1,25 dihydroxyvitamin D3 enhances the calcium response of keratinocytes

Abstract

The steroid hormone 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) regulates cell proliferation and differentiation. Intracellular calcium (Cai) concentrations play a crucial role in these events. From our previous studies, we have demonstrated a calcium receptor (CaR) in keratinocytes which appears to regulate the initial release of Cai from intracellular stores in response to extracellular calcium (Cao) and so is likely to participate in the differentiation process. In this study, we determined whether the ability of 1,25(OH)2D3 to enhance Ca++ -induced differentiation was mediated at least in part through changes in the CaR. Keratinocytes were grown in keratinocyte growth medium (KGM) with 0.03 mM, 0.1 mM, or 1.2 mM Ca and treated with 10(-8) M 1,25(OH)2D3 till harvest after 5, 7, 14, and 21 days. CaR mRNA levels were quantitated by polymerase chain reaction. The results were compared to the ability of 1,25(OH)2D3 to enhance calcium-stimulated increases in Cai. In cells grown in 0.03 mM Ca, the CaR mRNA levels decreased with time. 1,25(OH)2D3 stimulated the levels at 5 days and prevented the falloff over the subsequent 16 days. On the other hand, in cells grown in 0.1 or 1.2 mM Ca, the message levels remained high, and 1,25(OH)2D3 had no further effect. To study the functional relationship, we harvested cells after 5 and 7 days in culture following a 24 h treatment with 1,25(OH)2D3 or vehicle to measure the Cai response to 2 mM Cao. The preconfluent cells grown in 0.03 mM Ca showed a nearly twofold increase in the Cai response to Cao when pretreated with 1,25(OH)2D3, whereas the confluent cells and those grown in 1.2 mM Ca showed no enhancement by 1,25(OH)2D3. Studies with 45Ca influx into keratinocytes revealed that 1,25(OH)2D3 enhanced the influx in preconfluent and confluent cells when grown in KGM containing 0.03 mM Ca but not in cells grown in 1.2 mM calcium. We conclude that 1,25(OH)2D3 maintains the CaR mRNA levels in cells grown in 0.03 mM Ca, thus maintaining their responsiveness to Cao and so ensuring their ability to differentiate in response to the calcium signal.

UVB and Vitamin D in Psoriasis

“…Treatment of keratinocytes with a medium containing high calcium also stimulated keratinocyte differentiation by increasing the expression of involucrin and TGase I. 1,25(OH)2D also promoted keratinocyte differentiation, at least in part by increasing intracellular calcium and by increased expression of calcium receptors in keratinocytes (36). Calcitriol indirectly induces the expression of keratin 1, involucrin, TGase I, loricrin, and filaggrin, which are required for CE formation.…”

Calcium and 1,25(OH)2D: interacting drivers of epidermal differentiation

“…4 illustrates points at which 1,25(OH) 2 D interfaces with the calcium signaling system. The expression of the CaR is increased by 1,25(OH) 2 D, making the keratinocyte more sensitive to the prodifferentiating actions of calcium [45]. All of the PLC family members are induced by 1,25(OH) 2 D [46] as they are by calcium [31], and blocking PLC-␥1 expression prevents both 1,25(OH) 2 D and calcium stimulated differentiation [31,47].…”

<b>Effect of 1,25-dihydroxyvitamin D</b><b>₃</b><b> on spontaneous calcium responses in rat dental epithelial SF2 cells revealed by long-term </b><b>imaging </b>

“…How does VD3 modulate IP 3 -dependent Ca 2+ responses? It has been reported that VD3 promotes keratinocyte differentiation by increasing [Ca 2+ ] i via increased expression of phospholipase C (14,20). In addition to this genomic action, VD3 was postulated to act through a membrane-associated receptor to account for the rapid stimulation of Ca 2+ release from intracellular stores and subsequent Ca 2+ entry in skeletal muscle cells (16,19 ] i seems to be associated with similar directional cellular movements.…”

“…Many of the biological actions of VD3 are mediated by the nuclear vitamin D receptor (VDR), a ligand-dependent transcription factor belonging to the superfamily of steroid/thyroid hormone receptors (13). Moreover, VD3 modulates the intracellular Ca 2+ concentration ([Ca 2+ ] i ) in some cell types (14,16,19,20 …”