Phosphatidylcholine-specific Phospholipase C and RhoA are Involved in Thyrotropin -induced Activation of Phospholipase D in FRTL-5 Thyroid Cells

초록

We have investigated the possible involvement of phosphatidylcholine-specific phospholipase C (PC-PLC) as a source of diacylglycerol (DAG) for the thyroid stimulating hormone (TSH)-induced protein kinase C (PKC)/phospholipase D (PLD) activation in FRTL-5 thyroid cells. Treatment of TSH resulted in a both dose- and time-dependent increases in PLD activity up to 100 mU/ml and 60 min, respectively. TSH induced translocation of PKCa and RhoA from the cytosol to the membrane within 30 ~ 60 min. TSH also stimulated concurrently with PC hydrolysis and DAG/phosphorylcholine (PhoCho) production via PC-PLC. Pretreatment of cells with D609, a potent inhibitor of PC-PLC, led to significant inhibition of TSH-stimulated DAG and PhoCho production. Moreover, D609 pretreatment effectively inhibited the translocation of PKCa from the cytosol to the membrane and significantly decreased TSH-induced PLD activation. It was thus suggested that another regulating mechanism is needed to TSH-induced PLD activation. When introduced into the cells by scrape-loading, C3, an inhibitor of RhoA, partially but significantly inhibited PLD activity stimulated by TSH. According to our expectation, pretreatment of the cells with both C3 and D609 completely inhibited TSH-induced PLD activity. These findings suggest that DAG produced from cellular PC through PC-PLC plays a key role in TSH-induced PKC/PLD activation and that RhoA and PKCa are involved in the regulation of TSH-induced PLD activation in FRTL-5 thyroid cells.