Lipid second messenger regulation: the role of diacylglycerol kinases and their relevance to hypertension.

Extracellular stimuli elicit cellular responses through generation of intracellular second messengers. The lipid second messenger diacylglycerol is produced following activation of the phosphoinositide signalling system. Diacylglycerol is the physiological activator of protein kinase C but also interacts indirectly with other signalling molecules such as small G proteins. Diacylglycerol kinases convert diacylglycerol to phosphatidic acid so terminating signalling through diacylglycerol. However, phosphatidic acid itself has a lipid second messenger role, with targets distinct from those of its precursor diacylglycerol. Therefore, diacylglycerol kinases occupy a central position in signal transduction and regulation of their activity is crucial to cellular function. A family of nine mammalian diacylglycerol kinases have been identified. Their structural diversity and complex pattern of tissue expression suggests that they function in distinct cellular processes. In addition to the plasma membrane, diacylglycerol kinases are found at the nucleus and cytoskeleton and translocation between subcellular compartments occurs with agonist stimulation. In small arteries diacylglycerol kinase activity is increased by adrenergic stimulation implying a role in vascular smooth muscle responses. Due to their role as key regulators of protein kinase C activity diacylglycerol kinases may play a role in the cardiovascular changes that occur in hypertension and as such could represent novel therapeutic targets.