Depression of Type I Diacylglycerol Kinases in Pancreatic β-Cells From Male Mice Results in Impaired Insulin Secretion

Abstract

Diacylglycerol kinase (DGK) catalyzes the conversion of diacylglycerol (DAG) to phosphatidic acid. This study investigated the expression and function of DGK in pancreatic β-cells. mRNA expression of type I DGK isoforms (α, β, γ) was detected in mouse pancreatic islets and the β-cell line MIN6. Protein expression of DGKα and DGKγ was also detected in mouse β-cells and MIN6 cells. The type I DGK inhibitor R59949 inhibited high K(+)- and glucose-induced insulin secretion in MIN6 cells. Moreover, single knockdown of DGKα or DGKγ by small interfering RNA slightly but significantly decreased glucose- and high K(+)-induced insulin secretions, and the double knockdown further decreased them to the levels comparable with those induced by R59949. R59949 and DiC8, a membrane permeable DAG analog, decreased intracellular Ca(2+) concentration elevated by glucose and high K(+) in MIN6 cells. Real-time imaging in MIN6 cells expressing green fluorescent protein-tagged DGKα or DGKγ showed that the DGK activator phorbol 12-myristate 13-acetate rapidly induced translocation of DGKγ to the plasma membrane, whereas high K(+) slowly translocated DGKα and DGKγ to the plasma membrane. R59949 increased the DAG content in MIN6 cells when stimulated with high KCl, whereas it did not increase the DAG content but decreased the phosphatidic acid content when stimulated with high glucose. Finally, R59949 was confirmed to inhibit high K(+)-induced insulin secretion from mouse islets and glucose-induced insulin secretion from rat islets. These results suggest that DGKα and DGKγ are present in β-cells and that the depression of these DGKs causes a decrease in intracellular Ca(2+) concentration, thereby reducing insulin secretion.

Feedback regulation of insulin secretion by extended synaptotagmin‐1

“…DAG may also contribute to insulin secretion through PKC‐independent mechanisms involving, for example, Munc‐13. Contrasting with our observations from β cells lacking E‐Syt1, elevation of PM DAG by small interfering RNA—mediated knockdown of DAG kinase results in impaired insulin secretion (16). This could be explained by a dramatic impact on whole‐cell DAG levels rather than a local modulatory effect, as we observed after E‐Syt1 knockdown.…”

“…DAG plays essential roles in β cells, both acting as a second messenger for cellular signaling and as backbone for lipid synthesis. DAG also affects insulin secretion from β cells (14, 16, 17, 32). Therefore, we aimed to find out if E‐Syt1—mediated ER‐PM contacts regulate DAG in β cells.…”

“…The mechanism by which DAG contributes to the regulation of insulin secretion is unclear. DAG accumulation in pancreatic β cells, induced by inhibition or small interfering RNA—mediated knockdown of DAG kinase, results in impaired insulin secretion (16). However, increase of PM DAG levels using the DAG analog phorbol myristate acetate (PMA) or photoswitchable DAG in intact mouse islets instead stimulates insulin secretion (17, 18).…”

Diacylglycerol Kinase alpha is Involved in the Vitamin E-Induced Amelioration of Diabetic Nephropathy in Mice

“…Recently, we reported that DGKα is also involved in insulin secretion in pancreatic β-cells 16 . Indeed, the blood glucose concentrations of DGKα −/− mice were slightly higher than those of the DGKα +/+ mice (Fig.…”

A novel IRS-1-associated protein, DGKζ regulates GLUT4 translocation in 3T3-L1 adipocytes

“…Recently there were some reports showing that diacylglycerol kinase proteins or activity are involved in the regulation of insulin bioactivity in different tissues. For example, knockdown of type I DGK (α, β, γ) proteins in pancreatic β-cells from male mice results in impairment of insulin secretion 41 . The reduced DGKδ protein expression is accompanied by the increased DAG level and elevated PKC activity, resulting in the impairment of IRS-1 tyrosine phosphorylation in skeletal muscle 42 43 44 .…”