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Cellular Signalling 16 (2004) 983 – 989 www.elsevier.com/locate/cellsig Review article Diacylglycerol kinases Bai Luo, Debra S. Regier, Stephen M. Prescott, Matthew K. Topham * The Huntsman Cancer Institute, University of Utah, 2000 Circle of Hope, Salt Lake City, UT 84112-5550, USA Received 12 March 2004; accepted 29 March 2004 Available online 6 May 2004 Abstract Diacylglycerol kinases (DGKs) phosphorylate diacylglycerol to form phosphatidic acid. In most cases, members of this large family of enzymes appear to bind and regulate proteins activated by either diacylglycerol or phosphatidic acid. Proteins that appear to be regulated, in part, by DGKs include protein kinase Cs, RasGRPs, and phosphatidylinositol kinases. By modulating the activity of these proteins, DGKs potentially affect a number of biological events including—but likely not limited to—cell growth, neuronal transmission, and cytoskeleton remodeling. D 2004 Elsevier Inc. All rights reserved. Keywords: Diacylglycerol kinases; Diacylglycerol; Phosphatidic acid; Lipid signalling; Phosphatidylinositol; Nucleus; Cytoskeleton 1. Introduction Numerous intracellular signalling pathways are initiated when phospholipase C (PLC) enzymes hydrolyze phosphatidylinositol-4,5-bisphosphate (PIP2) [1]. The products of this reaction, diacylglycerol (DAG) and inositol-1,4,5-triphosphate, transiently rise and then fall back to basal levels. These second messengers initiate two predictable events: inositol-1,4,5-triphosphate binds to intracellular receptors causing calcium release from intracellular stores, while diacylglycerol recruits and often activates signalling proteins that contain cysteine-rich, C1 domains. Several proteins contain C1 domains, the best known are protein kinase C (PKC) isoforms, which regulate a broad array of cell functions [2]. Until recently, most of the physiological effects of DAG were attributed to activation of the PKCs. However, other DAG targets exist that likely also contribute to the downstream effects of diacylglycerol [3]. For example, DAG binds and activates the family of four RasGRP nucleotide exchange factors [4 – 7], it recruits the chimaer- Abbreviations: DGK, diacylglycerol kinase; DAG, diacylglycerol; PLC, phospholipase C; PIP2, phosphatidylinositol-4,5-bisphosphate; PKC, protein kinase C; PA, phosphatidic acid; PH, pleckstrin homology; SAM, sterile alpha motif; RA, Ras association; PIP5K, phosphatidylinositol 4phosphate 5-kinase; PI, phosphatidylinositol; NLS, nuclear localization signal. * Corresponding author. Tel.: +1-801-585-0304; fax: +1-801-5856345. E-mail address: [email protected] (M.K. Topham). 0898-6568/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.cellsig.2004.03.016 ins—Rac GTPase-activating proteins—to membrane compartments [8], and it can activate some ion channels [9]. Because DAG can modulate so many signalling proteins— and consequently affects numerous signalling events—it is crucial that intracellular DAG levels be tightly regulated. The adverse effects of excessive and/or prolonged DAG signalling are best illustrated by the tumor-promoting effects of the phorbol esters. These compounds are DAG analogues that can bind C1 domains, but are very slowly metabolized. Their tumorigenic effects are likely due to persistent activation of proteins that bind phorbol esters such as PKC and RasGRP isoforms. The effects of the phorbol esters have led many to hypothesize that prolonged elevation of DAG— which is seen in tumors and in transformed cell lines [10,11]—is the equivalent of an endogenous phorbol ester. DAG can be metabolized in three ways: hydrolysis of a fatty acyl chain by diacylglycerol lipase to generate a monoacylglycerol and a free fatty acid, addition of CDPcholine or -ethanolamine to form phosphatidylcholine or phosphatidylethanolamine, or by phosphorylating the free hydroxyl group to produce phosphatidic acid (PA). Under most circumstances, its conversion to PA is considered the major route for metabolism of signalling DAG, and the reaction is catalyzed by the diacylglycerol kinases. 2. The diacylglycerol kinase gene family DGK isoforms have been identified in organisms such as Caenorhabditis elegans [12,13], Drosophila melanogaster 984 B. Luo et al. / Cellular Signalling 16 (2004) 983–989 [14 –16], and Arabidopsis thaliana [17,18], while no DGK gene has been identified in yeast. Bacteria express only one DGK enzyme, and it is an integral membrane protein capable of phosphorylating in vitro other lipids such as ceramide [19]. Bacterial DGK does not appear to have structural elements allowing regulation of its activity, suggesting that it is constitutively active and is limited by access to its substrate(s). Based on shared structural motifs, DGK isoforms in multicellular organisms are classified into five subtypes. Because most of these organisms express at least one DGK ortholog of each subtype, the five DGK subtypes appear to have distinct functions. Nine mammalian DGK isoforms have been identified (Fig. 1). The heterogeneity of this gene family is similar to the PKC and PLC families, suggesting that the DGKs are not simply lipid biosynthetic enzymes, but also have signalling roles, since enzymes involved in biosynthetic pathways usually do not have extended families. All DGK isoforms have a catalytic domain that is necessary for kinase activity. Each catalytic domain has an ATP-binding site similar to protein kinase catalytic domains with the sequence Gly-X-Gly-X-X-Gly. Mutation of the second glycine in this motif to an aspartate or alanine renders the DGK catalytically inactive [20 – 22]. Mutation of that glycine to an aspartate was first noted in the Drosophila DGK, dDGK2 [15]. The mutant dDGK2 protein is expressed in the Drosophila strain rdgA, and causes rapid retinal degeneration after birth. Although protein kinase and DAG kinase catalytic domains share some similarities, there are important structural differences between them that may allow DGK catalytic domains to access DAG in lipid bilayers, a property not required for most protein kinases. In most cases, the DGK catalytic domains are composed of a single motif, but DGKs y and D have bipartite catalytic domains [23,24], indicating that these and perhaps other DGK catalytic domains may function as two independent units in a coordinated fashion. The DGK catalytic domains may also require other motifs for maximal activity because several DGK catalytic domains have very little DAG kinase activity when expressed as isolated subunits (M.K.T., unpublished observations). However, Sakane et al. [25] demonstrated that when expressed as an isolated subunit, the catalytic domain of DGKa retained about 60% of the activity of the wild-type enzyme. However, to compare their DAG kinase activities, this group used 100,000 g supernatants, which may have eliminated most of the more active, membrane-bound, wild-type enzyme in the 100,000 g pellets. Moreover, DGKa has an inhibitory motif that, Fig. 1. The mammalian DGK family. Based on structural motifs, the nine mammalian DGKs are divided into five subtypes. All mammalian DGKs have C1 and catalytic (kinase) domains. Also shown are EF hand motifs, pleckstrin homology (PH) domains, MARCKS homology domains, nuclear localization signals (NLS), sterile alpha motifs (SAM), PDZ-binding domains, ankyrin repeats, and Ras association (RA) domains. Alternative splicing of DGKs y, ~, and D generates even more structural diversity. Several DGKh splice variants have also been identified, but are not shown, and many mammalian DGKs contain other unique structural domains of unclear significance that are also not shown. B. Luo et al. / Cellular Signalling 16 (2004) 983–989 when deleted, yields a fully active enzyme (see below). Sakane et al. [25] found that the isolated DGKa catalytic domain had only 1/3 the activity of this fully active mutant. Thus, it appears that mammalian DGK catalytic domains, unlike bacterial DGK, require other motifs such as C1 domains for maximal activity. This suggests that these other motifs function in coordination with the catalytic domain. All DGKs have at least two cysteine-rich regions homologous to the C1A and C1B motifs of PKCs [26]. In theory, these domains may bind DAG, perhaps localizing DGKs to where DAG accumulates. However, no DGK C1 domain has so far been conclusively shown to bind DAG. In fact, structural predictions suggest that most DGK C1 domains may not bind DAG. For example, Hurley et al. [26] noted that the amino acid sequences of most DGK C1 domains differed enough from those in PKCs that many DGK C1 domains may not bind DAG. Most DGKs tested were unable to bind long-lived DAG-like analogues such as PDBu [27]. However, the inability of DGK C1 domains to bind DAG-like molecules may simply reflect exquisite selectivity of DGK C1 domains for authentic DAG, unlike other C1 domains such as those in PKCs which appear to be more promiscuous. Houssa and van Blitterswijk [28] noted that in DGKs, the C1 domain closest to the catalytic domain is highly conserved, including an extended motif of 15 amino acids not present in C1 domains of other proteins or in the DGK C1 motifs further from the catalytic domain. They noted that conserved residues in this extended motif may be critical for DAG kinase activity. Taken together, these data suggest that DGK C1 domains are structurally different from C1 domains in other proteins and that the different C1 domains of a single DGK isoform may have unique functions. However, distinct functions of individual C1 domains remain to be definitively demonstrated. In addition to the C1 and catalytic domains, DGKs have other regulatory domains that form the basis for dividing them into five subtypes. Type I DGKs [29 – 31] have calcium-binding EF hand motifs and are more active in the presence of calcium [32]. Type II DGKs have pleckstrin homology (PH) domains at their amino termini [23,24]. This domain in DGKy has been shown to bind weakly and nonselectively to phosphatidylinositols [33]. Type II DGKs also have sterile alpha motifs (SAM domain) at their carboxy termini. Nagaya et al. [21] demonstrated that the SAM domain of DGKy helped localize it to the endoplasmic reticulum, and this domain also appeared necessary for homo- and hetero-oligomerization of DGKs y and D [34,35]. The physiological significance of oligomerization is not clear at this point, although in some cases, it may suppress DAG kinase activity [34]. DGKq, the only type III enzyme, has an unusual specificity toward acyl chains of DAG, strongly preferring a specific fatty acid—arachidonate—at the sn-2 position [36]. Its preference for arachidonate-DAG suggests that DGKq may be a component of the biochemical pathway that accounts for the enrichment of phosphatidylinositols with arachidonate [37]. Type IV 985 DGKs [38,39] have domains similar to the phosphorylation site domain of the MARCKS protein. This domain in both DGKs ~ and L functions as a nuclear localization signal and it is phosphorylated by conventional PKC isoforms[22,39]. Its phosphorylation in DGK~ not only reduces nuclear localization [22], but also suppresses DAG kinase activity [40] and causes it to dissociate from the PKC [41]. Type IV DGKs also have four ankyrin repeats and carboxy terminal PDZ-binding domains [42]. The type V enzyme, DGKu, has three C1 domains, a putative PH domain, and a Ras association (RA) domain [43]. The function of its RA domain is not clear, and although most RA domains bind RasGTP, van Blitterswijk found that DGKu did not bind Ras [44]. 3. Phosphatidic acid produced by DGKs may have signalling properties Several reports indicate that phosphatidic acid, the product of the DGK reaction, has signalling properties. For example, studies have indicated that PA can stimulate DNA synthesis and is potentially mitogenic [45,46]. However, these properties may have also been caused by contaminating lysophosphatidic acid. Other work indicates that PA is involved in vesicle trafficking [47] and can bind and regulate the activity of numerous enzymes, including the phosphatidylinositol 5-kinases [48], Ras-GAP [49], PKC~ [50], PAK1 [51], and protein phosphatase 1 [52]. Phosphatidic acid also helps recruit Raf to the Ras signalling complex [53]. While the majority of signalling PA is likely derived from the phospholipase D reaction [54], it is possible that PA produced by DGKs also has a signalling role. This suggests that in some cases after terminating a DAG signal, DGKs subsequently activate a PA signalling event. Flores et al. [55] presented evidence in T lymphocytes suggesting that PA from the DGK reaction had a potential role in progression of cells to S phase of the cell cycle. We recently demonstrated that DGK~ associated with type Ia phosphatidylinositol 4-phosphate 5-kinase (PIP5K), a protein activated by PA [56]. We found that co-expression of DGK~ with the PIP5K increased its phosphatidylinositol kinase activity. In addition to these examples, it is possible that DGKs modulate the activity of other phosphatidic acid protein targets. 4. Regulation of DGK activity Activation of the DGKs is complex and unique for each DGK isotype. In most cases, DGKs must translocate to a membrane compartment to access DAG. However, translocation does not necessarily activate the enzyme [57]. In addition, DGK activity can be modified by other cofactors such as lipids and calcium, and several DAG kinases are also regulated by post-translational modifications. Finally, 986 B. Luo et al. / Cellular Signalling 16 (2004) 983–989 tissue-specific alternative splicing of DGKs h, g, y, ~, and D, and probably other isotypes, allows for additional regulation [31,34,35,58,59]. This complexity permits cell- or tissue-specific regulation of each DGK isotype depending on the availability of cofactors and the type of stimulus that the cell receives. DGKa is perhaps the best example of the contextually dependent, differential regulation of DGKs. DGKa translocated to at least two different membrane compartments in T lymphocytes depending upon the agonist used to activate the cells: from the cytosol to a perinuclear region in T cells stimulated with IL-2 [55,60], and to the plasma membrane upon activation of the T cell antigen receptor [20]. Once at a membrane compartment, the DAG kinase activity of DGKa can be modified by the availability of several cofactors. Calcium is known to bind to EF hand structures and stimulated DGKa activity in vitro [32]. Sanjuan et al. [20] demonstrated that deleting the EF hand motifs of DGKa caused it to associate with the plasma membrane and significantly increased its DAG kinase activity. This observation led to the hypothesis that in the absence of calcium, the EF hand structures of DGKa inhibit DAG kinase activity—possibly by masking a motif necessary for catalytic activity—and somehow reduce membrane association. Binding calcium releases the inhibition and causes translocation to the membrane, allowing maximal DAG kinase activity. When associated with the membrane, the activity of DGKa is further modified by binding to lipid components: phosphatidylserine, sphingosine [61,62], and the phosphatidylinositol (PI) 3-kinase lipid products, PI-3,4-P2 and PI3,4,5-P3 [63], activated DGKa in vitro and likely in vivo as well. Finally, DGKa can be phosphorylated by several protein kinases including some PKC isoforms [64,65] and Src kinase [66], which may further enhance its DAG kinase activity. Thus, numerous events are required to fully activate DGKa, combinations of which can fine-tune its activity to the appropriate level. Similar to DGKa, other DGK isotypes appear to be sensitively regulated by a number of factors. For example, type II DGKs have a PH domain that may affect intracellular localization by interacting with either phosphatidylinositols or with other proteins. Indeed, the PH domain of the type II DGKy could bind inositol phosphates [33]. However, the binding was nonselective and weaker than a typical high affinity protein – lipid interaction, suggesting that it may not be a physiological interaction. Its DAG kinase activity was not affected by PIP2 [23]. In contrast, the activity of DGK types III and IV can be modified by phosphatidylinositols and phosphatidylserine in opposing ways. DGKq, the type III enzyme, was inhibited by both PIP2 and phosphatidylserine, whereas DGK~ was activated by both lipids [67]. Like DGKa, the subcellular localization of type IV DGKs is exquisitely regulated. These enzymes have a nuclear localization signal that can be regulated by PKC phosphorylation [22,39]. Additionally, members of the syntrophin family of scaffolding proteins further regulate the subcellular location of DGK~ by associating with its carboxy terminal PDZbinding domain, anchoring the protein in the cytoplasm [42]. Further, Davidson et al. [68] recently demonstrated that activating the type I gonadotropin-releasing hormone receptor caused DGK~ to associate with active Src kinase and translocate to the plasma membrane. Association with Src significantly enhanced its DAG kinase activity. Finally, DGKu, a type V DGK, can be regulated through its association with active RhoA: binding this GTPase abolished its DAG kinase activity [44]. Thus, depending on the context of activation, the availability of cofactors, and the activation state of protein kinases, DGKs can be differentially regulated. 5. DAG kinase activity is confined to specific cell compartments A number of reports demonstrating agonist-dependent translocation of DGKs to distinct membrane compartments suggest that DGK activity is restricted to localized DAG pools generated after activation of receptors. Perhaps the best evidence of spatially restricted DAG kinase activity was demonstrated by van der Bend et al. [69]. This group measured DAG kinase activity in cells following receptor activation—which caused physiological DAG production— or after treating the cells with exogenous PLC—which caused global, nonspecific DAG generation. They detected significant DAG kinase activity upon activating a receptor, but found very little DAG kinase activity after treating the cells with exogenous PLC. Their data suggested that DGKs are active only in spatially restricted compartments following physiological generation of DAG. Consistent with this conclusion, Nurrish et al. [12] found in C. elegans that dgk1, an ortholog of human DGKu, regulated DAG signalling that was necessary for acetylcholine release. Their data suggested a model where serotonin signalling—which inhibits locomotion—activated the DGK to reduce DAG accumulation. DGKs appear to be active in a number of cell compartments. For example, Nagaya et al. [21] demonstrated that overexpressed DGKy partly localized in the endoplasmic reticulum, while Abramovici et al. [70] found endogenous DGK~ at the neuromuscular junction. Several groups have noted DGK activity in the cell fractions containing cytoskeleton components. For example, Tolias et al. [71] noted that DGK activity associated with a complex of proteins including a PIP5K, Rac, Rho, Cdc42, and Rho-GDI, all of which regulate cytoskeleton dynamics. We found that several DGK isotypes co-immunoprecipitated with either Rac, Rho, or Cdc42 when overexpressed in cells (M.K.T. and B.L., unpublished observations), and Houssa et al. [44] showed that active RhoA associated with DGKu. Additionally, we found that DGK~ interacted with human PIP5K type Ia and increased its activity by generating phosphatidic acid [56]. The physiological significance of these B. Luo et al. / Cellular Signalling 16 (2004) 983–989 interactions is not entirely clear, but there are data demonstrating that DGKs can modulate cytoskeleton remodeling. For example, DGK inhibitors—which primarily affect type I enzymes—augmented platelet secretion and aggregation [72], and Abramovici et al. [70] recently demonstrated that expression of a DGK~ mutant that localized strongly with the plasma membrane enhanced membrane ruffles and caused the formation of large intracellular vesicles. Consistent with an effect on cytoskeleton dynamics, endogenous DGK~ co-purified with components of the cytoskeleton [70] and it localized at the leading edge of both glioblastoma cells [73] and C2 myoblasts [70]. Together, these data suggest that DGKs have a broad role in regulating the cytoskeleton, but at this point, their specific roles are not clear. The nucleus has a phosphatidylinositol cycle that is regulated separately from the plasma membrane PI signalling [74]. Like its extranuclear counterpart, nuclear DAG signalling appears to be compartmentalized. Indeed, D’Santos et al. [75] demonstrated independently fluctuating pools of nuclear DAG which had distinct fatty acid compositions. This complexity is not surprising because diverse stimuli can lead to generation of nuclear DAG. For example, different growth factors (e.g. IGF-1 or thrombin) stimulated temporally distinct pulses of nuclear DAG [76,77], and several groups have demonstrated that nuclear DAG fluctuates independently of extranuclear DAG during the cell cycle [74]. Nuclear DAG was shown to peak shortly before S phase, suggesting that it may participate in the G1/S transition [78]. Most data support the conclusion that nuclear DAG promotes cell growth. Consistent with this, and emphasizing the importance of nuclear DAG signalling in the cell cycle, we found that cells overexpressing DGK~—which partly localized in the nucleus—accumulated at the G0/G1 transition, presumably because the kinase reduced nuclear DAG [22]. Several other DGKs have been detected in the nucleus. DGKs a and L, translocated to the nucleus [39,55,60], while a significant fraction of DGKu localized there constitutively [57]. By transfecting different DGK isotypes into COS-7 cells, we detected DGKs h, g, y, and q in the nucleus (M.K.T., unpublished observations). Nuclear DGKs appear to be confined to separate, distinct regions of the nucleus: DGKs u, ~, and L were noted in discrete regions within the body of the nucleus [22,39, 57,79] while DGKa appeared to predominantly localize around its periphery [55]. Combined with the complexity of nuclear DAG signalling, these data suggest that within the nucleus, DGKs regulate distinct pools of signalling DAG. Supporting this conclusion, experimental evidence suggests contrasting roles for the nuclear DGKs a and ~: overexpression of DGK~ inhibited progression from G1 to S phase of the cell cycle [22], while PA generated by nuclear DGKa appeared to be necessary for IL-2-mediated progression to S phase of the cell cycle [55]. The opposing function of these DGKs indicates both the importance and complexity of nuclear DGK activity and lipid signalling. 987 6. DGKs bind and regulate other signalling proteins Based on the evidence noted above, DGKs achieve specificity of function through a combination of post-translational modifications, the availability of cofactors, and through the availability and access to substrate DAG. DGKs appear to achieve an additional level of specificity by binding to protein partners in order to regulate their activity. This concept is consistent with an emerging body of evidence indicating that specificity in signal transduction is often achieved by gathering appropriate protein partners through scaffolding proteins [80]. DGKs appear to associate with proteins that are regulated by either DAG or PA. DGK~ provides the best example of this type of regulation. It binds and regulates at least three proteins, each of which is significantly affected by either DAG or PA. For example, by binding to RasGRP1, a DAG-dependent Ras guanine nucleotide exchange factor, DGK~ regulated the active state of Ras [73]. This regulation was selective: five other DGK isotypes did not significantly inhibit RasGRP1. Its inhibition of Ras was consistent with the phenotype of DGK~ knockout mice, which had hyperresponsive T cells, in part, due to prolonged Ras activation [81]. Regulation of RasGRP proteins may be a common theme: we found that DGK~ associated with and regulated RasGRP3 (M.K.T and D.S.R., unpublished observations). DGK~ also associated with PKCa to regulate its activity [41]. Their association was dynamic: once phosphorylated by the PKC, DGK~ no longer associated with it. Demonstrating the specificity of their interaction, we found that DGK~ did not bind or regulate PKCy. In each case, the DGK modulated the activity of its protein partner by metabolizing DAG. Conversely, we found that DGK~ also associated with and regulated, by generating PA, human PIP5K type Ia [56]. Based on the diversity of the mammalian DGK family many more examples of regulation through specific interactions will likely emerge in the near future. 7. DGKee modulates signalling events through its specificity DAG kinases may also be responsible for enriching phosphatidylinositols with specific lipid components. Phosphatidylinositols are enriched at the sn 2 position with unsaturated fatty acids, usually arachidonate [37]. While it may seem that the specific fatty acid components would not significantly affect the signalling ability of DAG, data suggest that some DAG targets, including PKCs, are specifically activated by unsaturated DAG [82]. How the fatty acid components of DAG affect target proteins is unclear, but one could speculate that these fatty acids may help enrich DAG in membrane microdomains where other signalling components reside. In vitro, most DGKs do not distinguish between the fatty acid components of DAG, suggesting that in vivo, phosphatidylinositols maintain 988 B. Luo et al. / Cellular Signalling 16 (2004) 983–989 their unsaturated fatty acid enrichment by coupling PIspecific phospholipase C enzymes with DAG kinases and other enzymes involved in resynthesizing PIP2. Coupling these enzymes, would maintain the fatty acid components of PIP2. Indeed, we found that DGK~ co-immunoprecipitated with the phosphoinositide-specific PLCs h1 and g (M.K.T. and B.L., unpublished observations) and with human PIPK type Ia [56]. Tabellini et al. [79] demonstrated that DGKu associated with PLCh1 and human PIPK type Ia. DGKq is unique among the DAG kinases because it selectively phosphorylates DAG with an arachidonate— an unsaturated fatty acid—in the sn 2 position [36]. This selectivity suggests that DGKq may have a more prominent role than other DGKs in enriching inositol phospholipids with unsaturated fatty acids. To examine the biological function of this DGK, we generated mice with targeted deletion of DGKq. Proper inositol lipid signalling is important for normal neuronal transmission, so in a collaborative effort, we studied seizure threshold in the mice. We found that DGKq null mice had significantly shorter seizures following electroconvulsive shock and they recovered faster than wild-type mice [83]. Examination of brain lipids demonstrated reduced levels of arachidonate in both PIP2 and DAG in the DGKq-deficient mice. These experiments underscore the importance of maintaining proper lipid composition of phosphatidylinositols and DAG and indicate that DGKq fulfills this role in some neuronal tissues. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] 8. Conclusions Diacylglycerol kinases influence signalling events by metabolizing DAG and/or by generating phosphatidic acid. As evidence accumulates, it is apparent that the structural diversity of DGK isoforms mirrors the range of functions and sites of action of these enzymes. DGKs appear to be precisely regulated through localization, lipid and nonlipid cofactors, post-translational modifications, and the availability of substrate DAG. DGKs achieve further specificity by binding to the proteins that they regulate. Most of the proteins regulated by DGKs appear to be targets of DAG or PA, but it is possible that DGKs may additionally affect signalling events by interacting with other proteins to recruit them to signalling complexes. Further studies of the regulation of lipid signalling should reveal additional roles for DGKs and more precise information about their regulation. [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] Acknowledgements [30] This work was supported by the Huntsman Cancer and R. Harold Burton Foundations. D.S.R. is supported by National Institutes of Health, National Research Service Award (1F32CA93048) from the National Cancer Institute. [31] [32] S.G. Rhee, Y.S. Bae, J. Biol. Chem. 272 (1997) 15045 – 15048. A. Toker, Front. Biosci. 3 (1998) d1134 – d1147. D. Ron, M.G. Kazanietz, FASEB J. 13 (1999) 1658 – 1676. J.O. Ebinu, D.A. Bottorff, E.Y.W. Chan, S.L. Stang, R.J. Dunn, J.C. Stone, Science 280 (1998) 1082 – 1086. H. Kawasaki, G.M. Springett, T. Shinichiro, J.J. Canales, P. Harlan, J.P. Blumenstiel, E.J. Chen, A. Bany, N. Mochizuki, A. Ashbacher, M. Matsuda, D.E. Housman, A.M. Graybiel, Proc. Natl. Acad. Sci. U. S. A. 95 (1998) 13278 – 13283. S. Yamashita, N. Mochizuki, Y. Ohba, M. Tobiume, Y. Okada, H. Sawa, K. Nagashima, M. Matsuda, J. Biol. Chem. 275 (2000) 25488 – 25493. Y. Yang, L. Li, G. Wong, S. Krilis, M. Madhusudhan, A. Sali, R. Stevens, J. Biol. Chem. 277 (2002) 25756 – 25774. M.J. Caloca, M.L. Garcia-Bermejo, P.M. Blumberg, N.E. Lewin, E. Kremmer, H. Mischak, S. Wang, K. Narco, B. Bienfait, V.E. Marquez, M.G Kazanietz, Proc. Natl. Acad. Sci. U. S. A. 96 (1999) 11854 – 11859. P. Lucas, K. Ukhanov, T. Leinders-Zufall, F. Zufall, Neuron 40 (2003) 551 – 561. M. Kato, S. Kawai, T. Takenawa, J. Biol. Chem. 262 (1987) 5696 – 5704. H. Kato, S. Kawai, T. Takenawa, Biochem. Biophys. Res. Commun. 154 (1988) 959 – 966. S. Nurrish, L. Segalat, J.M. Kaplan, Neuron 24 (1999) 231 – 242. K.G. Miller, M.D. Emerson, J.B. Rand, Neuron 24 (1999) 323 – 333. I. Masai, T. Hosoya, S.-I. Kojima, Y. Hotta, Proc. Natl. Acad. Sci. U. S. A. 89 (1992) 6030 – 6034. I. Masai, A. Okazaki, T. Hosoya, Y. Hotta, Proc. Natl. Acad. Sci. U. S. A. 90 (1993) 11157 – 11161. N. Harden, S.F. Yap, M.-A. Chiam, L. Lim, Biochem. J. 289 (1993) 439 – 444. T. Katagiri, T. Mizoguchi, K. Shinozaki, Plant Mol. Biol. 30 (1996) 647 – 653. F.C. Gomez-Merino, C.A. Brearley, M. Ornatowska, M.E. AbdelHaliem, M.I. Zanor, B. Mueller-Roeber, J. Biol. Chem. 279 (2004) 8230 – 8241. J. Preiss, C.R. Loomis, W.R. Bishop, R. Stein, J.E. Niedel, R.M. Bell, J. Biol. Chem. 261 (1986) 8597 – 8600. M.A. Sanjuan, D.A. Jones, M. Izquierdo, I. Merida, J. Cell Biol. 153 (2001) 207 – 219. H. Nagaya, I. Wada, Y.-J. Jia, H. Kanoh, Mol. Biol. Cell 13 (2002) 302 – 316. M.K. Topham, M. Bunting, G.A. Zimmerman, T.M. McIntyre, P.J. Blackshear, S.M. Prescott, Nature 394 (1998) 697 – 700. F. Sakane, S.I. Imai, M. Kai, I. Wada, H. Kanoh, J. Biol. Chem. 271 (1996) 8394 – 8401. T.M. Klauck, X. Xu, B. Mousseau, S. Jaken, J. Biol. Chem. 271 (1996) 19781 – 19788. F. Sakane, M. Kai, I. Wada, S. Imai, H. Kanoh, Biochem. J. 318 (1996) 583 – 590. J.H. Hurley, A.C. Newton, P.J. Parker, P.M. Blumberg, Y. Nishizuka, Protein Sci. 6 (1997) 477 – 480. M. Shindo, K. Irie, A. Masuda, H. Ohigashi, Y. Shirai, K. Miyasaka, N. Saito, J. Biol. Chem. 278 (2003) 18448 – 18454. B. Houssa, W.J. van Blitterswijk, Biochem. J. 331 (1998) 677 – 680. F. Sakane, K. Yamada, H. Kanoh, C. Yokoyama, T. Tanabe, Nature 344 (1990) 345 – 348. K. Goto, H. Kondo, Proc. Natl. Acad. Sci. U. S. A. 90 (1993) 7598 – 7602. M. Kai, F. Sakane, S.-I. Imai, I. Wada, H. Kanoh, J. Biol. Chem. 269 (1994) 18492 – 18498. K. Yamada, F. Sakane, N. Matsushima, H. Kanoh, Biochem. J. 321 (1997) 59 – 64. B. Luo et al. / Cellular Signalling 16 (2004) 983–989 [33] H. Takeuchi, T. Kanematsu, Y. Misumi, F. Sakane, H. Konishi, U. Kikkawa, Y. Watanabe, M. Katan, M. Hirata, Biochim. Biophys. Acta 1359 (1997) 275 – 285. [34] T. Murakami, F. Sakani, S. Imai, K. Houkin, H. Kanoh, J. Biol. Chem. 278 (2003) 34364 – 34372. [35] F. Sakane, S. Imai, K. Yamada, T. Murakami, S. Tsushima, H. Kanoh, J. Biol. Chem. 277 (2002) 43519 – 43526. [36] W. Tang, M. Bunting, G.A. Zimmerman, T.M. McIntyre, S.M. Prescott, J. Biol. Chem. 271 (1996) 10237 – 10241. [37] S.M. Prescott, P.W. Majerus, J. Biol. Chem. 256 (1981) 579 – 582. [38] M. Bunting, W. Tang, G.A. Zimmerman, T.M. McIntyre, S.M. Prescott, J. Biol. Chem. 271 (1996) 10230 – 10236. [39] L. Ding, E. Traer, T.M. McIntyre, G.A. Zimmerman, S.M. Prescott, J. Biol. Chem. 273 (1998) 32746 – 32752. [40] B. Luo, S.M. Prescott, M.K. Topham, J. Biol. Chem. 278 (2003) 39542 – 39547. [41] B. Luo, S.M. Prescott, M.K. Topham, J. Cell. Biol. 160 (2003) 929 – 937. [42] A. Hogan, L. Shepherd, J. Chabot, S. Quenneville, S.M. Prescott, M.K. Topham, S.H. Gee, J. Biol. Chem. 276 (2001) 26526 – 26533. [43] B. Houssa, D. Schaap, J. van der Wal, K. Goto, A. Yamakawa, M. Shibata, T. Takenawa, W.J. van Blitterswijk, J. Biol. Chem. 272 (1997) 10422 – 10428. [44] B. Houssa, J. de Widt, O. Kranenburg, W.H. Moolenaar, W.J. van Blitterswijk, J. Biol. Chem. 274 (1999) 6820 – 6822. [45] E.J. van Corven, A. Van Rijswijk, K. Jalink, R.L. van der Bend, W.J. van Blitterswijk, W.H. Moolenaar, Biochem. J. 281 (1992) 163 – 169. [46] T.C. Knauss, F.E. Jaffer, H.E. Abboud, J. Biol. Chem. 265 (1990) 14457 – 14463. [47] A. Siddhanta, D. Shields, J. Biol. Chem. 273 (1998) 17995 – 17998. [48] H. Ishihara, Y. Shibasaki, N. Kizuki, T. Wada, Y. Yazaki, T. Asano, Y. Oka, J. Biol. Chem. 273 (1998) 8741 – 8748. [49] M.-H. Tsai, C.-L. Yu, F.S. Wei, D.W. Stacey, Science 243 (1988) 522 – 526. [50] C. Limatola, D. Schaap, D. Moolenaar, W.J. van Blitterswijk, Biochem. J. 304 (1994) 1001 – 1008. [51] G.M. Bokoch, A.M. Reilly, R.H. Daniels, C.C. King, A. Olivera, S. Spiegel, U.G. Knaus, J. Biol. Chem. 273 (1998) 8137 – 8144. [52] K. Kishikawa, C.E. Chalfant, D.K. Perry, A. Bielawska, Y.A. Hannun, J. Biol. Chem. 274 (1999) 21335 – 21341. [53] M.A. Rizzo, K. Shome, S.C. Watkins, G. Romero, J. Biol. Chem. 275 (2000) 23911 – 23918. [54] J.H. Exton, Physiol. Rev. 77 (1997) 303 – 319. [55] I. Flores, T. Casaseca, C. Martinez-A, H. Kanoh, I. Merida, J. Biol. Chem. 271 (1996) 10334 – 10340. [56] B. Luo, S.M. Prescott, M.K. Topham, Cell. Signal. (2004) (in press). [57] W.J. van Blitterswijk, B. Houssa, Cell. Signal. 12 (2000) 595 – 605. [58] A. Caricasole, E. Bettini, C. Sala, R. Roncarati, N. Kobayashi, F. Caldara, K. Goto, G.C. Terstappen, J. Biol. Chem. 277 (2001) 4790 – 4796. 989 [59] L. Ding, M. Bunting, M.K. Topham, T.M. McIntyre, G.A. Zimmerman, S.M. Prescott, Proc. Natl. Acad. Sci. U. S. A. 94 (1997) 5519 – 5524. [60] I. Wada, M. Kai, S. Imai, F. Sakane, H. Kanoh, FEBS Lett. 393 (1996) 48 – 52. [61] F. Sakane, K. Yamada, H. Kanoh, FEBS Lett. 255 (1989) 409 – 413. [62] K. Yamada, F. Sakane, Biochim. Biophys. Acta 1169 (1993) 211 – 216. [63] A. Cipres, S. Carrasco, E. Merino, E. Diaz, M. Krishna, J.R. Falck, C. Martinez, I. Merida, J. Biol. Chem. 278 (2003) 35629 – 35635. [64] H. Kanoh, K. Yamada, F. Sakane, T. Imaizumi, Biochem. J. 258 (1989) 455 – 462. [65] D. Schaap, J. van der Wal, W.J. van Blitterswijk, R.L. van der Bend, H.L. Ploegh, Biochem. J. 289 (1993) 875 – 881. [66] S. Cutrupi, G. Baldanzi, D. Gramaglia, A. Maffe, D. Schaap, E. Giraudo, W.J. van Blitterswijk, F. Bussolino, P.M. Comoglio, A. Graziani, EMBO J. 19 (2000) 4614 – 4622. [67] S. Thirugnannam, M.K. Topham, R.M. Epand, Biochemistry 40 (2001) 10607 – 10613. [68] L. Davidson, A.J. Pawson, R. Lopez de Maturana, S.H. Freestone, P. Barran, R.P. Millar, S. Maudsley, J. Biol. Chem. 279 (2004) 11906 – 11916. [69] R.L. van der Bend, J. de Widt, H. Hilkmann, W.J. van Blitterswijk, J. Biol. Chem. 269 (1994) 4098 – 4102. [70] H. Abramovici, A.B. Hogan, C. Obagi, M.K. Topham, S.H. Gee, Mol. Biol. Cell 14 (2003) 4499 – 4511. [71] K.F. Tolias, A.D. Couvillon, L.C. Cantley, C.L. Carpenter, Mol. Cell. Biol. 18 (1998) 762 – 770. [72] D.L. Nunn, S.P. Watson, Biochem. J. 243 (1987) 809 – 813. [73] M.K. Topham, S.M. Prescott, J. Cell Biol. 152 (2001) 1135 – 1143. [74] R.F. Irvine, Sci. STKE 150 (2002) RE13. [75] C.S. D’Santos, J.H. Clarke, R.F. Irvine, N. Divecha, Curr. Biol. 9 (1999) 437 – 440. [76] K.L. Leach, V.A. Ruff, M.B. Jarpe, L.D. Adams, D. Fabbro, D.M. Raben, J. Biol. Chem. 267 (1992) 21816 – 21822. [77] N. Divecha, H. Banfic, R.F. Irvine, EMBO J. 10 (1991) 3207 – 3214. [78] H. Banfic, M. Zizak, N. Divecha, R.F. Irvine, Biochem. J. 290 (1993) 633 – 636. [79] G. Tabellini, R. Bortul, S. Santi, M. Riccio, G. Baldini, A. Cappellini, A.M. Billi, R. Berezney, A. Ruggeri, L. Cocco, A.M. Martelli, Exp. Cell Res. 285 (2003) 143 – 154. [80] T. Pawson, J.D. Scott, Science 278 (1997) 2075 – 2080. [81] X. Zhong, E.A. Hainey, B.A. Olenchock, M.S. Jordan, J.S. Maltzman, K.E. Nichols, H. Shen, G.A. Koretzky, Nat. Immunol. 4 (2003) 882 – 890. [82] M.N. Hodgkin, T.R. Pettitt, A. Martin, R.H. Michell, A.J. Pemberton, M.J.O. Wakelam, Trends Biochem. Sci. 23 (1998) 200 – 204. [83] E.B. Rodriquez de Turco, W. Tang, M.K. Topham, F. Sakane, V.L. Marcheselli, C. Chen, A. Taketomi, S.M. Prescott, N.G. Bazan, Proc. Natl. Acad. Sci. U. S. A. 98 (2001) 4740 – 4745.