Negative feedback regulation of g _q signaling by protein kinase c is disrupted by diacylglycerol kinase ζ in cos-7 cells

Cellular response to G _q-linked agonists is shaped by regulatory inputs which determine signal strength and duration. Stimulation of phospholipase C-β (PLC-β) lipase activity results in an increase in the levels of diacylglycerol (DAG) and activation of protein kinase C (PKC) activity. PKC has been implicated in the feedback regulation of G _q signaling through actions on PLC-β and phospholipase D (PLD) lipase activity. As PKC activity is modulated by multiple layers of regulation, the physiological impact of PKC on G _q signaling is unclear. PKC signaling can be terminated by diacylglycerol kinases (DGKs) which are regulated in a cell-specific manner. The present studies investigated the contribution of the ubiquitously expressed DGKζ isoform in the regulation of PKC signaling and G _q response in transfected COS-7 cells. Genetic depletion of DGKζ protein with antisense oligonucleotides dramatically reduced DAG metabolism. The sustained increase in PKC signaling was associated with a pronounced inhibition of carbachol-stimulated lipase activity in cells co-transfected with m1 muscarinic receptor, Gα _q and either with or without PLC-β ₁. The data also reveal that sustained activation of PKC alone does not increase cellular PLD1 activity. Therefore, G ₁₂-activated RhoA is physiologically important for adequate stimulation of PLD1 activity. These data show that the impact of PKC on G _q signal transduction is determined by the background of cell-specific processes.