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The tumor microenvironment modulates cancer growth. Extracellular vesicles (EVs) have been identified as key mediators of intercellular communication, but their role in tumor growth is largely unexplored. Here, we demonstrate that EVs from sarcoma patients promote neoangiogenesis via a purinergic X receptor 4 (P2XR4) -dependent mechanism in vitro and in vivo. Using a proteomic approach, we analyzed the protein content of plasma EVs and identified critical activated pathways in human umbilical vein endothelial cells (HUVECs) and human progenitor hematopoietic cells (CD34+). We then showed that vessel formation was due to rapid mitochondrial activation, intracellular Ca2+ mobilization, increased extracellular ATP, and trafficking of the lysosomal P2XR4 to the cell membrane, which is required for cell motility and formation of stable branching vascular networks. Cell membrane translocation of P2XR4 was induced by proteins and chemokines contained in EVs (e.g. Del-1 and SDF-1). Del-1 was found expressed in many EVs from sarcoma tumors and several tumor types. P2XR4 blockade reduced EVs-induced vessels in angioreactors, as well as intratumor vascularization in mouse xenografts. Together, these findings identify P2XR4 as a key mediator of EVs-induced tumor angiogenesis via a signaling mediated by mitochondria-lysosome-sensing response in endothelial cells, and indicate a novel target for therapeutic interventions.

Inflammatory cells play key roles in restenosis upon vascular surgical procedures such as bypass grafts, angioplasty and stent deployment but the molecular mechanisms by which these cells affect restenosis remain unclear. The p110δ isoform of phosphoinositide 3-kinase (PI3K) is mainly expressed in white blood cells. Here, we have investigated whether p110δ PI3K is involved in the pathogenesis of restenosis in a mouse model of carotid injury, which mimics the damage following arterial grafts. We used mice in which p110δ kinase activity has been disabled by a knockin (KI) point mutation in its ATP-binding site (p110δD910A/D910A PI3K mice). Wild-type (WT) and p110δD910A/D910A mice were subjected to longitudinal carotid injury. At 14 and 30 days after carotid injury, mice with inactive p110δ showed strongly decreased infiltration of inflammatory cells (including T lymphocytes and macrophages) and vascular smooth muscle cells (VSMCs), compared with WT mice. Likewise, PI-3065, a p110δ-selective PI3K inhibitor, almost completely prevented restenosis after artery injury. Our data showed that p110δ PI3K plays a main role in promoting neointimal thickening and inflammatory processes during vascular stenosis, with its inhibition providing significant reduction in restenosis following carotid injury. p110δ-selective inhibitors, recently approved for the treatment of human B-cell malignancies, therefore, present a new therapeutic opportunity to prevent the restenosis upon artery injury.

The role of PI3K in T cell activation and costimulation has been controversial. We previously reported that a kinase-inactivating mutation (D910A) in the p110δ isoform of PI3K results in normal T cell development, but impaired TCR-stimulated cell proliferation in vitro. This proliferative defect can be overcome by providing CD28 costimulation, which raises the question as to whether p110δ activity plays a role in T cell activation in vivo, which occurs primarily in the context of costimulation. In this study, we show that the PI3K signaling pathway in CD28-costimulated p110δD910A/D910A T cells is impaired, but that ERK phosphorylation and NF-κB nuclear translocation are unaffected. Under in vitro conditions of physiological Ag presentation and costimulation, p110δD910A/D910A T cells showed normal survival, but underwent fewer divisions. Differentiation along the Th1 and Th2 lineages was impaired in p110δD910A/D910A T cells and could not be rescued by exogenous cytokines in vitro. Adoptive transfer and immunization experiments in mice revealed that clonal expansion and differentiation in response to Ag and physiological costimulation were also compromised. Thus, p110δ contributes significantly to Th cell expansion and differentiation in vitro and in vivo, also in the context of CD28 costimulation.

Mouse gene-targeting studies have documented a central role of the p110delta isoform of phosphoinositide 3-kinase (PI3K) in B-cell development and function. A defect in B-cell antigen receptor (BCR) signaling is key to this B-cell phenotype. Here we further characterize this signaling defect and report that a p110delta-selective small molecule inhibitor mirrors the effect of genetic inactivation of p110delta in BCR signaling. p110delta activity is indispensable for BCR-induced DNA synthesis and phosphorylation of Akt/protein kinase B (PKB), forkhead transcription factor/forkhead box O3a (FOXO3a), and p70 S6 kinase (p70 S6K), with modest effects on the phosphorylation of glycogen synthase kinase 3 alpha/beta (GSK3alpha/beta) and extracellular signal-regulated kinase (Erk). The PI3K-dependent component of intracellular calcium mobilization also completely relies on p110delta catalytic activity. Resting B cells with inactive p110delta fail to enter the cell cycle, correlating with an incapacity to up-regulate the expression of cyclins D2, A, and E, and to phosphorylate the retinoblastoma protein (Rb). p110delta is also critical for interleukin 4 (IL-4)-induced phosphorylation of Akt/PKB and FOXO3a, and protection from apoptosis. Taken together, these data show that defects observed in p110delta mutant mice are not merely a consequence of altered B-cell differentiation, and emphasize the potential utility of p110delta as a drug target in autoimmune diseases in which B cells play a crucial role.

Estradiol rapidly activates Src as well as the Src-dependent pathway in human mammary cancer-derived MCF-7 cells, in human prostate cancer-derived LNCaP cells and in Cos cells transiently expressing hERs [EMBO J. 15 (1996) 1292; EMBO J. 17 (1998) 2008]. In addition, estradiol immediately stimulates, yes, an ubiquitous member of the Src kinase family, in human colon carcinoma-derived Caco-2 cells [Cancer Res. 56 (1996) 4516]. Progestins and androgens activate the same pathway in human mammary and prostate cancer-derived cells [EMBO J. 17 (1998) 2008; EMBO J. 19 (2000) 5406]. We observed that estradiol also stimulates the phosphatidylinositol-3-kinase (PI3K)/AKT pathway in MCF-7 cells [EMBO J. 20 (2001) 6050]. In these cells, activation of the Src- and the PI3 K-dependent pathways is simultaneous and mediated by direct interactions of the two kinases with ERalpha. The signalling pathway activation by sex-steroid hormones leads to DNA synthesis and cell growth in human mammary and prostate cancer-derived cells [EMBO J. 19 (2000) 5406; EMBO J. 20 (2001) 6050; EMBO J. 18 (1999) 2500]. Furthermore, androgen stimulation of NIH3T3 fibroblasts activates the same pathways triggered by this hormone in LNCaP cells and promotes the S-phase entry or cytoskeleton changes in these cells [J. Cell Biol. 161 (2003) 547]. All the described effects are rapid and require classic steroid receptors, but, surprisingly, not their transcriptional activity. Indeed, a transcriptionally inactive mutant of hER mediates the estrogen-stimulated DNA synthesis of NIH3T3 fibroblasts [EMBO J. 18 (1999) 2500]. Furthermore, AR in NIH3T3 cells does not enter nuclei and is unable to respond to the hormone with transcription stimulation, whereas it activates signaling pathways and triggers important biological responses. Signaling pathway activation by steroids has also been described by other groups under different experimental conditions and/or in different cell types. In these cells, steroid stimulation triggers various effects, such as neuroprotection, vasorelaxation or bone protection [J. Neurosci. Res. 60 (2000) 32 1; Nature 407 (2000) 538; J. Cell Biochem. 76 (1999) 206]. Analysis of the mechanisms responsible for the hormone-dependent and steroid receptor-mediated pathway activation in epithelial as well as stromal cells reveals immediate association of steroid receptors with extranuclear signaling effectors [EMBO J. 17 (1998) 2008; Cancer Res. 56 (1996) 4516; EMBO J. 19 (2000) 5406; EMBO J. 20 (2001) 6050; J. Cell Biol. 161 (2003) 547]. These results further highlight the central role of the hormone-regulated protein-protein interactions in the steroid action. They also offer the possibility of interfering with important activities of hormones, such as proliferation or survival, cytoskeleton changes as well as invasiveness and vasorelaxation, without affecting the steroid effects that depend on receptor transcriptional activity. (C) 2004 Published by Elsevier Inc.

PI3Ks (phosphoinositide 3-kinases) regulate diverse signalling pathways involved in growth, proliferation, survival, differentiation and metabolism. In T cells, PI3Ks can be activated by a number of different receptors, including the TcR (T cell receptor), co-stimulatory receptors, cytokine receptors and chemokine receptors. However, the specific roles of PI3Ks downstream of these receptors vary. An inactivating mutation in the leucocyte-specific PI3K isoform p110 δ results in impaired TcR-dependent proliferation under circumstances where CD28 co-stimulation is blocked or not required. Recruitment and activation of PI3K by CD28 promotes survival by inducing increased expression of Bcl-XL. However, CD28 engages additional signals that regulate proliferation and interleukin-2 production independently of PI3K. Thus a model emerges whereby PI3K is involved in both TcR and CD28 signalling, but each receptor may only exploit a subset of the signalling pathways potentially controlled by PI3K activation.

Phosphoinositide 3-kinases (PI3Ks) play an important role in a variety of cellular functions, including phagocytosis. PI3Ks are activated during phagocytosis induced by several receptors and have been shown to be required for phagocytosis through the use of inhibitors such as wortmannin and LY294002. Mammalian cells have multiple isoforms of PI3K, and the role of the individual isoforms during phagocytosis has not been addressed. The class I PI3Ks consist of a catalytic p110 isoform associated with a regulatory subunit. Mammals have three genes for the class IA p110 subunits encoding p110alpha, p110beta, and p110delta and one gene for the class IB p110 subunit encoding p110gamma. Here we report a specific recruitment of p110beta and p110delta (but not p110alpha) isoforms to the nascent phagosome during apoptotic cell phagocytosis by fibroblasts. By microinjecting inhibitory antibodies specific to class IA p110 subunits, we have shown that p110beta is the major isoform required for apoptotic cell and Fcgamma receptor-mediated phagocytosis by primary mouse macrophages. Macrophages from mice expressing a catalytically inactive form of p110delta showed no defect in the phagocytosis of apoptotic cells and IgG-opsonized particles, confirming the lack of a major role for p110delta in this process. Similarly, p110gamma-deficient macrophages phagocytosed apoptotic cells normally. Our findings demonstrate that p110beta is the major class I catalytic isoform required for apoptotic cell and Fcgamma receptor-mediated phagocytosis by primary macrophages.

We observed that sex steroid hormones, like growth factors, stimulate the Src/Ras/erk pathway of cell lines derived from human mammary or prostate cancers. In addition, hormone-dependent pathway activation can be induced in Cos cells, upon transfection of classic steroid receptors. Cross-talks between sex steroid receptors regulate their association with Src and consequent pathway activation. Oestradiol treatment of MCF-7 cells triggers simultaneous association of ER with Src and p85, the regulatory subunit of phosphatidylinositol-3-kinase (PI3-kinase) and activation of Src- and PI3-K-dependent pathways. Activation of the latter pathway triggers cyclin D1 transcription, that is unaffected by Mek-1 activation. This suggests that simultaneous activation of different signalling effectors is required to target different cell cycle components. Thus, a novel reciprocal cross-talk between the two pathways appears to be mediated by the ER. In all tested cells, activation of the signalling pathways has a proliferative role. Transcriptionally inactive ER expressed in NIH 3T3 cells responds to hormone causing Src/Ras/Erk pathway activation and DNA synthesis. This suggests that in these cells genomic activity is required for later events of cell growth.

The class IA isoforms of phosphoinositide 3-kinase (p110alpha, p110beta and p110delta) often have non-redundant functions in a given cell type. However, for reasons that are unclear, the role of a specific PI3K isoform can vary between cell types. Here, we compare the relative contributions of PI3K isoforms in primary and immortalised macrophages. In primary macrophages stimulated with the tyrosine kinase ligand colony-stimulating factor 1 (CSF1), all class IA PI3K isoforms participate in the regulation of Rac1, whereas p110delta selectively controls the activities of Akt, RhoA and PTEN, in addition to controlling proliferation and chemotaxis. The prominent role of p110delta in these cells correlates with it being the main PI3K isoform that is recruited to the activated CSF1 receptor (CSF1R). In immortalised BAC1.2F5 macrophages, however, the CSF1R also engages p110alpha, which takes up a more prominent role in CSF1R signalling, in processes including Akt phosphorylation and regulation of DNA synthesis. Cell migration, however, remains dependent mainly on p110delta. In other immortalised macrophage cell lines, such as IC-21 and J774.2, p110alpha also becomes more prominently involved in CSF1-induced Akt phosphorylation, at the expense of p110delta.These data show that PI3K isoforms can be differentially regulated in distinct cellular contexts, with the dominant role of the p110delta isoform in Akt phosphorylation and proliferation being lost upon cell immortalisation. These findings suggest that p110delta-selective PI3K inhibitors may be more effective in inflammation than in cancer.

The p110 isoforms of phosphoinositide 3-kinase (PI3K) are acutely regulated by extracellular stimuli. The class IA PI3K catalytic subunits (p110alpha, p110beta, and p110delta) occur in complex with a Src homology 2 (SH2) domain-containing p85 regulatory subunit, which has been shown to link p110alpha and p110delta to Tyr kinase signaling pathways. The p84/p101 regulatory subunits of the p110gamma class IB PI3K lack SH2 domains and instead couple p110gamma to G protein-coupled receptors (GPCRs). Here, we show, using small-molecule inhibitors with selectivity for p110beta and cells derived from a p110beta-deficient mouse line, that p110beta is not a major effector of Tyr kinase signaling but couples to GPCRs. In macrophages, both p110beta and p110gamma contributed to Akt activation induced by the GPCR agonist complement 5a, but not by the Tyr kinase ligand colony-stimulating factor-1. In fibroblasts, which express p110beta but not p110gamma, p110beta mediated Akt activation by the GPCR ligands stromal cell-derived factor, sphingosine-1-phosphate, and lysophosphatidic acid but not by the Tyr kinase ligands PDGF, insulin, and insulin-like growth factor 1. Introduction of p110gamma in these cells reduced the contribution of p110beta to GPCR signaling. Taken together, these data show that p110beta and p110gamma can couple redundantly to the same GPCR agonists. p110beta, which shows a much broader tissue distribution than the leukocyte-restricted p110gamma, could thus provide a conduit for GPCR-linked PI3K signaling in the many cell types where p110gamma expression is low or absent.

Mice lacking both the p110gamma and p110delta isoforms display severe impairment of thymocyte development. Here, we show that this phenotype is recapitulated in p110gamma-/-/p110delta(D910A/D910A) (p110gamma(KO)delta(D910A)) mice where the p110delta isoform has been inactivated by a point mutation. Moreover, we have examined the pathological consequences of the p110gammadelta deficiency, which include profound T-cell lymphopenia, T-cell and eosinophil infiltration of mucosal organs, elevated IgE levels, and a skewing toward Th2 immune responses. Using small-molecule selective inhibitors, we demonstrated that in mature T cells, p110delta, but not p110gamma, controls Th1 and Th2 cytokine secretion. Thus, the pathology in the p110gammadelta-deficient mice is likely to be secondary to a developmental block in the thymus that leads to lymphopenia-associated inflammatory responses.

The expression and function of the 8 distinct catalytic isoforms of PI 3-kinase (PI3K) in the nervous system are unknown. Whereas most PI3Ks have a broad tissue distribution, the tyrosine kinase-linked p110delta isoform has previously been shown to be enriched in leukocytes. Here we report that p110delta is also highly expressed in the nervous system. Inactivation of p110delta in mice did not affect gross neuronal development but led to an increased vulnerability of dorsal root ganglia neurons to exhibit growth cone collapse and decreases in axonal extension. Loss of p110delta activity also dampened axonal regeneration following peripheral nerve injury in adult mice and impaired functional recovery of locomotion. p110delta inactivation resulted in reduced neuronal signaling through the Akt protein kinase, and increased activity of the small GTPase RhoA. Pharmacological inhibition of ROCK, a downstream effector of RhoA, restored axonal extension defects in neurons with inactive p110delta, suggesting a key role of RhoA in p110delta signaling in neurons. Our data identify p110delta as an important signaling component for efficient axonal elongation in the developing and regenerating nervous system.

Physiological apoptosis is induced by a switch from survival to death signalling. Dysregulation of this process is frequently associated with cancer. A powerful model for this apoptotic switch is mammary gland involution, during which redundant milk-producing epithelial cells undergo apoptosis. Signal transducer and activator of transcription 3 (Stat3) is an essential mediator of this switch but the mechanism has not yet been defined. Stat3-dependent cell death during involution can be blocked by activation of Akt/protein kinase B (PKB), a downstream effector of the phosphoinositide-3-OH kinase (PI(3)K) pathway. Here we show that expression of the PI(3)K regulatory subunits p55alpha and p50alpha is induced by Stat3 during involution. In the absence of Stat3 in vivo, upregulation of p55alpha and p50alpha is abrogated, levels of activated Akt are sustained and apoptosis is prevented. Chromatin immunoprecipitation assays show that Stat3 binds directly to the p55alpha and p50alpha promoters in vivo. Overexpression of either p55alpha or p50alpha reduces levels of activated Akt. We propose a novel mechanism in which Stat3 regulates apoptosis by inducing expression of distinct PI(3)K regulatory subunits to downregulate PI(3)K-Akt-mediated survival signalling.

Phosphoinositide 3-kinases (PI3Ks) generate lipids that control a wide variety of intracellular signalling pathways. Part of this diversity in PI3K actions stems from the broad range of protein effectors of the PI3K lipids. A further layer of complexity is added by the existence of multiple isoforms of PI3K. Gene-targeting studies in the mouse have recently uncovered key roles for specific PI3K isoforms in immunity, metabolism and cardiac function. Remarkably, some of these actions do not require PI3K catalytic activity. In addition, loss-of-expression of certain PI3K genes leads to increased PI3K signalling following insulin stimulation. PI3K gene targeting has, in many cases, led to altered expression of the non-targeted PI3K subunits, making it difficult to exclude that some of the reported phenotypes result from 'knock-on' effects of PI3K gene deletion. Targeting strategies that take into account the complex interplay between members of the PI3K family will be crucial to gain a full understanding of the physiological roles of the isoforms of PI3K.

Expression of a dominant negative atypical protein kinase C (aPKC), PKCzeta, prevents nuclear translocation of extracellular regulated kinase 2 (ERK-2), p27 nuclear reduction, and DNA synthesis induced by estradiol in human mammary cancer-derived MCF-7 cells. aPKC action upstream of these events has been analyzed. In hormone-stimulated NIH 3T3 and Cos cells ectopically expressing human estrogen receptor alpha (hERalpha), aPKC is activated by phosphatidylinositol 3-kinase (PI 3-kinase) and, in turn, controls the Ras/MEK-1/ERK cascade. In MCF-7 and Cos cells stimulated by hormone, PI 3-kinase activates PKCzeta by Thr410 phosphorylation. Serine phosphorylation of PKCzeta is simultaneously induced. PKCzeta activation leads to recruitment of Ras to a multimolecular complex that also includes hERalpha, Src, PI 3-kinase, and aPKC. We propose that PKCzeta pushes Ras and the signaling complex close together in such a way that it facilitates the Src-dependent Ras activation. This activation is crucial for the interplay between estradiol-triggered signaling and cell cycle machinery.

In NIH3T3 cells, 0.001 nM of the synthetic androgen R1881 induces and stimulates association of androgen receptor (AR) with Src and phosphatidylinositol 3-kinase (Pl3-kinase), respectively, thereby triggering S-phase entry. 10 nM R1881 stimulates Rac activity and membrane ruffling in the absence of the receptor–Src–PI3-kinase complex assembly. The antiandrogen Casodex and specific inhibitors of Src and PI3-kinase prevent both hormonal effects, DNA synthesis and cytoskeletal changes. Neither low nor high R1881 concentration allows receptor nuclear translocation and receptor-dependent transcriptional activity in fibroblasts, although they harbor the classical murine AR. The very low amount of AR in NIH3T3 cells (7% of that present in LNCaP cells) activates the signaling pathways, but apparently is not sufficient to stimulate gene transcription. This view is supported by the appearance of receptor nuclear translocation as well as receptor-mediated transcriptional activity after overexpression of AR in fibroblasts. In addition, AR-negative Cos cells transiently transfected with a very low amount of hAR cDNA respond to low and high R1881 concentrations with signaling activation. Interestingly, they do not show significant transcriptional activation under the same experimental conditions. Fibroblasts are the first example of cells that respond to steroid hormones with activation of signaling pathways in the absence of endogenous receptor transcriptional activity. The data reported also show that hormone concentration can be crucial in determining the type of cell responsiveness.

The effects of dynamic exercise on restenosis after vascular injury are still unknown. The consequences of balloon dilation–induced injury on neointimal hyperplasia, vascular negative remodeling, and reendothelialization were assessed in sedentary and trained rats. Ex vivo eNOS vascular expression and activity were investigated in carotid arteries isolated from sedentary and exercised rats. The in vivo effects of eNOS inhibition by L-NMMA on vessel wall after balloon dilation were evaluated in sedentary and exercised rats. We also investigated the effects of exercise on neointimal formation in a rat stent model of vascular injury. Compared with sedentary group, the arteries isolated from trained rats showed higher levels of eNOS protein expression and activity 7 days after balloon dilation. A significant reduction of both neointimal hyperplasia and negative remodeling was observed 14 days after balloon injury in trained compared with sedentary rats. Moreover, we demonstrated that exercise training produced accelerated reendothelialization of the balloon injured arterial segments compared with sedentary. L-NMMA administration eliminated the benefits of physical training on vessel wall after balloon dilation. Finally, a decrease of neointimal hyperplasia as well as of platelet aggregation was observed after stent deployment in trained rats compared with sedentary. In conclusion, physical exercise could favorably affect restenosis after balloon angioplasty and stenting. Increase in eNOS expression and activity might contribute to the potential beneficial effects of exercise on the vessel wall after vascular injury.

The recent findings that oestradiol and progestins activate the Src/Ras/Erks signalling pathway raise the question of the role of this stimulation. Microinjection experiments of human mammary cancer-derived cells (MCF-7 and T47D) with cDNA of catalytically inactive Src or anti-Ras antibody prove that Src and Ras are required for oestradiol and progestin-dependent progression of cells through the cell cycle. The antitumoral ansamycin antibiotic, geldanamycin, disrupts the steroid-induced Ras-Raf-1 association and prevents Raf-1 activation and steroid-induced DNA synthesis. Furthermore, the selective MEK 1 inhibitor, PD 98059, inhibits oestradiol and progestin stimulation of Erk-2 and the steroid-dependent S-phase entry. The MDA-MB231 cells, which do not express oestradiol receptor, fail to respond to oestradiol in terms of Erk-2 activation and S-phase entry. Fibroblasts are made equally oestradiol-responsive in terms of DNA synthesis by transient transfection with either the wild-type or the transcriptionally inactive mutant oestradiol receptor (HE241G). Co-transfection of catalytically inactive Src as well as treatment with PD98059 inhibit the oestradiol-dependent S-phase entry of fibroblasts expressing either the wild-type oestrogen receptor or its transcriptionally inactive mutant. The data presented support the view that non-transcriptional action of the two steroids plays a major role in cell cycle progression.

The molecular mechanisms by which ovarian hormones stimulate growth of breast tumors are unclear. It has been reported previously that estrogens activate the signal‐transducing Src/p21 ras /Erk pathway in human breast cancer cells via an interaction of estrogen receptor (ER) with c‐Src. We now show that progestins stimulate human breast cancer T47D cell proliferation and induce a similar rapid and transient activation of the pathway which, surprisingly, is blocked not only by anti‐progestins but also by anti‐estrogens. In Cos‐7 cells transfected with the B isoform of progesterone receptor (PR B ), progestin activation of the MAP kinase pathway depends on co‐transfection of ER. A transcriptionally inactive PR B mutant also activates the signaling pathway, demonstrating that this activity is independent of transcriptional effects. PR B does not interact with c‐Src but associates via the N‐terminal 168 amino acids with ER. This association is required for the signaling pathway activation by progestins. We propose that ER transmits to the Src/p21 ras /Erk pathway signals received from the agonist‐activated PR B . These findings reveal a hitherto unrecognized cross‐talk between ovarian hormones which could be crucial for their growth‐promoting effects on cancer cells.

Class IA phosphoinositide 3-kinases (PI3Ks) are a family of p85/p110 heterodimeric lipid kinases that generate second messenger signals downstream of tyrosine kinases, thereby controlling cell metabolism, growth, proliferation, differentiation, motility, and survival. Mammals express three class IA catalytic subunits: p110α, p110β, and p110δ. It is unclear to what extent these p110 isoforms have overlapping or distinct biological roles. Mice expressing a catalytically inactive form of p110δ (p110δD910A) were generated by gene targeting. Antigen receptor signaling in B and T cells was impaired and immune responses in vivo were attenuated in p110δ mutant mice. They also developed inflammatory bowel disease. These results reveal a selective role for p110δ in immunity.