Oestradiol-17 beta modulates PAF-evoked phospholipase D activity but not inositide-lipid hydrolysis in human endometrial cell line, HEC-1B.

Platelet-activating factor (PAF) has been shown to stimulate phospholipase D (PLD) activity in human endometrium. The effect of 17 beta-oestradiol on PAF- and 12-O-tetradecanoylphorbol 13-acetate (TPA)-evoked PLD activity assayed as an accumulation of [3H]phosphatidylbutanol was examined in [3H]myristic acid labelled in a human endometrial epithelial cell line HEC-1B. TPA stimulated PLD activity in a dose-dependent manner whereas PAF had no significant effect on PLD activity. Following 48 h pretreatment with 100 nM 17 beta-oestradiol, PAF evoked PLD activity while leaving inositol trisphosphate accumulation in myo-[2-3H] inositol-labelled HEC-1B cells unaffected. In the 17 beta-oestradiol-treated cells, TPA-stimulated PLD activity was significantly elevated at 100 nM TPA (P < 0.05) and 1 microM TPA (P < 0.05) compared to responses in the untreated cells, suggesting that 17 beta-oestradiol may upregulate PKC activity. Interestingly, following a 30 min pretreatment of HEC-1B cells with a range of 17 beta-oestradiol concentrations. TPA (10 nM) and PAF (100 nM) stimulated PLD activity. However, TPA-stimulated PLD activity levels fell 10-fold while PAF-mediated PLD activity remained elevated at 10 nM and 100 nM concentrations of 17 beta-oestradiol suggesting a different mechanism of activation. These results indicate that 17 beta-oestradiol can upregulate PAF-induced PLD activity in HEC-1B cells.