PI 3-kinase p110beta: a new target for antithrombotic therapy

Signalling pathways involved in p47phox -dependent reactive oxygen species in platelets of endotoxemic rats

Thrombocytopenia during sepsis is associated with a less favourable clinical outcome. Overproduction of reactive oxygen species (ROS) by different cell types contributes to sepsis. Platelets generate ROS, but the upstream pathways of NADPH oxidase activation are not completely understood. Here, we designed experiments in washed platelets from lipopolysaccharide (LPS)-treated rats to investigate the p47^phox activation and ROS generation, and its modulation by c-Src family kinase (c-Src), phosphoinositide 3-kinase (PI3K), protein kinase C (PKC) and protein kinase G (PKG). Rats were injected intraperitoneally with LPS (1 mg/kg), and at 48 hours thereafter, arterial blood was collected and washed platelets were obtained. Washed platelets were pre-incubated with different inhibitors and subsequently activated or not with ADP. Flow cytometry, Western blotting and ELISA were performed. We found that LPS significantly increased the p47^phox phosphorylation and ROS generation compared with the control group (P < 0.05). The enhanced ROS production in the LPS group was unaffected by the non-selective SFKs inhibitor PP2, the PI3K inhibitor wortmannin or the Akt inhibitor PPI-1. The cyclic GMP levels were 115% higher in activated platelets of LPS compared with the saline group (P < 0.05). Moreover, in the LPS group, the sGC inhibitor ODQ, the PKG inhibitor Rp-8-Br and the PKC inhibitor GF109203X abrogated the increased p47^phox phosphorylation and reduced the ROS levels. In conclusion, selective inhibitors of cGMP-PKG and PKC-p47^phox pathways that regulate ROS generation by LPS in platelets may help control the redox balance in sepsis improving the survival of patients.

Repurposing of Approved Cardiovascular Drugs against Ischemic Cerebrovascular Disease by Disease-Disease Associated Network-Assisted Prediction

Stroke is one of the leading causes of death and disability globally, while intravenous thrombolysis with recombinant tissue plasminogen activator remains the only Food and Drug Administration (FDA)-approved therapy for ischemic stroke. The attempts to develop new treatments for acute ischemic stroke meet costly and spectacularly disappointing results, which requires both long time and high costs, whereas repurposing of safe existing drugs to new indications provides a cost-effective and not time-consuming alternative. Vascular protection is a promising strategy for improving stroke outcome, as vascular function is critical to both cardiovascular diseases (CVD) and ischemic cerebrovascular disease (ICD). Vascular function related biological processes and pathways maybe the critical associations between CVD and ICD. In this study, a multi-database, in silico target identification, gene function enrichment, and network pharmacology analysis integration approach was proposed and applied to investigate the FDA-approved CVD drugs repurposing for ICD. A list of 119 candidate drugs can be obtained for further investigation of their potential in ICD treatment. As a pleiotropic drug with multi-target, carvedilol was set an example to investigate its promising potential for ICD therapy. Our results indicated that the mode of action of carvedilol for ICD treatment may tightly associated with vascular function regulation and the mechanism is multi-target and multi-signaling pathway related. The disease-disease association network-assisted prediction needs further investigations. In summary, the proposed methods herein may provide a promising alternative to inferring novel disease indications for known drugs.

Platelet activation and prothrombotic properties in a mouse model of peritoneal sepsis

Sepsis is associated with thrombocytopenia and microvascular thrombosis. Studies have described platelets implication in this pathology but their kinetics of activation and behavior remain poorly known. We show in a mouse model of peritonitis, the appearance of platelet-rich thrombi in organ microvessels and organ damage. Complementary methods are necessary to characterize platelet activation during sepsis as circulating soluble markers and platelet-monocyte aggregates revealed early platelet activation, while surface activation markers were detected at later stage. A microfluidic based ex-vivo thrombosis assay demonstrated that platelets from septic mice have a prothrombotic behavior at shear rate encountered in microvessels. Interestingly, we found that even though phosphoinositide-3-kinase β-deficient platelet mice formed less thrombi in liver microcirculation, peritoneal sepsis activates a platelet alternative pathway to compensate the otherwise mandatory role of this lipid-kinase to form stable thrombi at high shear rate. Platelets are rapidly activated during sepsis. Thrombocytopenia can be attributed in part to platelet-rich thrombi formation in capillaries and platelet-leukocytes interactions. Platelets from septic mice have a prothrombotic phenotype at a shear rate encountered in arterioles. Further studies are necessary to unravel molecular mechanisms leading to this prothrombotic state of platelets in order to guide the development of future treatments of polymicrobial sepsis.

Impact of PI3Kα (Phosphoinositide 3-Kinase Alpha) Inhibition on Hemostasis and Thrombosis

Objective- PI3Kα (phosphoinositide 3-kinase alpha) is a therapeutic target in oncology, but its role in platelets and thrombosis remains ill characterized. In this study, we have analyzed the role of PI3Kα in vitro, ex vivo, and in vivo in 2 models of arterial thrombosis. Approach and Results- Using mice selectively deficient in p110α in the megakaryocyte lineage and isoform-selective inhibitors, we confirm that PI3Kα is not mandatory but participates to thrombus growth over a collagen matrix at arterial shear rate. Our data uncover a role for PI3Kα in low-level activation of the GP (glycoprotein) VI-collagen receptor by contributing to ADP secretion and in turn full activation of PI3Kβ and Akt/PKB (protein kinase B). This effect was no longer observed at high level of GP VI agonist concentration. Our study also reveals that over a vWF (von Willebrand factor) matrix, PI3Kα regulates platelet stationary adhesion contacts under arterial flow through its involvement in the outside-in signaling of vWF-engaged αIIbβ3 integrin. In vivo, absence or inhibition of PI3Kα resulted in a modest but significant decrease in thrombus size after superficial injuries of mouse mesenteric arteries and an increased time to arterial occlusion after carotid lesion, without modification in the tail bleeding time. Considering the more discrete and nonredundant role of PI3Kα compared with PI3Kβ, selective PI3Kα inhibitors are unlikely to increase the bleeding risk at least in the absence of combination with antiplatelet drugs or thrombopenia. Conclusions- This study provides mechanistic insight into the role of PI3Kα in platelet activation and arterial thrombosis.

Astilbe chinensis Modulates Platelet Function via Impaired MAPK and PLCγ2 Expression

Background

Platelets play major role in maintaining hemostasis while hyperactivation of platelets may lead to arterial thrombosis. Natural products and ethnomedicine have been shown to reduce the risk of cardiovascular diseases (CVDs). Astilbe chinensis is a perennial herb found in China, Korea, Russia, and Japan, which is also known for its medicinal effects, and has been used in Korean traditional medicine to treat inflammation, cancer, chronic bronchitis, and headache. We hypothesized that given herbal plant exhibits pharmacological activities against CVDs, and we specifically explored their effects on platelet function.

Methodology

Platelet aggregation was evaluated using standard light-transmission aggregometry. Intracellular calcium mobilization was assessed using Fura-2/AM, and granule secretion (ATP release) was measured in a luminometer. Fibrinogen binding to integrin α_IIbβ₃ was assessed using flow cytometry. Phosphorylation of mitogen-activated protein kinase (MAPK) signaling molecules and activation of the phosphoinositide 3-kinase (PI3K)/Akt were assessed using western blots, and further, glycoprotein VI (GPVI) signaling components were studied using immunoprecipitation.

Key Results

A. chinensis extracts potently and significantly inhibited platelet aggregation, calcium mobilization, granule secretion, and fibrinogen binding to integrin α_IIbβ₃. Moreover, it significantly inhibited MAPK phosphorylation and expression of GPVI downstream signaling molecules.

Conclusion

A. chinensis extract inhibited platelet aggregation and granule secretion and attenuated GPVI downstream signaling, indicating the potential therapeutic effects of this plant extract on the cardiovascular system and platelet function. We suggest that given plant extract may be a potent candidate to treat platelet-related CVDs and to be used as antiplatelet agent.

Intrinsic apoptosis circumvents the functional decline of circulating platelets but does not cause the storage lesion

BAK/BAX depletion in murine platelets reveals that intrinsic apoptosis is not required for the development of the platelet storage lesion. Restriction of platelet life span by intrinsic apoptosis is pivotal to maintain a functional, hemostatically reactive platelet population.

Profiling of phosphoinositide molecular species in human and mouse platelets identifies new species increasing following stimulation

Phosphoinositides are bioactive lipids essential in the regulation of cell signaling as well as cytoskeleton and membrane dynamics. Their metabolism is highly active in blood platelets where they play a critical role during activation, at least through two well identified pathways involving phospholipase C and phosphoinositide 3-kinases (PI3K). Here, using a sensitive high-performance liquid chromatography-mass spectrometry method recently developed, we monitored for the first time the profiling of phosphatidylinositol (PI), PIP, PIP₂ and PIP₃ molecular species (fatty-acyl profiles) in human and mouse platelets during the course of stimulation by thrombin and collagen-related peptide. Furthermore, using class IA PI3K p110α or p110β deficient mouse platelets and a pharmacological inhibitor, we show the crucial role of p110β and the more subtle role of p110α in the production of PIP₃ molecular species following stimulation. This comprehensive platelet phosphoinositides profiling provides important resources for future studies and reveals new information on phosphoinositides biology, similarities and differences in mouse and human platelets and unexpected dramatic increase in low-abundance molecular species of PIP₂ during stimulation, opening new perspectives in phosphoinositide signaling in platelets.

Pharmacological inactivation of the PI3K p110δ prevents breast tumour progression by targeting cancer cells and macrophages

Patient selection for PI3K-targeted solid cancer treatment was based on the PIK3CA/PTEN mutational status. However, it is increasingly clear that this is not a good predictor of the response of breast cancer cells to the anti-proliferative effect of PI3K inhibitors, indicating that isoform(s) other than p110α may modulate cancer cells sensitivity to PI3K inhibition. Surprisingly, we found that although no mutations in the p110δ subunit have been detected thus far in breast cancer, the expression of p110δ becomes gradually elevated during human breast cancer progression from grade I to grade III. Moreover, pharmacological inactivation of p110δ in mice abrogated the formation of tumours and the recruitment of macrophages to tumour sites and strongly affected the survival, proliferation and apoptosis of grafted tumour cells. Pharmacological inactivation of p110δ in mice with defective macrophages or in mice with normal macrophages but grafted with p110δ-lacking tumours suppressed only partly tumour growth, indicating a requisite role of p110δ in both macrophages and cancer cells in tumour progression. Adoptive transfer of δD910A/D910A macrophages into mice with defected macrophages suppressed tumour growth, eliminated the recruitment of macrophages to tumour sites and prevented metastasis compared with mice that received WT macrophages further establishing that inactivation of p110δ in macrophage prevents tumour progression. Our work provides the first in vivo evidence for a critical role of p110δ in cancer cells and macrophages during solid tumour growth and may pave the way for the use of p110δ inhibitors in breast cancer treatment.

Phosphatidylinositol 3-kinase β and δ isoforms play key roles in metastasis of prostate cancer DU145 cells

Metastasis is the main cause of the lethality of prostate cancer. Class I phosphatidylinositol 3-kinases (PI3Ks), which contain 4 isoforms, α, β, δ, and γ, are known to play important roles in cell growth, migration, invasion, and so on. However, the respective role of each PI3K isoform in cancer cell migration and invasion remains unknown. In a study that aimed to elucidate the respective role of the 4 PI3K isoforms, we investigated the change in migratory and invasive ability of DU145 cells after treatment with each PI3K isoform-specific inhibitor. Both migration and invasion of DU145 cells were potently blocked by each of the PI3Kβ inhibitors (GSK2636771 and TGX221) and PI3Kδ inhibitors (CAL101 and IC87114) while not obviously affected by PI3Kα inhibitor BYL719 or PI3Kγ inhibitor AS252424. Furthermore, knocking down PI3Kβ or PI3Kδ isoform led to a significant decrease in migration of DU145. The results suggest that PI3Kβ and PI3Kδ play key roles in prostate cancer cell migration, while PI3Kα and PI3Kγ might be redundant. Oral administration of GSK2636771 (100 mg/kg) and CAL101 (30 mg/kg) inhibited tumor growth in bone, an experimental model by intratibia injection of DU145 cells, with improved bone structure and bone mineral density analyzed by micro-computed tomography. Tissue staining indicated reduction of metastatic DU145 cells and osteoclasts in the bones of GSK2636771- and CAL101-treated mice compared to the untreated group. In summary, our results indicated the distinct roles of 4 PI3K isoforms in the migration of prostate cancer DU145 cells, and they demonstrated the in vitro and in vivo antimetastatic effect of PI3K-isoform specific inhibitors, most of which are in clinical trials.-Zhang, Z., Liu, J., Wang, Y., Tan, X., Zhao, W., Xing, X., Qiu, Y., Wang, R., Jin, M., Fan, G., Zhang, P., Zhong, Y., Kong, D. Phosphatidylinositol 3-kinase β and δ isoforms play key roles in metastasis of prostate cancer DU145 cells.

Compression force sensing regulates integrin αIIbβ3 adhesive function on diabetic platelets

Diabetes is associated with an exaggerated platelet thrombotic response at sites of vascular injury. Biomechanical forces regulate platelet activation, although the impact of diabetes on this process remains ill-defined. Using a biomembrane force probe (BFP), we demonstrate that compressive force activates integrin αIIbβ3 on discoid diabetic platelets, increasing its association rate with immobilized fibrinogen. This compressive force-induced integrin activation is calcium and PI 3-kinase dependent, resulting in enhanced integrin affinity maturation and exaggerated shear-dependent platelet adhesion. Analysis of discoid platelet aggregation in the mesenteric circulation of mice confirmed that diabetes leads to a marked enhancement in the formation and stability of discoid platelet aggregates, via a mechanism that is not inhibited by therapeutic doses of aspirin and clopidogrel, but is eliminated by PI 3-kinase inhibition. These studies demonstrate the existence of a compression force sensing mechanism linked to αIIbβ3 adhesive function that leads to a distinct prothrombotic phenotype in diabetes.

Endometrial cancer cells exhibit high expression of p110β and its selective inhibition induces variable responses on PI3K signaling, cell survival and proliferation

PTEN loss and constitutive activation of the class I phosphoinositide 3-kinase (PI3K) pathway are key drivers of endometrial tumorigenesis. In some cancer types, PTEN-deficient tumors are reliant on class I PI3K p110β (encoded by PIK3CB) activity but little is known about this contribution in endometrial tumorigenesis. In this study, we find that p110β is overexpressed in a panel of 7 endometrial cancer cell lines compared to non-transformed cells. Furthermore, in 234 clinically annotated patient samples, PIK3CB mRNA levels increase significantly in the early phase of tumorigenesis from precursors to low grade primary malignant lesions whereas PIK3CA levels are higher in non-endometrioid compared to endometrioid primary tumors. While high levels of either PIK3CA or PIK3CB associate with poor prognosis, only elevated PIK3CB mRNA levels correlate with a high cell cycle signature score in clinical samples. In cancer cell lines, p110α inhibition reduces cell viability by inducing cell death in PIK3CA mutant cells while p110β inhibition delayed proliferation in PTEN-deficient cells, but not in WT cells. Taken together, our findings suggest that PIK3CB/p110β contributes to some of the pleiotropic functions of PI3K in endometrial cancer, particularly in the early steps by contributing to cell proliferation.

Translational Implications of Platelets as Vascular First Responders

Platelets play a vital role in normal hemostasis to stem blood loss at sites of vascular injury by tethering and adhering to sites of injury, recruiting other platelets and blood cells to the developing clot, releasing vasoactive small molecules and proteins, and assembling and activating plasma coagulation proteins in a tightly regulated temporal and spatial manner. In synchrony with specific end products of coagulation, primarily cross-linked fibrin, a stable thrombus quickly forms. Far beyond physiological hemostasis and pathological thrombosis, emerging evidence supports platelets playing a pivotal role in vascular homeostasis, inflammation, cellular repair, regeneration, and wide range of autocrine and paracrine functions. In essence, platelets play both structural and functional roles as reporters, messengers, and active transporters surveying the vasculature for cues of environmental or developmental stimuli and participating as first responders.1 In this review, we will provide a contemporary perspective of platelet physiology, including fundamental, translational, and clinical constructs that apply directly to human health and disease.

Current and future antiplatelet therapies: emphasis on preserving haemostasis

Antiplatelet drugs, such as aspirin, P2Y₁₂ antagonists, and glycoprotein (GP) IIb/IIIa inhibitors, have proved to be successful in reducing the morbidity and mortality associated with arterial thrombosis. These agents are, therefore, the cornerstone of therapy for patients with acute coronary syndromes. However, these drugs all carry an inherent risk of bleeding, which is associated with adverse cardiovascular outcomes and mortality. Thus, the potential benefits of more potent, conventional antiplatelet drugs are likely be offset by the increased risk of bleeding. Data from experiments in vivo have highlighted potentially important differences between haemostasis and thrombosis, raising the prospect of developing new antiplatelet drugs that are not associated with bleeding. Indeed, in preclinical studies, several novel antiplatelet therapies that seem to inhibit thrombosis while maintaining haemostasis have been identified. These agents include inhibitors of phosphatidylinositol 3-kinase-β (PI3Kβ), protein disulfide-isomerase, activated GPIIb/IIIa, GPIIb/IIIa outside-in signalling, protease-activated receptors, and platelet GPVI-mediated adhesion pathways. In this Review, we discuss how a therapeutic ceiling has been reached with existing antiplatelet drugs, whereby increased potency is offset by elevated bleeding risk. The latest advances in our understanding of thrombus formation have informed the development of new antiplatelet drugs that are potentially safer than currently available therapies.

Functional characterization of a novel somatic oncogenic mutation of PIK3CB

Class I phosphoinositide 3-kinase (PI3K) enzymes have attracted considerable attention as drug targets in cancer therapy over the last 20 years. The signaling pathway triggered by class I PI3Ks is dysregulated in a range of tumor types, impacting cell proliferation, survival and apoptosis. Frequent oncogenic mutations of PIK3CA have previously been discovered. In contrast, reports of PIK3CB mutations have been limited; however, in most cases, those that have been identified have been shown to be activating and oncogenic. The functional characterization of a PIK3CB catalytic domain mutant, p110βE1051K, first discovered by others in castrate-resistant prostate cancer (mCRPC), is outlined in this report; our data suggest that p110βE1051K is a gain-of-function mutation, driving PI3K signaling, tumorigenic cell growth and migration. Tumor cells expressing p110βE1051K are sensitive to p110β inhibition; its characterization as an oncogenic driver adds to the rationale for targeting p110β and indicates a continuing need to further develop specific PI3K inhibitors for clinical development in cancer therapy.

Residual cyclooxygenase-1 activity and epinephrine reduce the antiplatelet effect of aspirin in patients with acute myocardial infarction

Aspirin treatment is essential in patients with acute myocardial infarction (AMI) to block platelet thromboxane (TXA)2 synthesis. Epinephrine is known to enhance platelet reactivity induced by other agonists and to be elevated in patients with AMI due to stress. Our objective was to study the influence of epinephrine on platelet TXA2 synthesis in patients treated with aspirin for AMI at early onset (within 48 hours) and the potential biochemical mechanisms involved in the functional response. Washed platelets from 45 patients with AMI and 10 aspirin-free controls were stimulated with arachidonic acid (AA) or AA + epinephrine, and aggregation and TXA2 synthesis were evaluated. Full platelet aggregation was recorded in 8/45 patients (18%) with a partial TXA2 inhibition (86%) vs. the aspirin-free controls. Platelets from the remaining 37 patients did not aggregate to AA and had TXA2 inhibition >95%. However, when platelets were simultaneously stimulated with AA + epinephrine, in 25/37 patients a large intensity of aggregation (73%) was observed and a 5.5-fold increase in TXA2 synthesis, although this remained residual (<5% of aspirin-free controls). This residual-TXA2 was critical in the functional response, as demonstrated by the complete inhibition by TXA2 receptor blockade or additional aspirin in vitro. The phosphatidylinositol-3-kinase activity and the cytosolic calcium levels participated in this platelet response elicited by a receptor cooperation mechanism, while the Rho/p160ROCK pathway or the blockade of the ADP receptors (P2Y1, P2Y12) were without effect. Residual-cyclooxygenase –1 activity and epinephrine enhance TXA2-dependent platelet function, which may reduce the clinical benefit of aspirin in patients with AMI.

Caffeine induces endothelial tissue factor expression via phosphatidylinositol 3-kinase inhibition

Tissue factor (TF) is the key activator of coagulation and is involved in acute coronary syndromes. Caffeine is often reported to increase cardiovascular risk; however, its effect on cardiovascular morbidity and mortality is controversial. Hence, this study was designed to investigate the impact of caffeine on endothelial TF expression in vitro. Caffeine concentration-dependently enhanced TF protein expression and surface activity in human endothelial cells stimulated by tumour necrosis factor (TNF)-α or thrombin. Caffeine inhibited phosphatidylinositol 3-kinase (PI3K) activity and this effect was comparable to that of the known PI3K inhibitor LY294002. Consistently, treatment of endothelial cells with LY294002 enhanced TNF-α induced TF expression to a similar extent as caffeine, and adenoviral expression of the active PI3K mutant (p110) reversed the effect of both caffeine and LY294002 on TF expression. Caffeine and LY294002 increased DNA binding capacity of the transcription factor nuclear factor κB, whereas the activation pattern of mitogen-activated protein kinases (MAPK) remained unaltered. Luciferase reporter assay revealed a caffeine dependent activation of the TF promoter, and RT-PCR revealed a dose dependent increase in TF mRNA levels when stimulated with caffeine in the presence of TNF-α. In conclusion, caffeine enhances TNF-α-induced endothelial TF protein expression as well as surface activity by inhibition of PI3K signalling. Since the caffeine concentrations applied in the present study are within the plasma range measured in humans, our findings indicate that caffeine enhances the prothrombotic potential of endothelial cells and underscore the importance of PI3K in mediating these effects.

Rac1-stimulated macropinocytosis enhances Gβγ activation of PI3Kβ

Phosphoinositide 3-kinases (PI 3-kinases) are regulated by a diverse range of upstream activators, including receptor tyrosine kinases (RTKs), G-protein-coupled receptors (GPCRs), and small GTPases from the Ras, Rho and Rab families. For the Class IA PI 3-kinase PI3Kβ, two mechanisms for GPCR-mediated regulation have been described: direct binding of Gβγ subunits to the C2-helical domain linker of p110β, and Dock180/Elmo1-mediated activation of Rac1, which binds to the Ras-Binding Domain of p110β. We now show that the integration of these dual pathways is unexpectedly complex. In breast cancer cells, expression of constitutively activated Rac1 (CA-Rac1) along with either GPCR stimulation or expression of Gβγ led to an additive PI3Kβ-dependent activation of Akt. Whereas CA-Rac1-mediated activation of Akt was blocked in cells expressing a mutated PI3Kβ that cannot bind Gβγ, Gβγ and GPCR-mediated activation of Akt was preserved when Rac1 binding to PI3Kβ was blocked. Surprisingly, PI3Kβ-dependent CA-Rac1 signaling to Akt was still seen in cells expressing a mutant p110β that cannot bind Rac1. Instead of directly binding to PI3Kβ, CA-Rac1 acts by enhancing Gβγ coupling to PI3Kβ, as CA-Rac1-mediated Akt activation was blocked by inhibitors of Gβγ. Cells expressing CA-Rac1 exhibited a robust induction of macropinocytosis, and inhibitors of macropinocytosis blocked the activation of Akt by CA-Rac1 or lysophosphatidic acid. Our data suggest that Rac1 can potentiate the activation of PI3Kβ by GPCRs through an indirect mechanism, by driving the formation of macropinosomes that serve as signaling platforms for Gβγ coupling to PI3Kβ.

Modulation of telomere protection by the PI3K/AKT pathway

Telomeres and the insulin/PI3K pathway are considered hallmarks of aging and cancer. Here, we describe a role for PI3K/AKT in the regulation of TRF1, an essential component of the shelterin complex. PI3K and AKT chemical inhibitors reduce TRF1 telomeric foci and lead to increased telomeric DNA damage and fragility. We identify the PI3Kα isoform as responsible for this TRF1 inhibition. TRF1 is phosphorylated at different residues by AKT and these modifications regulate TRF1 protein stability and TRF1 binding to telomeric DNA in vitro and are important for in vivo TRF1 telomere location and cell viability. Patient-derived breast cancer PDX mouse models that effectively respond to a PI3Kα specific inhibitor, BYL719, show decreased TRF1 levels and increased DNA damage. These findings functionally connect two of the major pathways for cancer and aging, telomeres and the PI3K pathway, and pinpoint PI3K and AKT as novel targets for chemical modulation of telomere protection.

Regulation of telomeres and the insulin/PI3K pathway both have roles in aging and cancer development but have not been functionally linked. Here the authors demonstrate that PI3K, via downstream targets, regulates TRF1 via phosphorylation.

The importance of blood platelet lipid signaling in thrombosis and in sepsis

Blood platelets are the first line of defense against hemorrhages and are also strongly involved in the processes of arterial thrombosis, a leading cause of death worldwide. Besides their well-established roles in hemostasis, vascular wall repair and thrombosis, platelets are now recognized as important players in other processes such as inflammation, healing, lymphangiogenesis, neoangiogenesis or cancer. Evidence is accumulating they are key effector cells in immune and inflammatory responses to host infection. To perform their different functions platelets express a wide variety of membrane receptors triggering specific intracellular signaling pathways and largely use lipid signaling systems. Lipid metabolism is highly active in stimulated platelets including the phosphoinositide metabolism with the phospholipase C (PLC) and the phosphoinositide 3-kinase (PI3K) pathways but also other enzymatic systems producing phosphatidic acid, lysophosphatidic acid, platelet activating factor, sphingosine 1-phosphate and a number of eicosanoids. While several of these bioactive lipids regulate intracellular platelet signaling mechanisms others are released by activated platelets acting as autocrine and/or paracrine factors modulating neighboring cells such as endothelial and immune cells. These bioactive lipids have been shown to play important roles in hemostasis and thrombosis but also in vessel integrity and dynamics, inflammation, tissue remodeling and wound healing. In this review, we will discuss some important aspects of platelet lipid signaling in thrombosis and during sepsis that is an important cause of death in intensive care unit. We will particularly focus on the implication of the different isoforms of PI3Ks and on the generation of eicosanoids released by activated platelets.

TGX-221 inhibits proliferation and induces apoptosis in human glioblastoma cells

Glioblastoma is the most common type of primary brain tumor in adults, with high mortality and morbidity rates. More effective therapeutic strategies are imperative. Previous studies have shown that the known p110-β-selective inhibitor TGX-221 blocks the activation of PKB/Akt in PTEN-deficient cells. We treated U87 and U251 glioblastoma cells with TGX-221 to determine the effect of TGX-221. We performed a Cell Counting Kit-8 (CCK-8) test, EDU staining and cell cycle distribution analysis and found that TGX-221 inhibited glioblastoma cell proliferation. Next, the effect of TGX-221 on cell apoptosis was investigated using flow cytometry. These results demonstrated that TGX-221 induced apoptosis in glioblastoma cells. Moreover, migration and invasion assays revealed that TGX-221 inhibited human glioblastoma cell migration and invasion. Collectively, our study revealed that TGX-221 could inhibit proliferation and induce apoptosis in glioblastoma cells.

Class III PI3K Positively Regulates Platelet Activation and Thrombosis via PI(3)P-Directed Function of NADPH Oxidase

OBJECTIVE

Class III phosphoinositide 3-kinase, also known as VPS34 (vacuolar protein sorting 34), is a highly conserved enzyme regulating important cellular functions such as NADPH oxidase (NOX) assembly, membrane trafficking, and autophagy. Although VPS34 is expressed in platelets, its involvement in platelet activation remains unclear. Herein, we investigated the role of VPS34 in platelet activation and thrombus formation using VPS34 knockout mice.

APPROACH AND RESULTS

Platelet-specific VPS34-deficient mice were generated and characterized. VPS34 deficiency in platelets did not influence tail bleeding time. In a ferric chloride-induced mesenteric arteriolar thrombosis model, VPS34^-/- mice exhibited a prolonged vessel occlusion time compared with wild-type mice (42.05±4.09 versus 18.30±2.47 minutes). In an in vitro microfluidic whole-blood perfusion assay, thrombus formation on collagen under arterial shear was significantly reduced for VPS34^-/- platelets. VPS34^-/- platelets displayed an impaired aggregation and dense granule secretion in response to low doses of collagen or thrombin. VPS34 deficiency delayed clot retraction but did not influence platelet spreading on fibrinogen. We also demonstrated that VPS34 deficiency altered the basal level of autophagy in resting platelets and hampered NOX assembly and mTOR (mammalian target of rapamycin) signaling during platelet activation. Importantly, we identified the NOX-dependent reactive oxygen species generation as the major downstream effector of VPS34, which in turn can mediate platelet activation. In addition, by using a specific inhibitor 3-methyladenine, VPS34 was found to operate through a similar NOX-dependent mechanism to promote human platelet activation.

CONCLUSIONS

Platelet VPS34 is critical for thrombosis but dispensable for hemostasis. VPS34 regulates platelet activation by influencing NOX assembly.

Integrin αIIbβ3 outside-in signaling

Integrin α_IIbβ₃ is a highly abundant heterodimeric platelet receptor that can transmit information bidirectionally across the plasma membrane, and plays a critical role in hemostasis and thrombosis. Upon platelet activation, inside-out signaling pathways increase the affinity of α_IIbβ₃ for fibrinogen and other ligands. Ligand binding and integrin clustering subsequently stimulate outside-in signaling, which initiates and amplifies a range of cellular events driving essential platelet processes such as spreading, thrombus consolidation, and clot retraction. Integrin α_IIbβ₃ has served as an excellent model for the study of integrin biology, and it has become clear that integrin outside-in signaling is highly complex and involves a vast array of enzymes, signaling adaptors, and cytoskeletal components. In this review, we provide a concise but comprehensive overview of α_IIbβ₃ outside-in signaling, focusing on the key players involved, and how they cooperate to orchestrate this critical aspect of platelet biology. We also discuss gaps in the current understanding of α_IIbβ₃ outside-in signaling and highlight avenues for future investigation.

ErbB2-positive mammary tumors can escape PI3K-p110α loss through downregulation of the Pten tumor suppressor

Breast cancer is the most common cancer among women and 30% will be diagnosed with an ErbB2-positive cancer. Forty percent of ErbB2-positive breast tumors have an activating mutation in p110α, a catalytic subunit of phosphoinositide 3-kinase (PI3K). Clinical and experimental data show that breast tumors treated with a p110α-specific inhibitor often circumvent inhibition and resume growth. To understand this mechanism of resistance, we crossed a p110α conditional (p110αflx/flx) mouse model with mice that overexpresses the ErbB2/Neu-IRES-Cre transgene (NIC) specifically in the mammary epithelium. Although mammary-specific deletion of p110α dramatically delays tumor onset, tumors eventually arise and are dependent on p110β. Through biochemical analyses we find that a proportion of p110α-deficient tumors (23%) display downregulation of the Pten tumor suppressor. We further demonstrate that loss of one allele of PTEN is sufficient to shift isoform dependency from p110α to p110β in vivo. These results provide insight into the molecular mechanism by which ErbB2-positive breast cancer escapes p110α inhibition.

Characterization of a novel p110β-specific inhibitor BL140 that overcomes MDV3100-resistance in castration-resistant prostate cancer cells

BACKGROUND

Our previous studies demonstrated that the class IA PI3K/p110β is critical in castration-resistant progression of prostate cancer (CRPC) and that targeting prostate cancer with nanomicelle-loaded p110β-specific inhibitor TGX221 blocked xenograft tumor growth in nude mice, confirming the feasibility of p110β-targeted therapy for CRPCs. To improve TGX221's aqueous solubility, in this study, we characterized four recently synthesized TGX221 analogs.

METHODS

TGX221 analog efficacy were examined in multiple prostate cancer cell lines with the SRB cell growth assay, Western blot assay for AKT phosphorylation and cell cycle protein levels. Target engagement with PI3K isoforms was evaluated with cellular thermal shift assay. PI3K activity was determined with the Kinase-Glo Plus luminescent kinase assay. Cell cycle distribution was evaluated with flow cytometry after propidium iodide staining.

RESULTS

As expected, replacing either one of two major functional groups in TGX221 by more hydrophilic groups dramatically improved the aqueous solubility (about 40-fold) compared to TGX221. In the CETSA assay, all the analogs dramatically shifted the melting curve of p110β protein while none of them largely affected the melting curves of p110α, p110γ, or Akt proteins, indicating target-specific engagement of these analogs with p110β protein. However, functional evaluation showed that only one of the analogs BL140 ubiquitously inhibited AKT phosphorylation in all CRPC cell lines tested with diverse genetic abnormalities including AR, PTEN, and p53 status. BL140 was superior than GSK2636771 (IC50 5.74 vs 20.49 nM), the only p110β-selective inhibitor currently in clinical trials, as revealed in an in vitro Kinase-Glo assay. Furthermore, BL140 exhibited a stronger inhibitory effect than GSK2636771 on multiple CRPC cell lines including a MDV3100-resistant C4-2B cell subline, indicating BL140 elimination of MDV3100 resistance. Mechanistic studies revealed that BL140 blocked G1 phase cell cycle entry by reducing cyclin D1 but increasing p27kip1 protein levels.

CONCLUSION

These studies suggested that BL140 is a promising p110β-specific inhibitor with multiple superb properties than GSK2636771 worthy for further clinical development.

A Cdc42/RhoA regulatory circuit downstream of glycoprotein Ib guides transendothelial platelet biogenesis

Blood platelets are produced by large bone marrow (BM) precursor cells, megakaryocytes (MKs), which extend cytoplasmic protrusions (proplatelets) into BM sinusoids. The molecular cues that control MK polarization towards sinusoids and limit transendothelial crossing to proplatelets remain unknown. Here, we show that the small GTPases Cdc42 and RhoA act as a regulatory circuit downstream of the MK-specific mechanoreceptor GPIb to coordinate polarized transendothelial platelet biogenesis. Functional deficiency of either GPIb or Cdc42 impairs transendothelial proplatelet formation. In the absence of RhoA, increased Cdc42 activity and MK hyperpolarization triggers GPIb-dependent transmigration of entire MKs into BM sinusoids. These findings position Cdc42 (go-signal) and RhoA (stop-signal) at the centre of a molecular checkpoint downstream of GPIb that controls transendothelial platelet biogenesis. Our results may open new avenues for the treatment of platelet production disorders and help to explain the thrombocytopenia in patients with Bernard-Soulier syndrome, a bleeding disorder caused by defects in GPIb-IX-V.

In-depth PtdIns(3,4,5)P3 signalosome analysis identifies DAPP1 as a negative regulator of GPVI-driven platelet function

The class I phosphoinositide 3-kinase (PI3K) isoforms play important roles in platelet priming, activation, and stable thrombus formation. Class I PI3Ks predominantly regulate cell function through their catalytic product, the signaling phospholipid phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P₃], which coordinates the localization and/or activity of a diverse range of binding proteins. Notably, the complete repertoire of these class I PI3K effectors in platelets remains unknown, limiting mechanistic understanding of class I PI3K-mediated control of platelet function. We measured robust agonist-driven PtdIns (3,4,5)P₃ generation in human platelets by lipidomic mass spectrometry (MS), and then used affinity-capture coupled to high-resolution proteomic MS to identify the targets of PtdIns (3,4,5)P₃ in these cells. We reveal for the first time a diverse platelet PtdIns(3,4,5)P₃ interactome, including kinases, signaling adaptors, and regulators of small GTPases, many of which are previously uncharacterized in this cell type. Of these, we show dual adaptor for phosphotyrosine and 3-phosphoinositides (DAPP1) to be regulated by Src-family kinases and PI3K, while platelets from DAPP1-deficient mice display enhanced thrombus formation on collagen in vitro. This was associated with enhanced platelet α/δ granule secretion and α_IIbβ₃ integrin activation downstream of the collagen receptor glycoprotein VI. Thus, we present the first comprehensive analysis of the PtdIns(3,4,5)P₃ signalosome of human platelets and identify DAPP1 as a novel negative regulator of platelet function. This work provides important new insights into how class I PI3Ks shape platelet function.

The Role of PI3K Isoforms in Regulating Bone Marrow Microenvironment Signaling Focusing on Acute Myeloid Leukemia and Multiple Myeloma

Despite the development of novel treatments in the past 15 years, many blood cancers still remain ultimately fatal and difficult to treat, particularly acute myeloid leukaemia (AML) and multiple myeloma (MM). While significant progress has been made characterising small-scale genetic mutations and larger-scale chromosomal translocations that contribute to the development of various blood cancers, less is understood about the complex microenvironment of the bone marrow (BM), which is known to be a key player in the pathogenesis of chronic lymphocytic leukaemia (CLL), AML and MM. This niche acts as a sanctuary for the cancerous cells, protecting them from chemotherapeutics and encouraging clonal cell survival. It does this by upregulating a plethora of signalling cascades within the malignant cell, with the phosphatidylinositol-3-kinase (PI3K) pathway taking a critical role. This review will focus on how the PI3K pathway influences disease progression and the individualised role of the PI3K subunits. We will also summarise the current clinical trials for PI3K inhibitors and how these trials impact the treatment of blood cancers.

The Phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3) Binder Rasa3 Regulates Phosphoinositide 3-kinase (PI3K)-dependent Integrin αIIbβ3 Outside-in Signaling

The class I PI3K family of lipid kinases plays an important role in integrin α_IIbβ₃ function, thereby supporting thrombus growth and consolidation. Here, we identify Ras/Rap1GAP Rasa3 (GAP1^IP4BP) as a major phosphatidylinositol 3,4,5-trisphosphate-binding protein in human platelets and a key regulator of integrin α_IIbβ₃ outside-in signaling. We demonstrate that cytosolic Rasa3 translocates to the plasma membrane in a PI3K-dependent manner upon activation of human platelets. Expression of wild-type Rasa3 in integrin α_IIbβ₃-expressing CHO cells blocked Rap1 activity and integrin α_IIbβ₃-mediated spreading on fibrinogen. In contrast, Rap1GAP-deficient (P489V) and Ras/Rap1GAP-deficient (R371Q) Rasa3 had no effect. We furthermore show that two Rasa3 mutants (H794L and G125V), which are expressed in different mouse models of thrombocytopenia, lack both Ras and Rap1GAP activity and do not affect integrin α_IIbβ₃-mediated spreading of CHO cells on fibrinogen. Platelets from thrombocytopenic mice expressing GAP-deficient Rasa3 (H794L) show increased spreading on fibrinogen, which in contrast to wild-type platelets is insensitive to PI3K inhibitors. Together, these results support an important role for Rasa3 in PI3K-dependent integrin α_IIbβ₃-mediated outside-in signaling and cell spreading.

P110β Inhibition Reduces Histone H3K4 Di-Methylation in Prostate Cancer

INTRODUCTION AND AIMS

Epigenetic alteration plays a major role in the development and progression of human cancers, including prostate cancer. Histones are the key factors in modulating gene accessibility to transcription factors and post-translational modification of the histone N-terminal tail including methylation is associated with either transcriptional activation (H3K4me2) or repression (H3K9me3). Furthermore, phosphoinositide 3-kinase (PI3 K) signaling and the androgen receptor (AR) are the key determinants in prostate cancer development and progression. We recently showed that prostate-targeted nano-micelles loaded with PI3 K/p110beta specific inhibitor TGX221 blocked prostate cancer growth in vitro and in vivo. Our objective of this study was to determine the role of PI3 K signaling in histone methylation in prostate cancer, with emphasis on histone H3K4 methylation.

METHODS

PI3 K non-specific inhibitor LY294002 and p110beta-specific inhibitor TGX221 were used to block PI3 K/p110beta signaling. The global levels of H3K4 and H3K9 methylation in prostate cancer cells and tissue specimens were evaluated by Western blot assay and immunohistochemical staining. A synthetic androgen R1881 was used to stimulate AR activity in prostate cancer cells. A castration-resistant prostate cancer (CRPC) specific human tissue microarray (TMA) was used to assess the global levels of H3K4me2 methylation by immunostaining approach.

RESULTS

Our data revealed that H3K4me2 levels were significantly elevated after androgen stimulation. With RNA silencing and pharmacology approaches, we further defined that inhibition of PI3 K/p110beta activity through gene-specific knocking down and small chemical inhibitor TGX221 abolished androgen-stimulated H3K4me2 methylation. Consistently, prostate cancer-targeted delivery of TGX221 in vivo dramatically reduced the global levels of H3K4me2 as assessed by immunohistochemical staining on tissue section of mouse xenografts from CRPC cell lines 22RV1 and C4-2. Finally, immunostaining data revealed a strong H3K4me2 immunosignal in CRPC tissues compared to primary tumors and benign prostate tissues.

CONCLUSIONS

Taken together, our results suggest that PI3 K/p110beta-dependent signaling is involved in androgen-stimulated H3K4me2 methylation in prostate cancer, which might be used as a novel biomarker for disease prognosis and targeted therapy. Prostate 77:299-308, 2017. © 2016 Wiley Periodicals, Inc.

Ginsenoside Rg3-enriched red ginseng extract inhibits platelet activation and in vivo thrombus formation

Background

Korean Red Ginseng has been used for several decades to treat many diseases, enhancing both immunity and physical strength. Previous studies have documented the therapeutic effects of ginseng, including its anticancer, antiaging, and anti-inflammatory activities. These activities are mediated by ginsenosides present in the ginseng plant. Ginsenoside Rg3, an effective compound from red ginseng, has been shown to have antiplatelet activity in addition to its anticancer and anti-inflammatory activities. Platelets are important for both primary hemostasis and the repair of the vessels after injury; however, they also play a crucial role in the development of acute coronary diseases. We prepared ginsenoside Rg3-enriched red ginseng extract (Rg3-RGE) to examine its role in platelet physiology.

Methods

To examine the effect of Rg3-RGE on platelet activation in vitro, platelet aggregation, granule secretion, intracellular calcium ([Ca²⁺]_i) mobilization, flow cytometry, and immunoblot analysis were carried out using rat platelets. To examine the effect of Rg3-RGE on platelet activation in vivo, a collagen plus epinephrine-induced acute pulmonary thromboembolism mouse model was used.

Results

We found that Rg3-RGE significantly inhibited collagen-induced platelet aggregation and [Ca²⁺]_i mobilization in a dose-dependent manner in addition to reducing ATP release from collagen-stimulated platelets. Furthermore, using immunoblot analysis, we found that Rg3-RGE markedly suppressed mitogen-activated protein kinase phosphorylation (i.e., extracellular stimuli-responsive kinase, Jun N-terminal kinase, p38) as well as the PI3K (phosphatidylinositol 3 kinase)/Akt pathway. Moreover, Rg3-RGE effectively reduced collagen plus epinephrine-induced mortality in mice.

Conclusion

These data suggest that ginsenoside Rg3-RGE could be potentially be used as an antiplatelet therapeutic agent against platelet-mediated cardiovascular disorders.

Downstream Regulatory Element Antagonist Modulator (DREAM), a target for anti-thrombotic agents

Circulating platelets participate in the process of numerous diseases including thrombosis, inflammation, and cancer. Thus, it is of great importance to understand the underlying mechanisms mediating platelet activation under disease conditions. Emerging evidence indicates that despite the lack of a nucleus, platelets possess molecules that are involved in gene transcription in nucleated cells. This review will summarize downstream regulatory element antagonist modulator (DREAM), a transcriptional repressor, and highlight recent findings suggesting its novel non-transcriptional role in hemostasis and thrombosis.

Class I phosphatidylinositol 3-kinase inhibitors for cancer therapy

The phosphatidylinositol 3-kinase (PI3K) pathway is frequently activated in human cancers. Class I PI3Ks are lipid kinases that phosphorylate phosphatidylinositol 4,5-bisphosphate (PIP2) at the 3-OH of the inositol ring to generate phosphatidylinositol 3,4,5-trisphosphate (PIP3), which in turn activates Akt and the downstream effectors like mammalian target of rapamycin (mTOR) to play key roles in carcinogenesis. Therefore, PI3K has become an important anticancer drug target, and currently there is very high interest in the pharmaceutical development of PI3K inhibitors. Idelalisib has been approved in USA and Europe as the first-in-class PI3K inhibitor for cancer therapy. Dozens of other PI3K inhibitors including BKM120 and ZSTK474 are being evaluated in clinical trials. Multifaceted studies on these PI3K inhibitors are being performed, such as single and combinational efficacy, resistance, biomarkers, etc. This review provides an introduction to PI3K and summarizes key advances in the development of PI3K inhibitors.

Nuclear DNA replication and repair in parasites of the genus Leishmania: Exploiting differences to develop innovative therapeutic approaches

Leishmaniasis is a common tropical disease that affects mainly poor people in underdeveloped and developing countries. This largely neglected infection is caused by Leishmania spp, a parasite from the Trypanosomatidae family. This parasitic disease has different clinical manifestations, ranging from localized cutaneous to more harmful visceral forms. The main limitations of the current treatments are their high cost, toxicity, lack of specificity, and long duration. Efforts to improve treatments are necessary to deal with this infectious disease. Many approved drugs to combat diseases as diverse as cancer, bacterial, or viral infections take advantage of specific features of the causing agent or of the disease. Recent evidence indicates that the specific characteristics of the Trypanosomatidae replication and repair machineries could be used as possible targets for the development of new treatments. Here, we review in detail the molecular mechanisms of DNA replication and repair regulation in trypanosomatids of the genus Leishmania and the drugs that could be useful against this disease.

Skeletal muscle PI3K p110β regulates expression of AMP-activated protein kinase

Skeletal muscle metabolic homeostasis is maintained through numerous biochemical and physiological processes. Two principal molecular regulators of skeletal muscle metabolism include AMP-activated protein kinase (AMPK) and phosphatidylinositol 3-kinase (PI3K); however, PI3K exists as multiple isoforms, and specific metabolic actions of each isoform have not yet been fully elucidated in skeletal muscle. Given this lack of knowledge, we performed a series of experiments to define the extent to which PI3K p110β mediated expression and (or) activation of AMPK in skeletal muscle. To determine the effect of p110β inhibition on AMPK expression and phosphorylation in cultured cells, C2C12 myoblasts were treated with a pharmacological inhibitor of p110β (TGX-221), siRNA against p110β, or overexpression of kinase-dead p110β. Expression and phosphorylation of AMPK were unaffected in myoblasts treated with TGX-221 or expressing kinase-dead p110β. However, expressions of total and phosphorylated AMPK at T172 were reduced in myoblasts treated with p110β siRNA. When normalized to expression of total AMPK, phosphorylation of AMPK S485/491 was elevated in p110β-deficient myoblasts. Similar results were observed in tibialis anterior muscle from mice with conditional deletion of p110β (p110β-mKO mice). Analysis of AMPK transcript expression revealed decreased expression of Prkaa2 in p110β-deficient myoblasts and in p110β-mKO muscle. Loss of p110β had no effect on oligomycin-stimulated phosphorylation of AMPK or phosphorylated Acetyl-CoA carboxylase (ACC), although oligomycin-induced AMPK and ACC phosphorylation were increased in p110β-deficient myoblasts compared to oligomycin-stimulated control myoblasts when normalized to levels of total AMPK or ACC. Overall, these results suggest that p110β positively regulates expression of AMPK in cultured myoblasts and in skeletal muscle in vivo; moreover, despite the reduced abundance of AMPK in p110β-deficient myoblasts, loss of p110β does not appear to impair AMPK activation following stimulus. These findings thus reveal a novel role for p110β in mediating skeletal muscle metabolic signaling.

DREAM plays an important role in platelet activation and thrombogenesis

Downstream regulatory element antagonist modulator (DREAM), a transcriptional repressor, is known to modulate pain responses. However, it is unknown whether DREAM is expressed in anucleate platelets and plays a role in thrombogenesis. By using intravital microscopy with DREAM-null mice and their bone marrow chimeras, we demonstrated that both hematopoietic and nonhematopoietic cell DREAMs are required for platelet thrombus formation following laser-induced arteriolar injury. In a FeCl₃-induced thrombosis model, we found that compared with wild-type (WT) control and nonhematopoietic DREAM knockout (KO) mice, DREAM KO control and hematopoietic DREAM KO mice showed a significant delay in time to occlusion. Tail bleeding time was prolonged in DREAM KO control mice, but not in WT or DREAM bone marrow chimeric mice. In vivo adoptive transfer experiments further indicated the importance of platelet DREAM in thrombogenesis. We found that DREAM deletion does not alter the ultrastructural features of platelets but significantly impairs platelet aggregation and adenosine triphosphate secretion induced by numerous agonists (collagen-related peptide, adenosine 5'-diphosphate, A23187, thrombin, or U46619). Biochemical studies revealed that platelet DREAM positively regulates phosphoinositide 3-kinase (PI3K) activity during platelet activation. Using DREAM-null platelets and PI3K isoform-specific inhibitors, we observed that platelet DREAM is important for α-granule secretion, Ca²⁺ mobilization, and aggregation through PI3K class Iβ (PI3K-Iβ). Genetic and pharmacological studies in human megakaryoblastic MEG-01 cells showed that DREAM is important for A23187-induced Ca²⁺ mobilization and its regulatory function requires Ca²⁺ binding and PI3K-Iβ activation. These results suggest that platelet DREAM regulates PI3K-Iβ activity and plays an important role during thrombus formation.

Emerging roles of RAC1 in treating lung cancer patients

The Ras-related C3 botulinum toxin substrate 1 (RAC1), a member of the Rho family of small guanosine triphosphatases, is critical for many cellular activities, such as phagocytosis, adhesion, migration, motility, cell proliferation, and axonal growth. In addition, RAC1 plays an important role in cancer angiogenesis, invasion, and migration, and it has been reported to be related to most cancers, such as breast cancer, gastric cancer, testicular germ cell cancer, and lung cancer. Recently, the therapeutic target of RAC1 in cancer has been investigated. In addition, some investigations have shown that inhibition of RAC1 can reverse drug-resistance in non-small cell lung cancer. In this review, we summarize the recent advances in understanding the role of RAC1 in lung cancer and the underlying mechanisms and discuss its value in clinical therapy.

Rac1-mediated membrane raft localization of PI3K/p110β is required for its activation by GPCRs or PTEN loss

We aimed to understand how spatial compartmentalization in the plasma membrane might contribute to the functions of the ubiquitous class IA phosphoinositide 3-kinase (PI3K) isoforms, p110α and p110β. We found that p110β localizes to membrane rafts in a Rac1-dependent manner. This localization potentiates Akt activation by G-protein-coupled receptors (GPCRs). Thus genetic targeting of a Rac1 binding-deficient allele of p110β to rafts alleviated the requirement for p110β-Rac1 association for GPCR signaling, cell growth and migration. In contrast, p110α, which does not play a physiological role in GPCR signaling, is found to reside in nonraft regions of the plasma membrane. Raft targeting of p110α allowed its EGFR-mediated activation by GPCRs. Notably, p110β dependent, PTEN null tumor cells critically rely upon raft-associated PI3K activity. Collectively, our findings provide a mechanistic account of how membrane raft localization regulates differential activation of distinct PI3K isoforms and offer insight into why PTEN-deficient cancers depend on p110β.

DOI:http://dx.doi.org/10.7554/eLife.17635.001

The pyrrolidinoindoline alkaloid Psm2 inhibits platelet aggregation and thrombus formation by affecting PI3K/Akt signaling

AIM

Psm2, one of the pyrrolidinoindoline alkaloids isolated from whole Selaginella moellendorffii plants, has shown a potent antiplatelet activity. In this study, we further evaluated the antiplatelet effects of Psm2, and elucidated the underlying mechanisms.

METHODS

Human platelet aggregation in vitro and rat platelet aggregation ex vivo were investigated. Agonist-induced platelet aggregation was measured using a light transmission aggregometer. The antithrombotic effects of Psm2 were evaluated in arteriovenous shunt thrombosis model in rats. To elucidate the mechanisms underlying the antiplatelet activity of Psm2, ELISAs, Western blotting and molecular docking were performed. The bleeding risk of Psm2 administration was assessed in a mouse tail cutting model, and the cytotoxicity of Psm2 was measured with MTT assay in EA.hy926 cells.

RESULTS

Psm2 dose-dependently inhibited human platelet aggregation induced by ADP, U4619, thrombin and collagen with IC50 values of 0.64, 0.37, 0.35 and 0.87 mg/mL, respectively. Psm2 (1, 3, 10 mg/kg) administered to rats significantly inhibited platelet aggregation ex vivo induced by ADP. Psm2 (1, 3, 10 mg/mL, iv) administered to rats with the A-V shunt dose-dependently decreased the thrombus formation. Psm2 inhibited platelet adhesion to fibrinogen and collagen with IC50 values of 84.5 and 96.5 mg/mL, respectively, but did not affect the binding of fibrinogen to GPIIb/IIIa. Furthermore, Psm2 inhibited AktSer473 phosphorylation, but did not affect MAPK signaling and Src kinase activation. Molecular docking showed that Psm2 bound to phosphatidylinositol 3-kinase β (PI3Kβ) with a binding free energy of -13.265 kcal/mol. In addition, Psm2 did not cause toxicity in EA.hy926 cells and produced only slight bleeding in a mouse tail cutting model.

CONCLUSION

Psm2 inhibits platelet aggregation and thrombus formation by affecting PI3K/Akt signaling. Psm2 may be a lead compound or drug candidate that could be developed for the prevention or treatment of thrombotic diseases.

Coincident signals from GPCRs and receptor tyrosine kinases are uniquely transduced by PI3Kβ in myeloid cells

Class I phosphoinositide 3-kinases (PI3Ks) catalyze production of the lipid messenger phosphatidylinositol 3,4,5-trisphosphate (PIP3), which plays a central role in a complex signaling network regulating cell growth, survival, and movement. This network is overactivated in cancer and inflammation, and there is interest in determining the PI3K catalytic subunit (p110α, p110β, p110γ, or p110δ) that should be targeted in different therapeutic contexts. Previous studies have defined unique regulatory inputs for p110β, including direct interaction with Gβγ subunits, Rac, and Rab5. We generated mice with knock-in mutations of p110β that selectively blocked the interaction with Gβγ and investigated its contribution to the PI3K isoform dependency of receptor tyrosine kinase (RTK) and G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor (GPCR) responses in primary macrophages and neutrophils. We discovered a unique role for p110β in supporting synergistic PIP3 formation in response to the coactivation of macrophages by macrophage colony-stimulating factor (M-CSF) and the complement protein C5a. In contrast, we found partially redundant roles for p110α, p110β, and p110δ downstream of M-CSF alone and a nonredundant role for p110γ downstream of C5a alone. This role for p110β completely depended on direct interaction with Gβγ, suggesting that p110β transduces GPCR signals in the context of coincident activation by an RTK. The p110β-Gβγ interaction was also required for neutrophils to generate reactive oxygen species in response to the Fcγ receptor-dependent recognition of immune complexes and for their β2 integrin-mediated adhesion to fibrinogen or poly-RGD+, directly implicating heterotrimeric G proteins in these two responses.

PDK1 Determines Collagen-Dependent Platelet Ca 2+ Signaling and Is Critical to Development of Ischemic Stroke In Vivo

Objective—

Activation of platelets by subendothelial collagen results in an increase of cytosolic Ca 2+ concentration ([Ca 2+ ] i ) and is followed by platelet activation and thrombus formation that may lead to vascular occlusion. The present study determined the role of phosphoinositide-dependent protein kinase 1 (PDK1) in collagen-dependent platelet Ca 2+ signaling and ischemic stroke in vivo.

Approach and Results—

Platelet activation with collagen receptor glycoprotein VI agonists collagen-related peptide or convulxin resulted in a significant increase in PDK1 activity independent of second-wave signaling. PDK1 deficiency was associated with reduced platelet phospholipase Cγ2–dependent inositol-1,4,5-trisphosphate production and intracellular [Ca 2+ ] i in response to stimulation with collagen-related peptide or convulxin. The defective increase of [Ca 2+ ] i resulted in a substantial defect in activation-dependent platelet secretion and aggregation on collagen-related peptide stimulation. Furthermore, Rac1 activation and spreading, adhesion to collagen, and thrombus formation under high arterial shear rates were significantly diminished in PDK1-deficient platelets. Mice with PDK1-deficient platelets were protected against arterial thrombotic occlusion after FeCl 3 -induced mesenteric arterioles injury and ischemic stroke in vivo. These mice had significantly reduced brain infarct volumes, with a significantly increased survival of 7 days after transient middle cerebral artery occlusion without increase of intracerebral hemorrhage. Tail bleeding time was prolonged in pdk1 −/− mice, reflecting an important role of PDK1 in primary hemostasis.

Conclusions—

PDK1 is required for Ca 2+ -dependent platelet activation on stimulation of collagen receptor glycoprotein VI, arterial thrombotic occlusion, and ischemic stroke in vivo.