Immunocytology with microwave-fixed fibroblasts shows 1 alpha,25-dihydroxyvitamin D3-dependent rapid and estrogen-dependent slow reorganization of vitamin D receptors

Phosphorylation of Human Retinoid X Receptor α at Serine 260 Impairs Its Subcellular Localization, Receptor Interaction, Nuclear Mobility, and 1α,25-Dihydroxyvitamin D3-dependent DNA Binding in Ras-transformed Keratinocytes

Human retinoid X receptor α (hRXRα) plays a critical role in DNA binding and transcriptional activity through heterodimeric association with several members of the nuclear receptor superfamily, including the human vitamin D receptor (hVDR). We previously showed that hRXRα phosphorylation at serine 260 through the Ras-Raf-MAPK ERK1/2 activation is responsible for resistance to the growth inhibitory effects of 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3), the biologically active metabolite of vitamin D3 To further investigate the mechanism of this resistance, we studied intranuclear dynamics of hVDR and hRXRα-tagged constructs in living cells together with endogenous and tagged protein in fixed cells. We find that hVDR-, hRXRα-, and hVDR-hRXRα complex accumulate in the nucleus in 1α,25(OH)2D3-treated HPK1A cells but to a lesser extent in HPK1ARas-treated cells. Also, by using fluorescence resonance energy transfer (FRET), we demonstrate increased interaction of the hVDR-hRXRα complex in 1α,25(OH)2D3-treated HPK1A but not HPK1ARas cells. In HPK1ARas cells, 1α,25(OH)2D3-induced nuclear localization and interaction of hRXRα are restored when cells are treated with the MEK1/2 inhibitor UO126 or following transfection of the non-phosphorylatable hRXRα Ala-260 mutant. Finally, we demonstrate using fluorescence loss in photobleaching and quantitative co-localization with chromatin that RXR immobilization and co-localization with chromatin are significantly increased in 1α,25(OH)2D3-treated HPK1ARas cells transfected with the non-phosphorylatable hRXRα Ala-260 mutant. This suggests that hRXRα phosphorylation significantly disrupts its nuclear localization, interaction with VDR, intra-nuclear trafficking, and binding to chromatin of the hVDR-hRXR complex.

Actin and Keratin are Binding Partners of the 1,25D3-MARRS Receptor/PDIA3/ERp57

We have shown that the 1,25D₃-MARRS receptor is necessary for the rapid, pre-genomic effects of 1,25(OH)₂D₃ on phosphate and/or calcium absorption in chick intestines. However, a clear understanding of the proteins involved in the signaling mechanisms by which the 1,25D₃-MARRS receptor facilitates 1,25(OH)₂D₃-mediated phosphate or calcium uptake, as well as other cellular effects, is still under investigation. We used co-immunoprecipitation studies and mass spectroscopy to identify actin and keratin as proteins that interact with the 1,25D₃-MARRS receptor. Using confocal microscopy, we visualized 1,25(OH)₂D₃- MARRS receptor localizations relative to actin and/or keratin distribution in chick enterocytes. Cells cultured in media containing phenol red had the 1,25D₃-MARRS receptor and actin localized largely in the nucleus, which was dispersed upon addition of (OH)₂ 1,25(OH)₂D₃. In the absence of phenol red, staining was cytoplasmic. Addition of steroid caused diminished staining at 10 s and 30 s, with a return of intensity between 1 and 5 min. Nuclear staining was observed after 1 min. We found that F-actin concentrations are maximal when 1,25D₃-MARRS receptor localizations within enterocytes are low suggesting that cyclical conversions of F-actin to G-actin are involved in the 1,25(OH)₂D₃-mediated redistribution of the 1,25D₃-MARRS receptor within the cell. We also found that keratin distribution remains constant with 1,25(OH)₂D₃ exposure when Factin depolymerizes into G-actin, which suggests that actin and keratin work in concert to facilitate hormonemediated redistribution of the 1,25D₃-MARRS receptor. We subsequently investigated whether the cyclical redistribution was related to either 1,25(OH)₂D₃-stimulated phosphate or calcium uptake, but no congruent pattern was found.

Inhibition of Methicillin-resistant Staphylococcus aureus-induced cytokines mRNA production in human bone marrow derived mesenchymal stem cells by 1,25-dihydroxyvitamin D3

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is the predominant cause of bone infection. Toll like receptors (TLRs) are an important segments of host response to infection and are expressed by a variety of cells including human mesenchymal stem cells (hMSCs). The active form of Vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)₂D₃) has potent immunoregulatory properties, but the mechanism remains poorly understood. The genomic action of 1,25(OH)₂D₃ is mediated by vitamin D receptor (VDR), hormone-regulated transcription factor. VDR interacts with co-activators and co-repressors are associated with chromatin histone modifications and transcriptional regulation. The aim of our study is to explore MRSA-induced TLRs-mediated pro-inflammatory cytokines expression in hMSCs. Further, we hypothesized that 1,25(OH)₂D₃ inhibits MRSA-induced cytokines synthesis in hMSCs via inhibition of NF-кB transcription factor. Finally, we explored the regulatory role of 1,25(OH)₂D₃ in MRSA-mediated global epigenetic histone H3 mark, such as, trimethylated histone H3 lysine 9 (H3K9me3), which is linked to gene silencing.

Results

Quantitative PCR data revealed that MRSA-infection predominantly induced expression of TLRs 1, 2, 6, NR4A2, and inflammatory cytokines IL-8, IL-6, TNFα in hMSCs. MRSA-mediated TLR ligands reduced osteoblast differentiation and increased hMSCs proliferation, indicating the disrupted multipotency function of hMSCs. Pretreatment of 1,25(OH)₂D₃ followed by MRSA co-culture inhibited nuclear translocation of NF-кB-p65, reduced expression of NR4A2 and pro-inflammatory cytokines IL-8, IL-6, and TNFα in hMSCs. Further, NF-κB-p65, VDR, and NR4A2 were present in the same nuclear protein complex, indicating that VDR is an active part of the nuclear protein complexes for transcriptional regulation. Finally, 1,25(OH)₂D₃ activated VDR, restores the global level of H3K9me3, to repress MRSA-stimulated inflammatory cytokine IL-8 expression. Pretreatment of 5-dAZA, DNA methylatransferases (Dnmts) inhibitor, dramatically re-expresses 1,25(OH)₂D₃-MRSA-mediated silenced IL-8 gene.

Conclusions

This data indicates that TLR 1, 2, and 6 can be used as markers for localized S. aureus bone infection. 1,25(OH)₂D₃-VDR may exhibits its anti-inflammatory properties in MRSA-stimulated infection by inhibiting nuclear translocation of NF-kB-p65 and transcripts of IL-8, IL-6, TNFα, and NR4A2 in hMSCs. Finally, 1,25(OH)₂D₃-activated VDR, acting as an epigenetic regulator, inhibits synthesis of cytokines in MRSA-stimulated infection by restoring the global level of H3K9me3, a histone H3 mark for gene silencing.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Where is the vitamin D receptor?

The vitamin D receptor (VDR) is a member of the nuclear receptor superfamily and plays a central role in the biological actions of vitamin D. VDR regulates the expression of numerous genes involved in calcium/phosphate homeostasis, cellular proliferation and differentiation, and immune response, largely in a ligand-dependent manner. To understand the global function of the vitamin D system in physiopathological processes, great effort has been devoted to the detection of VDR in various tissues and cells, many of which have been identified as vitamin D targets. This review focuses on the tissue- and cell type-specific distribution of VDR throughout the body.

Vitamin D and cancer: a review of molecular mechanisms

The population-based association between low vitamin D status and increased cancer risk can be inconsistent, but it is now generally accepted. These relationships link low serum 25OHD (25-hydroxyvitamin D) levels to cancer, whereas cell-based studies show that the metabolite 1,25(OH)2D (1,25-dihydroxyvitamin D) is a biologically active metabolite that works through vitamin D receptor to regulate gene transcription. In the present review we discuss the literature relevant to the molecular events that may account for the beneficial impact of vitamin D on cancer prevention or treatment. These data show that although vitamin D-induced growth arrest and apoptosis of tumour cells or their non-neoplastic progenitors are plausible mechanisms, other chemoprotective mechanisms are also worthy of consideration. These alternative mechanisms include enhancing DNA repair, antioxidant protection and immunomodulation. In addition, other cell targets, such as the stromal cells, endothelial cells and cells of the immune system, may be regulated by 1,25(OH)2D and contribute to vitamin D-mediated cancer prevention.

Identification of the vitamin D receptor in various cells of the mouse kidney

The kidney is the major, if not sole, site for the production of 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), the biologically active form of vitamin D that can stimulate calcium reabsorption in the kidney and may provide renoprotective benefits. The biological effects of 1,25(OH)₂D₃ are mediated through a nuclear hormone receptor, known as the vitamin D receptor (VDR). It is well accepted that the VDR is present in the distal renal convoluted tubule cells; however, whether VDR is present in other kidney cell types is uncertain. Using a highly specific and sensitive anti-VDR antibody, we determined its distribution in the mouse kidney by immunohistochemistry. Our results show that the VDR is not only present in the distal but is also found in the proximal tubules, but at 24-fold lower levels. The VDR was also found in the macula densa of the juxtaglomerular apparatus, glomerular parietal epithelial cells, and podocytes. In contrast, the VDR is either very low or absent in interstitial fibroblasts, glomerular mesangial cells, and juxtaglomerular cells. Thus, identification of VDR in the proximal tubule, macula densa, and podocytes suggests that 1,25(OH)₂D₃ plays a direct role in these cells under normal conditions.

Sciatic nerve crush evokes a biphasic TGF-beta and decorin modulation in the rat spinal cord

BACKGROUND AND AIM

Inherent property of the motoneurons of the peripheral nervous system is their ability to recover, at least in part, upon injury. To this end different factors are expressed and are thought to play important role in the regeneration processes. These factors are diverse, and range from transcription factors and chemokines, to molecules of the extracellular matrix. Transforming growth factor beta (TGF-beta) is a protein with diverse actions controlling cell growth and proliferation. In the extracellular matrix it is found bound to decorin a proteoglycan involved in cell adhesion and cell signaling. In the present study we investigate the expression of TGF-beta and decorin at different time points, in the regenerating sciatic nerve of a seven day old rat, having suffered nerve crush injury, over a period of one month.

MATERIALS AND METHODS

To achieve this, we evoked injury to male Wistar rats by exposing and applying pressure to the sciatic nerve using watchmaker's forceps. After that at 12 h, 24 h, 48 h, 72 h, one week, and one month intervals we investigated the gene expression of decorin using RT-PCR, and followed the expression of TGF-beta molecule by immunohistochemistry in frozen sections of the L4-L5 region of the rat spinal cord.

RESULTS

We report that both decorin mRNA and TGF- protein exhibit a concerted, biphasic expression after 12 hours and one month having the animal suffered the nerve crush.

DISCUSSION

Our data reveal a biphasic modulation of TGF-beta protein and decorin mRNA expression at lumbar segment of the spinal cord of animals having suffered unilateral sciatic nerve crush. We postulate that their concerted expression both at an early and a late phase after the nerve injury is of importance and can be part of a repair or neuroprotective mechanism as yet unclarified.

Identification of a highly specific and versatile vitamin D receptor antibody

The active form of vitamin D, 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) is critical for regulation of serum calcium and phosphorus levels and for proper maintenance of bone mineralization and neuromuscular function. Biological effects of 1,25(OH)2D3 are mediated through a nuclear steroid hormone receptor, known as the vitamin D receptor (VDR). The discovery of VDR in a number of different cell and tissue types, suggests that the physiological role of vitamin D may extend beyond the regulation of calcium homeostasis and bone function. Unfortunately, identification of tissues expressing VDR has been controversial due to low abundance of the receptor and quality of the antibodies used. Therefore, we elected to characterize a panel of commercially available VDR antibodies in order to identify antibodies with high specificity and sensitivity. To address these objectives, we have used multiple immunoassays to determine VDR expression in tissues from several organs from multiple species employing tissues from VDR knockout mice as critical negative controls. Many of the antibodies tested showed nonspecific binding that can account for divergent reports. However, one antibody, identified as D-6, is highly specific and extremely sensitive. The specificity, sensitivity, and versatility of this antibody make it the preferred antibody for identifying VDR expression in target tissues using immunological methods.

Molecular actions of vitamin D contributing to cancer prevention

The population-based relationship between low vitamin D status and increased cancer risk is now generally accepted. While these relationships are between serum 25 hydroxyvitamin D and cancer, cell-based studies show that the metabolite 1,25 dihydroxyvitamin D is biologically active and influences cell biology relevant to cancer through vitamin D receptor-mediated gene transcription. This review examines this paradox and also discusses the cell and gene targets influenced by 1,25 dihydroxyvitamin D that may account for the anti-cancer actions of vitamin D. A review of the literature shows that while vitamin D-induced growth arrest and apoptosis of tumor cells or their non-neoplastic progenitors are plausible mechanisms, other gene targets related to DNA repair and immunomodulation, and other cell targets such as the stromal cells and cells of the immune system, may be regulated by 1,25 dihydroxyvitamin D and contribute to vitamin D mediated cancer prevention.

Nucleo-cytoplasmic cycling of the vitamin D receptor in the enterocyte-like cell line, Caco-2

We examined the effects of 1,25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) on the distribution and mobility of the vitamin D receptor (VDR) in the enterocyte-like Caco-2 cell. Confocal microscopy showed that a green fluorescent protein-vitamin D receptor (GFP-VDR) fusion protein is predominantly nuclear (58%) and it does not associate with the apical or basolateral membrane of proliferating or polarized, differentiated cells. In contrast to the previously studied cell types, neither endogenous VDR nor GFP-VDR levels accumulate in the nucleus following 1,25(OH)(2)D(3) treatment (100 nM, 30 min). However, in nuclear photobleaching experiments nuclear GFP-VDR import was significantly increased by 1,25(OH)(2)D(3) during both an early (0-5 min) and later (30-35 min) period (20% per 5 min). Compared to the natural ligand, nuclear import of GFP-VDR was 60% lower in cells treated with the 1,25(OH)(2)D(3) analog, 1-alpha-fluoro-16-ene-20-epi-23-ene-26,27-bishomo-25-hydroxyvitamin D(3) (Ro-26-9228, 5 min, 100 nM). Downstream events like ligand-induced association of VDR with chromatin at 1 h and the accumulation of CYP24 mRNA were significantly lower in Ro-26-9228 treated cells compared to 1,25(OH)(2)D(3) (60 and 95% lower, respectively). Collectively our data are consistent with a role for ligand-induced nuclear VDR import in receptor activation. In addition, ligand-dependent VDR nuclear import appears to be balanced by export, thus accounting for the lack of nuclear VDR accumulation even when VDR import is significantly elevated.

Regulation of human epidermal keratinocyte differentiation by the vitamin D receptor and its coactivators DRIP205, SRC2, and SRC3

It has long been known that the active metabolite of vitamin D, 1,25 dihydroxyvitamin D(3), stimulates differentiation and inhibits proliferation in epidermal keratinocytes through interaction with the vitamin D receptor (VDR). VDR functions through the coordinate binding of vitamin D response elements in the DNA and specific coactivator proteins which help to initiate transcription. It was recently observed that VDR binds to two major coactivator complexes, DRIP (VDR-interacting protein) and SRC (steroid receptor coactivator), during keratinocyte differentiation. To determine the role of VDR and its coactivators in mediating keratinocyte differentiation, we developed an adenoviral system to knock down, or in the case of VDR, overexpress these genes. In order to study all stages of keratinocyte development, we employed an advanced differentiated normal human keratinocyte culture system that produces a multilayer phenotype similar to that of normal skin. These studies have shown that VDR, DRIP, and SRC are all required for promotion of both early and late keratinocyte differentiation. Additionally, each individual differentiation marker that was assayed has a different specificity for the coactivators that regulate its expression.

Noncalcemic actions of vitamin D receptor ligands

1alpha,25-Dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], the active metabolite of vitamin D(3), is known for the maintenance of mineral homeostasis and normal skeletal architecture. However, apart from these traditional calcium-related actions, 1,25-(OH)(2)D(3) and its synthetic analogs are being increasingly recognized for their potent antiproliferative, prodifferentiative, and immunomodulatory activities. These actions of 1,25-(OH)(2)D(3) are mediated through vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. Physiological and pharmacological actions of 1,25-(OH)(2)D(3) in various systems, along with the detection of VDR in target cells, have indicated potential therapeutic applications of VDR ligands in inflammation (rheumatoid arthritis, psoriatic arthritis), dermatological indications (psoriasis, actinic keratosis, seborrheic dermatitis, photoaging), osteoporosis (postmenopausal and steroid-induced osteoporosis), cancers (prostate, colon, breast, myelodysplasia, leukemia, head and neck squamous cell carcinoma, and basal cell carcinoma), secondary hyperparathyroidism, and autoimmune diseases (systemic lupus erythematosus, type I diabetes, multiple sclerosis, and organ transplantation). As a result, VDR ligands have been developed for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. Furthermore, encouraging results have been obtained with VDR ligands in clinical trials of prostate cancer and hepatocellular carcinoma. This review deals with the molecular aspects of noncalcemic actions of vitamin D analogs that account for the efficacy of VDR ligands in the above-mentioned indications.

Analysis of the vitamin D system in basal cell carcinomas (BCCs)

Using real-time PCR (LightCycler) and immunohistochemistry, we have analyzed expression of key components of the vitamin D system in basal cell carcinomas (BCCs) and normal human skin (NS). Increased VDR-immunoreactivity was demonstrated in BCCs using a streptavidin-peroxidase technique. RNA expression of vitamin D receptor (VDR) and of main enzymes involved in synthesis and metabolism of calcitriol (vitamin D-25-hydroxylase [25-OHase], 25-hydroxyvitamin D-1alpha-hydroxylase [1alpha-OHase], 1,25-dihydroxyvitamin D-24-hydroxylase [24-OHase]) was detected in BCCs and NS. Expression levels were determined as ratios between target genes (VDR, 1alpha-OHase, 25-OHase, 24-OHase) and the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as internal control. Median of mRNA ratios for VDR/GAPDH (BCCs: 16.54; NS: 0.00021), 1alpha-OHase/GAPDH (BCCs: 0.739; NS 0.000803) and 24-OHase/GAPDH (BCCs: 0.00585; NS 0.000000366) was significantly (Wilcoxon-Mann-Whitney U-test) elevated in BCCs. In contrast, median of mRNA ratio for 25-OHase/GAPDH (BCCs: 0.17; NS: 0.016) was not significantly altered in BCCs as compared to NS. Additionally, we report for the first time expression of 1alpha-OHase splice variants in BCCs and NS, that were detected using conventional RT-PCR. In conclusion, our findings provide supportive evidence for the concept that endogeneous synthesis and metabolism of vitamin D metabolites as well as VDR expression may regulate growth characteristics of BCCs. New vitamin D analogs that exert little calcemic side effects, their precursors, or inhibitors of 24-OHase may offer a new approach for the prevention or therapy of BCCs. The function of alternative transcripts of 1alpha-OHase that we describe here for the first time in BCCs and NS and their effect on activity level has to be investigated in future experiments.

Vitamin D receptor and retinoid X receptor interactions in motion

Vitamin D receptor (VDR) and retinoid X receptor (RXR) are members of the nuclear receptor superfamily and they bind target DNA sequences as heterodimers to regulate transcription. This article surveys the latest findings regarding the roles of dimerizing RXR in VDR function and emphasizes potential areas for future developments. We first highlight the importance of dimerization with RXR for both the ligand-independent (hair growth) and ligand-dependent functions of VDR (calcium homeostasis, bone development and mineralization, control of cell growth and differentiation). Emerging information regarding the regulatory control of dimerization based on biochemical, structural, and genetic studies is then presented. Finally, the main focus of this article is a new dynamic perspective of dimerization functions, based on recent research with fluorescent protein chimeras in living cells by microscopy. These studies revealed that both VDR and RXR constantly shuttle between the cytoplasm and the nucleus and between subnuclear compartments, and showed the transient nature of receptor--DNA and receptor--coregulator interactions. Because RXR dimerizes with most of the nuclear receptors, regulation of receptor dynamics by RXR has a broad significance.

Retinoid X receptor dominates the nuclear import and export of the unliganded vitamin D receptor

Liganded and unliganded vitamin D receptors (VDRs) carry out distinct functions; both types of functions require heterodimerization with retinoid X receptors (RXRs). Our recent studies with fluorescent protein chimeras of VDR and RXR, termed GFP-VDR, YFP-RXR, and RXR-BFP, indicated that RXR regulates VDR functions in part by regulating subcellular localization. Here we explored the mechanisms of this regulation. Photobleaching experiments demonstrated that YFP-RXR and both unliganded and liganded GFP-VDR shuttle constantly between nucleus and cytoplasm. To characterize RXR import, we identified a nuclear localization sequence (NLS) in the DNA-binding domain. Mutations in this NLS caused predominant cytoplasmic localization of nlsYFP-RXR and prevented transcriptional activity. The nlsRXR-BFP retained unliganded GFP-VDR in the cytoplasm and reduced baseline transcriptional activity. After calcitriol exposure, however, both GFP-VDR and nlsRXR-BFP entered the nucleus. We characterized receptor export rates and mechanisms using permeabilization experiments. Mutations in the calreticulin binding region slowed both GFP-VDR and YFP-RXR export. Coexpression of RXR-BFP slowed the export of unliganded GFP-VDR, whereas calcitriol treatment tripled the rate of GFP-VDR export. Treatment with leptomycin B, an inhibitor of CRM-1 receptor-mediated export, inhibited export of unliganded GFP-VDR but did not influence export of liganded GFP-VDR or YFP-RXR. Leptomycin B added before calcitriol similarly decreased hormone-induced luciferase activity but was ineffective when added subsequent to calcitriol. These results indicate that the unliganded and liganded VDR interact differently with the import and export receptors and with RXR. Most likely, the regulation of VDR nuclear import by RXR is essential for ligand-independent functions.

Androgen receptor (AR) coregulators: an overview

The biological action of androgens is mediated through the androgen receptor (AR). Androgen-bound AR functions as a transcription factor to regulate genes involved in an array of physiological processes, most notably male sexual differentiation and maturation, and the maintenance of spermatogenesis. The transcriptional activity of AR is affected by coregulators that influence a number of functional properties of AR, including ligand selectivity and DNA binding capacity. As the promoter of target genes, coregulators participate in DNA modification, either directly through modification of histones or indirectly by the recruitment of chromatin-modifying complexes, as well as functioning in the recruitment of the basal transcriptional machinery. Aberrant coregulator activity due to mutation or altered expression levels may be a contributing factor in the progression of diseases related to AR activity, such as prostate cancer. AR demonstrates distinct differences in its interaction with coregulators from other steroid receptors due to differences in the functional interaction between AR domains, possibly resulting in alterations in the dynamic interactions between coregulator complexes.

Stat1-vitamin D receptor interactions antagonize 1,25-dihydroxyvitamin D transcriptional activity and enhance stat1-mediated transcription

The cytokine gamma interferon (IFN-gamma) and the calcitropic steroid hormone 1,25-dihydroxyvitamin D (1,25D) are activators of macrophage immune function. In sarcoidosis, tuberculosis, and several granulomatoses, IFN-gamma induces 1,25D synthesis by macrophages and inhibits 1,25D induction of 24-hydroxylase, a key enzyme in 1,25D inactivation, causing high levels of 1,25D in serum and hypercalcemia. This study delineates IFN-gamma-1,25D cross talk in human monocytes-macrophages. Nuclear accumulation of Stat1 and vitamin D receptor (VDR) by IFN-gamma and 1,25D promotes protein-protein interactions between Stat1 and the DNA binding domain of the VDR. This prevents VDR-retinoid X receptor (RXR) binding to the vitamin D-responsive element, thus diverting the VDR from its normal genomic target on the 24-hydroxylase promoter and antagonizing 1,25D-VDR transactivation of this gene. In contrast, 1,25D enhances IFN-gamma action. Stat1-VDR interactions, by preventing Stat1 deactivation by tyrosine dephosphorylation, cooperate with IFN-gamma/Stat1-induced transcription. This novel 1,25D-IFN-gamma cross talk explains the pathogenesis of abnormal 1,25D homeostasis in granulomatous processes and provides new insights into 1,25D immunomodulatory properties.

Role of chaperones in nuclear translocation and transactivation of steroid receptors

Molecular chaperones assist proteins to reach their mature and functional conformation. It has become apparent in recent years that chaperones function as part of a multiprotein heterocomplex that is potentially involved not only in protein folding, but also in intracellular trafficking and in targeting proteins for degradation. In the case of steroid receptors, the activity of the chaperone heterocomplex, as well as the proteins comprising the heterocomplex, has an effect on the observed ligand-dependent transcriptional activity of the receptor. The direct interaction between chaperones and steroid receptors makes them potential therapeutic targets in a number of pathologic conditions. In the case of cancers with steroid receptor involvement, such as breast and prostate cancer, the inhibition of chaperone activity may inhibit tumor cell growth. Conversely, enhancement of chaperone activity may be beneficial in disorders of protein misfolding, as in the case of androgen receptor aggregates found in Spinal and Bulbar Muscular Atrophy.

Immunoreactivity of six monoclonal antibodies directed against 1,25-dihydroxyvitamin-D3 receptors in human skin

Using confocal laser scanning microscopy, we tested the suitability of five monoclonal mouse antibodies (IVA7E7, IVB12G12, IVG9C11, VD2F12, and VIIID8C12) that had been raised against different domains of the porcine intestinal 1,25-dihydroxyvitamin-D3 receptor (VDR), for the immunohistological detection of VDR in human skin. The VDR immunoreactivity of these antibodies was compared with the well-characterized VDR-staining pattern of the mouse monoclonal antibody 9A7gamma raised against chick intestinal VDR. All six antibodies revealed strong nuclear and qualitatively similar immunoreactivity in all cell layers of the viable epidermis. Our data demonstrate that the five mouse monoclonal antibodies are suitable for immunohistochemical detection of VDR in frozen sections. These antibodies show comparable staining patterns in human skin even though they had been raised against different functional domains of the 1,25-dihydroxyvitamin-D3 receptor.

A model for the cytoplasmic trafficking of signalling proteins involving the hsp90-binding immunophilins and p50cdc37

A number of transcription factors and protein kinases involved in signal transduction exist in heterocomplexes with the ubiquitous and essential protein chaperone hsp90. These signalling protein x hsp90 heterocomplexes are assembled by a multiprotein chaperone system comprising hsp90, hsp70, Hop, hsp40, and p23. In the case of transcription factors, the heterocomplexes with hsp90 also contain a high molecular weight immunophilin with tetratricopeptide repeat (TPR) motifs, such as FKBP52 or CyP-40. In the case of the protein kinases, the heterocomplexes contain p50cdc37. The immunophilins bind to a single TPR acceptor site on hsp90, and p50cdc37 binds to an adjacent site so that binding is exclusive for p50cdc37 or an immunophilin. Direct interaction of immunophilins with the transcription factors or p50cdc37 with the protein kinases leads to selection of different heterocomplexes after their assembly by a common mechanism. Studies with the glucocorticoid receptor, for which translocation from the cytoplasm to the nucleus is under hormonal control, suggest that dynamic assembly of the heterocomplexes is required for rapid movement of the receptor through the cytoplasm along cytoskeletal tracts. As for the similar short-range trafficking of vesicles along microtubules, there must be a mechanism for linking the signalling protein solutes to the molecular motors involved in movement. We present here a model in which the immunophilins and p50cdc37 target, respectively, the retrograde or anterograde direction of signalling protein movement by functioning as connectors that link the signalling proteins to the movement machinery.

Identification of amino acid sequence in the hinge region of human vitamin D receptor that transfers a cytosolic protein to the nucleus

The localization of human vitamin D receptor (VDR) in the absence of its ligand 1,25-dihydroxyvitamin D(3) was investigated using chimera proteins fused to green fluorescent protein (GFP) at either the N or C terminus, and the nuclear localization signal (NLS) was identified. Plasmids carrying the fusion proteins were transiently or stably introduced into COS7 cells, and the subcellular distribution of the fusion proteins was examined. GFP-tagged wild-type VDRs were located predominantly in nuclei but with a significant cytoplasmic presence, while GFP alone was equally distributed throughout the cells. 10(-8) M 1,25-dihydroxyvitamin D(3) promoted the nuclear import of VDR in a few hours. To identify the NLS, we constructed several mutated VDRs fused to GFP. Mutant VDRs that did not bind to DNA were also localized predominantly in nuclei, while the deletion of the hinge region resulted in the loss of preference for nucleus. A short segment of 20 amino acids in the hinge region enabled cytoplasmic GFP-tagged alkaline phosphatase to translocate to nuclei. These results indicate that 1) VDR is located predominantly in nuclei with a significant presence in cytoplasm without the ligand and 2) an NLS consisting of 20 amino acids in the hinge region facilitates the transfer of VDR to the nucleus.

Monoclonal anti-androgen receptor antibodies: production, characterization and potential diagnostic applications

Several monoclonal antibodies (mAbs) and novel mAb-based assays for the androgen receptors (AR) have been developed. Large amounts of the recombinant human AR protein produced by a baculovirus expression system were used as an antigen to produce mAbs. Twenty-nine AR-specific mAbs were first confirmed by Western blot analysis and were then characterized for their immunoglobulin isotypes, epitopes, and epitope localization in AR. Novel assays using flow cytometry and sandwich enzyme-linked immunosorbent assays (ELISA) were established to detect AR-expressing cells and to quantify soluble AR protein, respectively. Using immunostaining, we identified several anti-AR mAbs exclusively recognizing AR within the nuclei of the prostate cancer cell line LNCaP and of prostate tissues in both frozen and paraffin-embedded sections, whereas other mAbs could detect AR in both nuclear and cytoplasmic compartments. Interestingly, certain mAbs, such as G122-25 and G122-77, could distinguish the androgen-bound AR from the unoccupied AR. In sum, many purified AR protein and anti-AR mAbs, together with the assays developed, could be powerful tools for the study of functional AR and for the diagnosis of prostatic cancers.

Analysis of 1,25-dihydroxyvitamin D(3) receptors (VDR) in basal cell carcinomas

We have analyzed expression of 1,25-dihydroxyvitamin D(3) receptor (VDR) protein and mRNA in basal cell carcinomas (BCC) of human skin. VDR immunoreactivity in BCCs was compared with the staining pattern of the proliferation marker Ki-67 in the same tumors. Additionally, VDR staining was compared to staining pattern of apoptotic cells by terminal UTP nucleotide end labeling assay. Frozen sections of superficial type, nodular type, and fibrosing type BCCs were consistently immunoreactive for VDR (mAb 9A7gamma) with almost every tumor cell labeled (n = 15). In general, VDR staining was pronounced in peripheral tumor cells. VDR immunoreactivity was consistently stronger in tumor cells than in adjacent or unaffected epidermis. No visual correlation was found in BCCs comparing labeling patterns of Ki-67-positive or apoptotic cells and mAb 9A7gamma. VDR mRNA was increased in BCCs (n = 6) compared to normal human skin (n = 5), as revealed by reverse transcription-polymerase chain reaction analysis. Our findings indicate that VDR is strongly expressed in BCCs and may be involved in the growth regulation of this tumour, and VDR mRNA and protein are increased in BCCs as compared to normal human epidermis.

Hormone-dependent translocation of vitamin D receptors is linked to transactivation

Vitamin D receptor (VDR) acts as a transcription factor mediating genomic actions of calcitriol. Our earlier studies suggested that calcitriol induces translocation of cytoplasmic VDR, but the physiologic relevance of this finding remained uncertain. Previous studies demonstrated that the activation function 2 domain (AF-2) plays an essential role in VDR transactivation. To elucidate hormone-dependent VDR translocation and its role, we constructed green fluorescent protein (GFP) chimeras with full-length VDR (VDR-GFP), AF-2-truncated VDR (AF-2del-VDR-GFP), and ligand-binding domain (LBD)-truncated VDR (LBDdel-VDR-GFP). COS-7 cells were transiently transfected with these constructs. Western blot analysis, fluorescent microscopy, and transactivation assays showed that the generated chimeras are expressed and fluoresce and that VDR-GFP is transcriptionally active. After hormone treatment, cytoplasmic VDR-GFP translocated to the nucleus in a concentration-, time-, temperature-, and analog-specific manner. Hormone dose-response relationships for translocation and for transactivation were similar. Truncation of LBD and truncation of AF-2 each abolished hormone-dependent translocation and transactivation. Our data confirm a hormone-dependent VDR translocation, demonstrate that an intact AF-2 domain is required for this translocation, and indicate that translocation is part of the receptor activation process.

Estrogen regulation of intestinal calcium absorption in the intact and ovariectomized adult rat

Studies were carried out to examine the mechanism of action of estrogen on intestinal calcium absorption in the rat. Three-month-old Wistar rats were sham-operated or ovariectomized (OVX). They were fed a diet containing 0.4% Ca, 0.4% P, and 2000 IU vitamin D3/kg. Eight weeks after operation, both OVX and sham-operated rats were randomly assigned to eight treatment groups. Five groups received per 100 g of body weight 12.5 ng calcitriol (1, 25-dihydroxyvitamin D3); 7.5 microg of estradiol-benzoate; 7.5 microg of estradiol-benzoate and 0.1 mg of ICI 182780; 12.5 ng of calcitriol and 0.1 mg of ICI 182780; and 0.1 mg of ICI 182780, respectively. Three groups received the various vehicles used. Intestinal calcium absorption was measured in vivo using single pass perfusion of the duodenum. OVX did not change intestinal calcium absorption. A pharmacological dose of estradiol-benzoate caused a significant increase in intestinal absorption of calcium, which was comparable to that of a pharmacological dose of calcitriol in both OVX and sham-operated rats. Estrogen-induced rise in intestinal calcium absorption was completely blocked to basal level by the pure estrogen receptor (ER) antagonist ICI 182780. In contrast, ICI 182780 did not antagonize calcitriol-enhanced intestinal calcium absorption. Our findings suggest that estrogen stimulates intestinal calcium absorption via an ER.

Direct non-genomic effect of steroid hormones on superoxide anion generation in the bone resorbing osteoclasts

We have investigated the possible acute effect of steroid hormones, including 1alpha,25 dihydroxycholecalciferol (1alpha,25(OH)2D3) and estradiol, on the generation of superoxide anion (O2*-) in bone resorbing osteoclasts. Evidence is presented demonstrating acute non-genomic stimulatory action of 1alpha,25(OH)2D3 on the production of free radicals by rat osteoclasts cultured on calcified matrix. The increase in O2*- production was observed in the range of 6-10 s (n = 5) following exposure of enriched osteoclasts to 1alpha,25(OH)2D3 and was found to be transient with the peak response being in the range of 5-45 s (n = 5). The decline in the transient was much slower than the elevation, time for the decay being in the range 1-5 min (n = 5) and remained above the levels present prior to the addition. The exposure of the osteoclast to dexamethasone was found to have no effect on O2*- generation, whilst estradiol was found to be inhibitory. The mode of stimulation and the kinetics of the transients of O2*- in the bone resorbing osteoclasts produced by 1alpha,25(OH)2D3 were similar to that of parathyroid hormone (PTH) and pertussis. The exposure of the bone resorbing osteoclasts to cholera toxin was found to have no effect, suggesting that the stimulatory action is unlikely to be mediated via cAMP elevation. The importance of these observations is discussed in the context of calcium homeostasis and bone physiology.

1,25-Dihydroxyvitamin D3 receptors in the central nervous system of the rat embryo

We have mapped areas within the central nervous system (CNS) of the developing fetal rat which immunostain for the 1,25-dihydroxyvitamin D3 receptor (VDR). The VDR was detected from days 12 to 21 of gestation throughout the CNS; immunostaining was particularly intense in the neuroepithelium and within the differentiating fields of various areas of the brain. Cells within the spinal cord, dorsal root, and other ganglia exhibited positive staining for the VDR. The intensity of staining for the VDR diminished or disappeared in the neuroepithelium throughout the CNS during the later days of development, while in the differentiating fields single VDR immunoreactive cells were observed. The presence of the VDR in the CNS was confirmed by in situ hybridization and RNA-based polymerase chain reaction methods with di-deoxy sequencing of the resultant DNA product. These results support the hypothesis that 1, 25-dihydroxyvitamin D3, through interactions with the VDR, may play a role in the development of the CNS.

Immunohistochemical analysis of 1,25-dihydroxyvitamin D3 receptor in cervical carcinoma

The immunohistochemical localization and expression of 1,25-dihydroxyvitamin D3 receptors (VDR) has been investigated in normal human cervical tissue (n = 15) and in cervical carcinomas (n = 23). VDR immunoreactivity (monoclonal antibody 9A7gamma) was compared with the staining patterns of transglutaminase K, cytokeratin 10 and Ki-67 in these tumours. Moderate to strong nuclear immunoreactivity for VDR was detected in almost all cervical carcinomas analysed. VDR staining was homogeneous, with no visual differences between individual tumour cells. Some 60% of normal cervical tissues revealed weak immunoreactivity for VDR. In normal cervical tissue, nuclear VDR staining was confined to the lower cervical layers, predominantly to the basal cell layer. Both the intensity of VDR immunostaining and the number of VDR-positive cells were up-regulated in cervical carcinomas compared with normal cervical tissue. No visual correlation was found for the coexpression of VDR with markers of proliferation and differentiation. Our findings indicate that: (1) cervical tissue may be a new target organ for therapeutically applied vitamin D analogues; (2) VDR is up-regulated at the protein level in cervical carcinomas compared with normal cervical tissue; (3) up-regulation of VDR in cervical carcinoma is induced not exclusively by alterations in epithelial differentiation or proliferation, but by different, unknown mechanisms; and (4) calcitriol and new vitamin D analogues exerting fewer calcaemic side-effects may be promising new drugs for the treatment or chemoprevention of metastasizing cervical carcinomas as well as of cervical precancerous lesions.

Localization of 1,25-dihydroxyvitamin D3 receptor (VDR) expression in human prostate

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) has been found to have a variety of physiological functions, including effects on growth and differentiation in normal and malignant cells. The antiproliferative effects of 1,25(OH)2D3 are reported to be mediated through the genomic signaling pathway by binding to a specific high affinity receptor protein, the 1,25-dihydroxyvitamin D3 receptor (VDR). VDR has been localized in a variety of tissues, but little is known about VDR distribution in human prostate. In this study, we raised an antibody against a synthetic peptide corresponding to amino acids 10-24 of human vitamin D receptor. The sequence selected for immunization is identical in human, rat and mouse VDR. Based on this antibody, we developed an immunohistochemical method suitable for studying VDR expression in paraffin-embedded tissue. The immunohistochemical staining was verified using classical target organs for vitamin D (kidney, intestine, skin). With this method, we studied VDR localization on paraffin-embedded human prostatic tissue obtained from 8 patients undergoing radical prostatectomy for urinary bladder cancer and demonstrate VDR expression in the secretory epithelial and few stromal cells of human prostate. The nuclear staining in the secretory epithelial cells was concentrated near the nuclear membrane and in discrete foci in the nucleoplasm. This suggests that effects of 1,25-dihydroxyvitamin D3 are mediated through VDR in these cells. Moreover our result indicates that there are strong variations in VDR expression between prostatic samples.

Membrane receptors for steroid hormones: a case for specific cell surface binding sites for vitamin D metabolites and estrogens

Steroid hormones, including vitamin D metabolites and estrogens, activate target cells through specific receptors that discriminate among ligands based upon recognition of distinct structural features. For both classes of ligands, cell surface and nuclear receptors co-exist in many target cells. Upon ligand binding, these receptors generate both rapid and long lasting responses. While the structure of the nuclear receptors and their function as transcriptional activators of specific target genes is generally understood, the identity of the membrane receptors remains elusive. Using pharmacological, functional and biochemical approaches, new insights are being gained into nature of the cell surface receptors for both vitamin D metabolites and estrogens.

Calibration and standardization of microwave ovens for fixation of brain and peripheral nerve tissue

Rapid and reproducible fixation of brain and peripheral nerve tissue for light and electron microscopy studies can be done in a microwave oven. In this review we report a standardized nomenclature for diverse fixation techniques that use microwave heating: (1) microwave stabilization, (2) fast and ultrafast primary microwave-chemical fixation, (3) microwave irradiation followed by chemical fixation, (4) primary chemical fixation followed by microwave irradiation, and (5) microwave fixation used in various combinations with freeze fixation. All of these methods are well suited to fix brain tissue for light microscopy. Fast primary microwave-chemical fixation is best for immunoelectron microscopy studies. We also review how the physical characteristics of the microwave frequency and the dimensions of microwave oven cavities can compromise microwave fixation results. A microwave oven can be calibrated for fixation when the following parameters are standardized: irradiation time; water load volume, initial temperature, and placement within the oven; fixative composition, volume, and initial temperature; and specimen container shape and placement within the oven. Using two recently developed calibration tools, the neon bulb array and the agar-saline-Giemsa tissue phantom, we report a simple calibration protocol that identifies regions within a microwave oven for uniform microwave fixation.

Steroid receptor interactions with heat shock protein and immunophilin chaperones

We have provided a historical perspective on a body of steroid receptor research dealing with the structure and physiological significance of the untransformed 9S receptor that has often confused both novice and expert investigators. The frequent controversies and equivocations of earlier studies were due to the fact that the native, hormone-free state of these receptors is a large multiprotein complex that resisted description for many years because of its unstable and dynamic nature. The untransformed 9S state of the steroid and dioxin receptors has provided a unique system for studying the function of the ubiquitous, abundant, and conserved heat shock protein, hsp90. The hormonal control of receptor association with hsp90 provided a method of manipulating the receptor heterocomplex in a manner that was physiologically meaningful. For several steroid receptors, binding to hsp90 was required for the receptor to be in a native hormone-binding state, and for all of the receptors, hormone binding promoted dissociation of the receptor from hsp90 and conversion of the receptor to the DNA-binding state. Although the complexes between tyrosine kinases and hsp90 were discovered earlier, the hormonal regulation or steroid receptor association with hsp90 permitted much more rapid and facile study of hsp90 function. The observations that hsp90 binds to the receptors through their HBDs and that these domains can be fused to structurally different proteins bringing their function under hormonal control provided a powerful linkage between the hormonal regulation of receptor binding to hsp90 and the initial step in steroid hormone action. Because the 9S receptor hsp90 heterocomplexes could be physically stabilized by molybdate, their protein composition could be readily studied, and it became clear that these complexes are multiprotein structures containing a number of unique proteins, such as FKBP51, FKBP52, CyP-40, and p23, that were discovered because of their presence in these structures. Further analysis showed that hsp90 itself exists in a variety of native multiprotein heterocomplexes independent of steroid receptors and other 'substrate' proteins. Cell-free systems can now be used to study the formation of receptor heterocomplexes. As we outlined in the scheme of Fig. 1, the multicomponent receptor-hsp90 heterocomplex assembly system is being reconstituted, and the importance of individual proteins, such as hsp70, p60, and p23, in the assembly process is becoming recognized. It should be noted that our understanding of the mechanism and purpose of steroid receptor heterocomplex assembly is still at an early stage. We can now speculate on the roles of receptor-associated proteins in receptor action, both as individuals and as a group, but their actual functions are still vague or unknown. We can make realistic models about the chaperoning and trafficking of steroid receptors, but we don't yet know how these processes occur, we don't know where chaperoning occurs in the cell (e.g. Is it limited to the cytoplasm? Is it a diffuse process or does chaperoning occur in association with structural elements?), and, with the exception of the requirement for hormone binding, we don't know the extent to which the hsp90-based chaperone system impacts on steroid hormone action. It is not yet clear how far the discovery of this hsp90 heterocomplex assembly system will be extended to the development of a general understanding of protein processing in the cell. Because this assembly system is apparently present in all eukaryotic cells, it probably performs an essential function for many proteins. The bacterial homolog of hsp90 is not an essential protein, but hsp90 is essential in eukaryotes, and recent studies indicate that the development of the cell nucleus from prokaryotic progenitors was accompanied by the duplication of genes for hsp90 and hsp70 (698). (ABSTRACT TRUNCATED)

Subcellular distribution of normal and mutant vitamin D receptors in living cells. Studies with a novel fluorescent ligand

To understand the subcellular localization of the vitamin D receptor (VDR) and to measure VDR content in single cells, we recently developed a fluorescent labeled ligand, 4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene (BODIPY)-calcitriol. This tagged hormone has intact biological activity, high affinity and specific binding to the receptor, and enhanced fluorescent emission upon receptor binding. Using BODIPY-calcitriol, here we monitored the subcellular distribution of VDR in living cultured cells by microscopy. Time course studies showed that an equilibrium between the cytoplasmic and nuclear hormone binding developed within 5 min and was maintained thereafter. We found a substantial proportion of VDR residing in the cytoplasm, colocalized with endoplasmic reticulum, the Golgi complex, and microtubules. Confocal microscopy clarified the presence of VDR within discrete regions of the nucleus and along the nuclear envelope. There was no VDR in the plasma membrane. Low affinity BODIPY-calcitriol binding sites were in the mitochondria. Mutations in the VDR gene selectively and specifically altered BODIPY-calcitriol distribution. Defects in the hormone binding region of VDR prevented both nuclear and cytoplasmic hormone binding. Defects in the DNA binding region decreased the nuclear retention of VDR and prevented localization to nuclear foci. These results with BODIPY-calcitriol reveal cytoplasmic VDR localization in living cells and open the possibility of studying the three-dimensional architecture of intranuclear target sites.

Activation of Raf-mitogen-activated protein kinase signaling pathway by 1,25-dihydroxyvitamin D3 in normal human keratinocytes

The biologic effects of the vitamin D hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are believed to be mediated by an intracellular vitamin D receptor, which after ligand binding acts as a transcription factor modulating expression of a variety of genes. Besides having a well-known role in calcium metabolism, this hormone is an important regulator of proliferation in a majority of normal and neoplastic cells. Keratinocytes provide a convenient model for investigating the growth-related effects of vitamin D in normal cells. Growth of keratinocytes may be either stimulated or inhibited by 1,25(OH)2D3, depending on the degree of cell differentiation. We show here that 1,25(OH)2D3 stimulates DNA synthesis via sequential activation of Raf and the mitogen-activated protein kinase. Activation of these kinases is independent on protein and mRNA synthesis and is preceded by rapid tyrosine phosphorylation of an adaptor protein p66 (Shc) and formation of a complex between p66 Shc, a bridging molecule Grb2, and a Ras activator, mSos. Vitamin D receptor protein associates with Shc, indicating that this steroid hormone is able to signal through the transcription-independent pathways similar to those used by peptide hormones and cytokines.

Immunohistochemical detection of 1,25-dihydroxyvitamin D3 receptors (VDR) in human skin. A comparison of five antibodies

Increasing evidence suggests an important regulatory function for 1 alpha,25-dihydroxyvitamin D3 in the growth control of epidermal cells and in skin immunology. Using immunohistochemical techniques we investigated the in situ expression of 1,25-dihydroxyvitamin D3 receptors (VDR) in normal human skin with one monoclonal rat antibody and four monospecific polyclonal rat antibodies to the VDR. Polyclonal rabbit antibodies have been raised against synthetic peptides corresponding to different amino acid residues of the human VDR, including regions close to the DNA binding domain and the hormone-binding domain. All antibodies revealed positive immunoreactivity in normal human skin. The antibodies showed differences in subcellular immunoreactivity and staining-intensity. Differences in subcellular distribution of VDR immunoreactivity are caused by the different epitopes recognized by the antibodies and not by the affinity of the antibodies for VDR. It seems that the antibodies may recognize different functional modifications of the receptor molecule (i.e.: hormone bound vs. hormone free; DNA bound vs. non-DNA bound; VDR vs. VDR/retinoid-X receptor [RXR] heterodimers). Using these newly raised antibodies future studies will be carried out to analyse subcellular distribution of VDR immunoreactivity in skin pathology.

Age and gender effects on 1,25-dihydroxyvitamin D3-regulated gene expression

Several factors involved in regulation of bone mineral metabolism were compared in male and female Fischer 344 rats of different ages (1, 2.5, 6, and 18 months). Plasma 1,25-(OH)2D3 concentrations decreased with age in rats of both genders. Abundance of calbindin-D28K and its mRNA in kidney and calbindin-D9K and its mRNA in duodenum also decreased with age in both male and female rats. Renal 24-hydroxylase activity and 24-hydroxylase mRNA content were elevated significantly in 18-month-old males and females, compared with younger ages. These data suggest that increased renal catabolism of 1,25-(OH)2D3 may be responsible for low plasma 1,25-(OH)2D3 concentrations observed in older animals. Plasma PTH and 1,25-(OH)2D3 concentrations, renal 24-hydroxylase enzyme activity and 24-hydroxylase mRNA content, duodenal 24-hydroxylase mRNA abundance, and duodenal calbindin-D9K and calbindin-D9K mRNA content were greater in males than in females at 2.5 months of age. Lower plasma 1,25-(OH)2D3 concentrations in females seem to explain observed gender differences in expression of 1,25-(OH)2D3-stimulated genes. The combined effects of these gender differences at ages when peak bone density is being developed may contribute to the greater incidence of osteoporosis in females than in males.

Microtubules mediate cellular 25-hydroxyvitamin D3 trafficking and the genomic response to 1,25-dihydroxyvitamin D3 in normal human monocytes

The genomic actions of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are mediated by the intracellular vitamin D receptor (VDR). Although immunocytochemistry has shown that disruption of microtubular assembly prevents nuclear access of the sterol-VDR complex, the role of microtubules in the response to 1,25(OH)2D3 has not been studied in viable cells. Our studies examined this interaction in normal human monocytes. Monocytes convert 25(OH)D3 to 1,25(OH)2D3 and to 24-hydroxylated metabolites more polar than 1,25(OH)2D3. Microtubule disruption totally abolished the ability of exogenous 1,25(OH)2D3 to suppress its own synthesis and to induce 24-hydroxylase mRNA and activity, without affecting either total 1,25(OH)2D3 uptake or maximal 1,25(OH)2D3-VDR binding. Thus, intact microtubules are essential for 1,25(OH)2D3-dependent modulation of gene transcription. Interestingly, microtubule disruption also decreased monocyte 1,25(OH)2D3 synthesis, not by decreasing the Vmax of monocyte mitochondrial 1 alpha-hydroxylase but through an increase in the Km for 25(OH)2D3. We examined 25(OH)D3 transport. Microtubule disruption did not affect total cellular 25(OH)D3 uptake but reduced its intracellular trafficking to the mitochondria. Thus, microtubules participate in intracellular 25(OH)D3 transport, and their integrity determines normal 1,25(OH)2D3 synthesis.

Heat shock proteins and molecular chaperones: implications for adaptive responses in the skin

Recent advances in the biology of heat-shock proteins (hsps) are reviewed. These abundant and evolutionarily highly conserved proteins (also called stress proteins) act as molecular escorts. Hsps bind to other cellular proteins, help them to fold into their correct secondary structures, and prevent misfolding and aggregation during stress. Cytoplasmic hsp70 and hsp60 participate in complicated protein-folding pathways during the synthesis of new polypeptides. Close relatives of hsp70 and hsp60 assist in the transport and assembly of proteins inside intracellular organelles. Hsp90 may have a unique role, binding to the glucocorticoid receptor in a manner essential for proper steroid hormone action. Hsps may also be essential for thermotolerance and for prevention and repair of damage caused by ultraviolet B light. A unique class of T lymphocytes, the gamma delta T cells, exhibits a restricted specificity against hsps. These T cells may constitute a general, nonspecific immune mechanism directed against the hsps within invading organisms or against very similar hsps within invading organisms or against very similar hsps expressed by infected (stressed) keratinocytes. Immunologic cross-reactivity between hsps of foreign organisms and of the host may play a role in some autoimmune diseases. Although hsps are expressed in the skin, many questions remain about their role during injury, infection, and other types of cutaneous pathophysiology.

Emerging diversities in the mechanism of action of steroid hormones

The classical genomic action of steroid hormones acting through intracellular receptors is well recognized. Within this concept of action, questions regarding the ultimate fate of the hormone and lack of a tight correlation between tissue uptake and biological activity with receptor binding remain unanswered. Evidence has accumulated that steroid hormones can exert non-classical action that is characterized by rapid effect of short duration. In most of these cases, the hormone effects occurs at the membrane level and is not associated with entry into the cell. The possible mechanisms for these non-classical actions are: (a) changes in membrane fluidity; (b) steroid hormone acting on receptors on plasma membranes; (c) steroid hormones regulating GABAA receptors on plasma membranes; and (d) activation of steroid receptors by factors such as EGF, IGF-1 and dopamine. Data have also been obtained indicating that receptor-mediated insertion of steroid hormones into DNA may take place with the steroid acting as a transcription factor. These new proposed mechanism of action of steroid hormones should not be viewed as a challenge to the classical mechanism. These diverse modes of action provide for an integrated action of hormones which may be rapid and of short duration or prolonged to address the physiological needs of the individual.

Application of microwave fixation techniques in pathology to neuroscience studies: a review

The introduction of microwave energy into the scientist's repertoire of fixation modalities offers for the first time in relatively large specimens the potential for 'instantaneous' preservation of cellular structure for light and electron microscopy with minimal alteration of cellular biochemistry and antigenicity. Because of the rapid evolution of this new technology, we provide a classification system of newly generated microwave methods as applied to specimen preservation for microscopic analysis. With emphasis on neuronal tissue, we review qualitative and quantitative microscopy data of specimens fixed by two microwave methods in common use: (1) microwave stabilization and (2) fast and ultrafast, primary microwave-chemical fixation. In addition, we provide a table of neuropeptides or proteins in neuronal tissues that are preserved by various microwave fixation methods for histochemistry, immunohistochemistry, and immuno-electron microscopy studies. Commercial microwave ovens have limitations which can result in irreproducible fixation results. Therefore, we present a calibration protocol that is used to identify the best locations for fixation within large cavity (i.e., household) microwave ovens. We also provide a standardization protocol to improve the reproducibility of microwave fixation in calibrated, large-cavity microwave ovens.

Subnuclear distribution of the vitamin D receptor

The subnuclear distribution of the vitamin D receptor was investigated to begin addressing the contribution of nuclear architecture to vitamin D-responsive control of gene expression in ROS 17/2.8 rat osteosarcoma cells. The nuclear matrix is an anastomosing network of filaments that is functionally associated with DNA replication, transcription, and RNA processing. The representation of vitamin D receptor in the nuclear matrix and nonmatrix nuclear fractions was determined by the combined application of 1) sequence-specific interactions with the vitamin D receptor binding element of the rat bone-specific osteocalcin gene promoter and 2) Western blot analysis. Both methods confirmed the presence of vitamin D receptor in the nonmatrix nuclear fraction and the absence of detectable vitamin D receptors associated with the nuclear matrix. In contrast, these same nuclear matrix proteins preparations exhibited association with the general transcription factor AP-1 and a bone tissue-specific promoter binding factor NMP2. NMP-2 exhibits recognition for a promoter domain contiguous to the vitamin D-responsive element of the osteocalcin gene, although the vitamin D receptor does not appear to be a component of the nuclear matrix proteins. Interrelationships between nuclear matrix proteins and nonmatrix nuclear proteins, in mediating steroid hormone responsiveness of a vitamin D-regulated promoter, are therefore suggested.

The effect of androgens and antiandrogens on the immunohistochemical localization of the androgen receptor in accessory reproductive organs of male rats

The androgen receptor (AR) was localized immunohistochemically after different hormonal treatments in the ventral prostate, coagulating gland, seminal vesicle and epididymis of the adult rat. In the untreated controls AR-immunoreactivity was confined to the cell nuclei. One week after castration or treatment with the gonadotropin-releasing hormone antagonist Cetrorelix (150 micrograms/animal per day) a cytoplasmic staining occurred in the epithelial cells of the ventral prostate and in part of the coagulating gland and seminal vesicle. In contrast, the AR remained exclusively in the nuclei in the epididymal epithelium and the glandular smooth muscle layer even after 2 weeks of androgen depletion. Bolus injections of either dihydrotestosterone (1 mg/kg), the antiandrogen flutamide (40 mg/kg), or the novel non-steroidal antiandrogen casodex (40 mg/kg) to androgen-depleted animals eliminated cytoplasmic AR-immunoreactivity and restored the nuclear staining pattern in the ventral prostate. A sustained 2-week treatment with the antiandrogens resulted in a loss of weight in all organs but did not alter the distribution of AR-immunoreactivity. The data show an apparent cytoplasmic/nuclear ligand-dependent translocation of the AR in the ventral prostate, coagulating gland and seminal vesicle but not in the epididymis of the adult rat.