The varied biological functions of DGK activity in T cells and other immune cells are summarized in Table ?Table11. Table 1 Biological functions of DGKs in T cells and other immune cells.
DAG metabolism at the T cell-APC immunological synapseSanjuan et al. and function. We also highlight recent work that has uncovered previously unappreciated roles for DGK activity, for instance in invariant NKT cell development, anti-tumor and anti-viral CD8 responses, and the directional secretion of soluble effectors. Unc13 that is localized to pre-synaptic active zones of neurons and important for neurotransmitter secretion (33). Munc13-1, Munc13-2, and Munc13-3 isoforms bind to DAG with high affinity, and translocate to the plasma membrane in response to receptor stimulation. BMS-345541 In the immune system, the Munc13-4 isoform which lacks a C1 domain (34, 35) has been shown to be important for granule maturation and exocytosis in NK cells and cytotoxic T lymphocytes (CTLs) (36, 37), and for phagosomal maturation and killing of intracellular bacteria in neutrophils (38, 39). Further studies are required to investigate parallel roles for DAG-binding Munc13 isoforms in NK cells, CTLs, neutrophils, and other types of immune cells. Over-expressing human Munc13 in opossum renal epithelial cell lines enhanced their susceptibility to apoptosis BMS-345541 after DAG treatment, suggesting that Munc13 proteins may transduce apoptosis-inducing signals downstream of DAG in some cell types (40). The role of Munc13 proteins in T cell development and function remain poorly understood. Chimaerins, a family of proteins that possess Rac-specific GTPase Activating Protein (GAP) activity, contain C1 domains that bear about 40 percent homology to those of PKCs (41, 42). Chimaerin isoforms 2 and 2 are expressed at different levels in T cells and have been shown to participate in TCR signaling (43). Results from the study suggest that these chimaerin isoforms translocate to the immunological synapse upon T cell activation, but in a manner that is independent of canonical DAG-binding by the C1 domains. Catalytic activity of these chimaerins was found to play an important role in inhibiting TCR-mediated NFAT activation. Other studies have delineated a role for 2 chimaerin in mediating DAG-dependent changes in T cell adhesion and chemotaxis (44). In this study, expression of GFP-tagged 2 chimaerin revealed that active Rac and C1-dependent PMA binding could co-operate to induce sustained localization of 2 chimaerin to the plasma membrane in Jurkat T cells. Overexpression of GFP-2 chimaerin was associated with decreased CXCL12-induced static adhesion but enhanced CXCL12-induced migration. Chimaerin proteins therefore represent an important class of DAG effectors in T cells, but further work is required to dissect aspects of their function that are dependent on BMS-345541 and independent of DAG-binding. PA-Mediated Signaling Diacylglycerol kinases and enzymes of the phospholipase D (PLDs) family act as key mediators of PA production in immune cells by phosphorylating DAG and hydrolyzing PC, respectively (7, 45) (Figure ?(Figure1).1). On the other hand, enzymes such as lipins that possess PA phosphatase activity play a critical role in turning off PA-mediated signaling by removing PA (46). Cellular levels of PA have been shown to change dynamically in response to environmental stimuli, and a wealth of data has revealed a diverse array of functions for this bioactive lipid (47). Phosphatidic acid performs its signaling functions primarily by associating with Rabbit Polyclonal to CDK1/CDC2 (phospho-Thr14) a growing number of effector molecules that include kinases such as mammalian/mechanistic target of rapamycin (mTOR) and phosphatidylinositol-4-phosphate 5-kinase (PIP5K), and phosphatases such as Src homology region 2 domain-containing BMS-345541 phosphatase 1 (SHP1) (48). In mammalian HEK293 cells, treatment with exogenous PA was found to promote the phosphorylation of S6K1 and 4E-BP1, which are substrates of mTOR complex 1 (49). This phosphorylation was abolished by rapamycin, a bacterial macrolide that inhibits mTOR activity. Results from this study showed that mitogenic stimulation of HEK293 cells led to cellular PA accumulation within 5?min. Small unilamellar vesicles containing PA could also.