Regulation of Leukemic Cell Differentiation through the Vitamin D Receptor at the Levels of Intracellular Signal Transduction, Gene Transcription, and Protein Trafficking and Stability

Vitamin D Promotes Remyelination by Suppressing c-Myc and Inducing Oligodendrocyte Precursor Cell Differentiation after Traumatic Spinal Cord Injury

Demyelination due to oligodendrocytes loss occurs after traumatic spinal cord injury (TSCI). Several studies have suggested the therapeutic potential of vitamin D (VitD) in demyelinating diseases. However, experimental evidence in the context of TSCI is limited, particularly in the presence of prior VitD-deficiency. In the present study, a contusion and a transection TSCI rat model were used, representing mild and severe injury, respectively. Motor recovery was assessed in rats with normal VitD level or with VitD-deficiency after 8 weeks' treatment post-TSCI (Cholecalciferol, 500 IU/kg/day). The impact on myelin integrity was examined by transmission electron microscopy and studied in vitro using primary culture of oligodendrocytes. We found that VitD treatment post-TSCI effectively improved hindlimb movement in rats with normal VitD level irrespective of injury severity. However, cord-transected rats with prior deficiency did not seem to benefit from VitD supplementation. Our data further suggested that having sufficient VitD was essential for persevering myelin integrity after injury. VitD rescued oligodendrocytes from apoptotic cell death in vitro and enhanced their myelinating ability towards dorsal root axons. Enhanced myelination was mediated by increased oligodendrocyte precursor cells (OPCs) differentiation into oligodendrocytes in concert with c-Myc downregulation and suppressed OPCs proliferation. Our study provides novel insights into the functioning of VitD as a regulator of OPCs differentiation as well as strong preclinical evidence supporting future clinical testing of VitD for TSCI.

Antileukaemic Cell Proliferation and Cytotoxic Activity of Edible Golden Cordyceps (Cordyceps militaris) Extracts

Golden cordyceps (Cordyceps militaris) is a mushroom of the genus Cordyceps. It has been used as a food supplement for both healthy and ill people. In this study, the antileukaemic cell proliferation activities of golden cordyceps extracts were examined and compared with standard cordycepin (CDCP) in EoL-1, U937, and KG-1a cells. Wilms' tumour 1 (WT1) protein was used as a biomarker of leukaemic cell proliferation. The cytotoxicity of the extracts on leukaemic cells was determined using the MTT assay. Their inhibitory effects on WT1 protein expression and cell cycle progression of EoL-1 cells were investigated using Western blotting and flow cytometry, respectively. Induction of KG-1a cell differentiation (using CD11b as a marker) was determined using flow cytometry. The golden cordyceps extracts exhibited cytotoxic effects on leukaemic cells with the highest IC₅₀ value of 16.5 ± 3.9 µg/mL, while there was no effect on normal blood cells. The expression levels of WT1 protein in EoL-1 cells were decreased after treatment with the extracts. Moreover, cell cycle progression and cell proliferation were inhibited. The levels of CD11b increased slightly following the treatment. All these findings confirm the antileukaemic proliferation activity of golden cordyceps.

Gene expression during THP-1 differentiation is influenced by vitamin D3 and not vibrational mechanostimulation

Background

In injury or infection, monocytes migrate into the affected tissues from circulation and differentiate into macrophages which are subsequently involved in the inflammatory responses. Macrophage differentiation and activation have been studied in response to multiple chemokines and cytokines. However, mechanical, and physical stimuli can also influence macrophage differentiation, activation, cytokine production, and phagocytic activity.

Methods

In this study the macrophage differentiation from THP-1 monocytes was assessed upon the stimulation with 1,25-dihydroxyvitamin D3 and 1,000 Hz vibrations, using qPCR for quantification of transcript expression. Vitamin D binds the vitamin D receptor (VDR) and subsequently modulates the expression of a variety of genes in monocytes. The effects of the 1,000 Hz vibrational stimulation, and the combined treatment of vitamin D3 and 1000 Hz vibrations were unknown. The differentiation of macrophages was assessed by looking at transcription of macrophage markers (e.g., CD14, CD36), antigen presenting molecules (e.g., HLA-DRA), transcription factors (e.g., LEF-1, TCF7L2), and mechanosensors (e.g., PIEZO1 and PKD2).

Results

The results showed that vitamin D3 induced THP-1 macrophage differentiation, which was characterized by upregulation of CD14 and CD36, downregulation of HLA-DRA, upregulation of the PKD2 (TRPP2), and an inverse relationship between TCF7L2 and LEF-1, which were upregulated and downregulated respectively. The 1,000 Hz vibrations were sensed from the cells which upregulated PIEZO1 and TCF3, but they did not induce expression of genes that would indicate macrophage differentiation. The mRNA transcription profile in the cells stimulated with the combined treatment was comparable to that of the cells stimulated by the vitamin only. The 1,000 Hz vibrations slightly weakened the effect of the vitamin for the regulation of CD36 and HLA-DMB in the suspension cells, but without causing changes in the regulation patterns. The only exception was the upregulation of TCF3 in the suspension cells, which was influenced by the vibrations. In the adherent cells, the vitamin D3 cancelled the upregulating effect of the 1,000 Hz vibrations and downregulated TCF3. The vitamin also cancelled the upregulation of PIEZO1 gene by the 1,000 Hz vibrations in the combined treatment.

Conclusion

The mechanical stimulation with 1,000 Hz vibrations resulted in upregulation of PIEZO1 in THP-1 cells, but it did not affect the differentiation process which was investigated in this study. Vitamin D3 induced THP-1 macrophage differentiation and could potentially influence M2 polarization as observed by upregulation of CD36 and downregulation of HLA-DRA. In addition, in THP-1 cells undergoing the combined stimulation, the gene expression patterns were influenced by vitamin D3, which also ablated the effect of the mechanical stimulus on PIEZO1 upregulation.

Agonist binding directs dynamic competition among nuclear receptors for heterodimerization with retinoid X receptor

Retinoid X receptor (RXR) plays a pivotal role as a transcriptional regulator and serves as an obligatory heterodimerization partner for at least 20 other nuclear receptors (NRs). Given a potentially limiting/sequestered pool of RXR and simultaneous expression of several RXR partners, we hypothesized that NRs compete for binding to RXR and that this competition is directed by specific agonist treatment. Here, we tested this hypothesis on three NRs: peroxisome proliferator-activated receptor gamma (PPARγ), vitamin D receptor (VDR), and retinoic acid receptor alpha (RARα). The evaluation of competition relied on a nuclear translocation assay applied in a three-color imaging model system by detecting changes in heterodimerization between RXRα and one of its partners (NR1) in the presence of another competing partner (NR2). Our results indicated dynamic competition between the NRs governed by two mechanisms. First, in the absence of agonist treatment, there is a hierarchy of affinities between RXRα and its partners in the following order: RARα > PPARγ > VDR. Second, upon agonist treatment, RXRα favors the liganded partner. We conclude that recruiting RXRα by the liganded NR not only facilitates a stimulus-specific cellular response but also might impede other NR pathways involving RXRα.

Activation of the vitamin D receptor transcription factor stimulates the growth of definitive erythroid progenitors

The pathways that regulate the growth of erythroid progenitors are incompletely understood. In a computational analysis of gene expression changes during erythroid ontogeny, the vitamin D receptor (Vdr) nuclear hormone receptor transcription factor gene was identified in fetal and adult stages, but not at the embryonic stage of development. Vdr was expressed in definitive erythroid (EryD) progenitors and was downregulated during their maturation. Activation of Vdr signaling by the vitamin D3 agonist calcitriol increased the outgrowth of EryD colonies from fetal liver and adult bone marrow, maintained progenitor potential, and delayed erythroid maturation, as revealed by clonogenic assays, suspension culture, cell surface phenotype, and gene expression analyses. The early (cKit⁺CD71^lo/neg), but not the late (cKit⁺CD71^hi), EryD progenitor subset of Lin^negcKit⁺ cells was responsive to calcitriol. Culture of cKit⁺CD71^lo/neg progenitors in the presence of both vitamin D3 and glucocorticoid receptor ligands resulted in an increase in proliferation that was at least additive compared with either ligand alone. Lentivirus shRNA-mediated knockdown of Vdr expression abrogated the stimulation of early erythroid progenitor growth by calcitriol. These findings suggest that Vdr has a cell-intrinsic function in early erythroid progenitors. Targeting of downstream components of the Vdr signaling pathway may lead to new approaches for the expansion of erythroid progenitors ex vivo.

Vitamin D and its receptor polymorphisms: New possible prognostic biomarkers in leukemias

Several factors such as chromosomal translocations, gene mutations, and polymorphisms are involved in the pathogenesis of leukemia/lymphoma. Recently, the role of vitamin D (VD) and vitamin D receptor (VDR) polymorphisms in hematologic malignancies has been considered. In this review, we examine the possible role of VD levels, as well as VDR polymorphisms as prognostic biomarkers in leukemia/lymphoma. Relevant English language literature were searched and retrieved from Google Scholar search engine (1985-2017). The following keywords were used: vitamin D, vitamin D receptor, leukemia, lymphoma, and polymorphism. Increased serum levels of VD in patients with leukemia are associated with a better prognosis. However, low VD levels are associated with a poor prognosis, and VDR polymorphisms in various leukemias can have prognostic value. VD biomarker can be regarded as a potential prognostic factor for a number of leukemias, including acute myeloblastic leukemia (AML), chronic lymphoblastic leukemia (CLL), and diffuse large B-cell lymphoma (DLBCL). There is a significant relationship between different polymorphisms of VDR (including Taq I and Fok I) with several leukemia types such as ALL and AML, which may have prognostic value.

TLE4 regulation of wnt-mediated inflammation underlies its role as a tumor suppressor in myeloid leukemia

The presence of AML1-ETO (RUNX1-CBF2T1), a fusion oncoprotein resulting from a t(8;21) chromosomal translocation, has been implicated as a necessary but insufficient event in the development of a subset of acute myeloid leukemias (AML). While AML1-ETO prolongs survival and inhibits differentiation of hematopoietic stem cells (HSC), other contributory events are needed for cell proliferation and leukemogenesis. We have postulated that specific tumor suppressor genes keep the leukemic potential of AML1-ETO in check. In studying del(9q), one of the most common concomitant chromosomal abnormalities with t(8;21), we identified the loss of an apparent tumor suppressor, TLE4, that appears to cooperate with AML1-ETO to confer a leukemic phenotype. This study sought to identify the molecular basis of this cooperation. We show that the loss of TLE4 confers proliferative advantage to leukemic cells, simultaneous with an upregulation of a pro- inflammatory signature mediated through aberrant increases in Wnt signaling activity. We further demonstrate that inhibition of cyclooxygenase (COX) activity partly reverses the pro-leukemic phenotype due to TLE4 knockdown, pointing towards a novel therapeutic approach for myeloid leukemia.

Relationship between Structure and Conformational Change of the Vitamin D Receptor Ligand Binding Domain in 1α,25-Dihydroxyvitamin D3 Signaling

Vitamin D Receptor (VDR) belongs to the nuclear receptor (NR) superfamily. Whereas the structure of the ligand binding domain (LBD) of VDR has been determined in great detail, the role of its amino acid residues in stabilizing the structure and ligand triggering conformational change is still under debate. There are 13 α-helices and one β-sheet in the VDR LBD and they form a three-layer sandwich structure stabilized by 10 residues. Thirty-six amino acid residues line the ligand binding pocket (LBP) and six of these residues have hydrogen-bonds linking with the ligand. In 1α,25-dihydroxyvitamin D₃ signaling, H3 and H12 play an important role in the course of conformational change resulting in the provision of interfaces for dimerization, coactivator (CoA), corepressor (CoR), and hTAF_II 28. In this paper we provide a detailed description of the amino acid residues stabilizing the structure and taking part in conformational change of VDR LBD according to functional domains.

Induced myelomonocytic differentiation in leukemia cells is accompanied by noncanonical transcription factor expression

Transcription factors that drive non-neoplastic myelomonocytic differentiation are well characterized but have not been systematically analyzed in the leukemic context. We investigated widely used, patient-derived myeloid leukemia cell lines with proclivity for differentiation into granulocytes by retinoic acid (RA) and/or monocytes by 1,25-dihyrdroxyvitamin D3 (D3). Using K562 (FAB M1), HL60 (FAB M2), RA-resistant HL60 sublines, NB4 (FAB M3), and U937 (FAB M5), we correlated nuclear transcription factor expression to immunophenotype, G1/G0 cell cycle arrest and functional inducible oxidative metabolism. We found that myelomonocytic transcription factors are aberrantly expressed in these cell lines. Monocytic-lineage factor EGR1 was not induced by D3 (the monocytic inducer) but instead by RA (the granulocytic inducer) in lineage bipotent myeloblastic HL60. In promyelocytic NB4 cells, EGR1 levels were increased by D3, while Gfi-1 expression (which promotes the granulocytic lineage) was upregulated during D3-induced monocytic differentiation in HL60, and by RA treatment in monocytic U937 cells. Furthermore, RARα and VDR expression were not strongly correlated to differentiation. In response to different differentiation inducers, U937 exhibited the most distinct transcription factor expression profile, while similarly mature NB4 and HL60 were better coupled. Overall, the differentiation induction agents RA and D3 elicited cell-specific responses across these common FAB M1-M5 cell lines.

Increased oxygen consumption observed in phorbol 12-myristate 13-acetate stimulated human cultured promonocytic U937 cell lines treated with calcitriol and retinoic acid

OBJECTIVE

To investigate the effect of phorbol 12-myristate 13-acetate (PMA) and formyl-methionyl-leucyl-phenylalanine (FMLP) on oxygen consumption of differentiated and non-differentiated immune cell lines by retinoic acid and calcitriol treatment which might be useful in subsequent elicitation of immunological action during immunosuppressive states.

METHODS

PMA and FMLP were used to artificially stimulate reactive oxygen production in cultured promonocytic U937 cell line. Paralleled samples of the cultured cells were separately prepared with calcitriol (1, 25- dihydroxyvitamin D3) and retinoic acid followed by a 72-hour incubation period. The rate of respiratory burst was measured using the Clark oxygen electrode.

RESULTS

The average increase in cell concentrations per mL observed was significantly higher in retinoic acid-treated cells (9×10(6) cells/mL) when compared with calcitriol-treated samples (4×10(6) cells/mL). There was a marked increase in oxygen consumption of the calcitriol-treated cell lines against the retinoic acid-treated ones. Exposure of differentiated U937 cells to PMA and FMLP increased significantly (P<0.05) in their oxygen consumption when compared with the control. PMA calcitriol-treated cells resulted in 55% oxygen consumption more than the control while FMLP oxygen consumption increased 78% by comparison with the control.

CONCLUSIONS

The result demonstrated that calcitriol may serve as a physiological promoter of normal differentiation of precursor cells which may exert an immunological action. This effect could elicit a marker potential and increase immune cell activity of the host especially in immunosuppressed diseased states.

NADPH-cytochrome P450 reductase is regulated by all-trans retinoic acid and by 1,25-dihydroxyvitamin D3 in human acute myeloid leukemia cells

Acute myeloid leukemia (AML) cell lines can be driven to differentiate to monocyte-like cells by 1,25- dihydroxyvitamin D₃ (1,25D) and to granulocyte-like cells by all-trans-retinoic acid (ATRA). Both compounds activate their specific intracellular receptors, vitamin D receptor (VDR) and retinoic acid receptors (RARs) respectively. Inside the cells 1,25D is degraded to calcitrioic acid by a mitochondrial enzyme CYP24A1, while ATRA is degraded to several polar metabolites by CYP26. NADPH-cytochrome P450 oxidoreductase (POR) is a membrane-bound enzyme required for electron transfer to cytochrome P450 (CYP), vital in the processes of the metabolism of drugs and steroid production in humans. In this paper we report that POR in AML cells, from both cell lines and patients, is upregulated by ATRA and by 1,25D at the level of mRNA and protein. Partial silencing of POR in HL60 cells resulted in augmented differentiation response to 1,25D.