Promotion of HL-60 cell differentiation by 1,25-dihydroxyvitamin D3 regulation of protein kinase C levels and activity

The human cytomegalovirus lytic cycle is induced by 1,25-dihydroxyvitamin D3 in peripheral blood monocytes and in the THP-1 monocytic cell line

Human cytomegalovirus (HCMV) resides in a latent form in hematopoietic progenitors and undifferentiated cells within the myeloid lineage. Maturation and differentiation along the myeloid lineage triggers lytic replication. Here, we used peripheral blood monocytes and the monocytic cell line THP-1 to investigate the effects of 1,25-dihydroxyvitamin D3 on HCMV replication. Interestingly, 1,25-dihydroxyvitamin D3 induces lytic replication marked by upregulation of HCMV gene expression and production of infectious virus. Moreover, we demonstrate that the effects of 1,25-dihydroxyvitamin D3 correlate with maturation/differentiation of the monocytes and not by directly stimulating the MIEP. These results are somewhat surprising as 1,25-dihydroxyvitamin D3 typically boosts immunity to bacteria and viruses rather than driving the infectious life cycle as it does for HCMV. Defining the signaling pathways kindled by 1,25-dihydroxyvitamin D3 will lead to a better understanding of the underlying molecular mechanisms that determine the fate of HCMV once it infects cells in the myeloid lineage.

Potential anti-cancer activities and mechanisms of costunolide and dehydrocostuslactone

Costunolide (CE) and dehydrocostuslactone (DE) are derived from many species of medicinal plants, such as Saussurea lappa Decne and Laurus nobilis L. They have been reported for their wide spectrum of biological effects, including anti-inflammatory, anticancer, antiviral, antimicrobial, antifungal, antioxidant, antidiabetic, antiulcer, and anthelmintic activities. In recent years, they have caused extensive interest in researchers due to their potential anti-cancer activities for various types of cancer, and their anti-cancer mechanisms, including causing cell cycle arrest, inducing apoptosis and differentiation, promoting the aggregation of microtubule protein, inhibiting the activity of telomerase, inhibiting metastasis and invasion, reversing multidrug resistance, restraining angiogenesis has been studied. This review will summarize anti-cancer activities and associated molecular mechanisms of these two compounds for the purpose of promoting their research and application.

Structure-activity relationship studies of 5,7-dihydroxyflavones as naturally occurring inhibitors of cell proliferation in human leukemia HL-60 cells

Flavonoids are widely occurring polyphenols that are found in plants. The aim of this study was to investigate the structure-activity relationships of 5,7-dihydroxyflavones, with a focus on the effect of B ring structure substitution on the antiproliferative effects of the compounds in human leukemia HL-60 cells. We prepared a series of 5,7-dihydroxyflavones and evaluated their ability to inhibit the proliferation of HL-60 cells by using the MTT assay. The apoptosis- and cell differentiation-inducing ability of the most potent flavones were investigated using staining and morphological analyses. This study explored the antileukemic and chemopreventive potency of 5,7-dihydroxyflavones, particularly diosmetin and chrysoeriol, which have both hydroxy and methoxy groups on the B ring.

The Nrf2 transcription factor is a positive regulator of myeloid differentiation of acute myeloid leukemia cells

1α,25-dihydroxyvitamin D3 (1,25D) is a powerful differentiation agent, which has potential for treatment of acute myeloid leukemia (AML), but induces severe hypercalcemia at pharmacologically active doses. We have previously shown that carnosic acid (CA), the polyphenolic antioxidant from rosemary plant, markedly potentiates differentiation induced by low concentrations of 1,25D in human AML cell lines. Here, we demonstrated similar enhanced differentiation responses to the 1,25D/CA combination in primary leukemic cells derived from patients with AML, and determined the role of the Nrf2/antioxidant response element (Nrf2/ARE) pathway in these effects using U937 human monoblastic leukemia cells as the model. CA strongly transactivated the ARE-luciferase reporter gene, induced the ARE-responsive genes, NADP(H)-quinone oxidoreductase and the γ-glutamylcysteine synthetase heavy subunit, and elevated cellular glutathione levels. Interestingly, 1,25D potentiated the effects of CA on these activities. Stable transfection of wild-type (wt) Nrf2 resulted in the enhancement, while transfection of dominant-negative (dn) Nrf2 produced suppression of differentiation induced by the 1,25D/CA combination and, surprisingly, by 1,25D alone. These opposite effects were associated with a corresponding increase or decrease in vitamin D receptor and retinoid X receptor-α protein levels, and in vitamin D responsive element transactivation. Cells transfected with wtNrf2 and dnNrf2 also displayed opposing changes in the levels of the AP-1 family proteins (c-Jun and ATF2) and AP-1 transcriptional activity. Pretreatment with AP-1 decoy oligodeoxynucleotide markedly attenuated the differentiation in wtNrf2-transfected cells, suggesting that the pro-differentiation action of Nrf2 is mediated by functional AP-1. Our findings suggest that the Nrf2/ARE pathway plays an important part in the cooperative induction of myeloid leukemia cell differentiation by 1,25D and a plant polyphenol.

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.

Nargenicin enhances 1,25-dihydroxyvitamin D(3)- and all-trans retinoic acid-induced leukemia cell differentiation via PKCbetaI/MAPK pathways

A major goal in the treatment of acute myeloid leukemia (AML) is to achieve terminal differentiation and prevent drug resistance and side effects. Combined treatment with low doses of ATRA or 1,25-(OH)(2)D(3) that do not induce toxicity with another drug is one useful strategy for the treatment of AML. Actinomycetes are the well known sources of antibiotics and bioactive molecules. Previously, we isolated nargenicin from the culture broth of an actinomycete isolate, Nocardia sp. CS682. In this study, we evaluated the effects of nargenicin on cellular differentiation in a human myeloid leukemia HL-60 cell system. Nargenicin inhibited cell proliferation and induced HL-60 cell differentiation when administered in combination with 1,25-(OH)(2)D(3) or ATRA. In addition, western blot analyses and kinase inhibitor studies demonstrated that nargenicin primarily enhanced leukemia cell differentiation via PKCbeta1/MAPK pathways. The results of this study indicate that nargenicin has the ability to induce differentiation and suggest that it may be useful for the treatment of neoplastic diseases.

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.

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.

Enhancing effect of indirubin derivatives on 1,25-dihydroxyvitamin D3- and all-trans retinoic acid-induced differentiation of HL-60 leukemia cells

The induction of differentiation represents a new and promising approach to cancer therapy, well illustrated by the treatment of acute promyelocytic leukemia (APL) with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] or all-trans retinoic acid (ATRA). Using combinations of low, nontoxic concentrations of either 1,25-(OH)2D3 or ATRA and differentiation-enhancing chemicals, adverse effects such as hypercalcemic effects have been ameliorated, and long-term survival has been improved. Indirubin has been demonstrated to exert anti-leukemic effects in cases of chronic myelocytic leukemia. Previously, we synthesized a series of indirubin derivatives and evaluated their anti-proliferative properties against cancer cells. In this study, we determined the enhancing activities of these derivatives on 1,25-(OH)2D3- and ATRA-induced differentiation of human promyelocytic leukemia HL-60 cells. Importantly, some of these derivatives were found to synergistically enhance the differentiation of HL-60 cells in a concentration-dependent manner when coupled with low doses of either 1,25-(OH)2D3 or ATRA. The ability of indirubin derivatives to enhance the differentiation potential of 1,25-(OH)2D3 or ATRA may improve the ultimate outcomes of APL therapy.

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.

Induction of apoptosis in two human leukemia cell lines as well as differentiation in human promyelocytic cells by cyanidin-3-O-β-glucopyranoside

Little is known about the potentially chemopreventive mechanisms of anthocyanins apart from their antioxidant activity. We investigated the in vitro capacity of the anthocyanin cyanidin-3-O-beta-glucopyranoside (Cy-g) to induce apoptosis in T-lymphoblastoid, as well as apoptosis and differentiation in HL-60 promyelocytic cells. Although Cy-g-induced apoptosis (as well as necrosis) in the two systems, HL-60 cells were much less sensitive than T-lymphoblastoid cells. Moreover, treatment of HL-60 cells with Cy-g caused differentiation into macrophage-like cells and granulocytes. Concerning the mechanism of action, the induction of apoptosis in Jurkat T cells can be explained by a modulation of p53 and bax protein expression. At the molecular level, the induction of apoptosis and cytodifferentiation in HL-60 cells involved different proteins, thus suggesting that the effects of Cy-g on apoptosis and cytodifferentiation induction are two distinct events. These interesting biological properties should encourage further investigation into the chemopreventive and/or chemotherapeutic potential of Cy-g.

Differential involvement of protein kinase C in human promyelocytic leukemia cell differentiation enhanced by artemisinin

Artemisinin, a sesquiterpene lactone endoperoxide that exists in several medicinal plants, is a well-known anti-malarial agent. In this report, we investigated the effect of artemisinin on cellular differentiation in the human promyelocytic leukemia HL-60 cell culture system. Artemisinin markedly increased the degree of HL-60 leukemia cell differentiation when simultaneously combined with low doses of 1 alpha,25-dihydoxyvitamin D(3) [1,25-(OH)(2)D(3)] or all-trans retinoic acid (all-trans RA). Artemisinin by itself had very weak effects on the differentiation of HL-60 cells. Cytofluorometric analysis and cell morphologic studies indicated that artemisinin potentiated 1,25-(OH)(2)D(3)-induced cell differentiation predominantly into monocytes and all-trans RA-induced cell differentiation into granulocytes, respectively. Extracellular-regulated kinase (ERK) inhibitors markedly inhibited HL-60 cell differentiation induced by artemisinin in combination with 1,25-(OH)(2)D(3) or all-trans RA, whereas phosphatidylinositol 3-kinase (PI3-K) inhibitors did not. Particularly, protein kinase C (PKC) inhibitors inhibited HL-60 cell differentiation induced by artemisinin in combination with 1,25-(OH)(2)D(3) but not with all-trans RA. Artemisinin enhanced PKC activity and protein level of PKC beta I isoform in only 1,25-(OH)(2)D(3)-treated HL-60 cells. Taken together, these results indicate that artemisinin strongly enhanced 1,25-(OH)(2)D(3)- and all-trans RA-induced cell differentiation in which PKC is differentially involved in arteminisin-mediated enhancement of leukemia cell differentiation.

Potentiation of 1,25-dihydroxyvitamin D(3)-induced differentiation of human promyelocytic leukemia cells into monocytes by costunolide, a germacranolide sesquiterpene lactone

Costunolide, a germacranolide sesquiterpene lactone that exists in several medicinal plants, is known to be a possible anti-cancer and chemopreventive agent for tumorigenesis. In this report, we investigated the effect of costunolide on cellular differentiation in the human promyelocytic leukemia HL-60 cell culture system. Costunolide markedly increased the degree of HL-60 leukemia cell differentiation when simultaneously combined with 5nM 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)). Costunolide by itself had very weak effects on the differentiation of HL-60 cells. Cytofluorometric analysis and cell morphologic studies indicated that costunolide potentiated 1,25-(OH)(2)D(3)-induced cell differentiation predominantly into monocytes. Inhibitors for PKC, PI3-K, and ERK markedly inhibited HL-60 cell differentiation induced by costunolide in combination with 1,25-(OH)(2)D(3). In addition, pretreatment of HL-60 cells with costunolide before the 1,25-(OH)(2)D(3) addition also potentiated cell differentiation in a concentration- and time-dependent manner, and the enhanced levels of cell differentiation closely correlated with the inhibitory levels of NF-kappaB-binding activity by costunolide. These results indicate that PKC, PI3-K, ERK and NF-kappaB may be involved in 1,25-(OH)(2)D(3)-mediated cell differentiation enhanced by costunolide.

Enhancement of 1 alpha,25-dihydroxyvitamin D(3)-induced differentiation of human leukaemia HL-60 cells into monocytes by parthenolide via inhibition of NF-kappa B activity

1. Transcription factors such as NF-kappa B provide powerful targets for drugs to use in the treatment of cancer. In this report parthenolide (PT), a sesquiterpene lactone of herbal remedies such as feverfew (Tanacetum parthenium) with NF-kappa B inhibitory activity, markedly increased the degree of human leukaemia HL-60 cell differentiation when simultaneously combined with 5 nM 1 alpha,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)). PT by itself did not induce HL-60 cell differentiation. 2. Cytofluorometric analysis indicated that PT stimulated 1,25-(OH)(2)D(3)-induced differentiation of HL-60 cells predominantly into monocytes. 3. Pretreatment of HL-60 cells with PT before the 1,25-(OH)(2)D(3) addition also potentiated the 1,25-(OH)(2)D(3)-induced HL-60 cell differentiation in both a dose- and a time-dependent manner, in which the enhanced levels of cell differentiation closely correlated with the inhibitory levels of NF-kappa B binding activity by PT. 4. In contrast, santonin, a sesquiterpene lactone without an inhibitory activity of NF-kappa B binding to the kappa B sites, did not enhance the 1,25-(OH)(2)D(3)-induced HL-60 cell differentiation. 5. In transfection experiments, PT enhanced 1,25-(OH)(2)D(3)-induced VDRE-dependent promoter activity. Furthermore, PT restored 1,25-(OH)(2)D(3)-induced VDRE-dependent promoter activity inhibited by TNF-alpha, an activator of NF-kappa B signalling pathway. 6. These results indicate that PT strongly potentiates the 1,25-(OH)(2)D(3)-induced HL-60 cell differentiation into monocytes via the inhibition of NF-kappa B activity and provide evidence that inhibition of NF-kappa B activation can be a pre-requisite to the efficient entry of promyelocytic leukaemia cells into a differentiation pathway.

Retinoic acid causes MEK-dependent RAF phosphorylation through RARalpha plus RXR activation in HL-60 cells

Retinoic acid (RA) is known to cause the myeloid differentiation of HL-60 human myeloblastic leukemia cells in a process requiring MEK-dependent ERK2 activation. This RA-induced ERK2 activation appears after approximately 4 h and persists until the cells are differentiated and G0 arrested (Yen et al, 1998). This motivates the question of whether RA also activated RAF as part of a typical RAF/MEK/MAPK cascade. Retinoic acid is shown here to also increase the phosphorylation of RAF, but in an unusual way. Surprisingly, increased RAF phosphorylation is first detectable after 12 to 24 hours by phosphorylation-induced retardation of polyacrylamide gel electrophoretic mobility. The RA-induced increased RAF phosphorylation is still apparent after 72 hours of treatment when most cells are differentiated and G0 arrested. There is a progressive dose-response relationship with 10(-8), 10(-7), and 10(-6) M RA. The RA-induced RAF phosphorylation corresponds to increased in vitro kinase activity. Inhibition of MEK with a PD98059 dose which inhibits ERK2 phosphorylation and subsequent cell differentiation also inhibits RAF phosphorylation. RA-induced MEK-dependent RAF phosphorylation is not due to changes in the amount of cellular MEK. The induced RAF phosphorylation, as well as anteceding ERK2 activation, depends on ligand-induced activation of both an RARalpha receptor and an RXR receptor. This and the slow kinetics of activation suggest a need for prior RA-induced gene expression. In summary, RA induces a MEK-dependent prolonged RAF activation, whose slow onset occurs after ERK2 activation but still well before cell cycle arrest and cell differentiation. The RA-induced increased RAF phosphorylation thus differs from typical mitogenic growth factor signaling, features that may contribute to cell cycle arrest and differentiation instead of division as the cellular outcome.

Induction of human promyelocytic leukemia HL-60 cell differentiation into monocytes by silibinin: involvement of protein kinase C 1 1Abbreviations: 1,25-(OH)2D3, 1α,25-dihydroxyvitamin D3; ERK, extracellular signal-regulated kinase; mAb, monoclonal antibody; MAPK, mitogen-activated protein kinase; NBT, nitroblue tetrazolium; and PKC, protein kinase C

The effect of silibinin, an active component of Silybum marianum, on cellular differentiation was investigated in the human promyelocytic leukemia HL-60 cell culture system. Treatment of HL-60 cells with silibinin inhibited cellular proliferation and induced cellular differentiation in a dose-dependent manner. Cytofluorometric analysis and morphologic studies indicated that silibinin induced differentiation of HL-60 cells predominantly into monocytes. Importantly, strongly synergistic induction of differentiation into monocytes was observed when silibinin was combined with 5 nM 1alpha,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], a well-known differentiation inducer of HL-60 cells into the monocytic lineage. Silibinin enhanced protein kinase C (PKC) activity and increased protein levels of both PKCalpha and PKCbeta in 1,25-(OH)(2)D(3)-treated HL-60 cells. PKC and extracellular signal-regulated kinase (ERK) inhibitors significantly inhibited HL-60 cell differentiation induced by silibinin alone or in combination with 1,25-(OH)(2)D(3), indicating that PKC and ERK may be involved in silibinin-induced HL-60 cell differentiation.

Capsaicin potentiates 1,25-dihydoxyvitamin D3- and all-trans retinoic acid-induced differentiation of human promyelocytic leukemia HL-60 cells

Human promyelocytic leukemia HL-60 cells are differentiated into monocytic or granulocytic lineage when treated with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] or all-trans retinoic acid, respectively. In this study, the effect of capsaicin, an active component of the red pepper of the genus Capsocum, on cell differentiation was investigated in a HL-60 cell culture system. Treatment of HL-60 cells with 5-30 microg/ml capsaicin for 72 h inhibited cell proliferation and induced a small increase in cell differentiation. Interestingly, synergistic induction of HL-60 cell differentiation was observed when capsaicin was combined with either 5 nM 1,25-(OH)2D3 or 50 nM all-trans retinoic acid. Flow cytometric analysis indicated that combinations of 1,25-(OH)2D3 and capsaicin stimulated differentiation predominantly to monocytes whereas combinations of all-trans retinoic acid and capsaicin stimulated differentiation predominantly to granulocytes. Capsaicin enhanced protein kinase C activity in 1,25-(OH)2D3- and all-trans retinoic acid-treated HL-60 cells. In addition, inhibitors for protein kinase C [bisindolylmaleimide (GF-109203X), chelerythrine, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7)] and an inhibitor for extracellular signal-regulated kinase [2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one (PD-098059)] significantly inhibited HL-60 cell differentiation induced by capsaicin in combination with either 1,25-(OH)2D3 or all-trans retinoic acid. These results indicate that capsaicin potentiates 1,25-(OH)2D3- or all-trans retinoic acid-induced HL-60 cell differentiation and that both protein kinase C and extracellular signal-regulated kinase are involved in the cell differentiation synergistically enhanced by capsaicin.

Altered response of a human squamous cell carcinoma cell line to 1, 25-dihydroxyvitamin D(3) after transfer of a normal chromosome 11

Previous work in our laboratory using functional assays for tumorigenicity identified a tumor suppressor element on human chromosome 11q for the cutaneous squamous cell carcinoma cell line A388.6TG.c2. In this report, we screened a variety of agents for differential effects on A388.6TG.c2 compared to a growth-suppressed chromosome 11 microcell hybrid of A388.6TG.c2. One of the agents, 1, 25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3); calcitriol), exerted a growth-altering effect on A388.6TG.c2, which formed rounded cell clusters across the surface of the raft by Day 6 of treatment. In contrast, full-length chromosome 11 hybrids of A388.6TG.c2, as well as two other squamous cell carcinoma cell lines (FaDu and A431), when treated with 1,25(OH)(2)D(3), failed to demonstrate this cell-clumping phenotype. To pursue the hypothesis that the growth suppressor element is involved in altering the response to 1, 25(OH)(2)D(3), we tested microcell hybrids carrying t(X;11) chromosomes lacking large portions of 11q. Although these hybrids, like the parent A388.6TG.c2 cells, demonstrated extensive growth in organotypic cultures, they failed to form cell clusters with 1, 25(OH)(2)D(3) treatment. These results suggest that the chromosome 11 element that alters the response to 1,25(OH)(2)D(3) is distinct from the growth-suppressing element. An examination of differentiation marker expression revealed identical patterns of basal and suprabasal markers for A388.6TG.c2 and for a chromosome 11 hybrid with or without treatment with 1,25(OH)(2)D(3). Finally, characterization of candidate tumor suppressor gene PPP2R1B, which encodes for a subunit of protein phosphatase 2A (PP2A), showed seemingly insignificant alterations by cDNA sequence analysis. Collectively, the data suggest that human chromosome 11 contains two different tumor suppressor elements that may account for the two areas of loss of heterozygosity observed on the long arm of this chromosome.

Vitamin D analogs, 20-Epi-22-oxa-24a,26a,27a,-trihomo-1alpha,25(OH)2-vitamin D3, 1,24(OH)2-22-ene-24-cyclopropyl-vitamin D3 and 1alpha,25(OH)2-lumisterol3 prime NB4 leukemia cells for monocytic differentiation via nongenomic signaling pathways, involving calcium and calpain

Side-chain modified vitamin D analogs including 20-Epi-22-oxa-24a,26a,27a-trihomo-1alpha,2 5-dihydroxyvitamin D3 (KH1060), and 1,24-dihydroxy-22-ene-24-cyclopropyl-vitamin D3 (MC903) were originally designed to aid in the treatment of hyperproliferative disorders including psoriasis and cancer. Here we demonstrate that these analogs, as well as the 6-cis-locked conformer, 1alpha,25-dihydroxy-lumisterol3 (JN) prime NB4 cells for monocytic differentiation. Previously, the action of MC903 and KH1060 was presumed to be mediated by the nuclear vitamin D receptor (VDRnuc). Differentiation in response to all analogs was shown to be inhibited by 1beta,25-dihydroxyvitamin D3 (HL), the antagonist to the nongenomic activities of 1,25D3. These data suggest that although MC903 and KH1060 may bind the VDRnuc, that the differentiative activities of these agents requires nongenomic signaling pathways. Here we show that 1alpha,25(OH)2-d5-previtamin D3 (HF), JN, KH1060, and MC903 induce expression of PKC alpha and PKC delta and translocation of both isoforms to the particulate fraction, and PKC alpha to the nuclear fraction. The full differentiation response with combinations of analogs and TPA was inhibited 50% by the membrane permeable Ca2+ chelator, 1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) or calpain inhibitor I. These data demonstrate that intracellular free calcium and the calcium-dependent protease, calpain play critical roles in monocytic differentiation. Intracellular calcium appears to be most critical in the 1,25D3-priming stage of differentiation, while calpain is essential in the TPA maturation response.

c-myc intron element-binding proteins are required for 1, 25-dihydroxyvitamin D3 regulation of c-myc during HL-60 cell differentiation and the involvement of HOXB4

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) suppresses c-myc expression during differentiation of HL-60 cells along the monocytic pathway by blocking transcriptional elongation at the first exon/intron border of the c-myc gene. In the present study, the physiological relevance of three putative regulatory protein binding sites found within a 280-base pair region in intron 1 of the c-myc gene was explored. HL-60 promyelocytic leukemia cells were transiently transfected with three different c-myc promoter constructs cloned upstream of a chloramphenicol acetyltransferase (CAT) reporter gene. With the wild-type c-myc promoter construct (pMPCAT), which contains MIE1, MIE2, and MIE3 binding sites, 1,25-(OH)2D3 was able to decrease CAT activity by 45.4 +/- 7.9% (mean +/- S.E., n = 8). The ability of 1, 25-(OH)2D3 to inhibit CAT activity was significantly decreased to 18. 5 +/- 4.3% (59.3% reversal, p < 0.02) when examined with a MIE1 deletion construct (pMPCAT-MIE1). Moreover, 1,25-(OH)2D3 was completely ineffective at suppressing CAT activity in cells transfected with pMPCAT-287, a construct without MIE1, MIE2, and MIE3 binding sites (-6.5 +/- 10.9%, p < 0.002). MIE1- and MIE2-binding proteins induced by 1,25-(OH)2D3 had similar gel shift mobilities, while MIE3-binding proteins migrated differently. Furthermore, chelerythrine chloride, a selective protein kinase C (PKC) inhibitor, and a PKCbeta antisense oligonucleotide completely blocked the binding of nuclear proteins induced by 1,25-(OH)2D3 to MIE1, MIE2, and MIE3. A 1,25-(OH)2D3-inducible MIE1-binding protein was identified to be HOXB4. HOXB4 levels were significantly increased in response to 1,25-(OH)2D3. Taken together, these results indicate that HOXB4 is one of the nuclear phosphoproteins involved in c-myc transcription elongation block during HL-60 cell differentiation by 1,25-(OH)2D3.

Antisense oligonucleotides targeted against protein kinase Cbeta and CbetaII block 1,25-(OH)2D3-induced differentiation

It is now recognized that protein kinase C (PKC) plays a critical role in 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) promotion of HL-60 cell differentiation. In this study, the effects of phosphorothioate antisense oligonucleotides directed against PKCalpha, PKCbeta, PKCbetaI, and PKCbetaII on HL-60 promyelocyte cell differentiation and proliferation were examined. Cellular differentiation was determined by nonspecific esterase activity, nitro blue tetrazolium reduction, and CD14 surface antigen expression. Differentiation promoted by 1,25-(OH)2D3 (20 nM for 48 h) was inhibited similarly in cells treated with PKCbeta antisense (30 microM) 24 h prior to or at the same time as hormone treatment (86 +/- 9% inhibition; n = 4 versus 82 +/- 8% inhibition; n = 4 (mean +/- S.E.), respectively). In contrast, cells treated with PKCbeta antisense 24 h after 1, 25-(OH)2D3 were unaffected and fully differentiated. PKCalpha antisense did not block 1,25-(OH)2D3 promotion of HL-60 cell differentiation. Next, the ability of PKCbetaI- and PKCbetaII-specific antisense oligonucleotides to block 1,25-(OH)2D3 promotion of cell differentiation was examined. PKCbetaII antisense (30 microM) completely blocked CD14 expression induced by 1, 25-(OH)2D3, whereas PKCbetaI antisense had little effect. Interestingly, PKCbetaII antisense blocked differentiation by 87 +/- 7% (n = 2, mean +/- S.D.) but had no effect on 1,25-(OH)2D3 inhibition of cellular proliferation. These results indicate that the effects of 1,25-(OH)2D3 on HL-60 cell differentiation and proliferation can be dissociated by blocking PKCbetaII expression.