Jun N-terminal kinase pathway enhances signaling of monocytic differentiation of human leukemia cells induced by 1,25-dihydroxyvitamin D3

Vitamin D and Atherosclerosis: Unraveling the Impact on Macrophage Function

Vitamin D plays a crucial role in preventing atherosclerosis and in the regulation of macrophage function. This review aims to provide a comprehensive summary of the clinical evidence regarding the impact of vitamin D on atherosclerotic cardiovascular disease, atherosclerotic cerebrovascular disease, peripheral arterial disease, and associated risk factors. Additionally, it explores the mechanistic studies investigating the influence of vitamin D on macrophage function in atherosclerosis. Numerous findings indicate that vitamin D inhibits monocyte or macrophage recruitment, macrophage cholesterol uptake, and esterification. Moreover, it induces autophagy of lipid droplets in macrophages, promotes cholesterol efflux from macrophages, and regulates macrophage polarization. This review particularly focuses on analyzing the molecular mechanisms and signaling pathways through which vitamin D modulates macrophage function in atherosclerosis. It claims that vitamin D has a direct inhibitory effect on the formation, adhesion, and migration of lipid-loaded monocytes, thus exerting anti-atherosclerotic effects. Therefore, this review emphasizes the crucial role of vitamin D in regulating macrophage function and preventing the development of atherosclerosis.

Securinine Induces Differentiation of Human Promyelocytic Leukemic HL-60 Cells through JNK-Mediated Signaling Pathway

Acute myeloid leukemia is characterized by abnormal differentiation of hematopoietic stem cells, leading to the accumulation of immature myeloid cells. Differentiation therapy has been a successful treatment option for acute promyelocytic leukemia but suffers from adverse effects. Therefore, search for novel differentiation-inducing agents with minimal side effects is desirable. Securinine, a naturally-occurring alkaloid, induces differentiation in various leukemic cells and apoptosis in other types of cancers. However, the underlying molecular mechanism(s) remain elusive. Our study aimed to elucidate the possible molecular mechanism(s) and signaling events involved in securinine-induced differentiation of HL-60 cells. Securinine inhibited proliferation in a time- and dose-dependent manner and triggered differentiation. A higher CD14+ population indicated maturation toward monocytic lineage. Securinine caused cell cycle arrest at the G0/G1 phase and enhanced ROS generation. Quantitative gene expression analysis showed significant down-regulation of C/EBP-α, C/EBP-ε, GAΤΑ, and c-myc and up-regulation of the PU.1 gene. The expression of distinct protein kinases Lyn, Chk-2, Yes, FAK, c-Jun, and JNK were enhanced. Use of specific inhibitors of crucial intracellular signaling proteins indicated that JNK and ERK blockade resulted in a significant decline in differentiation. These data thus confirm that securinine induces differentiation through the activation of the JNK-ERK signaling pathway in HL-60 cells.

JNK1 as a signaling node in VDR-BRAF induction of cell death in AML

Numerous clinical studies of vitamin D, its derivatives or analogs, have failed to clearly demonstrate sustained benefits when used for the treatment of human malignant diseases. However, given the strong preclinical evidence of anti-neoplastic activity and the epidemiological associations suggesting that vitamin D compounds may have a place in cancer therapy, attempts are continuing to devise new approaches to their therapeutic use. This laboratory has developed a strategy to enhance the effectiveness of the currently standard therapy of Acute Myeloid Leukemia (AML) by the immediate addition of the vitamin D2 analog Doxercalciferol combined with the plant polyphenol-derived Carnosic acid to AML cells previously treated with Cytarabine (AraC). Enhancement of AML cell death was noted to be dependent on VDR and BRAF kinase. Here we document that the stress-related kinase JNK is an important additional component of cell death enhancement in this protocol. Either the Knock-down or the inhibition of JNK activity reduced the enhancement of AraC-induced cell death, and we show that JNK signaling to the apoptosis regulator BIM and Caspase executioners of cell death are downstream of VDR and BRAF. A clear understanding of the molecular basis for the increased efficacy of AraC in the therapy of AML is expected to bring this regimen to a clinical trial.

S100A9 induces differentiation of acute myeloid leukemia cells through TLR4

S100A8 and S100A9 are calcium-binding proteins predominantly expressed by neutrophils and monocytes and play key roles in both normal and pathological inflammation. Recently, both proteins were found to promote tumor progression through the establishment of premetastatic niches and inhibit antitumor immune responses. Although S100A8 and S100A9 have been studied in solid cancers, their functions in hematological malignancies remain poorly understood. However, S100A8 and S100A9 are highly expressed in acute myeloid leukemia (AML), and S100A8 expression has been linked to poor prognosis in AML. We identified a small subpopulation of cells expressing S100A8 and S100A9 in AML mouse models and primary human AML samples. In vitro and in vivo analyses revealed that S100A9 induces AML cell differentiation, whereas S100A8 prevents differentiation induced by S100A9 activity and maintains AML immature phenotype. Treatment with recombinant S100A9 proteins increased AML cell maturation, induced growth arrest, and prolonged survival in an AML mouse model. Interestingly, anti-S100A8 antibody treatment had effects similar to those of S100A9 therapy in vivo, suggesting that high ratios of S100A9 over S100A8 are required to induce differentiation. Our in vitro studies on the mechanisms/pathways involved in leukemic cell differentiation revealed that binding of S100A9 to Toll-like receptor 4 (TLR4) promotes activation of p38 mitogen-activated protein kinase, extracellular signal-regulated kinases 1 and 2, and Jun N-terminal kinase signaling pathways, leading to myelomonocytic and monocytic AML cell differentiation. These findings indicate that S100A8 and S100A9 are regulators of myeloid differentiation in leukemia and have therapeutic potential in myelomonocytic and monocytic AMLs.

DNA Repair in Despair-Vitamin D Is Not Fair

The role of vitamin D as a treatment option for neoplastic diseases, once considered to have a bright future, remains controversial. The preclinical studies discussed herein show compelling evidence that Vitamin D Derivatives (VDDs) can convert some cancer and leukemia cells to a benign phenotype, by differentiation/maturation, cell cycle arrest, or induction of apoptosis. Furthermore, there is considerable, though still evolving, knowledge of the molecular mechanisms underlying these changes. However, the attempts to clearly document that the treatment outcomes of human neoplastic diseases can be positively influenced by VDDs have been, so far, disappointing. The clinical trials to date of VDDs, alone or combined with other agents, have not shown consistent results. It is our contention, shared by others, that there were limitations in the design or execution of these trials which have not yet been fully addressed. Based on the connection between upregulation of JNK by VDDs and DNA repair, we propose a new avenue of attack on cancer cells by increasing the toxicity of the current, only partially effective, cancer chemotherapeutic drugs by combining them with VDDs. This can impair DNA repair and thus kill the malignant cells, warranting a comprehensive study of this novel concept. J. Cell. Biochem. 117: 1733-1744, 2016. © 2016 Wiley Periodicals, Inc.

Vitamin D Control of Hematopoietic Cell Differentiation and Leukemia

It is now well known that in the mammalian body vitamin D is converted by successive hydroxylations to 1,25-dihydroxyvitamin D (1,25D), a steroid-like hormone with pleiotropic properties. These include important contributions to the control of cell proliferation, survival and differentiation, as well as the regulation of immune responses in disease. Here, we present recent advances in current understanding of the role of 1,25D in myelopoiesis and lymphopoiesis, and the potential of 1,25D and analogs (vitamin D derivatives; VDDs) for the control of hematopoietic malignancies. The reasons for the unimpressive results of most clinical studies of the therapeutic effects of VDDs in leukemia and related diseases may include the lack of a precise rationale for the conduct of these studies. Further, clinical trials to date have generally used extremely heterogeneous patient populations and, in many cases, small numbers of patients, generally without controls. Although low calcemic VDDs have been used and combined with agents that can increase the leukemia cell killing or differentiation effects in acute leukemias, the sequencing of agents used for combination therapy should to be more clearly delineated. Most importantly, it is recommended that in future clinical trials the rationale for the basis of the enhancing action of drug combinations should be clearly articulated and the effects on anticancer immunity should also be evaluated.

GSK-3 Inhibition Sensitizes Acute Myeloid Leukemia Cells to 1,25D-Mediated Differentiation

1,25-dihydroxyvitamin D3 (1,25D), the biologically active form of vitamin D, is widely considered a promising therapy for acute myeloid leukemia (AML) based on its ability to drive differentiation of leukemic cells. However, clinical trials have been disappointing in part to dose-limiting hypercalcemia. Here we show how inhibiting glycogen synthase kinase 3 (GSK3) can improve the differentiation response of AML cells to 1,25D-mediated differentiation. GSK3 inhibition in AML cells enhanced the differentiating effects of low concentrations of 1,25D. In addition, GSK3 inhibition augmented the ability of 1,25D to induce irreversible growth inhibition and slow the progression of AML in mouse models. Mechanistic studies revealed that GSK3 inhibition led to the hyperphosphorylation of the vitamin D receptor (VDR), enabling an interaction between VDR and the coactivator, SRC-3 (NCOA3), thereby increasing transcriptional activity. We also found that activation of JNK-mediated pathways in response to GSK3 inhibition contributed to the potentiation of 1,25D-induced differentiation. Taken together, our findings offer a preclinical rationale to explore the repositioning of GSK3 inhibitors to enhance differentiation-based therapy for AML treatment. Cancer Res; 76(9); 2743-53. ©2016 AACR.

Evaluation of the lipopolysaccharide-induced transcription of the human TREM-1 gene in vitamin D3-matured THP-1 macrophage-like cells

Triggering receptor expressed on myeloid cells-1 (TREM-1) plays a role in inflammation by augmenting inflammatory responses through the production of pro-inflammatory cytokines. TREM-1 is expressed in mature macrophages, and is upregulated by stimulation with bacterial components, such as lipopolysaccharide (LPS). In the present study, the regulatory mechanisms responsible for the transcription of the human TREM-1 gene were examined using a human monocytic cell line (THP-1 cells). Reverse transcription-polymerase chain reaction (RT-PCR) revealed that TREM-1 mRNA was constitutively expressed at a low level in resting cells, and that its expression was upregulated by treatment with vitamin D3 (VitD3), but not by LPS. Importantly, TREM-1 mRNA expression was further upregulated by stimulation of the VitD3‑treated THP-1 cells with LPS. In addition, a luciferase reporter assay revealed that the serum response element (SRE) was involved in VitD3-induced promoter activity, whereas the activator protein-1 (AP-1) sites participated in the VitD3- and LPS-induced promoter activity. Of note, the CCAAT-enhancer-binding protein (C/EBP) site contributed not only to basal, but also to VitD3- and LPS-induced promoter activity. Transfection with transcription factor oligodeoxynucleotide (ODN) decoys indicated that transcription factors of the C/EBP and AP-1 families are likely involved in the basal, as well as in the VitD3- and LPS-induced TREM-1 transcription. Western blot analysis indicated that, of the members of the C/EBP family, C/EBPα was constitutively expressed in resting cells; its expression was enhanced by treatment with VitD3 and was further increased by treatment with VitD3 and LPS. Moreover, the expression of c-Fos and c-Jun (members of the AP-1 family) was augmented by treatment with both VitD3 and LPS. These observations indicate that members of the C/EBP family participate not only in basal, but also in the VitD3- and LPS-induced promoter activity of the human TREM-1 gene, and that members of the AP-1 family are involved in the VitD3- and LPS-induced promoter activity.

Vitamin D Protects Against Atherosclerosis via Regulation of Cholesterol Efflux and Macrophage Polarization in Hypercholesterolemic Swine

OBJECTIVE

Prevalence of vitamin D (VD) deficiency and its association with the risk of cardiovascular disease prompted us to evaluate the effect of VD status on lipid metabolism and atherosclerosis in hypercholesterolemic microswine.

APPROACH AND RESULTS

Yucatan microswine were fed with VD-deficient (0 IU/d), VD-sufficient (1000 IU/d), or VD-supplemented (3000 IU/d) high-cholesterol diet for 48 weeks. Serum lipids and 25(OH)-cholecalciferol levels were measured biweekly. Histology and biochemical parameters of liver and arteries were analyzed. Effect of 1,25(OH)2D3 on cholesterol metabolism was examined in human hepatocyte carcinoma cell line (HepG2) and human monocytic cell line (THP-1) macrophage-derived foam cells. VD deficiency decreased plasma high-density lipoprotein levels, expression of liver X receptors, ATP-binding membrane cassette transporter A1, and ATP-binding membrane cassette transporter G1 and promoted cholesterol accumulation and atherosclerosis in hypercholesterolemic microswine. VD promoted nascent high-density lipoprotein formation in HepG2 cells via ATP-binding membrane cassette transporter A1-mediated cholesterol efflux. Cytochrome P450 (CYP)27B1 and VD receptor were predominantly present in the CD206(+) M2 macrophage foam cell-accumulated cores in coronary artery plaques. 1,25(OH)2D3 increased the expression of liver X receptors, ATP-binding membrane cassette transporter A1, and ATP-binding membrane cassette transporter G1 and promoted cholesterol efflux in THP-1 macrophage-derived foam cells. 1,25(OH)2D3 decreased intracellular free cholesterol and polarized macrophages to M2 phenotype with decreased expression of tumor necrosis factor-α, interleukin-1β, interleukin-6 under lipopolysaccharide stimulation. 1,25(OH)2D3 markedly induced CYP27A1 expression via a VD receptor-dependent c-Jun N-terminal kinase (JNK) 1/2 signaling pathway and increased 27-hydroxycholesterol levels, which induced liver X receptors, ATP-binding membrane cassette transporter A1, and ATP-binding membrane cassette transporter G1 expression and stimulated cholesterol efflux that was inhibited by VD receptor antagonist and JNK1/2 signaling inhibitor in THP-1 macrophage-derived foam cell.

CONCLUSIONS

VD protects against atherosclerosis in hypercholesterolemic swine via controlling cholesterol efflux and macrophage polarization via increased CYP27A1 activation.

The Potential of Vitamin D-Regulated Intracellular Signaling Pathways as Targets for Myeloid Leukemia Therapy

The current standard regimens for the treatment of acute myeloid leukemia (AML) are curative in less than half of patients; therefore, there is a great need for innovative new approaches to this problem. One approach is to target new treatments to the pathways that are instrumental to cell growth and survival with drugs that are less harmful to normal cells than to neoplastic cells. In this review, we focus on the MAPK family of signaling pathways and those that are known to, or potentially can, interact with MAPKs, such as PI3K/AKT/FOXO and JAK/STAT. We exemplify the recent studies in this field with specific relevance to vitamin D and its derivatives, since they have featured prominently in recent scientific literature as having anti-cancer properties. Since microRNAs also are known to be regulated by activated vitamin D, this is also briefly discussed here, as are the implications of the emerging acquisition of transcriptosome data and potentiation of the biological effects of vitamin D by other compounds. While there are ongoing clinical trials of various compounds that affect signaling pathways, more studies are needed to establish the clinical utility of vitamin D in the treatment of cancer.

ERK5 pathway regulates transcription factors important for monocytic differentiation of human myeloid leukemia cells

Mitogen-activated protein kinases (MAPKs) are important transducers of external signals for cell growth, survival, and other cellular responses including cell differentiation. Several MAPK cascades are known with the MEK1/2-ERK1/2, JNK, and p38MAPKs receiving most attention, but the role of MEK5-ERK5 in intracellular signaling deserves more scrutiny, as this pathway transmits signals that can complement ERK/2 signaling. We hypothesized that the ERK5 pathway plays a role in the control of monocytic differentiation, which is disturbed in myeloid leukemia. We therefore examined the cellular phenotype and key molecular events which occur when human myeloid leukemia cells, acute (AML) or chronic (CML), are forced to differentiate by vitamin D derivatives (VDDs). This study was performed using established cell lines HL60 and U937, and primary cultures of blasts from 10 patients with ML. We found that ERK5 and its direct downstream target transcription factor MEF2C are upregulated by 1,25D in parallel with monocytic differentiation. Further, inhibition of ERK5 activity by specific pharmacological agents BIX02189 and XMD8-92 alters the phenotype of these cells by reducing the abundance of the VDD-induced surface monocytic marker CD14, and concomitantly increasing surface expression of the general myeloid marker CD11b. Similar results were obtained when the expression of ERK5 was reduced by siRNA or short hairpin (sh) RNA. ERK5 inhibition resulted in an expected decrease in MEF2C activation. We also found that in AML cells the transcription factor C/EBPβ is positively regulated, while C/EBPα is negatively regulated by ERK5. These findings provide new understanding of dysregulated differentiation in human myeloid leukemia.

Regulation of monocyte differentiation by specific signaling modules and associated transcription factor networks

Monocyte/macrophages are important players in orchestrating the immune response as well as connecting innate and adaptive immunity. Myelopoiesis and monopoiesis are characterized by the interplay between expansion of stem/progenitor cells and progression towards further developed (myelo)monocytic phenotypes. In response to a variety of differentiation-inducing stimuli, various prominent signaling pathways are activated. Subsequently, specific transcription factors are induced, regulating cell proliferation and maturation. This review article focuses on the integration of signaling modules and transcriptional networks involved in the determination of monocytic differentiation.

Methanol extract of Antrodia cinnamomea mycelia induces phenotypic and functional differentiation of HL60 into monocyte-like cells via an ERK/CEBP-β signaling pathway

Antrodia cinnamomea (named as Niu-chang-chih), a well-known Taiwanese folk medicinal mushroom, has a spectrum of biological activities, especially with anti-tumor property. This study was carried out for the first time to examine the potential role and the underlying mechanisms of A. cinnamomea in the differentiation of human leukemia HL60 cells. We found that the methanol extract of liquid cultured mycelia of A. cinnamomea (MEMAC) inhibited proliferation and induced G1-phase cell cycle arrest in HL60 cells. MEMAC could induce differentiation of HL60 cells into the monocytic lineage, as evaluated by the morphological change, nitroblue tetrazolium reduction assay, non-specific esterase assay, and expression of CD14 and CD11b surface antigens. In addition, MEMAC activated the extracellular signal-regulated kinase (ERK) pathway and increased CCAAT/enhancer-binding protein β (C/EBPβ) expression. Reverse transcriptase polymerase chain reaction analysis showed that MEMAC upregulated the expression of C/EBPβ and CD14 mRNA in HL60 cells. DNA affinity precipitation assay and chromatin immunoprecipitation analyses indicated that MEMAC enhanced the direct binding of C/EBPβ to its response element located at upstream of the CD14 promoter. Furthermore, inhibiting ERK pathway activation with PD98059 markedly blocked MEMAC-induced HL60 monocytic differentiation. Consistently, the MEMAC-mediated upregulation of C/EBPβ and CD14 was also suppressed by PD98059. These findings demonstrate that MEMAC-induced HL60 cell monocytic differentiation is via the activating ERK signaling pathway, and downstream upregulating the transcription factor C/EBPβ and differentiation marker CD14 gene, suggesting that MEMAC might be a potential differentiation-inducing agent for treatment of leukemia.

Thrombomodulin-induced differentiation of acute myelomonocytic leukemia cells via JNK signaling

We found recombinant human soluble thrombomodulin (rTM) induced growth arrest and differentiation of THP-1 cells by activating JNK/c-Jun signaling. Further activation of JNK by 1,25-(OH)(2)D(3) significantly enhanced rTM-mediated growth arrest and differentiation of THP-1 cells. Importantly, forced expression of domains 1, 2 and 3 of TM (TMD123) induced growth arrest and differentiation of leukemia cells freshly isolated from individuals with AMLs of M4/M5-French-American-British classification subtypes, but not those with less advanced AML. Further studies indicated that the epidermal growth factor-like domain of TM was critical for the anti-leukemia effects of TM and these effects were independent of protein C activation.

MicroRNA-32 upregulation by 1,25-dihydroxyvitamin D3 in human myeloid leukemia cells leads to Bim targeting and inhibition of AraC-induced apoptosis

1,25-Dihydroxyvitamin D(3) (1,25D) used to treat human acute myeloid leukemia (AML) cells induces features of normal monocytes, but the mechanisms underlying this response are not fully understood. We hypothesized that one or more microRNAs (miRNA) known to control mouse hematopoiesis and lineage commitment might contribute to the ability of 1,25D to control the malignant phenotype. Here we report that 1,25D markedly induces expression of miR-32 in human myeloid leukemia cells, in which it targets the 3'-untranslated region of the mRNA encoding the proapoptotic factor Bim to reduce its expression. RNAi-mediated suppression of the miRNA-processing enzymes Drosha and Dicer increased Bim levels, in support of the concept that Bim is under miRNA control in AML cells. Antisense-mediated suppression of miR-32 was sufficient to upregulate Bim expression in AML cells. Conversely, ectopic expression of miR-32 downregulated Bim expression and increased the differentiation response to 1,25D treatment in a manner that was associated with increased cell survival. The positive effects of miR-32 on cell survival were confirmed by evidence of increased cell death in AML cells preexposed to antisense miR-32 before treatment with arabinocytosine, a chemotherapeutic drug used to treat human AML. Together, our findings indicate that miR-32 blockade is sufficient to elevate Bim expression and sensitize AML cells to chemotherapy-induced apoptosis. Thus, agents which can inhibit miR-32 expression may offer clinical utility by enhancing therapeutic efficacy in human AML.

Oncoprotein Cot1 represses kinase suppressors of Ras1/2 and 1,25-dihydroxyvitamin D3-induced differentiation of human acute myeloid leukemia cells

Metabolites and derivatives of vitamin D are well-known inducers of monocytic differentiation, but the mechanistic basis for their action is not fully elucidated. Here we show that the product of protooncogene Cot1 represses the monocytic phenotype in human acute myeloid leukemia (AML) cells induced to differentiate by 1,25-dihydroxyvitamin D(3) (1,25D), even though the expression of cellular Cot1 increases early in the process of 1,25D-induced differentiation. Interestingly, the expression of the two members of the Kinase Suppressor of Ras (KSR) family of molecular scaffolds, known to be positive regulators of Ras signaling and of 1,25D-induced differentiation, increases in parallel with Cot1 in 1,25D-treated cells. However, KSR1/2 are negatively regulated by Cot1, as determined by transfection of siCot1, and confirmed by a reverse effect of ectopic expression of Cot1. The effect of Cot1 in AML cells appears to be cell-type specific, as previous reports in other cell types found KSR-2 to be a negative regulator of Cot1, a reverse relationship. Also in contrast to findings in other cells, in AML cells Cot1 exerts negative control on the MAP kinase pathways, since siCot1 increases the levels of activated Raf1, p90RSK, JNK1, c-jun, and p38, though not of MEK/ERK. These findings have implications for therapy of AML, since in AML cells active MAPKs hasten cell differentiation, and specific pharmacological inhibitors of Cot1 kinase activity have recently became available, thus making Cot1 a "druggable" target.

Isoforms of p38MAPK gamma and delta contribute to differentiation of human AML cells induced by 1,25-dihydroxyvitamin D₃

Inhibition of p38MAPK alpha/beta is known to enhance 1,25-dihydroxyvitamin (1,25D)-induced monocytic differentiation, but the detailed mechanism of this effect was not clear. We now show that the enhancement of differentiation becomes apparent with slow kinetics (12-24 h). Interestingly, the inhibition of p38MAPK alpha/beta by their selective inhibitor SB202190 (SB) leads to an upregulated expression of p38MAPK isoforms gamma and delta in 1,25D-treated AML cells, in cell lines and in primary culture. Although the expression and activating phosphorylations of p38MAPK alpha are also increased by an exposure of the cells to SB, its kinase activity is blocked by SB, as shown by reduced levels of phosphorylated Hsp27, a downstream target of p38MAPK alpha. A positive role of p38MAPKs in 1,25D-induced differentiation is shown by the inhibition of differentiation by antisense oligonucleotides to all p38MAPK isoforms. Other principal branches of MAPK pathways showed early (6 h) activation of MEK/ERK by SB, followed by activation of JNK1/2 pathway and enhanced expression and/or activation of PU.1, ATF-2 differentiation-related transcription factors. Taken together with previous reports, the results indicate that 1,25D-induced differentiation is enhanced by the activation of at least three branches of MAPK pathways (ERK1/2; p38MAPK gamma/delta; JNK1/2). This activation may result from the removal of feedback inhibition of an upstream regulator of those pathways, when p38MAPK alpha and beta are inhibited by SB.

Expression of MAP3 kinase COT1 is up-regulated by 1,25-dihydroxyvitamin D3 in parallel with activated c-jun during differentiation of human myeloid leukemia cells

The role of MAP kinase pathways in 1,25-dihydroxyvitamin D3 (1,25D)-induced differentiation of myeloid leukemia cells is well established, but the mechanisms by which 1,25D activates these pathways are not entirely clear. Following the finding that kinase suppressors of ras (KSR) 1 and 2 are directly regulated by 1,25D and participate in the monocytic differentiation process, we investigated if the COT1 oncogene (Tpl2 in the rat), known to interact with human KSR2 (hKSR2), is also involved in 1,25D-induced differentiation in leukemia cells. Here we report that the exposure of HL60 and U937 myeloid leukemia cells to 1,25D increases COT1 expression in a concentration-dependent manner. However, COT1 appears to have a differentiation-limiting role in these cells, as an exposure of HL60 and U937 cells to a pharmacological inhibitor of COT1 kinase activity, 4-(3-chloro-4-fluorophenylamino)-6-(pyridin-3-yl-methylamino-3-cyano-[1-7]-naphthyridine, results in increased 1,25D-induced differentiation. These findings provide an additional insight into the 1,25D-regulation of MAPK pathways that contribute to monocytic differentiation process of myeloid leukemia cells.

Targeting iron homeostasis induces cellular differentiation and synergizes with differentiating agents in acute myeloid leukemia

Differentiating agents have been proposed to overcome the impaired cellular differentiation in acute myeloid leukemia (AML). However, only the combinations of all-trans retinoic acid or arsenic trioxide with chemotherapy have been successful, and only in treating acute promyelocytic leukemia (also called AML3). We show that iron homeostasis is an effective target in the treatment of AML. Iron chelating therapy induces the differentiation of leukemia blasts and normal bone marrow precursors into monocytes/macrophages in a manner involving modulation of reactive oxygen species expression and the activation of mitogen-activated protein kinases (MAPKs). 30% of the genes most strongly induced by iron deprivation are also targeted by vitamin D3 (VD), a well known differentiating agent. Iron chelating agents induce expression and phosphorylation of the VD receptor (VDR), and iron deprivation and VD act synergistically. VD magnifies activation of MAPK JNK and the induction of VDR target genes. When used to treat one AML patient refractory to chemotherapy, the combination of iron-chelating agents and VD resulted in reversal of pancytopenia and in blast differentiation. We propose that iron availability modulates myeloid cell commitment and that targeting this cellular differentiation pathway together with conventional differentiating agents provides new therapeutic modalities for AML.

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

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

Vitamin D and differentiation in cancer

This paper reviews the current understanding of the vitamin D-induced differentiation of neoplastic cells, which results in the generation of cells that acquire near-normal, mature phenotype. Examples of the criteria by which differentiation is recognized in each cell type are provided, and only those effects of 1alpha,25-dihydroxyvitamin D(3) (1,25D) on cell proliferation and survival that are associated with the differentiation process are emphasized. The existing knowledge, often fragmentary, of the signaling pathways that lead to vitamin D-induced differentiation of colon, breast, prostate, squamous cell carcinoma, osteosarcoma, and myeloid leukemia cancer cells is outlined. The important distinctions between the different mechanisms of 1,25D-induced differentiation that are cell-type and cell-context specific are pointed out where known. There is a considerable body of evidence that the principal human cancer cells can be suitable candidates for chemoprevention or differentiation therapy with vitamin D. However, further studies are needed to fully understand the underlying mechanisms in order to improve the therapeutic approaches.

c-Jun N-terminal kinase 2 (JNK2) antagonizes the signaling of differentiation by JNK1 in human myeloid leukemia cells resistant to vitamin D

1,25-Dihydroxyvitamin D3 (1,25D) induces differentiation of myeloid leukemia cells, but resistant cells are also encountered. We studied the mechanistic basis for the resistance in a model system using enhancers of 1,25D, the antioxidant carnosic acid and a kinase inhibitor SB202190. Knock-down (KD) of JNK2p54 unexpectedly increased the intensity of differentiation induced by the 1,25D, carnosic acid and SB202190 (DCS) combination. This was associated with upregulation of activated JNK1p46, and the transcription factors regulated by the JNK pathway, c-Jun, ATF2 and JunB, as well as C/EBP beta. In contrast, KD of JNK1p46 reduced the intensity of DCS-induced differentiation, and partially abrogated activation of c-Jun/AP-1 transcription factors.

Differential enhancement of leukaemia cell differentiation without elevation of intracellular calcium by plant-derived sesquiterpene lactone compounds

BACKGROUND AND PURPOSE

All-trans retinoic acid (ATRA) induces complete remission in a majority of acute promyelocytic leukaemia patients, but resistance of leukaemic cells to ATRA and its toxicity, such as hypercalcaemia, lead to a limitation of treatment. Therefore, combination therapies with differentiation-enhancing agents at non-toxic concentrations of ATRA may overcome its side effects. Here, we investigated the effect of plant-derived sesquiterpene lactone compounds and their underlying mechanisms in ATRA-induced differentiation of human leukaemia HL-60 cells.

EXPERIMENTAL APPROACH

HL-60 cells were treated with four sesquiterpene lactones (helenalin, costunolide, parthenolide and sclareolide) and cell differentiation was determined by NBT reduction, Giemsa and cytofluorometric analyses. Signalling pathways were assessed by western blotting, gel-shift assay and kinase activity determinations and intracellular calcium levels were determined using a calcium-specific fluorescent probe.

KEY RESULTS

Helenalin, costunolide and parthenolide, but not sclareolide, increased ATRA-induced HL-60 cell differentiation into a granulocytic lineage. Signalling kinases PKC and ERK were involved in the ATRA-induced differentiation enhanced by all of the effective sesquiterpene lactones, but JNK and PI3-K were involved in the ATRA-induced differentiation enhanced by costunolide and parthenolide. Enhancement of cell differentiation closely correlated with inhibition of NF-kappaB DNA-binding activity by all three effective compounds. Importantly, enhancement of differentiation induced by 50 nM ATRA by the sesquiterpene lactones was not accompanied by elevation of basal intracellular calcium concentrations.

CONCLUSIONS AND IMPLICATIONS

These results indicate that plant-derived sesquiterpene lactones may enhance ATRA-mediated cell differentiation through distinct pathways.

Realgar-induced differentiation is associated with MAPK pathways in HL-60 cells

The clinical efficacy and safety of realgar (arsenic sulfide, As(4)S(4)) in the treatment of acute promyelocytic leukemia in China have given rise to an upsurge in research on the underlying mechanism. We prepared realgar nanoparticles (RNPs) to examine their effect on the differentiation of HL-60 cells. Treatment with RNPs at 6 microM for 72 h induced cell differentiation that was assessed by morphological change, NBT reductive ability, and elevation of CD11b expression at both mRNA and protein levels. The RNP-induced differentiation was synergized, enhanced and suppressed by the inhibition of p38 MAPK, JNK and ERK pathways, respectively. Our findings demonstrate that MAPK signaling pathways are closely related to the RNP-induced differentiation in HL-60 cells.

Enhancing effects of ceramide derivatives on 1,25-dihydroxyvitamin D(3)-induced differentiation of human HL-60 leukemia cells

Differentiation-inducing therapy by agents such as 1,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] represents a useful approach for the treatment for cancer, including acute myeloid leukemia (AML). Recent studies demonstrated that the combined administration of 1,25-(OH)(2)D(3) and differentiation-enhancing agents could alleviate the side effects of 1,25-(OH)(2)D(3) and improve the rate of long term survival. In this study, we determined the enhancing activities of ceramide derivatives on 1,25-(OH)(2)D(3)-induced differentiation of human myeloid leukemia HL-60 cells. Importantly, some of these derivatives -- namely, A2, B3, and H9 -- enhanced the 1,25-(OH)(2)D(3)-induced differentiation of HL-60 cells in a concentration-dependent manner. In addition, the morphologic studies using Giemsa staining and flow cytometric analysis demonstrated that the combined treatment of 1,25-(OH)(2)D(3) with one of the three analogues, A2, B3, and H9, directed the HL-60 cells into monocytic lineage, but not into granulocytic lineage. The inhibition studies demonstrated that A2, B3, and H9, enhanced 1,25-(OH)(2)D(3)-induced differentiation of HL-60 cells via the PI3-K/PKC/JNK/ERK pathways. The ability of ceramide derivatives to enhance the differentiation-inducing potential of 1,25-(OH)(2)D(3) may contribute to an effective therapy for AML.

Raf-1 signaling is required for the later stages of 1,25-dihydroxyvitamin D3-induced differentiation of HL60 cells but is not mediated by the MEK/ERK module

We are interested in determining the signaling pathways for 1,25-dihydroxyvitamin D3 (1,25D)-induced differentiation of HL60 leukemic cells. One possible candidate is Raf-1, which is known to signal cell proliferation and neoplastic transformation through MEK, ERK, and downstream targets. It can also participate in the regulation of cell survival and various forms of cell differentiation, though the precise pathways are less well delineated. Here we report that Raf-1 has a role in monocytic differentiation of human myeloid leukemia HL60, which is not mediated by MEK and ERK, but likely by direct interaction with p90RSK. Specifically, we show that Raf-1 and p90RSK are increasingly activated in the later stages of differentiation of HL60 cells, at the same time as activation of MEK and ERK is decreasing. Transfection of a wild-type Raf-1 construct enhances 1,25D-induced differentiation, while antisense Raf-1 or short interfering (si) Raf-1 reduces 1,25D-induced differentiation. In contrast, antisense oligodeoxynucleotides (ODN) and siRNAs to MEK or ERK have no detectable effect on differentiation. In late stage differentiating cells Raf-1 and p90RSK are found as a complex, and inhibition of Raf-1, but not MEK or ERK expression reduces the levels of phosphorylated p90 RSK. These findings support the thesis that Raf-1 signals cell proliferation and cell differentiation through different intermediary proteins.

1Alpha,25-dihydroxyvitamin D3-mediated stimulation of steroid sulphatase activity in myeloid leukaemic cell lines requires VDRnuc-mediated activation of the RAS/RAF/ERK-MAP kinase signalling pathway

1Alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) stimulates the activity of steroid sulphatase (STS) in myeloid cells [Hughes et al., 2001, 2005]. This was attenuated by inhibitors of phospholipase D (PLD) (n-butanol, 2,3-diphosphoglyceric acid, C(2)-ceramide) and phosphatidate phosphohydrolase (PAP) (propranolol and chlorpromazine), but was unaffected by inhibitors of phospholipase C. The 1alpha,25(OH)(2)D(3)-induced STS activity was also attenuated by inhibitors of protein kinase Calpha and protein kinase Cdelta (Go 6976, HBDDE and rottlerin), but not by an inhibitor of protein kinase Cbeta (LY379196). Additionally, 1alpha,25(OH)(2)D(3)-induced STS activity was attenuated by inhibitors of RAS (manumycin A), RAF (GW5074), MEK (PD098059 and U1026) and JNK (SP600125), but not p38 (PD169316). 1alpha,25(OH)(2)D(3) produced a rapid and long lasting stimulation of the ERK-MAP kinase signalling cascade in HL60 myeloid leukaemic cells. This 'non-genomic' effect of 1alpha,25(OH)(2)D(3) blocked by pharmacological antagonists of nuclear vitamin D receptors (VDR(nuc)) and does not appear to require hetero-dimerisation with the retinoid-X receptor (RXR). Inhibitors of the Src tyrosine kinase (PP1), RAS (manumycin A), RAS-RAF interactions (sulindac sulphide and RAS inhibitory peptide), RAF (GW5074 or chloroquine), and protein kinase Calpha (HBDDE) abrogated the 1alpha,25(OH)(2)D(3)-stimulated increase in ERK-MAP kinase activity. Taken together, these results show that 1alpha,25(OH)(2)D(3)/VDR(nuc) activation of the RAS/RAF/ERK-MAP kinase signalling pathway plays an important role in augmenting STS activity in human myeloid leukaemic cell lines.

Retinoid-mediated stimulation of steroid sulfatase activity in myeloid leukemic cell lines requires RARalpha and RXR and involves the phosphoinositide 3-kinase and ERK-MAP kinase pathways

All-trans retinoic acid and 9-cis-retinoic acid stimulate the activity of steroid sulfatase in HL60 acute myeloid leukemia cells in a concentration- and time-dependent manner. Neither of these 'natural retinoids' augmented steroid sulfatase activity in a HL60 sub-line that expresses a dominant-negative retinoic acid receptor alpha (RARalpha). Experiments with synthetic RAR and RXR agonists and antagonists suggest that RARalpha/RXR heterodimers play a role in the retinoid-stimulated increase in steroid sulfatase activity. The retinoid-driven increase in steroid sulfatase activity was attenuated by inhibition of phospholipase D (PLD), but not by inhibitors of phospholipase C. Experiments with inhibitors of protein kinase C (PKC) show that PKCalpha and PKCdelta play an important role in modulating the retinoid-stimulation of steroid sulfatase activity in HL60 cells. Furthermore, we show that pharmacological inhibition of the RAF-1 and ERK MAP kinases blocked the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells and, by contrast, inhibition of the p38-MAP kinase or JNK-MAP kinase had no effect. Pharmacological inhibitors of the phosphatidylinositol 3-kinase, Akt, and PDK-1 also abrogated the retinoid-stimulated increase in steroid sulfatase activity in HL60 cells. These results show that crosstalk between the retinoid-stimulated genomic and non-genomic pathways is necessary to increase steroid sulfatase activity in HL60 cells.

The requirement for and changing composition of the activating protein-1 transcription factor during differentiation of human leukemia HL60 cells induced by 1,25-dihydroxyvitamin D3

The activating protein-1 (AP-1) transcription factor complex is a heterogeneous entity, composed in mammalian cells of dimers chosen from a group of at least eight proteins belonging to three families: jun, fos, and activating transcription factor (ATF). The AP-1 complexes participate in diverse biological processes that include cell proliferation, survival, and differentiation. These seemingly contrasting functions have been attributed to the intensity and duration of the signals provided by AP-1, but the biological consequences of changing composition of the AP-1 complex have not been fully explored. Here, we show that functional AP-1 is required for 1,25-dihydroxyvitamin D3 (1,25D)-induced monocytic differentiation, and that the composition of the AP-1 protein complex that binds TRE, its cognate DNA element, changes as cells differentiate. In HL60 cells in an early stage of differentiation, the principal AP-1 components detected by gel shift analysis include c-jun, ATF-2, fos-B, fra-1, and fra-2. In cells with a more established monocytic phenotype, the demonstrable AP-1 components are c-jun, ATF-2, jun-B, and fos-B. Following the addition of 1 nmol/L of 1,25D, the cellular content of each of these four proteins markedly increased in a sustained manner, whereas the increases in c-fos, fra-1, fra-2, and jun-D were minimal, if any. Small increases in mRNA levels encoding all AP-1 component proteins, except c-fos, were also noted. These findings provide a basis for the previously found participation of the c-Jun N-terminal kinase pathway in 1,25D-induced differentiation of myeloid leukemia cells, and direct attention to jun-B and fos-B as new cellular therapeutic targets, that may promote replicative quiescence associated with differentiation of malignant cells.

The synthetic triterpenoid CDDO-imidazolide induces monocytic differentiation by activating the Smad and ERK signaling pathways in HL60 leukemia cells

Synthetic triterpenoids, CDDO (2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid) or CDDO-imidazolide [2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid imidazolide (CDDO-Im)], induce cell differentiation in myeloid leukemia cells but their mechanism of action is not known. CDDO-Im induces monocytic differentiation markers, CD14, and nonspecific esterase in HL60 leukemia cells. We show that CDDO-Im activates the extracellular signal–regulated kinase (ERK) signaling pathway and up-regulates CCAAT/enhancer-binding protein β, a transcription factor critical for monocytic differentiation. The monocytic differentiation induced by CDDO-Im was partially blocked by the mitogen-activated protein kinase/ERK kinase 1 inhibitor PD98059, suggesting that the mitogen-activated protein kinase-ERK1/2 pathway plays a role in the differentiation induced by CDDO-Im. Furthermore, CDDO-Im activates the transforming growth factor β (TGF-β)/Smad signaling pathway. CDDO-Im enhanced the phosphorylation of the receptor-regulated Smads, phospho-Smad3, and phospho-Smad1/5, but not phospho-Smad2, and induced the expression of Smad4. Monocytic differentiation induced by CDDO-Im was blocked by both TGF-β antibody and the bone morphogenetic protein (BMP) antagonist Noggin. This indicates that activation of the Smad signaling pathway by triterpenoids is an important mechanism of monocytic differentiation. CDDO-Im induced the synthesis of mRNA for TGF-β2, BMP6, TGF-β type II receptor, and BMP type II receptor. CDDO-Im synergized with members of the TGF-β superfamily or with 1α,25(OH)2vitamin D3 (D3) in monocytic differentiation, and the synergistic effect was particularly striking in combination with D3. The combination of triterpenoids and D3 may have a practical use in differentiation therapy of myeloid leukemia as well as for promoting the formation of bone and cartilage. [Mol Cancer Ther 2006;5(6):1452–8]

Induction of kinase suppressor of RAS-1(KSR-1) gene by 1, alpha25-dihydroxyvitamin D3 in human leukemia HL60 cells through a vitamin D response element in the 5'-flanking region

Differentiation therapy is being developed as an additional therapeutic option for the treatment of several forms of cancer, including myeloid leukemia. In model systems, the physiologically active form of vitamin D, 1, alpha25-dihydroxyvitamin D3 (1,25D), induces monocytic differentiation of human myeloid cells, but the mechanism is not clear. We report here, the first direct connection between the signal provided by 1,25D and the molecular circuitry known to be involved in monocytic differentiation. Specifically, we show that 1,25D selectively increases the expression of the gene encoding kinase suppressor of Ras-1 (KSR-1) in HL60 cells, while other differentiation-inducing agents such as 12-O-tetradecanoylphorbol-13-acetate, retinoic acid or dimethyl sulfoxide do not significantly increase KSR-1 expression. Further, the upregulation of KSR-1 gene by 1,25D is competed by ZK159222, an antagonist of vitamin D receptor (VDR) action, and can occur in the presence of protein synthesis inhibitor cycloheximide, showing that the effect is direct. Most importantly, we have identified a vitamin D responsive element (VDRE) in the promoter region of the human KSR-1 gene, to which VDR binds in a 1,25D-dependent manner, in vitro and in vivo. This binding is paralleled by increased association of RNA polymerase II with the transcription start site of KSR-1 gene, and the VDRE is functional in reporter assays. Our findings offer a potential mechanism for a signaling pathway that contributes to 1,25D-induced monocytic differentiation of human myeloid leukemia cells.

Cooperative antitumor effects of vitamin D3 derivatives and rosemary preparations in a mouse model of myeloid leukemia

1alpha,25-dihydroxyvitamin D(3) (1,25D(3)) is a powerful differentiation agent, which has potential for treatment of myeloid leukemias and other types of cancer, but the calcemia produced by pharmacologically active doses precludes the use of this agent in the clinic. We have shown that carnosic acid, the major rosemary polyphenol, enhances the differentiating and antiproliferative effects of low concentrations of 1,25D(3) in human myeloid leukemia cell lines (HL60, U937). Here we translated these findings to in vivo conditions using a syngeneic mouse leukemia tumor model. To this end, we first demonstrated that as in HL60 cells, differentiation of WEHI-3B D(-) murine myelomonocytic leukemia cells induced by 1 nM 1,25D(3) or its low-calcemic analog, 1,25-dihydroxy-16-ene-5,6-trans-cholecalciferol (Ro25-4020), can be synergistically potentiated by carnosic acid (10 microM) or the carnosic acid-rich ethanolic extract of rosemary leaves. This effect was accompanied by cell cycle arrest in G0 + G1 phase and a marked inhibition of cell growth. In the in vivo studies, i.p. injections of 2 microg Ro25-4020 in Balb/c mice bearing WEHI-3B D(-) tumors produced a significant delay in tumor appearance and reduction in tumor size, without significant toxicity. Another analog, 1,25-dihydroxy-16,23Z-diene-20-epi-26,27-hexafluoro-19-nor-cholecalciferol (Ro26-3884) administered at the same dose was less effective than Ro25-4020 and profoundly toxic. Importantly, combined treatment with 1% dry rosemary extract (mixed with food) and 1 microg Ro25-4020 resulted in a strong cooperative antitumor effect, without inducing hypercalcemia. These results indicate for the first time that a plant polyphenolic preparation and a vitamin D derivative can cooperate not only in inducing leukemia cell differentiation in vitro, but also in the antileukemic activity in vivo. These data may suggest novel protocols for chemoprevention or differentiation therapy of myeloid leukemia.

Cooperation between antioxidants and 1,25-dihydroxyvitamin D3 in induction of leukemia HL60 cell differentiation through the JNK/AP-1/Egr-1 pathway

Vitamin D derivatives have demonstrated anti-cancer activity, but their clinical use is precluded by hypercalcemia. Previously, we found that carnosic acid potentiates differentiation of human leukemia cells induced by low concentrations of 1alpha,25-dihydroxyvitamin D(3) (1,25D(3)). In this study, we investigated if this effect is a general property of antioxidants, and whether there is a common mechanism whereby antioxidants potentiate monocytic differentiation. We found that all antioxidants tested enhanced differentiation-related cell cycle arrest induced by a low (1 nM) concentration of 1,25D(3). Addition of antioxidants to 1,25D(3) activated the JNK pathway as indicated by increased phosphorylation of c-jun and ATF-2, although each compound alone had a minimal effect. Antioxidants also enhanced the 1,25D(3)-induced AP-1 DNA binding and transactivation ability. Expression of Egr-1 and c-fos was increased by combinations of antioxidants and 1,25D(3), in parallel with the activation of the JNK pathway. The potentiation of differentiation by antioxidants was inhibited by JNK inhibitor SP600125 and a dominant negative JNK 1/2 construct, and Egr-1 and c-fos expression was proportionally decreased, suggesting that JNK pathway regulates these transcription factors. While potentiating the prodifferentiation effect of 1,25D(3), antioxidants did not promote the elevation of basal levels of intracellular calcium by 1,25D(3). The results indicate that JNK-AP1 pathway has an important role in the potentiation of 1,25D(3)-induced differentiation by antioxidants, and regulates expression of Egr-1 and c-fos. Combinations of antioxidants with 1,25D(3) should be further evaluated for use in cancer chemoprevention and therapy.

The rationale for deltanoids in therapy for myeloid leukemia: role of KSR-MAPK-C/EBP pathway

The evidence for the promising potential for derivatives of Vitamin D (deltanoids) in the treatment of myeloid leukemias is increasing, but currently is not matched by the understanding of the precise mechanisms by which these anti-neoplastic effects are achieved. Unlike solid tumors in which growth retardation by deltanoids appears to result from inhibition of cell proliferation and the promotion of cell death by apoptosis, control of myeloid leukemia proliferation by deltanoids results from the induction of differentiation of the immature myelo-monocytic cells towards functional monocytic cells. We present here the accumulating evidence that a pathway that is initiated by deltanoid activation of Vitamin D receptor (VDR) and leads to monocytic differentiation of human myeloblastic HL60 cells, includes the MEK-ERK and JNK mitogen-activated protein kinases (MAPKs), their positive and negative regulators and a downstream effector C/EBPbeta. As in other cells, the abundance of VDR protein increases shortly after an exposure of HL60 cells to 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2) D(3)). Other early events include a parallel upregulation of kinase suppressor of Ras (KSR-1) and the activation of the ERK MAPK pathway and data suggest that KSR-1 acts to amplify the signal provided by low concentrations of 1alpha,25(OH)(2) D(3). Maintenance of monocytic differentiation may be enhanced by JNK, but diminished by p38, MAPK signaling. Downstream, one of the targets of these pathways is C/EBPbeta, which can directly interact with the promoter for CD14, a gene characteristically expressed in monocytes. Importantly, in freshly obtained acute myeloid leukemia (AML)-M2 cells exposed to PRI-2191, a novel deltanoid with a modified side chain, upregulation of C/EBPbeta paralleled the induction of monocytic differentiation. These data provide a basis for the hypothesis that deltanoid-induced upregulation of C/EBPbeta bypasses the block to granulocytic differentiation in myeloid leukemia cells by redirecting the cells to monocytic differentiation.

Translational study of vitamin D differentiation therapy of myeloid leukemia: effects of the combination with a p38 MAPK inhibitor and an antioxidant

Human myeloid leukemia cell lines are induced to terminal differentiation into monocyte lineage by 1,25-dihydroxyvitamin D3 (1,25D3) or its analogs (deltanoids). However, translation of these findings to the clinic is limited by calcemic effects of deltanoids. Strategies to overcome this problem include combination of deltanoids with other compounds to induce differentiation at lower, noncalcemic, deltanoid concentrations. We previously showed that either carnosic acid, an antioxidant, or SB202190, a p38 MAPK inhibitor, increase the potency of 1,25D3 in the HL60 cell line. Here, we report that simultaneous addition of both these agents further increases differentiation potency of deltanoids in this cell line and in freshly obtained leukemic cells ex vivo. Activity of MAPK pathways showed that increased differentiation was associated with enhanced activity of JNK pathway in all responding cell subtypes. Our studies suggest that patients with CML or AML subtypes M2 and M4, but not M1, M3 or M4eo, are particularly suitable for this combination therapy. We conclude that the established cell line HL60 presents a good model for some, but not all, subtypes of myeloid leukemia, and that the JNK pathway plays an important role in monocytic differentiation of human leukemic cells ex vivo, as well as in vitro.

MK-886 enhances tumour necrosis factor-alpha-induced differentiation and apoptosis

We investigated the role of the 5-lipoxygenase (5-LOX) pathway of arachidonic acid metabolism in tumour necrosis factor-alpha (TNF-alpha)-induced differentiation of human leukemic HL-60 cells using MK-886, an inhibitor of 5-LOX activating protein. MK-886 augmented cell cycle arrest and differentiation induced by TNF-alpha; however, both effects were probably 5-LOX-independent, because a general LOX inhibitor, NDGA, had no effect. Apoptosis was significantly elevated after combined TNF-alpha and MK-886 treatment, which could be partially associated with changes of Mcl-1 protein expression. NF-kappaB signalling or activation of JNKs were not modulated by MK-886. Thus, in addition to apoptosis, MK-886 can enhance TNF-alpha-induced differentiation.

Immunophenotypic changes induced on human HL60 leukaemia cells by 1alpha,25-dihydroxyvitamin D3 and 12-O-tetradecanoyl phorbol-13-acetate

1alpha,25-Dihydroxyvitamin D3 (1,25D3) induces HL60 cells to acquire a monocyte-like phenotype, while cells treated with 12-O-tetradecanoyl phorbol-13-acetate (TPA) resemble macrophages. Using a microarray of 82 CD antibodies, 24 cluster of differentiation (CD) antigens were detected on HL60 cells. 1,25D3 induced the following antigens in decreasing order of the change: CD14, CD11c, CD11b, CD54, CD86, CD38 and CD66c, with repression of CD117, CD71, CD95, CD45 and CD64. TPA induced the following antigens in decreasing order of the change: CD11c, CD9, CD11b, CD54, CD38, CD45RO and CD66c, with repression of CD4, CD117, CD95, CD71 and CD64. The results presented provide a basis for monitoring differentiation therapy of myeloid leukaemias in patients.

Magnolol and honokiol enhance HL-60 human leukemia cell differentiation induced by 1,25-dihydroxyvitamin D3 and retinoic acid

Magnolol (MG) and honokiol (HK), two lignans showing anti-inflammatory and anti-oxidant properties and abundantly available in the medicinal plants Magnolia officinalis and M. obovata, were found to enhance HL-60 cell differentiation initiated by low doses of 1,25-dihydroxyvitamin D3 (VD3) and all-trans-retinoic acid (ATRA). Cells expressing membrane differentiation markers CD11b and CD14 were increased from 4% in non-treated control to 8-16% after being treated with 10-30 microM MG or HK. When added to 1 nM VD3, MG or HK increased markers expressing cells from approximately 30% to 50-80%. When either MG or HK was added to 20 nM ATRA, only CD11b, but not CD14, expressing cells were increased from 9% to 24-70%. Under the same conditions, adding MG or HK to VD3 or ATRA treatment further enlarged the G0/G1 cell population and increased the expression of p27(Kip1), a cyclin-dependent kinase inhibitor. Pharmacological studies using PD098059 (a MEK inhibitor), SB203580 (a p38 MAPK inhibitor) and SP600125 (a JNK inhibitor) suggested that the MEK pathway was important for VD3 and ATRA-induced differentiation and also its enhancement by MG or HK, the p38 MAPK pathway had a inhibitory effect and the JNK pathway had little influence. It is evident that MG and HK are potential differentiation enhancing agents which may allow the use of low doses of VD3 and ATRA in the treatment for acute promyelocytic leukemia.

Paraoxonase 2 (PON2) expression is upregulated via a reduced-nicotinamide-adenine-dinucleotide-phosphate (NADPH)-oxidase-dependent mechanism during monocytes differentiation into macrophages

Paraoxonase 2 (PON2) is a member of the paraoxonases gene family. PON2 is ubiquitously present in cells, including macrophages, and it was shown to protect against cellular oxidative stress. The aim of the present study was to analyze mechanisms involved in PON2 expression during monocyte/macrophage differentiation. PON2 expression was analyzed in vitro in THP-1 cells differentiated with 1alpha,25-dihydroxyvitamin D3 and in vivo in mouse peritoneal macrophages (MPM) isolated at increasing time intervals after intraperitoneal thioglycollate injection. PON2 expression (mRNA and protein) and activity gradually increased during monocyte/macrophage differentiation, up to five fold and eight fold in vitro and in vivo, respectively. This effect was associated with a gradual increase in cellular superoxide anion production. Supplementation of vitamin E to Balb/C mice inhibited the reduced nicotinamide adenine dinuleotide phosphate (NADPH)-oxidase-dependent increase in cellular superoxide anion production by 50% and down-regulated PON2 mRNA expression and activity by 30 and 60%, respectively. Furthermore, PON2 expression was lower by nine fold in MPM isolated from P47(phox-/-) (inactive NADPH oxidase) mice, in comparison to MPM from control mice. PON2 expression was found to be regulated, at least in part, by the transcription factor AP-1, as suggested by decreased JDP2 (AP-1 repressor) protein expression in the nucleus and by decreased PON2 expression in the presence of a Jun N-terminal kinase inhibitor (SP600125). The present study demonstrates, for the first time, that PON2 expression increases in monocytes during their maturation into macrophage as a result of NADPH-oxidase activation, and this process is partly regulated by the transcription factor AP-1. PON2 stimulation may represent a compensatory mechanism against the increase in cellular superoxide anion production and atherogenesis.

Enhancement by other compounds of the anti-cancer activity of vitamin D(3) and its analogs

Differentiation therapy holds promise as an alternative to cytotoxic drug therapy of cancer. Among compounds under scrutiny for this purpose is the physiologically active form of vitamin D(3), 1,25-dihydroxyvitamin D(3), and its chemically modified derivatives. However, the propensity of vitamin D(3) and its analogs to increase the levels of serum calcium has so far precluded their use in cancer patients except for limited clinical trials. This article summarizes the range of compounds that have been shown to increase the differentiation-inducing and antiproliferative activities of vitamin D(3) and its analogs, and discusses the possible mechanistic basis for this synergy in several selected combinations. The agents discussed include those that have differentiation-inducing activity of their own that is increased by combination with vitamin D(3) or analogs, such as retinoids or transforming growth factor-beta and plant-derived compounds and antioxidants, such as curcumin and carnosic acid. Among other compounds discussed here are dexamethasone, nonsteroidal anti-inflammatory drugs, and inhibitors of cytochrome P450 enzymes, for example, ketoconazole. Thus, recent data illustrate that there are extensive, but largely unexplored, opportunities to develop combinatorial, differentiation-based approaches to chemoprevention and chemotherapy of human cancer.

Betulinic acid enhances 1alpha,25-dihydroxyvitamin D3-induced differentiation in human HL-60 promyelocytic leukemia cells

Betulinic acid (BA) is a pentacyclic triterpene found in a number of medicinal plants and has been shown to cause apoptosis in a number of cell lines. We report here that BA may also have an effect on HL-60 cell differentiation. BA was cytotoxic to HL-60 cells with an IC50 of 5.7 microM after a 72-h treatment. Flow cytometry analysis showed that after exposure to 1-12 microM of BA for 72 h, approximately 10% of viable cells were in the sub-G1, presumably apoptotic, phase. At the same time differentiation was induced in approximately 10% (at 1 microM BA) to a maximum of 20% (at 6 microM BA) of cells as judged by the NBT-reduction test, and the expression of membrane markers CD11b and CD14. On the other hand, at 1 and 5 nM, 1alpha,25-dihydroxyvitamin D3 (DHD3) induced differentiation in approximately 10 and 70% of cells, respectively. At 1 nM DHD3, the addition of 1 microM BA increased differentiated cells from 10 to 43% and with 3 microM BA the increase was to 80%. BA also enhanced the effects of DHD3 in the expansion of the G1 cell population with a concomitant decrease of S phase cells. The effects of DHD3 and BA on CD11b and CD14 expression were inhibited by PD98059, a MEK inhibitor. Our results suggest that BA may enhance the effect of DHD3 in inducing mitogen-activated protein kinase kinase/extracellular signal-regulated protein kinase-mediated HL-60 cell differentiation.

Retinoblastoma protein and CCAAT/enhancer-binding protein beta are required for 1,25-dihydroxyvitamin D3-induced monocytic differentiation of HL60 cells

Derivatives of vitamin D (deltanoids) are well known to have the ability to induce differentiation of a variety of malignant cells, including human leukemia cells, but the signaling pathways that lead to such an outcome are unclear. In this study we investigated the role of the retinoblastoma protein (pRb) and the CCAAT/enhancer-binding protein (C/EBP) beta in 1,25-dihydroxyvitamin D(3) (1,25D(3))-induced monocytic differentiation of human leukemia HL60 cells. It was found that in this system, pRb is up-regulated within 12 h of exposure to the inducer, and the kinetics of its increase parallel the appearance of the early markers of differentiation, CD14 and monocyte-specific esterase. The increase in pRb expression was accompanied by a similar increase in C/EBPbeta protein, and these two proteins coimmunoprecipitated, suggesting formation of a complex. Oligonucleotides antisense to pRb or C/EBPbeta (but not to C/EBPalpha) or containing the C/EBP-binding sequence ("decoys"), all inhibited 1,25D(3)-induced differentiation. Inhibition of signaling by vitamin D receptor or by mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase and c-Jun-NH(2)-terminal kinase pathways using pharmacological inhibitors ZK159222, PD98059, or SP600125, respectively, inhibited pRb and C/EBPbeta expression and differentiation in a coordinate manner. In contrast, inhibition of the p38MAPK pathway by SB202190 potentiated differentiation and the up-regulation of pRb and C/EBPbeta. We suggest that 1,25D(3) may signal monocytic differentiation of HL60 cells in a vitamin D receptor-dependent manner that includes activation of extracellular signal-regulated kinase and c-Jun-NH(2)-terminal kinase MAPK pathways, which then up-regulate pRb and C/EBPbeta expression and in turn initiate the differentiation process.