[Contralateral infarction in the territory of the recurrent artery of Heubner after anterior communicating artery aneurysm surgery].

We report a rare case of postoperative infarction in the territory of the contralateral recurrent artery of Heubner (RAH) after surgery. A 67-year-old male was treated by the right pterional approach with clipping surgery for an unruptured anterior communicating artery aneurysm projecting inferiorly. Postoperative CT scan revealed infarctions in the left caudate head and the left putamen. In this case, the RAH probably coursed inferiorly to the A1 segment and was behind the aneurysmal dome. These infarctions were considered to result from occlusion of the left RAH because the clip blade extended too far beyond the aneurysmal neck.

Diacylglycerol kinase gamma serves as an upstream suppressor of Rac1 and lamellipodium formation.

Nine diacylglycerol kinase (DGK) isozymes have been identified. However, our knowledge of their individual functions is still limited. Here, we demonstrate the role of DGKgamma in regulating Rac1-governed cell morphology. We found that the expression of kinase-dead DGKgamma, which acts as a dominant-negative mutant, and inhibition of endogenous DGKgamma activity with R59949 induced lamellipodium and membrane ruffle formation in NIH3T3 fibroblasts in the absence of growth factor stimulation. Reciprocally, lamellipodium formation induced by platelet-derived growth factor was significantly inhibited upon expression of constitutively active DGKgamma. Moreover, the constitutively active DGKgamma mutant suppressed integrin-mediated cell spreading. These effects are isoform-specific because, in the same experiments, none of the corresponding mutants of DGKalpha and DGKbeta, closely related isoforms, affected cell morphology. These results suggest that DGKgamma specifically participates in the Rac1-mediated signaling pathway leading to cytoskeletal reorganization. In support of this, DGKgamma co-localized with dominant-active Rac1 especially in lamellipodia. Moreover, we found that endogenous DGKgamma was physically associated with cellular Rac1. Dominant-negative Rac1 expression blocked the lamellipodium formation induced by kinase-dead DGKgamma, indicating that DGKgamma acts upstream of Rac1. This model is supported by studies demonstrating that kinase-dead DGKgamma selectively activated Rac1, but not Cdc42. Taken together, these results strongly suggest that DGKgamma functions through its catalytic action as an upstream suppressor of Rac1 and, consequently, lamellipodium/ruffle formation.

Regulatory role of diacylglycerol kinase gamma in macrophage differentiation of leukemia cells.

Although nine diacylglycerol kinase (DGK) isozymes have been identified, our knowledge of their individual functions is still limited. Here we report that the levels of DGKgamma mRNA/protein in human leukemia HL-60 and U937 cells were rapidly and markedly decreased upon cellular differentiation into macrophages. In contrast, the enzyme expression remained almost unchanged in granulocytic differentiation pathway. Interestingly, the overexpression of wild-type or constitutively active DGKgamma, but not its kinase-dead mutant, markedly inhibited phorbol ester-induced cell attachment and nonspecific esterase activity, which are hallmarks of macrophage differentiation. We noted in this case that no effects were observed for the corresponding constructs of a closely related isozyme, DGKalpha. Prior to the cell attachment, phorbol ester induced translocation of DGKgamma from the cytoplasm to the cell periphery, resulting in its co-localization with F-actin together with protein kinase Cdelta. The results suggest that DGKgamma negatively regulates macrophage differentiation through its catalytic action operating on the cytoskeleton.

Alternative splicing of the human diacylglycerol kinase delta gene generates two isoforms differing in their expression patterns and in regulatory functions.

Diacylglycerol kinase (DGK) plays an important role in signal transduction through modulating the balance between two signaling lipids, diacylglycerol and phosphatidic acid. DGKdelta (type II isozyme) contains a pleckstrin homology domain at the N terminus and a sterile alpha motif domain at the C terminus. We identified another DGKdelta isoform (DGKdelta2, 135 kDa) that shared the same sequence with DGKdelta previously cloned (DGKdelta1, 130 kDa) except for the 52 residues N-terminally extended. Analysis of panels of human normal and tumor tissue cDNAs revealed that DGKdelta2 was ubiquitously expressed in all normal and tumor tissues examined, whereas the transcript of DGKdelta1 was detected only in ovary and spleen, and in a limited set of tumor-derived cells. The expression of DGKdelta2 was induced by treating cells with epidermal growth factor and tumor-promoting phorbol ester. In contrast, the levels of mRNA and protein of DGKdelta1 were suppressed by phorbol ester treatment. It thus becomes clear that the two DGKdelta isoforms are expressed under distinct regulatory mechanisms. DGKdelta1 was translocated through its pleckstrin homology domain from the cytoplasm to the plasma membrane in response to phorbol ester stimulation, whereas DGKdelta2 remained in the cytoplasm even after stimulation. Further experiments showed that the delta2-specific N-terminal sequence blocks the phorbol ester-dependent translocation of this isoform. Co-immunoprecipitation analysis of differently tagged DGKdelta1 and DGKdelta2 proteins showed that they were able to form homo- as well as hetero-oligomers. Taken together, alternative splicing of the human DGKdelta gene generates at least two isoforms, differing in their expressions and regulatory functions.