Vitamin D regulated keratinocyte differentiation: role of coactivators

Skin microbiome considerations for long haul space flights

Dysbiosis of the human skin microbiome has long been associated with changes to the pH of the skin, dermal immune function and chronic skin conditions. Dermatological issues have been noted as the most prevalent medical presentation in the microgravity environment of space. The change in gravitational forces has been implicated in human immuno-suppression, also impacted by changes in the gastrointestinal-skin axis and its impact on Vitamin D metabolism, altered microbial gene expression in resident flora (leading changes in biofilm formation) and increased virulence factors in potential pathogens. There are also other stressors to the skin microbiome unique to space travel, including increased exposure to radiation, prolonged periods of dry washing technique, air quality and changes in microbe replication and growth parameters. Optimal microbiome health leads to enhanced skin barrier manufacture and maintenance, along with improved skin immune function and healing. In a microgravity environment expected to be experienced during long space flights, disruptions to the skin microbiome, coupled with increased virulence of pathological viruses and bacteria has implications for holistic skin health, astronaut cognitive function and mental health, and is coupled with slowed rates of wound healing. Scenario management for holistic skin health and restoration of microbiome homeostasis on long space flights require consideration.

Low vitamin D-modulated calcium-regulating proteins in psoriasis vulgaris plaques: S100A7 overexpression depends on joint involvement

Psoriasis is an inflammatory skin disease with or without joint involvement. In this disease, the thickened epidermis and impaired barrier are associated with altered calcium gradients. Calcium and vitamin D are known to play important roles in keratinocyte differentiation and bone metabolism. Intracellular calcium is regulated by calcium-sensing receptor (CASR), calcium release-activated calcium modulator (ORAI) and stromal interaction molecule (STIM). Other proteins modulated by vitamin D play important roles in calcium regulation e.g., calbindin 1 (CALB1) and transient receptor potential cation channel 6 (TRPV6). In this study, we aimed to investigate the expression of calcium-regulating proteins in the plaques of patients with psoriasis vulgaris with or without joint inflammation. We confirmed low calcium levels, keratinocyte hyperproliferation and an altered epidermal barrier. The CASR, ORAI1, ORAI3, STIM1, CALB1 and TRPV6 mRNA, as well as the sterol 27-hydroxylase (CYP27A1), 25-hydroxyvitamin D3 1-α-hydroxylase (CYP27B1) and 1,25-dihydroxyvitamin D3 24-hydroxylase (CYP24A1) protein levels were low in the plaques of patients with psoriasis. We demonstrated S100 calcium-binding protein A7 (S100A7) overexpression in the plaques of patients with psoriasis vulgaris with joint inflammation, compared with those without joint involvement. We suggest an altered capacity to regulate the intracellular Ca2+ concentration ([Ca2+]i), characterized by a reduced expression of CASR, ORAI1, ORAI3, STIM1, CALB1 and TRPV6 associated with diminished levels of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], which may be associated with an altered balance between keratinocyte proliferation and differentiation in the psoriatic epidermis. Additionally, differences in S100A7 expression depend on the presence of joint involvement.

MEP50/PRMT5 Reduces Gene Expression by Histone Arginine Methylation and this Is Reversed by PKCδ/p38δ Signaling

PKCδ and p38δ are key proteins in a cascade that stimulates keratinocyte differentiation. This cascade activates transcription of involucrin (hINV) and other genes associated with differentiation. Protein arginine methyltransferase 5 (PRMT5) is an arginine methyltransferase that symmetrically dimethylates arginine residues. This protein interacts with a cofactor, MEP50, and symmetrically dimethylates arginine eight of histone 3 (H3R8me2s) and arginine three of histone 4 (H4R3me2s) to silence gene expression. We use the involucrin gene as a tool to understand the relationship between PKCδ/p38δ and PRMT5/MEP50 signaling. MEP50 suppresses hINV mRNA level and promoter activity. This is associated with increased arginine dimethylation of hINV gene-associated H3/H4. We further show that the PKCδ/p38δ keratinocyte differentiation cascade reduces PRMT5 and MEP50 expression, association with the hINV gene promoter, and H3R8me2s and H4R2me2s formation. We propose that PRMT5/MEP50-dependent methylation is an epigenetic mechanism that assists in silencing of hINV expression, and that PKCδ signaling activates gene expression by directly activating transcription and by suppressing PRMT5/MEP50 dependent arginine dimethylation of promoter associated histones. This is an example of crosstalk between PKCδ/p38δ signaling and PRMT5/MEP50 epigenetic silencing.

Improve efficacy of topical ALA-PDT by calcipotriol through up-regulation of coproporphyrinogen oxidase

BACKGROUND

Topical 5-aminolevulinic acid-mediated photodynamic therapy (topical ALA-PDT) is effective for treating oral precancerous lesions. The aim of this in vivo and in vitro study was to examine whether the efficacy of topical ALA-PDT could be further improved by calcipotriol (CAL).

METHODS

Precancerous lesions in the buccal pouch of hamsters were induced by dimethylbenz(a)anthracene (DMBA). Lesions were treated with multiple topical ALA-PDT with or without CAL pretreatment. ALA-induced protoporphyrine IX (PpIX) was monitored by in situ fluorescence measurement. The effect of CAL on heme-related enzymes (CPOX, PPOX, and FECH) were examined in an in vitro model using human squamous cell carcinoma (SCC) cells (SCC4, SAS) using Western blots.

RESULTS

Fluorescence spectroscopy revealed that PpIX reached its peak level in precancerous epithelial cells of buccal pouch at 2.5 or 3.5h without or with CAL pretreatment, respectively. Both treatment regimens showed similar response rates, but the complete response was achieved after 5 times of ALA-PDT and 3 times of CAL-ALA-PDT (p<0.001). Pretreatment of SCC cells with 10(-8) or 10(-7)M CAL could result in a significant cell death (p<0.05) and an elevation of CPOX protein level.

CONCLUSION

Topical CAL can improve the efficacy of ALA-PDT in treating precancerous lesions, likely through the increase in CPOX level and in PpIX production.

Systematic identification and characterization of novel human skin-associated genes encoding membrane and secreted proteins

Through bioinformatics analyses of a human gene expression database representing 105 different tissues and cell types, we identified 687 skin-associated genes that are selectively and highly expressed in human skin. Over 50 of these represent uncharacterized genes not previously associated with skin and include a subset that encode novel secreted and plasma membrane proteins. The high levels of skin-associated expression for eight of these novel therapeutic target genes were confirmed by semi-quantitative real time PCR, western blot and immunohistochemical analyses of normal skin and skin-derived cell lines. Four of these are expressed specifically by epidermal keratinocytes; two that encode G-protein-coupled receptors (GPR87 and GPR115), and two that encode secreted proteins (WFDC5 and SERPINB7). Further analyses using cytokine-activated and terminally differentiated human primary keratinocytes or a panel of common inflammatory, autoimmune or malignant skin diseases revealed distinct patterns of regulation as well as disease associations that point to important roles in cutaneous homeostasis and disease. Some of these novel uncharacterized skin genes may represent potential biomarkers or drug targets for the development of future diagnostics or therapeutics.

Skn-1a/Oct-11 and ΔNp63α exert antagonizing effects on human keratin expression

The formation of a stratified epidermis requires a carefully controlled balance between keratinocyte proliferation and differentiation. Here, we report the reciprocal effect on keratin expression of ΔNp63, pivotal in normal epidermal morphogenesis and maintenance, and Skn-1a/Oct-11, a POU transcription factor that triggers and regulates the differentiation of keratinocytes. The expression of Skn-1a markedly downregulated ΔNp63-driven K14 expression in luciferase reporter assays. The extent of downregulation was comparable to the inhibition of Skn-1a-mediated K10 expression upon expression of ΔNp63. ΔNp63, mutated in the protein-protein interaction domain (SAM domain; mutated in human ectodermal dysplasia syndrome), was significantly less effecting in downregulating K10, raising the possibility of a direct interaction among Skn-1a and ΔNp63. Immunolocalization in human skin biopsies revealed that the expression of the two transcription factors is partially overlapping. Co-immunoprecipitation experiments did not, however, demonstrate a direct interaction between ΔNp63 and Skn-1a, suggesting that the antagonistic effects of Skn-1a and p63 on keratin promoter transactivation is probably through competition for overlapping binding sites on target gene promoter or through an indirect interaction.

Nuclear targeting of cyclin-dependent kinase 2 reveals essential roles of cyclin-dependent kinase 2 localization and cyclin E in vitamin D-mediated growth inhibition

1,25-Dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)), inhibits proliferation of a variety of cell types including adenocarcinoma of the prostate. We have previously shown that 1,25-(OH)(2)D(3) increases the stability of the cyclin-dependent kinase inhibitor p27(KIP1), decreases cyclin-dependent kinase 2 (CDK2) activity, and promotes G(1) phase accumulation in human prostate cancer cells. These effects correlate with cytoplasmic relocalization of CDK2. In this study, we investigated the role of CDK2 cytoplasmic relocalization in the antiproliferative effects of 1,25-(OH)(2)D(3). CDK2 was found to be necessary for prostate cancer cell proliferation. Although induced by 1,25-(OH)(2)D(3), the cyclin-dependent kinase inhibitor p27(KIP1) was dispensable for 1,25-(OH)(2)D(3)-mediated growth inhibition. Reduction in CDK2 activity by 1,25-(OH)(2)D(3) was associated with decreased T160 phosphorylation, a residue whose phosphorylation in the nucleus is essential for CDK2 activity. Ectopic expression of cyclin E was sufficient to overcome 1,25-(OH)(2)D(3)-mediated cytoplasmic mislocalization of CDK2 and all antiproliferative effects of 1,25-(OH)(2)D(3), yet endogenous levels of cyclin E or binding to CDK2 were not affected by 1,25-(OH)(2)D(3). Similarly, knockdown of the CDK2 substrate retinoblastoma, which causes cyclin E up-regulation, resulted in resistance to 1,25-(OH)(2)D(3)-mediated growth inhibition. Human prostate cancer cells resistant to growth inhibition by 1,25-(OH)(2)D(3) but retaining fully functional vitamin D receptors were developed. These cells did not exhibit 1,25-(OH)(2)D(3)-mediated cytoplasmic relocalization of CDK2. Targeting CDK2 to the nucleus of 1,25-(OH)(2)D(3)-sensitive cancer cells blocked G(1) accumulation and growth inhibition by 1,25-(OH)(2)D(3). These data establish central roles for CDK2 nuclear-cytoplasmic trafficking and cyclin E in the mechanism of 1,25-(OH)(2)D(3)-mediated growth inhibition in prostate cancer cells.

Upregulation of MMP-9 production by TNFalpha in keratinocytes and its attenuation by vitamin D

MMP-9, a member of the matrix metalloproteinase family that degrades collagen IV and processes chemokines and cytokines, participates in epidermal remodeling in response to stress and injury. Limited activity of MMP-9 is essential while excessive activity is deleterious to the healing process. Tumor necrosis factor (TNFalpha), a key mediator of cutaneous inflammation, is a powerful inducer of MMP-9. Calcitriol, the hormonally active vitamin D metabolite, and its analogs are known to attenuate epidermal inflammation. We aimed to examine the modulation of MMP-9 by calcitriol in TNFalpha-treated keratinocytes. The immortalized HaCaT keratinocytes were treated with TNFalpha in the absence of exogenous growth factors or active ingredients. MMP-9 production was quantified by gelatin zymography and real-time RT-PCR. Activation of signaling cascades was assessed by western blot analysis and DNA-binding activity of transcription factors was determined by EMSA. Exposure to TNFalpha markedly increased the protein and mRNA levels of MMP-9, while pretreatment with calcitriol dose dependently reduced this effect. Employing specific inhibitors we established that the induction of MMP-9 by TNFalpha was dependent on the activity of the epidermal growth factor receptor, c-Jun-N-terminal kinase (JNK), NFkappaB and extracellular signal-regulated kinase-1/2. The effect of calcitriol was associated with inhibition of JNK activation and reduction of DNA-binding activities of the transcription factors activator protein-1 (AP-1) and NFkappaB following treatment with TNFalpha. By down-regulating MMP-9 levels active vitamin D derivatives may attenuate deleterious effects due to excessive TNFalpha-induced proteolytic activity associated with cutaneous inflammation.

Cell and molecular biology of the novel protein tyrosine-phosphatase-interacting protein 51

This chapter examines the current state of knowledge about the expression profile, as well as biochemical properties and biological functions of the evolutionarily conserved protein PTPIP51. PTPIP51 is apparently expressed in splice variants and shows a particularly high expression in epithelia, skeletal muscle, placenta, and germ cells, as well as during mammalian development and in cancer. PTPIP51 is an in vitro substrate of Src- and protein kinase A, the PTP1B/TCPTP protein tyrosine phosphatases and interacts with 14-3-3 proteins, the Nuf2 kinetochore protein, the ninein-interacting CGI-99 protein, diacylglycerol kinase alpha, and also with itself forming dimers and trimers. Although the precise cellular function remains to be elucidated, the current data implicate PTPIP51 in signaling cascades mediating proliferation, differentiation, apoptosis, and motility.

Development and progression of secondary hyperparathyroidism in chronic kidney disease: lessons from molecular genetics

The identification of the calcium-sensing receptor (CaSR) and the clarification of its role as the major regulator of parathyroid gland function have important implications for understanding the pathogenesis and evolution of secondary hyperthyroidism in chronic kidney disease (CKD). Signaling through the CaSR has direct effects on three discrete components of parathyroid gland function, which include parathyroid hormone (PTH) secretion, PTH synthesis, and parathyroid gland hyperplasia. Disturbances in calcium and vitamin D metabolism that arise owing to CKD diminish the level of activation of the CaSR, leading to increases in PTH secretion, PTH synthesis, and parathyroid gland hyperplasia. Each represents a physiological adaptive response by the parathyroid glands to maintain plasma calcium homeostasis. Studies of genetically modified mice indicate that signal transduction via the CaSR is a key determinant of parathyroid cell proliferation and parathyroid gland hyperplasia. Because enlargement of the parathyroid glands has important implications for disease progression and disease severity, it is possible that clinical management strategies that maintain adequate calcium-dependent signaling through the CaSR will ultimately prove useful in diminishing parathyroid gland hyperplasia and in modifying disease progression.

The vitamin D pathway: a new target for control of the skin's immune response?

The surface of our skin is constantly challenged by a wide variety of microbial pathogens, still cutaneous infections are relatively rare. Within cutaneous innate immunity the production of antimicrobial peptides (AMPs) is a primary system for protection against infection. Many AMPs can be found on the skin, and these include molecules that were discovered for their antimicrobial properties, and other peptides and proteins first known for activity as chemokines, enzymes, enzyme inhibitors and neuropeptides. Cathelicidins were among the first families of AMPs discovered on the skin. They are now known to have two distinct functions; they have direct antimicrobial activity and will initiate a host cellular response resulting in cytokine release, inflammation and angiogenesis. Dysfunction of cathelicidin is relevant in the pathogenesis of several cutaneous diseases including atopic dermatitis where cathelicidin induction is suppressed, rosacea, where cathelicidin peptides are abnormally processed to forms that induce cutaneous inflammation and a vascular response, and psoriasis, where a cathelicidin peptide can convert self-DNA to a potent stimulus of an autoinflammatory cascade. Recent work has unexpectedly identified vitamin D3 as a major factor involved in the regulation of cathelicidin expression. Therapies targeting the vitamin D3 pathway and thereby cathelicidin may provide new treatment modalities in the management of infectious and inflammatory skin diseases.

Systemic PPARgamma ligation inhibits allergic immune response in the skin

We have shown previously that specific ligands of the peroxisome proliferator-activated receptor-gamma (PPARgamma) inhibit the systemic allergic immune response. The objective of this study was to investigate the impact of PPARgamma-ligand treatment on the local allergic immune response. We established a murine model exhibiting clinical and histological features of AD-like skin lesions with high reproducibility. In this model, the PPARgamma ligand was applied in an either preventive or therapeutic manner via systemic and local routes. The affected skin areas were assessed by standardized skin score, histological analyses, and immunohistochemical examinations. Our data show that systemic application of PPARgamma ligand by a preventive protocol led to significantly reduced onset of eczematous skin lesions. This was confirmed by histology, showing decreased skin thickness accompanied by significantly reduced infiltrations of CD4+ and CD8+ lymphocytes but also mast cells. Additionally, early allergen-specific IgE and IgG1 responses were reduced (day 21/35), whereas IgG2a levels remained unchanged. In conclusion, our results demonstrate that PPARgamma-ligand treatment inhibits not only systemic allergic immune response, but also local allergen-mediated dermatitis. Our findings point to therapeutic strategies, including a PPARgamma-ligand-based treatment.

Vitamin D resistance

Vitamin D is a secosteroid of nutritional origin but can also be generated in the skin by ultraviolet light. After two hydroxylations 1,25-(OH)2 vitamin D avidly binds and activates the vitamin D receptor (VDR), a nuclear transcription factor, hereby regulating a large number of genes. The generation of VDR deficient mice has expanded the knowledge on vitamin D from a calcium-regulating hormone to a humoral factor with extensive actions. The effects of the vitamin D system on calcium and bone homeostasis are largely mediated by promoting active intestinal calcium transport via the induction of the epithelial calcium channel TRPV6. Although VDR is redundant in bone, it may regulate the differentiation and function of several bone cells. In skin, VDR expression in keratinocytes is essential in a ligand-independent manner for the maintenance of the normal hair cycle. Therefore, VDR but not vitamin D deficiency results in alopecia. Moreover, 1,25-(OH)2 vitamin D impairs the proliferation not only of keratinocytes but also of many cell types by regulating the expression of cell cycle genes, leading to a G1 cell cycle arrest. In addition, VDR inactivation in mice results in high renin hypertension, cardiac hypertrophy and thrombogenesis. Finally, a dual effect of vitamin D was observed in the immune system where it stimulates the innate immune system while tapering down excessive activation of the acquired immune system. Taken together, the vitamin D endocrine system not only regulates calcium homeostasis but affects several systems mainly by altering gene expression but also by ligand-independent actions.

Identification and characterization of noncalcemic, tissue-selective, nonsecosteroidal vitamin D receptor modulators

Vitamin D receptor (VDR) ligands are therapeutic agents for the treatment of psoriasis, osteoporosis, and secondary hyperparathyroidism. VDR ligands also show immense potential as therapeutic agents for autoimmune diseases and cancers of skin, prostate, colon, and breast as well as leukemia. However, the major side effect of VDR ligands that limits their expanded use and clinical development is hypercalcemia that develops as a result of the action of these compounds mainly on intestine. In order to discover VDR ligands with less hypercalcemia liability, we sought to identify tissue-selective VDR modulators (VDRMs) that act as agonists in some cell types and lack activity in others. Here, we describe LY2108491 and LY2109866 as nonsecosteroidal VDRMs that function as potent agonists in keratinocytes, osteoblasts, and peripheral blood mononuclear cells but show poor activity in intestinal cells. Finally, these nonsecosteroidal VDRMs were less calcemic in vivo, and LY2108491 exhibited more than 270-fold improved therapeutic index over the naturally occurring VDR ligand 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in an in vivo preclinical surrogate model of psoriasis.

Programmed cell death of stressed keratinocytes and its inhibition by vitamin D: The role of death and survival signaling pathways

The epidermis is confronted with multiple environmental and pathophysiological stresses. This study shows that TNFalpha, oxidative stress, hyperosmotic and heat shock induced both caspase-dependent and independent cell death in human HaCaT keratinocytes. The hormonal form of vitamin D, 1,25(OH)2D3, which is an autocrine hormone in the epidermis, protected the cells from all the examined stresses and pathways leading to cell death. We aimed to define the signaling pathways that determine the life-death balance of stressed keratinocytes and participate in their protection by 1,25(OH)2D3. As assessed by employing specific inhibitors, the survival pathways mediated by the EGF receptor, ERK, PI-3K or Src kinase, or basal transcriptional activity are important for unstressed cell survival. However, only the EGF receptor, PI-3K and the Src kinase pathways mediate the survival of stressed cells in a stimulus-specific manner. Inhibition of the p38 and/or the JNK death pathways reduced caspase activation induced by oxidative stress, hyperosmotic shock and TNFalpha. The protective effect of 1,25(OH)2D3 was not mediated by the examined survival pathways. 1,25(OH)2D3 inhibited the stress-induced activation of p38 and JNK. Since mimicking this effect by pharmacological inhibition resulted in the attenuation of caspase activation, we infer that these pathways are involved in keratinocyte protection by 1,25(OH)2D3.

Identification of vitamin D receptor as a target of p63

p63, a p53 homolog has been shown to play a role in development and cancer. p63 is essential for both commitment of ectoderm to stratified epithelia and for the proliferative potential of epithelial stem cells. p63 knockout mice are born with severe development defects and lack organs of epithelial origin. In addition, p63 has also been shown to play a role in cancer development through the differential regulation of genes with tumor suppressor function and genes involved in metastasis. In order to understand the role of p63 in cancer and development, genes that are specifically regulated by p63 but not p53 were identified. In this study, we provide evidence that p63gamma specifically upregulates vitamin D Receptor (VDR). In contrast, p53 does not appear to be involved in upregulation of VDR expression. Additionally, we demonstrate that a naturally occurring p63 missense mutant, p63gamma (R279H) and p14(ARF), both act in a dominant negative manner to inhibit p63gamma-mediated upregulation of VDR. Furthermore, using chromatin immunoprecipitation assays, we demonstrated that p63 directly binds to the VDR promoter in vivo. Our findings clearly demonstrate that VDR is a direct target of p63 and suggests that p63 may play a role in cancer and differentiation through modulation of the VDR pathway.

The preventive effect of vitamin D3 on radiation-induced hair toxicity in a rat model

Our aim is to investigate the protective effect of vitamin D3 especially from radiation-induced hair toxicity. A model of skin radiation injury was developed and a single fraction of 20 Gy Gamma irradiation was applied to the right dorsal skin of fourteen rats. All animals were randomly divided into 2 groups: Group I: irradiation alone (n = 7) and Group II: irradiation and 0.2 microg vitamin D3 given IM (n = 7). Fifty days after post-irradiation rats were sacrificed. The outcomes were evaluated on the basis of histopathological findings and immunohistochemical staining for Vitamin D receptor (VDR) in skin and hair follicles. The number of hair follicles in the radiation field for the group of animals irradiated without pretreatment was significantly lower than outside of the irradiated area (p = 0.016) as it is expected. Contrarily the number of hair follicles did not show significant difference in the pretreated group between the irradiated field and outside of the fields (p = 0,14). Skin of the vitamin D3 pretreated group demonstrated stronger immunoreactivity for VDR compared to irradiation alone group. These results indicate that administration of vitamin D3 may protect hair follicles from radiation toxicity. Further clinical trials should be conducted to prove the preventive effect of vitamin D3 as well as dosing and timing of the agent on radiation-induced alopecia.

Vitamin D receptor (VDR) ablation alters carcinogen-induced tumorigenesis in mammary gland, epidermis and lymphoid tissues

The Vitamin D receptor (VDR) and its ligand, 1,25(OH)(2)D(3), regulate cell proliferation, differentiation and apoptosis in vitro, yet the physiological significance of this regulation is unclear. In these studies, we used VDR knockout (VDRKO) mice to examine the impact of VDR on chemical carcinogen-induced tumorigenesis in vivo. Wild type (WT) and VDRKO littermates were fed a high calcium diet to prevent disturbances in calcium homeostasis and were gavaged with dimethylbenzanthracence (DMBA) using a protocol designed to induce mammary tumors. Compared to WT littermates, VDRKO mice exhibited an increased incidence of mammary gland hyperplasia and a higher percentage of hormone independent tumors with squamous differentiation. VDR ablation also significantly enhanced tumor development in epidermis and lymphoid tissues, but did not affect tumor development in ovary, uterus, lung or liver. These data indicate that VDR ablation alters susceptibility to DMBA-induced carcinogenesis in a tissue specific fashion, and provide support that optimal VDR signaling may act to suppress tumorigenesis.

Molecular pathways involved in the anti-apoptotic effect of 1,25-dihydroxyvitamin D3 in primary human keratinocytes

We previously reported that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] protects primary human keratinocytes against ultraviolet (UV)B-induced apoptosis. Here, we confirmed the anti-apoptotic effect of 1,25(OH)2D3 in keratinocytes, using cisplatin and doxorubicin as apoptotic triggers. We further showed that 1,25(OH)2D3 activates two survival pathways in keratinocytes: the MEK/extracellular signal regulated kinase (ERK) and the phosphatidylinositol 3-kinase (PI-3K)/Akt pathway. Activation of ERK and Akt by 1,25(OH)2D3 was transient, required a minimal dose of 10(-9) M and could be blocked by actinomycin D and cycloheximide. Moreover, inhibition of Akt or ERK activity with respectively a PI-3K inhibitor (LY294002) or MEK inhibitors (PD98059, UO126), partially or totally suppressed the anti-apoptotic capacity of 1,25(OH)2D3. Finally, 1,25(OH)2D3 changed the expression of different apoptosis regulators belonging to the Bcl-2 family. Indeed, 1,25(OH)2D3 treatment increased levels of the anti-apoptotic protein Bcl-2 and decreased levels of the pro-apoptotic proteins Bax and Bad in a time- and dose-dependent way. Induction of Bcl-2 by 1,25(OH)2D3 was further shown to be mediated by ERK and, to a lesser extent, by Akt. In conclusion, 1,25(OH)2D3 clearly protects keratinocytes against apoptosis (1) by activating the MEK/ERK and the PI-3K/Akt survival pathways and (2) by increasing the Bcl-2 to Bax and Bad ratio.

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.

Transcriptional profiling of keratinocytes reveals a vitamin D-regulated epidermal differentiation network

1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] regulates mineral homeostasis and exhibits potent anti-proliferative, prodifferentiative, and immunomodulatory activities. It mediates these effects by binding to the vitamin D receptor (VDR), which belongs to the superfamily of steroid/thyroid hormone nuclear receptors. As a result of keratinocyte differentiation and anti-proliferation activities, 1,25(OH)(2)D(3) and its synthetic analogs are therapeutically effective in psoriasis and show promise for the treatment of actinic keratosis and squamous cell carcinoma. To elucidate the VDR signaling pathway in keratinocytes, we examined the gene expression profile with 1,25(OH)(2)D(3) treatment using oligonucleotide microarrays. Out of the 12,600 genes investigated, 82 were upregulated and 16 were downregulated and many of these were involved in differentiation, proliferation, and immune response. We have identified three vitamin D-responsive chromosomal loci (1p36, 19q13, and 6p25) and show the induction of various class II tumor suppressor/growth-regulatory genes in response to 1,25(OH)(2)D(3). Finally, quantitative differences in gene expression revealed a vitamin D-regulated differentiation network and identified peptidylarginine deiminases, kallikreins, serine proteinase inhibitor family members, Kruppel-like factor 4, and c-fos as vitamin D-responsive genes, whose protein products may play an important role in epidermal differentiation in normal and diseased state.

Regulation of Involucrin Gene Expression

The epidermis is a dynamic renewing structure that provides life-sustaining protection from the environment. The major cell type of the epidermis, the epidermal keratinocyte, undergoes a carefully choreographed program of differentiation. Alteration of these events results in a variety of debilitating and life-threatening diseases. Understanding how this process is regulated is an important current goal in biology. In this review, we summarize the literature regarding regulation of involucrin, an important marker gene that serves as a model for understanding the mechanisms that regulate the differentiation process. Current knowledge describing the role of transcription factors and signaling cascades in regulating involucrin gene expression are presented. These studies describe a signaling cascade that includes the novel protein kinase C isoforms, Ras, MEKK1, MEK3, and a p38delta-extracellular signal regulated kinase 1/2 complex. This cascade regulates activator protein one, Sp1, and CCATT/enhancer-binding protein transcription factor DNA binding to two discrete involucrin promoter regions, the distal- and proximal-regulatory regions, to regulate involucrin gene expression.

Treatment of skin papillomas with topical alpha-lactalbumin-oleic acid

BACKGROUND

We studied the effect on skin papillomas of topical application of a complex of alpha-lactalbumin and oleic acid (often referred to as human alpha-lactalbumin made lethal to tumor cells [HAMLET]) to establish proof of the principle that alpha-lactalbumin-oleic acid kills transformed cells but not healthy, differentiated cells.

METHODS

Forty patients with cutaneous papillomas that were resistant to conventional treatment were enrolled in a randomized, placebo-controlled, double-blind study, in which alpha-lactalbumin-oleic acid or saline placebo was applied daily for three weeks and the change in the volume of each lesion was recorded. After this first phase of the study, 34 patients participated in the second phase, an open-label trial of a three-week course of alpha-lactalbumin-oleic acid. Approximately two years after the end of the open-label phase of the study, 38 of the original 40 patients were examined, and long-term follow-up data were obtained.

RESULTS

In the first phase of the study, the lesion volume was reduced by 75 percent or more in all 20 patients in the alpha-lactalbumin-oleic acid group, and in 88 of 92 papillomas; in the placebo group, a similar effect was evident in only 3 of 20 patients (15 of 74 papillomas) (P<0.001). After the patients in the initial placebo group had been treated with alpha-lactalbumin-oleic acid in the second phase of the study, a median reduction of 82 percent in lesion volume was observed. At follow-up two years after the end of the second phase, all lesions had completely resolved in 83 percent of the patients treated with alpha-lactalbumin-oleic acid, and the time to resolution was shorter in the group originally assigned to receive alpha-lactalbumin-oleic acid than among patients originally in the placebo group (2.4 vs. 9.9 months; P<0.01). No adverse reactions were reported, and there was no difference in the outcomes of treatment between immunocompetent and immunosuppressed patients.

CONCLUSIONS

Treatment with topical alpha-lactalbumin-oleic acid has a beneficial and lasting effect on skin papillomas.

1,25-Dihydroxyvitamin D3 inhibits ultraviolet B-induced apoptosis, Jun kinase activation, and interleukin-6 production in primary human keratinocytes

We investigated the capacity of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] to protect human keratinocytes against the hazardous effects of ultraviolet B (UVB)-irradiation, recognized as the most important etiological factor in the development of skin cancer. Cytoprotective effects of 1,25(OH)(2)D(3) on UVB-irradiated keratinocytes were seen morphologically and quantified using a colorimetric survival assay. Moreover, 1,25(OH)(2)D(3) suppressed UVB-induced apoptotic cell death. An ELISA, detecting DNA-fragmentation, demonstrated that pretreatment of keratinocytes with 1,25(OH)(2)D(3) 1 microM for 24 h reduced UVB-stimulated apoptosis by 55-70%. This suppression required pharmacological concentrations 1,25(OH)(2)D(3) and a preincubation period of several hours. In addition, 1,25(OH)(2)D(3) also inhibited mitochondrial cytochrome c release (90%), a hallmark event of UVB-induced apoptosis. Furthermore, we demonstrated that 1,25(OH)(2)D(3) reduced two important mediators of the UV-response, namely, c-Jun-NH(2)-terminal kinase (JNK) activation and interleukin-6 (IL-6) production. As shown by Western blotting, pretreatment of keratinocytes with 1,25(OH)(2)D(3) 1 microM diminished UVB-stimulated JNK activation with more than 30%. 1,25(OH)(2)D(3) treatment (1 microM) reduced UVB-induced IL-6 mRNA expression and secretion with 75-90%. Taken together, these findings suggest the existence of a photoprotective effect of active vitamin D(3) and create new perspectives for the pharmacological use of active vitamin D compounds in the prevention of UVB-induced skin damage and carcinogenesis.