Synergistic induction of HL60 cell differentiation by ketoconazole and 1-desoxy analogues of vitamin D3

Nuclear Morphological Remodeling in Human Granulocytes Is Linked to Prenylation Independently from Cytoskeleton

Nuclear shape modulates cell behavior and function, while aberrant nuclear morphologies correlate with pathological phenotype severity. Nevertheless, functions of specific nuclear morphological features and underlying molecular mechanisms remain poorly understood. Here, we investigate a nucleus-intrinsic mechanism driving nuclear lobulation and segmentation concurrent with granulocyte specification, independently from extracellular forces and cytosolic cytoskeleton contributions. Transcriptomic regulation of cholesterol biosynthesis is equally concurrent with nuclear remodeling. Its putative role as a regulatory element is supported by morphological aberrations observed upon pharmacological impairment of several enzymatic steps of the pathway, most prominently the sterol ∆14-reductase activity of laminB-receptor and protein prenylation. Thus, we support the hypothesis of a nuclear-intrinsic mechanism for nuclear shape control with the putative involvement of the recently discovered GGTase III complex. Such process could be independent from or complementary to the better studied cytoskeleton-based nuclear remodeling essential for cell migration in both physiological and pathological contexts such as immune system function and cancer metastasis.

Cooperative antiproliferative and differentiation-enhancing activity of medicinal plant extracts in acute myeloid leukemia cells

Acute myeloid leukemia (AML) is an aggressive hematopoietic malignancy with poor prognosis and limited treatment options. Sea buckthorn (Hippophae rhamnoides) berries, dog rose (Rosa canina) rosehips, and garden sage (Salvia officinalis) and oregano (Origanum vulgare) aerial parts are widely used in traditional medicine and exhibit antitumor effects in preclinical models. However, these plants remain scarcely tested for antileukemic activity. Here, we show that their water-ethanol leaf extracts reduced the growth and viability of AML cells and, at non-cytotoxic doses, potentiated cell differentiation induced by a low concentration of 1α,25-dihydroxyvitamin D3, the hormonal form of vitamin D, in a cell type-dependent manner. The latter effect was accompanied by upregulation of the vitamin D receptor protein components and its transcriptional activity. Furthermore, at minimally effective doses the extracts cooperated with one another to produce marked cytostatic effects associated with a partial S-phase arrest and a modest induction of apoptosis. In contrast, these combinations only slightly affected the growth and viability of proliferating normal human peripheral blood mononuclear cells. In addition, the extracts strongly inhibited microsomal lipid peroxidation and protected normal erythrocytes against hypoosmotic shock. Our results suggest that further exploration of the enhanced antileukemic effects of the combinations tested here may lead to the development of alternative therapeutic and preventive approaches against 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.

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.

Cellular zinc homeostasis is a regulator in monocyte differentiation of HL-60 cells by 1 alpha,25-dihydroxyvitamin D3

It was reported previously that zinc-deficient mice show impaired lymphopoiesis. At the same time, monocyte numbers in these animals are increased, indicating a negative impact of zinc on monocyte development. Here, we investigate the role of zinc homeostasis in the differentiation of myeloid precursors into monocytes. Reduced gene expression of several zinc transporters, predominantly from the Zip family, was observed during 1 alpha, 25-dihydroxyvitamin D(3) (1,25D(3))-induced differentiation of HL-60 cells. This was accompanied by a reduction of intracellular-free zinc, measured by FluoZin-3. Amplifying this reduction with the zinc chelator TPEN or zinc-depleted cell-culture medium enhanced 1,25D(3)-induced expression of monocytic surface markers CD11b and CD14 on HL-60, THP-1, and NB4 cells. In contrast, differentiation of NB4 cells to granulocytes was not zinc-sensitive, pointing toward a specific effect of zinc on monocyte differentiation. Further, monocyte functions, such as TNF-alpha secretion, phagocytosis, and oxidative burst, were also augmented by differentiation in the presence of TPEN. The second messenger cAMP promotes monocyte differentiation. We could show that zinc inhibits the cAMP-synthesizing enzyme adenylate cyclase, and chelation of zinc by TPEN increases cAMP generation after stimulation with the adenylate cyclase activator forskolin. Based on our in vitro results and the in vivo observations from the literature, we suggest a model in which the intracellular-free zinc concentration limits AC activity, and the decrease of zinc after 1,25D(3) treatment promotes differentiation by relieving AC inhibition. Thus, cellular zinc homeostasis acts as an endogenous modulator of monocyte differentiation.

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.

Induction of differentiation of human leukemia cells by combinations of COX inhibitors and 1,25-dihydroxyvitamin D3 involves Raf1 but not Erk 1/2 signaling

Differentiation therapy of cancer is being explored as a potential modality for treatment of myeloid leukemia, and derivatives of vitamin D are gaining prominence as agents for this form of therapy. Cyclooxygenase (COX) inhibitors have been reported to enhance 1,25-dihydroxyvitamin D(3) (1,25D)-induced monocytic differentiation of promyeloblastic HL60 cells, but the mechanisms of this effect are not fully elucidated, and whether this potentiation can occur in other types of myeloid leukemia is not known. We found that combination treatment with 1,25D and non-specific COX inhibitors acetyl salicylic acid (ASA) or indomethacin can robustly potentiate differentiation of other types of human leukemia cells, i.e., U937, THP-1, and that ASA +/- 1,25D is effective in primary AML cultures. Increased cell differentiation is paralleled by arrest of the cells in the G(1) phase of the cell cycle, and by increased phosphorylation of Raf1 and p90RSK1 proteins. However, there is no evidence that this increase in phosphorylation of Raf1 is transmitted through the ERK module of the MAPK signaling cascade. Transfection of small interfering (si) RNA to Raf1 decreased differentiation of U937 cells induced by a combination of ASA or indomethacin with 1,25D. However, phosphorylation levels of ERK1/2, though not of p90RSK, were increased when P-Raf1 levels were decreased by the siRNA, suggesting that in this system the ERK module does not function in the conventional manner. Identification of the strong antiproliferative activity of ASA/1,25D combinations associated with monocytic differentiation has implications for cancer chemoprevention in individuals who have a predisposition to myeloid leukemia.

Differentiation-inducing potency of the seco-steroid JK-1624F2-2 can be increased by combination with an antioxidant and a p38MAPK inhibitor which upregulates the JNK pathway

Low calcemic analogs of vitamin D are candidates for differentiation therapy of human myeloid leukemias. We report here that the seco-steroid synthesized to have resistance to intracellular degradation and low calcemia-inducing activity, 1alpha-hydroxymethyl-3beta-16-ene-24,24-difluoro-25-hydroxy-vitamin D(3) (JKF), induces monocytic differentiation in four established human myeloid leukemia cell lines, HL60, U937, THP-1, NB-4, and murine myeloid leukemia cells WEHI-3B D(-). JKF has differentiation-inducing potency which is slightly lower than the physiologically active form of vitamin D, 1,25(OH)(2)vitamin D(3) (1,25D). However, simultaneous addition of carnosic acid (CA), an antioxidant, and SB20190 (SB), an inhibitor of p38MAP kinase, increases the differentiation efficiency of JKF to a level similar to the level observed when 1,25D is used in such combinations. We also show for the first time that SB inhibits the phosphorylation of MAPKAPK2, a downstream target of p38MAPK, but upregulates the phosphorylation of at least one of the isoforms of JNK (p46 JNK1) and of c-jun in all four human myeloid cell lines studied here. These studies indicate that the JNK1 pathway is positively associated with monocytic differentiation of several subtypes of myeloid leukemia cells arrested at different developmental stages. Further, since JKF is less calcemic than 1,25D, the data suggest that JKF combined with CA and SB is likely to have a therapeutic advantage over 1,25D-based experimental regimens for myeloid leukemias.

Expression of human kinase suppressor of Ras 2 (hKSR-2) gene in HL60 leukemia cells is directly upregulated by 1,25-dihydroxyvitamin D(3) and is required for optimal cell differentiation

Induction of terminal differentiation of neoplastic cells offers potential for a novel approach to cancer therapy. One of the agents being investigated for this purpose in preclinical studies is 1,25-dihydroxyvitamin D(3) (1,25D), which can convert myeloid leukemia cells into normal monocyte-like cells, but the molecular mechanisms underlying this process are not fully understood. Here, we report that 1,25D upregulates the expression of hKSR-2, a new member of a small family of proteins that exhibit evolutionarily conserved function of potentiating ras signaling. The upregulation of hKSR-2 is direct, as it occurs in the presence of cycloheximide, and occurs primarily at the transcriptional level, via activation of vitamin D receptor, which acts as a ligand-activated transcription factor. Two VDRE-type motifs identified in the hKSR-2 gene bind VDR-RXR alpha heterodimers present in nuclear extracts of 1,25D-treated HL60 cells, and chromatin immunoprecipitation assays show that these VDRE motifs bind VDR in 1,25D-dependent manner in intact cells, coincident with the recruitment of RNA polymerase II to these motifs. Treatment of the cells with siRNA to hKSR-2 reduced the proportion of the most highly differentiated cells in 1,25D-treated cultures. These results demonstrate that hKSR-2 is a direct target of 1,25D in HL60 cells, and is required for optimal monocytic differentiation.

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.

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.

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.

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.

Profiling 1,25-dihydroxyvitamin D3-regulated gene expression by microarray analysis

Vitamin D was discovered as a preventive agent of nutritional rickets, a defect in bone development due to inadequate uptake of dietary calcium. However, a variety of studies over the last several years has revealed that Vitamin D controls much more than calcium homeostasis. In particular, there is widespread evidence that the hormonal form of Vitamin D, 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], is an important regulator of cellular differentiation and proliferation. Direct genomic signaling by 1,25(OH)(2)D(3) occurs through the Vitamin D receptor, which is a nuclear receptor and a ligand-activated regulator of gene transcription. 1,25(OH)(2)D(3) can therefore directly regulate patterns of gene expression within a target cell. The development of high throughput genomics technologies have greatly enhanced our capacity to identify the genetic and biochemical changes associated with the physiological actions of 1,25(OH)(2)D(3). Microarray analyses of expression profiles in 1,25(OH)(2)D(3)-treated cells have underlined its widespread effects on cellular differentiation and proliferation. They have provided a molecular basis for the accumulating epidemiological and preclinical evidence indicating that 1,25(OH)(2)D(3) can act as a chemopreventive agent against several malignancies including cancers of the prostate and colon. In addition, they have underlined the therapeutic potential of 1,25(OH)(2)D(3) analogues as modulators of immune system function.

Kinase suppressor of RAS (KSR) amplifies the differentiation signal provided by low concentrations 1,25-dihydroxyvitamin D3

The activity of kinase suppressor of ras (KSR), a kinase or a molecular scaffold upstream from Raf-1, is involved in the MEK/ERK MAP kinase cascade which can signal cell growth, survival, or differentiation, depending on the cellular context. We provide evidence here that KSR is upregulated in HL60 cells undergoing differentiation induced by low (0.3-3 nM) concentrations of 1,25-dihydroxyvitamin D(3) (1,25D(3)), and an antisense oligo (AS), but not a sense oligo, to KSR inhibits this differentiation. The inhibition of differentiation by AS-KSR oligo was less apparent when the concentration of 1,25D(3) was increased, suggesting that at the higher concentrations of 1,25D(3) KSR is not essential for the signaling of the differentiated phenotype. The reduced differentiation of HL60 cells exposed to AS-KSR was paralleled by reduced phosphorylation of Raf-1 Ser 259, and of p90RSK, used here as read-out for MAPK cascade activity. Conversely, ectopic expression of Flag-tagged wild type KSR potentiated the differentiation-inducing effects of low concentrations of 1,25D(3). Additional data suggest that the kinase activity of KSR is required for these effects, as transfection of a kinase inactive KSR construct did not significantly increase the 1,25D(3)-induced differentiation. Enzyme assays performed with KSR immunoprecipitated from 1,25D(3)-treated cells showed kinase activity when recombinant Raf-1 was used as the substrate, but not when the 1,25D(3)-treated cells were pretreated with AS-KSR oligos. Taken together, these data suggest that KSR participates in signaling of monocytic differentiation by augmenting the strength of the signal transmitted through Raf-1 to downstream targets.

Carnosic acid and promotion of monocytic differentiation of HL60-G cells initiated by other agents

BACKGROUND

Carnosic acid is a plant-derived polyphenol food preservative with chemoprotective effects against carcinogens when tested in animals. Recently, we showed that carnosic acid potentiates the effects of 1alpha,25-dihydroxyvitamin D3 (1alpha,25[OH]2D3) and of all-trans-retinoic acid (ATRA) on differentiation of human leukemia cells. We now examine the mechanisms associated with carnosic acid-induced enhancement of cell differentiation (in subline HL60-G) initiated by 1alpha,25(OH)2D3, ATRA, or 12-O-tetradecanoylphorbol-13-acetate (TPA).

METHODS

We evaluated monocytic differentiation markers (CD11b, CD14, and monocytic serine esterase), cell cycle parameters, and cell proliferation rates after treatment of cells with different agents with or without carnosic acid. We also assessed the abundance of the vitamin D receptor (VDR), retinoid X receptor (RXR)-alpha, retinoic acid receptor (RAR)-alpha, and cell cycle-associated proteins by immunoblot analysis (p27, early growth response gene [EGR]-1, and p35Nck5a), the expression of corresponding genes by reverse transcription-polymerase chain reaction (RT-PCR), and the activity of VDR by electrophoretic mobility shift analysis. The two-sided nonparametric Kruskal-Wallis one-way analysis-of-variance test with Dunn's adjustment was used for statistical analyses.

RESULTS

Monocytic differentiation induced by low (1 nM) concentrations of 1alpha,25(OH)2D3, ATRA, or TPA was enhanced by carnosic acid (10 microM), as shown by the increased expression of monocytic serine esterase (P<.001, P<.001, and P =.043, respectively) and of CD11b (P =.008, P =.046, and P =.041, respectively). Increased expression of CD14 was seen only for 1alpha,25(OH)2D3 and ATRA (P =.009 and P =.048, respectively) and also for several cell cycle-associated proteins. Carnosic acid in combination with 1alpha,25(OH)2D3 and ATRA resulted in decreased cell proliferation and blocked the cell cycle transition from G1 to S phase (P<.05). Carnosic acid alone increased the expression of VDR and RXR-alpha, but the expression was greatly enhanced in the presence of 1alpha,25(OH)2D3 and ATRA. In combination with TPA, carnosic acid potentiated the expression of VDR and RAR-alpha.

CONCLUSION

Carnosic acid enhances a program of gene expression consistent with 1alpha,25(OH)2D3-, ATRA-, or TPA-induced monocytic differentiation of HL60-G cells.

Phosphorylation of raf-1 by kinase suppressor of ras is inhibited by "MEK-specific" inhibitors PD 098059 and U0126 in differentiating HL60 cells

Determination of the involvement of MAP kinase cascades in signaling cell growth or differentiation is aided by the use of the inhibitors PD 098059 [2-(2'-amino-3'-methoxyphenyl)oxananphthalen-4-one] and U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene], believed to be MEK-specific kinase inhibitors. We report here that the activity of kinase suppressor of ras (KSR-1), a kinase upstream of raf-1, is inhibited by both these compounds at concentrations similar to those that inhibit MEK-1. Further, in HL60 cells induced to differentiate with 1,25-dihydroxyvitamin D(3) raf-1 and p90RSK, but not ERK1/2, are coregulated, and their expression as well as monocytic differentiation is inhibited in parallel by PD 098059. Thus, in this system raf-1 is phosphorylated by KSR-1, and PD 098059 as well as U0126 inhibits this phosphorylation. This suggests great caution in the interpretation of experiments that utilize these pharmacological inhibitors of kinase activity as evidence for a role for the MEK--ERK module in ras or raf-1 signaling.

Inhibition of p38MAP kinase potentiates the JNK/SAPK pathway and AP-1 activity in monocytic but not in macrophage or granulocytic differentiation of HL60 cells

Monocytic differentiation of HL60 cells induced by 1,25-dihydroxyvitamin D(3) (1,25 D(3)) has been recently shown (Exp Cell Res 258, 425, 2000) to be enhanced by an exposure to SB203580 or to SB202190, specific inhibitors of p38MAP kinase, with concomitant up-regulation of the c-jun N terminal kinase (JNK) pathway. In the present study we inquired if this enhancement and the JNK up-regulation are limited to 1,25 D(3)-induced differentiation, or if they occur more generally in HL60 cell differentiation. We found that dimethylsulfoxide (DMSO)-induced differentiation, and to a lesser extent tetradecanoylphorbol acetate (TPA)-induced macrophage differentiation were also potentiated by the p38MAPK inhibitors, but that granulocytic differentiation in response to all-trans retinoic acid (RA) was not. The enhancement of differentiation by p38MAPK inhibitors was accompanied by an activation of the JNK MAPK pathway, as shown by the phosphorylation levels of these kinases and by AP-1 binding, but only in 1,25 D(3)-treated cells. This shows that an up-regulation of the JNK stress pathway during 1,25 D(3)-induced monocytic differentiation occurs selectively in this lineage of differentiation and is not necessary for the expression of the differentiated phenotype.

Combined supplementation of vanadium and 1alpha,25-dihydroxyvitamin D(3) inhibit diethylnitrosamine-induced rat liver carcinogenesis

A combination of a differentiation-inducing agent like 1alpha, 25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] with a compound that blocks entry of calcium into cells like vanadium (V) may offer a new approach to differentiation therapy and address the problem of hypercalcemia. Initiation of hepatocarcinogenesis was performed by a single intraperitoneal injection of diethylnitrosamine (DEN) (200 mg/kg b.wt.) in male Sprague-Dawley rats. Supplementation of V, 1, 25(OH)(2)D(3), or both V and 1,25(OH)(2)D(3) were started 4 weeks prior to DEN injection and continued thereafter till 20th week. It was observed that supplementation of V (0.5 ppm) in drinking water ad libitum or 1,25(OH)(2)D(3) (3 microg/ml propylene glycol) per os twice weekly for the entire period of the experiment significantly reduces the number and size of hyperplastic nodules while the combination treatment offered an additive effect in reducing it to 37.5% from 83.3%. V-1,25(OH)(2)D(3) combination was also effective in elevating the level of hepatic microsomal cytochrome P-450 (Cyt. P-450) (P<0.001). Moreover, A significant reduced level of cytosolic glutathione (GSH) (P<0.001) and glutathione S-transferase (GST) (P<0.001) activity as well as reduction in the appearance of gamma-glutamyltranspeptidase (GGT)-positive foci (P<0.001) as compared to carcinogen control were observed in V plus 1, 25(OH)(2)D(3) treated group. These results suggest that V may be useful in combination with 1,25(OH)(2)D(3) in the inhibition of experimental rat hepatocarcinogenesis.

Inhibition of p38 MAP kinase activity up-regulates multiple MAP kinase pathways and potentiates 1,25-dihydroxyvitamin D(3)-induced differentiation of human leukemia HL60 cells

Differentiation therapy for neoplastic diseases has potential for supplementing existing treatment modalities but its implementation has been slow. One of the reasons is the lack of full understanding of the complexities of cellular pathways through which signals for differentiation lead to cell maturation. This was addressed in this study using HL60 cells, a well-established model of differentiation of neoplastic cells. SB 203580 and SB 202190, specific inhibitors of a signaling protein p38 MAP kinase, were found to markedly accelerate monocytic differentiation of HL60 cells induced by low concentrations of 1,25-dihydroxyvitamin D(3) (1,25D(3)). Surprisingly, inhibition of p38 activity resulted in sustained enhancement of p38 phosphorylation and of its in vitro activity in the absence of the inhibitor, indicating up-regulation of the upstream components of the p38 pathway. In addition, SB 203580 or SB 202190 treatment of HL60 cells resulted in a prolonged activation of the JNK and, to a lesser extent, the ERK pathways. The data are consistent with the hypothesis that in HL60 cells an interruption of a negative feedback loop from a p38 target activates a common regulator of multiple MAPK pathways. The possibility also exists that JNK and/or ERK pathways amplify a differentiation signal provided by 1,25D(3).

Recent developments in the use of vitamin D analogues

The non-classical effects of 1alpha,25-dihydroxyvitamin D(3) (1alpha, 25(OH)(2)D(3)) create possible therapeutic applications for immune modulation (e.g., autoimmune diseases and graft rejection), inhibition of cell proliferation (e.g., psoriasis, cancer) and induction of cell differentiation (e.g., cancer). The major drawback related to the use of 1alpha,25(OH)(2)D(3) is its calcaemic effect, which prevents the application of pharmacological concentrations. Intensive research has led to the development of analogues of 1(2)D(3) characterised by a clear dissociation of the antiproliferative and prodifferentiating capacity from the calcaemic effects. Due to this dissociation, these analogues can be used not only for the treatment of bone disorders but also for non-classical applications. In the present review, a summary is given on the use of the 1alpha,25(OH)(2)D(3) analogues for the treatment of cancer, skin and immune disorders and for the prevention of graft rejection. Moreover a brief overview is given on the use of analogues for secondary hyperparathyroidism.

Differentiation-related changes in the cell cycle traverse

This review examines recent developments relating to the interface between cell proliferation and differentiation. It is suggested that the mechanism responsible for this transition is more akin to a "dimmer" than to a "switch," that it is more useful to refer to early and late stages of differentiation rather than to "terminal" differentiation, and examples of the reversibility of differentiation are provided. An outline of the established paradigm of cell cycle regulation is followed by summaries of recent studies that suggest that this paradigm is overly simplified and should be interpreted in the context of different cell types. The role of inhibitors of cyclin-dependent kinases in differentiation is discussed, but the data are still inconclusive. An increasing interest in the changes in G2/M transition during differentiation is illustrated by examples of polyploidization during differentiation, such as megakaryocyte maturation. Although the retinoblastoma protein is currently maintaining its prominent role in control of proliferation and differentiation, it is anticipated that equally important regulators will be discovered and provide an explanation at the molecular level for the gradual transition from proliferation to differentiation.

Metabolism of 1alpha,25(OH)2D3 and its 20-epi analog integrates clonal expansion, maturation and apoptosis during HL-60 cell differentiation

Induction of growth arrest and monocyte differentiation of HL-60 leukemia cells by 1alpha,25 dihydroxyvitamin D3 (1alpha,25(OH)2D3) is well established. By contrast, we have observed, that 1alpha,25(OH)2D3 and its metabolites play separate roles in clonal expansion and survival of differentiating HL-60 cells. Cells that had differentiated by 48 h (CD14 positive) grew slower than control cells, whereas CD14 negative cells were growing faster at this time point. Inhibiting 1alpha,25(OH)2D3 or 1alpha,25(OH)2-20-epi-D3 metabolism, by the 25(OH)D3-24-hydroxylase inhibitor ketoconazole, abolished hyperproliferation of CD14 negative cells. Instead, both the onset of differentiation and subsequent apoptosis were enhanced. These events were associated with immediate up-regulation of the cyclin-dependent kinase inhibitor p21(waf1) and a lack of sustained expression, respectively. Stimulation and inhibition of growth by vitamin D3-related compounds was observed to be concentration and metabolite specific. Low amounts of 1alpha,25(OH)2-20-epi-D3 and 1alpha,24,25(OH)3-20-epi-D3 stimulated HL-60 cell growth. At higher concentrations, 1alpha,25(OH)2-20-epi-D3 was a more potent inducer than 1alpha,24,25(OH)3-20-epi-D3 of HL-60 differentiation; 1alpha,25(OH)2-20-epi-24-oxo-D3 was exclusively pro-differentiative at all concentrations. 1alpha,25(OH)2-20-epi-D3 and 1alpha,24,25(OH)3-20-epi-D3 stimulated proliferation of KG-1a leukemia cells, but neither of these compounds nor 1alpha,25(OH)3-20-epi-24-oxo-D3 exerted pro-differentiative effects on these cells. These findings shed new light on the pro- and anti-proliferative effects of 1alpha,25(OH)2D3 and lead to the postulate that metabolism of 1alpha,25(OH)2D3 and its 20-epi analog regulates different subsets of genes so as to co-ordinate population expansion and the differentiation process. Furthermore, 1alpha,25(OH)2D3 metabolism and/or sensitivity to the effects of metabolites may be altered in transformed cells to derive a clonal advantage.

1alpha,25-dihydroxyvitamin D3 inhibits in vitro invasiveness through the extracellular matrix and in vivo pulmonary metastasis of B16 mouse melanoma

We investigated the role of 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) in modulating tumor cell invasiveness through the extracellular matrix (ECM) and pulmonary metastasis in B16 mouse melanoma. The pretreatment of B16 cells for 48 hours with 1alpha,25(OH)2D3 significantly inhibited in vitro invasiveness through the ECM by a mechanism that is not directly correlated with the inhibition of cell proliferation. When cells were treated with 1alpha,25(OH)2D3 for only 8 hours during the assay, no inhibitory effect was observed, suggesting that pretreatment with the hormone for more than 8 hours is necessary to inhibit the invasive potential of B16 cells. The activity of B16 cells to adhere to reconstituted basement membrane (Matrigel) and type IV collagenolysis was inhibited by pretreatment of the cells with 1alpha,25(OH)2D3 for 48 hours. Cell motility was not influenced by the hormone. Mice were inoculated subcutaneously with 3 x 106 B16 cells and were given 1alpha,25(OH)2D3 (0.5 microg/kg) or vehicle daily for 28 days, beginning 1 day after tumor inoculation. In the 1alpha,25(OH)2D3-treated group, no significant inhibition in exponential tumor growth, body weight, and serum level of calcium was observed until the twenty-eighth day. The mean serum concentration of the hormone was about 50 ng/mL, and there were no significant changes in its concentration during the treatment period. In both spontaneous and experimental metastasis models of tumor-bearing mice, treatment with 1alpha,25(OH)2D3 inhibited pulmonary metastasis. These findings suggest that 1alpha,25(OH)2D3 acts on B16 cells, inhibiting invasiveness through the ECM that is caused by the inhibition of cell adhesion to the ECM and the degradation of the ECM by the cells. 1alpha,25(OH)2D3 may have the potential to inhibit metastasis by a mechanism that is not exclusively based on its anti-cell proliferative effect.