Impaired nuclear localization of vitamin D receptor in leukemia cells resistant to calcitriol-induced differentiation

Ultrasound-mediated nanobubbles loaded with STAT6 siRNA inhibit TGF-β1-EMT axis in LUSC cells via overcoming the polarization of M2-TAMs

M2-like tumor-associated macrophages (M2-TAMs) are closely correlated with metastasis and poor clinical outcomes in lung squamous cell carcinoma (LUSC). Previous studies have demonstrated that STAT6 is an important signaling molecule involved in the polarization of M2-TAMs, EMT is the main way for TAMs to promote tumor progression. However, little attention has been paid to the effect of STAT6 inhibition on LUSC, and it is difficult to achieve an ideal gene silencing effect in immune cells using traditional gene transfection methods. Here, we investigated the optimal concentration of 12-myristic 13-acetate (PMA), lipopolysaccharide (LPS) for the induction of THP-1 into M1-TAMs and M2-TAMs. The expression of pSTAT6 and STAT6 was confirmed in three types of macrophages, and it was demonstrated that pSTAT6 can be used as a specific target of M2-TAMs derived from THP-1. Ultrasound-mediated nanobubble destruction (UMND) is a non-invasive and safe gene delivery technology. We also synthesized PLGA-PEI nanobubbles (NBs) to load and deliver STAT6 small interfering RNA (siRNA) into M2-TAMs via UMND. The results show that the NBs could effectively load with siRNA and had good biocompatibility. We found that UMND enhanced the transfection efficiency of siRNA, as well as the silencing effect of pSTAT6 and the inhibition of M2-TAMs. Simultaneously, when STAT6 siRNA entered M2-TAMs by UMND, proliferation, migration, invasion and EMT in LUSC cells could be inhibited via the transforming growth factor-β1 (TGF-β1) pathway. Therefore, our results confirm that UMND is an ideal siRNA delivery strategy, revealing its potential to inhibit M2-TAMs polarization and ultimately treat LUSC.

Vitamin D and cancer

The role of vitamin D in the prevention of chronic diseases including cancer, has received a great deal of attention during the past few decades. The term "Cancer" represents multiple disease states with varying biological complexities. The strongest link between vitamin D and cancer is provided by ecological and studies like observational, in preclinical models. It is apparent that vitamin D exerts diverse biological responses in a tissue specific manner. Moreover, several human factors could affect bioactivity of vitamin D. The mechanism(s) underlying vitamin D initiated anti-carcinogenic effects are diverse and includes changes at the muti-system levels. The oncogenic environment could easily corrupt the traditional role of vitamin D or could ensure resistance to vitamin D mediated responses. Several researchers have identified gaps in our knowledge pertaining to the role of vitamin D in cancer. Further areas are identified to solidify the role of vitamin D in cancer control strategies.

Choosing the Right Cell Line for Acute Myeloid Leukemia (AML) Research

Immortalized cell lines are widely used in vitro tools in oncology and hematology research. While these cell lines represent artificial systems and may accumulate genetic aberrations with each passage, they are still considered valuable models for pilot, preliminary, and screening studies. Despite their limitations, cell lines are cost-effective and provide repeatable and comparable results. Choosing the appropriate cell line for acute myeloid leukemia (AML) research is crucial for obtaining reliable and relevant results. Several factors should be considered when selecting a cell line for AML research, such as specific markers and genetic abnormalities associated with different subtypes of AML. It is also essential to evaluate the karyotype and mutational profile of the cell line, as these can influence the behavior and response to the treatment of the cells. In this review, we evaluate immortalized AML cell lines and discuss the issues surrounding them concerning the revised World Health Organization and the French-American-British classifications.

Calcitriol and Calcidiol Can Sensitize Melanoma Cells to Low⁻LET Proton Beam Irradiation

Proton beam irradiation promises therapeutic utility in the management of uveal melanoma. Calcitriol (1,25(OH)₂D₃)—the biologically active metabolite of vitamin D₃—and its precursor, calcidiol (25(OH)D₃), exert pleiotropic effects on melanoma cells. The aim of the study was to evaluate the effect of both calcitriol and calcidiol on melanoma cell proliferation and their response to proton beam irradiation. Three melanoma cell lines (human SKMEL-188 and hamster BHM Ma and BHM Ab), pre-treated with 1,25(OH)₂D₃ or 25(OH)D₃ at graded concentrations (0, 10, 100 nM), were irradiated with 0–5 Gy and then cultured in vitro. Growth curves were determined by counting the cell number every 24 h up to 120 h, which was used to calculate surviving fractions. The obtained survival curves were analysed using two standard models: linear-quadratic and multi-target single hit. Calcitriol inhibited human melanoma proliferation at 10 nM, while only calcidiol inhibited proliferation of hamster lines at 10 and 100 nM doses. Treatment with either 1,25(OH)₂D₃ or 25(OH)D₃ radio sensitized melanoma cells to low doses of proton beam radiation. The strength of the effect increased with the concentration of vitamin D₃. Our data suggest that vitamin D₃ may be an adjuvant that modifies proton beam efficiency during melanoma therapy.

The Use of 1α,25-Dihydroxyvitamin D₃ as an Anticancer Agent

The notion that vitamin D can influence the incidence of cancer arose from epidemiological studies. The major source of vitamin D in the organism is skin production upon exposure to ultra violet-B. The very first observation of an inverse correlation between exposure of individuals to the sun and the likelihood of cancer was reported as early as 1941. In 1980, Garland and Garland hypothesised, from findings from epidemiological studies of patients in the US with colon cancer, that vitamin D produced in response to sun exposure is protective against cancer as opposed to sunlight per se. Later studies revealed inverse correlations between sun exposure and the occurrence of prostate and breast cancers. These observations prompted laboratory investigation of whether or not vitamin D had an effect on cancer cells. Vitamin D is not active against cancer cells, but the most active metabolite 1α,25-dihydroxyvitamin D₃ (1,25D) has profound biological effects. Here, we review the anticancer action of 1,25D, clinical trials of 1,25D to date and the prospects of the future therapeutic use of new and low calcaemic analogues.

IL-18-induced interaction between IMP3 and HuR contributes to COX-2 mRNA stabilization in acute myeloid leukemia

Acute myeloid leukemia is the majority type presented in leukemia patients. Forcing malignant cells to undergo differentiation is 1 strategy for acute myeloid leukemia therapy. However, the failure of acute myeloid leukemia patients to achieve remission as a result of drug resistance remains a challenge. In this study, we found that the abundances of the proinflammatory cytokine IL-18 and its receptor (IL-18R) correlated with the occurrence of drug resistance in AML patients during standard treatment. Cyclooxygenase 2 (COX-2) has been suggested to have an antiapoptotic role in chemoresistant cancer cells. IL-18 treatment resulted in an increase in COX-2 expression through the post-transcriptional regulation of COX-2 mRNA in differentiated U937 cells and showed antiapoptotic activity in U937 and THP-1 cells. Two RNA-binding proteins, human antigen R and insulin-like growth factor mRNA-binding protein 3, mediated the stabilization of COX-2 mRNA. IL-18 induced the shuttling of human antigen R and insulin-like growth factor mRNA-binding protein 3 from the nucleus to the cytoplasm and facilitated their interaction; subsequently, this complex bound to the 3' untranslated region of COX-2 mRNA and affected its stability. We demonstrated further that JNK and/or ERK1/2 regulated human antigen R nucleocytoplasmic shuttling, mediating IL-18 stabilization of cyclooxygenase 2 mRNA.

The vitamin D receptor in dopamine neurons; its presence in human substantia nigra and its ontogenesis in rat midbrain

There is growing evidence that vitamin D is a neuroactive steroid capable of regulating multiple pathways important for both brain development and mature brain function. In particular, there is evidence from rodent models that prenatal vitamin D deficiency alters the development of dopaminergic pathways and this disruption is associated with altered behavior and neurochemistry in the adult brain. Although the presence of the vitamin D receptor (VDR) has been noted in the human substantia nigra, there is a lack of direct evidence showing that VDR is present in dopaminergic cells. Here we confirm that the VDR is present in the nucleus of tyrosine hydroxylase (TH)-positive neurons in both the human and rat substantia nigra, and it emerges early in development in the rat, between embryonic day 12 (E12) and E15. Consistent evidence based on immunohistochemistry, real-time PCR and western blot confirmed a pattern of increasing VDR expression in the rat midbrain until weaning. The nuclear expression of VDR in TH-positive neurons during critical periods of brain development suggests that alterations in early life vitamin D status may influence the orderly development of dopaminergic neurons.

New vitamin D analogs as potential therapeutics in melanoma

Extensive evidence shows that the active form of vitamin D3--1α,25-dihydroxyvitamin D3--plays an important role in cancer prevention, has tumorostatic activity and may potentially be used in therapy for melanoma. Vitamin D3 and its analogs (secosteroids) exert multiple effects on cancer cells, including inhibition of cell growth and induction of differentiation. Activity of secosteroids depends on multiple cellular factors, including expression of the vitamin D receptor. Despite its endogenous origin, the key drawback for the use of pharmacologically effective doses of 1α,25-dihydroxyvitamin D3 is its hypercalcemic effect leading to profound toxicity. The solution may lie in properties of vitamin D3 analogs with modified side chains, which demonstrate low calcemic activity but conserve the anti-tumor properties. Noncalcemic vitamin D compounds were found to be potent in multiple studies that mandate further clinical testing. Finally, recent studies revealed alternative metabolic pathways for secosteroids and new targets in the cells, which opens up new therapeutic possibilities.

Down-regulation of NF-kappaB signals is involved in loss of 1alpha,25-dihydroxyvitamin D3 responsiveness

Vitamin D anti-tumor effect is often found reduced in the late stages of cancer. To uncover vitamin D resistance mechanism, we established a vitamin D-resistant human prostate cancer LNCaP cell line, LNCaP-R, by chronic exposure of cells to 1alpha,25-dihydroxyvitamin D(3) (1,25-VD). The vitamin D receptor (VDR)-mediated transcriptional activity was reduced in LNCaP-R, whereas VDR expression level and DNA-binding capacity were similar compared to parental cells (LNCaP-P). The expressions of the key factors involved in VDR transactivity, including CYP24A1 and VDR-associated proteins are all increased in LNCaP-R cells, and yet treatment with ketoconazole, P450 enzymes inhibitor, as well as trichostatin A (TSA), a histone deacetylase inhibitor, did not sensitize LNCaP-R cells response to vitamin D, suggesting that neither a local 1,25-VD availability, nor VDR-associated proteins are responsible for the vitamin D resistance. Interestingly, nuclear factor-kappaB (NF-kappaB) signaling, which is critical for 1,25-VD/VDR activity was found reduced in LNCaP-R cells, thereby treatment with NF-kappaB activator, 12-O-tetradecanoylphorbol-13-acetate (TPA), can sensitize LNCaP-R vitamin D response. Together, we conclude that NF-kappaB signaling is critical for vitamin D sensitivity, and dysregulation of this pathway would result in vitamin D resistance and disease progression.

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.

Side-chain modified vitamin D analogs induce rapid accumulation of VDR in the cell nuclei proportionately to their differentiation-inducing potential

1,25-Dihydroxyvitamin D(3) (1,25D) regulates gene transcription through a nuclear vitamin D receptor (VDR) which acts as a ligand-regulated transcription factor. Some structural vitamin D analogs (VDAs) are selective in their biological actions, because they retain cell-differentiating potential, while their calcemic activity is reduced. In this article we have shown that in untreated HL60 cells the expression level of VDR is low, in spite of constant presence of VDR mRNA. Furthermore we have shown that one of the most rapid effects of either 1,25D or VDAs is nuclear accumulation of VDR, which is proportional to the differentiation-inducing potential of given analog. We observed this effect not only in HL60 cells, but also in blast cells isolated from patients with acute myeloid leukemias. After longer incubation time of the cells with various VDAs, the expression levels of VDR have become unrelated to the final differentiation effect.

Mechanisms of nuclear vitamin D receptor resistance in Harvey-ras-transfected cells

The hormone 1,25 dihydroxyvitamin D (1,25(OH)(2)D) binds to the nuclear vitamin D receptor (nVDR), which heterodimerizes with retinoid X receptor alpha (RXRalpha), and this complex interacts with specific response elements [vitamin D response elements (VDREs)] to regulate gene transcription. Previous results show a significant reduction in 1,25(OH)(2)D-induced nVDR transcriptional activity in fibroblast (C3H10T1/2) cells transfected with the Harvey ras gene (ras cells) compared with parental cells. The purpose of this study was to investigate the mechanisms by which the H-ras gene interferes with nVDR transcriptional activity. Similar to the ras cells, transcriptional activity of the nVDR was reduced following induction of the H-ras gene for 9 days. The ras cells expressed similar protein levels of RXRalpha with the parent cells, and overexpression of the wild-type RXRalpha plasmid did not restore 1,25(OH)(2)D-mediated nVDR activity in ras cells. Inhibiting activation of extracellular signal-regulated kinase (ERK1/2) had no effect on nVDR activity in ras cells. Furthermore, the binding of nVDR to VDREs was reduced in 1,25(OH)(2)D-treated ras cells. In addition, neither treatment of ras cells with an inhibitor (ketoconazole) of the 1,25(OH)(2)D degradative enzyme, 24-hydroxylase, nor the protein kinase C inhibitors, bisindoylmaleimide I and Gö 6976, had an effect on nVDR activity. In contrast, inhibition of phosphatidylinositol 3-kinase (PI3K) with LY294002 resulted in a 1.6-fold significant increase in the nVDR activity in the ras cells. Taken together, these results indicate that PI3K may, at least in part, mediate the suppression of the 1,25(OH)(2)D regulation of nVDR transcriptional activity by the H-ras gene, leading to reduced ability to associate with response elements.

Resistance to 1,25D-induced differentiation in human acute myeloid leukemia HL60-40AF cells is associated with reduced transcriptional activity and nuclear localization of the vitamin D receptor

The anti-neoplastic effects of 1,25-dihydroxyvitamin D3 (1,25D) are well documented in numerous tumor cell systems and animal models of cancer. However, despite this pre-clinical success, the clinical use of 1,25D is currently impeded by the dose-limiting hypercalcemia, and the risk of development of resistance to 1,25D. In this study, we investigated the mechanism of resistance to 1,25D of HL60-40AF cells, a model of drug-resistant acute myeloid leukemia, derived from HL60 cells by cultivation in the presence of 1,25D. The data indicate that transcriptional activity of vitamin D receptor (VDR) in 40AF cells increases only briefly when the cells are treated with 1,25D, despite greater basal cellular levels of VDR protein in the resistant than in the 1,25D-sensitive cells. Analysis of the 40AF VDR mRNA sequence indicated alterations in the 5' untranslated region (UTR), but coding domain variations were not observed. When resistance to 1,25D-induced differentiation of 40AF cells was reversed by a combination of 1,25D with potentiators of differentiation (plant derived antioxidants and a p38MAPK inhibitor), an increase in the level of nuclear VDR, as well as an increase in CYP24 mRNA expression was observed. These data suggest that decreased ability of 1,25D to induce VDR nuclear localization and the consequent VDR target gene transcription may be an important reason for the resistance of 40AF cells to 1,25D. Further, our data show that VDR localization and phosphorylation can be increased by combining 1,25D with potentiators of differentiation. Analysis of the mechanisms that underlie the reduction and potentiation of 1,25D-mediated changes in VDR activity may lead to the identification of new cellular targets that enhance 1,25D-induced monocytic differentiation.

Expressions of polypeptide: N-acetylgalactosaminyltransferase in leukemia cell lines during 1,25-dihydroxyvitamin D3 induced differentiation

The effect of 1,25-dihydroxyvitamin D3 [1,25(OH)(2)D3] on two leukemia cell lines, K562 and SHI-1, and its relation to the expression of different subtypes of polypeptide: N-acetylgalactosaminyltransferase (pp-GalNAc-T) was studied. With morphological and cell flow-cytometric method, it was found that 1,25(OH)(2)D3 induced the differentiation of both leukemia cell lines toward monocytic lineage, but not affected the cell growth and apoptosis. The expressions of different subtypes of pp-GalNAc-T, the initial glycosyltransferase in O-glycan synthesis, were studied with RT-PCR before and after the treatment of different concentrations of 1,25(OH)(2)D3. Among fourteen subtypes of pp-GalNAc-T (T1 approximately T14), K562 cells obviously expressed pp-GalNAc-T2, T4, T5, T7 (T2 was the highest) and SHI-1 cells apparently expressed pp-GalNAcT1, T2, T3 and T4 (T4 was the highest) only. After K562 cells were treated 1, 25(OH)(2)D3 for 72 h, pp-GalNAc-T2, T4, T5, T7 were increased in a dose dependent manner. In contrast, pp-GalNAc-T1 and T2, especially T1, were up-regulated in SHI-1 cells by 1,25(OH)(2)D3, but T3 was unchanged and T4 was down-regulated. The different alterations of pp-GalNAc-Ts in these two cell lines were probably related to the different structural changes of O-glycans during 1,25(OH)(2)D3 induced differentiation.

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.

Studies on the mechanism of action of a proline-rich polypeptide complex (PRP): effect on the stage of cell differentiation

A proline-rich polypeptide complex (PRP) with immunoregulatory and procognitive activities shows beneficial effects in Alzheimer's disease (AD). The mechanism of action of PRP in AD is not yet clarified. Here, we present results of the effect of PRP on Vitamin D3-induced phenotypic (CD11b and CD14) and functional (phagocytic) differentiation/maturation of monocytes/macrophages using the premonocytic HL-60 cell line as a model. This cell line can be induced to differentiate into monocyte/macrophage cells by incubation with Vitamin D3. However, when Vitamin D3 was applied together with PRP, a 30-40% inhibition of the expression of the differentiation markers and an over-60% inhibition of phagocytic ability were observed. When PRP was administered to the cells after treatment with Vitamin D3, no attenuation of the differentiation/maturation process of the HL-60 cells was observed. This indicates that PRP affects the early stages of differentiation/maturation of these cells. Our results, therefore, suggest that PRP, which affects the differentiation/maturation processes of cells of monocyte/macrophage lineage, may regulate in this way the inflammatory processes in which these cells participate.

Expression of VDR and CYP24A1 mRNA in human tumors

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its analogues have been shown to inhibit proliferation of human cancer cells mediated by vitamin D receptor (VDR). The over-expression of 25-hydroxyvitamin D-24-hydroxylase (CYP24A1), an enzyme involved in the metabolism of 1,25(OH)2D3 and its analogues, is associated with poor prognosis of some human cancers. In this study, we employed real-time reverse transcription PCR to examine the expression of VDR and CYP24A1 mRNA in a cohort of human breast, lung, colon and ovary tumor samples. We found that CYP24A1 mRNA was significantly up-regulated in colon, ovary and lung tumors, but down-regulated in breast tumor relative to the analogous normal tissues. As a comparison, VDR mRNA was modestly down-regulated in colon, breast and lung tumors, but highly up-regulated in ovarian tumors. Treatment of two breast cancer cell lines, SW-620 and MCF-7, and one colon cancer cell line, HT-29, by 1,25(OH)2D3 for 48 h profoundly stimulated CYP24A1 mRNA expression (EC50=0.6, 0.8 and 29.5 nM in SW-620, HT-29 and MCF-7, respectively), but did not significantly affect VDR mRNA expression. Growth as assessed by DNA synthesis was modestly arrested by 1,25(OH)2D3 after 72 h of incubation, but was not altered after a 5-day incubation period. These data suggest that the VDR signaling pathway may be compromised via the modulation of CYP24A1 and VDR in human tumors.