Anchorage-dependent expression of the vitamin D receptor in normal human keratinocytes

Designing a label-free electrochemical aptasensor based on polypyrrole-l-cysteine-reduced graphene oxide nanocomposite for detection of 25-hydroxyvitamin D3

Reliable and precise quantification of 25-hydroxyvitamin D3 in clinical samples is vital because vitamin D3 deficiency lead to several disorders, such as mental illness, osteoporosis, and coronavirus disease. Herein, we report the fabrication of a novel electrochemical aptasensor using a nanocomposite, including reduced graphene oxide, pyrrole, and l-cysteine, for the sensitive detection of 25-hydroxyvitamin D3 . Subsequently, the aptamer of 25-hydroxyvitamin D3 was immobilized on the surface of the modified electrode. Differential pulse voltammetry signals were utilized for studying the binding and measurement of 25-hydroxyvitamin D3 based on the oxidation peak. Under the optimum conditions, the designed electrochemical aptasensor exhibited a linear detection range of 0.001-150 nM, with a limit of detection of 0.006 nM. Furthermore, the proposed aptasensor selectively detected 25-hydroxyvitamin D3 compared to other analogs. Moreover, this aptasensor was successfully applied for the detection of 25-hydroxyvitamin D3 in human serum samples, which were quantified by the enzyme-linked immunosorbent assay method. The acceptable recoveries of 82.67%-111.07% demonstrated that this proposed electrochemical aptasensor can be a promising alternative for clinical methods of vitamin D determination.

Protection from Ultraviolet Damage and Photocarcinogenesis by Vitamin D Compounds

Exposure of skin cells to UV radiation results in DNA damage, which if inadequately repaired, may cause mutations. UV-induced DNA damage and reactive oxygen and nitrogen species also cause local and systemic suppression of the adaptive immune system. Together, these changes underpin the development of skin tumours. The hormone derived from vitamin D, calcitriol (1,25-dihydroxyvitamin D₃) and other related compounds, working via the vitamin D receptor and at least in part through endoplasmic reticulum protein 57 (ERp57), reduce cyclobutane pyrimidine dimers and oxidative DNA damage in keratinocytes and other skin cell types after UV. Calcitriol and related compounds enhance DNA repair in keratinocytes, in part through decreased reactive oxygen species, increased p53 expression and/or activation, increased repair proteins and increased energy availability in the cell when calcitriol is present after UV exposure. There is mitochondrial damage in keratinocytes after UV. In the presence of calcitriol, but not vehicle, glycolysis is increased after UV, along with increased energy-conserving autophagy and changes consistent with enhanced mitophagy. Reduced DNA damage and reduced ROS/RNS should help reduce UV-induced immune suppression. Reduced UV immune suppression is observed after topical treatment with calcitriol and related compounds in hairless mice. These protective effects of calcitriol and related compounds presumably contribute to the observed reduction in skin tumour formation in mice after chronic exposure to UV followed by topical post-irradiation treatment with calcitriol and some, though not all, related compounds.

1,25(OH)2D3 regulates the proangiogenic activity of pericyte through VDR-mediated modulation of VEGF production and signaling of VEGF and PDGF receptors

We have previously demonstrated that the active form of vitamin D (calcitriol; 1,25(OH)₂D₃) is a potent inhibitor of retinal neovascularization. However, the underlying molecular and cellular mechanisms involved remained poorly understood. Perivascular supporting cells including pericytes (PC) play important roles during angiogenesis, vascular maturation, and stabilization of blood vessels. How 1,25(OH)₂D₃ affects retinal PC proliferation and migration, and whether these effects are mediated through vitamin D receptor (VDR), are unknown. Here, we determined the impact of 1,25(OH)₂D₃ on retinal PC prepared from wild‐type (Vdr+/+) and VDR‐deficient (Vdr−/−) mice. Retinal PC expressed significantly higher VDR levels compared to retinal endothelial cells (EC). Unlike retinal EC, 1,25(OH)₂D₃ significantly decreased PC proliferation and migration and resulted in a G₀/G₁ cell cycle arrest. Although 1,25(OH)₂D₃ did not inhibit the proliferation of Vdr−/− PC, it did inhibit their migration. PC adhesion to various extracellular matrix (ECM) proteins and ECM production were also affected by incubation of PC with 1,25(OH)₂D₃. Vdr−/− PC were more adherent compared with Vdr+/+ cells. Mechanistically, incubation of Vdr+/+ PC with 1,25(OH)₂D₃ resulted in an increased expression of vascular endothelial growth factor (VEGF) and attenuation of signaling through VEGF‐R2 and platelet‐derived growth factor receptor‐beta. Incubation with soluble VEGF‐R1 (sFlt‐1) partially reversed the effect of VEGF on Vdr+/+ PC. In addition, incubation of Vdr+/+ PC with VEGF or inhibition of VEGF‐R2 increased VDR expression. Together, these results suggest an important role for retinal PC as a target for vitamin D and VDR action for attenuation of angiogenesis.

Highly sensitive detection of 25-HydroxyvitaminD3 by using a target-induced displacement of aptamer

For the prevention of 25-HydroxyvitaminD₃ deficiency, in this study, aptamers which can bind to 25-HydroxyvitaminD₃ with high specificity and affinity, were successfully developed by using immobilization-free, graphene oxide-based systemic evolution of ligands by exponential enrichment (GO-SELEX) method. The 9 sequences including VDBA14 aptamer were obtained out of 16 aptamer candidates, based on the specificity and affinity of the aptamers confirmed by both the gold nanoparticles (AuNPs)-based colorimetric assay and the isothermal titration calorimetry (ITC) method. Among them, the aptamer, VDBA14, developed in this study was found to show a great affinity to 25-HydroxyvitaminD₃, with 11nM of its Kd value. Moreover, the circular dichroism (CD) analysis data indicated the target-induced displacement of the aptamer VDBA14clearly. In addition, this target-induced change of the aptamer was also confirmed again by conducting two different experimental formats, the use of streptavidin-coated 96-well plates and the use of magnetic beads. The results clearly indicated that the structure of VDBA14 aptamer was changed upon the binding of the target, 25-HydroxyvitaminD₃, and so the indicator sequences (partially complementary to the aptamer sequence) tagged with an enzyme as a signaling molecule could be de-hybridized from the aptamer. Finally, the limit of detection for vitamin D based on AuNPs-based colorimetric assay using VDBA14 aptamer was found to be 1µM. All these results were taken together, the aptamer which was developed could play an exquisite role in the fields of early medical diagnosis of vitamin D deficiency with accurate, rapid and simple analytical method.

The NC11 domain of human collagen XVI induces vasculogenic mimicry in oral squamous cell carcinoma cells

Collagen XVI, a fibril-associated collagen with interrupted triple helix (FACIT) collagen, is involved in oral squamous cell carcinoma (OSCC) and glioblastoma progression. The NC11 domain of collagen XVI has been described previously with a strong implication in physiological processes. We detected the non-collagenous (NC) 11-domain in supernatants of OSCC cells after recombinant expression of full-length collagen XVI and in sera from OSCC patients and healthy individuals. Stable expression of NC11-green fluorescent protein (GFP) fusion protein in OSCC cells initiated proliferation control and block of anchorage-independent growth. Moreover, the NC11 domain triggered the generation of tubular-like net structures on laminin-rich matrix in contrast to mock-GFP control cells and cells expressing full-length collagen XVI. Taqman® quantitative PCR and diaminobenzidine staining in 2D- and 3D cell culture revealed a significantly increased gene and protein expression of VEGFR1, VEGFR2 and uPAR in recombinant NC11-GFP-expressing cells. Specific VEGF receptor inhibition with Axitinib or fetal calf serum heat inactivation prevented formation of tubular-like net structures. Accordantly, NC11-GFP coated culture slides led to an increase of focal adhesion contact formation and the upregulation of VEGFR1 and uPAR in three different non-transfected OSCC cell lines. In summary, we suggest that the NC11 domain of collagen XVI is a potential biomarker for OSCC and triggers vasculogenic mimicry via upregulation of endothelial receptors VEGFR1, VEGFR2 and uPAR in 2D- and 3D OSCC cell culture conditions.

Calcitriol treatment improves methyl aminolaevulinate-based photodynamic therapy in human squamous cell carcinoma A431 cells

BACKGROUND

Photodynamic therapy (PDT) using methyl aminolaevulinate (MAL) provides a new, approved method for treatment of skin cancer and its precursors. However, MAL-based PDT is not very efficient for poorly differentiated skin carcinoma. Thus, novel strategies to enhance the PDT effect are needed.

OBJECTIVES

In order to improve the efficacy of MAL-based PDT, we investigated the effect of adding calcitriol, a prodifferentiation hormone, to human squamous cell carcinoma A431 cells in vitro.

METHODS

A short course (24 h) of calcitriol pretreatment was applied in A431 cells, and, subsequently, MAL-induced protoporphyrin IX (PpIX) was measured.

RESULTS

Calcitriol pretreatment of the cells elevated their PpIX levels. Furthermore, the cell damage after exposure to blue light was significantly higher in calcitriol-treated cells. Increased photoinactivation correlated with higher levels of PpIX in the calcitriol-pretreated cells.

CONCLUSIONS

Calcitriol enhances MAL-based PDT in A431 cells.

STAT5a/PPARγ Pathway Regulates Involucrin Expression in Keratinocyte Differentiation

Signal transducers and activators of transcription (STATs) are critical to growth factor-mediated intracellular signal transduction. We observed the rapid expression and activation of STAT5a during keratinocyte differentiation induced by suspension culture. STAT5a expression preceded that of involucrin, an important molecule in the terminal differentiation of keratinocytes. To determine whether STAT5a regulated involucrin expression, we expressed a dominant-negative (dn) STAT5a that blocks the dimerization of STAT5 and inhibits its nuclear translocation. We found that dn-STAT5a inhibited involucrin expression in keratinocytes. Given that STAT5 regulates adipogenesis via activating the peroxisome proliferator-activated receptor (PPAR) gamma signal, we hypothesized that STAT5a regulated involucrin expression in the same manner. To test this hypothesis, we examined the expression and transactivation of PPARgamma in a suspension culture of keratinocytes. Suspension culture induced PPARgamma expression and triggered PPARgamma transactivation rapidly and dn-STAT5a downregulated this induction and suppressed PPARgamma transactivation. Furthermore, preincubation with the PPARgamma/retinoid X-receptor inhibitor HX-531 or the introduction of a dn-PPARgamma prevented the activation of involucrin promoter and inhibited its induction. This report provides early evidence of a major role for STAT5a in the differentiation of keratinocytes, where it contributes to involucrin expression by activating the PPARgamma signal.

1α,25-Dihydroxyvitamin D3 Targets PTEN-Dependent Fibronectin Expression to Restore Thyroid Cancer Cell Adhesiveness

We have previously reported that the hormonal form of 1alpha,25-dihydroxyvitamin D3 (1,25-VD3), and its noncalciomimetic analog EB1089, arrest the growth of human thyroid cancer cells by increasing the cell cycle inhibitor p27. In the present study, we investigated whether the tumor-suppressive effects of vitamin D (VD) compounds may also be mediated by mechanisms that govern cell adhesiveness. Both 1,25-VD3 and EB1089 increased cell adhesiveness, an effect that was accompanied by consistent increases in fibronectin (FN) expression. Introduction of small interfering RNA against FN resulted in down-regulation of FN expression and diminished cell adhesiveness to a collagen-type I matrix. To determine whether this action of 1,25-VD3 was mediated through the PTEN/phosphoinositol 3-kinase pathway, we examined whether this tumor suppressor protein/dual phosphatase can influence FN expression and consequently cell adhesiveness Overexpression of wild-type PTEN induced FN expression as well as cell adhesiveness. In contrast, introduction of mutant forms of PTEN failed to induce FN and led to diminished cell adhesiveness. Conversely, small interfering RNA-mediated PTEN down-regulation attenuated FN expression as well as cell adhesiveness. The attenuated FN expression was also associated with relative insensitivity to 1,25-VD3 growth-suppressive action. Cells down-regulated for FN demonstrated a more aggressive growth pattern in xenografted mice and were also relatively insensitive to 1,25-VD3 treatment. Taken together, our findings highlight the significance of FN in modulating thyroid cancer cell adhesiveness and, at least in part, in mediating VD actions on neoplastic cell growth.

Psoriatic architecture constructed by epidermal remodeling

Epidermal remodeling is the concept that epidermal architecture is determined by a simple self-organizing mechanism; epidermal hyperproliferation constructs typical psoriatic architecture. This is based on the assumption that the enlargements in both the two-dimensional proliferative compartment (basal cell layer) and three-dimensional whole epidermal volume coexist. During this process, the dermal papillae become markedly, but passively, expanded by enlargement of the proliferative compartment. This creates a considerable shrinkage force against the crowded basal cell layer, which is forced to lose adherence to the dermal extracellular matrix (ECM). This results in anoikis, a type of apoptosis characterized by cell detachment, and, consequently, a markedly diminished epidermal turnover time in psoriasis. The papillary shrinkage force also explains the fact that dermal papillary height does not exceed a certain limit. At the cessation of hyperproliferation a normalisation remodeling takes place toward normal tissue architecture. Thus the concept of epidermal remodeling explains the self-organizing mechanism of the architectural change in psoriasis, which is essentially a reversible disorder depending on epidermal hyperproliferation.

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.

1,25-Dihydroxyvitamin D down-regulates cell membrane growth- and nuclear growth-promoting signals by the epidermal growth factor receptor

1,25(OH)(2)D(3) antiproliferative properties are widely known. However, the molecular bases of these properties are only partially elucidated. Since 1,25(OH)(2)D(3) effectively arrests growth in many tumors and hyperplastic tissues whose growth is driven by co-expression of EGFR and its ligand TGF-alpha, it was hypothesized that 1,25(OH)(2)D(3) could affect the TGF-alpha/EGFR-autocrine growth loop. This study examined 1,25(OH)(2)D(3) regulation of EGFR-growth signals, using human epidermoid A431 cells, in which the overexpression of EGFR and TGF-alpha constitute the major autocrine mitogenic signal. 1,25(OH)(2)D(3) inhibited autocrine and EGF-induced A431 cell proliferation. Furthermore, 1,25(OH)(2)D(3) changed the cellular localization of both TGF-alpha and EGFR and inhibited ligand-dependent phosphorylation of EGFR and ERK1/2. In addition, 1,25(OH)(2)D(3) impaired autocrine and EGF-induced nuclear translocation of activated EGFR and, consequently, its binding to AT-rich DNA sequences and transcriptional activation of the cyclin D1 promoter. These results demonstrate that 1,25(OH)(2)D(3) alters EGFR membrane trafficking and down-regulates EGFR growth signaling.

Get a ligand, get a life: integrins, signaling and cell survival

Programmed cell death is crucial for the development and maintenance of multicellular organisms. The decision to live, or to die, depends, at the cellular level, upon the cell's interaction with extracellular cues that trigger cell signaling pathways promoting survival or death. The extracellular matrix (ECM) influences the execution of the apoptotic program through the actions of adhesion receptors. Among these, integrins initiate a variety of downstream signaling events in response to ECM ligation. Integrins directly activate survival pathways via the PI 3-kinase and MAPK pathways and act as essential cofactors for their stimulation by growth factors. Conversely, elevated integrin expression in the absence of appropriate ligands, or in the presence of natural or synthetic antagonists, can promote apoptosis under otherwise permissive growth conditions. Integrins thus act in a crucial biosensory role, coordinating survival or death responses as a function of ECM composition. This dual function provides an elegant mechanism through which tissue-remodeling events may regulate cell death or survival in a temporal, ECM-governed manner.

Vitamin D receptor expression is linked to cell cycle control in normal human keratinocytes

To improve our understanding of the cutaneous vitamin D system, we studied vitamin D receptor (VDR) gene regulation in cultured human keratinocytes. Because VDR and its ligand 1 alpha,25-dihydroxyvitamin D(3) have been implicated in epidermal growth control, we investigated VDR expression as related to cellular proliferation by using different cell cycle synchronization protocols. Keratinocytes, deprived of growth factors, were forced into quiescence and a concomitant loss of VDR expression was observed. Mitogenic stimulation of these G(0) cells however quickly upregulated VDR levels several hours ahead the G(1)-S transition point. Growth arrest at the G(1)-S border by mimosine treatment or at the metaphase by nocodazole also downregulated VDR levels but a restoration of VDR expression was again quickly achieved after reentering the cell cycle. These findings indicate that VDR expression in keratinocytes is restricted to actively cycling cells, but not limited to one particular phase of the cell cycle.

Suppression of vitamin D receptor and induction of retinoid X receptor alpha expression during squamous differentiation of cultured keratinocytes

To gain more insight in the role of the vitamin D system in epidermal differentiation, we studied the expression of the vitamin D receptor and its heterodimeric partner retinoid X receptor alpha in cultured normal human keratinocytes during squamous differentiation, as triggered by different approaches. Northern and western blot analysis allowed us to investigate mRNA and protein levels of these nuclear receptors and of markers for growth control (c-myc, cyclin D1, p21WAF1) and differentiation (keratinocyte transglutaminase, small proline rich proteins). Growing cells to postconfluence was a potent stimulus for growth arrest and differentiation with concomitant suppression of vitamin D receptor and induction of retinoid X receptor alpha, at both the mRNA and the protein level. These changes could be prevented by concomitant treatment with epidermal growth factor or keratinocyte growth factor. Subjecting the cells to a calcium switch leading to stratification and differentiation lowered vitamin D receptor protein levels without affecting vitamin D receptor mRNA and induced both retinoid X receptor alpha mRNA and protein. Interferon-gamma and the phorbolester 12-O-tetradecanoyl phorbol 13-acetate, two well-known inducers of keratinocyte differentiation, both inhibited vitamin D receptor expression but only interferon-gamma induced retinoid X receptor alpha. The decreased vitamin D receptor expression was accompanied by reduced vitamin D responsiveness (as assessed by 24-hydroxylase mRNA induction) in postconfluent, high calcium, and 12-O-tetradecanoyl phorbol 13-acetate treated keratinocytes but not with interferon-gamma treatment. Taken together, our results associate vitamin D receptor expression with undifferentiated, proliferating keratinocytes, whereas retinoid X receptor alpha expression appears to be related to the differentiated phenotype. Therefore, proliferating and differentiating keratinocytes may be differentially targeted by active vitamin D metabolites.

The flavonoid apigenin suppresses vitamin D receptor expression and vitamin D responsiveness in normal human keratinocytes

Apigenin, a flavonoid with chemopreventive properties, induces cellular growth arrest, with concomitant inhibition of intracellular signaling cascades and decreased proto-oncogene expression. We report that apigenin potently inhibited vitamin D receptor (VDR) mRNA and protein expression in human keratinocytes without changes in VDR mRNA half-life. Concurrently, downregulation of retinoid X receptor alpha, a dramatic loss of c-myc mRNA, and upregulation of p21(WAF1) took place. Furthermore, a nearly complete suppression of vitamin D responsiveness was observed as estimated by induction of 24-hydroxylase mRNA. The apigenin effect on VDR expression was shared by some other (quercetine and fisetine) but not all tested flavonoids. Interestingly, the apigenin-mediated VDR suppression was counteracted by the NFkappaB inhibitors sodium salicylate and caffeic acid phenethyl ester. The presented results propose suppression of nuclear receptor levels as a novel mechanism whereby flavonoids exert their pleiotropic effects. This study may also contribute to the understanding of the regulation of VDR expression in epidermal keratinocytes.