Diacylglycerol kinase (DGK) has been suggested to be a pharmacological target of d‐α‐tocopherol for diabetic renal dysfunctions. However, the DGK subtypes involved in the d‐α‐tocopherol‐induced improvement of diabetic renal dysfunctions and the activation mechanisms of DGK by d‐α‐tocopherol are still unknown. Therefore, using GFP‐tagged DGKα, β, γ, ɛ and ζ, we analyzed their response to d‐α‐tocopherol and its derivatives. Only DGKα was translocated from the cytoplasm to the plasma membrane with elevation of kinase activity. In addition, troglitazone and trolox possessing ‘chroman ring’ similarly to d‐α‐tocopherol, induced the subtype‐specific translocation of DGKα. Furthermore, the translocation of DGKα was abolished by pretreatment with tyrosine kinase inhibitors or by mutation on Tyr‐334 of the kinase (YF mutant). d‐α‐tocopheryl succinate enhanced the Src‐mediated tyrosine phosphorylation of wild‐type DGKα but the same reagent did not enhance that of the YF mutant. These results demonstrate that tyrosine phosphorylation on Tyr‐334 and chroman ring are important for the d‐α‐tocopherol‐induced translocation of DGKα.

Diacylglycerol kinase (DGK) is a lipid kinase converting diacylglycerol to phosphatidic acid, and regulates many enzymes including protein kinase C, phosphatidylinositol 4-phosphate 5-kinase, and mTOR. To date, ten mammalian DGK subtypes have been cloned and divided into five groups, and they show subtype-specific tissue distribution. Therefore, each DGK subtype is thought to be involved in respective cellular responses by regulating balance of the two lipid messengers, diacylglycerol and phosphatidic acid. Indeed, the recent researches using DGK knockout mice have clearly demonstrated the importance of DGK in the immune system and its pathophysiological roles in heart and insulin resistance in diabetes. Especially, most subtypes show high expression in brain with subtype specific regional distribution, suggesting that each subtype has important and unique functions in brain. Recently, neuronal functions of some DGK subtypes have accumulated. Here, we introduce DGKs with their structural motifs, summarize the enzymatic properties and neuronal functions, and discuss the possibility of DGKs as a therapeutic target of the neuronal diseases.

Diacylglycerol kinases (DGKs) convert diacylglycerol (DG) to phosphatidic acid, and both lipids are known to play important roles in lipid signal transduction. Thereby, DGKs are considered to be a one of the key players in lipid signaling, but its physiological function remains to be solved. In an effort to investigate one of nine subtypes, we found that DGKγ came to be localized in the nucleus with time in all cell lines tested while seen only in the cytoplasm at the early stage of culture, indicating that DGKγ is transported from the cytoplasm to the nucleus. The nuclear transportation of DGKγ didn't necessarily need DGK activity, but its C1 domain was indispensable, suggesting that the C1 domain of DGKγ acts as a nuclear transport signal. Furthermore, to address the function of DGKγ in the nucleus, we produced stable cell lines of wild-type DGKγ and mutants, including kinase negative, and investigated their cell size, growth rate, and cell cycle. The cells expressing the kinase-negative mutant of DGKγ were larger in size and showed slower growth rate, and the S phase of the cells was extended. These findings implicate that nuclear DGKγ regulates cell cycle.

Beef from Japanese Black cattle (Japanese Wagyu) is renowned for its flavor characteristics. To clarify the key metabolites contributing to this rich and sweet aroma of beef, an omics analysis combined with GC-olfactometry (GC-O) and metabolomics analysis with gas chromatography–mass spectrometry (GC-MS) were applied. GC-O analysis identified 39 odor-active odorants from the volatile fraction of boiled beef distilled by solvent-assisted flavor evaporation. Eight odorants predicted to contribute to Wagyu beef aroma were compared between Japanese Black cattle and Holstein cattle using a stable isotope dilution assay with GC–tandem quadrupole mass spectrometry. By correlating the sensory evaluation values of retronasal aroma, γ-hexalactone, γ-decalactone, and γ-undecalactone showed a high correlation with the Wagyu beef aroma. Metabolomics data revealed a high correlation between the amounts of odorants and multiple metabolites, such as glutamine, decanoic acid, lactic acid, and phosphoric acid. These results provide useful information for assessing the aroma and quality of beef.

Aroma is an essential factor for meat quality. The meat of Japanese Black cattle exhibits fine marbling and a rich and sweet aroma with a characteristic lactone composition. The mechanism of lactone formation associated with beef aroma has not been elucidated. In this study, we examined the precursors of γ-hexalactone, an indicator of the sweet aroma of beef and identified the mechanism underlying γ-hexalactone production. A low-temperature vacuum system was used to prepare beef tallow from Japanese Black cattle and Holstein cattle. The odor components were identified using headspace–gas chromatography. The analysis revealed that γ-hexalactone, γ-dodecalactone, δ-tetradecalactone, and δ-hexadecalactone were present as sweet aroma components of beef tallow prepared from marbling and muscle. Since we previously reported that γ-hexalactone formation correlates with linoleic acid content in beef, we analyzed ten oxidized fatty acids derived from linoleic acid by liquid chromatography–triple quadrupole mass spectrometry and detected two hydroxy-octadecadienoic acids (9S-HODE and 13S-HODE) in beef tallow. Significant differences in arachidonic acid 15-lipoxygenase and cyclooxygenase protein expression levels among subcutaneous fat, intramuscular fat, and muscle tissue were observed. Our results suggest that the combination of linoleic acid and the expression of lipid oxidase derived from beef muscle and intramuscular fat produce hydroxy fatty acids that result in a sweet aroma.