1,25-dihydroxyvitamin D-3 induces phospholipase D-1 expression in primary mouse epidermal keratinocytes

The hormone 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3) elicits the programm ed pattern of differentiation in epidermal keratinocytes. Based on data ind icating a potential role of phospholipase D (PLD) in mediating keratinocyte differentiation, we investigated the effect of 1,25(OH),D, on PLD expressi on, A 24-h exposure to 1,25(OH)(2)D-3 stimulated PLD-1, but not PLD-2, mRNA expression. This 1,25(OH)(2)D-3-enhanced expression was accompanied by inc reased total PLD and PLD-1 activity. Time course studies indicated that 1,2 5(OH)(2)D-3 induced PLD-1 expression by 8 h, with a maximal increase at 20- 24 h. Exposure to 1,25(OH)(2)D-3 inhibited proliferation over the same time period with similar kinetics. Expression of the early (spinous) differenti ation marker keratin 1 decreased in response to 1,25(OH)(2)D-3 over 12-24 h , Treatment with 1,25(OH)(2)D-3 enhanced the activity of transglutaminase, a late (granular) differentiation marker, by 12 h with a maximal increase a fter 24 h. In situ hybridization studies demonstrated that the highest leve ls of PLD-1 expression are in the more differentiated (spinous and granular ) layers of the epidermis, with little expression in basal keratinocytes. O ur results suggest a role for PLD expression/activity during keratinocyte d ifferentiation.