Role of MAP kinases in the 1,25-dihydroxyvitamin D3-induced transactivation of the rat cytochrome P450C24 (CYP24) promoter. Specific functions for ERK1/ERK2 and ERK5

Mechanoresponsive ETS1 causes endothelial dysfunction and arterialization in varicose veins via NOTCH4/DLL4 signaling

Varicose veins are the most common venous disorder in humans and are characterized by hemodynamic instability due to valvular insufficiency and orthostatic lifestyle factors. It is unclear how changes in biomechanical signals cause aberrant remodeling of the vein wall. Our previous studies suggest that Notch signaling is implicated in varicose vein arterialization. In the arterial system, mechanoresponsive ETS1 is a transcriptional activator of the endothelial Notch, but its involvement in sensing disrupted venous flow and varicose vein formation has not been investigated. Here, we use human varicose veins and cultured human venous endothelial cells to show that disturbed venous shear stress activates ETS1-NOTCH4/DLL4 signaling. Notch components were highly expressed in the neointima, whereas ETS1 was upregulated in all histological layers of varicose veins. In vitro microfluidic flow-based studies demonstrate that even minute changes in venous flow patterns enhance ETS1-NOTCH4/DLL4 signaling. Uniform venous shear stress, albeit an inherently low-flow system, does not induce ETS1 and Notch proteins. ETS1 activation under altered flow was mediated primarily by MEK1/2 and, to a lesser extent, by MEK5 but was independent of p38 MAP kinase. Endothelial cell-specific ETS1 knockdown prevented disturbed flow-induced NOTCH4/DLL4 expression. TK216, an inhibitor of ETS-family, prevented the acquisition of arterial molecular identity and loss of endothelial integrity in cells exposed to the ensuing altered shear stress. We conclude that ETS1 senses blood flow disturbances and may promote venous remodeling by inducing endothelial dysfunction. Targeting ETS1 rather than downstream Notch proteins could be an effective and safe strategy to develop varicose vein therapies.

The vitamin D receptor agonist EB1089 can exert its antiviral activity independently of the vitamin D receptor

Vitamin D has been shown to have antiviral activity in a number of different systems. However, few studies have investigated whether the antiviral activity is exerted through the vitamin D receptor (VDR). In this study, we investigated whether the antiviral activity of a vitamin D receptor agonist (EB1089) towards dengue virus (DENV) was modulated by VDR. To undertake this, VDR was successively overexpressed, knocked down and retargeted through mutation of the nuclear localization signal. In no case was an effect seen on the level of the antiviral activity induced by EB1089, strongly indicating that the antiviral activity of EB1089 is not exerted through VDR. To further explore the antiviral activity of EB1089 in a more biologically relevant system, human neural progenitor cells were differentiated from induced pluripotent stem cells, and infected with Zika virus (ZIKV). EB1089 exerted a significant antiviral effect, reducing virus titers by some 2Log10. In support of the results seen with DENV, no expression of VDR at the protein level was observed. Collectively, these results show that the vitamin D receptor agonist EB1089 exerts its antiviral activity independently of VDR.

Calcifediol: Mechanisms of Action

Due to its essential role in calcium and phosphate homeostasis, the secosteroid hormone calcitriol has received growing attention over the last few years. Calcitriol, like other steroid hormones, may function through both genomic and non-genomic mechanisms. In the traditional function, the interaction between the biologically active form of vitamin D and the vitamin D receptor (VDR) affects the transcription of thousands of genes by binding to repeated sequences present in their promoter region, named vitamin D-responsive elements (VDREs). Non-transcriptional effects, on the other hand, occur quickly and are unaffected by inhibitors of transcription and protein synthesis. Recently, calcifediol, the immediate precursor metabolite of calcitriol, has also been shown to bind to the VDR with weaker affinity than calcitriol, thus exerting gene-regulatory properties. Moreover, calcifediol may also trigger rapid non-genomic responses through its interaction with specific membrane vitamin D receptors. Membrane-associated VDR (mVDR) and protein disulfide isomerase family A member 3 (Pdia3) are the best-studied candidates for mediating these rapid responses to vitamin D metabolites. This paper provides an overview of the calcifediol-related mechanisms of action, which may help to better understand the vitamin D endocrine system and to identify new therapeutic targets that could be important for treating diseases closely associated with vitamin D deficiency.

Calcifediol: Why, When, How Much?

Vitamin D deficiency is a constantly growing health problem worldwide. Adults affected with hypovitaminosis D could experience negative consequences on their musculoskeletal system and extra-skeletal health. In fact, an optimal vitamin D status is essential to ensure the correct bone, calcium, and phosphate homeostasis. To improve vitamin D status, it is important to not only increase the intake of food fortified with vitamin D, but also to administer vitamin D supplementation when required. Vitamin D3 (cholecalciferol) is the most widely used supplement. In recent years, the administration of calcifediol (25(OH)D3), the direct precursor of the biologically active form of vitamin D3, as oral vitamin D supplementation has progressively grown. Here, we report the potential medical benefits of some peculiar biological actions of calcifediol, discussing the possible specific clinical scenarios in which the oral intake of calcifediol could be most effective to restore the correct serum levels of 25(OH)D3. In summary, the aim of this review is to provide insights into calcifediol-related rapid non-genomic responses and the possible use of this vitamin D metabolite as a supplement for the treatment of people with a higher risk of hypovitaminosis D.

Latest Knowledge on the Role of Vitamin D in Hypertension

Hypertension is the third leading cause of the global disease burden, and while populations live longer, adopt more sedentary lifestyles, and become less economically concerned, the prevalence of hypertension is expected to increase. Pathologically elevated blood pressure (BP) is the strongest risk factor for cardiovascular disease (CVD) and related disability, thus making it imperative to treat this disease. Effective standard pharmacological treatments, i.e., diuretics, angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blocker (ARBs), beta-adrenergic receptor blockers (BARBs), and calcium channel blockers (CCBs), are available. Vitamin D (vitD) is known best for its role in bone and mineral homeostasis. Studies with vitamin D receptor (VDR) knockout mice show an increased renin-angiotensin-aldosterone system (RAAS) activity and increased hypertension, suggesting a key role for vitD as a potential antihypertensive agent. Similar studies in humans displayed ambiguous and mixed results. No direct antihypertensive effect was shown, nor a significant impact on the human RAAS. Interestingly, human studies supplementing vitD with other antihypertensive agents reported more promising results. VitD is considered a safe supplement, proposing its great potential as antihypertensive supplement. The aim of this review is to examine the current knowledge about vitD and its role in the treatment of hypertension.

The Association between Vitamin D and the Components of Male Fertility: A Systematic Review

OBJECTIVE

Previous systematic reviews of the effects of vitamin D on the components of male fertility have been inconclusive. This article systematically reviews the latest research to examine the relationship between vitamin D, semen quality parameters, and sex hormones production.

METHODS

MEDLINE, Cochrane, and Web of Science databases were searched using the appropriate keywords.

RESULTS

Observational studies indicate significant correlation between vitamin D levels and sperm parameters, with a particular emphasis on sperm motility, and partially suggest a relationship between higher serum testosterone and vitamin D levels. Additionally, interventional studies confirmed that vitamin D supplementation has a positive effect on sperm motility, especially progressive. However, most randomized clinical trials indicate that vitamin D treatment does not have any significant effect on testosterone or other hormone levels.

CONCLUSIONS

Although our findings add to the discussion regarding the effect of vitamin D on male fertility, there is still no solid evidence to support the use of vitamin D supplementation to improve the outcomes of patients with impaired sperm parameters and hormonal disorders. Additional dedicated clinical studies are needed to clarify the relationship between vitamin D and male fertility, along with its components.

Rapid Nontranscriptional Effects of Calcifediol and Calcitriol

Classically, a secosteroid hormone, vitamin D, has been implicated in calcium and phosphate homeostasis and has been associated with the pathogenesis of rickets and osteomalacia in patients with severe nutritional vitamin D deficiency. The spectrum of known vitamin D-mediated effects has been expanded in recent years. However, the mechanisms of how exactly this hormone elicits its biological function are still not fully understood. The interaction of this metabolite with the vitamin D receptor (VDR) and, subsequently, with the vitamin D-responsive element in the region of specific target genes leading to the transcription of genes whose protein products are involved in the traditional function of calcitriol (known as genomic actions). Moreover, in addition to these transcription-dependent mechanisms, it has been recognized that the biologically active form of vitamin D₃, as well as its immediate precursor metabolite, calcifediol, initiate rapid, non-genomic actions through the membrane receptors that are bound as described for other steroid hormones. So far, among the best candidates responsible for mediating rapid membrane response to vitamin D metabolites are membrane-associated VDR (VDRm) and protein disulfide isomerase family A member 3 (Pdia3). The purpose of this paper is to provide an overview of the rapid, non-genomic effects of calcifediol and calcitriol, whose elucidation could improve the understanding of the vitamin D₃ endocrine system. This will contribute to a better recognition of the physiological acute functions of vitamin D₃, and it could lead to the identification of novel therapeutic targets able to modulate these actions.

In Vitro Non-Genomic Effects of Calcifediol on Human Preosteoblastic Cells

Several recent studies have demonstrated that the direct precursor of vitamin D₃, the calcifediol [25(OH)D₃], through the binding to the nuclear vitamin D receptor (VDR), is able to regulate the expression of many genes involved in several cellular processes. Considering that itself may function as a VDR ligand, although with a lower affinity, respect than the active form of vitamin D, we have assumed that 25(OH)D₃ by binding the VDR could have a vitamin’s D₃ activity such as activating non-genomic pathways, and in particular we selected mesenchymal stem cells derived from human adipose tissue (hADMSCs) for the in vitro assessment of the intracellular Ca²⁺ mobilization in response to 25(OH)D₃. Our result reveals the ability of 25(OH)D₃ to activate rapid, non-genomic pathways, such as an increase of intracellular Ca²⁺ levels, similar to what observed with the biologically active form of vitamin D₃. hADMSCs loaded with Fluo-4 AM exhibited a rapid and sustained increase in intracellular Ca²⁺ concentration as a result of exposure to 10⁻⁵ M of 25(OH)D₃. In this work, we show for the first time the in vitro ability of 25(OH)D₃ to induce a rapid increase of intracellular Ca²⁺ levels in hADMSCs. These findings represent an important step to better understand the non-genomic effects of vitamin D₃ and its role in endocrine system.

Vitamin D upregulates the macrophage complement receptor immunoglobulin in innate immunity to microbial pathogens

Vitamin D deficiency remains a global concern. This ‘sunshine’ vitamin is converted through a multistep process to active 1,25-dihydroxyvitamin D₃ (1,25D), the final step of which can occur in macrophages. Here we demonstrate a role for vitamin D in innate immunity. The expression of the complement receptor immunoglobulin (CRIg), which plays an important role in innate immunity, is upregulated by 1,25D in human macrophages. Monocytes cultured in 1,25D differentiated into macrophages displaying increased CRIg mRNA, protein and cell surface expression but not in classical complement receptors, CR3 and CR4. This was associated with increases in phagocytosis of complement opsonised Staphylococcus aureus and Candida albicans. Treating macrophages with 1,25D for 24 h also increases CRIg expression. While treating macrophages with 25-hydroxyvitamin D₃ does not increase CRIg expression, added together with the toll like receptor 2 agonist, triacylated lipopeptide, Pam3CSK4, which promotes the conversion of 25-hydroxyvitamin D₃ to 1,25D, leads to an increase in CRIg expression and increases in CYP27B1 mRNA. These findings suggest that macrophages harbour a vitamin D-primed innate defence mechanism, involving CRIg.

Annabelle Small et al. report a new role for vitamin D in innate immunity. They find that the vitamin D metabolite 1,25D increases phagocytosis and expression of complement receptor immunoglobulin (CRIg) by macrophages and that treatment of macrophages with a toll like receptor 2 agonist promotes conversion of 25-hydroxyvitamin D3 to 1,25D.

A hierarchical regulatory network analysis of the vitamin D induced transcriptome reveals novel regulators and complete VDR dependency in monocytes

The transcription factor vitamin D receptor (VDR) is the high affinity nuclear target of the biologically active form of vitamin D₃ (1,25(OH)₂D₃). In order to identify pure genomic transcriptional effects of 1,25(OH)₂D₃, we used VDR cistrome, transcriptome and open chromatin data, obtained from the human monocytic cell line THP-1, for a novel hierarchical analysis applying three bioinformatics approaches. We predicted 75.6% of all early 1,25(OH)₂D₃-responding (2.5 or 4 h) and 57.4% of the late differentially expressed genes (24 h) to be primary VDR target genes. VDR knockout led to a complete loss of 1,25(OH)₂D₃–induced genome-wide gene regulation. Thus, there was no indication of any VDR-independent non-genomic actions of 1,25(OH)₂D₃ modulating its transcriptional response. Among the predicted primary VDR target genes, 47 were coding for transcription factors and thus may mediate secondary 1,25(OH)₂D₃ responses. CEBPA and ETS1 ChIP-seq data and RNA-seq following CEBPA knockdown were used to validate the predicted regulation of secondary vitamin D target genes by both transcription factors. In conclusion, a directional network containing 47 partly novel primary VDR target transcription factors describes secondary responses in a highly complex vitamin D signaling cascade. The central transcription factor VDR is indispensable for all transcriptome-wide effects of the nuclear hormone.

Inhibition of Estrogen Sulfotransferase (SULT1E1/EST) Ameliorates Ischemic Acute Kidney Injury in Mice

BACKGROUND

Studies have suggested that estrogens may protect mice from AKI. Estrogen sulfotransferase (SULT1E1, or EST) plays an important role in estrogen homeostasis by sulfonating and deactivating estrogens, but studies on the role of SULT1E1 in AKI are lacking.

METHODS

We used the renal ischemia-reperfusion model to investigate the role of SULT1E1 in AKI. We subjected wild-type mice, Sult1e1 knockout mice, and Sult1e1 knockout mice with liver-specific reconstitution of SULT1E1 expression to bilateral renal ischemia-reperfusion or sham surgery, either in the absence or presence of gonadectomy. We assessed relevant biochemical, histologic, and gene expression markers of kidney injury. We also used wild-type mice treated with the SULT1E1 inhibitor triclosan to determine the effect of pharmacologic inhibition of SULT1E1 on AKI.

RESULTS

AKI induced the expression of Sult1e1 in a tissue-specific and sex-specific manner. It induced expression of Sult1e1 in the liver in both male and female mice, but Sult1e1 induction in the kidney occurred only in male mice. Genetic knockout or pharmacologic inhibition of Sult1e1 protected mice of both sexes from AKI, independent of the presence of sex hormones. Instead, a gene profiling analysis indicated that the renoprotective effect was associated with increased vitamin D receptor signaling. Liver-specific transgenic reconstitution of SULT1E1 in Sult1e1 knockout mice abolished the protection in male mice but not in female mice, indicating that Sult1e1's effect on AKI was also tissue-specific and sex-specific.

CONCLUSIONS

SULT1E1 appears to have a novel function in the pathogenesis of AKI. Our findings suggest that inhibitors of SULT1E1 might have therapeutic utility in the clinical management of AKI.

Vitamin D: Newer Concepts of Its Metabolism and Function at the Basic and Clinical Level

The interest in vitamin D continues unabated with thousands of publications contributing to a vast and growing literature each year. It is widely recognized that the vitamin D receptor (VDR) and the enzymes that metabolize vitamin D are found in many cells, not just those involved with calcium and phosphate homeostasis. In this mini review I have focused primarily on recent studies that provide new insights into vitamin D metabolism, mechanisms of action, and clinical applications. In particular, I examine how mutations in vitamin D metabolizing enzymes—and new information on their regulation—links vitamin D metabolism into areas such as metabolism and diseases outside that of the musculoskeletal system. New information regarding the mechanisms governing the function of the VDR elucidates how this molecule can be so multifunctional in a cell-specific fashion. Clinically, the difficulty in determining vitamin D sufficiency for all groups is addressed, including a discussion of whether the standard measure of vitamin D sufficiency, total 25OHD (25 hydroxyvitamin) levels, may not be the best measure—at least by itself. Finally, several recent large clinical trials exploring the role of vitamin D supplementation in nonskeletal diseases are briefly reviewed, with an eye toward what questions they answered and what new questions they raised.

Protein Kinase D3 promotes the cell proliferation by activating the ERK1/c-MYC axis in breast cancer

Breast cancer is the second leading death cause of cancer death for all women. Previous study suggested that Protein Kinase D3 (PRKD3) was involved in breast cancer progression. In addition, the protein level of PRKD3 in triple‐negative breast adenocarcinoma was higher than that in normal breast tissue. However, the oncogenic mechanisms of PRKD3 in breast cancer is not fully investigated. Multi‐omic data showed that ERK1/c‐MYC axis was identified as a major pivot in PRKD3‐mediated downstream pathways. Our study provided the evidence to support that the PRKD3/ERK1/c‐MYC pathway play an important role in breast cancer progression. We found that knocking out PRKD3 by performing CRISPR/Cas9 genome engineering technology suppressed phosphorylation of both ERK1 and c‐MYC but did not down‐regulate ERK1/2 expression or phosphorylation of ERK2. The inhibition of ERK1 and c‐MYC phosphorylation further led to the lower protein level of c‐MYC and then reduced the expression of the c‐MYC target genes in breast cancer cells. We also found that loss of PRKD3 reduced the rate of the cell proliferation in vitro and tumour growth in vivo, whereas ectopic (over)expression of PRKD3, ERK1 or c‐MYC in the PRKD3‐knockout breast cells reverse the suppression of the cell proliferation and tumour growth. Collectively, our data strongly suggested that PRKD3 likely promote the cell proliferation in the breast cancer cells by activating ERK1‐c‐MYC axis.

Molecular Mechanism of Cancer Susceptibility Associated with Fok1 Single Nucleotide Polymorphism of VDR in Relation to Breast Cancer

Breast cancer is the leading cause of death among women worldwide. It is a multi-factorial disease caused by genetic and environmental factors. Vitamin D has been hypothesized to lower the risk of breast cancer via the nuclear vitamin D receptor (VDR). Genetic variants of these vitamin D metabolizing genes may alter the bioavailability of vitamin D, and hence modulate the risk of breast cancer.

Examination of VDR/RXR/DRIP205 Interaction, Intranuclear Localization, and DNA Binding in Ras-Transformed Keratinocytes and Its Implication for Designing Optimal Vitamin D Therapy in Cancer

Retinoid X receptor (RXR) occupies a central position within the nuclear receptor superfamily, serving as an obligatory partner to numerous other nuclear receptors, including vitamin D receptor (VDR). In the current study, we examined whether phosphorylation of RXRα at serine 260 affects VDR/RXR and VDR interacting protein (DRIP) 205 coactivator recruitment, interactions, and binding of the VDR/human RXRα (hRXRα)/DRIP205 complex to chromatin. Serine 260 is a critical amino acid on the hRXRα that is located in close spatial proximity to regions of coactivator and corepressor interactions. Using fluorescence resonance energy transfer and immunofluorescence studies, we showed that the physical interaction between hRXRα and DRIP205 coactivator was impaired in human keratinocytes with the ras oncogene (HPK1Aras) or transfected with the wild-type hRXRα. Furthermore, the nuclear colocalization of VDR/DRIP205, hRXRα/DRIP205, and VDR/hRXRα/DRIP205 complex binding to chromatin is impaired in the HPK1Aras cells when compared with the normal human keratinocytes (HPK1A cells). However, transfection with the nonphosphorylatable hRXRα (S260A) mutant or treatment with the mitogen-activated protein kinase (MAPK) inhibitor UO126 rescued their nuclear localization, interaction, and binding of the complex to chromatin in the HPK1Aras cells. In summary, we have demonstrated, using highly specific intracellular tagging methods in live and fixed cells, important alterations of the vitamin D signaling system in cancer cells in which the ras-raf-MAPK system is activated, suggesting that specific inhibition of this commonly activated pathway could be targeted therapeutically to enhance vitamin D efficacy.

Constitutively active RAS signaling reduces 1,25 dihydroxyvitamin D-mediated gene transcription in intestinal epithelial cells by reducing vitamin D receptor expression

High vitamin D status is associated with reduced colon cancer risk but these studies ignore the diversity in the molecular etiology of colon cancer. RAS activating mutations are common in colon cancer and they activate pro-proliferative signaling pathways. We examined the impact of RAS activating mutations on 1,25 dihydroxyvitamin D (1,25(OH)₂D)-mediated gene expression in cultured colon and intestinal cell lines. Transient transfection of Caco-2 cells with a constitutively active mutant K-RAS (G12 V) significantly reduced 1,25(OH)₂D-induced activity of both a human 25-hydroxyvitamin D, 24 hydroxyase (CYP24A1) promoter-luciferase and an artificial 3X vitamin D response element (VDRE) promoter-luciferase reporter gene. Young Adult Mouse Colon (YAMC) and Rat Intestinal Epithelial (RIE) cell lines with stable expression of mutant H-RAS had suppressed 1,25(OH)₂D-mediated induction of CYP24A1 mRNA. The RAS effects were associated with lower Vitamin D receptor (VDR) mRNA and protein levels in YAMC and RIE cells and they could be partially reversed by VDR overexpression. RAS-mediated suppression of VDR levels was not due to either reduced VDR mRNA stability or increased VDR gene methylation. However, chromatin accessibility to the VDR gene at the proximal promoter (-300bp), an enhancer region at -6kb, and an enhancer region located in exon 3 was significantly reduced in RAS transformed YAMC cells (YAMC-RAS). These data show that constitutively active RAS signaling suppresses 1,25(OH)₂D-mediated gene transcription in colon epithelial cells by reducing VDR gene transcription but the mechanism for this suppression is not yet known. These data suggest that cancers with RAS-activating mutations may be less responsive to vitamin D mediated treatment or chemoprevention.

Vitamin D and the brain: Genomic and non-genomic actions

1,25(OH)₂D₃ (vitamin D) is well-recognized as a neurosteroid that modulates multiple brain functions. A growing body of evidence indicates that vitamin D plays a pivotal role in brain development, neurotransmission, neuroprotection and immunomodulation. However, the precise molecular mechanisms by which vitamin D exerts these functions in the brain are still unclear. Vitamin D signalling occurs via the vitamin D receptor (VDR), a zinc-finger protein in the nuclear receptor superfamily. Like other nuclear steroids, vitamin D has both genomic and non-genomic actions. The transcriptional activity of vitamin D occurs via the nuclear VDR. Its faster, non-genomic actions can occur when the VDR is distributed outside the nucleus. The VDR is present in the developing and adult brain where it mediates the effects of vitamin D on brain development and function. The purpose of this review is to summarise the in vitro and in vivo work that has been conducted to characterise the genomic and non-genomic actions of vitamin D in the brain. Additionally we link these processes to functional neurochemical and behavioural outcomes. Elucidation of the precise molecular mechanisms underpinning vitamin D signalling in the brain may prove useful in understanding the role this steroid plays in brain ontogeny and function.

Vitamin D: Musculoskeletal health

Perhaps the role of Vitamin D supplementation has been most exhaustively studied in calcium absorption, skeletal wellbeing, muscular potency, balance and risk of falling. Nonetheless, new data has emerged and the recent research on sarcopenia makes the topic increasingly interesting. Given the socioeconomic burden of the musculoskeletal consequences of hypovitaminosis D it is vital to keep abreast with the latest literature in the field. The recommended Vitamin D supplementation dose should suffice to increase the serum 25 hydroxyvitamin D level to 30 ng/mL (75 nmol/L) and this level should be optimally maintained with a maintenance dose, particularly for those diagnosed with osteoporosis.

Glypican-based drug releasing titania implants to regulate BMP2 bioactivity as a potential approach for craniosynostosis therapy

Advances in molecular biology and nanomedicine based therapies hold promise to obviate the need of multiple surgical interventions (associated with current management) in craniosynostosis by preventing bone re-ossification. One such adjunctive therapy involves application of glypicans 1 and 3 (GPC1 and GPC3) that are BMP inhibitors implicated in downregulating the BMP2 activity in prematurely fusing sutures. Electrochemically anodized Titania nanotube (TNT) arrays have been recognized as a promising localized, long-term drug delivery platform for bone-related therapies. This study presents the application of nanoengineered TNT/Ti implants loaded with recombinant glypicans for craniosynostosis therapy. By using Dual luciferase Reporter assay, we tested the biofunctionality of eluted glypicans from the TNT/Ti implants for BMP2 bioactivity regulation in C2C12 murine myoblast cell line. BMP2 activity was inhibited significantly for up to 15days by the glypicans released from polymer-coated TNT/Ti implants, indicating their potential application in adjunctive craniosynostosis treatment.

PTH and Vitamin D

PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.

The Non-Genomic Actions of Vitamin D

Since its discovery in 1920, a great deal of effort has gone into investigating the physiological actions of vitamin D and the impact its deficiency has on human health. Despite this intense interest, there is still disagreement on what constitutes the lower boundary of adequacy and on the Recommended Dietary Allowance. There has also been a major push to elucidate the biochemistry of vitamin D, its metabolic pathways and the mechanisms that mediate its action. Originally thought to act by altering the expression of target genes, it was realized in the mid-1980s that some of the actions of vitamin D were too rapid to be accounted for by changes at the genomic level. These rapid non-genomic actions have attracted as much interest as the genomic actions and they have spawned additional questions in an already busy field. This mini-review attempts to summarise the in vitro and in vivo work that has been conducted to characterise the rapid non-genomic actions, the mechanisms that give rise to these properties and the roles that these play in the overall action of vitamin D at the cellular level. Understanding the effects of vitamin D at the cellular level should enable the design of elegant human studies to extract the full potential of vitamin D to benefit human health.

Vitamin D Signaling Modulators in Cancer Therapy

The antiproliferative and pro-apoptotic effects of 1α,25-dihydroxycholecalciferol (1,25(OH)2D3, 1,25D3, calcitriol) have been demonstrated in various tumor model systems in vitro and in vivo. However, limited antitumor effects of 1,25D3 have been observed in clinical trials. This may be attributed to a variety of factors including overexpression of the primary 1,25D3 degrading enzyme, CYP24A1, in tumors, which would lead to rapid local inactivation of 1,25D3. An alternative strategy for improving the antitumor activity of 1,25D3 involves the combination with a selective CYP24A1 inhibitor. The validity of this approach is supported by numerous preclinical investigations, which demonstrate that CYP24A1 inhibitors suppress 1,25D3 catabolism in tumor cells and increase the effects of 1,25D3 on gene expression and cell growth. Studies are now required to determine whether selective CYP24A1 inhibitors+1,25D3 can be used safely and effectively in patients. CYP24A1 inhibitors plus 1,25D3 can cause dose-limiting toxicity of vitamin D (hypercalcemia) in some patients. Dexamethasone significantly reduces 1,25D3-mediated hypercalcemia and enhances the antitumor activity of 1,25D3, increases VDR-ligand binding, and increases VDR protein expression. Efforts to dissect the mechanisms responsible for CYP24A1 overexpression and combinational effect of 1,25D3/dexamethasone in tumors are underway. Understanding the cross talk between vitamin D receptor (VDR) and glucocorticoid receptor (GR) signaling axes is of crucial importance to the design of new therapies that include 1,25D3 and dexamethasone. Insights gained from these studies are expected to yield novel strategies to improve the efficacy of 1,25D3 treatment.

Immune Modulation by Vitamin D and Its Relevance to Food Allergy

Apart from its classical function in bone and calcium metabolism, vitamin D is also involved in immune regulation and has been linked to various cancers, immune disorders and allergic diseases. Within the innate and adaptive immune systems, the vitamin D receptor and enzymes in monocytes, dendritic cells, epithelial cells, T lymphocytes and B lymphocytes mediate the immune modulatory actions of vitamin D. Vitamin D insufficiency/deficiency early in life has been identified as one of the risk factors for food allergy. Several studies have observed an association between increasing latitude and food allergy prevalence, plausibly linked to lower ultraviolet radiation (UVR) exposure and vitamin D synthesis in the skin. Along with mounting epidemiological evidence of a link between vitamin D status and food allergy, mice and human studies have shed light on the modulatory properties of vitamin D on the innate and adaptive immune systems. This review will summarize the literature on the metabolism and immune modulatory properties of vitamin D, with particular reference to food allergy.

Mechanistic Effects of Calcitriol in Cancer Biology

Besides its classical biological effects on calcium and phosphorus homeostasis, calcitriol, the active vitamin D metabolite, has a broad variety of actions including anticancer effects that are mediated either transcriptionally and/or via non-genomic pathways. In the context of cancer, calcitriol regulates the cell cycle, induces apoptosis, promotes cell differentiation and acts as anti-inflammatory factor within the tumor microenvironment. In this review, we address the different mechanisms of action involved in the antineoplastic effects of calcitriol.

Increased CYP24A1 expression is associated with BRAF(V600E) mutation and advanced stages in papillary thyroid carcinoma

OBJECTIVE

1α, 25(OH)2 D3 (calcitriol), the active form of vitamin D, has been shown to exert antiproliferative effects in many cancers. Overexpression of CYP24A1, the primary vitamin D-inactivating enzyme, is also observed in a variety of human cancers, thus potentially neutralizing the antitumour effect of 1α, 25(OH)2 D3. This study investigates the expression of CYP24A1 and the effect of BRAF(V600E) on its expression in thyroid cancer.

METHODS

We investigated 60 papillary thyroid carcinoma (PTC) specimens for CYP24A1 expression and its association with BRAF mutation and disease progression. CYP24A1 expression was measured by real-time RT-PCR, and BRAF(V600E) mutation was detected by PCR-DNA sequencing analysis. The interaction between BRAF(V600E) and CYP24A1 expression was determined by Western blot analysis and real-time RT-PCR.

RESULTS

CYP24A1 expression was increased in PTC as compared to benign multinodular goitre. The expression was further increased in stage III and IV tumours. There is a strong correlation between CYP24A1 overexpression and BRAF(V600E) mutation (P < 0·01). In thyroid cancer cell lines expressing BRAF(V600E) , CYP24A1 expression was significantly higher when compared to those without BRAF(V600E) expression. BRAF(V600E) transgene expression in CAL62 cell line can induce CYP24A1 expression. Furthermore, BRAF(V600E) inhibitor PLX4720 can significantly down-regulate CYP24A1 expression and enhance the antiproliferative effects of calcitriol in thyroid cancer cell lines.

CONCLUSION

CYP24A1 overexpression is a poor prognostic indicator for PTC and may reflect BRAF(V600E) mutation and MARK activation. The crosstalk between vitamin D and MAPK signalling pathways results in resistance to calcitriol-mediated antitumour effects, and the resistance can be reversed by BRAF(V600E) inhibitor PLX4720.

Vitamin D activities for health outcomes

Reports describing significant health risks due to inadequate vitamin D status continue to generate considerable interest amongst the medical and lay communities alike. Recent research on the various molecular activities of the vitamin D system, including the nuclear vitamin D receptor and other receptors for 1,25-dihydroxyvitamin D and vitamin D metabolism, provides evidence that the vitamin D system carries out biological activities across a wide range of tissues similar to other nuclear receptor hormones. This knowledge provides physiological plausibility of the various health benefits claimed to be provided by vitamin D and supports the proposals for conducting clinical trials. The vitamin D system plays critical roles in the maintenance of plasma calcium and phosphate and bone mineral homeostasis. Recent evidence confirms that plasma calcium homeostasis is the critical factor modulating vitamin D activity. Vitamin D activities in the skeleton include stimulation or inhibition of bone resorption and inhibition or stimulation of bone formation. The three major bone cell types, which are osteoblasts, osteocytes and osteoclasts, can all respond to vitamin D via the classical nuclear vitamin D receptor and metabolize 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D to activate the vitamin D receptor and modulate gene expression. Dietary calcium intake interacts with vitamin D metabolism at both the renal and bone tissue levels to direct either a catabolic action on the bone through the endocrine system when calcium intake is inadequate or an anabolic action through a bone autocrine or paracrine system when calcium intake is sufficient.

Regulation of bone morphogenetic protein signalling and cranial osteogenesis by Gpc1 and Gpc3

From birth, the vault of the skull grows at a prodigious rate, driven by the activity of osteoblastic cells at the fibrous joints (sutures) that separate the bony calvarial plates. One in 2500 children is born with a medical condition known as craniosynostosis because of premature bony fusion of the calvarial plates and a cessation of bone growth at the sutures. Bone morphogenetic proteins (BMPs) are potent growth factors that promote bone formation. Previously, we found that Glypican-1 (GPC1) and Glypican-3 (GPC3) are expressed in cranial sutures and are decreased during premature suture fusion in children. Although glypicans are known to regulate BMP signalling, a mechanistic link between GPC1, GPC3 and BMPs and osteogenesis has not yet been investigated. We now report that human primary suture mesenchymal cells coexpress GPC1 and GPC3 on the cell surface and release them into the media. We show that they inhibit BMP2, BMP4 and BMP7 activities, which both physically interact with BMP2 and that immunoblockade of endogenous GPC1 and GPC3 potentiates BMP2 activity. In contrast, increased levels of GPC1 and GPC3 as a result of overexpression or the addition of recombinant protein, inhibit BMP2 signalling and BMP2-mediated osteogenesis. We demonstrate that BMP signalling in suture mesenchymal cells is mediated by both SMAD-dependent and SMAD-independent pathways and that GPC1 and GPC3 inhibit both pathways. GPC3 inhibition of BMP2 activity is independent of attachment of the glypican on the cell surface and post-translational glycanation, and thus appears to be mediated by the core glypican protein. The discovery that GPC1 and GPC3 regulate BMP2-mediated osteogenesis, and that inhibition of endogenous GPC1 and GPC3 potentiates BMP2 responsiveness of human suture mesenchymal cells, indicates how downregulation of glypican expression could lead to the bony suture fusion that characterizes craniosynostosis.

24-Hydroxylase in cancer: impact on vitamin D-based anticancer therapeutics

The active vitamin D hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plays a major role in regulating calcium homeostasis and bone mineralization. 1,25(OH)2D3 also modulates cellular proliferation and differentiation in a variety of cell types. 24-Hydroxylase, encoded by the CYP24A1 gene, is the key enzyme which converts 1,25(OH)2D3 to less active calcitroic acid. Nearly all cell types express 24-hydroxylase, the highest activity being observed in the kidney. There is increasing evidence linking the incidence and prognosis of certain cancers to low serum 25(OH)D3 levels and high expression of vitamin D 24-hydroxylase, supporting the idea that elevated CYP24A1 expression may stimulate degradation of vitamin D metabolites including 25(OH)D3 and 1,25(OH)2D3. The over expression of CYP24A1 in cancer cells may be a factor affecting 1,25(OH)2D3 bioavailability and anti-proliferative activity pre-clinically and clinically. The combination of 1,25(OH)2D3 with CYP24A1 inhibitors enhances 1,25(OH)2D3 mediated signaling and anti-proliferative effects and may be useful in overcoming effects of aberrant CYP24A1 expression. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Phorbol esters enhance 1α,25-dihydroxyvitamin D3-regulated 25-hydroxyvitamin D-24-hydroxylase (CYP24A1) gene expression through ERK-mediated phosphorylation of specific protein 3 (Sp3) in Caco-2 cells

Phorbol 12-myristate 13-acetate (PMA) increased 1,25(OH)(2)D(3)-induced human 25 hydroxyvitamin d-24 hydroxylase (hCYP24A1) gene expression and vitamin D receptor (VDR) binding to the hCYP24A1 promoter. It did not alter transient receptor potential cation channel, subfamily V, member 6 (TRPV6) expression, VDR binding to the TRPV6 promoter, or VDR binding to a crude chromatin preparation. PMA activated Extracellular signal-Regulated Kinases (ERK) 1/2 and p38 mitogen activated protein kinases (MAPK) and inhibiting these kinases reduced 1,25(OH)(2)D(3)-induced and PMA-enhanced hCYP24A1 promoter activity. Mithramycin A inhibits Specific Protein (Sp) family member binding to DNA and reduced 1,25(OH)(2)D(3)-induced and PMA-enhanced hCYP24A1 promoter activity. Sp1 or Sp3 siRNA knockdown reduced 1,25(OH)(2)D(3)-regulated hCYP24A1 promoter activity but only Sp3 siRNA reduced PMA-enhanced hCYP24A1 promoter activity. PMA increased MAPK-dependent Sp3 phosphorylation, Sp3-VDR interactions, and Sp3 binding to the hCYP24A1 promoter. These data suggest that MAPK signaling contributes to 1,25(OH)(2)D(3)-induced and PMA-enhanced CYP24A1 gene transcription by modulating Sp3 function.

Effect of phorbol 12-myristate 13-acetate activated signaling pathways on 1α, 25 dihydroxyvitamin D3 regulated human 25-hydroxyvitamin D3 24-hydroxylase gene expression in differentiated Caco-2 cells

Phorbol-12-myristate-13-acetate (PMA), a protein kinase C(PKC) activator, can modulate 1α, 25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3))-induced expression of the 24-hydroxylase (CYP24A1) gene but this has not been studied in differentiated enterocytes, a primary 1,25(OH)(2) D(3) target cell. We found that in differentiated Caco-2 cells, an established model of the mature absorptive epithelial cell, PMA significantly enhanced 1,25(OH)(2)D(3)-induced human CYP24A1 (hCYP24A1) mRNA accumulation and hCYP24A1 promoter-luciferase reporter gene activation by 150%. Reporter gene studies further identified the region between -298 and +74 bp in the hCYP24A1 promoter as critical for the PMA enhancing effect and chromatin immunoprecipitation (ChIP) analysis showed that PMA enhanced 1,25(OH)(2)D(3)-induced binding of vitamin D receptor to this region. PMA can activate PKC, ERK1/2, and p38 MAP kinases and inhibition of these signaling pathways reduced both 1,25(OH)(2)D(3)-induced hCYP24A1 gene transcription and the enhancing effect of PMA. The PMA enhancing effect on 1,25(OH)(2)D(3) action was evident in a minimal promoter with three osteocalcin VDREs and was reduced after mutation of a putative vitamin D stimulatory site in the hCYP24A1 promoter. In contrast, mutation of a Ets binding site (EBS) in the hCYP24A1 promoter had no impact on 1,25(OH)(2)D(3) action or the PMA enhancing effect. These data suggest that in the differentiated enterocyte PMA-induced activation of several signaling pathways contribute to 1,25(OH)(2)D(3)-induced hCYP24A1 gene expression through multiple regulatory motifs within the proximal hCYP24A1 promoter.

Development of an efficient, non-viral transfection method for studying gene function and bone growth in human primary cranial suture mesenchymal cells reveals that the cells respond to BMP2 and BMP3

Background

Achieving efficient introduction of plasmid DNA into primary cultures of mammalian cells is a common problem in biomedical research. Human primary cranial suture cells are derived from the connective mesenchymal tissue between the bone forming regions at the edges of the calvarial plates of the skull. Typically they are referred to as suture mesenchymal cells and are a heterogeneous population responsible for driving the rapid skull growth that occurs in utero and postnatally. To better understand the molecular mechanisms involved in skull growth, and in abnormal growth conditions, such as craniosynostosis, caused by premature bony fusion, it is essential to be able to easily introduce genes into primary bone forming cells to study their function.

Results

A comparison of several lipid-based techniques with two electroporation-based techniques demonstrated that the electroporation method known as nucleofection produced the best transfection efficiency. The parameters of nucleofection, including cell number, amount of DNA and nucleofection program, were optimized for transfection efficiency and cell survival. Two different genes and two promoter reporter vectors were used to validate the nucleofection method and the responses of human primary suture mesenchymal cells by fluorescence microscopy, RT-PCR and the dual luciferase assay. Quantification of bone morphogenetic protein (BMP) signalling using luciferase reporters demonstrated robust responses of the cells to both osteogenic BMP2 and to the anti-osteogenic BMP3.

Conclusions

A nucleofection protocol has been developed that provides a simple and efficient, non-viral alternative method for in vitro studies of gene and protein function in human skull growth. Human primary suture mesenchymal cells exhibit robust responses to BMP2 and BMP3, and thus nucleofection can be a valuable method for studying the potential competing action of these two bone growth factors in a model system of cranial bone growth.

Cell-Type-Specific Effects of Silibinin on Vitamin D-Induced Differentiation of Acute Myeloid Leukemia Cells Are Associated with Differential Modulation of RXRα Levels

Plant polyphenols have been shown to enhance the differentiation of acute myeloid leukemia (AML) cells induced by the hormonal form of vitamin D(3) (1α,25-dihydroxyvitamin D(3); 1,25D). However, how these agents modulate 1,25D effects in different subtypes of AML cells remains poorly understood. Here, we show that both carnosic acid (CA) and silibinin (SIL) synergistically enhancd 1,25D-induced differentiation of myeloblastic HL60 cells. However, in promonocytic U937 cells, only CA caused potentiation while SIL attenuated 1,25D effect. The enhanced effect of 1,25D+CA was accompanied by increases in both the vitamin D receptor (VDR) and retinoid X receptor alpha (RXRα) protein levels and vitamin D response element (VDRE) transactivation in both cell lines. Similar increases were observed in HL60 cells treated with 1,25D + SIL. In U937 cells, however, SIL inhibited 1,25D-induced VDRE transactivation concomitant with downregulation of RXRα at both transcriptional and posttranscriptional levels. These inhibitory effects correlated with the inability of SIL, with or without 1,25D, to activate the Nrf2/antioxidant response element signaling pathway in U937 cells. These results suggest that opposite effects of SIL on 1,25D-induced differentiation of HL60 and U937 cells may be determined by cell-type-specific signaling and transcriptional responses to this polyphenol resulting in differential modulation of RXRα expression.

Vitamin D actions to regulate calcium and skeletal homeostasis

The endocrine action of plasma 1,25-dihydroxyvitamin D plays a key role in the regulation of plasma calcium and phosphate homeostasis with activities on the intestine, kidney and bone. A current, controversial question is whether vitamin D exerts direct actions on bone cells to regulate bone mineral homeostasis. Results from clinical, rodent model and in vitro studies on human bone cells provide an impressive body of data to support this proposal particularly at the level of serum 25-hydroxyvitamin D status. Each of the major bone cell types is capable of metabolising vitamin D to the active metabolite, 1,25-dihydroxyvitamin D. Thus under conditions when bone tissue synthesis of 1,25-dihydroxyvitamin D is optimal, vitamin D activity enhances bone mineral status. Dietary calcium and phosphate intakes are the critical environmental cues together with vitamin D status to determine whether 1,25-dihydroxyvitamin D exerts an anabolic or catabolic action on bone mineral status.

Regulation of mouse Cyp24a1 expression via promoter-proximal and downstream-distal enhancers highlights new concepts of 1,25-dihydroxyvitamin D(3) action

CYP24A1 functions in vitamin D target tissues to degrade 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). Thus, the concentration of this enzyme and the regulation of its expression is a primary determinant of the overall biological activity of 1,25(OH)(2)D(3) within cells. The principle regulator of CYP24A1 expression is 1,25(OH)(2)D(3) itself, which functions through the vitamin D receptor to upregulate the transcriptional activity of the Cyp24a1 gene. In this report, we explore the mechanism of this regulation using recently developed ChIP-chip and ChIP-seq techniques that permit an unbiased search for enhancer elements that participate in this transcriptional control. Our studies both confirm a regulatory region defined earlier and located proximal to the transcriptional start site (TSS) of mouse Cyp24a1 (-160 and -265nt) and identify a novel intergenic region located downstream of the transcription unit that contains two enhancers (+35 and +37kb) that facilitate 1,25(OH)(2)D(3)-dependent upregulation of Cyp24a1 expression. Interestingly, while C/EBPβ also binds under basal conditions to a site located immediately upstream of the Cyp24a1 promoter (-345nt), occupancy by this factor is strikingly increased following 1,25(OH)(2)D(3) treatment. The locations and activities of these regulatory regions that mediate 1,25(OH)(2)D(3) actions were confirmed in mice in vivo. We conclude that the mechanism through which 1,25(OH)(2)D(3) induces the CYP24A1 enzyme, thereby autoregulating its own destruction, involves both promoter-proximal as well as downstream-distal enhancers. These findings highlight new concepts regarding the molecular mechanism of action of 1,25(OH)(2)D(3) and other hormonal regulators.

p38γ activation triggers dynamical changes in allosteric docking sites

Mitogen-activated protein kinases (MAPKs) are serine-threonine kinases that participate in signal transduction pathways. p38 MAPKs have four isoforms (p38α, p38β, p38γ, and p38δ) which are involved in multiple cellular functions such as proliferation, differentiation, survival, and migration. MAPK kinases phosphorylate p38s in the dual-phosphorylation motif, Thr-Gly-Tyr, located in their activation loop, which induces a conformational change that increases ATP binding affinity and catalytic activity. Several works have proposed that MAPK dynamics is a key factor in determining their function. However, we still do not understand the dynamical changes that lead to MAPK activation. In this work we have used molecular dynamics techniques to study the dynamical changes associated with p38γ activation, the only fully active MAPK crystallized so far. We performed MD simulations of p38γ in three different states, fully active with ATP, active without ATP, and inactive. We found that the dynamical fluctuations of the docking sites, important for protein-protein interactions, are regulated allosterically by changes in the active site. Interestingly, in the phosphorylated and ATP-bound states the whole protein dynamics lead to concerted motions of whole protein domains in contrast to the inactive state. The binding/unbinding of ATP participates in the reorientation of the two domains and in the regulation of protein plasticity. Our study shows that beyond the conformational changes associated with MAPK activation their correlated dynamics are highly regulated by phosphorylation and ATP binding. This means that MAPK plasticity may have a role in their catalytic activity, specificity, and protein-protein interactions and, therefore, in the outcome of the signaling network.

Successful drug development despite adverse preclinical findings part 2: examples

To illustrate the process of addressing adverse preclinical findings (APFs) as outlined in the first part of this review, a number of cases with unexpected APF in toxicity studies with drug candidates is discussed in this second part. The emphasis is on risk characterization, especially regarding the mode of action (MoA), and risk evaluation regarding relevance for man. While severe APFs such as retinal toxicity may turn out to be of little human relevance, minor findings particularly in early toxicity studies, such as vasculitis, may later pose a real problem. Rodents are imperfect models for endocrine APFs, non-rodents for human cardiac effects. Liver and kidney toxicities are frequent, but they can often be monitored in man and do not necessarily result in early termination of drug candidates. Novel findings such as the unusual lesions in the gastrointestinal tract and the bones presented in this review can be difficult to explain. It will be shown that well known issues such as phospholipidosis and carcinogenicity by agonists of peroxisome proliferator-activated receptors (PPAR) need to be evaluated on a case-by-case basis. The latter is of particular interest because the new PPAR α and dual α/γ agonists resulted in a change of the safety paradigm established with the older PPAR α agonists. General toxicologists and pathologists need some understanding of the principles of genotoxicity and reproductive toxicity testing. Both types of preclinical toxicities are major APF and clinical monitoring is difficult, generally leading to permanent use restrictions.

Constitutive activation of the mitogen-activated protein kinase pathway impairs vitamin D signaling in human prostate epithelial cells

We studied the effect of prolonged activation of mitogen-activated protein kinase (MAPK) signaling on 1,25 dihydroxyvitamin D (1,25(OH)(2)D(3)) action in the immortalized human prostate epithelial cell line RWPE1 and its Ki-Ras transformed clone RWPE2. 1,25(OH)(2)D(3)-treatment caused growth arrest and induced gene expression in both cell lines but the response was blunted in RWPE2 cells. Vitamin D receptor (VDR) levels were lower in RWPE2 cells but VDR over-expression did not increase vitamin-D-mediated gene transcription in either cell line. In contrast, MAPK inhibition restored normal vitamin D transcriptional responses in RWPE2 cells and MAPK activation with constitutively active MEK1R4F reduced vitamin-D-regulated transcription in RWPE1 cells. 1,25(OH)(2)D(3)-mediated transcription depends upon the VDR and its heterodimeric partner the retinoid X receptor (RXR) so we studied whether changes in the VDR-RXR transcription complex occur in response to MAPK activation. Mutation of putative phosphorylation sites in the activation function 1 (AF-1) domain (S32A, T82A) of RXRalpha restored 1,25(OH)(2)D(3)-mediated transactivation in RWPE2 cells. Mammalian two-hybrid and co-immunoprecipitation assays revealed a vitamin-D-independent interaction between steroid receptor co-activator-1 (SRC-1) and RXRalpha that was reduced by MAPK activation and was restored in RWPE2 cells by mutating S32 and T82 in the RXRalpha AF-1 domain. Our data show that a common contributor to cancer development, prolonged activation of MAPK signaling, impairs 1,25(OH)(2)D(3)-mediated transcription in prostate epithelial cells. This is due in part to the phosphorylation of critical amino acids in the RXRalpha AF-1 domain and impaired co-activator recruitment.

Lipopolysaccharide modifies amiloride-sensitive Na+ transport processes across human airway cells: role of mitogen-activated protein kinases ERK 1/2 and 5

Bacterial lipopolysaccharides (LPS) are potent inducers of proinflammatory signaling pathways via the activation of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK), causing changes in the processes that control lung fluid homeostasis and contributing to the pathogenesis of lung disease. In human H441 airway epithelial cells, incubation of cells with 15 µg ml⁻¹ LPS caused a significant reduction in amiloride-sensitive I_sc from 15 ± 2 to 8 ± 2 µA cm⁻² (p = 0.01, n = 13) and a shift in IC₅₀ amiloride of currents from 6.8 × 10⁻⁷ to 6.4 × 10⁻⁶ M. This effect was associated with a decrease in the activity of 5 pS, highly Na⁺ selective, amiloride-sensitive <1 µM channels (HSC) and an increase in the activity of ∼18 pS, nonselective, amiloride-sensitive >10 µM cation channels (NSC) in the apical membrane. LPS decreased αENaC mRNA and protein abundance, inferring that LPS inhibited αENaC gene expression. This correlated with the decrease in HSC activity, indicating that these channels, but not NSCs, were comprised of at least αENaC protein. LPS increased NF-κB DNA binding activity and phosphorylation of extracellular signal-related kinase (ERK)1/2, but decreased phosphorylation of ERK5 in H441 cells. Pretreatment of monolayers with PD98059 (20 µM) inhibited ERK1/2 phosphorylation, promoted phosphorylation of ERK5, increased αENaC protein abundance, and reversed the effect of LPS on I_sc and the shift in amiloride sensitivity. Inhibitors of NF-κB activation were without effect. Taken together, our data indicate that LPS acts via ERK signaling pathways to decrease αENaC transcription, reducing HSC/ENaC channel abundance, activity, and transepithelial Na⁺ transport in H441 airway epithelial cells.

Hypergravity modulates vitamin D receptor target gene mRNA expression in mice

The possibility of pathological calcium metabolism is a critical health concern introduced by long-term space travel. Because vitamin D plays an important role in calcium homeostasis, we evaluated the effects of hypergravity on the expression of genes involved in vitamin D and calcium metabolism in ICR mice. When exposed to 2G hypergravity for 2 days, the mRNA expression of renal 25-hydroxyvitamin D 24-hydroxylase (Cyp24a1) was increased and that of 25-hydroxyvitamin D 1alpha-hydroxylase (Cyp27b1) was decreased. Although hypergravity decreased food intake and increased the expression of starvation-induced genes, the changes in Cyp24a1 and Cyp27b1 expression were not due to starvation, suggesting that hypergravity affects these genes directly. Hypergravity decreased plasma 1alpha,25-dihydroxyvitamin D(3) levels in ICR mice, suggesting a consequence of decreased Cyp27b1 and increased Cyp24a1 expression. Although 1alpha-hydroxyvitamin D(3) [1alpha(OH)D(3)] treatment induced the expression of vitamin D receptor (VDR) target genes in the kidney of 2G-exposed ICR mice to similar levels as controls, 1alpha(OH)D(3) increased the intestinal expression of Cyp24a1 in ICR mice. Hypergravity-dependent changes of Cyp24a1 and Cyp27b1 expression were diminished in mice exposed to hypergravity for 14 days, which may represent an adaptation to hypergravity stress. Hypergravity exposure also increased Cyp24a1 expression in the kidney of C57BL/6J mice. We examined the effects of hypergravity on VDR-null mice and found that renal Cyp27b1 expression in VDR-null mice was decreased by hypergravity while renal Cyp24a1 expression was not detected in VDR-null mice. Thus hypergravity modifies the expression of genes involved in vitamin D metabolism.

Effects of MAPK signaling on 1,25-dihydroxyvitamin D-mediated CYP24 gene expression in the enterocyte-like cell line, Caco-2

We examined the role of the extracellular signal regulated kinases (ERK) in 1,25-dihydroxyvitamin D (1,25(OH)(2)D(3))-induced gene expression in the differentiated Caco-2 cells. 1,25(OH)(2)D(3)-regulated expression of the 25-hydroxyvitamin D, 24-hydroxylase (CYP24) gene (both natural gene and promoter construct) was strongly modulated by altering ERK activity (i.e., reduced by MEK inhibitors and dominant negative (dn) ERK1 and ERK2, activated by epidermal growth factor) but ERK inhibition had no effect on 1,25(OH)(2)D(3)-regulated expression of the transient receptor potential cation channel, subfamily V, member 6 (TRPV6). ERK5-mediated phosphorylation of the transcription factor Ets-1 enhanced 1,25(OH)(2)D(3)-mediated CYP24 gene transcription in proliferating but not differentiated Caco-2 cells due to reduced levels of ERK5 and Ets-1 (total and phosphoprotein levels) in differentiated cells. MEK inhibition reduced 1,25(OH)(2)D(3)-induced 3X-VDRE promoter activity but had no impact on the association of vitamin D receptor (VDR) with chromatin suggesting a role for co-activator recruitment in ERK-modulation of vitamin D-regulated CYP24 gene activation. Chromatin immunoprecipitation assays revealed that the ERK1/2 target, mediator 1 (MED1), is recruited to the CYP24, but not the TRPV6, promoter following 1,25(OH)(2)D(3) treatment. MED1 phosphorylation was sensitive to activators and inhibitors of the ERK1/2 signaling and MED1 siRNA reduced 1,25(OH)(2)D(3)-regulated human CYP24 promoter activity. This suggests ERK1/2 signaling enhances 1,25(OH)(2)D(3) effects on the CYP24 promoter by MED1-mediated events. Our data show that there are both promoter-specific and cell stage-specific roles for the ERK signaling pathway on 1,25(OH)(2)D(3)-mediated gene induction in enterocyte-like Caco-2 cells.

Mechanical stretch regulates the expression of matrix metalloproteinase in rheumatoid arthritis fibroblast-like synoviocytes

Mechanical stretch plays a crucial role in articular joints. In rheumatoid arthritis (RA), it is well known that fibroblast-like synoviocytes (FLS) produce matrix metalloproteinases (MMPs), resulting in local invasion into and degradation of bone and cartilage. We sought to examine whether mechanical stretch regulates the expression and underlying signal pathways of MMP secretion (MMP-1, -3, -13) in RA-FLS. FLS were grown on elastic silicone membrane in an equibiaxial strain apparatus and were exposed to 6% mechanical stretch (equivalent to gentle stretch exercise) for 15 min and 75 min, respectively. Semiquantitative PCR and real-time PCR were used to measure and analyze gene expression. Protein levels were determined by Western blotting. The results showed that 15 min of mechanical stretch inhibited MMP-1 and MMP-13 mRNA and protein level. However, the degree of inhibition by 75 min of stretch in expression of MMP-1 and MMP-13 was lower compared with 15 min stretch groups. The mRNA expression of ERK-1, ets-1 and citied-2 were increased by 6% mechanical stretch under both time points, however c-jun and c-fos mRNA level were affected differently after 15 min and 75 min mechanical stretch compared to control group. There were no significant changes on MMP-3 and ets-2 mRNA level under both 6% mechanical stretch time points. In the presence of pro-inflammatory cytokines (IL-1beta and TNF-alpha), the stretch also reduced the mRNA expression of MMP-1 and MMP-13. In short, our results showed that gentle mechanical strain affects MMP-1 and MMP-13 expression, potentially through the ERK-1-ets-1-cited-2-c-jun signaling pathway.

CYP24 promoter activity is affected by mechanical stress and mitogen-activated protein kinase in MG63 osteoblast-like cells

PURPOSE

For bone homeostasis, vitamin D plays an important role in the regulation of calcium. The enzyme CYP24 inactivates vitamin D and is involved in its regulation. However, the mechanism of expression of CYP24 in osteoblastic cells under mechanical stress is not clear. In this study we investigated CYP24 promoter activity in stretched osteoblastic cells and the participation of mitogen-activated protein kinase (MAPK) in expression of CYP24.

METHODS

MG63 osteoblastic cells were cultured on silicon-bottomed plates. Cells were transfected with a reporter gene that contained a CYP24 promoter. After activated vitamin D, 1,25(OH)2D3, was added or not added, cells were stretched. Stretched and non-stretched cells were investigated by luciferase dual assay. Cells were also investigated similarly using medium with an ERK1/2 inhibitor or p38 inhibitor.

RESULTS

The CYP24 promoter was activated by 1,25(OH)2D3 and the promoter activity decreased in stretched cells. Inhibitor of MAPK decreased CYP24 promoter activity. However, CYP24 promoter activity decreased with mechanical stress after addition of p38 inhibitor, while it did not decrease with mechanical stress after addition of ERK1/2 inhibitor. The CYP24 promoter was not activated without 1,25(OH)2D3 in any case.

CONCLUSION

Mechanical stress and MAPK control CYP24 promoter activity in the presence of Vitamin D in MG63 osteoblast-like cells.

Chronic ethanol consumption leads to disruption of vitamin D3 homeostasis associated with induction of renal 1,25 dihydroxyvitamin D3-24-hydroxylase (CYP24A1)

Bone loss resulting from chronic ethanol (EtOH) abuse is frequently accompanied by altered vitamin D3 homeostasis. In the current study, we examined EtOH effects in a female rat model in which control or EtOH-containing diets were infused intragastrically. EtOH treatment reduced plasma 1,25-dihydroxycholecalciferol (1,25 (OH)2 D3) coincident with a decrease in renal CYP27B1 (25(OH)D3 1alpha-hydroxylase) mRNA and an increase in expression of renal CYP24A1 (1,25 (OH)2 D3- 24-hydroxylase). EtOH induction of CYP24A1 occurred as a result of increased transcription and was also observed in vitro in primary cultures of rat renal proximal tubule cells (RPTCs) and in NRK-52E cells. Synergistic induction of CYP24A1 by EtOH in combination with 1,25 (OH)2 D3 was observed. The major EtOH metabolizing enzymes, alcohol dehydrogenase-1 and CYP2E1, were induced by EtOH in RPTCs. Inhibition of EtOH metabolism by 4-methylpyrazole inhibited the induction of CYP24A1 mRNA. CYP24A1 mRNA induction in RPTCs was also inhibited by the protein synthesis inhibitor cycloheximide. CYP24A1 was also induced after hydrogen peroxide treatment, and EtOH treatment of RPTCs resulted in production of reactive oxygen species as measured by flow cytometry using the fluorescent probe dichlorofluorescin acetate. In addition, inhibition of MAPK signaling pathways with the MAPK kinase inhibitor U0126 or the p38 inhibitor SB203580 inhibited EtOH induction of CYP24A1. Our data suggest that EtOH reduces circulating 1,25 (OH)2 D3 concentrations as the result of CYP24A1 induction that is mediated via MAPK activation resulting from renal oxidative stress produced by local metabolism of EtOH via CYP2E1 and antidiuretic hormone-1.

Antineoplastic agents target the 25-hydroxyvitamin D3 24-hydroxylase messenger RNA for degradation: implications in anticancer activity

Calcitriol or 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] has antitumor activity and hence its levels in patients may play an important role in disease outcome. Here, we report that the antineoplastic agents, daunorubicin hydrochloride, etoposide, and vincristine sulfate inhibited the ability of 1,25(OH)(2)D(3) to cause the accumulation of mRNA for kidney 25-hydroxyvitamin D(3) 24-hydroxylase (CYP24), an enzyme which catabolizes this hormone. This was not due to a drug-induced cytotoxic effect, reduction in the expression of the vitamin D receptor or inhibition of the vitamin D receptor-mediated activation of the mitogen-activated protein kinases or CYP24 promoter activity. Interestingly, there was selective degradation of CYP24 mRNA in the presence of the drugs. This was accompanied by an enhancement in the levels of 1,25(OH)(2)D(3) in cells incubated with 25-hydroxy vitamin D(3). These data identify a novel mechanism of action of some commonly used antineoplastic agents which by decreasing the stability of CYP24 mRNA would prolong the bioavailability of 1,25(OH)(2)D(3) for anticancer actions.

Reshaping the way we view vitamin D signalling and the role of vitamin D in health

Although the biological requirement for vitamin D can be met by epidermal exposure to UV light, there are a number of conditions where this production does not occur or is not sufficient to meet biological needs. When this happens, vitamin D must be consumed and is a nutrient. However, two distinct observations have caused researchers to rethink certain dogma in vitamin D biology. First, it appears that in addition to the hormonally active form of 1,25 dihydroxyvitamin D (1,25(OH)2D), circulating levels of 25 hydroxyvitamin D have a critical importance for optimal human health. This and other data suggest that extra-renal production of 1,25(OH)2D contributes to Ca homeostasis and cancer prevention. Second, in addition to its role in the transcriptional activation of genes through the vitamin D receptor there is now compelling evidence that 1,25(OH)2D has a second molecular mode of action; the rapid activation of second-messenger and kinase pathways. The purpose of this second mode of action is only now being explored. The present review will discuss how these two areas are reshaping our understanding of vitamin D metabolism and action.

Clinical validity of the lung cancer biomarkers identified by bioinformatics analysis of public expression data

Identification of molecular markers often leads to important clinical applications such as early diagnosis, prognosis, and drug targeting. Lung cancer, the leading cause of cancer-related deaths, still lacks reliable molecular markers. We have combined the bioinformatics analysis of the public gene expression data and clinical validation to identify biomarker genes for non-small-cell lung cancer. The serial analysis of gene expression and the expressed sequence tag data were meta-analyzed to produce a list of the differentially expressed genes in lung cancer. Through careful inspection of the predicted genes, we selected 20 genes for experimental validation using semiquantitative reverse transcriptase-PCR. The microdissected clinical specimens used in the study consisted of three groups: lung tissues from benign diseases and the paired (cancer and pathologic normal) tissues from non-small-cell lung cancer patients. After extensive statistical analyses, seven genes (CBLC, CYP24A1, ALDH3A1, AKR1B10, S100P, PLUNC, and LOC147166) were identified as potential diagnostic markers. Quantitative real-time PCR was carried out to additionally assess the value of the seven identified genes leading to the confirmation of at least two genes (CBLC and CYP24A1) as highly probable novel biomarkers. The gene properties of the identified markers, especially their relationship to lung cancer and cell signaling pathway regulation, further suggest their potential value as drug targets as well.

MAP kinases and the control of nuclear events

The mitogen-activated protein kinases (MAPKs) are a family of serine/threonine kinases that play an essential role in signal transduction by modulating gene transcription in the nucleus in response to changes in the cellular environment. They include the extracellular signal-regulated protein kinases (ERK1 and ERK2); c-Jun N-terminal kinases (JNK1, JNK2, JNK3); p38s (p38alpha, p38beta, p38gamma, p38delta) and ERK5. The molecular events in which MAPKs function can be separated in discrete and yet interrelated steps: activation of the MAPK by their upstream kinases, changes in the subcellular localization of MAPKs, and recognition, binding and phosphorylation of MAPK downstream targets. The resulting pattern of gene expression will ultimately depend on the integration of the combinatorial signals provided by the temporal activation of each group of MAPKs. This review will focus on how the specificity of signal transmission by MAPKs is achieved by scaffolding molecules and by the presence of structural motifs in MAPKs that are dynamically regulated by phosphorylation and protein-protein interactions. We discuss also how MAPKs recognize and phosphorylate their target nuclear proteins, including transcription factors, co-activators and repressors and chromatin-remodeling molecules, thereby affecting an intricate balance of nuclear regulatory molecules that ultimately control gene expression in response to environmental cues.