The dual effect of Rac2 on phospholipase D2 regulation that explains both the onset and termination of chemotaxis

Mammalian phospholipase D: Function, and therapeutics

Despite being discovered over 60 years ago, the precise role of phospholipase D (PLD) is still being elucidated. PLD enzymes catalyze the hydrolysis of the phosphodiester bond of glycerophospholipids producing phosphatidic acid and the free headgroup. PLD family members are found in organisms ranging from viruses, and bacteria to plants, and mammals. They display a range of substrate specificities, are regulated by a diverse range of molecules, and have been implicated in a broad range of cellular processes including receptor signaling, cytoskeletal regulation and membrane trafficking. Recent technological advances including: the development of PLD knockout mice, isoform-specific antibodies, and specific inhibitors are finally permitting a thorough analysis of the in vivo role of mammalian PLDs. These studies are facilitating increased recognition of PLD's role in disease states including cancers and Alzheimer's disease, offering potential as a target for therapeutic intervention.

Overexpression of Ras-Related C3 Botulinum Toxin Substrate 2 Radiosensitizes Melanoma Cells In Vitro and In Vivo

Radioresistance is the major obstacle in the radiotherapy of the malignant melanoma. Thus, it is of importance to increase the radiosensitivity of melanoma cells. In the present study, the radioresistant melanoma cell line OCM-1 with inducible overexpression of Ras-related C3 botulinum toxin substrate 2 was established based on a radiation-inducible early growth response gene (Egr-1) promoter. The effects of Ras-related C3 botulinum toxin substrate 2 overexpression on the radiosensitivity of melanoma cells exposed to either X-rays or carbon ion beams were evaluated in cultured cells as well as xenograft tumor models. In addition, both reactive oxygen species yield and the NADPH oxidase activity were measured in the irradiated melanoma cells. It was found that the radiation-inducible overexpression of Ras-related C3 botulinum toxin substrate 2 sensitized the melanoma cells to both X-rays and carbon ion irradiation by enhancing the NADPH oxidase activity and the subsequent reactive oxygen species production. Besides, the overexpression of Ras-related C3 botulinum toxin substrate 2 enhanced the tumor-killing effect of radiotherapy in xenograft tumors significantly. The results of this study indicate that Ras-related C3 botulinum toxin substrate 2 is promising in increasing the radiosensitivity of melanoma cells, which provides experimental evidence and theoretical basis for clinical radiosensitization of the malignant melanoma.

PLD-Specific Small-Molecule Inhibitors Decrease Tumor-Associated Macrophages and Neutrophils Infiltration in Breast Tumors and Lung and Liver Metastases

Phospholipase D-2 (PLD2) has a key role in breast cancer formation and metastasis formation with PLD small inhibitors reducing primary tumor growth. This study aimed to evaluate the importance of targeting PLD on the tumor microenvironment. We provide evidence about the beneficial effect of PLD inhibitors [FIPI (dual PLD1/PLD2) or VU0155072-2 (PLD2 inhibitor)] on avoiding infiltration of tumor-helping macrophages and neutrophils. Tumor growth and metastasis within the primary tumors had low (<20% over controls) PLD enzyme activity. Unexpectedly, we found that the inhibitors also affected PLD2 gene expression and protein albeit at a lesser extent. The later could indicate that targeting both the actual PLD enzyme and its activity could be beneficial for potential cancer treatments in vivo. F4/80 and Ly6G staining of macrophages and neutrophils, respectively, and Arg1 staining data were consistent with M2 and N2 polarization. NOS2 staining increased in xenotransplants upon treatment with PLD2 inhibitors suggesting the novel observation that an increased recruitment of M1 macrophages occurred in primary tumors. PLD inhibitor-treated primary tumors had large, fragile, necrotic areas that were Arg1+ for M2 macrophages. The xenotransplants also caused the formation of large F4/80+ and Ly6G+ (>100 μm) clusters in lungs. However, PLD inhibitors, particularly FIPI, were able to diminish leukocyte presence. Ex vivo chemotaxis and PLD activity of peripheral blood neutrophils (PMN) and peritoneal macrophages was also determined. Whereas PMN had impaired functionality, macrophages did not. This significantly increased ("emboldened") macrophage function was due to PLD inhibition. Since tumor-associated leukocytes in primary tumors and metastases were targeted via PLD inhibition, we posit that these inhibitors have a key role in cancer regression, while still affording an appropriate inflammatory response at least from off-site innate immunity macrophages.

PLD Protein-Protein Interactions With Signaling Molecules and Modulation by PA

We describe methods for studying phospholipase D (PLD) interactions with signaling proteins and modulation of these interactions by the PLD reaction product, phosphatidic acid (PA). PLD is fundamental to the physiological maintenance of cellular/intracellular membranes, protein trafficking, cytoskeletal dynamics, membrane remodeling, cell proliferation, meiotic division and sporulation. PA is an acidic phospholipid involved in the biosynthesis of many other lipids that affects the enzymatic activities of many different signaling proteins via protein-lipid interactions or as a substrate. The involvement of PLD as an effector of protein-protein interactions and downstream signaling via PA-mediated processes has led to the investigation of PA-binding domains in target protein partners. We present here data and protocols detailing the interaction between PLD2-Rac2 interaction and modulation of this interaction by PA. We describe biochemical techniques to measure interactions between PLD, PA, and the small GTPase Rac2, which are associated in the cell. We found two maxima concentrations of PA that contributed to association or dissociation of Rac2 with PLD2, as well as the PLD2 lipase and guanine nucleotide exchange factor (GEF) activities. Fluctuations in the Rac2-PLD2 protein-protein binding interaction facilitate shuttling of Rac2 and/or PLD2 within the cell dependent on local cellular PA concentration. Fluorescence resonance emission transfer stoichiometry for PLD2 and Rac2 binding yielded a 3:1 ratio of Rac2:PLD2. Detection of PA in mammalian cells with a new biosensor showed colocalization in and around the nucleus. We also described methods for quantitation of PA in biological materials by HPLC electrospray ionization tandem mass spectrometry.

Mechanism of enzymatic reaction and protein-protein interactions of PLD from a 3D structural model

The phospholipase D (PLD) superfamily catalyzes the hydrolysis of cell membrane phospholipids generating the key intracellular lipid second messenger phosphatidic acid. However, there is not yet any resolved structure either from a crystallized protein or from NMR of any mammalian PLDs. We propose here a 3D model of the PLD2 by combining homology and ab initio 3 dimensional structural modeling methods, and docking conformation. This model is in agreement with the biochemical and physiological behavior of PLD in cells. For the lipase activity, the N- and C-terminal histidines of the HKD motifs (His 442/His 756) form a catalytic pocket, which accommodates phosphatidylcholine head group (but not phosphatidylethanolamine or phosphatidyl serine). The model explains the mechanism of the reaction catalysis, with nucleophilic attacks of His 442 and water, the latter aided by His 756. Further, the secondary structure regions superimposed with bacterial PLD crystal structure, which indicated an agreement with the model. It also explains protein-protein interactions, such as PLD2-Rac2 transmodulation (with a 1:2 stoichiometry) and PLD2 GEF activity both relevant for cell migration, as well as the existence of binding sites for phosphoinositides such as PIP2. These consist of R236/W238 and R557/W563 and a novel PIP2 binding site in the PH domain of PLD2, specifically R210/R212/W233. In each of these, the polar inositol ring is oriented towards the basic amino acid Arginine. Since tumor-aggravating properties have been found in mice overexpressing PLD2 enzyme, the 3D model of PLD2 will be also useful, to a large extent, in developing pharmaceuticals to modulate its in vivo activity.

Phospholipase D in cell signaling: from a myriad of cell functions to cancer growth and metastasis

Phospholipase D (PLD) enzymes play a double vital role in cells: they maintain the integrity of cellular membranes and they participate in cell signaling including intracellular protein trafficking, cytoskeletal dynamics, cell migration, and cell proliferation. The particular involvement of PLD in cell migration is accomplished: (a) through the actions of its enzymatic product of reaction, phosphatidic acid, and its unique shape-binding role on membrane geometry; (b) through a particular guanine nucleotide exchange factor (GEF) activity (the first of its class assigned to a phospholipase) in the case of the mammalian isoform PLD2; and (c) through protein-protein interactions with a wide network of molecules: Wiskott-Aldrich syndrome protein (WASp), Grb2, ribosomal S6 kinase (S6K), and Rac2. Further, PLD interacts with a variety of kinases (PKC, FES, EGF receptor (EGFR), and JAK3) that are activated by it, or PLD becomes the target substrate. Out of these myriads of functions, PLD is becoming recognized as a major player in cell migration, cell invasion, and cancer metastasis. This is the story of the evolution of PLD from being involved in a large number of seemingly unrelated cellular functions to its most recent role in cancer signaling, a subfield that is expected to grow exponentially.

CSF-1 receptor signaling in myeloid cells

The CSF-1 receptor (CSF-1R) is activated by the homodimeric growth factors colony-stimulating factor-1 (CSF-1) and interleukin-34 (IL-34). It plays important roles in development and in innate immunity by regulating the development of most tissue macrophages and osteoclasts, of Langerhans cells of the skin, of Paneth cells of the small intestine, and of brain microglia. It also regulates the differentiation of neural progenitor cells and controls functions of oocytes and trophoblastic cells in the female reproductive tract. Owing to this broad tissue expression pattern, it plays a central role in neoplastic, inflammatory, and neurological diseases. In this review we summarize the evolution, structure, and regulation of expression of the CSF-1R gene. We discuss the structures of CSF-1, IL-34, and the CSF-1R and the mechanism of ligand binding to and activation of the receptor. We further describe the pathways regulating macrophage survival, proliferation, differentiation, and chemotaxis downstream from the CSF-1R.

Macrophage migration arrest due to a winning balance of Rac2/Sp1 repression over β-catenin-induced PLD expression

Monocytes and neutrophils infiltrate into tissues during inflammation and stay for extended periods of time until the initial insult is resolved or sometimes remain even longer in the case of chronic inflammation. The mechanism as to why phagocytes become immobilized after the initial cell migration event is not understood completely. Here, we show that overexpression or hyperactivation of Rac2 decreases sustained chemotactic responses of macrophages to MCP-1/CCL2. The resulting leukocyte arrest is not caused by a diminished availability of the cytokine receptor CCR2 that remains intact during MCP-1 stimulation. We show a novel mechanism that links the Rac2-dependent arrest of chemotaxis to decreased expression of PLD2 through the transcription regulator Sp1. Prolonged Rac2 activity leads to nuclear overactivation of Sp1, which acts as a repressor for PLD2. Also, another signaling component plays a regulatory role: β-catenin. Although early times of stimulation (≈ 20 min) with MCP-1/CCL2 resulted in activation of β-catenin with a positive effect on PLD2, after ≈ 3 h of stimulation, the levels of β-catenin were reduced and not able to prevent the negative effect of Rac2 on PLD2 activity. This is a novel molecular mechanism underlying immobilization of monocyte/macrophage migration that is important for the physiological maintenance of leukocytes at the site of inflammation. If this immobilization is prolonged enough, it could lead to chronic inflammation.

Friedreich's ataxia, frataxin, PIP5K1B: echo of a distant fracas

"Frataxin fracas" were the words used when referring to the frataxin-encoding gene (FXN) burst in as a motive to disqualify an alternative candidate gene, PIP5K1B, as an actor in Friedreich's ataxia (FRDA) (Campuzano et al., 1996; Cossee et al., 1997; Carvajal et al., 1996). The instrumental role in the disease of large triplet expansions in the first intron of FXN has been thereafter fully confirmed, and this no longer suffers any dispute (Koeppen, 2011). On the other hand, a recent study suggests that the consequences of these large expansions in FXN are wider than previously thought and that the expression of surrounding genes, including PIP5K1B, could be concurrently modulated by these large expansions (Bayot et al., 2013). This recent observation raises a number of important and yet unanswered questions for scientists and clinicians working on FRDA; these questions are the substratum of this paper.

Phosphatidic acid, phospholipase D and tumorigenesis

Phospholipase D (PLD) is a membrane protein with a double role: maintenance of the structural integrity of cellular or intracellular membranes and involvement in cell signaling through the product of the catalytic reaction, PA, and through protein-protein interaction with a variety of partners. Cross-talk during PLD signaling occurs with other cancer regulators (Ras, PDGF, TGF and kinases). Elevation of either PLD1 or PLD2 (the two mammalian isoforms of PLD) is able to transform fibroblasts and contribute to cancer progression. Elevated total PLD activity, as well as overexpression, is present in a wide variety of cancers such as gastric, colorectal, renal, stomach, esophagus, lung and breast. PLD provides survival signals and is involved in migration, adhesion and invasion of cancer cells, and all are increased during PLD upregulation or, conversely, they are decreased during PLD loss of function. Eventhough the end results of PLD action as relates to downstream signaling mechanisms are still currently being elucidated, invasion, a pre-requisite for metastasis, is directly affected by PLD. This review will introduce the classical mammalian PLD's, PLD1 and PLD2, followed by the mechanisms of intracellular regulation and a status of current investigation in the crucial involvement of PLD in cancer, mostly through its role in cell migration, invasion and metastasis, that has grown exponentially in the last few years.

Phospholipase D (PLD) drives cell invasion, tumor growth and metastasis in a human breast cancer xenograph model

Breast cancer is one of the most common malignancies in human females in the world. One protein that has elevated enzymatic lipase activity in breast cancers in vitro is phospholipase D (PLD), which is also involved in cell migration. We demonstrate that the PLD2 isoform, which was analyzed directly in the tumors, is crucial for cell invasion that contributes critically to the growth and development of breast tumors and lung metastases in vivo. We used three complementary strategies in a SCID mouse model and also addressed the underlying molecular mechanism. First, the PLD2 gene was silenced in highly metastatic, aggressive breast cancer cells (MDA-MB-231) with lentivirus-based shRNA, which were xenotransplanted in SCID mice. The resulting mouse primary mammary tumors were reduced in size (65%, p<0.05) and their onset delayed when compared to control tumors. Second, we stably overexpressed PLD2 in low-invasive breast cancer cells (MCF-7) with a biscistronic MIEG retroviral vector and observed that these cells were converted into a highly aggressive phenotype, as primary tumors that formed following xenotransplantation were larger, grew faster and developed lung metastases more readily. Third, we implanted osmotic pumps into SCID xenotransplanted mice that delivered two different small-molecule inhibitors of PLD activity (FIPI and NOPT). These inhibitors led to significant (>70%, p<0.05) inhibition of primary tumor growth, metastatic axillary tumors and lung metastases. In order to define the underlying mechanism, we determined that the machinery of PLD-induced cell invasion is mediated by phosphatidic acid (PA), WASp, Grb2 and Rac2 signaling events that ultimately affect actin polymerization and cell invasion. In summary, this study shows that PLD has a central role in the development, metastasis and level of aggressiveness of breast cancer, raising the possibility that PLD2 could be used as a new therapeutic target.

A GEF-to-phospholipase molecular switch caused by phosphatidic acid, Rac and JAK tyrosine kinase that explains leukocyte cell migration

Phospholipase D2 (PLD2) is a cell-signaling molecule that bears two activities: a guanine-nucleotide exchange factor (GEF) and a lipase that reside in the PX/PH domains and in two HKD domains, respectively. Upon cell stimulation, the GEF activity yields Rac2-GTP and the lipase activity yields phosphatidic acid (PA). In the present study, we show for the first time that these activities regulate one another. Upon cell stimulation, both GEF and lipase activities are quickly (within ∼3 min) elevated. As soon as it is produced, PA positively feeds back on the GEF and further activates it. Rac2-GTP, on the other hand, is inhibitory to the lipase activity. PLD2 would remain downregulated if it were not for the contribution of the tyrosine kinase Janus kinase 3 (JAK3), which restores lipase action (by phosphorylation at Y415). Conversely, the GEF is inhibited upon phosphorylation by JAK3 and is effectively terminated by this action and by the increasing accumulation of PA at >15 min of cell stimulation. This PA interferes with the ability of the GEF to bind to its substrate (Rac2-GTP). Thus, both temporal inter-regulation and phosphorylation-dependent mechanisms are involved in determining a GEF-lipase switch within the same molecule. Human neutrophils stimulated by interleukin-8 follow a biphasic pattern of GEF and lipase activation that can be explained by such an intramolecular switch. This is the first report of a temporal inter-regulation of two enzymatic activities that reside in the same molecule with profound biological consequences in leukocyte cell migration.

Identification of the catalytic site of phospholipase D2 (PLD2) newly described guanine nucleotide exchange factor activity

We have demonstrated that phospholipase D2 (PLD2) is a guanine nucleotide exchange factor (GEF) for Rac2 and determined the PLD2 domains and amino acid site(s) responsible for its GEF activity. Experiments using GST fusion proteins or GST-free counterparts, purified proteins revealed that the PX domain is sufficient to exert GEF activity similar to full-length PLD2. The PLD2-GEF catalytic site is formed by a hydrophobic pocket of residues Phe-107, Phe-129, Leu-166, and Leu-173, all of which are in the PX domain. A nearby Arg-172 is also important in the overall activity. PX mutants altering any of those five amino acids fail to have GEF activity but still bind to Rac2, while their lipase activity was mostly unaffected. In addition to the PX domain, a region in the pleckstrin homology domain (Ile-306-Ala-310) aids in the PX-mediated GEF activity by providing a docking site to hold Rac2 in place during catalysis. We conclude that PLD2 is a unique GEF, with the PX being the major catalytic domain for its GEF activity, whereas the pleckstrin homology domain assists in the PX-mediated activity. The physiological relevance of this novel GEF in cell biology is demonstrated here in chemotaxis and phagocytosis of leukocytes, as the specific PX and PH mutants abolished cell function. Thus, this study reveals for the first time the catalytic site that forms the basis for the mechanism behind the GEF activity of PLD2.

Structure analysis between the SWAP-70 RHO-GEF and the newly described PLD2-GEF

Small GTPases like Rac2 are crucial regulators of many cell functions central to life itself. Our laboratory has recently found that phospholipase D2 (PLD2) can act as a guanine nucleotide exchange factor (GEF) for Rac2. PLD2 has a Pleckstrin Homology (PH) domain but does not bear a Dbl homology (DH) or DOCK homology region (DHR) domain. It has, however, a Phox (PX) domain upstream of its PH domain. To better understand the novel finding of PLD2 as an enhancer of GDP/GTP exchange, we modeled the N-terminal portion of PLD2 (as the crystal structure of this protein has not as of yet been resolved), and studied the correlation with two known GEFs, SWAP-70 and the Leukemic Associated RhoGEF (LARG). Structural similarities between PLD2's PH and SWAP-70s or LARG's PH domain are very extensive, while similarities between PLD2's PX and SWAP-70s or LARG's DH domains are less evident. This indicates that PLD functions as a GEF utilizing its PH domain and part of its PX domain and possibly other regions. All this makes PLD unique, and an entirely new class of GEF. By bearing two enzymatic activities (break down of PC and GDP/GTP exchange), it is realistic to assume that PLD is an important signaling node for several intracellular pathways. Future experiments will ascertain how the newly described PLD2's GEF is regulated in the context of cell activation.

Increased cell growth due to a new lipase-GEF (Phospholipase D2) fastly acting on Ras

We report the novel finding that Phospholipase D2 (PLD2), through its PX and PH domains, binds specifically to Ras and catalyzes the GDP/GTP exchange (i.e., is a GEF), with potency comparable to Ras-GRF-1, a known Ras-GEF. Cells overexpressing PLD2-GEF inactive mutants (F129Y and R172C/L173A) fail to stimulate cell proliferation compared to the wild type-expressing cells. The GEF effect on Ras follows a faster kinetics than other GTPase substrates (such as Rac2 or Rac1) and is a better substrate, too. The GEF action is due to PLD2 (protein) itself, independent of the lipase product PA. PA can still have a fine-tuning regulatory effect on Ras-GTP depending upon its cellular concentration. Rapidly growing human breast cancer cells MDA-MB 231 (but not the slow growing MCF7 counterpart) have high levels of endogenous PLD2-GEF which correlates with high Ras activation. The PLD2-"GEF" activity is even higher than the classical "lipase" activity and is abrogated with GEF single point mutants, particularly F129Y, and concomitantly with a slow rate of cell growth. This can be crucial to cancer biology in that not only Ras mutations explain abnormal growth, but the existence of a new GEF for Ras: a GEF molecule that happens to be a phospholipase.

Biochemical and cellular implications of a dual lipase-GEF function of phospholipase D2 (PLD2)

PLD2 plays a key role in cell membrane lipid reorganization and as a key cell signaling protein in leukocyte chemotaxis and phagocytosis. Adding to the large role for a lipase in cellular functions, recently, our lab has identified a PLD2-Rac2 binding through two CRIB domains in PLD2 and has defined PLD2 as having a new function, that of a GEF for Rac2. PLD2 joins other major GEFs, such as P-Rex1 and Vav, which operate mainly in leukocytes. We explain the biochemical and cellular implications of a lipase-GEF duality. Under normal conditions, GEFs are not constitutively active; instead, their activation is highly regulated. Activation of PLD2 leads to its localization at the plasma membrane, where it can access its substrate GTPases. We propose that PLD2 can act as a "scaffold" protein to increase efficiency of signaling and compartmentalization at a phagocytic cup or the leading edge of a leukocyte lamellipodium. This new concept will help our understanding of leukocyte crucial functions, such as cell migration and adhesion, and how their deregulation impacts chronic inflammation.

Cloning of PLD2 from baculovirus for studies in inflammatory responses

The enzyme PLD hydrolyzes phosphodiester bonds of lipids in cell membranes. Phosphatidic acid, a chief product of PLD enzymatic activity, is a pleiotropic second messenger with key roles in membrane trafficking, cell invasion, cell growth, and anti-apoptosis. We describe in the present study molecular, cellular, and physiological methods to understand the mechanism of how the PLD2 isozyme regulates the process of inflammation. We describe here (1) a method that details phospholipase D2 (PLD2) cloning in the pBac expression vector, (2) the large-scale infection of Sf21 insect cells for protein production, (3) protein purification by TALON cobalt metal affinity matrix and subsequent assessment of PLD2 protein and lipase activity, (4) application of purified PLD2 protein for the study of Rac2 GTPase biology involving GTP binding by a pull-down assay and GTP/GDP exchange activity, (5) a method of PLD2 expression that involves mammalian cells, (6) a physiological application as relates to adhesion, chemotaxis, and phagocytosis, and (7) a model that integrates the results of a PLD-GTPase interaction from the molecular to the physiological contexts.

Phospholipase D2 (PLD2) is a guanine nucleotide exchange factor (GEF) for the GTPase Rac2

We have discovered that the enzyme phospholipase D2 (PLD2) binds directly to the small GTPase Rac2, resulting in PLD2 functioning as a guanine nucleotide exchange factor (GEF), because it switches Rac2 from the GDP-bound to the GTP-bound states. This effect is large enough to be meaningful (∼72% decrease for GDP dissociation and 300% increase for GTP association, both with PLD2), it has a half-time of ∼7 min, is enhanced with increasing PLD2 concentrations, and compares favorably with other known GEFs, such as Vav-1. The PLD2-Rac2 protein-protein interaction is sufficient for the GEF function, because it can be demonstrated in vitro with just recombinant proteins without lipid substrates, and a catalytically inactive lipase (PLD2-K758R) has GEF activity. Apart from this function, exogenous phosphatidic acid by itself (300 pM) increases GTP binding and enhances PLD2-K758R-mediated GTP binding (by ∼34%) but not GDP dissociation. Regarding the PLD2-Rac2 protein-protein association, it involves, for PLD2, residues 263-266 within a Cdc42/Rac interactive binding region in the PH domain, as well as the PX domain, and it involves, for Rac2, residue N17 within its Switch-1 region. PLD2's GEF function is demonstrated in living cells, because silencing PLD2 results in reduced Rac2 activity, whereas PLD2-initiated Rac2 activation enhances cell adhesion, chemotaxis, and phagocytosis. There are several known GEFs, but we report that this GEF is harbored in a phospholipase. The benefit to the cell is that PLD2 brings spatially separated molecules together in a membrane environment, ready for fast intracellular signaling and cell function.

The exquisite regulation of PLD2 by a wealth of interacting proteins: S6K, Grb2, Sos, WASp and Rac2 (and a surprise discovery: PLD2 is a GEF)

Phospholipase D (PLD) catalyzes the conversion of the membrane phospholipid phosphatidylcholine to choline and phosphatidic acid (PA). PLD's mission in the cell is two-fold: phospholipid turnover with maintenance of the structural integrity of cellular/intracellular membranes and cell signaling through PA and its metabolites. Precisely, through its product of the reaction, PA, PLD has been implicated in a variety of physiological cellular functions, such as intracellular protein trafficking, cytoskeletal dynamics, chemotaxis of leukocytes and cell proliferation. The catalytic (HKD) and regulatory (PH and PX) domains were studied in detail in the PLD1 isoform, but PLD2 was traditionally studied in lesser detail and much less was known about its regulation. Our laboratory has been focusing on the study of PLD2 regulation in mammalian cells. Over the past few years, we have reported, in regards to the catalytic action of PLD, that PA is a chemoattractant agent that binds to and signals inside the cell through the ribosomal S6 kinases (S6K). Regarding the regulatory domains of PLD2, we have reported the discovery of the PLD2 interaction with Grb2 via Y169 in the PX domain, and further association to Sos, which results in an increase of de novo DNA synthesis and an interaction (also with Grb2) via the adjacent residue Y179, leading to the regulation of cell ruffling, chemotaxis and phagocytosis of leukocytes. We also present the complex regulation by tyrosine phosphorylation by epidermal growth factor receptor (EGF-R), Janus Kinase 3 (JAK3) and Src and the role of phosphatases. Recently, there is evidence supporting a new level of regulation of PLD2 at the PH domain, by the discovery of CRIB domains and a Rac2-PLD2 interaction that leads to a dual (positive and negative) effect on its enzymatic activity. Lastly, we review the surprising finding of PLD2 acting as a GEF. A phospholipase such as PLD that exists already in the cell membrane that acts directly on Rac allows a quick response of the cell without intermediary signaling molecules. This provides only the latest level of PLD2 regulation in a field that promises newer and exciting advances in the next few years.