Heterogeneity of lipid second messenger-metabolizing enzyme, diacylglycerol kinase, in the brain in terms of molecule, localization, and function.

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Diacylglycerol kinase (DGK), which catalyzes phosphorylation of lipid second messenger, DG to phosphatidic acid (PA), is thought to be a key enzyme in the regulation of DG levels and, as a result, to be responsible for attenuating the activation of PKC. We have so far cloned several isozymes from rat brain cDNA library, and performed detailed examination of their gene expression in the brain by in situ hybridization histochemistry. In this study we analyzed precise subcellular localization of the isozymes in cDNA-transfected COS cells using green fluorescent protein-fusion expression vector. DGK-alpha was localized diffusely in both cytoplasm and nucleus in the cells. DGK-beta was distributed throughout the cytoplasm in the shape of filamentous structure, which is quite similar to the location of actin filament. DGK-gamma was seen as a reticular structure in the juxtanuclear position, which is coincided with Golgi apparatus marker. DGK-zeta was located mostly in the nucleus, as suggested by the presence of nuclear localizing signal in its primary structure. DGK-epsilon was widespread to the perinuclear area, which resembles the location pattern of endoplasmic reticulum. These data clearly show the heterogeneity of DGK in subcellular localization as well as molecular structure, suggesting that each isozyme may be responsible for the metabolism of DG, which is produced at specific subcellular site upon stimulation. Therefore it is highly conceivable that each DGK isozyme plays a unique role in the signal transduction.