Control of cell differentiation during proliferation. I. Monocytic differentiation of HL-60 promyelocytes

Biochemical characteristics of a human myeloid leukemia cell differentiation factor

A human lymphocyte-derived maturation-inducing activity, which mediates the differentiation of human myeloid leukemia cells HL-60 to monocytic cells, was purified and characterized. The maturation inducer is a single polypeptide with a molecular mass of 54,300 Daltons. A Pl range of 8.0-8.5 was determined along with the amino acid composition of the inducer. In cell cultures, the purified inducer mediated a growth reduction and a differentiation of leukemia cells to mature monocytes-macrophages, possessing complement receptors and phagocytic capacity.

Expression of intermediate filament proteins in TPA-induced MPC-11 and HL-60 cells

Under normal culture conditions, the tumor cell lines MPC-11 and HL-60 exhibit high rates of proliferation and show a peculiar expression of intermediate filament proteins as they appear to synthesize only lamin B. A 48-h exposure of murine plasmacytomas MPC-11 to the phorbol ester TPA reduces their growth and induces vimentin synthesis without affecting the composition of their nuclear lamina. When applied to human leukemic promyelocytes HL-60, such treatment promotes their maturation into macrophage-like cells: their proliferative ability is suppressed, a differentiated phenotype is developed, and their content in intermediate filament proteins now includes vimentin and a full complement of lamins A, B, and C. In the present study, a kinetic analysis of vimentin and lamin A/C expression in relation to proliferation and differentiation has been performed in these two cellular systems. Proliferation rates of MPC-11 and HL-60 populations were evaluated by monitoring cell growth and measuring thymidine incorporation. Maturation of HL-60 cells was assessed by Giemsa staining and percentage of adherent cells. Expression of vimentin and lamins A/C was analyzed using immunofluorescence and immunoblotting techniques. Our data show that there is a relationship between the level of vimentin expression and the extent of growth inhibition in both systems. They also suggest that the expression of lamins A/C during the TPA-induced maturation of HL-60 promyelocytes might be part of the processes which lock these cells into the macrophage pathway.

Improved coupling between proliferation-arrest and differentiation-induction in ML-1 human myeloblastic leukemia cells

Proliferation and differentiation are coupled in normal cells and are aberrant in leukemia cells. The studies reported here were aimed at more effectively coupling proliferation-arrest and differentiation-induction in a human myeloblastic leukemia cell line (ML-1). This was accomplished by using reduced serum conditions in conjunction with a differentiation-inducing agent: cells were first incubated in reduced serum [0.3% fetal bovine serum (FBS)] instead of standard conditions (7.5% FBS) and, second, exposed to 12-O-tetradecanoylphorbol-13-acetate (TPA). The effects of this protocol were as follows: first, cell proliferation was slowed and cells accumulated in G0/G1 phase of the cell cycle; this occurred with only a minimal decrease in viability [to approximately 88-92% (0.3% FBS) from greater than or equal to 96% (7.5% FBS)]. Second, the induction of differentiation was accelerated; this allowed the time of exposure to TPA to be decreased. Acceleration of induction was very pronounced when cells were maintained in 0.3% FBS both before and during exposure to TPA, with TPA at concentrations above the minimum sufficient for induction but below those causing significant cytotoxicity; as little as 1 hour of TPA exposure resulted in near-maximal induction (approximately 80%) with this protocol, compared to the greater than or equal to 1 day required with previous standard protocols. In sum, conditions that slow ML-1 cell proliferation (0.3% FBS) enhance TPA-induced differentiation, substantially narrowing the time frame of induction; these conditions should be useful for studying the molecular mechanisms that underlie the induction process.

Induction of differentiation of HL-60 cells by protein kinase C inhibitor, K252a

To clarify the role of protein kinase C and protein kinase A in cell proliferation and differentiation, the effects of K252a and its derivatives (K252b, KT5720), which have different inhibitory activity to these protein kinases, on the proliferation and differentiation of HL-60 cells were investigated. The proliferation and DNA synthesis of the HL-60 cells were inhibited by K252a in a dose dependent manner. However, K252b and KT5720 which are more specific inhibitors of protein kinase C or protein kinase A, respectively, had no observable effect on cell proliferation. K252a (40nM) enhanced the differentiation of HL-60 cells induced by 1,25(OH)2D3, retinoic acid and DMSO. K252b and KT5720 did not affect 1,25(OH)2D3-induced differentiation. K252a significantly inhibited the differentiation induced by PMA. These results demonstrate that K252a but not its derivatives can function as an antitumor drug and enhancer of the differentiation induced by various inducers.

Mechanism of regulating human leukemia cell growth and differentiation by a lymphokine

Human myelogenous leukemia cells can be induced to differentiate in vitro along the monocyte-macrophage pathway by a T cell lymphokine maturation inducer. Maturation inducer has now been purified from a human T cell line and determined to be a single chain protein with an approximate molecular weight of 53,500. It induces the differentiation and proliferation of human leukemic HL-60 promyelocytes in a dosage-dependent fashion. Initial interaction with cells at G1 phase induced the cells to enter proliferating S phase. Subsequent differentiation from S phase was dependent on an optimal inducer quantity (18.7 pM - 18.7 nM) which mediated growth cessation and termination differentiation to monocytes-macrophages. When inducer quantity was more or less than this optimal range, the cells did not undergo differentiation but were continuously stimulated to proliferate. This may represent an important proliferation mechanism of leukemic cells.

Effects of simultaneous and sequential exposure to granulocytic and monocytic inducers on the choice of differentiation pathway in HL-60 promyelocytic leukemia cells

HL-60 promyelocytic leukemic cells were induced to differentiate by the combination of two alternative inducers: phorbol-12-myristate 13-acetate (PMA) and either dimethyl sulfoxide (DMSO) or retinoic acid (RA). Simultaneous exposure to optimal concentrations of PMA and either DMSO or RA potentiated PMA-induced differentiation into monocyte-macrophages. Granulocytic inducers combined with lower concentration of PMA competed with the latter for the differentiation pathway, producing monocyte-macrophages, granulocytes, paramyeloid and giant multinucleated cells. Lineage specificity of cells treated sequentially with two discrete exposures to alternative inducers depended on the order of exposure. The first exposure initiated differentiation into the pathway specific for the inducer used. The second exposure determined lineage specificity and stimulated terminal differentiation. Thus, treatment with RA for 24-72 h followed by PMA resulted in monocyte-macrophage differentiation; reversed order of exposure resulted in granulocytic differentiation. The switch in the differentiation pathway occurred at the relatively advanced stages of differentiation.

Induction of differentiation of mouse myeloid leukemia M1 cells by serum of patients with chronic myeloid leukemia

We examined the capacities of sera from patients with myeloid leukemia to induce differentiation in mouse myeloid leukemic M1 cells. Higher differentiation-inducing activity (D-activity) was detected in sera of patients with chronic myelomonocytic leukemia or chronic myeloid leukemia (CML) than in sera of patients with acute myeloid leukemia and normal volunteers. The D-activity in the sera was lost on heating the sera at 56 degrees for 30 min. The major peak of D-activity on Sephadex G-200 gel filtration had an apparent molecular weight of 160,000. The origin of the D-activity in sera of patients with CML was studied by culturing fractions of peripheral blood cells of patients with D-activity for 3 days and then measuring the ability of the conditioned medium (CM) to induce differentiation of M1 cells. The cells in the myeloblast and promyelocyte fraction differentiated spontaneously into macrophage-like cells during culture for 3 days and the cells in the late granulopoietic cell fraction differentiated into neutrophil-like cells. Higher D-activity was present in CM of cells in the myeloblast and promyelocyte fraction than in CMs of late granulopoietic cell fractions. These results suggest that human leukemic cells produce D-activity for M1 cells during their differentiation into macrophage-like cells.

Modulation of the transferrin receptor during DMSO-induced differentiation in HL-60 cells

When HL-60 cells are induced to differentiate by dimethyl sulfoxide along a granulocytic pathway there is a fivefold decrease in the total number of transferrin receptors within 3 days, as compared to untreated cells. This decrease is due primarily to a rapid decline in the synthesis of the receptor rather than an increase in the degradation of the receptor. The decrease in transferrin receptor synthesis is a specific and early event that precedes the cessation of cell proliferation, differentiation, and the decrease in total protein synthesis.

Induction of HL-60 monocytic cell differentiation promoted by a perturbation of DNA synthesis: hydroxyurea promotes action of TPA

Control of terminal cell differentiation was studied using the human promyelocytic leukemia cell line, HL-60. HL-60 cells are known to undergo terminal monocytic differentiation when continuously exposed to 1.6 nM tetradecanoylphorbol acetate (TPA). The dose-response relationship between TPA concentration and induced differentiation is relatively steep. TPA (1.1 nM) induces little G1/0 specific growth inhibition or phenotypic differentiation. In contrast, pretreating the cells with a pulse exposure to hydroxyurea promotes their capability to terminally differentiate in response to TPA. Initially exponentially proliferating cells exposed for 20 h, approximately one doubling time, to 0.3 mM hydroxyurea, a subcytotoxic dose, underwent rapid G1/0 specific growth arrest and cell differentiation in response to subsequent exposure to 1.1 nM TPA. The extent of terminal differentiation was comparable to that induced by 1.6 nM TPA. The results support the hypothesis that early events in induction of terminal HL-60 cell differentiation depend on an S phase-specific process which may involve gene amplification.

Differentiation induction in myelodysplasia and acute myeloid leukaemia: use of synergistic drug combinations

DNA synthesis inhibitors and vincristine greatly enhance the response of leukaemic and dysplastic cells to differentiation inducing agents such as retinoic acid (RET). Differentiation induction therapy is an attractive therapeutic approach in myelodysplasia (MDS) and in acute myeloid leukaemia (AML) in the elderly, since it should be possible to increase the production of mature cells, at the expense of precursor cells, without incurring the complications of intensive cytotoxic therapy. Single agent differentiation therapy has, however, not been highly successful. We have therefore investigated the use of synergistic combinations of agents. We treated nine patients (6 with MDS, 3 with AML) with 13-cis-retinoic acid (up to 100 mg/m2/day) in combination with either 6-thioguanine (20-40 mg/day in 14-57 day courses) or with vincristine (1-2 mg as a single injection during a four-day course of RET). Seven patients responded with an increase in the mature cells of at least one haemopoietic lineage. A concomitant decrease in marrow blasts was observed in 3/4 responding patients. The retention of dysplastic and karyotypic abnormalities and lack of a hypoplastic phase all suggested that differentiation induction was occurring in vivo. Prior failure to respond to therapy with single agents (RET in two and cytosine arabinoside in five patients) suggests that the synergy observed in vitro operates in vivo. In-vitro studies on marrow cells from seven patients demonstrated synergistic differentiation induction in 6/7 samples. The seventh patient was one of the two who did not respond clinically. The second of these clinically unresponsive patients had cells which were relatively refractory to RET in vitro, suggesting that in-vivo and in-vitro responses may be related.

Control of HL-60 monocytic differentiation. Different pathways and uncoupled expression of differentiation markers

Control of expression of the terminally differentiated phenotype was studied using the human promyelocytic leukemia cell line HL-60. Three known inducers of HL-60 monocytic differentiation were compared: 1,25-dihydroxy vitamin D3, tetradecanoylphorbol acetate (TPA), and sodium butyrate. At concentrations where all three inducers resulted in similar courses of G1/0-specific growth arrest, the kinetics of appearance of certain differentiation markers typically characteristic of mature monocytic cells was determined. The markers were inducible oxidative metabolism, non-specific esterase activity, and the cell surface determinants Mo1, My4, and Mo2. The results indicate that: Regulation of the expression of these markers during induced monocytic differentiation is not controlled in common. The three monocytic inducers do not induce the same metabolic cascade leading to differentiation. Similar states of differentiation could thus be reached by different pathways apparently due to the fact that control of expression of different differentiation markers was not tightly coupled.

Tumor necrosis factor and lymphotoxin induce differentiation of human myeloid cell lines in synergy with immune interferon

We show that the cytotoxins tumor necrosis factor (TNF) or lymphotoxin (LT), at concentrations of approximately 10(-11) M induce monocytic differentiation of human myeloid cell lines. After 5 d of culture in the presence of rTNF and LT, a significant proportion of the myeloid cell lines express monocyte differentiation antigens and ANAE activity, and become able to reduce nitroblue tetrazolium (NBT) and mediate low levels of ADCC against tumor target cells. These markers of differentiation, however, are maximally induced when rIFN-gamma, at concentrations as low as 4 U/ml, is present simultaneously with the cytotoxins, and the two classes of cytokines act synergistically to induce terminal differentiation. The appearance of monocytic antigens is accompanied by acquisition of morphology and other functional properties of mature monocytic cells, such as chemiluminescence and phagocytosis, and by expression of FcR for monomeric IgG. A decrease in cell proliferation accompanies induced differentiation, and is not due to the cytotoxic properties of TNF or LT, as indicated in simultaneous analysis of surface phenotype and cell cycle. The lack of cytotoxicity of TNF on the HL-60 cell line is also demonstrated by the enhancing effect of TNF on HL-60 cell growth and nucleoside uptake in the first 2 d of culture. These data show that the cytotoxins TNF and LT mediate complex effects on cells of the myelomonocytic lineage and, in synergy with IFN-gamma, can fully induce immature myeloid cells to differentiate into cells with phenotypic, functional, and proliferative characteristics of terminally differentiated myelomonocytic cells.

Cell cycle dependence of calmodulin levels during HL-60 proliferation and myeloid differentiation. No changes during pre-commitment

The putative role of Ca2+ and calmodulin in regulating cell proliferation and differentiation was tested in HL-60 human promyelocytic leukemia cells. The dependence of retinoic acid (RA)-induced terminal myeloid differentiation of HL-60 promyelocytic leukemia cells on calmodulin levels and calcium ion flux was ascertained. RA-treated and untreated control cells were stained for cellular DNA with a Hoechst dye. Populations of G1/0, S and G2 + M phase cells were isolated by fluorescence activated cell sorting (FACS). Cytosolic calmodulin levels were then measured as a function of cell cycle phase for RA-treated and untreated cells using a radioimmunoassay. RA-treated cells were measured at early times, corresponding to the pre-commitment state, and late times, when significant cell differentiation had occurred. Cellular calmodulin levels increased with progression through the cell cycle. In contrast, no difference in calmodulin levels was observed between RA-untreated or -treated cells in the same cell cycle phases at early or late times. RA-induced HL-60 terminal myeloid differentiation was thus apparently not regulated by cellular cytosolic calmodulin levels. These conclusions were supported by the effects of calmodulin antagonists and calcium flux inhibitors. The calmodulin antagonists trifluoperazine and compound 48/80 both retarded cell growth in a concentration-dependent manner. But at concentrations where cellular effect was evidenced by slight growth inhibition, neither antagonist inhibited RA-induced cell differentiation or G1/0 growth arrest. The same was true of the gated calcium channel inhibitors, verapamil and nitrendipene, and the passive calcium flux inhibitor, CoCl2. RA-induced HL-60 cell differentiation and arrest in G0 was thus apparently not strongly dependent on cellular calmodulin levels or calcium flux. This is in strong contrast to murine erythroleukemia cells. The results argue against a central regulatory role for calmodulin or calcium flux in control of HL-60 growth arrest or differentiation.

Cell-cycle differences of HL-60 leukemia cells fractionated by centrifugal elutriation

HL-60 leukemia cells were fractionated into G1 and S/G2 populations using a rapid centrifugal elutriation technique, and studied for differences between the cell-cycle phases. The G1 fraction was found to contain smaller cells with a sedimentation velocity of 7 mm/h. The S/G2 fraction consisted of larger cells with a sedimentation velocity of 125 mm/h. The latter fraction was found to have a peak level of the enzyme (2'-5')An-binding protein, as compared to the G1 fraction, indicating a possible role for (2'-5')An-binding protein and its products in the growth regulation of these leukemic cells. In addition, cytofluorometric analysis of fractionated HL-60 cells indicates that elutriation is an effective fractionation method, rapidly yielding large numbers of cells for study, without the use of chemical treatments.

Human leukemia cell maturation induced by a T-cell lymphokine isolated from medium conditioned by normal lymphocytes

Human myelogeneous leukemia cells in liquid culture can be induced to mature along the monocyte/macrophage pathway by a maturation inducer derived from the conditioned medium of activated human T lymphocytes. Serum-free conditioned medium was used for the isolation of the T-cell lymphokine. The maturation inducer was purified approximately equal to 6000-fold by ammonium sulfate precipitation, low-salt elution from DEAE-Sepharose CL-6B, gel filtration on Bio-Gel A-0.5m, and NaDodSO4/PAGE under nonreducing conditions. The molecular weight of the maturation inducer was 36,000-58,000 on NaDodSO4/PAGE. Terminal differentiation associated with inhibition of leukemia cell proliferation and expression of mature cell properties was observed with the isolated maturation inducer, identical to the activity observed with the unfractionated conditioned medium. Cell-cycle analysis revealed that the proportion of replicating S-phase cells was reduced from 40% to 7% after initial interaction of the maturation inducer with cells. The differentiating cells simultaneously acquired monocyte antigen, membrane complement receptors, phagocytic function, and monocyte/macrophage morphology. The maturation-inducing activity is dose-dependent, with more inducer causing the development of more mature cells in a shorter time period. The maturation inducer was shown to be stable after pH 2 treatment, independent of interleukin 2 and colony-stimulating factor, devoid of alpha-, beta-, and gamma-interferon, and not affected by antibody to interferon. The maturation inducer may play a role as a physiological regulator of monocytic and leukemia cell development.

Control of HL-60 myeloid differentiation. Evidence of uncoupled growth and differentiation control, S-phase specificity, and two-step regulation

Myeloid differentiation of HL-60 human promyelocytic leukemia cells was studied during DMSO-induced differentiation. G 1/0-specific growth arrest could occur without the usual associated subsequent phenotypic differentiation into mature myeloid cells, suggesting that growth arrest and phenotypic differentiation are separately regulated. In the course of differentiating, the cells achieved a semi-stable intermediate state where they had a labile, pre-commitment memory of exposure to inducer, but were not yet committed to differentiation. This state was associated with a nuclear structural change previously found to be associated with the precommitment memory state. The process of differentiation could thus be resolved into two steps, early events up through development of pre-commitment memory and late events subsequents to pre-commitment memory. The kinetics of terminal cell differentiation indicated that the cellular regulatory event initiating a program of differentiation in response to inducer was S phase-specific. A comparison of the present results for DSMO to previous results for retinoic acid (RA)-induced HL-60 myeloid differentiation showed that the two inducers effect different cellular pathways for differentiation of HL-60 cells to mature myeloid cells, but with certain common features including the above S-phase specificity and pre-commitment memory.

Synergistic interaction between differentiation inducers and DNA synthesis inhibitors: a new approach to differentiation induction in myelodysplasia and acute myeloid leukaemia

Numerous agents induce differentiation and maturation of neoplastic and dysplastic myeloid cells in vitro and some of these agents have been used with limited success in the treatment of patients with myelodysplastic syndromes (MDS) and myeloid leukaemias. We recently proposed that physiological and pharmacological agents which enhance differentiation and maturation in vitro act by two fundamentally different routes: (1) by hastening the progression through various differentiation/maturation steps; (2) by slowing proliferation (usually by inhibition of DNA synthesis). In order to test this thesis we looked for synergistic effects on differentiation using pairs of agents from the two groups in cultures of cells from myelodysplastic and acute myeloid leukaemia (AML) patients and from normal marrow donors. The results with three MDS, two AML and three normal samples show that combinations of differentiation inducing agents (retinoic acid, N-methylformamide) with DNA synthesis inhibitors (6-mercaptopurine, cytosine arabinoside and aphidicolin) produce a differentiation inducing effect equivalent to that of 10-100, or even 1000 fold higher concentrations of single agents. Myelotoxic effects in vitro were not synergistic. The use of these synergistic combinations should greatly enhance the usefulness of differentiation inducers in the therapy of MDS and myeloid leukaemia.

Control of cell differentiation during proliferation. II. Myeloid differentiation and cell cycle arrest of HL-60 promyelocytes preceded by nuclear structural changes

The time-dependent dynamics of nuclear structure, cell cycle transit and arrest, and cellular differentiation were studied using the human promyelocytic leukemia cell line HL-60. Myeloid differentiation of HL-60 cells was induced by 10(-6) M beta, all trans, retinoic acid (RA). During exponential growth the cells had G1, S, G2 and M durations of 9, 11, 0.5 and 0.5 h respectively. Significant growth arrest in the G1/0 phase of the cell cycle was apparent after 48 h of RA exposure or after two division cycles. Thereafter, cells arrested in G1/0 with wide dispersion in times of arrest which extended over several cell cycle generation times. The kinetics of phenotypic differentiation, detected by phorbol myristate acetate inducible superoxide production, paralleled those of G1/0 growth arrest with similar lag and dispersion. These kinetics are consistent with a model hypothesizing the existence of an S-phase differentiation control (DC) point regulating both terminal proliferation and differentiation. Before any cell differentiation or termination of cell proliferation occurred, the nuclei of RA-treated cells underwent a structural change detected by narrow-angle light scatter measured with flow cytometry. Narrow-angle light scatter was transiently reduced, reaching a nadir at 24-48 h and returning to control values at 96 h. This change was independent of cell cycle phase or total nuclear protein content. It was associated with a morphological change of the nuclear membrane from a smooth to dimpled or pitted structure. These findings focus attention on the potential significance of nuclear structural reorganization as an early event during cell differentiation.

Membrane origin for a signal eliciting a program of cell differentiation

Evidence is presented to indicate that the retiNOic acid (RA)-induced program of myeloid differentiation and growth arrest by HL-60 human promyelocytic leukemia cells was initiated by a signal originating at the cell membrane. Free RA and RA covalently immobilized on a solid substrate elicited similar kinetics of differentiation and G1/0-specific growth arrest. No evidence of cell-induced RA detachment from the solid substrate was found. The data explain why HL-60 cells which are deficient in cellular RA-binding protein (CRABP) nevertheless respond to RA.

Dependence of HL-60 myeloid cell differentiation on continuous and split retinoic acid exposures: precommitment memory associated with altered nuclear structure

The cell differentiation of HL-60 human leukemic promyelocytes along the myeloid pathway due to various continuous and distributed exposures to retinoic acid was studied. HL-60 myeloid differentiation was a continuously driven process; significant terminal cell differentiation occurred only after a minimum exposure to inducer of two division cycles. Cells so committed to differentiation retained a heritable, finite memory of differentiation commitment over a further division cycle. Prior to becoming committed, cells acquired precommitment memory of exposure to inducer. Precommitment memory abbreviated the subsequent exposure to inducer needed for commitment to differentiation. Precommitment memory was semistable. It was heritable, but was lost after four division cycles. The acquisition and loss of precommitment memory correlated with alterations in nuclear architecture detected by narrow angle light scatter using flow cytometry. The altered nuclear architecture first occurred before any overt cell differentiation or growth arrest. It was thus an early event in the induced program of terminal cell differentiation. Alterations in relative abundances of cytoplasmic proteins also occurred prior to overt cell differentiation or growth arrest. One of these was a 17 kdalton, anionic, probably Ca2+ binding, protein. Retinoic acid thus induced early cellular changes, including cytoplasmic and nuclear alterations, within one cell cycle when cell differentiation was not yet apparent.