Targeting pleckstrin-2/Akt signaling reduces proliferation in myeloproliferative neoplasm models

Myeloproliferative neoplasms (MPNs) are characterized by the activated JAK2/STAT pathway. Pleckstrin-2 (Plek2) is a downstream target of the JAK2/STAT5 pathway and is overexpressed in patients with MPNs. We previously revealed that Plek2 plays critical roles in the pathogenesis of JAK2-mutated MPNs. The nonessential roles of Plek2 under physiologic conditions make it an ideal target for MPN therapy. Here, we identified first-in-class Plek2 inhibitors through an in silico high-throughput screening approach and cell-based assays, followed by the synthesis of analogs. Plek2-specific small-molecule inhibitors showed potent inhibitory effects on cell proliferation. Mechanistically, Plek2 interacts with and enhances the activity of Akt through the recruitment of downstream effector proteins. The Plek2-signaling complex also includes Hsp72, which protects Akt from degradation. These functions were blocked by Plek2 inhibitors via their direct binding to the Plek2 dishevelled, Egl-10 and pleckstrin (DEP) domain. The role of Plek2 in activating Akt signaling was further confirmed in vivo using a hematopoietic-specific Pten-knockout mouse model. We next tested Plek2 inhibitors alone or in combination with an Akt inhibitor in various MPN mouse models, which showed significant therapeutic efficacies similar to that seen with the genetic depletion of Plek2. The Plek2 inhibitor was also effective in reducing proliferation of CD34-positive cells from MPN patients. Our studies reveal a Plek2/Akt complex that drives cell proliferation and can be targeted by a class of antiproliferative compounds for MPN therapy.

ARFs get the BioID treatment: what have we been missing?

Li et al present the results of a proximity-interaction screen in mammalian cells for the effector proteins of 25 members of the Arf family of small GTPases. This study has generated an important resource for those working in several areas of cell biology and provided an initial characterisation of two new cellular roles for some of the least well studied members of this family, the regulation of PLD1 by ARL11/14 in phagocytosis, and the regulation of PI4KB by ARL5A/5B in the Golgi.

"Ask me what I need": A call for shifting responsibility upwards and creating inclusive learning environments in clinical placement

BACKGROUND

Ontario's human-rights legislation and institutions' support for students with disabilities have influenced these students' increased enrolment in the postsecondary environment. Yet more attention is paid to in-classroom than to out-of-classroom experiences. Students with disabilities enrolled in nursing are least likely to be accommodated. This has significant implications for access and equity upon graduation, as clinical placements are a bridge between school and employment.

OBJECTIVES

To explore clinical instructors' and students who identify with disabilities' perspectives on nursing clinical placements.

METHOD

A descriptive case-report was used: interactive take-home diaries were completed and semi-structured interviews were conducted with clinical instructors (n-14) and nursing students with disabilities (n-14) in Ontario. An iterative inductive analysis was undertaken.

RESULTS

Three overarching themes were identified: (a) an immovable clinical environment in relation to technology and time, (b) a perceived conflict between nursing and disability identity, and (c) a need to shift responsibility upwards while listening to lived experience. The clinical environment is a highly contested space; different identity groups have distinct roles and differing degrees of power within it.

CONCLUSION

Our research calls for a shift in the nursing landscape to be led by education and medical institutions that can build supportive networks, develop clear policies and listen to nursing students with disabilities.

Analysis of HLA-G expression in renal tissue in lupus nephritis: a pilot study

BACKGROUND

The study aimed to investigate whether HLA-G antigen is expressed in the kidneys of patients affected by lupus nephritis (LN) and whether its detection in renal biopsies could be adopted as a marker of treatment response and prognosis.

METHODS

Thirty renal biopsies from patients with LN were selected and analyzed through immunohistochemistry. Laboratory and clinical data were retrospectively collected at baseline, 6 and 12 months and at the latest clinical appointment. A number of patients (63.3%) were treated with rituximab (RTX) +/- methylprednisolone in the induction phase. The expression of HLA-G in glomeruli, tubules and infiltrating cells was examined and compared between lupus patients who achieved either complete or partial renal response and those who did not respond to treatment.

RESULTS

HLA-G staining was observed in the glomeruli of 20 of 30 samples from patients with LN. The expression of the antigen was detected in podocytes, along glomerular capillary walls, on parietal glomerular epithelial cells and within the juxtaglomerular apparatus. Seventy per cent of patients whose glomeruli expressed HLA-G achieved partial or complete response at 6 months and 75% at the latest available follow up compared with 30% and 40%, respectively, of those who did not show any expression. The pattern of staining in tubules and infiltrating cells was highly variable precluding any clinical correlation.

CONCLUSION

This study demonstrates that HLA-G is expressed in renal tissue in LN. Our retrospective data suggest that its expression could correlate with response to treatment.

Quantitation of class IA PI3Ks in mice reveals p110-free-p85s and isoform-selective subunit associations and recruitment to receptors

Class IA PI3Ks have many roles in health and disease. The rules that govern intersubunit and receptor associations, however, remain unclear. We engineered mouse lines in which individual endogenous class IA PI3K subunits were C-terminally tagged with 17aa that could be biotinylated in vivo. Using these tools we quantified PI3K subunits in streptavidin or PDGFR pull-downs and cell lysates. This revealed that p85α and β bound equivalently to p110α or p110β but p85α bound preferentially to p110δ. p85s were found in molar-excess over p110s in a number of contexts including MEFs (p85β, 20%) and liver (p85α, 30%). In serum-starved MEFs, p110-free-p85s were preferentially, compared with heterodimeric p85s, bound to PDGFRs, consistent with in vitro assays that demonstrated they bound PDGFR-based tyrosine-phosphorylated peptides with higher affinity and co-operativity; suggesting they may act to tune a PI3K activation threshold. p110α-heterodimers were recruited 5-6× more efficiently than p110β-heterodimers to activated PDGFRs in MEFs or to PDGFR-based tyrosine-phosphorylated peptides in MEF-lysates. This suggests that PI3Kα has a higher affinity for relevant tyrosine-phosphorylated motifs than PI3Kβ. Nevertheless, PI3Kβ contributes substantially to acute PDGF-stimulation of PIP3 and PKB in MEFs because it is synergistically, and possibly sequentially, activated by receptor-recruitment and small GTPases (Rac/CDC42) via its RBD, whereas parallel activation of PI3Kα is independent of its RBD. These results begin to provide molecular clarity to the rules of engagement between class IA PI3K subunits in vivo and past work describing "excess p85," p85α as a tumor suppressor, and differential receptor activation of PI3Kα and PI3Kβ.

Genome organization and chromatin analysis identify transcriptional downregulation of insulin-like growth factor signaling as a hallmark of aging in developing B cells

BACKGROUND

Aging is characterized by loss of function of the adaptive immune system, but the underlying causes are poorly understood. To assess the molecular effects of aging on B cell development, we profiled gene expression and chromatin features genome-wide, including histone modifications and chromosome conformation, in bone marrow pro-B and pre-B cells from young and aged mice.

RESULTS

Our analysis reveals that the expression levels of most genes are generally preserved in B cell precursors isolated from aged compared with young mice. Nonetheless, age-specific expression changes are observed at numerous genes, including microRNA encoding genes. Importantly, these changes are underpinned by multi-layered alterations in chromatin structure, including chromatin accessibility, histone modifications, long-range promoter interactions, and nuclear compartmentalization. Previous work has shown that differentiation is linked to changes in promoter-regulatory element interactions. We find that aging in B cell precursors is accompanied by rewiring of such interactions. We identify transcriptional downregulation of components of the insulin-like growth factor signaling pathway, in particular downregulation of Irs1 and upregulation of Let-7 microRNA expression, as a signature of the aged phenotype. These changes in expression are associated with specific alterations in H3K27me3 occupancy, suggesting that Polycomb-mediated repression plays a role in precursor B cell aging.

CONCLUSIONS

Changes in chromatin and 3D genome organization play an important role in shaping the altered gene expression profile of aged precursor B cells. Components of the insulin-like growth factor signaling pathways are key targets of epigenetic regulation in aging in bone marrow B cell precursors.

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.

Effectiveness of interventions to promote physical activity and/or decrease sedentary behaviour among rural adults: a systematic review and meta-analysis

Physical inactivity and overweight and obesity are more prevalent among rural than urban populations. This study aimed to review published evidence of the effectiveness of interventions to increase physical activity (PA) and/or decrease sedentary behaviour (SB) among rural adults and to identify factors associated with effectiveness. Seven electronic databases were searched for controlled trials of a PA or SB intervention. Meta-analysis was conducted using random effects models and meta-regression. Thirteen studies were included in the qualitative synthesis (n = 4,848 participants) and 12 in the meta-analysis (n = 4,820). All studies were interventions to increase PA. Overall, there was no effect on PA (standardized mean difference [SMD] 0.11; 95% confidence interval [CI] -0.04, 0.25) or SB (SMD 0.07; 95% CI -0.33, 0.20). In PA subgroup analyses, studies employing objective outcome measures demonstrated effects in favour of the intervention (SMD 0.65, 95% CI 0.30, 1.00), while those using self-reported measures did not (SMD 0.00; 95% CI -0.11, 0.10). This review highlights significant gaps in our understanding of how best to promote PA and reduce SB among rural adults. Future studies should use objective measures of PA as study outcomes. The absence of interventions to decrease SB is of concern, with immediate action required to address this large knowledge gap.

The Inositol-3-Phosphate Synthase Biosynthetic Enzyme Has Distinct Catalytic and Metabolic Roles

Inositol levels, maintained by the biosynthetic enzyme inositol-3-phosphate synthase (Ino1), are altered in a range of disorders, including bipolar disorder and Alzheimer's disease. To date, most inositol studies have focused on the molecular and cellular effects of inositol depletion without considering Ino1 levels. Here we employ a simple eukaryote, Dictyostelium discoideum, to demonstrate distinct effects of loss of Ino1 and inositol depletion. We show that loss of Ino1 results in an inositol auxotrophy that can be rescued only partially by exogenous inositol. Removal of inositol supplementation from the ino1(-) mutant resulted in a rapid 56% reduction in inositol levels, triggering the induction of autophagy, reduced cytokinesis, and substrate adhesion. Inositol depletion also caused a dramatic generalized decrease in phosphoinositide levels that was rescued by inositol supplementation. However, loss of Ino1 triggered broad metabolic changes consistent with the induction of a catabolic state that was not rescued by inositol supplementation. These data suggest a metabolic role for Ino1 that is independent of inositol biosynthesis. To characterize this role, an Ino1 binding partner containing SEL1L1 domains (Q54IX5) and having homology to mammalian macromolecular complex adaptor proteins was identified. Our findings therefore identify a new role for Ino1, independent of inositol biosynthesis, with broad effects on cell metabolism.

Inactivation of the Class II PI3K-C2β Potentiates Insulin Signaling and Sensitivity

In contrast to the class I phosphoinositide 3-kinases (PI3Ks), the organismal roles of the kinase activity of the class II PI3Ks are less clear. Here, we report that class II PI3K-C2β kinase-dead mice are viable and healthy but display an unanticipated enhanced insulin sensitivity and glucose tolerance, as well as protection against high-fat-diet-induced liver steatosis. Despite having a broad tissue distribution, systemic PI3K-C2β inhibition selectively enhances insulin signaling only in metabolic tissues. In a primary hepatocyte model, basal PI3P lipid levels are reduced by 60% upon PI3K-C2β inhibition. This results in an expansion of the very early APPL1-positive endosomal compartment and altered insulin receptor trafficking, correlating with an amplification of insulin-induced, class I PI3K-dependent Akt signaling, without impacting MAPK activity. These data reveal PI3K-C2β as a critical regulator of endosomal trafficking, specifically in insulin signaling, and identify PI3K-C2β as a potential drug target for insulin sensitization.

Perturbations of PIP3 signalling trigger a global remodelling of mRNA landscape and reveal a transcriptional feedback loop

PIP3 is synthesized by the Class I PI3Ks and regulates complex cell responses, such as growth and migration. Signals that drive long-term reshaping of cell phenotypes are difficult to resolve because of complex feedback networks that operate over extended times. PIP3-dependent modulation of mRNA accumulation is clearly important in this process but is poorly understood. We have quantified the genome-wide mRNA-landscape of non-transformed, breast epithelium-derived MCF10a cells and its response to acute regulation by EGF, in the presence or absence of a PI3Kα inhibitor, compare it to chronic activation of PI3K signalling by cancer-relevant mutations (isogenic cells expressing an oncomutant PI3Kα allele or lacking the PIP3-phosphatase/tumour-suppressor, PTEN). Our results show that whilst many mRNAs are changed by long-term genetic perturbation of PIP3 signalling ('butterfly effect'), a much smaller number do so in a coherent fashion with the different PIP3 perturbations. This suggests a subset of more directly regulated mRNAs. We show that mRNAs respond differently to given aspects of PIP3 regulation. Some PIP3-sensitive mRNAs encode PI3K pathway components, thus suggesting a transcriptional feedback loop. We identify the transcription factor binding motifs SRF and PRDM1 as important regulators of PIP3-sensitive mRNAs involved in cell movement.

The effect of intrauterine infusion of dextrose on clinical endometritis cure rate and reproductive performance of dairy cows

The main objective of this study was to evaluate the intrauterine administration use of 200 mL of 50% dextrose solution as a treatment against clinical endometritis (CE); CE cure rate and reproductive performance were evaluated. Additionally, the association of several relevant risk factors, such as retained placenta (RP), metritis, CE, anovulation, hyperketonemia, and body condition score with reproductive performance, early embryonic mortality, and CE were evaluated. A total of 1,313 Holstein cows housed on 4 commercial dairy farms were enrolled in the study. At 7±3 DIM cows were examined for metritis and had blood collected to determine serum β-hydroxybutyrate concentration. To determine if cows had ovulated at least once before 44±3 DIM, the presence of a corpus luteum was evaluated by ovarian ultrasonography at 30±3 DIM and at 44±3 DIM. At 30±3 DIM, CE was diagnosed using the Metricheck device (SimcroTech, Hamilton, New Zealand); cows with purulent or mucopurulent vaginal discharge were diagnosed as having CE. Cows diagnosed with CE (n=175) were randomly allocated into 2 treatment groups: treatment (intrauterine infusion of 200 mL of 50% dextrose) or control (no infusion). Clinical endometritis cows were re-evaluated as described above at 44±3 DIM, and cows that were free of purulent or mucopurulent vaginal discharge were considered cured. Intrauterine infusion of dextrose tended to have a detrimental effect on CE cure rate, and treatment did not have an effect on first-service conception rate and early embryonic mortality. A multivariable Cox's proportional hazard model was performed to evaluate the effect of several variables on reproductive performance; the variables RP, CE, parity, anovulation, and the interaction term between parity and anovulation were associated with hazard of pregnancy. Cows that did not have RP or CE were more likely to conceive than cows that were diagnosed with RP or CE. Cows that had RP were at 3.36 times higher odds of losing their pregnancy than cows that did not have RP. In addition, cows diagnosed with CE were at 2.16 higher odds of losing their pregnancy than cows without CE. In conclusion, intrauterine infusion of 200 mL of 50% dextrose solution as a treatment for CE had a strong statistical tendency to decrease CE cure rate, did not improve first-service conception rate and early embryonic mortality, and did not decrease calving-to-conception interval.

The phosphoinositide 3-kinase isoform PI3Kβ regulates osteoclast-mediated bone resorption in humans and mice

Objective

While phosphoinositide 3-kinases (PI3Ks) are involved in various intracellular signal transduction processes, the specific functions of the different PI3K isoforms are poorly understood. We have previously shown that the PI3Kβ isoform is required for arthritis development in the K/BxN serum–transfer model. Since osteoclasts play a critical role in pathologic bone loss during inflammatory arthritis and other diseases, we undertook this study to test the role of PI3Kβ in osteoclast development and function using a combined genetic and pharmacologic approach.

Methods

The role of PI3Kβ in primary human and murine osteoclast cultures was tested with the PI3Kβ-selective inhibitor TGX221 and by using PI3Kβ^−/− mice. The trabecular bone architecture of PI3Kβ^−/− mice was evaluated using micro–computed tomography and histomorphometric analyses.

Results

The expression of PI3Kβ was strongly and specifically up-regulated during in vitro osteoclast differentiation. In vitro development of large multinucleated osteoclasts from human or murine progenitors and their resorption capacity were strongly reduced by the PI3Kβ inhibitor TGX221 or by the genetic deficiency of PI3Kβ. This was likely due to defective cytoskeletal reorganization and vesicular trafficking, since PI3Kβ^−/− mouse multinucleated cells failed to form actin rings and retained intracellular acidic vesicles and cathepsin K. In contrast, osteoclast-specific gene expression and the survival and apoptosis of osteoclasts were not affected. PI3Kβ^−/− mice had significantly increased trabecular bone volume and showed abnormal osteoclast morphology with defective resorption pit formation.

Conclusion

PI3Kβ plays an important role in osteoclast development and function and is required for in vivo bone homeostasis.

Phosphoinositide 3-kinase δ gene mutation predisposes to respiratory infection and airway damage

Genetic mutations cause primary immunodeficiencies (PIDs) that predispose to infections. Here, we describe activated PI3K-δ syndrome (APDS), a PID associated with a dominant gain-of-function mutation in which lysine replaced glutamic acid at residue 1021 (E1021K) in the p110δ protein, the catalytic subunit of phosphoinositide 3-kinase δ (PI3Kδ), encoded by the PIK3CD gene. We found E1021K in 17 patients from seven unrelated families, but not among 3346 healthy subjects. APDS was characterized by recurrent respiratory infections, progressive airway damage, lymphopenia, increased circulating transitional B cells, increased immunoglobulin M, and reduced immunoglobulin G2 levels in serum and impaired vaccine responses. The E1021K mutation enhanced membrane association and kinase activity of p110δ. Patient-derived lymphocytes had increased levels of phosphatidylinositol 3,4,5-trisphosphate and phosphorylated AKT protein and were prone to activation-induced cell death. Selective p110δ inhibitors IC87114 and GS-1101 reduced the activity of the mutant enzyme in vitro, which suggested a therapeutic approach for patients with APDS.

Early experience in laparoscopic colectomy for refractory colitis in children

There is limited literature endorsing the laparoscopic approach for the treatment of refractory colitis in children. We report our experiences of paediatric laparoscopic colectomies performed for ulcerative colitis. A retrospective review over a three year period was undertaken. Operative time, length of stay, post-operative analgesia, time to commencement of diet, and complications were recorded. Nine laparoscopic colectomies were performed. Median operative time was 320 minutes (range--240-475). Mean time to commencement of full diet was 3.9 days (range 2-8). Median length of stay was 6 days (range--5-16). In our experience, laparoscopic colectomy in children is a feasible and superior method to open colectomy and in our opinion, facilitates further restorative procedures and will become the default method of treatment in the near future.

Phosphoinositide 3-OH kinase regulates integrin-dependent processes in neutrophils by signaling through its effector ARAP3

ARAP3, a GTPase activating protein for Rho and Arf family GTPases, is one of many phosphoinositide 3-OH kinase (PI3K) effectors. In this study, we investigate the regulatory input of PI3K upstream of ARAP3 by analyzing neutrophils from an ARAP3 pleckstrin homology (PH) domain point mutation knock-in mouse (R302, 303A), in which ARAP3 is uncoupled from activation by PI3K. ARAP3 PH domain point mutant neutrophils are characterized by disturbed responses linked to stimulation by either integrin ligands or immobilized immune complexes. These cells exhibit increased β2 integrin inside-out signaling (binding affinity and avidity), and our work suggests the disturbed responses to immobilized immune complexes are secondary to this. In vitro, neutrophil chemotaxis is affected in the mutant. In vivo, ARAP3 PH domain point mutant bone marrow chimeras exhibit reduced neutrophil recruitment to the peritoneum on induction of sterile peritonitis and also reduced inflammation in a model for rheumatoid arthritis. The current work suggests a dramatic regulatory input of PI3K into the regulation of β2 integrin activity, and processes dependent on this, by signaling through its effector ARAP3.

Functional redundancy of class I phosphoinositide 3-kinase (PI3K) isoforms in signaling growth factor-mediated human neutrophil survival

We have investigated the contribution of individual phosphoinositide 3-kinase (PI3K) Class I isoforms to the regulation of neutrophil survival using (i) a panel of commercially available small molecule isoform-selective PI3K Class I inhibitors, (ii) novel inhibitors, which target single or multiple Class I isoforms (PI3Kα, PI3Kβ, PI3Kδ, and PI3Kγ), and (iii) transgenic mice lacking functional PI3K isoforms (p110δ^KOγ^KO or p110γ^KO). Our data suggest that there is considerable functional redundancy amongst Class I PI3Ks (both Class IA and Class IB) with regard to GM-CSF-mediated suppression of neutrophil apoptosis. Hence pharmacological inhibition of any 3 or more PI3K isoforms was required to block the GM-CSF survival response in human neutrophils, with inhibition of individual or any two isoforms having little or no effect. Likewise, isolated blood neutrophils derived from double knockout PI3K p110δ^KOγ^KO mice underwent normal time-dependent constitutive apoptosis and displayed identical GM-CSF mediated survival to wild type cells, but were sensitized to pharmacological inhibition of the remaining PI3K isoforms. Surprisingly, the pro-survival neutrophil phenotype observed in patients with an acute exacerbation of chronic obstructive pulmonary disease (COPD) was resilient to inactivation of the PI3K pathway.

Day-case laparoscopic Nissen fundoplication

INTRODUCTION

For day-case laparoscopic surgery to be successful, patient selection is of the utmost importance. This study aimed to assess the feasibility of day-case laparoscopic Nissen fundoplication and to identify factors that may lead to readmission and overstay.

METHODS

A retrospective review of all patients who underwent day-case laparoscopic Nissen fundoplication over a 4-year period (2006 through 2010) was undertaken. Patient age, social circumstances, and other demographics were recorded as well as any comorbidities and ASA score. The primary endpoint measured was rate of readmission and overstay.

RESULTS

A total of 72 patients fulfilled the inclusion criteria for day-case surgery. Five patients (6.94%) required admission immediately following the procedure, ie, overstayed or were readmitted. The rates were 1.38% (P=.05, CI 95%) for readmission and 5.55% (P=.05, CI 95%) for overstay. Six (8.33%) patients were classified as ASA III, and 3 (50%) were readmitted or overstayed.

CONCLUSION

Day-case laparoscopic Nissen fundoplication is a feasible, safe option. The authors conclude that ASA score of III and increasing age correlate with an increasing incidence of overstay and readmission. Therefore, we would recommend the use of integrated pathways and advanced planning to reduce these rates.

Moving towards a better understanding of chemotaxis

Eukaryotic cells are thought to move across supporting surfaces through a combination of coordinated processes: polarisation; extension of dynamic protrusions from a leading edge; adhesion-associated stabilisation of some protrusions; centripetal pulling against those leading adhesions; and de-adhesion at the rear. Gradients of extracellular ligands can be detected by cells and then used to guide them either towards the source (in the case of a chemoattractant) or away from the source (in the case of a chemorepellent)--such migration is termed chemotaxis. Recent work suggests that chemotaxis probably emerges from the ability of cells to spatially encode extracellular gradients of ligands, a process for which phosphoinositide 3'-kinase (PI3K) signals alone are insufficient, and to use that vectorial information to bias movement by enhancing the survival, and not the formation, of the protrusions that experience the greatest stimulation.

PI(3)Kgamma has an important context-dependent role in neutrophil chemokinesis

The directional movement of cells in a gradient of external stimulus is termed chemotaxis and is important in many aspects of development and differentiated cell function. Phophoinositide 3-kinases (PI(3)Ks) are thought to have critical roles within the gradient-sensing machinery of a variety of highly motile cells, such as mammalian phagocytes, allowing these cells to respond quickly and efficiently to shallow gradients of soluble stimuli. Our analysis of mammalian neutrophil migration towards ligands such as fMLP shows that, although PtdIns(3,4)P(2) and PtdIns(3,4,5)P(3) accumulate in a PI(3)Kgamma-dependent fashion at the up-gradient leading-edge, this signal is not required for efficient gradient-sensing and gradient-biased movement. PI(3)Kgamma activity is however, a critical determinant of the proportion of cells that can move, that is, respond chemokinetically, in reaction to fMLP. Furthermore, this dependence of chemokinesis on PI(3)Kgamma activity is context dependent, both with respect to the state of priming of the neutrophils and the type of surface on which they are migrating. We propose this effect of PI(3)Kgamma is through roles in the regulation of some aspects of neutrophil polarization that are relevant to movement, such as integrin-based adhesion and the accumulation of polymerized (F)-actin at the leading-edge.

Gbetagammas and the Ras binding domain of p110gamma are both important regulators of PI(3)Kgamma signalling in neutrophils

Through their ability to regulate production of the key lipid messenger PtdIns(3,4,5)P(3), the class I phosphatidylinositol-3-OH kinases (PI(3)Ks) support many critical cell responses. They, in turn, can be regulated by cell-surface receptors through signals acting on either their adaptor subunits (for example, through phosphotyrosine or Gbetagammas) or their catalytic subunits (for example, through GTP-Ras). The relative significance of these controlling inputs is undefined in vivo. Here, we have studied the roles of Gbetagammas, the adaptor p101, Ras and the Ras binding domain (RBD) in the control of the class I PI(3)K, PI(3)Kgamma, in mouse neutrophils. Loss of p101 leads to major reductions in the accumulation of PtdIns(3,4,5)P(3), activation of protein kinase B (PKB) and in migration towards G-protein activating ligands in vitro, and to an aseptically inflamed peritoneum in vivo. Loss of sensitivity of PI(3)Kgamma to Ras unexpectedly caused similar reductions, but additionally caused a substantial loss in production of reactive oxygen species (ROS). We conclude that Gbetagammas, p101 and the Ras-RBD interaction all have important roles in the regulation of PI(3)Kgamma in vivo and that they can simultaneously, but differentially, control distinct PI(3)Kgamma effectors.

Receptor association and tyrosine phosphorylation of S6 kinases

Ribosomal protein S6 kinase (S6K) is activated by an array of mitogenic stimuli and is a key player in the regulation of cell growth. The activation process of S6 kinase involves a complex and sequential series of multiple Ser/Thr phosphorylations and is mainly mediated via phosphatidylinositol 3-kinase (PI3K)-3-phosphoinositide-dependent protein kinase-1 (PDK1) and mTor-dependent pathways. Upstream regulators of S6K, such as PDK1 and protein kinase B (PKB/Akt), are recruited to the membrane via their pleckstrin homology (PH) or protein-protein interaction domains. However, the mechanism of integration of S6K into a multi-enzyme complex around activated receptor tyrosine kinases is not clear. In the present study, we describe a specific interaction between S6K with receptor tyrosine kinases, such as platelet-derived growth factor receptor (PDGFR). The interaction with PDGFR is mediated via the kinase or the kinase extension domain of S6K. Complex formation is inducible by growth factors and leads to S6K tyrosine phosphorylation. Using PDGFR mutants, we have shown that the phosphorylation is exerted via a PDGFR-src pathway. Furthermore, src kinase phosphorylates and coimmunoprecipitates with S6K in vivo. Inhibitors towards tyrosine kinases, such as genistein and PP1, or src-specific SU6656, but not PI3K and mTor inhibitors, lead to a reduction in tyrosine phosphorylation of S6K. In addition, we mapped the sites of tyrosine phosphorylation in S6K1 and S6K2 to Y39 and Y45, respectively. Mutational and immunofluorescent analysis indicated that phosphorylation of S6Ks at these sites does not affect their activity or subcellular localization. Our data indicate that S6 kinase is recruited into a complex with RTKs and src and becomes phosphorylated on tyrosine/s in response to PDGF or serum.

ARAP3 is essential for formation of lamellipodia after growth factor stimulation

Rho and Arf family small GTPases control dynamic actin rearrangements and vesicular trafficking events. ARAP3 is a dual GAP for RhoA and Arf6 that is regulated by phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3], a product of the phosphoinositide 3-kinase (PI3K) signalling pathway. To investigate the physiological function of ARAP3, we used an RNAi-based approach in an endothelial cell model. ARAP3-deficient cells showed increased activities of RhoA and Arf6. Phenotypically, they were more rounded than control counterparts and displayed very fine stress fibres. ARAP3-deficient cells were not capable of producing lamellipodia upon growth factor stimulation, a process known to depend on PI3K and Rac activities. Rac was transiently activated in stimulated ARAP3 RNAi cells although its cellular localisation was altered, a likely consequence of increased Arf6 activity. We conclude that ARAP3 recruitment to sites of elevated PtdIns(3,4,5)P3 is crucial to allow localised inactivation of RhoA and cycling of Arf6, both of which are necessary to allow growth factor-stimulated formation of lamellipodia.

Purification of ARAP3 and Characterization of GAP Activities

ARAP3 is a dual Arf and Rho GTPase activating protein (GAP) that was identified from pig leukocyte cytosol using a phosphatidylinositol-(3,4,5)-trisphosphate (PtdIns[3,4,5]P3) affinity matrix in a targeted proteomics study. ARAP3's domain structure includes five PH domains, an Arf GAP domain, three ankyrin repeats, a Rho GAP domain, and a Ras association domain. ARAP3 is a PtdIns(3,4,5)P3-dependent GAP for Arf6 both in vitro and in vivo. It acts as a Rap-GTP-activated RhoA GAP in vitro, and this activation depends on a direct interaction between ARAP3 and Rap-GTP; in vivo PtdIns(3,4,5)P3 seems to be required to allow ARAP3's activation as a RhoA GAP by Rap-GTP. Overexpression of ARAP3 in pig aortic endothelial (PAE) cells causes the PI3K-dependent loss of adhesion to the substratum and interferes with lamellipodium formation. This overexpression phenotype depends on ARAP3's intact abilities to bind PtdIns(3,4,5)P3, to interact with Rap-GTP, and to be a catalytically active RhoA and Arf6 GAP.

Phosphoinositide 3-kinases as drug targets in cancer

The past two years have seen phosphoinositide 3-kinases (PI3Ks) move from being seen as potential targets for chemotherapeutics, to one of them--PI3Kalpha--being generally accepted as validated. A huge amount of work indicated that there was an important role for PI3Ks in tumour progression and, particularly, in the control of proliferation, survival and regulation of the potential oncogene PKB. These links were further strengthened by studies showing that the tumour suppressor, PTEN, is an antagonist of PI3K signalling and that somatic mutations of p110alpha (PIK3CA) are present in a variety of cancers. We now know that three of the most frequent mutations in cancer constitutively activate PI3Kalpha and, when expressed in cells, they drive the oncogenic transformation and chronic activation of downstream signalling by molecules such as PKB, S6K and 4E bp1 that is commonly seen in cancer cells. A large body of research into the cellular roles of PI3Ks has also further validated them as potential foci for cancer chemotherapy, with several additional PI3K effectors controlling cell proliferation and apoptosis having been described. Furthermore, molecules important to the processes of metastasis, development of multi-drug resistance, the 'Warburg effect', angiogenesis and cell growth (i.e. distinct to proliferation) have been found to depend upon, or to be driven by, PI3K activity.

p84, a New Gβγ-Activated Regulatory Subunit of the Type IB Phosphoinositide 3-Kinase p110γ

A variety of genetic and inhibitor studies have shown that phosphoinositide 3-kinase gamma (PI3Kgamma) plays an essential role in a number of physiological responses, including neutrophil chemotaxis, mast cell degranulation, and cardiac function []. PI3Kgamma is currently thought to be composed of a p110gamma catalytic subunit and a single regulatory subunit, p101. The binding of p110gamma to p101 dramatically increases the activation of the complex by Gbetagamma subunits and, hence, is thought to be critical for the coupling of PI3Kgamma to G protein coupled receptors []. Here, we characterize a new regulatory subunit for PI3Kgamma. p84 is present in human, mouse, chicken, frog, and fugu genomes and is located beside the p101 locus. It is broadly expressed in cells of the murine immune system. Both recombinant and endogenous p84 bind p110gamma specifically and with high affinity. Binding of p84 to p110gamma substantially increases the ability of Gbetagamma to stimulate phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P(3)) production both in vitro and in vivo. However, the p84/p110gamma heterodimer is approximately 4-fold less sensitive to Gbetagammas than p101/p110gamma. Endogenous murine p84 expression is substantially reduced in the absence of p110gamma expression. We conclude that p110gamma has two potential regulatory subunits in vivo, p84 and p101.

ARAP3 is a PI3K- and rap-regulated GAP for RhoA

Rho and Arf family small GTPases are well-known regulators of cellular actin dynamics. We recently identified ARAP3, a member of the ARAP family of dual GTPase activating proteins (GAPs) for Arf and Rho family GTPases, in a screen for PtdIns(3,4,5)P(3) binding proteins. PtdIns(3,4,5)P(3) is the lipid product of class I phosphoinositide 3OH-kinases (PI3Ks) and is a signaling molecule used by growth factor receptors and integrins in the regulation of cell dynamics. We report here that as a Rho GAP, ARAP3 prefers RhoA as a substrate and that it can be activated in vitro by the direct binding of Rap proteins to a neighbouring Ras binding domain (RBD). This activation by Rap is GTP dependent and specific for Rap versus other Ras family members. We found no evidence for direct regulation of ARAP3's Rho GAP activity by PtdIns(3,4,5)P(3) in vitro, but PI3K activity was required for activation by Rap in a cellular context, suggesting that PtdIns(3,4,5)P(3)-dependent translocation of ARAP3 to the plasma membrane may be required for further activation by Rap. Our results indicate that ARAP3 is a Rap-effector that plays an important role in mediating PI3K-dependent crosstalk between Ras, Rho, and Arf family small GTPases.

LL5beta is a phosphatidylinositol (3,4,5)-trisphosphate sensor that can bind the cytoskeletal adaptor, gamma-filamin

We identified a potential phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P(3)) binding pleckstrin homology domain in the data bases and have cloned and expressed its full coding sequence (LL5beta). The protein bound PtdIns(3,4,5)P(3) selectively in vitro. Strikingly, a substantial proportion of LL5beta became associated with an unidentified intracellular vesicle population in the context of low PtdIns(3,4,5)P(3) levels produced by the addition of wortmannin or LY294002. In addition, expression of platelet-derived growth factor-receptor mutants unable to activate type 1A phosphoinositide 3-kinase (PI3K) or serum starvation in porcine aortic endothelial cells lead to redistribution of LL5beta to this vesicle population. Importantly, pleckstrin homology domain mutants of LL5beta that could not bind PtdIns(3,4,5)P(3) were constitutively localized to this vesicle population. At increased PtdIns(3,4,5)P(3) levels, LL5beta was redirected to a predominantly cytoplasmic distribution, presumably through a PI3K-dependent block on its targeting to the vesicular compartment. Furthermore, at high, hormone-stimulated PtdIns(3,4,5)P(3) levels, it became significantly plasma-membrane localized. The distribution of LL5beta is thus dramatically and uniquely sensitive to low levels of PtdIns(3,4,5)P(3) indicating it can act as a sensor of both low and hormone-stimulated levels of PtdIns(3,4,5)P(3). In addition, LL5beta bound to the cytoskeletal adaptor, gamma-filamin, tightly and in a PI3K-independent fashion, both in vitro and in vivo. This interaction could co-localize heterologously expressed gamma-filamin with GFP-LL5beta in the unidentified vesicles.

Activation of phosphoinositide 3-kinase gamma by Ras

BACKGROUND

Type I phosphoinositide 3-kinases are responsible for the hormone-sensitive synthesis of the lipid messenger phosphatidylinositol(3,4,5)-trisphosphate. Type IA and IB subfamily members contain a Ras binding domain and are stimulated by activated Ras proteins both in vivo and in vitro. The mechanism of Ras activation of type I PI3Ks is unknown, in part because no robust in vitro assay of this event has been established and characterized. Other Ras effectors, such as Raf and phosphoinositide-phospholipase Cepsilon, have been shown to be translocated into the plasma membrane, leading to their activation.

RESULTS

We show that posttranslationally lipid-modified, activated N-, H-, K-, and R-Ras proteins can potently and substantially activate PI3Kgamma when using a stripped neutrophil membrane fraction as a source of phospholipid substrate. We have found GTPgammaS-loaded Ras can significantly (6- to 8-fold) activate PI3Kgamma when using artificial phospholipid vesicles containing their substrate, and this effect is a result of both a decrease in apparent Km for phosphatidylinositol(4,5)-bisphosphate and an increase in the apparent Vmax. However, neither in vivo nor in the two in vitro assays of Ras activation of PI3Kgamma could we detect any evidence of a Ras-dependent translocation of PI3Kgamma to its source of phospholipid substrate.

CONCLUSIONS

Our data suggest that Ras activate PI3Kgamma at the level of the membrane, by allosteric modulation and/or reorientation of the PI3Kgamma, implying that Ras can activate PI3Kgamma without its membrane translocation. This view is supported by structural work that has suggested binding of Ras to PI3Kgamma results in a change in the structure of the catalytic pocket.

Roles of PI3Ks in leukocyte chemotaxis and phagocytosis

Through selective disruption of phosphoinositide 3-kinase (PI3K) activity and the use of green fluorescent protein tagged derivatives of domains capable of specifically binding the lipid products of PI3Ks in vivo, it has been shown that this family of signalling enzymes have vital and distinct roles in chemotaxis, phagocytosis and phagosome maturation in leukocytes.

The crystal structure of the PX domain from p40(phox) bound to phosphatidylinositol 3-phosphate

More than 50 human proteins with a wide range of functions have a 120 residue phosphoinositide binding module known as the PX domain. The 1.7 A X-ray crystal structure of the PX domain from the p40(phox) subunit of NADPH oxidase bound to PtdIns(3)P shows that the PX domain embraces the 3-phosphate on one side of a water-filled, positively charged pocket and reveals how 3-phosphoinositide specificity is achieved. A chronic granulomatous disease (CGD)-associated mutation in the p47(phox) PX domain that abrogates PtdIns(3)P binding maps to a conserved Arg that does not directly interact with the phosphoinositide but instead appears to stabilize a critical lipid binding loop. The SH3 domain present in the full-length protein does not affect soluble PtdIns(3)P binding to the p40(phox) PX domain.

Red cell antibodies in patients with homozygous sickle cell disease: a comparison of patients in Jamaica and the United Kingdom

The transfusion history and frequency of red cell antibodies in patients with homozygous sickle cell (SS) disease have been compared in 190 subjects from the Jamaican cohort study and 37 patients attending a sickle cell clinic in Manchester, England. The proportion of patients transfused did not differ between the groups although the number of units transfused and the frequency of red cell antibodies were significantly greater in the Manchester group. Immune antibodies occurred in three Jamaicans (2.6% of those transfused) and 16 UK subjects (76% of those transfused). Multiple antibodies occurred in 10 (63%) UK subjects but in no Jamaicans. Indications for transfusion also differed between the groups, Jamaican patients typically receiving 1-2 units for acute anaemia or acute chest syndrome, whereas UK patients frequently had multiple transfusions in preoperative exchange or prophylaxis programmes. The greater red cell alloimmunization among UK patients probably reflects both the greater use of transfusion and the disparity between donor and recipient populations in the UK.

Crystal structure and functional analysis of Ras binding to its effector phosphoinositide 3-kinase gamma

Ras activation of phosphoinositide 3-kinase (PI3K) is important for survival of transformed cells. We find that PI3Kgamma is strongly and directly activated by H-Ras G12V in vivo or by GTPgammaS-loaded H-Ras in vitro. We have determined a crystal structure of a PI3Kgamma/Ras.GMPPNP complex. A critical loop in the Ras binding domain positions Ras so that it uses its switch I and switch II regions to bind PI3Kgamma. Mutagenesis shows that interactions with both regions are essential for binding PI3Kgamma. Ras also forms a direct contact with the PI3Kgamma catalytic domain. These unique Ras/PI3Kgamma interactions are likely to be shared by PI3Kalpha. The complex with Ras shows a change in the PI3K conformation that may represent an allosteric component of Ras activation.

Structural determinants of phosphoinositide 3-kinase inhibition by wortmannin, LY294002, quercetin, myricetin, and staurosporine

The specific phosphoinositide 3-kinase (PI3K) inhibitors wortmannin and LY294002 have been invaluable tools for elucidating the roles of these enzymes in signal transduction pathways. The X-ray crystallographic structures of PI3Kgamma bound to these lipid kinase inhibitors and to the broad-spectrum protein kinase inhibitors quercetin, myricetin, and staurosporine reveal how these compounds fit into the ATP binding pocket. With a nanomolar IC50, wortmannin most closely fits and fills the active site and induces a conformational change in the catalytic domain. Surprisingly, LY294002 and the lead compound on which it was designed, quercetin, as well as the closely related flavonoid myricetin bind PI3K in remarkably different orientations that are related to each other by 180 degrees rotations. Staurosporine/PI3K interactions are reminiscent of low-affinity protein kinase/staurosporine complexes. These results provide a rich basis for development of isoform-specific PI3K inhibitors with therapeutic potential.

Structural determinants of phosphoinositide 3-kinase inhibition by wortmannin, LY294002, quercetin, myricetin, and staurosporine

The specific phosphoinositide 3-kinase (PI3K) inhibitors wortmannin and LY294002 have been invaluable tools for elucidating the roles of these enzymes in signal transduction pathways. The X-ray crystallographic structures of PI3Kgamma bound to these lipid kinase inhibitors and to the broad-spectrum protein kinase inhibitors quercetin, myricetin, and staurosporine reveal how these compounds fit into the ATP binding pocket. With a nanomolar IC50, wortmannin most closely fits and fills the active site and induces a conformational change in the catalytic domain. Surprisingly, LY294002 and the lead compound on which it was designed, quercetin, as well as the closely related flavonoid myricetin bind PI3K in remarkably different orientations that are related to each other by 180 degrees rotations. Staurosporine/PI3K interactions are reminiscent of low-affinity protein kinase/staurosporine complexes. These results provide a rich basis for development of isoform-specific PI3K inhibitors with therapeutic potential.

Colorectal carcinomas in mice lacking the catalytic subunit of PI(3)Kgamma

Phosphoinositide-3-OH kinases (PI(3)Ks) constitute a family of evolutionarily conserved lipid kinases that regulate a vast array of fundamental cellular responses, including proliferation, transformation, differentiation and protection from apoptosis. PI(3)K-mediated activation of the cell survival kinase PKB/Akt, and negative regulation of PI(3)K signalling by the tumour suppressor PTEN (refs 3, 4) are key regulatory events in tumorigenesis. Thus, a model has arisen that PI(3)Ks promote development of cancers. Here we report that genetic inactivation of the p110gamma catalytic subunit of PI(3)Kgamma (ref. 8) leads to development of invasive colorectal adenocarcinomas in mice. In humans, p110gamma protein expression is lost in primary colorectal adenocarcinomas from patients and in colon cancer cell lines. Overexpression of wild-type or kinase-dead p110gamma in human colon cancer cells with mutations of the tumour suppressors APC and p53, or the oncogenes beta-catenin and Ki-ras, suppressed tumorigenesis. Thus, loss of p110gamma in mice leads to spontaneous, malignant epithelial tumours in the colorectum and p110gamma can block the growth of human colon cancer cells.

Structural insights into phosphoinositide 3-kinase catalysis and signalling

Phosphoinositide 3-kinases (PI3Ks) are ubiquitous lipid kinases that function both as signal transducers downstream of cell-surface receptors and in constitutive intracellular membrane and protein trafficking pathways. All PI3Ks are dual-specificity enzymes with a lipid kinase activity which phosphorylates phosphoinositides at the 3-hydroxyl, and a protein kinase activity. The products of PI3K-catalysed reactions, phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3), PtdIns(3,4)P2 and PtdIns(3)P, are second messengers in a variety of signal transduction pathways, including those essential to cell proliferation, adhesion, survival, cytoskeletal rearrangement and vesicle trafficking. Here we report the 2.2 A X-ray crystallographic structure of the catalytic subunit of PI3Kgamma, the class I enzyme that is activated by heterotrimeric G-protein betagamma subunits and Ras. PI3Kgamma has a modular organization centred around a helical-domain spine, with C2 and catalytic domains positioned to interact with phospholipid membranes, and a Ras-binding domain placed against the catalytic domain where it could drive allosteric activation of the enzyme.