All trans retinoic acid induces apoptosis in acute promyelocytic NB4 cells when combined with isoquinolinediol, a poly(ADP-ribose) polymerase inhibitor

All-trans retinoic acid inhibits the differentiation, maturation, and function of human monocyte-derived dendritic cells

All-trans retinoic acid (ATRA) affects on the function of antigen presenting cells with somewhat controversies. We investigated the effects of ATRA on differentiation, maturation and function of human monocyte-derived dendritic cells (DCs). Low dose (10(-14)M) or high dose (10(-6)M) of ATRA was added either when monocytes were differentiated into immature DCs (imDCs) or mature DCs (mDCs) were induced. Apoptotic cell populations were dramatically increased in imDCs or mDCs with increasing concentration of ATRA. The productions of IL-12p40 and IL-12p70 were significantly suppressed in imDCs or mDCs induced by the addition of ATRA in the dose-dependent manner, whereas IL-10 was increased. DCs cultured with ATRA induced the differentiation of naïve T cells towards a helper T cell type 2 (Th2) response and expansion of CD4(+)CD25(+)Foxp3(+) regulatory T cells. Allostimulatory capacity of DCs was suppressed with increasing concentration of ATRA. These findings suggest that ATRA inhibits the effects on the differentiation, maturation and function of human monocyte-derived DCs in vitro and also enhance the differentiation of naïve T cell toward the Th2 type.

Guanosine acts intracellularly to initiate apoptosis in NB4 cells: A role for nucleoside transport

Guanosine initiated apoptosis in NB4 cells in a transport-dependent manner. Apoptosis was partially attributed to an imbalance in nucleosides with some protection upon the addition of pyrimidines. The effect of guanosine on cell proliferation and viability was biphasic whereby cells were able to recover from an initial cell cycle arrest and re-enter the cell cycle upon removal of guanosine in a time-dependent fashion. However, exposure to guanosine beyond 24 h prevented recovery and ultimately led to death. Death occurred with a decrease in bcl-2 protein expression, thus suggesting that the pathway to apoptosis involved change(s) in the intracellular environment that were ultimately sensed by the mitochondria. Expression of the unique guanosine-specific nucleoside transporter csg in NB4 cells may provide an opportunity to harness guanosine-mediated cell death in the treatment of APL and related malignancies while sparing normal cells.

Cooperative action of 1α,25-dihydroxyvitamin D3 and retinoic acid in NB4 acute promyelocytic leukemia cell differentiation is transcriptionally controlled

All-trans-retinoic acid (RA) and 1alpha,25-dihydroxyvitamin D3 (1,25D3) are involved in the control of hematopoiesis and have been suggested to play a role in cellular differentiation and are as such potent inducers of differentiation of myeloid leukemia cells. In this study, we show that, in promyelocytic NB4 cells, addition of 1,25D3 enhances terminal granulocytic RA-dependent differentiation concomitant with the enhanced activation of the RA transcriptional activity through an RARbeta promoter. By EMSA and ChIP assays, we further demonstrate that, while both VDR and RAR are bound to the RARbeta promoter in NB4 cells, addition of 1,25D3 increases VDR binding to this promoter, while that of RA induces the release of VDR and increases the binding of RAR. Thus, contrary to normal myeloid cells, 1,25D3 does not act as a transrepressor of RA transcriptional activity in leukemic cells, suggesting that transcriptional regulation of RA-target genes may be modified in malignant cells. In promyelocytic leukemic cells, the combination of 1,25D3 and RA results in both enhanced transactivation and differentiation.

The Notch ligand, Delta-1, alters retinoic acid (RA)-induced neutrophilic differentiation into monocytic and reduces RA-induced apoptosis in NB4 cells

Effects of Notch activation on retinoic acid (RA)-induced differentiation and apoptosis were investigated. NB4, an acute promyelocytic leukemia (APL) cell line, undergoes neutrophilic differentiation and apoptosis by RA. Notch activation induced by a recombinant Notch ligand, Delta-1, did not affect the growth by itself. Treatment with RA plus Delta-1 made part of NB4 cells monocyte-like shaped and reduced the apoptosis. Similar phenomenon was also observed in primary APL cells. RA treatment induced cleavage of caspase-8 and PARP in NB4. Delta-1 suppressed the RA-induced cleavage of them, which may be a possible mechanism through which Delta-1 suppressed the RA-induced apoptosis.

All- trans-retinoic acid increases cytotoxicity of 1-beta-D-arabinofuranosylcytosine in NB4 cells

PURPOSE

Clinically, the benefits of combining all- trans-retinoic acid (ATRA) with chemotherapy have been well documented in the treatment of acute promyelocytic leukemia (APL). Changes in nucleoside transporter expression and activity have been shown to occur in NB4 cells in vitro following treatment with ATRA. In this study we investigated whether ATRA treatment increases sensitivity to ara-C in NB4 cells. Specifically, we examined the role of ATRA-associated changes in nucleoside transporter expression and activity in eliciting ara-C cytotoxicity.

METHODS

Cellular uptake of [(3)H]-ara-C and nucleoside transporter abundance were determined in untreated cells and cells treated with 1 microM ATRA for 12-72 h using an inhibitor and oil stop procedure, and an equilibrium [(3)H]-NBMPR binding assay, respectively. Cytotoxicity of ara-C and the apoptotic response prior to and following ATRA treatment were determined using the MTT viability assay and the TUNEL assay, respectively.

RESULTS

ATRA treatment increased ara-C cytotoxicity and potency, ara-C transport, and augmented ara-C-induced apoptosis. The combination effect was supraadditive under some conditions and sequence-dependent whereby the maximum effect was seen when the addition of ATRA preceded the addition of ara-C, and when ara-C administration closely followed ATRA administration.

CONCLUSIONS

The ATRA-induced increase in cytotoxicity of ara-C was, in part, the result of an increase in the functional expression of nucleoside transporters, and a role for bcl-2 was also indicated. Our results would suggest that timing of ara-C therapy should be tied to maximal es transporter expression, which is likely to be 24 h after ATRA treatment begins. It remains to be seen whether the response in the clinic can be further enhanced in APL by taking advantage of ara-C transporter regulation by ATRA.

Physiology and pathophysiology of poly(ADP-ribosyl)ation

One of the immediate eukaryotic cellular responses to DNA breakage is the covalent post-translational modification of nuclear proteins with poly(ADP-ribose) from NAD+ as precursor, mostly catalysed by poly(ADP-ribose) polymerase-1 (PARP-1). Recently several other polypeptides have been shown to catalyse poly(ADP-ribose) formation. Poly(ADP-ribosyl)ation is involved in a variety of physiological and pathophysiological phenomena. Physiological functions include its participation in DNA-base excision repair, DNA-damage signalling, regulation of genomic stability, and regulation of transcription and proteasomal function, supporting the previously observed correlation of cellular poly(ADP-ribosyl)ation capacity with mammalian life. The pathophysiology effects are mediated through PARP-1 overactivity, which can cause cell suicide by NAD+ depletion. It is apparent that the latter effect underlies the pathogenesis of a wide range of disease states including type-1 diabetes, ischaemic infarcts in various organs, and septic or haemorrhagic shock. Therefore pharmacological modulation of poly(ADP-ribosyl)ation may prove to be an exciting option for various highly prevalent, disabling and even lethal diseases.