Regulation of phospholipase D (PLD) in growth plate chondrocytes by 24R,25-(OH)2D3 is dependent on cell maturation state (resting zone cells) and is specific to the PLD2 isoform

Many of the effects of 1 alpha ,25-(OH)(2)D-3 and 24R,25-(OH)(2)D-3 on costochondral chondrocytes are mediated by the protein kinase C (PKC) signal transduction pathway. 1 alpha ,25-(OH)(2)D-3 activates PKC in costochondral growth zone chondrocytes through a specific membrane receptor (1 alpha ,25-mVDR), involving rapid increases in diacylglycerol via a phospholipase C (PLC)-dependent mechanism. 24R,25-(OH)(2)D-3 activates PKC in resting zone chondrocytes. Although diacylglycerol is increased by 24R,25-(OH)(2)D-3, PLC is not involved, suggesting a phospholipase D (PLD)-dependent mechanism. Here, we show that resting zone and growth zone cells express mRNAs for PLD1a, PLD1b, and PLD2. Both cell types have PLD activity, but levels are higher in resting zone cells. 24R,25-(OH)(2)D-3, but not 24S,25-(OH)(2)D-3 or 1 alpha ,25-(OH)(2)D-3, stimulates PLD activity in resting zone cells within 3 min via nongenomic mechanisms. Neither la,25-(OH)(2)D-3 nor 24R,25-(OH)(2)D-3 affected PLD in growth zone cells. Basal and 24R,25-(OH)(2)D-3-stimulated PLD were inhibited by the PLD inhibitors wortmannin and EDS. Inhibition of phosphatidylinositol S-kinase (PI 3-kinase), PKC, phosphatidylinositol-specific PLC (PI-PLC), and phosphatidylcholine-specific PLC (PC-PLC) had no effect on PLD activity. Thus, 24R,25-(OH)(2)D-3 stimulates PLD, and PI 3-kinase, PI-PLC and PKC are not involved, whereas PLD is required for stimulation of PKC by 24R,25(OH)(2)D-3 Pertussis toxin, GDP betaS, and GTP gammaS had no effect on 24R,25-(OH)(2)D-3-dependent PLD when added to cell cultures, indicating that G-proteins are not involved. These data show that PKC activation in resting zone cells is mediated by PLD and suggest that a functional 24R,25-(OH)(2)D-3-mVDR is required. The results also support the conclusion that the 24R,25-(OH)(2)D-3-responsive PLD is PLD2, since this PLD isoform is G-protein-independent. (C) 2001 Elsevier Science B.V. All rights reserved.