123 Tunneling nanotubes in human keratinocytes treated with vitamin D

The vitamin D receptor (VDR) and its ligand 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] are required for normal keratinocyte differentiation. Both the epidermis and the hair follicle are disrupted in VDR-null mice. Hairless (Hr), a presumptive transcription factor with no known ligand, when mutated, disrupts hair follicle cycling similar to the effects of VDR mutations. Hr, like VDR, is found in the nuclei of keratinocytes in both epidermis and hair follicle. To investigate the potential interaction between Hr and VDR on keratinocyte differentiation, we examined the effect of Hr expression on vitamin D-responsive genes in normal human keratinocytes. Inhibition of Hr expression in keratinocytes potentiated the induction of vitamin D-responsive genes, including involucrin, transglutaminase, phospholipase C-γ1, and 25-hydroxyvitamin D-24-hydroxylase (24-hydroxylase) by 1,25(OH)2D3. Overexpression of Hr in human keratinocytes suppressed the induction of these vitamin D-responsive genes by 1,25(OH)2D3. Coimmunoprecipitation, DNA mobility shift assays, and chromatin immunoprecipitation revealed that Hr binds to VDR in human keratinocytes. Hr binding to the VDR was eliminated by 1,25(OH)2D3, which recruited the coactivator vitamin D receptor-interacting protein 205 (DRIP205) to the VDR/vitamin D response element complex. These data indicate that Hr functions as a corepressor of VDR to block 1,25(OH)2D3 action on keratinocytes.

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Mitochondrial potassium channels: A novel calcitriol target

Cellular & Molecular Biology Letters ◽

10.1186/s11658-021-00299-0 ◽

2022 ◽

Vol 27 (1) ◽

Author(s):

Anna M. Olszewska ◽

Adam K. Sieradzan ◽

Piotr Bednarczyk ◽

Adam Szewczyk ◽

Michał A. Żmijewski

Keyword(s):

Vitamin D ◽

Potassium Channels ◽

Potassium Channel ◽

Mitochondrial Membrane ◽

Human Keratinocytes ◽

Inner Mitochondrial Membrane ◽

Open Probability ◽

Expression Of Genes ◽

High Calcium ◽

Genes Encoding

Abstract Background Calcitriol (an active metabolite of vitamin D) modulates the expression of hundreds of human genes by activation of the vitamin D nuclear receptor (VDR). However, VDR-mediated transcriptional modulation does not fully explain various phenotypic effects of calcitriol. Recently a fast non-genomic response to vitamin D has been described, and it seems that mitochondria are one of the targets of calcitriol. These non-classical calcitriol targets open up a new area of research with potential clinical applications. The goal of our study was to ascertain whether calcitriol can modulate mitochondrial function through regulation of the potassium channels present in the inner mitochondrial membrane. Methods The effects of calcitriol on the potassium ion current were measured using the patch-clamp method modified for the inner mitochondrial membrane. Molecular docking experiments were conducted in the Autodock4 program. Additionally, changes in gene expression were investigated by qPCR, and transcription factor binding sites were analyzed in the CiiiDER program. Results For the first time, our results indicate that calcitriol directly affects the activity of the mitochondrial large-conductance Ca2+-regulated potassium channel (mitoBKCa) from the human astrocytoma (U-87 MG) cell line but not the mitochondrial calcium-independent two-pore domain potassium channel (mitoTASK-3) from human keratinocytes (HaCaT). The open probability of the mitoBKCa channel in high calcium conditions decreased after calcitriol treatment and the opposite effect was observed in low calcium conditions. Moreover, using the AutoDock4 program we predicted the binding poses of calcitriol to the calcium-bound BKCa channel and identified amino acids interacting with the calcitriol molecule. Additionally, we found that calcitriol influences the expression of genes encoding potassium channels. Such a dual, genomic and non-genomic action explains the pleiotropic activity of calcitriol. Conclusions Calcitriol can regulate the mitochondrial large-conductance calcium-regulated potassium channel. Our data open a new chapter in the study of non-genomic responses to vitamin D with potential implications for mitochondrial bioenergetics and cytoprotective mechanisms.

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Tumor Necrosis Factor-α Regulation of 1,25-Dihydroxy vitamin D Production by Human Keratinocytes*

Endocrinology ◽

10.1210/endo-129-1-33 ◽

1991 ◽

Vol 129 (1) ◽

pp. 33-38 ◽

Cited By ~ 54

Author(s):

DANIEL D. BIKLE ◽

SREEKUMAR PILLAI ◽

ELAINE GEE ◽

MARA HINCENBERGS

Keyword(s):

Vitamin D ◽

Tumor Necrosis Factor ◽

Tumor Necrosis ◽

Tumor Necrosis Factor Α ◽

Human Keratinocytes ◽

Factor Α ◽

Necrosis Factor

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20-Hydroxyvitamin D2is a noncalcemic analog of vitamin D with potent antiproliferative and prodifferentiation activities in normal and malignant cells

AJP Cell Physiology ◽

10.1152/ajpcell.00203.2010 ◽

2011 ◽

Vol 300 (3) ◽

pp. C526-C541 ◽

Cited By ~ 67

Author(s):

Andrzej T. Slominski ◽

Tae-Kang Kim ◽

Zorica Janjetovic ◽

Robert C. Tuckey ◽

Radoslaw Bieniek ◽

...

Keyword(s):

Vitamin D ◽

Catalytic Efficiency ◽

Human Keratinocytes ◽

Melanoma Cells ◽

Time Dependent ◽

Epidermal Keratinocytes ◽

Dependent Manner ◽

Cell Type ◽

Comparable Rate

20-hydroxyvitamin D2[20(OH)D2] inhibits DNA synthesis in epidermal keratinocytes, melanocytes, and melanoma cells in a dose- and time-dependent manner. This inhibition is dependent on cell type, with keratinocytes and melanoma cells being more sensitive than normal melanocytes. The antiproliferative activity of 20(OH)D2is similar to that of 1,25(OH)2D3and of newly synthesized 1,20(OH)2D2but significantly higher than that of 25(OH)D3. 20(OH)D2also displays tumorostatic effects. In keratinocytes 20(OH)D2inhibits expression of cyclins and stimulates involucrin expression. It also stimulates CYP24 expression, however, to a significantly lower degree than that by 1,25(OH)2D3or 25(OH)D3. 20(OH)D2is a poor substrate for CYP27B1 with overall catalytic efficiency being 24- and 41-fold lower than for 25(OH)D3with the mouse and human enzymes, respectively. No conversion of 20(OH)D2to 1,20(OH)2D2was detected in intact HaCaT keratinocytes. 20(OH)D2also demonstrates anti-leukemic activity but with lower potency than 1,25(OH)2D3. The phenotypic effects of 20(OH)D2are mediated through interaction with the vitamin D receptor (VDR) as documented by attenuation of cell proliferation after silencing of VDR, by enhancement of the inhibitory effect through stable overexpression of VDR and by the demonstration that 20(OH)D2induces time-dependent translocation of VDR from the cytoplasm to the nucleus at a comparable rate to that for 1,25(OH)2D3. In vivo tests show that while 1,25(OH)2D3at doses as low as 0.8 μg/kg induces calcium deposits in the kidney and heart, 20(OH)D2is devoid of such activity even at doses as high as 4 μg/kg. Silencing of CY27B1 in human keratinocytes showed that 20(OH)D2does not require its transformation to 1,20(OH)2D2for its biological activity. Thus 20(OH)D2shows cell-type dependent antiproliferative and prodifferentiation activities through activation of VDR, while having no detectable toxic calcemic activity, and is a poor substrate for CYP27B1.

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