Human Myeloblastic Leukemia ML-1 Cells Research Articles

Synergistic induction of gene expression during the differentiation into mature macrophage in human myeloblastic leukemia cells treated with TPA and KH1060

Treatment of human myeloblastic leukemia ML-1 cells with the phorbol ester TPA in combination with the vitamin D 3 analogue KH1060 will induce a synergistic differentiation to mature macrophage with multinuclei. To investigate the mechanism underlying this differentiation and the synergistic effect, a cDNA microarray and Northern blot analysis were used to examine gene expression profiles of ML-1 cells treated with TPA and/or KH1060. Results show that KH1060 enhanced several TPA-induced gene expressions and that TPA enhanced several KH1060-induced gene expressions. Studies with inhibitors of signaling molecules suggested that PKC and MAPK pathways play an important role in the differentiation induced by TPA and KH1060, and that they are associated with the synergistic induction of genes. The results of this study indicate the possibility that the expression of various genes are induced synergistically by cross-talk between TPA and KH1060 signals. It is likely that the synergistic effect on gene expression leads to the synergistic induction of differentiation by both reagents.

N-terminal Truncation of Antiapoptotic MCL1, but Not G2/M-induced Phosphorylation, Is Associated with Stabilization and Abundant Expression in Tumor Cells

The antiapoptotic BCL2 family member MCL1 is normally up- and down-modulated in response to environmental signals and conditions, but is constitutively expressed in cancer where it promotes cell survival and drug resistance. A post-translational modification identified here, truncation at the N terminus, was found to act along with previously described ERK- and GSK3-induced phosphorylation events to regulate the turnover of the MCL1 protein and thus its availability for antiapoptotic effects. Although both N-terminally truncated and full-length MCL1 contain sequences enriched in proline, glutamic acid, serine, and threonine and were susceptible to proteasomal degradation, the truncated form decayed less rapidly and was maintained for an extended period in the presence of ERK activation. This was associated with extended cell survival because the truncated form of MCL1 (unlike those of BCL2 and BCLX) retained antiapoptotic activity. N-terminal truncation slightly increased the electrophoretic mobility of MCL1 and differed from the phosphorylation/band shift to decreased mobility, which occurs in the G2/M phase and was not found to affect MCL1 turnover. The N-terminally truncated form of MCL1 was expressed to varying extents in normal lymphoid tissues and was the predominant form present in lymphomas from transgenic mice and human tumor lines of B-lymphoid origin. The degradation versus stabilized expression of antiapoptotic MCL1 is thus controlled by N-terminal truncation as well as by ERK- and GSK3 (but not G2/M)-induced phosphorylation. These modifications may contribute to dysregulated MCL1 expression in cancer and represent targets for promoting its degradation to enhance tumor cell death.

Granulocyte macrophage colony-stimulating factor enhances retinoic acid-induced gene expression

We reported previously that treatment of human myeloblastic leukemia ML-1 cells with all-trans retinoic acid (ATRA) in combination with GM-CSF enhances the granulocytic differentiation, which is induced only slightly by ATRA alone. To investigate the mechanism underlying this differentiation and the synergistic effect of ATRA and GM-CSF, we used cDNA microarray to examine gene expression profiles of ML-1 cells treated with ATRA and/or GM-CSF. We identified 22 up-regulated genes in ML-1 cells treated with both reagents and examined the expression of these genes in cells treated with ATRA and/or GM-CSF by Northern blot analysis. Comparison of cells treated with both reagents and cells treated with ATRA or GM-CSF alone revealed that expression of nine of the 19 genes was induced synergistically by combined treatment with ATRA and GM-CSF. Expression of most of these genes was increased only slightly by ATRA alone, and this induction was enhanced by the addition of GM-CSF. These results indicate that GM-CSF enhances ATRA-induced gene expression. Moreover, studies with inhibitors of signaling molecules suggested that activation of JAK2 is associated with the synergistic induction of several genes by ATRA and GM-CSF. JAK2 inhibitor suppressed induction of NBT-reducing activity in ML-1 cells treated with both reagents. It is likely that the enhancer effect of GM-CSF on ATRA-induced gene expression leads to the differentiation induced synergistically by ATRA combined with GM-CSF. Further studies of the mechanism underlying this effect may identify better approaches for the treatment of RA-insensitive leukemia.

Comprehensive search for X-ray-responsive elements and binding factors in the regulatory region of the GADD45a gene.

The growth arrest and DNA damage-inducible protein 45alpha (GADD45a) gene is responsive to a variety of DNA-damaging agents. It is known that induction of the GADD45a gene is regulated in a p53-dependent manner after ionizing irradiation. Our previous study showed that X-ray irradiation increased the transcription rate of the GADD45a gene much earlier than the maximum accumulation of stabilized p53 protein in human myeloblastic leukemia ML-1 cells. We hypothesized that some transcription factor(s) may cooperate with p53 in regulating the GADD45a gene early after the irradiation of ML-1 cells. This idea is supported by recent studies showing that the p53-dependent activation of several genes in human and mouse cells requires some additional transcription factors, such as Sp1, GKLF, Ets1, and IRF-1. To examine the possible involvement of cooperating factors in transcriptional regulation of the GADD45a gene by ionizing radiation, we comprehensively searched for the X-ray-inducible binding locus of the nuclear factor throughout the upstream region (-2244 bp/+89 bp) and the third intron (+1389 bp/+2488 bp) of the GADD45a gene by EMSA using 136 probes. The X-ray-responsive binding of nuclear factors was detected at eight loci. Oct, NF-kappaB, HNF, NF-AT, and KLF family transcription factors were identified by a competition assay. It is possible that some of these factors cooperate with p53 to mediate transcriptional regulation of the GADD45a gene after ionizing irradiation.

GM-CSF induces expression of gp91phox and stimulates retinoic acid-induced p47phox expression in human myeloblastic leukemia cells.

All-trans retinoic acid (ATRA) combined with granulocyte macrophage colony-stimulating factor (GM-CSF) synergistically increases superoxide-generating activity in human myeloblastic leukemia ML-1 cells. ATRA is known to increase the expression of some NADPH components; however, little is known about the effect of GM-CSF on the expression of these components. We examined the expression of NADPH oxidase components in ML-1 cells treated with ATRA, GM-CSF, or a combination of ATRA and GM-CSF. Expression of p47phox and gp91phox proteins increased markedly after treatment with both reagents. p47phox expression was increased by ATRA alone, and the expression was increased synergistically by the combination of ATRA with GM-CSF. gp91phox was increased by ATRA or GM-CSF alone. The expression of p47phox and gp91phox mRNA underwent similar changes to those seen in protein level. These results indicate that GM-CSF induces expression of gp91phox and enhances ATRA-induced p47phox expression. We speculate that the remarkable induction of gp91phox and p47phox protein is associated with an increase in superoxide-generating activity due to the synergistic effect of ATRA plus GM-CSF.

Involvement of diverse protein kinase C isoforms in the differentiation of ML-1 human myeloblastic leukemia cells induced by the vitamin D 3 analogue KH1060 and the phorbol ester TPA

We reported previously that diverse combination of the vitamin D 3 analogue KH1060 together with 12- O-tetradecanoylphorbol-13-acetate (TPA) synergistically induces the differentiation of ML-1 cells into mature macrophages. To investigate the mechanism involved in their interaction, we examined the role of protein kinase C (PKC) in the differentiation of ML-1 cells to mature macrophages. We found that the specific PKC inhibitor GF109203 suppressed the morphological change and the α-naphthyl acetate esterase activity induced in ML-1 cells by treatment with KH1060 plus TPA. This treatment increased the translocation of PKCα, PKCε, and PKCθ from cytosol to membranes. ML-1 cells treated with KH1060 alone increased translocation of PKCθ, whereas cells treated with TPA alone increased translocation of PKCα and PKCε. These data showed that in human myeloblastic leukemia cells, diverse isoforms of PKC, including PKCα, ε, and θ, participate in the regulation of cell differentiation.

Cellular pharmacokinetics and pharmacodynamics of the deoxycytidine analog 2′-C-cyano-2′-deoxy-1-β-d-arabino-pentofuranosylcytosine (CNDAC)

The pharmacokinetics and pharmacodynamics of the novel clinical candidate 2′-C-cyano-2′-deoxy-1-β-d-arabino-pentofuranosylcytosine (CNDAC) were investigated in human lymphoblastoid CCRF-CEM cells and human myeloblastic leukemia ML-1 cells. Formation of CNDAC 5′-mono-, di-, and triphosphate (CNDACTP) was concentration-dependent; nucleotide accumulation was greater in the lymphoid cells than in the myeloid cells. The nucleotides were eliminated with linear kinetics from both lines, but were retained more effectively by the ML-1 cells. DNA synthesis was selectively inhibited by a 4-hr treatment with CNDAC in CCRF-CEM and ML-1 cells; the ic50 values were 1 and 0.8 μM, respectively. Evaluation of the polymerization reaction of a primer on an M13mp19(+) template by human DNA polymerase α indicated that CNDACTP was incorporated effectively (Km = 0.22 μM) opposite a complementary dGMP in the template strand. CNDACTP competed with the normal substrate, dCTP, for incorporation, and the two nucleotides showed similar substrate efficiencies (Vmax/Km: dCTP = 0.91; CNDACTP = 0.77). Primer extension was potently inhibited by CNDAC triphosphate (Ki = 23 nM); once the analog had been incorporated, further extension was not observed in vitro, suggesting that primers containing a 3′-terminal nucleotide analog were high Km substrates for polymerase α. Thus, the ability of human leukemia cells to effectively accumulate and retain CNDACTP, coupled with the favorable kinetics of competition for incorporation into DNA, and the relatively strong ability of the analog to terminate further extension, are likely to contribute to the cytotoxic action of CNDAC.

NF-κB (p65/RelA) as a regulator of TNFα-mediated ML-1 cell differentiation

ML-1 human myeloblastic leukemia cells, suspended in serum-depleted medium, proliferate when the insulin-like growth factor-1 (IGF-1) and transferrin (Tf) are supplied, but differentiate to monocytes when these factors are replaced by the tumor necrosis factor-alpha (TNF-alpha). Induction of differentiation, but not of proliferation, involved the selective activation of diverse members of the NF-kappaB family of proteins. In differentiation-induced cells, NF-kappaB (p65) was translocated from the cytoplasm to the nucleus, whereas NF-kappaB (p75) remained localized to the cytoplasm. In contrast, NF-kappaB (p52) was present in the nuclei of proliferation- as well as of differentiation-induced ML-1 cells. The differentiation-specific translocation of NF-kappaB (p65) from the cytoplasm to the nucleus was mediated by an increase in the level of NIK, the NF-kappaB-inducing kinase which, through phosphorylation of IkappaB kinase alpha (Ikappakalpha), causes a decrease in the level of IkappaBalpha, allowing p65 to move from the cytoplasm to the nucleus. The p52/p65 heterodimer formed in the nucleus, bound specifically to the promoter of the tumor suppressor protein p53, effecting a 25 to 30-fold increase in the level of this protein. As we reported previously (Li et al, Cancer Res 1998; 58: 4282-4287), that increase led to the decreased expression of proliferating cell nuclear antigen (PCNA) and to the loss of proliferation-associated DNA synthesis. The ensuing uncoupling of growth from differentiation was followed by the initiation of the monocyte-specific differentiation program.

Complex regulation of CDKs and G1 arrest during the granulocytic differentiation of human myeloblastic leukemia ML-1 cells.

We previously reported that all-trans retinoic acid (ATRA) and granulocyte-macrophage colony-stimulating factor (GM-CSF) synergistically induced granulocytic differentiation in human myeloblastic leukemia ML-1 cells. The combination of these agents also suppressed DNA-synthesis. In the present study, we investigated the suppression of cyclin dependent kinase (CDK) activities resulting in G1 arrest in differentiated ML-1 cells. We show that treatment of ML-1 cells with ATRA plus GMCSF results in G1 arrest and suppression of CDK activities. Protein levels of the G1 CDKs were essentially unchanged during this time. However, we observed an increase in CDK2-bound p27 and CDK4-bound p18, and a decrease in CDK6-bound cyclin D3. These results suggest that complex regulation of CDKs play a key role in G1 arrest of ML-1 after treatment with ATRA and GM-CSF. We also showed that an increase in CDK2-bound p27 and CDK4-bound p18 are caused by treatment with ATRA and a decrease in CDK6-bound cyclin D3 is induced synergistically by treatment with both reagents. Furthermore, we propose that the changes in binding of p18 and cyclin D3 to CDKs are due to changes at the protein expression level and that the increase in p27 binding to CDK2 is due to a novel mechanism.

Hypophosphorylation of pRB and repression of cyclin D3 and cdc25A during the granulocytic differentiation of human myeloblastic leukemia ML-1 cells

Recently we succeeded in inducing synergistic differentiation toward granulocytes in human myeloblastic leukemia ML-1 cells by treatment of ATRA in combination with GM-CSF. To research the mechanism of this differentiation process, we examined expression of cell cycle-related genes that are concerned with cell growth and differentiation. We detected change to the hypophosphorylated form of pRB and down-regulation of cyclin D3 and cdc25A during induced differentiation. Furthermore, these marked alterations were hardly detected in ML-1 cells treated with ATRA or GM-CSF alone. These results suggest that hypophosphorylation of pRB and repression of cyclin D3 and cdc25A are induced synergistically by treatment with ATRA plus GM-CSF in ML-1 cells.

A Requirement for K+-Channel Activity in Growth Factor–Mediated Extracellular Signal-Regulated Kinase Activation in Human Myeloblastic Leukemia ML-1 Cells

Voltage-gated K+ channels have been shown to be required for proliferation of various types of cells. Much evidence indicates that K+-channel activity is required for G1 progression of the cell cycle in different cell backgrounds, suggesting that K+-channel activity is required for early-stage cell proliferation in these cells. However, little is known about the molecular mechanisms that underlie this phenomenon. We have shown in human myeloblastic leukemia ML-1 cells that K+ channels are activated by epidermal growth factor (EGF), whereas serum starvation deprivation suppressed their activity. In addition, voltage-gated K+ channels are required for G1/S-phase transition of the cell cycle. We report here that suppression of K+ channels prevented the activation of extracellular signal-regulated protein kinase 2 (ERK-2) in response to EGF and serum. However, blockade of K+ channels did not prevent ERK-2 activation induced by 12-O-tetradecanoyl-phorbol 13-acetate (TPA). Elimination of extracellular Ca2+ did not alter either ERK-2 activation or the effect of K+-channel blockade on ERK-2 activation. Our data demonstrate that the K+ channel is a part of the EGF-mediated mitogenic signal-transduction process and is required for initiation of the EGF-mediated mitogen-activated protein kinase (MAPK) pathways. Our findings may thus explain why an increase in K+-channel activity is associated with cell proliferation in many types of cells, including ML-1 cells.

Differential expression of proteins regulating cell cycle progression in growth vs. differentiation

The level of various G1 cyclins and cyclin-dependent kinases (cdks) present in the nuclei of synchronized ML-1 human myeloblastic leukemia cells was determined as a function of time after initiation of cell growth with insulin-like growth factor-1 (IGF-1) and transferrin (Tf), and following induction of differentiation with transforming growth factor- β1 (TGF- β1). Cyclin E and cdk2 were expressed at relatively high levels in the nuclei of proliferation-stimulated cells, whereas cyclin D1 and cdk5 were expressed at comparably high levels in the nuclei of differentiation-induced cells. In the nuclear extracts from proliferation-stimulated cells, cyclin E complexed specifically with cdk2, whereas in nuclear extracts from differentiation-induced cells, cyclin D1 bound specifically to cdk5. Increased cyclin E/cdk2 expression was accompanied by increased DNA synthesis, whereas increased cyclin D1/cdk5 levels correlated with decreased DNA synthesis. In both growth- and differentiation-induced cells, cyclin D2 expression preceded the expression of cyclin D3, and a significantly larger amount of these cyclins was present in differentiation- as compared to proliferation-induced cells. In contrast, cdk4 and cdk6 were present at similar levels in the nuclear extracts from both growth- and differentiation-induced cells. These data show that, in ML-1 cells, the proliferation-associated progression from G1 to S, as well as the differentiation-associated transit from G1 to maturation is accompanied by the expression of specific cyclin/cdk pairs, comprising cdk2/cyclin E in growth and cdk5/cyclin D1 in differentiation.

Induction of differentiation and down-regulation of c- myb gene expression in ML-1 human myeloblastic leukemia cells by the clinically effective anti-leukemia agent meisoindigo

Meisoindigo, a second generation derivative of indirubin, is an effective chemotherapeutic agent with very low toxicity used in the treatment of chronic myeloid leukemia. To determine the nature of this activity, the effect of a nontoxic concentration (0.72 μg/mL) of this compound on ML-1 human myeloblastic leukemic cells was examined. At such a concentration, differentiation induction was found to be the most pronounced drug effect. During the 3-day drug incubation period, the viable cell number remained essentially constant, with approximately 48% of the cells demonstrating a mature phenotype with increased acid phosphatase activity and nitroblue tetrazolium dye reduction. As observed with other DNA-specific agents, induction of ML-1 differentiation by meisoindigo was accompanied by the down-regulation of c- myb gene expression. These data suggest that induction of leukemic cell differentiation associated with decreased c- myb expression may be one of the mechanisms of the antitumor action of meisoindigo.

MCL-1, a member of the BCL-2 family, is induced rapidly in response to signals for cell differentiation or death, but not to signals for cell proliferation

mcl-1 was identified as an "early-induction" gene that increases in expression during the differentiation of ML-1 human myeloblastic leukemia cells. The mcl-1 gene product proved to be a member of the bcl-2 gene family and, like bcl-2, to have the capacity to promote cell viability. The pattern of expression of mcl-1 has now been characterized, the aim being to determine whether increased expression is consistently associated with differentiation-induction and whether expression is also associated with other changes in proliferative state or cell viability. Expression of the mcl-1 mRNA was found to increase rapidly in ML-1 cells exposed to inducers of monocyte/macrophage differentiation (phorbol esters or lymphocyte conditioned medium), but not cells exposed to an inducer of granulocyte differentiation (retinoic acid). Expression also increased rapidly in response to certain cytotoxic agents (colchicine and vinblastine), but did not increase during serum stimulation or growth-arrest in reduced serum. Increased expression of mcl-1 occurred during the initiation of cell differentiation or death and was not inhibited by cycloheximide, in agreement with the designation of mcl-1 as an early-induction gene. Increased transcription contributed to the increase in expression, and turnover of the mcl-1 mRNA was rapid. These findings suggest that mcl-1 may serve as a modulator of cell viability that can undergo rapid upregulation as well as downregulation, with upregulation harbingering the initiation of cell differentiation or death.

Activation of casein kinase II in ML-1 human myeloblastic leukemia cells requires IGF-1 and transferrin.

Casein kinase II (CK II), a key enzyme involved in the regulation of cell growth, has been variously reported to be activated by diverse mitogens, including insulin-like growth factor 1 (IGF-1) and epidermal growth factor (EGF). Activation of the enzyme is generally carried out in the presence of serum, and we examined the question whether serum components participate in the activation process. We demonstrated previously that ML-1 cells require IGF-1 plus transferrin (TF) for growth and transforming growth factor beta or tumor necrosis factor alpha plus TF for differentiation. We now found that CK II is activated only when the cells are exposed to both IGF-1 and TF or when TF is replaced in this combination with relatively high levels of iron salts. Induction of differentiation with TGF-beta and TF did not result in CK II activation. These results show that CK II activation in ML-1 cells requires the application of both components of the growth signal, IGF-1 and TF, demonstrating that the growth factor alone is incapable of enhancing the activity of the enzyme.

Regulation of c-myb expression in ML-1 human myeloblastic leukemia cells by c-ets-1 protein

C-myb and c-ets-1 have variously been demonstrated to function as protooncogenes. Using a human leukemic cell line, ML-1, we have examined the mechanism by which these genes participate in establishing the sustained proliferation mode that is characteristic of the transformed cell. In the absence of serum, ML-1 cells were found to require IGF-1 and transferrin (TF) for growth and TGF-β or TNF-α plus TF for differentiation. Upon administration of the growth factors, c-myb expression increased within 60 min, whereas after addition of the differentiation factors c-myb expression ceased completely within 3 hr. A correlation was found to exist between the level of c-ets-1 protein in the cells, the extent to which that protein is bound to intron I of the myb gene and the amount of c-myb mRNA that is expressed. Upon administration of growth factors, a sizable increase in the intracellular, and particularly, in the intranuclear level of c-ets-1 protein was observed, whereas a pronounced decrease in the level of this protein occurred after exposure to the differentiation factors. These data demonstrated that the level at which an oncogene-specified transcription factor is expressed can affect the expression of other target oncogenes involved in the regulation of cell proliferation. Stimulated expression of such transcription factor can then lead to the continuous proliferation cycle characteristic of the cancer cell.

Differential effect of growth- and differentiation-inducing factors on the release of eicosanoids and phospholipids from ML-1 human myeloblastic leukemia cells

In the absence of serum, growth of ML-1 human myeloblastic leukemia cells is induced by the insulin-like growth factor-1 (IGF 1) together with transferrin (Tf), whereas monocytic differentiation is initiated by the transforming growth factor-β (TGF-β) in combination with Tf. Initiation of growth was followed by the rapid release of arachidonic acid (AA), hydroxyeicosatetraenoic acids (HETEs) and phospholipids into the culture medium. In contrast, induction of differentiation occurred without the release of these lipids beyond the level present in control. Inhibitors of enzymes involved in the formation of AA and of HETEs, including phospholipase A 2 and lipoxygenases, caused interference with growth but not with differentiation, and an inhibitor of the cyclooxygenase path affected neither growth nor differentiation. These results indicate that the initiation of ML-1 cell growth but not of cell differentiation is dependent upon the increased formation of AA and its derivatives formed primarily via the lipoxygenase path.

Analysis by Polymerase Chain Reaction of c- myc Expression in Human Leukemia Cells Induced to Differentiate by Heptachlor and 12- O-Tetradecanoylphorbol-13-acetate

Heptachlor, a chlorinated hydrocarbon insecticide, was previously demonstrated to be able to induce differentiation of human myeloblastic leukemia ML-1 cells into monocyte- or macrophage-like cells, a phenomenon similar to that caused by the known tumor promoter 12- O-tetradecanoylphorbol-13-acetate (TPA). Studies have also shown that chemically induced myeloid differentiation of human promyclocytic leukemia HL-60 cells is associated with a decline in the steady-state c- myc proto-oncogene expression. In this study, the polymerase chain reaction (PCR) was combined with primer-extension reverse transcription for the detection of subtle changes in the level of myc mRNA transcription in ML-1 cells exposed to either heptachlor or TPA. Three sets of 5′ primers (S1, S2, and S3) within the region bordered by two promoter sequences (P1 and P2) and a fourth 5′ sequence (S4) downstream of P2 were individually paired with a 3′ primer sequence (S5) for the synthesis of portions of the first exon of the c- myc oncogene. The results indicated that when S2, S3, and S4 5′ primers were used, an initial increase of myc gene expression was detected and was followed by a rapid decline of myc transcripts in cells which had been exposed to TPA. However, when the S1 5′ primer was used in the PCR assay, RNA transcription was shown to be less efficient. Heptachlor, under the same assay conditions, decreased the expression of the myc oncogene, but did not cause an initial stimulation. Marked depression in c- myc expression was further detected in ML-1 cells exposed to chlordane, a heptachlor-related, chlorinated hydrocarbon insecticide, but not to toxaphene, another chlorinated hydrocarbon insecticide. In addition, heptachlor was shown to stimulate the in vitro protein kinase C (PKC) activity and the binding of [ 3H]PDBu to ML-1, indicating a dissociation of PKC activation and myc expression in ML-1 induced to differentiate by heptachlor.

Alterations in a voltage-gated K+ current during the differentiation of ML-1 human myeloblastic leukemia cells

A voltage-gated K+ current has been identified in ML-1 human myeloid leukemia cells, with the use of the whole-cell patch-clamp technique. ML-1 cells proliferate in tissue culture as immature myeloblasts and can be induced to differentiate to nonproliferative monocyte/macrophages. In the myeloblastic cells, activation of the K+ current occurs upon depolarization of the membrane potential to above -40 mV; inactivation of this current is also voltage dependent and follows a simple exponential time course with a time constant (Ti) of 900 msec at 0 mV. The current is inhibited by 4-aminopyridine (IC50 of 80 microM at 0 mV), but is much less sensitive to tetraethylammonium of Ba2+. In cells exposed to the differentiation-inducer 12-O-tetradecanoylphorbol-13-acetate (TPA), dramatic alterations in the K+ current occur: upon exposure to 10 nM TPA during whole-cell recording, the amplitude of the voltage-activated current initially increases (within 4 min) and later decreases (at approximately 30-50 min). Upon addition of 0.5 nM TPA to cells in tissue culture, the current shows suppressed activation and accelerated inactivation in the early stages of differentiation (10-fold decrease in Ti at approximately 7 hr) and is completely suppressed in the later stages (3 days). Thus, this voltage-gated K+ current is suppressed early in the induction of differentiation and associated loss of proliferation in myeloid ML-1 cells exposed to TPA; this parallels the fact that channels of a similar type are activated upon the stimulation of proliferation in lymphoid cells exposed to mitogens.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of transferrin as a progression factor for ML-1 human myeloblastic leukemia cell differentiation

We have previously demonstrated (Guan X.-P., Hromchak, R. A., and Bloch, A. (1989) Cancer Commun. 1, 111-115) that ML-1 human myeloblastic leukemia cells differentiate to monocyte/macrophage-like cells by the sequential action of competence and progression factors. Tumor necrosis factor-alpha, transforming growth factor-beta, and the phorbol ester tetradecanoylphorbol acetate were found to induce competence, whereas a 77-kDa glycoprotein (DF77) isolated from mitogen-stimulated human leukocyte-conditioned medium initiated progression. In this communication we show DF77 to be an isoform of human transferrin. Hemin or soluble iron complexes did not induce differentiation progression, suggesting that the participation of transferrin in ML-1 cell differentiation may not be related to its iron-carrying capacity.