Leukemia cell differentiation: cellular and molecular interactions of retinoids and vitamin D

Transmembrane signalling in human monocyte/mesangial cell co-cultures: role of cytosolic Ca(2+)

BACKGROUND

Adhesion of monocytes triggers apoptosis, cytotoxicity, cytokine release, and later proliferation of cultured human mesangial cells (HMC). In the search for transmembrane signals transducing the interaction of HMC adhesion molecules with leukocyte counterreceptors, we measured variations of cytosolic Ca(2+) ([Ca(2+)](i)) in HMC and monocytes of the U937 cell line during 6-h co-cultures.

METHODS

Monolayer cultures of HMC and suspensions of U937 cells were loaded with the fluoroprobe fura 2-AM and subsequently co-cultured for 6 h while separately monitoring by microfluorometry the Ca(2+)-dependent 500 nm fluorescent emission of each cell line at fixed intervals upon excitation at 340/380 nm.

RESULTS

U937 and peripheral blood monocyte adhesion was followed in HMC by a slow, progressive rise of [Ca(2+)](i) from basal levels of 96+/-9 nM to 339+/-54 at 60 min and 439+/-44 nM at 3 h. The [Ca(2+)](i) elevation reached a steady state thereafter, while parallel monolayers incubated with control media maintained resting levels throughout the co-culture with stable fluoroprobe retention. Receptor sensitivity to vasoconstrictor agents, including compounds not released by monocytes, such as angiotensin II, was rapidly downregulated in HMC co-cultured with U937 cells. No [Ca(2+)](i) changes could be elicited by the octapeptide or by the TxA(2) analogue, U-46619, as early as 30 min after exposure to U937 cells. No [Ca(2+)](i) changes were observed in U937 cells throughout the co-culture. Conditioned media from monocytes and from co-cultured HMC+U937 cells had no effect on [Ca(2+)](i) of HMC. Ca(2+) entry leading to fura 2 saturation was still inducible by Ca(2+) ionophores, such as ionomycin and 4-Br-A23187, which also inhibited the responses to vasoconstrictors. Ca(2+)-free solutions prevented the [Ca(2+)](i) rise as well as subsequent receptor inactivation, implicating Ca(2+) influx through store-operated Ca(2+) channels (SOC), a major pathway for Ca(2+) entry in these cultured cells. Ca(2+) influx was confirmed by Mn(2+)-quenching of fura 2.

CONCLUSIONS

In HMC, early changes in [Ca(2+)](i) signal for monocyte adhesion in a co-culture model of glomerular inflammation. This signalling mechanism may mediate the functional responses elicited in glomerular cells by leukocytes, including downregulation of receptors for vasoactive agents.

Effects of vitamin D on the growth of normal and malignant B-cell progenitors

As the effects of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25-(OH)2-D3) (VD, calcitriol) on the proliferation and differentiation potential of normal and leukaemic cells in vitro of myeloid lineage are known, we investigated the response to VD on the growth of both normal and malignant lymphoid progenitors. Effects of vitamin D on normal human lymphoid progenitors and B lineage acute lymphoblastic leukaemia (ALL) progenitors were assessed by using an in vitro cell colony assay specific for either B or T cell lineages. The expression of VDR on B untreated malignant progenitors at diagnosis was investigated by RT-PCR analysis. VD induced a significant inhibition of normal lymphoid cell progenitors growth of both T and B lineage. VD inhibited significantly also the growth of malignant B cell lineage lymphoid progenitors, without inducing cytotoxic effect. As it has been reported that VD effects on activated lymphocytes are mediated by 1,25-(OH)2-D3 nuclear receptor (VDR), we investigated VDR expression on malignant B cell progenitors. We did not detect VDR expression on these cells examined at diagnosis. We demonstrated that VD inhibited in vitro the clonogenic growth of both normal and malignant lymphoid B cell progenitors and that this inhibitory effect on malignant B cell progenitors was not related to VDR. Our work contributes to understanding of the mechanism of action of this hormone in promoting cellular inhibition of clonal growth of malignant lymphoid B cell progenitors, suggesting that the regulation of some critical growth and differentiation factor receptors could be a key physiological role of this hormone.

Orchestration of multiple arrays of signal cross-talk and combinatorial interactions for maturation and cell death: another vision of t(15;17) preleukemic blast and APL-cell maturation

Despite intensive molecular biology investigations over the past 10 years, and an important breakthrough on how PML-RARalpha, the fusion protein resulting from t(15;17), can alter RARalpha and PML functions, no definitive views on how leukemia is generated and by what mechanism(s) the normal phenotype is restored, are yet available. 'Resistances' to pharmacological levels of all-trans-retinoic acid (ATRA) have been observed in experimental in vivo and in vitro models. In this review, we emphasize the key role played by signal cross-talk for both normal and neoplastic hemopoiesis. After an overview of reported experimental data on APL-cell maturation and apoptosis, we apply our current knowledge on signaling pathways to underline those which might generate signal cross-talks. The design of biological models suitable to decipher the integration of signal cross-talks at the transcriptional level should be our first priority today, to generate some realistic therapeutic approaches After 'Ten Years of Molecular APL', we still know very little about how the disease develops and how effective medicines work.

Sensitization to TNF-induced apoptosis by 1,25-dihydroxy vitamin D(3) involves up-regulation of the TNF receptor 1 and cathepsin B

The active form of vitamin D(3), 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), induces caspase-independent apoptosis in MCF-7 and T47D breast cancer cells. Before the appearance of apoptotic cells at Day 4 after the addition of 1,25(OH)(2)D(3), the MCF-7 cells are sensitized to the caspase-mediated apoptosis induced by TNF. We studied the mechanism underlying the cross talk between these 2 distinct death pathways in MCF-7 and T47D cells. Whereas 1,25(OH)(2)D(3) pre-treatment enhanced TNF-induced apoptosis of TNF sensitive MCF-7 cells, it failed to render TNF resistant T47D cells sensitive to this cytokine. Opposing to an earlier report suggesting that cytosolic phospholipase A(2) (cPLA(2)) mediates the 1,25(OH)(2)D(3)-induced sensitization to TNF, we could not detect any cPLA(2) protein in MCF-7 cells and its overexpression had no effect on cellular sensitivity to 1,25(OH)(2)D(3) or the combination with TNF. The sensitization of MCF-7 cells to TNF-induced apoptosis by pre-treatment with 1,25(OH)(2)D(3) may instead be partially explained by an increased surface expression of the TNF receptor 1 (TNF-R1). In line with this, not only the TNF-induced activation of caspases and apoptosis but also that of NF-kappaB was enhanced by 1,25(OH)(2)D(3) pre-treatment. Furthermore, 1,25(OH)(2)D(3) enhanced TNF-induced NF-kappaB activation in T47D cells suggesting that it potentiates TNF signaling in general. Interestingly, the lysosomal protease cathepsin B, which expression is up-regulated by 1,25(OH)(2)D(3), was released from the lysosomes upon TNF treatment, and inhibition of its activity rescued 1,25(OH)(2)D(3) treated MCF-7 cells from TNF-induced apoptosis. In conclusion, 1,25(OH)(2)D(3) may enhance TNF-induced apoptosis by increasing the expression of both the TNF-R1 and cathepsin B.

1,25-dihydroxyvitamin D3 and retonic acid analogues induce differentiation in breast cancer cells with function- and cell-specific additive effects

Vitamin D3 derivatives and retinoids can induce cell cycle arrest, differentiation and cell death in many cell lines. These compounds can act cooperatively in some of their functions and may be of potential use either individually or in combination in the treatment of breast cancer. The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), all-trans retinoic acid (ATRA) and several analogues were evaluated on malignant phenotypic traits of breast cancer cell lines MCF-7, T-47D and MDA-MB-231. Both 1,25(OH)2D3 and ATRA caused a decrease in anchorage independent colony formation in MCF-7 and T-47D cells in a dose-dependent manner. The effects of 1,25(OH)2D3 10(-10) and 10(-9) M were synergistic with ATRA 10(-8) M in T-47D cells but were antagonistic in both MCF-7 and in T-47D cells at most concentrations. Both 1,25(OH)2D3 and ATRA individually induced an accumulation of MCF-7 cells in the G1 phase of the cell cycle and an associated increase in p21WAFI/CiP1, p27KiP1 and a dephosphorylation of Rb but the effects were not additive. Both compounds inhibited the invasive capacity of MDA-MB-231 cells. 1,25(OH)2D3 but not ATRA caused an increase in E-cadherin levels in MDA-MB-231 cells. These two functions were not additive. The compounds 1,25(OH)2D3, a noncalcemic analogue 1,25(OH)2-16-ene-23-yne-D3, ATRA, AGN195183, an RARalpha-specific agonist, and AGN190168 (tazarotene), an RARbeta/gamma-selective agonist, induced differentiation as determined by measurements of lipid droplet formation. The individual effects of 1,25(OH)2-16-ene-23-yne-D3 combined with ATRA or with tazarotene at 10(-9) M each were additive in MCF-7 and MDA-MB-231 cells on lipid formation. The data demonstrate that both 1,25(OH)2D3, ATRA, and selected analogues induce a more differentiated phenotype in breast cancer cells with additive effects that are function- and cell-specific.

Modulation of CD157 expression in multi-lineage myeloid differentiation of promyelocytic cell lines

CD157/BST-1 is expressed on mature myeloid cells but not on their precursors in vivo. Also CD38, a homologous gene to CD157, is upregulated in promyelocytic HL-60 cells by the monocyte and granulocyte differentiation-inducing 1alpha,25dihydroxyvitamin D3 (VD3) and all-trans retinoic acid (ATRA), respectively. We have examined whether CD157 expression is upregulated when the promyeloid HL-60 and/or U937 cells are induced to differentiate into mature phenotypes in vitro. VD3 treatment irreversibly upregulated the expression of CD157 in HL-60 cells but not in U937 cells in a time- and concentration-dependent manner when analyzed by flow cytometry, immunoblotting and/or RT-PCR. Different monocyte and granulocyte lineage inducers induced CD157 expression to varying extents while the macrophage differentiation-inducing phorbol 12-myristate 13-acetate (PMA) induced its down-regulation. Time-kinetics of VD3 treatment of HL-60 cells showed that the appearance of CD157 and CD11b (a differentiation marker) antigens were not substantial up to 24 hours but increased subsequently although the appearance of CD38 became significant within 6 hours. Two-color staining of VD3-treated HL-60 cells displayed an apparently linear correlation between CD157 and CD11b expression. Dibutyryl cAMP (cAMP agonist) and forskolin (cAMP-increasing agent) augmented the VD3-dependent induction of CD157 and CD11b expression while PGE1 (cAMP-decreasing agent) inhibited it, suggesting the involvement of a cAMP-dependent mechanism in VD3-induced CD157 upregulation. Co-treatment of HL-60 cells with VD3 plus TNF-alpha or ara-C produced an additive effect on CD157 upregulation. The upregulated CD157 in the VD3-differentiated HL-60 cells was able to activate CD157-dependent tyrosine kinase signal when cross-linked with anti-CD157 antibody.

Mechanisms involved in the pro- and anti-apoptotic role of NO in human leukemia

Nitric oxide (NO) exerts contrasting effects on apoptosis, depending on its concentration, flux and cell type. In some situations, NO activates the transduction pathways leading to apoptosis, whereas in other cases NO protects cells against spontaneous or induced apoptosis. The redox state of the cells appears to be a crucial parameter for the determination of the ultimate action of NO on cell multiplication and survival. Apoptosis is mostly associated with the delivery of NO by chemical donors and with myelomonocytic cells, whereas antiapoptotic effects seem to be related to the endogenous production of NO by NO synthases and is observed more frequently in cells of the B lymphocyte lineage. Pro-apoptotic effects are often observed when NO reacts with superoxide to produce the highly toxic peroxynitrite. Through the induction of damages to DNA, NO stimulates the expression of enzymes and transcription factors involved in DNA repair and modulation of apoptosis, such as the tumor suppressor p53. The latter molecule transactivates the expression of pro-apoptotic genes, such as bax, and that of the cyclin-dependent kinase inhibitor p21, whereas it down-regulates the expression of the anti-apoptotic protein bcl-2. On the other hand, NO inactivates caspases through oxidation and S-nitrosylation of the active cystein, providing an efficient means to block apoptosis. Other protective effects of NO on apoptosis rely on the stimulation of cGMP-dependent protein kinase (PKG), modulation of the members of the bcl-2/bax family that control the mitochondrial pore transition permeability, induction of the heat shock protein HSP 70 and interaction with the ceramide pathway. A defect in the apoptotic process contributes to the accumulation of tumoral cells in leukemia, notably in B-CLL. A better knowledge of the targets of NO would provide efficient means to control cell apoptosis, and hence would possibly lead to the development of new therapeutic approaches for diseases where an alteration of apoptosis is involved.

Differential and antagonistic effects of 9-cis-retinoic acid and vitamin D analogues on pancreatic cancer cells in vitro

Retinoids and vitamin D are known to exert important anti-tumour effects in a variety of cell types. In this study the effects of 9-cis-retinoic acid (9cRA) the vitamin D analogues EB1089 and CB1093 on three pancreatic adenocarcinoma cell lines were investigated. All compounds caused inhibition of in vitro growth but the vitamin D analogues were generally the more potent growth inhibitors. They were also more effective on their own than in combination with 9cRA. Growth arrest correlated with an increased proportion of cells in the G0/G1 phase. Apoptosis was induced in the three cell lines by 9cRA, whereas neither EB1089 nor CB1093 had this effect. Furthermore, addition of EB1089 or CB1093 together with 9cRA resulted in significantly reduced apoptosis. Our results show that retinoic acids as well as vitamin D analogues have inhibitory effects on pancreatic tumour cells but different and antagonistic mechanisms seem to be employed.

The role of RAR and RXR activation in retinoid-induced tissue factor suppression

Excessive expression of tissue factor (TF) is a common finding in leukaemic cells and may contribute to thrombotic complications in patients. Retinoic acid has been shown to induce differentiation and reduce TF expression in acute promyelocytic leukaemia (APL) cells in vitro, and to induce remission in APL patients. Treatment of the APL cell line NB4 with the specific retinoic acid receptor-alpha (RARalpha) agonists Ro4-6055 or TTNPB resulted in down-regulation of TF expression and in induction of differentiation. The activation of RARbeta, RARgamma or retinoid X receptor (RXR) did not suppress the constitutive TF expression in NB4 cells. Moreover, the RARalpha antagonist Ro41-5253 blocked the retinoid-induced down-regulation of TF. In contrast, in the monoblastic U-937 cell line only a partial suppression of TF antigen expression and activity was observed by treatment with the RAR agonist TTNPB or the RXR agonist SR11237 alone. However, the combination of TTNPB and SR11237 resulted in a pronounced down-regulation of TF expression and induction of differentiation in U-937 cells. We show for the first time that the activation of both subunits of the RARalpha-RXR transcriptional complex is needed for TF suppression in U-937 cells, whereas in NB4 cells RARalpha activation alone is sufficient. Thus, distinct molecular mechanisms for TF suppression seem to be operating in leukaemic cell lines of different origin.

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.