Stimulation of phosphorylation of mitogen-activated protein kinase by 1alpha,25-dihydroxyvitamin D3 in promyelocytic NB4 leukemia cells: a structure-function study

Vitamin D receptor involves in the protection of intestinal epithelial barrier function via up-regulating SLC26A3

BACKGROUND

Vitamin D receptor (VDR) and SLC26A3 (DRA) have been identified as pivotal protective factors in maintaining gut homeostasis in IBD patients. However, the specific mechanism underlying the increased intestinal susceptibility to inflammation induced by the loss of VDR and whether DRA participates in the role of VDR regulating intestinal epithelial barrier function are undefined.

AIM

The current study is undertaken to elucidate the regulatory effects of VDR on DRA and VDR prevents intestinal epithelial barrier dysfunction via up-regulating the expression of DRA.

METHODS

WT and VDR^-/- mice are used as models for intestinal epithelial response. Paracellular permeability is measured by TEER and FD-4 assays. Immunohistochemistry, immunofluorescence, qPCR and immunoblotting are performed to determine the effects of VDR and DRA on gut epithelial barrier function.

RESULTS

VDR^-/- mice exhibits significant hyperpermeability of intestine with greatly decreased levels of ZO-1 and Claudin1 proteins. DRA is located on the intestinal epithelial apical membrane and is tightly modulated by VDR in vivo and in vitro via activating ERK1/2 MAPK signaling pathway. Notably, the current study for the first time demonstrates that VDR maintains intestinal epithelial barrier integrity via up-regulating DRA expression and the lack of DRA induced by VDR knockdown leads to a more susceptive condition for intestine to DSS-induced colitis.

CONCLUSION

Our study provides evidence and deep comprehension regarding the role of VDR in modulating DRA expression in gut homeostasis and makes novel contributions to better generally understanding the links between VDR, DRA and intestinal epithelial barrier function.

The Calcitriol/Vitamin D Receptor System Regulates Key Immune Signaling Pathways in Chronic Lymphocytic Leukemia

Simple Summary

Calcitriol, the biologically active form of vitamin D, modulates a plethora of cellular processes following its receptor ligation, namely the vitamin D receptor (VDR). Epidemiological studies have linked low blood levels of vitamin D to adverse disease outcome in several B cell malignancies, including chronic lymphocytic leukemia (CLL), for as yet undetermined reasons. In this study, we sought to obtain deeper biological insight into the role of vitamin D in the pathophysiology of CLL. To this end, we investigated whether the calcitriol/VDR system is functional in CLL and analyzed key signaling pathways that are regulated by calcitriol supplementation, while also exploring the role of microenvironmental signals in the regulation of calcitriol/VDR system. Overall, we provide evidence that the calcitriol/VDR system is functional in CLL, regulating signaling pathways critical for cell survival/proliferation. Although microenvironmental triggers can modulate VDR expression and function, calcitriol appears to act independently, alluding to a potential clinical utility of vitamin D supplementation in CLL.

Abstract

It has been proposed that vitamin D may play a role in prevention and treatment of cancer while epidemiological studies have linked vitamin D insufficiency to adverse disease outcomes in various B cell malignancies, including chronic lymphocytic leukemia (CLL). In this study, we sought to obtain deeper biological insight into the role of vitamin D and its receptor (VDR) in the pathophysiology of CLL. To this end, we performed expression analysis of the vitamin D pathway molecules; complemented by RNA-Sequencing analysis in primary CLL cells that were treated in vitro with calcitriol, the biologically active form of vitamin D. In addition, we examined calcitriol effects ex vivo in CLL cells cultured in the presence of microenvironmental signals, namely anti-IgM/CD40L, or co-cultured with the supportive HS-5 cells; and, CLL cells from patients under ibrutinib treatment. Our study reports that the calcitriol/VDR system is functional in CLL regulating signaling pathways critical for cell survival and proliferation, including the TLR and PI3K/AKT pathways. Moreover, calcitriol action is likely independent of the microenvironmental signals in CLL, since it was not significantly affected when combined with anti-IgM/CD40L or in the context of the co-culture system. This finding was also supported by our finding of preserved calcitriol signaling capacity in CLL patients under ibrutinib treatment. Overall, our results indicate a relevant biological role for vitamin D in CLL pathophysiology and allude to the potential clinical utility of vitamin D supplementation in patients with CLL.

Vitamin D and male reproductive system

Vitamin D deficiency is a highly prevalent worldwide condition and affects people of all ages. The most important role of vitamin D is the regulation of intestinal calcium absorption and metabolism of calcium and phosphorus to maintain muscle and bone homeostasis. Furthermore, in recent years it has been discovered that the vitamin D receptor (VDR) is widely distributed in many organs and tissues where vitamin D can perform other actions that include the modulation of the immune response, insulin secretion, anti-proliferative effect on cells of vascular smooth muscle, modulation of the renin-angiotensin-aldosterone system and regulates cell growth in several organs. The VDR is widely distributed in the male reproductive system. Vitamin D induces changes in the spermatozoa's calcium and cholesterol content and in protein phosphorylation to tyrosine/threonine residues. These changes could be involved in sperm capacitation. Vitamin D seems to regulate aromatase expression in different tissues. Studies analyzing seasonal variations of sex steroids in male populations yield conflicting results. This is probably due to the wide heterogeneity of the populations included according to age, systemic diseases and obesity.

Vitamin D as Supplemental Therapy for Pneumocystis Pneumonia

The combination of all-trans retinoic acid (ATRA) and primaquine (PMQ) has been shown to be effective for therapy of Pneumocystis pneumonia (PCP). Since a high concentration of ATRA has significant adverse effects, the possibility that vitamin D can be used to replace ATRA for PCP therapy was investigated. C57BL/6 mice were immunosuppressed by depleting CD4(+) cells and infected with Pneumocystis murina 1 week after initiation of immunosuppression. Three weeks after infection, the mice were treated orally for 3 weeks with vitamin D3 (VitD3) alone, PMQ alone, a combination of VitD3 and PMQ (VitD3-PMQ), or a combination of trimethoprim and sulfamethoxazole (TMP-SMX). Results showed that VitD3 (300 IU/kg/day) had a synergistic effect with PMQ (5 mg/kg/day) for therapy of PCP. Flow cytometric studies showed that this VitD3-PMQ combination recovered the CD11b(low) CD11c(high) alveolar macrophage population in mice with PCP as effectively as TMP-SMX. The VitD3-PMQ combination also reduced the massive infiltration of inflammatory cells into the lungs and the severity of lung damage. VitD3 was also shown to reduce the dose of TMP-SMX required for effective treatment of PCP. Taken together, results of this study suggest that a VitD3-PMQ combination can be used as an alternative therapy for PCP.

Impact of 1, 25-(OH)2D3 on Left Ventricular Hypertrophy in Type 2 Diabetic Rats

OBJECTIVE

To investigate the impact of 1, 25-(OH)2D3 on left ventricular hypertrophy (LVH) in type 2 diabetic rats.

METHODS

Type 2 diabetic mellitus (DM) model rats were established by intraperitoneally injecting with 30 mg/kg streptozotocin. After 8 weeks, 19 male rats were identified as diabetic with left ventricular hypertrophy (LVH) by ultrasound examination, and randomly assigned into three groups: untreated (DM-LVH, n=7), treated with insulin (DM-LVH+INS, n=6), and treated with 1, 25-(OH)2D3 (DM-LVH+VD, n=6). Healthy male rats were used as the controls group (n=6). The fasting blood glucose and the insulin level were determined weekly. The left ventricular mass index, myocardial collagen content, collagen volume fraction, and 1, 25-(OH)2D3-receptor level were determined by 4 weeks later.

RESULTS

In the DM-LVH model group, the insulin level was significantly decreased compared with the non-diabetic control group (P<0.05), whereas the blood glucose, left ventricular mass index, myocardial collagen content, collagen volume fraction, and 1, 25-(OH)2D3-receptor expression were significantly increased (all P<0.05). In the DM-LVH+INS and DM-LVH+VD groups, the insulin levels were significantly increased compared with the DM-LVH model group (P<0.05), whereas the other parameters were significantly decreased (all P<0.05).

CONCLUSION

1, 25-(OH)2D3 could reverse LVH in diabetic rats and that the mechanism may involve stimulating insulin secretion and reducing blood glucose via direct up-regulation of 1, 25-(OH)2D3-receptor expression.

Vitamin D deficiency and severe asthma

Vitamin D has received tremendous amount of attention recently due to the ever-increasing reports of association between vitamin D deficiency and a wide range of conditions, from cancer to fertility to longevity. The fascination of disease association with vitamin D deficiency comes from the relatively easy solution to overcome such a risk factor, that is, either by increase in sun exposure and/or diet supplementation. Many reviews have been written on a protective role of vitamin D in asthma and related morbidities; here, we will summarize the epidemiological evidence supporting a role of vitamin D against hallmark features of severe asthma, such as airway remodeling and asthma exacerbations. Furthermore, we discuss data from in vitro and in vivo studies which provide insights on the potential mechanisms of how vitamin D may protect against severe asthma pathogenesis and how vitamin D deficiency may lead to the development of severe asthma. Approximately 5-15% of asthmatic individuals suffer from the more severe forms of disease in spite of aggressive therapies and they are more likely to have irreversible airflow obstruction associated with airway remodeling. At present drugs commonly used to control asthma symptoms, such as corticosteroids, do not significantly reverse or reduce remodeling in the airways. Hence, if vitamin D plays a protective role against the development of severe asthma, then the most effective therapy may simply be a healthy dose of sunshine.

Defective female reproductive function in 1,25(OH)2D-deficient mice results from indirect effect mediated by extracellular calcium and/or phosphorus

We used mice with targeted deletion of 25-hydroxyvitamin D 1α-hydroxylase [1α(OH)ase(-/-)] to investigate the effects of calcium and phosphorus on defects in the reproductive system of 1,25-dihydroxyvitamin D [1,25(OH)(2)D]-deficient female mice. The 1α(OH)ase(-/-) mice and their wild-type littermates were fed either a normal diet or a rescue diet (high calcium, phosphate, and lactose) starting from weaning until 3 mo of age. We then determined serum calcium and phosphorus levels, assessed gonadotropin and gonadal hormone production, and evaluated folliculogenesis, corpus luteum formation, ovarian angiogenesis, uterus development, and fertility. Results showed that hypocalcemic and hypophosphatemic female 1α(OH)ase(-/-) mice developed infertility accompanied by decreased estrogen and progestogen levels, elevated follicle-stimulating hormone and luteinizing hormone levels, defects in follicular development and corpus luteum formation, uterine hypoplasia, and decreased ovarian expression of angiogenic factors including vascular endothelial growth factor (VEGF), angiopoietin-1 and -2, and Tie-2. When serum calcium and phosphorus were normalized by the rescue diet, the defective reproductive phenotype in the female 1α(OH)ase(-/-) mice, including the dysfunction in the hypothalamic-pituitary-ovarian axis, and ovarian angiogenesis were reversed. These results indicate that the infertility seen in 1,25(OH)(2)D-deficient mice is not a direct effect of active vitamin D deficiency on the reproductive system but is an indirect effect mediated by extracellular calcium and phosphorus.

Structural basis of the histidine-mediated vitamin D receptor agonistic and antagonistic mechanisms of (23S)-25-dehydro-1α-hydroxyvitamin D3-26,23-lactone

TEI-9647 antagonizes vitamin D receptor (VDR) mediated genomic actions of 1α,25(OH)2D3in human cells but is agonistic in rodent cells. The presence of Cys403, Cys410 or of both residues in the C-terminal region of human VDR (hVDR) results in antagonistic action of this compound. In the complexes of TEI-9647 with wild-type hVDR (hVDRwt) and H397F hVDR, TEI-9647 functions as an antagonist and forms a covalent adduct with hVDR according to MALDI–TOF MS. The crystal structures of complexes of TEI-9647 with rat VDR (rVDR), H305F hVDR and H305F/H397F hVDR showed that the agonistic activity of TEI-9647 is caused by a hydrogen-bond interaction with His397 or Phe397 located in helix 11. Both biological activity assays and the crystal structure of H305F hVDR complexed with TEI-9647 showed that the interaction between His305 and TEI-9647 is crucial for antagonist activity. This study indicates the following stepwise mechanism for TEI-9647 antagonism. Firstly, TEI-9647 forms hydrogen bonds to His305, which promote conformational changes in hVDR and draw Cys403 or Cys410 towards the ligand. This is followed by the formation of a 1,4-Michael addition adduct between the thiol (–SH) group of Cys403 or Cys410 and theexo-methylene group of TEI-9647.

Interaction between vitamin D receptor with caveolin-3 and regulation by 1,25-dihydroxyvitamin D3 in adult rat cardiomyocytes

We show that 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) and a synthetic non-genotropic vitamin D analog agonist, 1a,25(OH)2-lumisterol (JN), exhibit similar rapid effects on sarcomere shortening (contraction) of isolated adult cardiomyocyte. We also report that the vitamin D receptor (VDR) specifically interacts with caveolin-3 in the t-tubules and sarcolemma of isolated adult rat cardiac myocytes. Confocal immunofluorescence microscopy analysis showed co-localization of VDR and caveolin-3 in the t-tubules and sarcolemma of cardiomyocytes. Co-immunoprecipitation studies using VDR antibodies revealed that caveolin-3 specifically co-precipitates with the VDR and similarly the VDR is co-precipitated with caveolin-3 antibody. VDR is also in association with Serca-2, the sarcoplasmic reticulum Ca2+-ATPase, as demonstrated by co-immunoprecipitation, suggesting a role of VDR in regulating cardiac contractility by direct interaction with Serca-2. Treatment of isolated adult rat cardiomyocytes with 10 nM 1,25(OH)2D3 for 1 h caused decreased association between VDR and caveolin-3. These discoveries of the association between VDR and caveolin-3 and the regulation of this interaction by 1,25(OH)2D3 are fundamentally important in understanding 1,25(OH)2D3 signal transduction in heart cells and suggest a novel mechanism for VDR in the regulation of heart structure and function.

Activation of rapid signaling pathways does not contribute to 1 alpha,25-dihydroxyvitamin D3-induced growth inhibition of mouse prostate epithelial progenitor cells

The active form of vitamin D, 1 alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D) inhibits the growth of prostate epithelial cells, however the underlying mechanisms have not been clearly delineated. In the current study, the impact of 1,25(OH)(2)D on the rapid activation of extracellular-regulated kinase (ERK) 1/2 and protein kinase C alpha (PKC alpha), and the role of these pathways in growth inhibition was examined in immortalized mouse prostate epithelial cells, MPEC3, that exhibit stem/progenitor cell characteristics. 1,25(OH)(2)D treatment suppressed the growth of MPEC3 in a dose and time dependent manner (e.g., 21% reduction at three days with 100 nM 1,25(OH)(2)D treatment). However, ERK1/2 activity was not altered by 100 nM 1,25(OH)(2)D treatment for time points from 1 min to 1 h in either serum-containing or serum-free medium. Similarly, PKC alpha activation (translocation onto the plasma membrane) was not regulated by short-term treatment of 100 nM 1,25(OH)(2)D. In conclusion, 1,25(OH)(2)D did not mediate rapid activation of ERK1/2 or PKC alpha in MPEC3 and therefore the growth inhibitory effect of 1,25(OH)(2)D is independent of rapid activation of these signaling pathways in this cell type.

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.

Combination treatment with progesterone and vitamin D hormone may be more effective than monotherapy for nervous system injury and disease

More than two decades of pre-clinical research and two recent clinical trials have shown that progesterone (PROG) and its metabolites exert beneficial effects after traumatic brain injury (TBI) through a number of metabolic and physiological pathways that can reduce damage in many different tissues and organ systems. Emerging data on 1,25-dihydroxyvitamin D(3) (VDH), itself a steroid hormone, have begun to provide evidence that, like PROG, it too is neuroprotective, although some of its actions may involve different pathways. Both agents have high safety profiles, act on many different injury and pathological mechanisms, and are clinically relevant, easy to administer, and inexpensive. Furthermore, vitamin D deficiency is prevalent in a large segment of the population, especially the elderly and institutionalized, and can significantly affect recovery after CNS injury. The combination of PROG and VDH in pre-clinical and clinical studies is a novel and compelling approach to TBI treatment.

The vitamin D sterol-vitamin D receptor ensemble model offers unique insights into both genomic and rapid-response signaling

Steroid hormones serve as chemical messengers in a wide number of species and target tissues by transmitting signals that result in both genomic and nongenomic responses. Genomic responses are mediated by the formation of a ligand-receptor complex with its cognate steroid hormone nuclear receptor (NR). Nongenomic responses can be mediated at the plasma membrane by a membrane-localized NR. The focus of this Review is on the structural attributes and molecular mechanisms underlying vitamin D sterol (VDS)-vitamin D receptor (VDR) selective and stereospecific regulation of nongenomic and genomic signaling. The VDS-VDR conformational ensemble model describes how VDSs can selectively initiate or block either nongenomic or genomic biological responses by interacting with two VDR ligand-binding pockets, one kinetically favored by 1alpha,25(OH)(2)D(3) (1,25D) and the other thermodynamically favored. We describe the variables that affect the three major elements of the model: the conformational flexibility of the unliganded (apo) protein, the flexibility of the VDS, and the physicochemical selectivity of the VDR genomic pocket (VDR-GP) and alternative pocket (VDR-AP). We also discuss how these three factors collectively provide a rational explanation for the complexities of VDS regulation of cell biology and highlight the current limitations of the model.

1,25-dihydroxyvitamin D(3) rapidly stimulates the solvent drag-induced paracellular calcium transport in the duodenum of female rats

A calcium-regulating hormone 1alpha,25-dihydroxyvitamin D(3) (1,25-[OH](2)D(3)) has been known to rapidly stimulate the transcellular active calcium transport in the chick duodenum. However, its effects on the solvent drag-induced paracellular calcium transport, which normally contributes approximately 70% of the total active calcium transport, and the underlying mechanism were unknown. The present study aimed to investigate the rapid nongenomic actions of physiological concentrations of 1,25-(OH)(2)D(3), i.e., 1, 10, and 100 nmol/l, on the duodenal calcium absorption in female rats. Quantitative real-time PCR revealed strong expressions of the classical vitamin D receptor (VDR) and the membrane-associated rapid response steroid binding receptors (MARRS) in both small and large intestines. By using the Ussing chamber technique, we found that duodenal epithelia acutely exposed to 10 and 100 nmol/l 1,25-(OH)(2)D(3) rapidly increased the solvent drag-induced calcium transport, but not the transcellular calcium transport, in a dose-response manner. On the other hand, 3-day daily injections of 1,25-(OH)(2)D(3) enhanced the transcellular active duodenal calcium transport. The 1,25-(OH)(2)D(3)-stimulated solvent drag-induced transport was abolished by the phosphatidylinositol 3-kinase (PI3K) inhibitors, 200 nmol/l wortmannin and 75 micromol/l LY294002, as well as PKC (1 micromol/l GF109203X) and MEK inhibitors (10 micromol/l U0126). Although 100 nmol/l 1,25-(OH)(2)D(3) did not alter the transepithelial mannitol flux, indicating no widening of the tight junction, it decreased the transepithelial resistance and increased both sodium and chloride permeability through the paracellular channel. We conclude that 1,25-(OH)(2)D(3) uses the nongenomic signaling pathways involving PI3K, PKC, and MEK to rapidly enhance the solvent drag-induced calcium transport, partly by altering the charge-selective property of the duodenal epithelium at least for the pathways involving PI3K and MEK.

Vitamin D, the renin-angiotensin system, and insulin resistance

Insulin resistance is characterized by the systemic impairment of insulin action and is usually the result of aging, obesity, chronic inflammation, or another factor that may contribute to the inhibition of the insulin signaling pathway. Insulin resistance is accompanied by defects in lipid metabolism and blood coagulation, hypertension, obesity, and vascular inflammation in a syndrome called syndrome X or metabolic syndrome. Metabolic syndrome is involved in the development of atherosclerosis with consequent cardiovascular complications including acute myocardial infarction, stroke, and vascular disease. Recent data have shown that vitamin D acts as a negative regulator of the renin gene and that vitamin D deficiency is followed by increased renin-angiotensin II expression. The link between the insulin signaling pathway/insulin resistance and the renin-angiotensin system has been well documented in previous studies. The present review focuses on disorders characterized by a reduction in vitamin D concentration or its receptor function and the development of insulin resistance or metabolic syndrome, and discusses also possible therapeutic interventions.

Vitamin D receptor levels and binding are reduced in aged rat intestinal subcellular fractions

The hormonal form of vitamin D, 1alpha,25(OH)(2)-vitaminD(3) [1alpha,25(OH)(2)D(3)], stimulates signal transduction pathways in intestinal cells. To gain insight into the relative importance of the vitamin D receptor (VDR) in the rapid hormone responses, the amounts and localization of the VDR were evaluated in young (3 months) and aged (24 months) rat intestinal cells. Immune-fluorescence and Western blot studies showed that VDR levels are diminished in aged enterocytes. Confocal microscopy assays revealed that the VDR and other immune-reactive proteins have mitochondrial, membrane, cytosol and perinuclear localization. Western blot analysis using specific antibodies detected the 60 and 50 kDa bands expected for the VDR in the cytosol and microsomes and, to a lesser extent, in the nucleus and mitochondria. Low molecular weight immune-reactive proteins were also detected in young enterocytes subcellular fractions. Since changes in hormone receptor levels appear to constitute a common manifestation of the ageing process, we also analyzed 1alpha,25(OH)(2)D(3) binding properties and VDR levels in subcellular fractions from young and aged rats. In competition binding assays, employing [(3)H]-1alpha,25(OH)(2)D(3) and 1alpha,25(OH)(2)D(3), we have detected specific binding in all subcellular fractions, with maximum binding in mitochondrial and nuclear fractions. Both, VDR protein levels and 1alpha,25(OH)(2)D(3) binding, were diminished with ageing. Age-related declines in VDR may have important consequences for correct receptor/effector coupling in the duodenal tissues and may explain age-related declines in the hormonal regulation of signal transduction pathways that we previously reported.

The bioactive lipid sphingosylphosphorylcholine induces differentiation of mouse embryonic stem cells and human promyelocytic leukaemia cells

Sphingosylphosphorylcholine (SPC) is the major component of high-density lipoproteins (HDL) in blood plasma. The bioactive lipid acts mainly via G protein coupled receptors (GPCRs). Similar to ligands of other GPCRs, SPC has multiple biological roles including the regulation of proliferation, migration, angiogenesis, wound healing and heart rate. Lysophospholipids and their receptors have also been implicated in cell differentiation. A potential role of SPC in stem cell or tumour cell differentiation has been elusive so far. Here we examined the effect of SPC on the differentiation of mouse embryonic stem (ES) cells and of human NB4 promyelocytic leukemia cells, a well established tumour differentiation model. Our data show that mouse embryonic stem cells and NB4 cells express the relevant GPCRs for SPC. We demonstrate both at the level of morphology and of gene expression that SPC induces neuronal and cardiac differentiation of mouse ES cells. Furthermore, SPC induces differentiation of NB4 cells by a mechanism which is critically dependent on the activity of the MEK-ERK cascade. Thus, the bioactive lipid SPC is a novel differentiation inducing agent both for mouse ES cells, but also of certain human tumour cells.

Raf-1 signaling is required for the later stages of 1,25-dihydroxyvitamin D3-induced differentiation of HL60 cells but is not mediated by the MEK/ERK module

We are interested in determining the signaling pathways for 1,25-dihydroxyvitamin D3 (1,25D)-induced differentiation of HL60 leukemic cells. One possible candidate is Raf-1, which is known to signal cell proliferation and neoplastic transformation through MEK, ERK, and downstream targets. It can also participate in the regulation of cell survival and various forms of cell differentiation, though the precise pathways are less well delineated. Here we report that Raf-1 has a role in monocytic differentiation of human myeloid leukemia HL60, which is not mediated by MEK and ERK, but likely by direct interaction with p90RSK. Specifically, we show that Raf-1 and p90RSK are increasingly activated in the later stages of differentiation of HL60 cells, at the same time as activation of MEK and ERK is decreasing. Transfection of a wild-type Raf-1 construct enhances 1,25D-induced differentiation, while antisense Raf-1 or short interfering (si) Raf-1 reduces 1,25D-induced differentiation. In contrast, antisense oligodeoxynucleotides (ODN) and siRNAs to MEK or ERK have no detectable effect on differentiation. In late stage differentiating cells Raf-1 and p90RSK are found as a complex, and inhibition of Raf-1, but not MEK or ERK expression reduces the levels of phosphorylated p90 RSK. These findings support the thesis that Raf-1 signals cell proliferation and cell differentiation through different intermediary proteins.

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.

The requirement for and changing composition of the activating protein-1 transcription factor during differentiation of human leukemia HL60 cells induced by 1,25-dihydroxyvitamin D3

The activating protein-1 (AP-1) transcription factor complex is a heterogeneous entity, composed in mammalian cells of dimers chosen from a group of at least eight proteins belonging to three families: jun, fos, and activating transcription factor (ATF). The AP-1 complexes participate in diverse biological processes that include cell proliferation, survival, and differentiation. These seemingly contrasting functions have been attributed to the intensity and duration of the signals provided by AP-1, but the biological consequences of changing composition of the AP-1 complex have not been fully explored. Here, we show that functional AP-1 is required for 1,25-dihydroxyvitamin D3 (1,25D)-induced monocytic differentiation, and that the composition of the AP-1 protein complex that binds TRE, its cognate DNA element, changes as cells differentiate. In HL60 cells in an early stage of differentiation, the principal AP-1 components detected by gel shift analysis include c-jun, ATF-2, fos-B, fra-1, and fra-2. In cells with a more established monocytic phenotype, the demonstrable AP-1 components are c-jun, ATF-2, jun-B, and fos-B. Following the addition of 1 nmol/L of 1,25D, the cellular content of each of these four proteins markedly increased in a sustained manner, whereas the increases in c-fos, fra-1, fra-2, and jun-D were minimal, if any. Small increases in mRNA levels encoding all AP-1 component proteins, except c-fos, were also noted. These findings provide a basis for the previously found participation of the c-Jun N-terminal kinase pathway in 1,25D-induced differentiation of myeloid leukemia cells, and direct attention to jun-B and fos-B as new cellular therapeutic targets, that may promote replicative quiescence associated with differentiation of malignant cells.

Induction of kinase suppressor of RAS-1(KSR-1) gene by 1, alpha25-dihydroxyvitamin D3 in human leukemia HL60 cells through a vitamin D response element in the 5'-flanking region

Differentiation therapy is being developed as an additional therapeutic option for the treatment of several forms of cancer, including myeloid leukemia. In model systems, the physiologically active form of vitamin D, 1, alpha25-dihydroxyvitamin D3 (1,25D), induces monocytic differentiation of human myeloid cells, but the mechanism is not clear. We report here, the first direct connection between the signal provided by 1,25D and the molecular circuitry known to be involved in monocytic differentiation. Specifically, we show that 1,25D selectively increases the expression of the gene encoding kinase suppressor of Ras-1 (KSR-1) in HL60 cells, while other differentiation-inducing agents such as 12-O-tetradecanoylphorbol-13-acetate, retinoic acid or dimethyl sulfoxide do not significantly increase KSR-1 expression. Further, the upregulation of KSR-1 gene by 1,25D is competed by ZK159222, an antagonist of vitamin D receptor (VDR) action, and can occur in the presence of protein synthesis inhibitor cycloheximide, showing that the effect is direct. Most importantly, we have identified a vitamin D responsive element (VDRE) in the promoter region of the human KSR-1 gene, to which VDR binds in a 1,25D-dependent manner, in vitro and in vivo. This binding is paralleled by increased association of RNA polymerase II with the transcription start site of KSR-1 gene, and the VDRE is functional in reporter assays. Our findings offer a potential mechanism for a signaling pathway that contributes to 1,25D-induced monocytic differentiation of human myeloid leukemia cells.

1α,25(OH)2-Vitamin D3 stimulates intestinal cell p38 MAPK activity and increases c-Fos expression

In intestinal cells, as in other target cells, the steroid hormone 1alpha,25(OH)(2)-Vitamin D(3) (1alpha,25(OH)(2)D(3)) regulates gene expression via the specific intracellular Vitamin D receptor and induces fast non-transcriptional responses involving stimulation of transmembrane signal transduction pathways. We have previously shown that the hormone activates the extracellular signal-regulated mitogen-activated protein (MAP) kinase isoforms ERK1 and ERK2 in rat intestinal cells. In the present study, we have demonstrated that 1alpha,25(OH)(2)D(3) also induces the phosphorylation and activation of p38 MAPK in these cells. The hormone effects were time and dose-dependent, with maximal stimulation at 2min (+3-fold) and 1nM. 1alpha,25(OH)(2)D(3)-dependent p38 phosphorylation was suppressed by SB 203580, a selective inhibitor of p38 MAPK. Ca(2+) chelation with EGTA, inhibition of the c-Src-tyrosine kinase family with PP1 or protein kinase A (PKA) with Rp-cAMP, attenuated hormone activation of p38 MAPK. The physiological significance of 1alpha,25(OH)(2)D(3)-dependent activation of ERK1/2 and p38 MAP kinases was addressed by monitoring c-Fos expression. Incubation of intestinal cells with the hormone was followed by a rapid induction of c-Fos expression which was blocked by SB 203580 and partially suppressed by the ERK1/2 inhibitor PD 98059. Our results suggest that 1alpha,25(OH)(2)D(3) activates p38 MAPK, involving Ca(2+), c-Src and PKA as upstream regulators, and that p38 MAPK has a central role in hormone-induction of the oncoprotein c-Fos in rat intestinal cells.

Vitamin D

The vitamin D endocrine system plays an essential role in calcium homeostasis and bone metabolism, but research during the past two decades has revealed a diverse range of biological actions that include induction of cell differentiation, inhibition of cell growth, immunomodulation, and control of other hormonal systems. Vitamin D itself is a prohormone that is metabolically converted to the active metabolite, 1,25-dihydroxyvitamin D [1,25(OH)(2)D]. This vitamin D hormone activates its cellular receptor (vitamin D receptor or VDR), which alters the transcription rates of target genes responsible for the biological responses. This review focuses on several recent developments that extend our understanding of the complexities of vitamin D metabolism and actions: the final step in the activation of vitamin D, conversion of 25-hydroxyvitamin D to 1,25(OH)(2)D in renal proximal tubules, is now known to involve facilitated uptake and intracellular delivery of the precursor to 1alpha-hydroxylase. Emerging evidence using mice lacking the VDR and/or 1alpha-hydroxylase indicates both 1,25(OH)(2)D(3)-dependent and -independent actions of the VDR as well as VDR-dependent and -independent actions of 1,25(OH)(2)D(3). Thus the vitamin D system may involve more than a single receptor and ligand. The presence of 1alpha-hydroxylase in many target cells indicates autocrine/paracrine functions for 1,25(OH)(2)D(3) in the control of cell proliferation and differentiation. This local production of 1,25(OH)(2)D(3) is dependent on circulating precursor levels, providing a potential explanation for the association of vitamin D deficiency with various cancers and autoimmune diseases.

Nongenotropic, Anti-Apoptotic Signaling of 1α,25(OH)2-Vitamin D3 and Analogs through the Ligand Binding Domain of the Vitamin D Receptor in Osteoblasts and Osteocytes

Because sex steroids regulate the life span of bone cells by modulating cytoplasmic kinase activity via a nongenotropic action of their classical receptors, we have explored the possibility that the vitamin D nuclear receptor (VDR) might exhibit similar nongenotropic actions. We report that the conformationally flexible full VDR agonist, 1alpha,25(OH)2-vitamin D3 (1alpha,25(OH)2D3), and the 6-s-cis-locked 1alpha,25(OH)2-lumisterol3 (JN) analog, also acting through the VDR but with poor transcriptional activity, protected murine osteoblastic or osteocytic cells from apoptosis. This effect was reproduced in HeLa cells transiently transfected with either wild type VDR or a mutant consisting of only the VDR ligand binding domain. The VDR ligand binding domain bound [3H]1alpha,25(OH)2D3 as effectively as wild type VDR but did not induce vitamin D response element-mediated transcription. The anti-apoptotic effects of 1alpha,25(OH)2D3 and the 6-s-cis-locked 1alpha,25(OH)2-lumisterol3 analog in calvaria cells were blocked by three cytoplasmic kinase inhibitors: Src kinase inhibitor 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1), phosphatidylinositol 3 kinase inhibitor Wortmannin, and the JNK kinase inhibitor SP600125. However, inhibition of p38 with SB203580 or ERK with either U0126 or a transfected dominant negative MEK did not interfere with these anti-apoptotic actions. Further, 1alpha,25(OH)2D3 induced rapid (5 min) association of VDR with Src kinase in OB-6 cells. Finally, actinomycin D or cycloheximide prevented the anti-apoptotic effect of 1alpha,25(OH)2D3, indicating that transcriptional events are also required. These findings suggest that nongenotropic modulation of kinase activity is also a general property of the VDR and that ligands that activate nongenotropic signals, but lack transcriptional activity, display different biological profiles from the steroid hormone 1alpha,25(OH)2D3.

Molecular mechanism of the vitamin D antagonistic actions of (23S)-25-dehydro-1alpha-hydroxyvitamin D3-26,23-lactone depends on the primary structure of the carboxyl-terminal region of the vitamin d receptor

We reported that (23S)-25-dehydro-1alpha-hydroxyvitamin D(3)-26,23-lactone (TEI-9647) antagonizes vitamin D receptor (VDR)-mediated genomic actions of 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] in human cells but is agonistic in rodent cells. Human and rat VDR ligand-binding domains are similar, but differences in the C-terminal region are important for ligand binding and transactivation and might determine the agonistic/antagonistic effects of TEI-9647. We tested TEI-9647 on 1alpha,25(OH)(2)D(3) transactivation using SaOS-2 cells (human osteosarcoma) or ROS 24/1 cells (rat osteosarcoma) cotransfected with human or rodent VDR and a reporter. In both cell lines, TEI-9647 was antagonistic with wild-type human (h)VDR, but agonistic with overexpressed wild-type rat (r)VDR. VDR chimeras substituting the hVDR C-terminal region (activation function 2 domain) with corresponding rVDR residues diminished antagonism and increased agonism of TEI-9647. However, substitution of 25 C-terminal rVDR residues with corresponding hVDR residues diminished agonism and increased antagonism of TEI-9647. hVDR mutants (C403S, C410N) demonstrated that Cys403 and/or 410 was necessary for TEI-9647 antagonism of 1alpha,25(OH)(2)D(3) transactivation. These results suggest that species specificity of VDR, especially in the C-terminal region, determines the agonistic/antagonistic effects of TEI-9647 that determine, in part, VDR interactions with coactivators and emphasize the critical interaction between TEI-9647 and the two C-terminal hVDR Cys residues to mediate the antagonistic effect of TEI-9647.

1?,25-dihydroxyvitamin D3 stimulates steroid sulphatase activity in HL60 and NB4 acute myeloid leukaemia cell lines by different receptor-mediated mechanisms

Steroid sulphatase is a key enzyme in the biosynthesis of bioactive estrogens and androgens from highly abundant inactive circulating sulphated steroid precursors. Little is known about how the expression/activity of this enzyme is regulated. In this article, we show that of 1alpha,25(OH)2D3 stimulates an increase steroid sulphatase activity in the HL60 myeloid leukaemic cell line that is inhibited by a specific nuclear VDR (VDRnuc) antagonist and unaffected by plasma membrane-associated vitamin D receptor (VDRmem) agonists and antagonists. 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in HL60 cells was augmented by RXR agonists, blocked by RXR-specific antagonists, and RAR specific agonists and antagonists had no effect. In contrast, the 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in the NB4 myeloid leukaemic cell line was unaffected by the specific VDRnuc and RXR antagonists, but was blocked by a VDRmem-specific antagonist and was increased by VDRmem-specific agonists. The findings reveal that VDRnuc-RXR-heterodimers play a key role in the 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in HL60 cells. However, in NB4 cells, VDRnuc-derived signals do not play an obligatory role, and non-genomic VDRmem-derived signals are important.

The functional consequences of cross-talk between the vitamin D receptor and ERK signaling pathways are cell-specific

The actions of the active metabolite of 1,25-(OH)2D3 (1,25-D) are mediated primarily by the vitamin D receptor (VDR), a member of the nuclear receptor family of ligand-activated transcription factors. Although their ligands cause transcriptional activation, many of the ligands also rapidly activate cellular signaling pathways through mechanisms that have not been fully elucidated. We find that 1,25-D causes a rapid, but sustained activation of ERK (extracellular signal-regulated kinase) in bone cell lines. However, the effect of ERK activation on VDR transcriptional activity was cell line-specific. Inhibition of ERK activation by the MEK inhibitor, U0126, stimulated VDR activity in MC3T3-E1 cells, but inhibited the activity in MG-63 cells as well as in HeLa cells. VDR is not a known target of ERK. We found that the ERK target responsible for reduced VDR activity in MC3T3-E1 cells is RXRalpha. MC3T3-E1 cells express lower levels of RXRbeta and RXRgamma than either HeLa or MG-63 cells. Although overexpression of RXRalpha in MC3T3-E1 cells increased VDR activity, U0126 further enhanced the activity. In contrast, overexpression of RXRgamma stimulated VDR activity but abrogated the stimulation by U0126. Thus, although 1,25-D treatment activates ERK in many cell types, subsequently inducing changes independent of VDR, the effects of treatment with 1,25-D on the transcriptional activity of VDR are RXR isoform-specific. In cells in which RXRalpha is the VDR partner, the transcriptional activation of VDR by 1,25-D is attenuated by the concomitant activation of ERK. In cells utilizing RXRgamma, ERK activation enhances VDR transcriptional activity.

Identification of an alternative ligand-binding pocket in the nuclear vitamin D receptor and its functional importance in 1alpha,25(OH)2-vitamin D3 signaling

Structural and molecular studies have shown that the vitamin D receptor (VDR) mediates 1alpha,25(OH)2-vitamin D3 gene transactivation. Recent evidence indicates that both VDR and the estrogen receptor are localized to plasma membrane caveolae and are required for initiation of nongenomic (NG) responses. Computer docking of the NG-specific 1alpha,25(OH)2-lumisterol to the VDR resulted in identification of an alternative ligand-binding pocket that partially overlaps the genomic pocket described in the experimentally determined x-ray structure. Data obtained from docking five different vitamin D sterols in the genomic and alternative pockets were used to generate a receptor conformational ensemble model, providing an explanation for how VDR and possibly the estrogen receptor can have genomic and NG functionality. The VDR model is compatible with the following: (i) NG chloride channel agonism and antagonism; (ii) variable ligand-stabilized trypsin digest banding patterns; and (iii) differential transcriptional activity, employing different VDR point mutants and 1alpha,25(OH)2-vitamin D3 analogs.

The vitamin D receptor is present in caveolae-enriched plasma membranes and binds 1 alpha,25(OH)2-vitamin D3 in vivo and in vitro

The steroid hormone 1 alpha,25(OH)(2)-vitamin D(3) (1,25D) regulates gene transcription through a nuclear receptor [vitamin D receptor (VDR)] and initiation of rapid cellular responses through a putative plasma membrane-associated receptor (VDR(mem)). This study characterized the VDR(mem) present in a caveolae-enriched membrane fraction (CMF), a site of accumulation of signal transduction agents. Saturable and specific [(3)H]-1,25D binding in vitro was found in CMF of chick, rat, and mouse intestine; mouse lung and kidney; and human NB4 leukemia and rat ROS 17/2.8 osteoblast-like cells; in all cases the 1,25D K(D) binding dissociation constant = 1-3 nM. Our data collectively support the classical VDR being the VDR(mem) in caveolae: 1) VDR antibody immunoreactivity was detected in CMF of all tissues tested; 2) competitive binding of [(3)H]-1,25D by eight analogs of 1,25D was significantly correlated between nuclei and CMF (r(2) = 0.95) but not between vitamin D binding protein (has a different ligand binding specificity) and CMF; 3) confocal immunofluorescence microscopy of ROS 17/2.8 cells showed VDR in close association with the caveolae marker protein, caveolin-1, in the plasma membrane region; 4) in vivo 1,25D pretreatment reduced in vitro [(3)H]-1,25D binding by 30% in chick and rat intestinal CMF demonstrating in vivo occupancy of the CMF receptor by 1,25D; and 5) comparison of [(3)H]-1,25D binding in VDR KO and WT mouse kidney tissue showed 85% reduction in VDR KO CMF and 95% reduction in VDR KO nuclear fraction. This study supports the presence of VDR as the 1,25D-binding protein associated with plasma membrane caveolae.

Kinase suppressor of RAS (KSR) amplifies the differentiation signal provided by low concentrations 1,25-dihydroxyvitamin D3

The activity of kinase suppressor of ras (KSR), a kinase or a molecular scaffold upstream from Raf-1, is involved in the MEK/ERK MAP kinase cascade which can signal cell growth, survival, or differentiation, depending on the cellular context. We provide evidence here that KSR is upregulated in HL60 cells undergoing differentiation induced by low (0.3-3 nM) concentrations of 1,25-dihydroxyvitamin D(3) (1,25D(3)), and an antisense oligo (AS), but not a sense oligo, to KSR inhibits this differentiation. The inhibition of differentiation by AS-KSR oligo was less apparent when the concentration of 1,25D(3) was increased, suggesting that at the higher concentrations of 1,25D(3) KSR is not essential for the signaling of the differentiated phenotype. The reduced differentiation of HL60 cells exposed to AS-KSR was paralleled by reduced phosphorylation of Raf-1 Ser 259, and of p90RSK, used here as read-out for MAPK cascade activity. Conversely, ectopic expression of Flag-tagged wild type KSR potentiated the differentiation-inducing effects of low concentrations of 1,25D(3). Additional data suggest that the kinase activity of KSR is required for these effects, as transfection of a kinase inactive KSR construct did not significantly increase the 1,25D(3)-induced differentiation. Enzyme assays performed with KSR immunoprecipitated from 1,25D(3)-treated cells showed kinase activity when recombinant Raf-1 was used as the substrate, but not when the 1,25D(3)-treated cells were pretreated with AS-KSR oligos. Taken together, these data suggest that KSR participates in signaling of monocytic differentiation by augmenting the strength of the signal transmitted through Raf-1 to downstream targets.

Rapid modulation of osteoblast ion channel responses by 1alpha,25(OH)2-vitamin D3 requires the presence of a functional vitamin D nuclear receptor

1alpha,25(OH)(2)-Vitamin D(3) (1,25D) modulates osteoblast gene expression of bone matrix proteins via a nuclear vitamin D receptor (VDR) and also modifies the electrical state of the plasma membrane through rapid nongenomic mechanisms still not fully understood. The physiological significance of 1,25D membrane-initiated effects remains unclear. To elucidate whether the VDR is required for 1,25D-promoted electrical responses, we studied 1,25D modulation of ion channel activities in calvarial osteoblasts isolated from VDR knockout (KO) and WT mice. At depolarizing potentials, Cl(-) currents were significantly potentiated (13.5 +/- 1.6-fold increase, n = 12) by 5 nM 1,25D in VDR WT but not in KO (0.96 +/- 0.3 fold increase, n = 11) osteoblasts. L-type Ca(2+) currents significantly shift their peak activation by -9.3 +/- 0.7 mV (n = 10) in the presence of 5 nM 1,25D in VDR WT but not in KO cells, thus facilitating Ca(2+) influx. Furthermore, we found that 1,25D significantly increased whole-cell capacitance in VDR WT (DeltaCap = 2.3 +/- 0.4 pF, n = 8) but not in KO osteoblasts (DeltaCap = 0.3 +/- 0.1 pF, n = 8); this corresponds to a rapid (1-2 min) fusion in WT of 71 +/- 33 versus in KO only 9 +/- 6 individual secretory granules. We conclude that, in calvarial osteoblasts, 1,25D modulates ion channel activities only in cells with a functional VDR and that this effect is coupled to exocytosis. This is a demonstration of the requirement of a functional classic steroid receptor for the rapid hormonal modulation of electric currents linked to secretory activities in a target cell.

Inhibition of serum-stimulated mitogen activated protein kinase by 1?,25(OH)2-vitamin D3 in MCF-7 breast cancer cells

1alpha,25-Dihydroxyvitamin D3 [1alpha,25(OH)2D3], the hormonally active form of vitamin D3, has been shown to be a potent negative growth regulator of breast cancer cells both in vitro and in vivo. 1alpha,25(OH)2D3 acts through two different mechanisms. In addition to regulating gene transcription via its specific intracellular receptor (vitamin D receptor, VDR), 1alpha,25(OH)2D3 induces rapid, non-transcriptional responses involving activation of transmembrane signal transduction pathways, like growth factors and peptide hormones. The mechanisms that mediate the antiproliferative effects of 1alpha,25(OH)2D3 in breast cancer cells are not fully understood. Particularly, there is no information about the early non-genomic signal transduction effectors modulated by the hormone. The present study shows that 1alpha,25(OH)2D3 rapidly inhibits serum induced activation of ERK-1 and ERK-2 MAP kinases. The tyrosine kinase Src is involved in the pathway leading to activation of ERK 1/2 by serum. Furthermore, 1alpha,25(OH)2D3 increases the tyrosine-phosphorylated state of Src and inhibits its kinase activity, while induces the association of the VDR with Src, either in the presence or absence of serum. In parallel, the hormone rapidly increases the amounts of VDR associated to plasma membranes (PM). Pretreatment with the tyrosine phosphatase inhibitors orthovanadate or bpV (phen) prevented mitogen-activated protein kinase (MAPK) inhibition by 1alpha,25(OH)2D3. These data altogether suggest that 1alpha,25(OH)2D3 inhibits the MAPK cascade by inactivating Src tyrosine kinase through a mechanism mediated by the VDR and tyrosine phosphatases.

The rapid effects of 1,25-dihydroxyvitamin D3 require the vitamin D receptor and influence 24-hydroxylase activity: studies in human skin fibroblasts bearing vitamin D receptor mutations

If both rapid and genomic pathways may co-exist in the same cell, the involvement of the nuclear vitamin D receptor (VDR) in the rapid effects of 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) remains unclear. We therefore studied rapid and long term effects of 1,25-(OH)(2)D(3) in cultured skin fibroblasts from three patients with severe vitamin D-resistant rickets and one age-matched control. Patients bear homozygous missense VDR mutations that abolished either VDR binding to DNA (patient 1, mutation K45E) or its stable ligand binding (patients 2 and 3, mutation W286R). In patient 1 cells, 1,25-(OH)(2)D(3) (1 pm-10 nm) had no effect on either intracellular calcium or 24-hydroxylase (enzyme activity and mRNA expression). In contrast, cells bearing the W286R mutation had calcium responses to 1,25-(OH)(2)D(3) (profile and magnitude) and 24-hydroxylase responses to low (1 pm-100 pm) 1,25-(OH)(2)D(3) concentrations (activity, CYP24, and ferredoxin mRNAs) similar to those of controls. The blocker of Ca(2+) channels, verapamil, impeded both rapid (calcium) and long term (24-hydroxylase activity, CYP24, and ferredoxin mRNAs) responses in patient and control fibroblasts. The MEK 1/2 kinase inhibitor PD98059 also blocked the CYP24 mRNA response. Taken together, these results suggest that 1,25-(OH)(2)D(3) rapid effects require the presence of VDR and control, in part, the first step of 1,25-(OH)(2)D(3) catabolism via increased mRNA expression of the CYP24 and ferredoxin genes in the 24-hydroxylase complex.

Nongenomic steroid action: controversies, questions, and answers

Steroids may exert their action in living cells by several ways: 1). the well-known genomic pathway, involving hormone binding to cytosolic (classic) receptors and subsequent modulation of gene expression followed by protein synthesis. 2). Alternatively, pathways are operating that do not act on the genome, therefore indicating nongenomic action. Although it is comparatively easy to confirm the nongenomic nature of a particular phenomenon observed, e.g., by using inhibitors of transcription or translation, considerable controversy exists about the identity of receptors that mediate these responses. Many different approaches have been employed to answer this question, including pharmacology, knock-out animals, and numerous biochemical studies. Evidence is presented for and against both the participation of classic receptors, or proteins closely related to them, as well as for the involvement of yet poorly understood, novel membrane steroid receptors. In addition, clinical implications for a wide array of nongenomic steroid actions are outlined.

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.

1alpha,25-dihydroxyvitamin D(3) and 24R,25-dihydroxyvitamin D(3) modulate growth plate chondrocyte physiology via protein kinase C-dependent phosphorylation of extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase

Membrane-mediated increases in protein kinase C (PKC) activity and PKC-dependent physiological responses of growth plate chondrocytes to vitamin D metabolites depend on the state of endochondral maturation; 1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)] regulates growth zone (GC) cells, whereas 24R,25-(OH)(2)D(3) regulates resting zone (RC) cells. Different mechanisms, including protein kinase A signaling, mediate the effects of 1alpha,25-(OH)(2)D(3) and 24R,25-(OH)(2)D(3) on PKC, suggesting that different mechanisms may also regulate any MAPK involvement in the physiological responses. This study used confluent cultures of rat costochondral chondrocytes as a model. 1alpha,25-(OH)(2)D(3) stimulated MAPK specific activity in GC in a time- and dose-dependent manner, evident within 9 min. 24R,25-(OH)(2)D(3) stimulated MAPK in RC; increases were dose dependent, occurred after 9 min, and were greatest at 90 min. In both cells the effect was due to ERK1/2 activation (p42 > p44 in GC; p42 = p44 in RC). MAPK activation was dependent on PKC, but not protein kinase A. The effect of 1alpha,25-(OH)(2)D(3) required phospholipase C, and the effect of 24R,25-(OH)(2)D(3) required phospholipase D. Inhibition of cyclooxygenase activity reduced the effect of 1alpha,25-(OH)(2)D(3) on MAPK in GC and enhanced the effect of 24R,25-(OH)(2)D(3) in RC. Based on MAPK inhibition with PD98059, ERK1/2 MAPK mediated the effect of 24R,25-(OH)(2)D(3) on [(3)H]thymidine incorporation and [(35)S]sulfate incorporation by RC, but only partially mediated the effect of 1alpha,25-(OH)(2)D(3) on GC. ERK1/2 was not involved in the regulation of alkaline phosphatase specific activity by either metabolite. This paper supports the hypothesis that 1alpha,25-(OH)(2)D(3) regulates the physiology of GC via rapid membrane-mediated signaling pathways, and some, but not all, of the response to 1alpha,25-(OH)(2)D(3) is via the ERK family of MAPKs. In contrast, 24R,25-(OH)(2)D(3) exerts its effects on RC via PKC-dependent MAPK. Whereas 1alpha,25-(OH)(2)D(3) increases MAPK activity via phospholipase C and increased prostaglandin production, 24R,25-(OH)(2)D(3) increases MAPK via phospholipase D and decreased prostaglandin production. The cell specificity, metabolite stereospecificity, and the dependence on PKC argue for the participation of membrane receptors for 1alpha,25-(OH)(2)D(3) and 24R,25-(OH)(2)D(3) in the regulation of ERK1/2 in the growth plate.

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.

1,25-dihydroxyvitamin D3 stimulates vascular endothelial growth factor release in aortic smooth muscle cells: role of p38 mitogen-activated protein kinase

Vitamin D3 plays an important role in the regulation of mineral homeostasis, cell differentiation, and proliferation. However, the exact role of vitamin D3 in vascular smooth muscle cells remains unclear. In the present study, we investigated whether vitamin D3 induces vascular endothelial growth factor (VEGF) release in aortic smooth muscle A10 cells. 1,25-Dihydroxyvitamin D3 (1,25(OH)2VD3), an active form of vitamin D3, stimulated the VEGF release while 24,25-dihydroxyvitamin D3 (24,25(OH)2VD3), an inactive form of vitamin D3, had little effect on the release. The stimulatory effect of 1,25(OH)2VD3 was dose dependent in the range between 10 pM and 10 nM. 1,25(OH)2VD3 induced the phosphorylation of p38 mitogen-activated protein (MAP) kinase but 24,25(OH)2VD3 did not. PD169316 and SB203580, specific inhibitors of p38 MAP kinase, significantly reduced the 1,25(OH)2VD3-stimulated release of VEGF. On the contrary, SB202474, a negative control for p38 MAP kinase inhibitor, had little effect on the VEGF release. PD169316 attenuated the 1,25(OH)2VD3-induced phosphorylation of p38 MAP kinase. These results strongly suggest that 1,25(OH)2VD3 stimulates the release of VEGF in aortic smooth muscle cells via p38 MAP kinase activation.

The vitamin D receptor mediates rapid changes in muscle protein tyrosine phosphorylation induced by 1,25(OH)(2)D(3)

It has been recently shown that the fast non-genomic responses of 1,25(OH)(2)-vitamin D(3) [1,25(OH)(2)D(3)] in skeletal muscle cells involve tyrosine phosphorylation of MAP kinase (ERK1/2), c-Src kinase and the oncoprotein c-myc. In the present work, blockade of vitamin D receptor (VDR) expression (> or =80%) by preincubation of chick embryonic muscle cells with three different antisense oligonucleotides against the VDR mRNA (AS-VDR ODNs) significantly reduced (-94%) 1,25(OH)(2)D(3) stimulation of c-myc tyrosine phosphorylation and inhibited c-Src tyrosine dephosphorylation implying lack of c-Src activation by the hormone. Coimmunoprecipitation experiments revealed that 1,25(OH)(2)D(3) induces the formation of complexes between c-Src and c-myc, in agreement with the above results and previous studies showing hormone-dependent association between c-Src and tyrosine phosphorylated VDR and c-Src mediated c-myc tyrosine phosphorylation. MAPK tyrosine phosphorylation by 1,25(OH)(2)D(3) was affected to a lesser extent (-35%) by transfection with AS-VDR ODNs implying that both VDR-dependent and VDR-independent signalling mediate hormone stimulation of MAPK. These are the first results providing direct evidence on the participation of the VDR in non-genomic 1,25(OH)(2)D(3) signal transduction. Activation of tyrosine phosphorylation cascades through this mechanism may contribute to hormone regulation of muscle growth.

The tyrosine kinase c-Src is required for 1,25(OH)2-vitamin D3 signalling to the nucleus in muscle cells

We have recently shown that the hormonal form of vitamin D3, 1,25(OH)2-vitamin D3 (1,25(OH)2D3), stimulates the enzymatic activity of the non-receptor protein tyrosine kinase c-Src in skeletal muscle cells. In this study we show that intracellular and extracellular Ca2+ chelation with BAPTA and EGTA, respectively, blocked hormone stimulation of c-Src activity/dephosphorylation, indicating that the calcium messenger system is an upstream activator of c-Src. Tyrosine phosphorylation and stimulation of the growth-related mitogen-activated protein kinase (MAPK) by 1,25(OH)2D3 was shown to be dependent on activation of c-Src, since pretreatment with the c-Src specific inhibitor PP1 or muscle cell transfection with an antisense oligodeoxynucleotide directed against c-Src mRNA markedly reduced hormone stimulation of MAPK phosphorylation. Evidence was obtained indicating that MAPK is then translocated to the cell nucleus in active phosphorylated form and induces the expression of c-myc oncoprotein, as the MAPK kinase (MEK) inhibitor PD98059 abolished stimulation of c-myc synthesis by 1,25(OH)2D3. In addition, the hormone rapidly stimulated tyrosine phosphorylation of c-myc. In cells pretreated with PP1 (4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo-D3,4-pyrimidine), the 1,25(OH)2D3-induced increase in tyrosine phosphorylation of c-myc was suppressed. Taken together, these results demonstrate that 1,25(OH)2D3 stimulates proliferation-associated signalling pathways in skeletal muscle cells and implicate c-Src kinase as mediator of this response.

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.

Inhibitory effects of 1alpha,25-dihydroxyvitamin D(3) on the G(1)-S phase-controlling machinery

The nuclear hormone 1alpha,25-dihydroxyvitamin D(3) induces cell cycle arrest, differentiation, or apoptosis depending on target cell type and state. Although the antiproliferative effect of 1alpha,25-dihydroxyvitamin D(3) has been known for years, the molecular basis of the cell cycle blockade by 1alpha,25-dihydroxyvitamin D(3) remains largely unknown. Here we have investigated the mechanisms underlying the G(1) arrest induced upon 1alpha,25-dihydroxyvitamin D(3) treatment of the human breast cancer cell line MCF-7. Twenty-four-hour exposure of exponentially growing MCF-7 cells to 1alpha,25-dihydroxyvitamin D(3) impeded proliferation by preventing S phase entry, an effect that correlated with appearance of the growth-suppressing, hypophosphorylated form of the retinoblastoma protein (pRb), and modulation of cyclin-dependent kinase (cdk) activities of cdk-4, -6, and -2. Time course immunochemical and biochemical analyses of the cellular and molecular effects of 1alpha,25-dihydroxyvitamin D(3) treatment for up to 6 d revealed a dynamic chain of events, preventing activation of cyclin D1/cdk4, and loss of cyclin D3, which collectively lead to repression of the E2F transcription factors and thus negatively affected cyclin A protein expression. While the observed 10-fold inhibition of cyclin D1/cdk 4-associated kinase activity appeared independent of cdk inhibitors, the activity of cdk 2 decreased about 20-fold, reflecting joint effects of the lower abundance of its cyclin partners and a significant increase of the cdk inhibitor p21(CIP1/WAF1), which blocked the remaining cyclin A(E)/cdk 2 complexes. Together with a rapid down-modulation of the c-Myc oncoprotein in response to 1alpha,25-dihydroxyvitamin D(3), these results demonstrate that 1alpha,25-dihydroxyvitamin D(3) inhibits cell proliferation by targeting several key regulators governing the G(1)/S transition.