Diacylglycerol kinase θ is translocated and phosphoinositide 3-kinase-dependently activated by noradrenaline but not angiotensin II in intact small arteries

Diacylglycerol (DG) kinase (DGK) phosphorylates the lipid second messenger DG to phosphatidic acid. We reported previously that noradrenaline (NA), but not angiotensin II (AII). increases membrane-associated DGK activity in rat small arteries [Ohanian and Heagerty (1994) Biochem. J. 300, 51-56]. Here, we have identified this DGK activity as DGK theta, present in both smooth muscle and endothelial cells of these small vessels. Subcellular fractionation of artery homogenates revealed that DGK theta was present in nuclear: plasma membrane (and/or Golgi) and cytosolic fractions. Upon NA stimulation, DGK theta translocated towards the membrane and cytosol (155 and 153% increases relative to the control, respectively) at 30 s, followed by a return to near-basal levels at 5 min; AII was without effect. Translocation to the membrane was to both Triton-soluble and -insoluble fractions. NA, but not All transiently increased DGK theta activity in immunoprecipitates( 126 % at 60 s). Membrane translocation and DGK theta activation were regulated differently: NA-induced DGK theta activation, but not translocation, was dependent on transient activation of phosphoinositide 3-kinase (PI 3-K). In addition, DGK activity co-immunoprecipitated with protein kinase B, a downstream effector of PI 3-K, and was increased greatly by NA stimulation. The rapid and agonist-specific activation of DGK theta suggests that this pathway may have a physiological role in vascular smooth-muscle responses.