Targeting PI3K isoforms and SHIP in the immune system: new therapeutics for inflammation and leukemia

Structure-Activity Studies on Bis-Sulfonamide SHIP1 Activators

The SH2-containing inositol polyphosphate 5-phosphatase 1 (SHIP1) enzyme opposes the activity of PI3K and therefore is of interest in the treatment of inflammatory disorders. Recent results also indicate that SHIP1 promotes phagolysosomal degradation of lipids by microglia, suggesting that the enzyme may be a target for the treatment of Alzheimer's disease. Therefore, small molecules that increase SHIP1 activity may have benefits in these areas. Recently we discovered a bis-sulfonamide that increases the enzymatic activity of SHIP1. A series of similar SHIP1 activators have been synthesized and evaluated to determine structure-activity relationships and improve in vivo stability. Some new analogs have now been found with improved potency. In addition, both the thiophene and the thiomorpholine in the parent structure can be replaced by groups without a low valent sulfur atom, which provides a way to access activators that are less prone to oxidative degradation.

N1-Benzyl Tryptamine Pan-SHIP1/2 Inhibitors: Synthesis and Preliminary Biological Evaluation as Anti-Tumor Agents

Inhibition of phosphatidylinositol 3,4,5-trisphosphate 5-phosphatase (SHIP) with small molecule inhibitors leads to apoptosis in tumor cells. Inhibitors that target both SHIP1 and SHIP2 (pan-SHIP1/2 inhibitors) may have benefits in these areas since paralog compensation is not possible when both SHIP paralogs are being inhibited. A series of tryptamine-based pan-SHIP1/2 inhibitors have been synthesized and evaluated for their ability to inhibit the SHIP paralogs. The most active compounds were also evaluated for their effects on cancer cell lines.

The Role of PI3K Isoforms in Autoimmune Disease

Aberrant overactivation of the immune system can give rise to chronic and persistent self-attack, culminating in autoimmune disease. This is currently managed therapeutically using potent immunosuppressive and anti-inflammatory drugs. Class I phosphoinositide-3-kinases (PI3Ks) have been identified as ideal therapeutic targets for autoimmune diseases given their wide-ranging roles in immunological processes. Although progress has been hampered by issues such as poor drug tolerance and drug resistance, several PI3K inhibitors have now received regulatory approval with many others in development, including several intended to suppress the immune response in autoimmune and inflammatory diseases. This chapter reviews the evidence for contribution of aberrant PI3K activity to a range of autoimmune diseases (rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis and type I diabetes) and possible therapeutic application of isoform-specific PI3K inhibitors as immunosuppressive drugs.

Strategy for Leukemia Treatment Targeting SHP-1,2 and SHIP

Protein tyrosine phosphatases (PTPs) are modulators of cellular functions such as differentiation, metabolism, migration, and survival. PTPs antagonize tyrosine kinases by removing phosphate moieties from molecular signaling residues, thus inhibiting signal transduction. Two PTPs, SHP-1 and SHP-2 (SH2 domain-containing phosphatases 1 and 2, respectively) and another inhibitory phosphatase, SH2 domain-containing inositol phosphatase (SHIP), are essential for cell function, which is reflected in the defective phenotype of mutant mice. Interestingly, SHP-1, SHP-2, and SHIP mutations are identified in many cases of human leukemia. However, the impact of these phosphatases and their mutations regarding the onset and progression of leukemia is controversial. The ambiguity of the role of these phosphatases imposes challenges on the development of targeting therapies for leukemia. This fundamental problem, confronted by the expanding investigational field of leukemia, will be addressed in this review, which will include a discussion of the molecular mechanisms of SHP-1, SHP-2, and SHIP in normal hematopoiesis and their role in leukemia. Clinical development of leukemic therapies achieved by targeting these phosphatases will be addressed as well.

Allosteric Site on SHIP2 Identified Through Fluorescent Ligand Screening and Crystallography: A Potential New Target for Intervention

Src homology 2 domain-containing inositol phosphate phosphatase 2 (SHIP2) is one of the 10 human inositol phosphate 5-phosphatases. One of its physiological functions is dephosphorylation of phosphatidylinositol 3,4,5-trisphosphate, PtdIns(3,4,5)P₃. It is therefore a therapeutic target for pathophysiologies dependent on PtdIns(3,4,5)P₃ and PtdIns(3,4)P₂. Therapeutic interventions are limited by the dearth of crystallographic data describing ligand/inhibitor binding. An active site-directed fluorescent probe facilitated screening of compound libraries for SHIP2 ligands. With two additional orthogonal assays, several ligands including galloflavin were identified as low micromolar Ki inhibitors. One ligand, an oxo-linked ethylene-bridged dimer of benzene 1,2,4-trisphosphate, was shown to be an uncompetitive inhibitor that binds to a regulatory site on the catalytic domain. We posit that binding of ligands to this site restrains L4 loop motions that are key to interdomain communications that accompany high catalytic activity with phosphoinositide substrate. This site may, therefore, be a future druggable target for medicinal chemistry.

Tribbles Pseudokinase 2 (TRIB2) Regulates Expression of Binding Partners in Bovine Granulosa Cells

Members of the Tribbles (TRIB) family of pseudokinases are critical components of intracellular signal transduction pathways in physiological and pathological processes. TRIBs, including TRIB2, have been previously shown as signaling mediators and scaffolding proteins regulating numerous cellular events such as proliferation, differentiation and cell death through protein stability and activity. However, the signaling network associated with TRIB2 and its binding partners in granulosa cells during ovarian follicular development is not fully defined. We previously reported that TRIB2 is differentially expressed in growing dominant follicles while downregulated in ovulatory follicles following the luteinizing hormone (LH) surge or human chorionic gonadotropin (hCG) injection. In the present study, we used the yeast two-hybrid screening system and in vitro coimmunoprecipitation assays to identify and confirm TRIB2 interactions in granulosa cells (GCs) of dominant ovarian follicles (DFs), which yielded individual candidate binding partners including calmodulin 1 (CALM1), inhibin subunit beta A (INHBA), inositol polyphosphate phosphatase-like 1 (INPPL1), 5'-nucleotidase ecto (NT5E), stearoyl-CoA desaturase (SCD), succinate dehydrogenase complex iron sulfur subunit B (SDHB) and Ras-associated protein 14 (RAB14). Further analyses showed that all TRIB2 binding partners are expressed in GCs of dominant follicles but are differentially regulated throughout the different stages of follicular development. CRISPR/Cas9-driven inhibition along with pQE-driven overexpression of TRIB2 showed that TRIB2 differently regulates expression of binding partners, which reveals the importance of TRIB2 in the control of gene expression linked to various biological processes such as proliferation, differentiation, cell migration, apoptosis, calcium signaling and metabolism. These data provide a larger view of potential TRIB2-regulated signal transduction pathways in GCs and provide strong evidence that TRIB2 may act as a regulator of target genes during ovarian follicular development.

All Trans Retinoic Acid, Transforming Growth Factor β and Prostaglandin E2 in Mouse Plasma Synergize with Basophil-Secreted Interleukin-4 to M2 Polarize Murine Macrophages

In previous studies we found that macrophages (MФs) from SH2-containing inositol-5'-phosphatase (SHIP) deficient mice are M2 polarized while their wild type (WT) counterparts are M1 polarized and that this difference in MФ phenotype can be recapitulated during in vitro derivation from bone marrow if mouse plasma (MP), but not fetal calf serum, is added to standard M-CSF-containing cultures. In the current study we investigated the mechanism by which MP skews SHIP-/- but not +/+ MФs to an M2 phenotype. Our results suggest that SHIP-/- basophils constitutively secrete higher levels of IL-4 than SHIP+/+ basophils and this higher level of IL-4 is sufficient to skew both SHIP+/+ and SHIP-/- MФs to an M2 phenotype, but only when MP is present to increase the sensitivity of the MФs to this level of IL-4. MP increases the IL-4 sensitivity of both SHIP+/+ and -/- MФs not by increasing cell surface IL-4 or CD36 receptor levels, but by triggering the activation of Erk and Akt and the production of ROS, all of which play a critical role in sensitizing MФs to IL-4-induced M2 skewing. Studies to identify the factor(s) in MP responsible for promoting IL-4-induced M2 skewing suggests that all-trans retinoic acid (ATRA), TGFβ and prostaglandin E2 (PGE2) all play a role. Taken together, these results indicate that basophil-secreted IL-4 plays an essential role in M2 skewing and that ATRA, TGFβ and PGE2 within MP collaborate to dramatically promote M2 skewing by acting directly on MФs to increase their sensitivity to IL-4.

Profound blockade of T cell activation requires concomitant inhibition of different class I PI3K isoforms

PI3K inhibitors have emerged as potential therapeutic tools for a variety of diseases, and thus, a vast array of compounds with specificity for different PI3K isoforms is being developed. Gaining knowledge about the contribution of the different isoforms to PI3K function will allow selecting the most appropriate inhibitor for each pathology. In this study, we have addressed the effect of PI3K inhibitors with specificity for different class I PI3K isoforms on primary human T cell activation. In particular, we have analyzed proliferation, expression of activation and differentiation markers, apoptosis induction, cytokine secretion and Akt phosphorylation in T cells stimulated in vitro with anti-CD3 and anti-CD28 monoclonal antibodies and cultured with either one of these compounds: p110β-specific inhibitor TGX-221, p110δ-specific inhibitor IC-87114, p110γ inhibitor AS-242525 or pan-class I PI3K inhibitor BKM120. Inhibition of any of the isoforms led to an impairment of T cell activation, mainly of cytokine secretion and granzyme B expression. However, only complete blockade of class I PI3K activity with the pan-class I inhibitor effectively abrogated T cell proliferation. These results indicate that these three p110 isoforms (β, δ and γ) take part in T cell activation, but all of them are dispensable for T cell proliferation.

Synthesis and initial evaluation of quinoline-based inhibitors of the SH2-containing inositol 5'-phosphatase (SHIP)

Recently, inhibition of the SH2-containing inositol 5'-phosphatase 1 (SHIP1) has become an attractive strategy for facilitating engraftment of MHC-I mismatched bone marrow grafts, increasing the number of adult stem cells in vivo, and inducing mobilization of hematopoietic stem cells. Utilizing high-throughput screening, two quinoline small molecules (NSC13480 and NSC305787) that inhibit SHIP1 enzymatic activity were discovered. New syntheses of these inhibitors have been developed which verified the relative stereochemistry of these structures. Utilizing this synthetic route, some analogs of these quinolines have been prepared and tested for their ability to inhibit SHIP. These structure activity studies determined that an amine tethered to the quinoline core is required for SHIP inhibition. SHIP inhibition may explain the antitumor effects of similar quinoline amino alcohols and provides an impetus for further synthetic studies in this class of compounds.

Sparse Modeling Reveals miRNA Signatures for Diagnostics of Inflammatory Bowel Disease

The diagnosis of inflammatory bowel disease (IBD) still remains a clinical challenge and the most accurate diagnostic procedure is a combination of clinical tests including invasive endoscopy. In this study we evaluated whether systematic miRNA expression profiling, in conjunction with machine learning techniques, is suitable as a non-invasive test for the major IBD phenotypes (Crohn's disease (CD) and ulcerative colitis (UC)). Based on microarray technology, expression levels of 863 miRNAs were determined for whole blood samples from 40 CD and 36 UC patients and compared to data from 38 healthy controls (HC). To further discriminate between disease-specific and general inflammation we included miRNA expression data from other inflammatory diseases (inflammation controls (IC): 24 chronic obstructive pulmonary disease (COPD), 23 multiple sclerosis, 38 pancreatitis and 45 sarcoidosis cases) as well as 70 healthy controls from previous studies. Classification problems considering 2, 3 or 4 groups were solved using different types of penalized support vector machines (SVMs). The resulting models were assessed regarding sparsity and performance and a subset was selected for further investigation. Measured by the area under the ROC curve (AUC) the corresponding median holdout-validated accuracy was estimated as ranging from 0.75 to 1.00 (including IC) and 0.89 to 0.98 (excluding IC), respectively. In combination, the corresponding models provide tools for the distinction of CD and UC as well as CD, UC and HC with expected classification error rates of 3.1 and 3.3%, respectively. These results were obtained by incorporating not more than 16 distinct miRNAs. Validated target genes of these miRNAs have been previously described as being related to IBD. For others we observed significant enrichment for IBD susceptibility loci identified in earlier GWAS. These results suggest that the proposed miRNA signature is of relevance for the etiology of IBD. Its diagnostic value, however, should be further evaluated in large, independent, clinically well characterized cohorts.

Inhibition of serum- and glucocorticoid-inducible kinase 1 enhances TLR-mediated inflammation and promotes endotoxin-driven organ failure

Serum- and glucocorticoid-regulated kinase (SGK)1 is associated with several important pathologic conditions and plays a modulatory role in adaptive immune responses. However, the involvement and functional role of SGK1 in innate immune responses remain entirely unknown. In this study, we establish that SGK1 is a novel and potent negative regulator of TLR-induced inflammation. Pharmacologic inhibition of SGK1 or suppression by small interfering RNA enhances proinflammatory cytokine (TNF, IL-12, and IL-6) production in TLR-engaged monocytes, a result confirmed in Cre-loxP-mediated SGK1-deficient cells. SGK1 inhibition or gene deficiency results in increased phosphorylation of IKK, IκBα, and NF-κB p65 in LPS-stimulated cells. Enhanced NF-κB p65 DNA binding also occurs upon SGK1 inhibition. The subsequent enhancement of proinflammatory cytokines is dependent on the phosphorylation of TGF-β-activated kinase 1 (TAK1), as confirmed by TAK1 gene silencing. In vivo relevance was established in a murine endotoxin model, in which we found that SGK1 inhibition aggravates the severity of multiple organ damage and enhances the inflammatory response by heightening both proinflammatory cytokine levels and neutrophil infiltration. These findings have identified an anti-inflammatory function of SGK1, elucidated the underlying intracellular mechanisms, and establish, for the first time, that SGK1 holds potential as a novel target for intervention in the control of inflammatory diseases.

Phosphatidylinositol-3,4,5-triphosphate and cellular signaling: implications for obesity and diabetes

Phosphatidylinositol-3,4,5-triphosphate (PtdIns(3,4,5)P₃) is one of the most important phosphoinositides and is capable of activating a wide range of proteins through its interaction with their specific binding domains. Localization and activation of these effector proteins regulate a number of cellular functions, including cell survival, proliferation, cytoskeletal rearrangement, intracellular vesicle trafficking, and cell metabolism. Phosphoinositides have been investigated as an important agonist-dependent second messenger in the regulation of diverse physiological events depending upon the phosphorylation status of their inositol group. Dysregulation in formation as well as metabolism of phosphoinositides is associated with various pathophysiological disorders such as inflammation, allergy, cardiovascular diseases, cancer, and metabolic diseases. Recent studies have demonstrated that the impaired metabolism of PtdIns(3,4,5)P₃ is a prime mediator of insulin resistance associated with various metabolic diseases including obesity and diabetes. This review examines the current status of the role of PtdIns(3,4,5)P₃ signaling in the regulation of various cellular functions and the implications of dysregulated PtdIns(3,4,5)P₃ signaling in obesity, diabetes, and their associated complications.

Molecular control of PtdIns(3,4,5)P3 signaling in neutrophils

Neutrophils play critical roles in innate immunity and host defense. However, excessive neutrophil accumulation or hyper-responsiveness of neutrophils can be detrimental to the host system. Thus, the response of neutrophils to inflammatory stimuli needs to be tightly controlled. Many cellular processes in neutrophils are mediated by localized formation of an inositol phospholipid, phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3), at the plasma membrane. The PtdIns(3,4,5)P3 signaling pathway is negatively regulated by lipid phosphatases and inositol phosphates, which consequently play a critical role in controlling neutrophil function and would be expected to act as ideal therapeutic targets for enhancing or suppressing innate immune responses. Here, we comprehensively review current understanding about the action of lipid phosphatases and inositol phosphates in the control of neutrophil function in infection and inflammation.

Detection and manipulation of phosphoinositides

Phosphoinositides (PIs) are minor components of cell membranes, but play key roles in cell function. Recent refinements in techniques for their detection, together with imaging methods to study their distribution and changes, have greatly facilitated the study of these lipids. Such methods have been complemented by the parallel development of techniques for the acute manipulation of their levels, which in turn allow bypassing the long-term adaptive changes implicit in genetic perturbations. Collectively, these advancements have helped elucidate the role of PIs in physiology and the impact of the dysfunction of their metabolism in disease. Combining methods for detection and manipulation enables the identification of specific roles played by each of the PIs and may eventually lead to the complete deconstruction of the PI signaling network. Here, we review current techniques used for the study and manipulation of cellular PIs and also discuss advantages and disadvantages associated with the various methods. This article is part of a Special Issue entitled Phosphoinositides.

PI3K signalling in inflammation

PI3Ks regulate several key events in the inflammatory response to damage and infection. There are four Class I PI3K isoforms (PI3Kα,β,γ,δ), three Class II PI3K isoforms (PI3KC2α, C2β, C2γ) and a single Class III PI3K. The four Class I isoforms synthesise the phospholipid 'PIP3'. PIP3 is a 'second messenger' used by many different cell surface receptors to control cell movement, growth, survival and differentiation. These four isoforms have overlapping functions but each is adapted to receive efficient stimulation by particular receptor sub-types. PI3Kγ is highly expressed in leukocytes and plays a particularly important role in chemokine-mediated recruitment and activation of innate immune cells at sites of inflammation. PI3Kδ is also highly expressed in leukocytes and plays a key role in antigen receptor and cytokine-mediated B and T cell development, differentiation and function. Class III PI3K synthesises the phospholipid PI3P, which regulates endosome-lysosome trafficking and the induction of autophagy, pathways involved in pathogen killing, antigen processing and immune cell survival. Much less is known about the function of Class II PI3Ks, but emerging evidence indicates they can synthesise PI3P and PI34P2 and are involved in the regulation of endocytosis. The creation of genetically-modified mice with altered PI3K signalling, together with the development of isoform-selective, small-molecule PI3K inhibitors, has allowed the evaluation of the individual roles of Class I PI3K isoforms in several mouse models of chronic inflammation. Selective inhibition of PI3Kδ, γ or β has each been shown to reduce the severity of inflammation in one or more models of autoimmune disease, respiratory disease or allergic inflammation, with dual γ/δ or β/δ inhibition generally proving more effective. The inhibition of Class I PI3Ks may therefore offer a therapeutic opportunity to treat non-resolving inflammatory pathologies in humans. This article is part of a Special Issue entitled Phosphoinositides.

SHIP1 is targeted by miR-155 in acute myeloid leukemia

The SH2 domain-containing inositol 5'-phosphatase 1 (SHIP1) has been implicated as a suppressor of hematopoietic transformation as its activity can inhibit the PI3K/Akt signaling pathway. Reduced activity of SHIP1 has been observed in acute myeloid leukemia (AML). SHIP1 is a target of microRNA-155 (miR-155). Therefore, the aim of the present study was to investigate the role of miR-155/SHIP1 in the pathogenesis of AML. We examined the levels of SHIP1 protein and miR-155 in tissue samples of patients with AML and in AML cell lines. In addition, we investigated cell proliferation, apoptosis and expression of SHIP1/PI3K/AKT pathway molecules in the THP-1 and U937 cell lines after miR-155 inhibitor or mimics were transfected. We showed that the levels of SHIP1 protein were significantly decreased in tissue samples of patients with some subtypes of AML (M4 or M5) and in AML cell lines with concomitant overexpression of miR-155. In addition, we demonstrated that decreased expression of SHIP1 in the AML cell lines was a consequence of increased levels of miR-155 and can therefore be reversed in vitro through inhibition of miR-155, with subsequent inhibition of cell proliferation and promotion of cell apoptosis. In conclusion, expression of the SHIP1 protein is targeted by miR-155 in AML. miR-155 acts as an onco-miR, and the miR-155/SHIP1/PI3K/AKT signaling pathway could play an important role in the pathogenesis of AML.

Structural basis for phosphoinositide substrate recognition, catalysis, and membrane interactions in human inositol polyphosphate 5-phosphatases

SHIP2, OCRL, and INPP5B belong to inositol polyphosphate 5-phophatase subfamilies involved in insulin regulation and Lowes syndrome. The structural basis for membrane recognition, substrate specificity, and regulation of inositol polyphosphate 5-phophatases is still poorly understood. We determined the crystal structures of human SHIP2, OCRL, and INPP5B, the latter in complex with phosphoinositide substrate analogs, which revealed a membrane interaction patch likely to assist in sequestering substrates from the lipid bilayer. Residues recognizing the 1-phosphate of the substrates are highly conserved among human family members, suggesting similar substrate binding modes. However, 3- and 4-phosphate recognition varies and determines individual substrate specificity profiles. The high conservation of the environment of the scissile 5-phosphate suggests a common reaction geometry for all members of the human 5-phosphatase family.

Role of phosphatidylinositol 3,4,5-trisphosphate in cell signaling

Many lipids present in cellular membranes are phosphorylated as part of signaling cascades and participate in the recruitment, localization, and activation of downstream protein effectors. Phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) is one of the most important second messengers and is capable of interacting with a variety of proteins through specific PtdIns(3,4,5)P3 binding domains. Localization and activation of these effector proteins controls a myriad of cellular functions including cell survival, proliferation, cytoskeletal rearrangement, and gene expression. Aberrations in the production and metabolism of PtdIns(3,4,5)P3 have been implicated in many human diseases including cancer, diabetes, inflammation, and heart disease. This chapter provides an overview of the role of PtdIns(3,4,5)P3 in cellular regulation and the implications of PtdIns(3,4,5)P3 dysregulation in human diseases. Additionally, recent attempts at targeting PtdIns(3,4,5)P3 signaling via small molecule inhibitors are summarized.