differentiate along either a granulocytic or monocytic pathway under appropriate culture conditions. Differentiation was determined by changes in cell morphology, nonspecific esterase (NSE) content, hydrogen peroxide (H2O2) production, and expression of the cell surface differentiation antigens LeuM3 (CD14) and OKM1 (CD11). Using a model system in which HL-60 cells were cultured in medium that selectively lacked one amino acid (AA), it was seen that deprivation of HL-60 cells for essential (but not nonessential) AAs results in decreased cell growth and viability and in differentiation of 30% to 60% of the surviving population of cells specifically along the monocytic pathway. This differentiation is irreversible as well as time- and dose- dependent. Culture of HL-60 cells in essential AA-deficient medium potentiated the differentiative effects of recombinant human interferon- gamma (IFN-gamma), recombinant human tumor necrosis factor (TNF), and dihydroxyvitamin D3 (D3), all of which have previously been shown to induce monocytic differentiation of HL-60 cells. Differentiated cells had decreased DNA and RNA synthesis, but protein synthesis was unchanged compared with control cells. The protein synthesis inhibitor cycloheximide prevented differentiation, indicating the necessity of protein synthesis in this process. Cell cycle analysis revealed that an increased proportion of cells cultured in AA-deficient medium was arrested in G0-G1 (80% and 50% for AA-deficient and control cells, respectively). These results suggest that alterations of AA metabolism and subsequent perturbations in DNA and RNA synthesis may be important in initiating differentiation or in augmenting cytokine-induced differentiation of HL-60 cells into more mature, nonreplicating, monocyte-like cells.     

Activities derived from established human myeloid cell lines reverse the suppression of cell line colony formation by lactoferrin and transferrin

Myeloid cell lines were evaluated for the release of substances needed for colony formation by their own colony-forming cells (CFC) and by other myeloid cell lines. Dialyzed U937 conditioned medium (CM) had no effect on the cloning efficiency of U937 cells, whether or not U937 CFC had been induced for MHC class-II antigens by preincubation of these cells for 72 h with indomethacin and human gamma interferon (HuIFN gamma). Dialyzed U937 CM, however, restored colony formation of HuIFN gamma-induced U937 cells suppressed by lactoferrin (LF) or transferrin (TF). Dialyzed U937 CM did not restore colony formation of U937 cells suppressed by acidic isoferritins (AIF) or prostaglandin E2 (PGE2). Detection of the growth-restoring effects of U937 CM required that U937 CM be prepared in the presence of indomethacin or that the CM be dialyzed to remove inhibitors of U937 colony formation. Dialyzed U937 CM did not inactivate LF. Dialyzed U937 CM did not stimulate or enhance colony formation of normal human bone marrow granulocyte-macrophage (CFU-GM), erythroid (BFU-E), or multipotential (CFU-GEMM) progenitor cells, but did contain potent inhibitory activity against these progenitor cells. HL-60, EM2, EM3, and K562 cells were also evaluated. HL-60-, EM3-, and K562-CFC that were not preincubated with HuIFN gamma did not express MHC class-II antigens, and colony formation by these cells was not influenced by LF, TF, or AIF. Noninduced EM2-CFC constitutively expressed MHC class-II antigens, and colony formation by these cells was suppressed by LF, TF, and AIF. After induction of MHC class-II antigens on HL-60- and EM3-CFC by HuIFN gamma, colony formation by these cells was suppressed by LF, TF, and AIF. Colony formation by HuIFN gamma-induced EM2 cells was more responsive to inhibition by LF, TF, and AIF than was colony formation by noninduced EM2 cells. K562 cells were not induced into a responsive state to LF, TF, or AIF by HuIFN gamma. Dialyzed CM from HL-60, EM2, and EM3 cells contained activities that restored colony formation by their own LF-suppressed CFC. The activities present in dialyzed CM from U937, HL-60, EM2, and EM3 cells may be similar since they could each restore LF-suppressed colony formation of U937, HL-60, EM2, or EM3 cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Early changes in phosphatidylcholine metabolism in human acute promyelocytic leukemia cells stimulated to differentiate by phorbol ester

The HL-60 leukemia cell line derived from a human acute promyelocytic leukemia is stimulated to differentiate into macrophages within 24-28 hr after exposure to the phorbol ester, 12-O-tetradecanoylphorbol-13- acetate (TPA). We studied early alterations (within 90 min of exposure to TPA) in phosphatidylcholine metabolism in HL-60 cells and found that phosphatidylcholine synthesis by methylation is phosphatidylethanolamine was inhibited in a dose-dependent fashion. In contrast, synthesis of phosphatidylcholine from endogenous choline was enhanced and correlated inversely with the degree of inhibition of the methylation pathway. Phorbol ester congeners of TPA caused similar alterations in phosphatidylcholine metabolism in direct relationship to their capacity to induce differentiation in HL-60 cells. Perturbation of phosphatidylcholine metabolism is an early membrane even in TPA- induced HL-60 cell differentiation.