Erythroleukemia Cell Line HEL Research Articles

A Carbon 21 Steroidal Glycoside with Pregnane Skeleton from Cynanchum atratum Bunge Promotes Megakaryocytic and Erythroid Differentiation in Erythroleukemia HEL Cells through Regulating Platelet-Derived Growth Factor Receptor Beta and JAK2/STAT3 Pathway.

Erythroleukemia is a rare form of acute myeloid leukemia (AML). Its molecular pathogenesis remains vague, and this disease has no specific therapeutic treatments. Previously, our group isolated a series of Carbon 21 (C-21) steroidal glycosides with pregnane skeleton from the root of Cynanchum atratum Bunge. Among them, we found that a compound, named BW18, can induce S-phase cell cycle arrest and apoptosis via the mitogen-activated protein kinase (MAPK) pathway in human chronic myeloid leukemia K562 cells. However, its anti-tumor activity against erythroleukemia remains largely unknown. In this study, we aimed to investigate the anti-erythroleukemia activity of BW18 and the underlying molecular mechanisms. Our results demonstrated that BW18 exhibited a good anti-erythroleukemia activity in the human erythroleukemia cell line HEL and an in vivo xenograft mouse model. In addition, BW18 induced cell cycle arrest at the G2/M phase and promoted megakaryocytic and erythroid differentiation in HEL cells. Furthermore, RNA sequencing (RNA-seq) and rescue assay demonstrated that overexpression of platelet-derived growth factor receptor beta (PDGFRB) reversed BW18-induced megakaryocytic differentiation in HEL cells, but not erythroid differentiation. In addition, the network pharmacology analysis, the molecular docking and cellular thermal shift assay (CETSA) revealed that BW18 could inactivate Janus tyrosine kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathway, which might mediate BW18-induced erythroid differentiation. Taken together, our findings elucidated a novel role of PDGFRB in regulating erythroleukemia differentiation and highlighted BW18 as an attractive lead compound for erythroleukemia treatment.

EloA promotes HEL polyploidization upon PMA stimulation through enhanced ERK1/2 activity

Megakaryocytes (MKs) are the unique non-pathological cells that undergo polyploidization in mammals. The polyploid formation is critical for understanding the MK biology, and transcriptional regulation is involved in the differentiation and maturation of MKs. However, little is known about the functions of transcriptional elongation factors in the MK polyploidization. In this study, we investigated the role of transcription elongation factor EloA in the polyploidy formation during the MK differentiation. We found that EloA was highly expressed in the erythroleukemia cell lines HEL and K562. Knockdown of EloA in HEL cell line was shown to impair the phorbol myristate acetate (PMA) induced polyploidization process, which was used extensively to model megakaryocytic differentiation. Selective over-expression of EloA mutants with Pol II elongation activity partially restored the polyploidization. RNA-sequencing revealed that knockdown of EloA decelerated the transcription of genes enriched in the ERK1/2 cascade pathway. The phosphorylation activity of ERK1/2 decreased upon the EloA inhibition, and the polyploidization process of HEL was hindered when ERK1/2 phosphorylation was inhibited by PD0325901 or SCH772984. This study evidenced a positive role of EloA in HEL polyploidization upon PMA stimulation through enhanced ERK1/2 activity.

JAK2 inhibition in JAK2V617F-bearing leukemia cells enriches CD34+ leukemic stem cells that are abolished by the telomerase inhibitor GRN163L

The activating-mutation of JAK2V617F drives the development of myeloproliferative neoplasms (MPNs). Several JAK2 inhibitors such as ruxolitinib and gandotinib (LY2784544) currently in clinical trials and, provide improvements in MPNs including myelofibrosis. However, JAK2 inhibitors are non-curative and murine experiments show that JAK2 inhibitors don’t eradicate MPN stem cells and it is currently unclear how they escape. We thus determined the effect of the specific JAK2V617F inhibitor LY2784544 on leukemic stem (CD34+) cells (LSCs) using the JAK2V617F-bearing erythroleukemia cell line HEL. The LY2784544 treatment caused a transient proliferation inhibition and apoptosis of HEL cells, but a recovery occurred within a week. Thereafter, the continuous LY2784544 exposure induced the accumulation of CD34+ LSCs, and the CD34+ cells increased from 2% to >90% by week 9, which was accompanied by increased clonogenic potentials. LY2784544 was capable of stimulating CD34 expression even in CD34− HEL cells, which indicated cellular de-differentiation. A significantly enhanced expression of the stem cell factor KLF4 was observed in LY2784544-treated HEL cells. Inhibiting KLF4 expression attenuated LY2784544-mediated accumulation of CD34+ LSCs. Moreover, the telomerase inhibitor GRN163L abolished the LY2784544-effect. JAK2 inhibitors thus cause enrichment of LSCs and are unlikely to cure MPN as a monotherapy. Simultaneously targeting JAK2V617F and KLF4 or telomerase may be a novel strategy for MPN therapy, which should be of significance both biologically and clinically.

Implication of Hypoxia-Inducible Factor-1 (HIF-1) As a New Therapeutic Target in JAK2V617F Positive Myeloproliferative Neoplasms (MPN)

Myeloproliferative neoplasms (MPN) are a heterogeneous group of malignancies including polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). The JAK2V617F mutation can be found in 90% of PV and approximately 50% of ET and PMF patients. Hypoxia-inducible factors (HIFs) are master transcriptional regulators of the response to decreases in cellular oxygen levels. Unveiling the function of deregulated HIF-1 signaling in normal and malignant hematopoiesis was the aim of several recent publications, highlighting the importance of HIF-1 for the maintenance of leukemic stem cells (LSCs) in acute and chronic myeloid leukemia (AML/CML). In a JAK2V617F knock-in mouse model and in patients, JAK2V617F was shown to induce the accumulation of reactive oxygen species (ROS) in the hematopoietic stem cell compartment, leading to a stabilization of HIF-1α protein. Further, aberrant STAT5 and PI3K/AKT/mTOR signaling induced HIF-1α expression on the transcriptional and translational level. Ruxolitinib treatment inhibited growth and reduced the expression of HIF-1α and its target gene VEGF in the JAK2V617F human erythroleukemia cell line HEL. In several leukemic cell lines constitutive expression of HIF-1α was reported, even under normoxic conditions. However, it still remains unknown whether HIF-1α plays a role in JAK2V617F positive MPN. In this study, we investigated the role HIF-1α signaling in JAK2V617F positive MPN in vitro.We retrovirally transduced the murine bone marrow cell line 32D with JAK2V617F or JAK2WT. Western blot analysis revealed significant increases in HIF-1α protein levels in JAK2V617F positive cells compared to JAK2WT controls after cultivation in normoxic conditions and this effect was abrogated by treatment with the JAK1/JAK2 inhibitor ruxolitinib. Inhibition of HIF-1, binding to hypoxia response elements (HRE), by low doses of echinomycin (1 nM), significantly impaired proliferation and survival. Using an Annexin-V/7-AAD flow cytometry assay apoptosis was found to be selectively induced in JAK2V617F positive, but not JAK2WT cells after echinomycin treatment. Additionally, BrdU/7-AAD cell cycle analysis revealed that only JAK2V617F positive cells were significantly arrested in G0/1 phase. These findings were consistent with shRNA-mediated knockdown (KD) of HIF-1α in JAK2V617F transduced 32D cells in presence but not the absence of HIF-2 antagonist 2. Inhibition of HIF-2 was necessary due to a compensatory increase of HIF-2α protein levels, shown by Western Blot analysis, counteracting HIF-1α-KD mediated effects. We isolated PBMCs and BMMNCs from JAK2V617F positive patients or healthy controls using Ficoll density gradient centrifugation. Echinomycin significantly abrogated the colony formation ability alone and in combination with ruxolitinib. In vitro treatment with echinomycin significantly decreased cell number and viability of 8 JAK2V617F positive BMMNC samples (4 PV, 3 PMF, 1 preMF; p[1nM]=0.0169, p[5nM]=0.0009) and 7 PBMC samples (6 PV, 1 PMF; p[1nM]=0.0156, p[5nM]=0.0156) in a dose-dependent manner. In contrast, PBMCs from 6 healthy donors were unaffected by the treatment. The same effect was observed in heterozygous and homozygous iPS cell-derived progenitors from JAK2V617F positive PV patients, whereas JAK2WT cells were unaffected by the treatment. Collectively, our data indicate that targeting HIF-1 might represent a novel therapeutic approach in classical Philadelphia-chromosome-negative MPN. DisclosuresBrümmendorf:Pfizer: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Janssen: Consultancy; Merck: Consultancy; Takeda: Consultancy.

A novel synthesized 3’, 5’-diprenylated chalcone mediates the proliferation of human leukemia cells by regulating apoptosis and autophagy pathways

Leukemia is a hematologic malignancy with poor prognosis in humans and chemotherapy is the main strategy for treating leukemia patients. Novel drugs with better selectivity and lower toxicity are required for the treatment of patients. A novel 3’,5’-diprenylated chalcone, (E)-1-(2-hydroxy-4-methoxy-3,5-diprenyl) phenyl-3-(3- pyridinyl)-propene-1-one (C10) is a potential new anti-leukemia agent. In this study, we investigated the molecular mechanisms of the anti-leukemia effects of C10 on different leukemia cells in vitro. C10 showed strong inhibition of proliferation of the human erythroleukemia cell line HEL and human myeloid leukemia cell line K562, and several cell and flow cytometer assays showed that inhibition by C10 was due to the regulation of gene expression or phosphorylation in the apoptosis and autophagy pathways. The results showed that C10 regulated the expression of Bax, c-Myc, Bcl-2, P38/AMPK and ERK 1/2, activated the expression of Caspase-3, -8, and PARP at the protein level in the apoptosis pathway of the two leukemia cell types, and inhibited the expression of erythroleukemia carcinogene Fli-1 in the human erythroleukemia cell line HEL. Additionally,treatment with the compound induced a time-dependent increase in expression of LC 3A/B via inhibiting the AKT-mTOR pathway, which is associated with cell autophagy. Taken together, the above results suggest that the novel synthesized 3’,5’-diprenylated chalcone can prevent the growth of leukemia cells by inducing apoptosis and autophagy.

Regulation of Ruxolitinib on matrix metalloproteinase in JAK2V617F positive myeloroliferative neoplasms cells

目的探讨JAK2抑制剂Ruxolitinib对JAK2V617F突变阳性的骨髓增殖性肿瘤（MPN）细胞内基质金属蛋白酶（MMP）调控的影响。方法①收集2012年1月到2015年12月保定市第一医院收治的40例未经治疗的JAK2V617F阳性MPN患者，以15名健康志愿者为对照组。免疫组化法检测两组骨髓活检组织中磷酸化JAK2（p-JAK2）、基质金属蛋白酶2（MMP-2）、MMP-9的表达水平。选取JAK2V617F阳性MPN患者骨髓细胞，体外应用Ruxolitinib干预，测定干预前后细胞迁移力和MMP-2、MMP-9表达。②不同浓度Ruxolitinib（0、50、100、250、500、1 000 nmol/L）作用于人红白血病细胞株HEL细胞不同时间后CCK-8检测细胞活力，Tanswell小室检测细胞迁移，荧光定量PCR检测JAK2、MMP-2、MMP-9 mRNA水平变化，Western blot检测p-JAK2、MMP-2、MMP-9蛋白表达。结果①MPN组p-JAK2、MMP-2、MMP-9蛋白表达均高于对照组[（78.56±24.55）%对（41.59±17.29）%、（48.25±18.74）%对（22.79±13.89）%、（53.29±19.28）%对（15.56±14.96）%，P值均<0.05]。Spearman相关分析显示MMP-2、MMP-9蛋白水平与JAK2V617F突变量呈正相关（r=0.526, P=0.001；r=0.543, P=0.001）。②Ruxolitinib能够呈时间和剂量依赖性抑制HEL细胞增殖。③迁移实验结果显示5 nmol/L Ruxolitinib作用MPN原代细胞及HEL细胞24 h后迁移至下室细胞数均少于无Ruxolitinib组（154.7±27.5对320.3±67.3，t=13.47，P=0.001；70.7±10.5对135.3±16.7，t=13.89，P=0.001）。④JAK2、MMP-2、MMP-9 mRNA及蛋白表达随Ruxolitinib剂量增加而降低。结论Ruxolitinib通过调控JAK2信号通路抑制MMP-2、MMP-9表达而抑制MPN细胞迁移能力。

Anti-angiogenic effect of interferon on JAK2V617F positive myeloproliferative neoplasms and its anti-angiogenic mechanisms

To research the suppressive effect of interferon α2b (IFN-α2b) on angiogenesis of JAK2 tyrosine kinase gene point mutation (JAK2V617F) positive myeloproliferative neoplasm (MPN) and its anti-angiogenic mechanisms. (1) A total of 42 cases of JAK2V617F positive MPN patients in the No.1 Hospital of Baoding were selected between January 2012 and October 2014, including the newly diagnosed group before treatment (n=25) and the IFN-α2b treatment group (n=17). Ten cases of idiopathic immune thrombocytopenic purpura (ITP) patients were enrolled as controls. JAK2V617F/JAK2 ratio was detected by real-time fluorescent quantitative PCR to measure mutation; the expression levels of phosphorylated JAK2 (p-JAK2), vascular endothelial growth factor (VEGF), hypoxia-inducible factor-1α (HIF-1α) and CD105 marked microvascular density (MVD) in bone marrow were detected by immunohistochemistry. The correlations were analyzed among JAK2V617F mutation burden and VEGF, HIF-1α, and MVD. (2) Human erythroleukemia cell line HEL cells were treated with different concentrations of IFN-α2b. The apoptosis was detected by Hoechst staining method. The cell viability was detected by CCK-8 test. Cell migration ability was tested by transwell chambers. The protein expression levels of p-JAK2, VEGF, and HIF-1α were detected by Western blot. (1)The ratio of JAK2V617F/JAK2 in the IFN-α2b treatment group (22.69% ± 12.64%) was significantly lower than that in the newly diagnosed group (46.17% ± 19.32%) (P<0.01). The expression levels of p-JAK2, VEGF, and HIF-1α in the newly diagnosed group (82.41% ± 11.65%, 64.72% ± 25.01%, 45.12% ± 20.28%) were significantly higher than those in the IFN-α2b treatment group (60.93% ± 20.57%, 36.58% ± 15.95%, 32.15% ± 14.27%) and the control group (43.05% ± 12.59%, 25.69%± 1 3.75%, 25.07% ± 15.49%) (all P<0.01). MVD in the newly diagnosed group (26.58% ± 5.93%) was significantly higher than that in the treatment group (15.86%± 4.27%) and the control group (10.76% ± 4.01%) (P<0.01). Spearman correlation analysis showed positive correlation of JAK2V617F mutation with VEGF and MVD (r=0.589, P<0.05; r=0.577, P<0.05). (2)The apoptosis of HEL cells were increased after treated with 30 000 U/L of IFN-α2b in HEL cells after 24 h. The proliferation of HEL cell were inhibited by different concentrations of IFN-α2b in time- and dose-dependent manner. The number of membrane-permeating HEL cells after treated with 5 000 U/L of IFN-α2b in HEL cells after 24 h was significantly lower than that in the untreated cells (52.9 ± 7.5 vs 77.3 ± 6.1) (P<0.05). The expression levels of p-JAK2, VEGF, and HIF-1α were decreased in a dose-dependent manner. IFN-α2b may exert an anti-angiogenic effect by inhibiting the VEGF, HIF-1α, and MVD expression in MPN via JAK2 signal pathway.

Missense mutations in the ABCB6 transporter cause dominant familialpseudohyperkalemia

Familial Pseudohyperkalemia (FP) is a dominant red cell trait characterized by increased serum [K(+)] in whole blood stored at or below room temperature, without additional hematological abnormalities. Functional gene mapping and sequencing analysis of the candidate genes within the 2q35-q36 critical interval identified-in 20 affected individuals among three multigenerational FP families-two novel heterozygous missense mutations in the ABCB6 gene that cosegregated with disease phenotype. The two genomic substitutions altered two adjacent nucleotides within codon 375 of ABCB6, a porphyrin transporter that, in erythrocyte membranes, bears the Langereis blood group antigen system. The ABCB6 R375Q mutation did not alter the levels of mRNA or protein, or protein localization in mature erythrocytes or erythroid precursor cells, but it is predicted to modestly alter protein structure. ABCB6 mRNA and protein levels increase during in vitro erythroid differentiation of CD34(+) erythroid precursors and the erythroleukemia cell lines HEL and K562. These data suggest that the two missense mutations in residue 375 of the ABCB6 polypeptide found in affected individuals of families with chromosome 2-linked FP could contribute to the red cell K(+) leak characteristic of this condition.

The HDAC inhibitor Givinostat modulates the hematopoietic transcription factors NFE2 and C-MYB in JAK2V617F myeloproliferative neoplasm cells

We investigated the mechanism of action of the histone deacetylase inhibitor Givinostat (GVS) in Janus kinase 2 (JAK2)(V617F) myeloproliferative neoplasm (MPN) cells. GVS inhibited colony formation and proliferation and induced apoptosis at doses two- to threefold lower in a panel of JAK2(V617F) MPN compared to JAK2 wild-type myeloid leukemia cell lines. By global gene expression analysis, we observed that at 6 hours, GVS modulated 293 common genes in the JAK2(V617F) cell lines HEL and UKE1, of which 19 are implicated in cell cycle regulation and 33 in hematopoiesis. In particular, the hematopoietic transcription factors NFE2 and C-MYB were downmodulated by the drug specifically in JAK2(V617F) cells at both the RNA and protein level. GVS also inhibited JAK2-signal transducer and activator of transcription 5-extracellular signal-regulated kinase 1/2 phosphorylation, but modulation of NFE2 and C-MYB was JAK2-independent, as shown using the JAK2 inhibitor TG101209. GVS had a direct effect on the NFE2 promoters, as demonstrated by specific enrichment of associated histone H3 acetylated at lysine 9. Modulation by GVS of NFE2 was also observed in freshly isolated CD34(+) cells from MPN patients, and was accompanied by inhibition of their proliferation and differentiation toward the erythroid lineage. We conclude that GVS acts on MPN cells through dual JAK2-signal transducer and activator of transcription 5-extracellular signal-regulated kinase 1/2 inhibition and downmodulation of NFE2 and C-MYB transcription.

Apoptosis induced by ZnPcH1-based photodynamic therapy in Jurkat cells and HEL cells

Photodynamic therapy (PDT) can selectively and effectively kill tumor cells, and photosensitization is the key to these anti-tumor effects. In this study, we investigated the killing mechanisms of the photosensitizer ZnPcH1 (a mono-α-substituted zinc(II) phthalocyanine synthesized in China), in the acute lymphoid leukemia cell line Jurkat and the acute erythroleukemia cell line HEL. Results from acridine orange/ethidium bromide fluorescence staining, DNA gel electrophoresis, and Annexin-V(FITC/PI) double-stained flow cytometry analysis indicated that ZnPcH1-PDT induced apoptosis in Jurkat and HEL cells, with Jurkat cells being more sensitive. Following ZnPcH1-PDT treatment, upregulation of p53 and Bax, downregulation of HSP70, Bcl-2 and Akt, and inhibition of the phosphorylation of Akt and GSK3β were observed. Our results establish a theoretical basis for the application of ZnPcH1-PDT in the treatment of acute leukemia.

Down-regulation of EDAG expression by retrovirus-mediated small interfering RNA inhibits the growth and IL-8 production of leukemia cells

Embryonic development associated gene (EDAG), which is overexpressed in hematopoietic neoplasms and leukemia cell lines, has been reported to participate in the leukemia cell differentiation and proliferation. This study investigated whether retrovirus-mediated transfer of a siRNA against EDAG can reduce the growth of leukemia cells which highly express EDAG in vitro and in vivo. The stable transfected cells were identified with RT-PCR, the effect of EDAG/siRNA on the growth of the human erythroleukemia cell line HEL was analyzed by MTT assay, and angiogenic factor IL-8 release was evaluated by ELISA and RT-PCR. The results showed that EDAG/siRNA can silence the expression of EDAG in HEL cells. Down-regulation of EDAG expression by retrovirus-mediated siRNA inhibited the cell proliferation and tumor growth. Knockdown of EDAG expression by siRNA is also associated with decreased expression of the anti-angiogenic factor IL-8, suggesting that EDAG stimulates tumor growth at least in part by regulating angiogenesis. This study suggests that siRNA-mediated gene silencing of EDAG could potentially be a therapeutic strategy for EDAG over-expressing leukemia cells.

In malignant myeloid cells expression of Daxx downregulates expression of p53 and of the inhibitors of apoptosis proteins

The role of Daxx, in particular its ability to promote or hinder proliferation, still remains controversial. In order to elucidate the functional relevance of Daxx in malignant myelocytes, the erythroleukemia cell line HEL was stably transfected with a Daxx-expressing vector or with the respective Daxx-negative control vector. Assessing the molecular consequences of ectopic Daxx-expression, we present evidence that Daxx downregulates p53. Moreover, we demonstrate that Daxx overexpressing myelocytes downregulate the proapoptotic Bcl-2 family member Bax, while expression of antiapoptotic Bcl-2 is not influenced. Furthermore, expression of Daxx diminishes expression levels of the initiator-procaspase-8 and -10, and the executioner procaspase-7, whereas the procaspase-3, -6 and -9 remain unaltered. The altered protein levels of the caspases in Daxx overexpressing myelocytes are accompanied by a decrease of expression levels of the inhibitor of apoptosis proteins (IAPs) cIAP-1, -2 and survivin. Despite the described impact of Daxx expression on major molecules of the apoptotic cascade, expression of Daxx in neoplastic myelocytes does not impact on the rate of proliferation. Upon a proapoptotic stimulus such as serum withdrawal Daxx is unable to maintain its influence on expression levels of p53, Bax, IAPs and the procaspase-8, -10 and -7.

Pharmacological characterization of adenosine A 2B receptors : Studies in human mast cells co-expressing A 2A and A 2B adenosine receptor subtypes

Characterization of A 2B receptors is hampered by the lack of selective pharmacological probes and often relies on their relative affinity to agonists that are selective at other receptor types. This approach is limited because the affinity of A 2B receptors for putative A 3 agonists has not been determined. Using the human erythroleukemia cell line HEL as a cellular model for A 2B-mediated adenylate cyclase activation, we found the following potencies (pD 2) for the non-selective agonist 5′- N-ethylcarboxamidoadenosine (NECA) (5.65 ± 0.04), the putative A 3 agonists N 6-benzyl-NECA (4.17 ± 0.06) and N 6-(3-iodobenzyl)- N-methyl-5′-carbamoyl-adenosine (IB-MECA) (3.7 ± 0.02), and the A 2A agonist 4-[( N-ethyl-5′-carbamoyladenos-2-yl)-aminoethyl]-phenylpropionic acid (CGS21680) (2.8 ± 0.1). Because of the lack of a selective agonist, characterization of A 2B receptor function is difficult in cells co-expressing A 2A receptors. In the human mast cell line HMC-1, NECA induced cAMP accumulation with a concentration-response relationship best fitted to a two-sited model (pD 2 7.69 ± 0.42 and 5.92 ± 0.21 for high- and low-affinity sites), suggesting the presence of both A 2A and A 2B receptors in these cells. We demonstrated that A 2B receptors can be selectively activated with NECA in the presence of the selective A 2A antagonist 5-amino-7-(phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5- c] pyrimidine (SCH 58261). Under these conditions, the concentration-response relationship of NECA for cyclic AMP accumulation was now best fitted to a one-site model (pD 2 5.68 ± 0.03, Hill slope 0.93 ± 0.06, 95% confidence intervals 0.8 to 1.06)corresponding to selective activation of A 2B receptors. Using the approaches developed in this study, we determined that A 2B, and not A 2A or A 3, receptors account for all the calcium mobilization induced by NECA in HMC-1 cells.

Coupled and uncoupled induction of fos and jun transcription by different second messengers in cells of hematopoietic origin

The nuclear oncoproteins fos and jun are associated as a heterodimer which binds to TPA (PMA or TPA: phorbol 12-myristate 13-acetate)- responsive promoter elements (TRE), the recognition site for the transcription factor AP-1. The fos/jun heterodimer has a higher affinity to the TRE and stimulates transcription of responsive genes more than the jun homodimer. The association of these two oncoproteins may play a central role in signal transduction and regulation of cell proliferation and differentiation. We further defined the regulation of fos and jun by studying their inducibility by second messengers in cells of hematopoietic origin. In THP-1 monocytic leukemia cells fos and jun mRNA levels are regulated in a coupled manner by second messengers activated after membrane phospholipid turnover. Addition of phospholipase C to cells, as well as stimulation of protein kinase C and release of intracellular Ca2+, caused a rapid induction of fos and jun mRNA levels, but the induction of jun mRNA showed a more persistant and less transient pattern than fos. In contrast to the phosphoinositol system, stimulation of the adenylate cyclase pathway in THP-1 cells induced only fos transcription whereas jun mRNA levels remained unchanged. A similar uncoupling of fos and jun inducibility was found after phorbol ester addition to the human erythroleukemia cell line HEL and the human promyelocytic cell line HL-60. The uncoupling of fos and jun levels might predispose cells to the formation of combinatorial transcription complexes of a different composition and activity than the fos/jun heterodimer. Indeed, nuclear extracts from THP-1 cells before or after activation of the phosphinositol or adenylate cyclase second messenger pathways revealed a correlation in fos and jun expression and specific binding of the heterocomplex to a TRE sequence.

Platelet-derived growth factor Phorbol ester induces the expression of the B-chain but not of the A-chain in HEL cells

It was shown previously [(1984) EMBO J. 3, 453-459] that after treatment of the human erythroleukemia cell line HEL with phorbol ester and dimethyl sulfoxide there was a marked increase in the amounts of megakaryotic markers, especially of platelet α-granule proteins and platelet glycoproteins. In order to investigate this differentiation process further we have studied the expression of the mRNA encoding PDGF-A and PDGF-B (c-sis). Upon addition of the phorbol ester to the culture medium the expression of the c-sis transcript was enhanced about 7-fold over a period of 4 days. With dimethyl sulfoxide there was no significant stimulation of the expression. Addition of cycloheximide to HEL cells treated for a short period with phorbol ester superinduced the expression of the c-sis gene. The HEL cells did not express the A-chain mRNA even in the presence of phorbol ester or dimethyl sulfoxide. This leads us to propose that synthesis of the PDGF-A chain and PDGF-B chain is differentially regulated in the megakaryocytic-like HEL cell line.

Erythroleukemia cell lines HEL and K-562: changes in isoenzyme profiles and morphology during induction of differentiation.

The effects of the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) and of hemin on the human erythroleukemia cell lines HEL and K-562 were studied using the parameters cellular morphology, cell proliferation, positivity in the nitro-blue tetrazolium (NBT)-reduction test, adherence to surface, development of pseudopodia, and isoenzyme profiles of carboxylic esterase, acid phosphatase, hexosaminidase and lactate dehydrogenase (LDH) separated by isoelectric focusing on horizontal polyacrylamide gels. TPA and hemin induced similar morphological changes in HEL and K-562, erythrocyte-like cells were seen to be the predominant population after exposure to hemin. Both TPA and hemin led to cessation of cell proliferation and to a dose-dependent decrease in the number of viable nucleated cells. Whereas HEL cells treated with TPA became positive in the NBT-reduction test, adhered to plastic surface and showed pseudopodia, HEL cells exposed to hemin and K-562 cells cultured with TPA or hemin did not show these markers indicative of the macrophage-cell lineage. TPA-treated HEL cells exhibited isoenzyme patterns which were characteristically seen in cells of the monocyte-macrophage complex. 'Myeloid isoenzyme profiles' were found in TPA-treated K-562 cells. As evidenced by the above described phenotypical changes, HEL cells appeared to differentiate along the macrophage and erythroid cell lineages. Induced K-562 cells displayed myeloid and erythrocytic markers.