The 145-kDa protein induced to associate with Shc by multiple cytokines is an inositol tetraphosphate and phosphatidylinositol 3,4,5-triphosphate 5-phosphatase

SHIP-1 regulates the differentiation and function of Tregs via inhibiting mTORC1 activity

Cell metabolism is crucial for orchestrating the differentiation and function of regulatory T cells (Tregs). However, the underlying mechanism that coordinates cell metabolism to regulate Treg activity is not completely understood. As a pivotal molecule in lipid metabolism, the role of SHIP-1 in Tregs remains unknown. In this study, we found SHIP-1 Treg KO mice (SHIP-1 specifically deleted in regulatory T cells) had severe autoimmunity with increased Tregs in the thymus and disrupted peripheral T cell homeostasis. Mechanistically, CD4Cre Ship-1flox/flox mice were found to have increased Treg precursors and SHIP-1 KO Tregs had reduced migration and stability, which caused decreased Tregs in the spleen. Additionally, the suppressive function of Tregs from SHIP-1 KO mice was diminished, along with their promotion of anti-tumor immunity. Interestingly, the PI3K-mTORC1, but not mTORC2, signaling axis was enhanced in SHIP-1 KO Tregs. In vivo treatment of SHIP-1 Treg KO mice with rapamycin rescued the abnormal Treg percentages and peripheral T cell homeostasis, as well as Treg suppressive function. Furthermore, the treatment of wild-type mice with SHIP-1 inhibitor enhanced anti-tumor activity. Our study highlights the SHIP-1-PI3K-mTORC1 axis that regulates Treg differentiation and function, and it is a potential target for cancer treatment.

Loss of Inpp5d has disease-relevant and sex-specific effects on glial transcriptomes

INTRODUCTION

Inpp5d is genetically associated with Alzheimer's disease risk. Loss of Inpp5d alters amyloid pathology in models of amyloidosis. Inpp5d is expressed predominantly in microglia but its function in brain is poorly understood.

METHODS

We performed single-cell RNA sequencing to study the effect of Inpp5d loss on wild-type mouse brain transcriptomes.

RESULTS

Loss of Inpp5d has sex-specific effects on the brain transcriptome. Affected genes are enriched for multiple neurodegeneration terms. Network analyses reveal a gene co-expression module centered around Inpp5d in female mice. Inpp5d loss alters Pleotrophin (PTN), Prosaposin (PSAP), and Vascular Endothelial Growth Factor A (VEGFA) signaling probability between cell types.

DISCUSSION

Our data suggest that the normal function of Inpp5d is entangled with mechanisms involved in neurodegeneration. We report the effect of Inpp5d loss without pathology and show that this has dramatic effects on gene expression. Our study provides a critical reference for researchers of neurodegeneration, allowing separation of disease-specific changes mediated by Inpp5d in disease from baseline effects of Inpp5d loss.

HIGHLIGHTS

Loss of Inpp5d has different effects in male and female mice. Genes dysregulated by Inpp5d loss relate to neurodegeneration. Total loss of Inpp5d in female mice collapses a conserved gene co-expression module. Loss of microglial Inpp5d affects the transcriptome of other cell types.

Ikaros sets the threshold for negative B-cell selection by regulation of the signaling strength of the AKT pathway

Inhibitory phosphatases, such as the inositol-5-phosphatase SHIP1 could potentially contribute to B-cell acute lymphoblastic leukemia (B-ALL) by raising the threshold for activation of the autoimmunity checkpoint, allowing malignant cells with strong oncogenic B-cell receptor signaling to escape negative selection. Here, we show that SHIP1 is differentially expressed across B-ALL subtypes and that high versus low SHIP1 expression is associated with specific B-ALL subgroups. In particular, we found high SHIP1 expression in both, Philadelphia chromosome (Ph)-positive and ETV6-RUNX1-rearranged B-ALL cells. As demonstrated by targeted knockdown of SHIP1 by RNA interference, proliferation of B-ALL cells in vitro and their tumorigenic spread in vivo depended in part on SHIP1 expression. We investigated the regulation of SHIP1, as an important antagonist of the AKT signaling pathway, by the B-cell-specific transcription factor Ikaros. Targeted restoration of Ikaros and pharmacological inhibition of the antagonistic casein kinase 2, led to a strong reduction in SHIP1 expression and at the same time to a significant inhibition of AKT activation and cell growth. Importantly, the tumor suppressive function of Ikaros was enhanced by a SHIP1-dependent additive effect. Furthermore, our study shows that all three AKT isoforms contribute to the pro-mitogenic and anti-apoptotic signaling in B-ALL cells. Conversely, hyperactivation of a single AKT isoform is sufficient to induce negative selection by increased oxidative stress. In summary, our study demonstrates the regulatory function of Ikaros on SHIP1 expression in B-ALL and highlights the relevance of sustained SHIP1 expression to prevent cells with hyperactivated PI3K/AKT/mTOR signaling from undergoing negative selection.

Phosphatidylinositol 3,4-bisphosphate: Out of the shadows and into the spotlight

Phosphoinositide 3-kinases regulate many cellular functions, including migration, growth, proliferation, and cell survival. Early studies equated the inhibition of Class I PI3Ks with loss of; phosphatidylinositol 3,4,5-trisphosphate (PIP3), but over time, it was realised that these; treatments also depleted phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2). In recent years, the; use of better tools and an improved understanding of its metabolism have allowed for the; identification of specific roles of PI(3,4)P2. This includes the production of PI(3,4)P2 and the; activation of its effector Akt2 in response to growth factor signalling. In contrast, a lysosomal pool of PI(3,4)P2 is a negative regulator of mTORC1 during growth factor deprivation. A growing body of literature also demonstrates that PI(3,4)P2 controls many dynamic plasmalemmal processes. The significance of PI(3,4)P2 in cell biology is increasingly evident.

Concomitant double-fusion of PLEKHA7-ALK and INPP5D-ALK reveals favorable alectinib sensitivity in lung adenocarcinoma: a case report and literature review

Anaplastic lymphoma kinase (ALK) gene fusion is a classic driver mutation in non-small cell lung cancer (NSCLC); however, ALK double-fusion variants in NSCLC have rarely been reported. In this study, we reported a case with extremely uncommon ALK double-fusion variants. A 32-year-old female diagnosed with lung adenocarcinoma, who had developed multiple intrapulmonary and brain metastases, experienced worsening of her condition despite undergoing prior chemotherapy. Subsequent testing using next-generation sequencing (NGS) detected the presence of PLEKHA7-ALK and INPP5D-ALK double-fusion. The prescription of alectinib revealed potent efficacy and resulted in an increase in the survival rate. This case presented two uncommon and concomitant ALK fusion partners in NSCLC; more importantly, the INPP5D-ALK subtype has not been reported, therefore this study broadens the spectrum of ALK double-fusion variants and provides insight into the use of ALK inhibitors for the treatment of NSCLC in patients with double ALK fusions.

Actin-binding protein profilin1 is an important determinant of cellular phosphoinositide control

Membrane polyphosphoinositides (PPIs) are lipid-signaling molecules that undergo metabolic turnover and influence a diverse range of cellular functions. PPIs regulate the activity and/or spatial localization of a number of actin-binding proteins (ABPs) through direct interactions; however, it is much less clear whether ABPs could also be an integral part in regulating PPI signaling. In this study, we show that ABP profilin1 (Pfn1) is an important molecular determinant of the cellular content of PI(4,5)P2 (the most abundant PPI in cells). In growth factor (EGF) stimulation setting, Pfn1 depletion does not impact PI(4,5)P2 hydrolysis but enhances plasma membrane (PM) enrichment of PPIs that are produced downstream of activated PI3-kinase, including PI(3,4,5)P3 and PI(3,4)P2, the latter consistent with increased PM recruitment of SH2-containing inositol 5' phosphatase (SHIP2) (a key enzyme for PI(3,4)P2 biosynthesis). Although Pfn1 binds to PPIs in vitro, our data suggest that Pfn1's affinity to PPIs and PM presence in actual cells, if at all, is negligible, suggesting that Pfn1 is unlikely to directly compete with SHIP2 for binding to PM PPIs. Additionally, we provide evidence for Pfn1's interaction with SHIP2 in cells and modulation of this interaction upon EGF stimulation, raising an alternative possibility of Pfn1 binding as a potential restrictive mechanism for PM recruitment of SHIP2. In conclusion, our findings challenge the dogma of Pfn1's binding to PM by PPI interaction, uncover a previously unrecognized role of Pfn1 in PI(4,5)P2 homeostasis and provide a new mechanistic avenue of how an ABP could potentially impact PI3K signaling byproducts in cells through lipid phosphatase control.

INPP5D regulates inflammasome activation in human microglia

Microglia and neuroinflammation play an important role in the development and progression of Alzheimer's disease (AD). Inositol polyphosphate-5-phosphatase D (INPP5D/SHIP1) is a myeloid-expressed gene genetically-associated with AD. Through unbiased analyses of RNA and protein profiles in INPP5D-disrupted iPSC-derived human microglia, we find that reduction in INPP5D activity is associated with molecular profiles consistent with disrupted autophagy and inflammasome activation. These findings are validated through targeted pharmacological experiments which demonstrate that reduced INPP5D activity induces the formation of the NLRP3 inflammasome, cleavage of CASP1, and secretion of IL-1β and IL-18. Further, in-depth analyses of human brain tissue across hundreds of individuals using a multi-analytic approach provides evidence that a reduction in function of INPP5D in microglia results in inflammasome activation in AD. These findings provide insights into the molecular mechanisms underlying microglia-mediated processes in AD and highlight the inflammasome as a potential therapeutic target for modulating INPP5D-mediated vulnerability to AD.

Microglial function, INPP5D/SHIP1 signaling, and NLRP3 inflammasome activation: implications for Alzheimer's disease

Recent genetic studies on Alzheimer's disease (AD) have brought microglia under the spotlight, as loci associated with AD risk are enriched in genes expressed in microglia. Several of these genes have been recognized for their central roles in microglial functions. Increasing evidence suggests that SHIP1, the protein encoded by the AD-associated gene INPP5D, is an important regulator of microglial phagocytosis and immune response. A recent study from our group identified SHIP1 as a negative regulator of the NLRP3 inflammasome in human iPSC-derived microglial cells (iMGs). In addition, we found evidence for a connection between SHIP1 activity and inflammasome activation in the AD brain. The NLRP3 inflammasome is a multiprotein complex that induces the secretion of pro-inflammatory cytokines as part of innate immune responses against pathogens and endogenous damage signals. Previously published studies have suggested that the NLRP3 inflammasome is activated in AD and contributes to AD-related pathology. Here, we provide an overview of the current understanding of the microglial NLRP3 inflammasome in the context of AD-related inflammation. We then review the known intracellular functions of SHIP1, including its role in phosphoinositide signaling, interactions with microglial phagocytic receptors such as TREM2 and evidence for its intersection with NLRP3 inflammasome signaling. Through rigorous examination of the intricate connections between microglial signaling pathways across several experimental systems and postmortem analyses, the field will be better equipped to tailor newly emerging therapeutic strategies targeting microglia in neurodegenerative diseases.

SHIP1 therapeutic target enablement: Identification and evaluation of inhibitors for the treatment of late-onset Alzheimer's disease

INTRODUCTION

The risk of developing Alzheimer's disease is associated with genes involved in microglial function. Inositol polyphosphate-5-phosphatase (INPP5D), which encodes Src homology 2 (SH2) domain-containing inositol polyphosphate 5-phosphatase 1 (SHIP1), is a risk gene expressed in microglia. Because SHIP1 binds receptor immunoreceptor tyrosine-based inhibitory motifs (ITIMs), competes with kinases, and converts PI(3,4,5)P3 to PI(3,4)P2, it is a negative regulator of microglia function. Validated inhibitors are needed to evaluate SHIP1 as a potential therapeutic target.

METHODS

We identified inhibitors and screened the enzymatic domain of SHIP1. A protein construct containing two domains was used to evaluate enzyme inhibitor potency and selectivity versus SHIP2. Inhibitors were tested against a construct containing all ordered domains of the human and mouse proteins. A cellular thermal shift assay (CETSA) provided evidence of target engagement in cells. Phospho-AKT levels provided further evidence of on-target pharmacology. A high-content imaging assay was used to study the pharmacology of SHIP1 inhibition while monitoring cell health. Physicochemical and absorption, distribution, metabolism, and excretion (ADME) properties were evaluated to select a compound suitable for in vivo studies.

RESULTS

SHIP1 inhibitors displayed a remarkable array of activities and cellular pharmacology. Inhibitory potency was dependent on the protein construct used to assess enzymatic activity. Some inhibitors failed to engage the target in cells. Inhibitors that were active in the CETSA consistently destabilized the protein and reduced pAKT levels. Many SHIP1 inhibitors were cytotoxic either at high concentration due to cell stress or they potently induced cell death depending on the compound and cell type. One compound activated microglia, inducing phagocytosis at concentrations that did not result in significant cell death. A pharmacokinetic study demonstrated brain exposures in mice upon oral administration.

DISCUSSION

3-((2,4-Dichlorobenzyl)oxy)-5-(1-(piperidin-4-yl)-1H-pyrazol-4-yl) pyridine activated primary mouse microglia and demonstrated exposures in mouse brain upon oral dosing. Although this compound is our recommended chemical probe for investigating the pharmacology of SHIP1 inhibition at this time, further optimization is required for clinical studies.

Highlights

Cellular thermal shift assay (CETSA) and signaling (pAKT) assays were developed to provide evidence of src homology 2 (SH2) domain-contaning inositol phosphatase 1 (SHIP1) target engagement and on-target activity in cellular assays.A phenotypic high-content imaging assay with simultaneous measures of phagocytosis, cell number, and nuclear intensity was developed to explore cellular pharmacology and monitor cell health.SHIP1 inhibitors demonstrate a wide range of activity and cellular pharmacology, and many reported inhibitors are cytotoxic.The chemical probe 3-((2,4-dichlorobenzyl)oxy)-5-(1-(piperidin-4-yl)-1H-pyrazol-4-yl) pyridine is recommended to explore SHIP1 pharmacology.

INPP5D/SHIP1: Expression, Regulation and Roles in Alzheimer's Disease Pathophysiology

Alzheimer's disease (AD) is the most common form of dementia, accounting for approximately 38.5 million cases of all-cause dementia. Over 60% of these individuals live in low- and middle-income countries and are the worst affected, especially by its deleterious effects on the productivity of both patients and caregivers. Numerous risk factors for the disease have been identified and our understanding of gene-environment interactions have shed light on several gene variants that contribute to the most common, sporadic form of AD. Microglial cells, the innate immune cells of the central nervous system (CNS), have long been established as guardians of the brain by providing neuroprotection and maintaining cellular homeostasis. A protein with a myriad of effects on various important signaling pathways that is expressed in microglia is the Src Homology 2 (SH2) domain-containing Inositol 5' Phosphatase 1 (SHIP1) protein. Encoded by the INPP5D (Inositol Polyphosphate-5-Phosphatase D) gene, SHIP1 has diminutive effects on most microglia signaling processes. Polymorphisms of the INPP5D gene have been found to be associated with a significantly increased risk of AD. Several studies have elucidated mechanistic processes by which SHIP1 exerts its perturbations on signaling processes in peripheral immune cells. However, current knowledge of the controllers of INPP5D/SHIP1 expression and the idiosyncrasies of its influences on signaling processes in microglia and their relevance to AD pathophysiology is limited. In this review, we summarize these discoveries and discuss the potential of leveraging INPP5D/SHIP1 as a therapeutic target for Alzheimer's disease.

SHIP1 Is Present but Strongly Downregulated in T-ALL, and after Restoration Suppresses Leukemia Growth in a T-ALL Xenotransplantation Mouse Model

Acute lymphoblastic leukemia (ALL) is the most common cause of cancer-related death in children. Despite significantly increased chances of cure, especially for high-risk ALL patients, it still represents a poor prognosis for a substantial fraction of patients. Misregulated proteins in central switching points of the cellular signaling pathways represent potentially important therapeutic targets. Recently, the inositol phosphatase SHIP1 (SH2-containing inositol 5-phosphatase) has been considered as a tumor suppressor in leukemia. SHIP1 serves as an important negative regulator of the PI3K/AKT signaling pathway, which is frequently constitutively activated in primary T-ALL. In contrast to other reports, we show for the first time that SHIP1 has not been lost in T-ALL cells, but is strongly downregulated. Reduced expression of SHIP1 leads to an increased activation of the PI3K/AKT signaling pathway. SHIP1-mRNA expression is frequently reduced in primary T-ALL samples, which is recapitulated by the decrease in SHIP1 expression at the protein level in seven out of eight available T-ALL patient samples. In addition, we investigated the change in the activity profile of tyrosine and serine/threonine kinases after the restoration of SHIP1 expression in Jurkat T-ALL cells. The tyrosine kinase receptor subfamilies of NTRK and PDGFR, which are upregulated in T-ALL subgroups with low SHIP1 expression, are significantly disabled after SHIP1 reconstitution. Lentiviral-mediated reconstitution of SHIP1 expression in Jurkat cells points to a decreased cellular proliferation upon transplantation into NSG mice in comparison to the control cohort. Together, our findings will help to elucidate the complex network of cell signaling proteins, further support a functional role for SHIP1 as tumor suppressor in T-ALL and, much more importantly, show that full-length SHIP1 is expressed in T-ALL samples.

Targeted hyperactivation of AKT through inhibition of ectopic expressed SHIP1 induces cell death in colon carcinoma cells and derived metastases

Current therapeutic approaches for colorectal cancer (CRC) focus on the suppression of oncogenic kinase signaling. Here, we test the hypothesis that targeted hyperactivation of the PI3K/AKT-signaling may lead to trigger CRC cell death. Recently we found that hematopoietic SHIP1 is ectopically expressed in CRC cells. Here we show that SHIP1 is more strongly expressed in metastatic cells than in the primary cancer cells, which allows for an increase in AKT signaling in metastatic cells, giving them an advantage from an evolutionary point of view. Mechanistically, the increased SHIP1 expression reduces the activation of the PI3K/ AKT signaling to a value that is below the threshold that leads to cell death. This mechanism gives the cell a selection advantage. We show that genetic hyperactivation of PI3K/AKT-signaling or blocking the activity of the inhibitory phosphatase SHIP1, induces acute cell death in CRC cells, because of excessive accumulation of reactive oxygen species. Our results demonstrate that CRC cells critically depend on mechanisms to fine-tune PI3K/AKT activity and show SHIP1 inhibition as an unexpectedly promising concept for CRC therapy.

Potential Pathogenic Impact of Cow’s Milk Consumption and Bovine Milk-Derived Exosomal MicroRNAs in Diffuse Large B-Cell Lymphoma

Epidemiological evidence supports an association between cow’s milk consumption and the risk of diffuse large B-cell lymphoma (DLBCL), the most common non-Hodgkin lymphoma worldwide. This narrative review intends to elucidate the potential impact of milk-related agents, predominantly milk-derived exosomes (MDEs) and their microRNAs (miRs) in lymphomagenesis. Upregulation of PI3K-AKT-mTORC1 signaling is a common feature of DLBCL. Increased expression of B cell lymphoma 6 (BCL6) and suppression of B lymphocyte-induced maturation protein 1 (BLIMP1)/PR domain-containing protein 1 (PRDM1) are crucial pathological deviations in DLBCL. Translational evidence indicates that during the breastfeeding period, human MDE miRs support B cell proliferation via epigenetic upregulation of BCL6 (via miR-148a-3p-mediated suppression of DNA methyltransferase 1 (DNMT1) and miR-155-5p/miR-29b-5p-mediated suppression of activation-induced cytidine deaminase (AICDA) and suppression of BLIMP1 (via MDE let-7-5p/miR-125b-5p-targeting of PRDM1). After weaning with the physiological termination of MDE miR signaling, the infant’s BCL6 expression and B cell proliferation declines, whereas BLIMP1-mediated B cell maturation for adequate own antibody production rises. Because human and bovine MDE miRs share identical nucleotide sequences, the consumption of pasteurized cow’s milk in adults with the continued transfer of bioactive bovine MDE miRs may de-differentiate B cells back to the neonatal “proliferation-dominated” B cell phenotype maintaining an increased BLC6/BLIMP1 ratio. Persistent milk-induced epigenetic dysregulation of BCL6 and BLIMP1 expression may thus represent a novel driving mechanism in B cell lymphomagenesis. Bovine MDEs and their miR cargo have to be considered potential pathogens that should be removed from the human food chain.

Activated Src kinases downstream of BCR-ABL and Flt3 induces proteasomal degradation of SHIP1 by phosphorylation of tyrosine 1021

Within the various subtypes of ALL, patients with a BCR-ABL-positive background as well as with a genetic change in the KMT2A gene have by far the worst survival probabilities. Interestingly, both subtypes are characterized by highly activated tyrosine kinases. SHIP1 serves as an important negative regulator of the PI3K/AKT signaling pathway, which is often constitutively activated in ALL. The protein expression of SHIP1 is decreased in most T-ALL and in some subgroups of B-ALL. In this study, we analyzed the expression of SHIP1 protein in detail in the context of groups with aberrant activated tyrosine kinases, namely BCR-ABL (Ph+) and Flt3 (KMT2A translocations). We demonstrate that constitutively activated Src kinases downstream of BCR-ABL and receptor tyrosine kinases reduce the SHIP1 expression in a SHIP1-Y1021 phosphorylated-dependent manner with subsequent ubiquitin marked proteasomal degradation. Inhibition of BCR-ABL (Imatinib), Flt3 (Quizartinib) or Src-Kinase-Family (Saracatinib) leads to significant reconstitution of SHIP1 protein expression. These results further support a functional role of SHIP1 as tumor suppressor protein and could be the basis for the establishment of a targeted therapy form.

INPP5D/SHIP1 regulates inflammasome activation in human microglia

Microglia and neuroinflammation are implicated in the development and progression of Alzheimer's disease (AD). To better understand microglia-mediated processes in AD, we studied the function of INPP5D/SHIP1, a gene linked to AD through GWAS. Immunostaining and single nucleus RNA sequencing confirmed that INPP5D expression in the adult human brain is largely restricted to microglia. Examination of prefrontal cortex across a large cohort revealed reduced full length INPP5D protein levels in AD patient brains compared to cognitively normal controls. The functional consequences of reduced INPP5D activity were evaluated in human induced pluripotent stem cell derived microglia (iMGLs), using both pharmacological inhibition of the phosphatase activity of INPP5D and genetic reduction in copy number. Unbiased transcriptional and proteomic profiling of iMGLs suggested an upregulation of innate immune signaling pathways, lower levels of scavenger receptors, and altered inflammasome signaling with INPP5D reduction. INPP5D inhibition induced the secretion of IL-1ß and IL-18, further implicating inflammasome activation. Inflammasome activation was confirmed through visualization of inflammasome formation through ASC immunostaining in INPP5D-inhibited iMGLs, increased cleaved caspase-1 and through rescue of elevated IL-1ß and IL-18 with caspase-1 and NLRP3 inhibitors. This work implicates INPP5D as a regulator of inflammasome signaling in human microglia.

Reduced expression and activity of patient-derived SHIP1 phosphatase domain mutants

The characterization of dysregulated proteins in cell signaling pathways is important for the development of therapeutic approaches. The PI3K/AKT/mTOR pathway is frequently upregulated in cancer cells and the SH2-containing inositol 5-phosphatase SHIP1 can act as a negative regulator of the PI3K/AKT pathway. In this study, we investigated different patient-derived mutations within the conserved phosphatase domain of SHIP1. We could demonstrate that 2 out of 7 SHIP1-phosphatase domain mutations (G585K and R673Q) possessed reduced protein expression and reduced enzymatic activity in comparison to SHIP1 wild type (WT) protein and two additional mutations (E452K, R551Q) possessed reduced enzymatic activity at a comparable expression level compared to SHIP1 WT in the cell line H1299. The investigated mutations resulted in protein expression levels that were up to 93% lower than those of the SHIP1 WT for SHIP1 mutant R673Q and the enzymatic activity was below the detection limit of the performed phosphatase assay. Whereas the protein level of the R673Q mutant was reduced in comparison to SHIP1 WT the mRNA level was comparable indicating a post-transcriptional regulation. SHIP1 R673Q was rapidly degraded, with a calculated half-life of l.5 h. In addition, SHIP1 R673Q levels were significantly increased by the treatment with the proteasome inhibitor MG-132 in comparison to the DMSO control. Therefore, SHIP1 was confirmed as the target of enhanced proteasomal degradation. Computational analysis of the wild type and mutant protein structures revealed that the loss of the positively charged arginine residue R673 is associated with the loss of two salt bridges to the negatively charged amino acids D617 and E634 leading to an intramolecular instability of the mutated SHIP1 R673Q protein. Six out of seven SHIP1 mutants significantly affected the PI3K/AKT/mTOR pathway in the three cancer cell lines H1299, Reh and Sem. Four out of seven SHIP1 mutants affected phosphorylation of AKT and its target GSK3β positively compared to SHIP1 WT, whereas a negative effect on the phosphorylation of S6 was found in five out of seven mutants. In general, SHIP1 mutants impacting signal transduction were either associated with decreased SHIP1 activity or SHIP1 expression or both. Overall, the presented results indicate a regulation of the protein expression and activity of SHIP1 by patient-derived mutations in its phosphatase domain.

Pathological Roles of INPP5D in Alzheimer's Disease

Current hypothesis of Alzheimer's disease (AD) postulates that amyloid β (Aβ) deposition in the brain causes tau inclusion in neurons and leads to cognitive decline. The discovery of the genetic association between triggering receptor expressed on myeloid cells 2 (TREM2) with increased AD risk points to a causal link between microglia and AD pathogenesis, and revealed a crucial role of TREM2-dependent clustering of microglia around amyloid plaques that prevents Aβ toxicity to facilitate tau deposition near the plaques. Here we review the physiological and pathological roles of another AD risk gene expressed in microglia, inositol polyphosphate-5-polyphosphatase D (INPP5D), which encodes a phosphoinositide phosphatase. Evidence suggests that its risk polymorphisms alter the expression level and/or function of INPP5D, while concomitantly affecting tau levels in cerebrospinal fluids. In β-amyloidosis mice, INPP5D was upregulated upon Aβ deposition and negatively regulated the microglial clustering toward amyloid plaques. INPP5D seems to exert its function by acting antagonistically at downstream of the TREM2 signaling pathway, suggesting that it is a novel regulator of the protective barrier by microglia. Further studies to elucidate INPP5D's role in AD may help in developing new therapeutic targets for AD treatment.

Identification and Prioritization of PET Neuroimaging Targets for Microglial Phenotypes Associated with Microglial Activity in Alzheimer's Disease

Activation of microglial cells accompanies the progression of many neurodegenerative disorders, including Alzheimer's disease (AD). Development of molecular imaging tools specific to microglia can help elucidate the mechanism through which microglia contribute to the pathogenesis and progression of neurodegenerative disorders. Through analysis of published genetic, transcriptomic, and proteomic data sets, we identified 19 genes with microglia-specific expression that we then ranked based on association with the AD characteristics, change in expression, and potential druggability of the target. We believe that the process we used to identify and rank microglia-specific genes is broadly applicable to the identification and evaluation of targets in other disease areas and for applications beyond molecular imaging.

Myo-D-inositol Trisphosphate Signalling in Oomycetes

Oomycetes are pathogens of plants and animals, which cause billions of dollars of global losses to the agriculture, aquaculture and forestry sectors each year. These organisms superficially resemble fungi, with an archetype being Phytophthora infestans, the cause of late blight of tomatoes and potatoes. Comparison of the physiology of oomycetes with that of other organisms, such as plants and animals, may provide new routes to selectively combat these pathogens. In most eukaryotes, myo-inositol 1,4,5 trisphosphate is a key second messenger that links extracellular stimuli to increases in cytoplasmic Ca2+, to regulate cellular activities. In the work presented in this study, investigation of the molecular components of myo-inositol 1,4,5 trisphosphate signaling in oomycetes has unveiled similarities and differences with that in other eukaryotes. Most striking is that several oomycete species lack detectable phosphoinositide-selective phospholipase C homologues, the enzyme family that generates this second messenger, but still possess relatives of myo-inositol 1,4,5 trisphosphate-gated Ca2+-channels.

Modulation of IL-4/IL-13 cytokine signaling in the context of allergic disease

Aberrant activation of CD4 T_H2 cells and excessive production of T_H2 cytokines such as IL-4 and IL-13 have been implicated in the pathogenesis of allergic diseases. Generally, IL-4 and IL-13 utilize Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathways for induction of inflammatory gene expression and the effector functions associated with disease pathology in many allergic diseases. However, it is increasingly clear that JAK/STAT pathways activated by IL-4/IL-13 can themselves be modulated in the presence of other intracellular signaling programs, thereby changing the overall tone and/or magnitude of IL-4/IL-13 signaling. Apart from direct activation of the canonic JAK/STAT pathways, IL-4 and IL-13 also induce proinflammatory gene expression and effector functions through activation of additional signaling cascades. These alternative signaling cascades contribute to several specific aspects of IL-4/IL-13-associated cellular and molecular responses. A more complete understanding of IL-4/IL-13 signaling pathways, including the precise conditions under which noncanonic signaling pathways are activated, and the impact of these pathways on cellular- and host-level responses, will better allow us to design agents that target specific pathologic outcomes or tailor therapies for the treatment of uncommon disease endotypes.

JAK2-V617F is a negative regulation factor of SHIP1 protein and thus influences the AKT signaling pathway in patients with Myeloproliferative Neoplasm (MPN)

BACKGROUND

Myeloproliferative neoplasms (MPN) are a group of chronic haematological disorders. At the molecular level of MPN cells, the gain-of-function mutation V617F of the Janus kinase 2 (JAK2) leads to a constitutive activation of the downstream signaling cascade and is a conventional criteria for diagnosis. Here, the functional role of the tumor suppressor SHIP1 (SH2 domain containing inositol-5 phosphatase 1) in the pathogenesis of MPNs was investigated.

METHODS

Primary blood samples of MPN-patients were analysed using Western Blot technique regarding the level of SHIP1 expression. Moreover, SHIP1 and SHIP1-mutations were lentivirally transduced in the JAK2-V617F-positive UKE-1 cell line and expression was monitored over time. In addition, we examined SHIP1 reconstitution by inhibition of JAK2-V617F. Furthermore, we transfected SHIP1-expressing cells with a JAK2-V617F respectively a BCR-ABL construct and investigated changes in SHIP1 expression.

RESULTS

Four out of five MPN-patient samples showed a loss or a reduction in SHIP1 expression. We identified JAK2 as a negative regulator of SHIP1 expression in MPN cells and inhibition of JAK2-V617F implicates a reconstituted SHIP1 expression. This is significant because SHIP1 negatively regulates the AKT signaling pathway and in consequence the reconstitution of SHIP1 expression leads to a decreased cell growth. Moreover, we examined the impact of SHIP1 and patient-derived SHIP1-mutations on AKT phosphorylation and show the benefit of a combined therapy in MPN cells with inhibitors of the AKT/mTOR pathway.

CONCLUSION

In summary, the data suggest that SHIP1 may play a role during the development of MPNs and could be the basis for establishing a targeted therapy.

SENP1 promotes MCL pathogenesis through regulating JAK-STAT5 pathway and SOCS2 expression

Mantle cell lymphoma (MCL) is highly aggressive and its treatment remains challenging, understanding its pathogenesis is critical for future targeted therapy. SUMO specific proteases 1 (SENP1) is an important protein that regulates the balance between SUMOylation and deSUMOylation. We found that SENP1 was upregulated in MCL patient samples and cell lines. Knockdown of SENP1 could inhibit the proliferation and promote the apoptosis of MCL cells. We also found that SENP1 knockdown caused inhibition of the JAK-STAT5 pathway and upregulation of tumor suppressor cytokine signaling 2 (SOCS2). Moreover, MCL tumor growth in vivo was significantly suppressed after SENP1 knockdown in a xenograft nude mouse model. In summary, our results showed that SENP1 is involved in the pathogenesis of MCL and may be a potential therapeutic target.

The Crossroads between RAS and RHO Signaling Pathways in Cellular Transformation, Motility and Contraction

Ras and Rho proteins are GTP-regulated molecular switches that control multiple signaling pathways in eukaryotic cells. Ras was among the first identified oncogenes, and it appears mutated in many forms of human cancer. It mainly promotes proliferation and survival through the MAPK pathway and the PI3K/AKT pathways, respectively. However, the myriad proteins close to the plasma membrane that activate or inhibit Ras make it a major regulator of many apparently unrelated pathways. On the other hand, Rho is weakly oncogenic by itself, but it critically regulates microfilament dynamics; that is, actin polymerization, disassembly and contraction. Polymerization is driven mainly by the Arp2/3 complex and formins, whereas contraction depends on myosin mini-filament assembly and activity. These two pathways intersect at numerous points: from Ras-dependent triggering of Rho activators, some of which act through PI3K, to mechanical feedback driven by actomyosin action. Here, we describe the main points of connection between the Ras and Rho pathways as they coordinately drive oncogenic transformation. We emphasize the biochemical crosstalk that drives actomyosin contraction driven by Ras in a Rho-dependent manner. We also describe possible routes of mechanical feedback through which myosin II activation may control Ras/Rho activation.

GPI-AP: Unraveling a New Class of Malignancy Mediators and Potential Immunotherapy Targets

With millions of cases diagnosed annually and high economic burden to cover expensive costs, cancer is one of the most difficult diseases to treat due to late diagnosis and severe adverse effects from conventional therapy. This creates an urgent need to find new targets for early diagnosis and therapy. Progress in research revealed the key steps of carcinogenesis. They are called cancer hallmarks. Zooming in, cancer hallmarks are characterized by ligands binding to their cognate receptor and so triggering signaling cascade within cell to make response for stimulus. Accordingly, understanding membrane topology is vital. In this review, we shall discuss one type of transmembrane proteins: Glycosylphosphatidylinositol-Anchored Proteins (GPI-APs), with specific emphasis on those involved in tumor cells by evading immune surveillance and future applications for diagnosis and immune targeted therapy.

PTEN and Other PtdIns(3,4,5)P3 Lipid Phosphatases in Breast Cancer

The phosphoinositide 3-kinase (PI3K)/AKT signalling pathway is hyperactivated in ~70% of breast cancers. Class I PI3K generates PtdIns(3,4,5)P₃ at the plasma membrane in response to growth factor stimulation, leading to AKT activation to drive cell proliferation, survival and migration. PTEN negatively regulates PI3K/AKT signalling by dephosphorylating PtdIns(3,4,5)P₃ to form PtdIns(4,5)P₂. PtdIns(3,4,5)P₃ can also be hydrolysed by the inositol polyphosphate 5-phosphatases (5-phosphatases) to produce PtdIns(3,4)P₂. Interestingly, while PTEN is a bona fide tumour suppressor and is frequently mutated/lost in breast cancer, 5-phosphatases such as PIPP, SHIP2 and SYNJ2, have demonstrated more diverse roles in regulating mammary tumourigenesis. Reduced PIPP expression is associated with triple negative breast cancers and reduced relapse-free and overall survival. Although PIPP depletion enhances AKT phosphorylation and supports tumour growth, this also inhibits cell migration and metastasis in vivo, in a breast cancer oncogene-driven murine model. Paradoxically, SHIP2 and SYNJ2 are increased in primary breast tumours, which correlates with invasive disease and reduced survival. SHIP2 or SYNJ2 overexpression promotes breast tumourigenesis via AKT-dependent and independent mechanisms. This review will discuss how PTEN, PIPP, SHIP2 and SYNJ2 distinctly regulate multiple functional targets, and the mechanisms by which dysregulation of these distinct phosphoinositide phosphatases differentially affect breast cancer progression.

From beta amyloid to altered proteostasis in Alzheimer's disease

Alzheimer's disease (AD) is an age related neurodegenerative disorder causing severe disability and important socio-economic burden, but with no cure available to date. To disentangle this puzzling disease genetic studies represented an important way for the comprehension of pathogenic mechanisms. Abnormal processing and accumulation of amyloid-β peptide (Aβ) has been considered the main cause and trigger factor of the disease. The amyloid cascade theory has fallen into crisis because the failure of several anti-amyloid drugs trials and because of the simple equation AD = abnormal Aβ deposition is not always the case. We now know that multiple neurodegenerative diseases share common pathogenic mechanisms leading to accumulation of misfolded protein species. Genome Wide Association studies (GWAS) led to the identification of large numbers of DNA common variants (SNPs) distributed on different chromosomes and modulating the Alzheimer's risk. GWAS genes fall into several common pathways such as immune system and neuroinflammation, lipid metabolism, synaptic dysfunction and endocytosis, all of them addressing to novel routes for different pathogenic mechanisms. Other hints could be derived from epidemiological and experimental studies showing some lifestyles may have a major role in the pathogenesis of many age-associated diseases by modifying cell metabolism, proteostasis and microglia mediated neuroinflammation.

Characterization of the substrate specificity of the inositol 5-phosphatase SHIP1

SHIP1 is an inositol 5-phosphatase which is well established for its tumour suppressor potential in leukaemia. Enzymatically, two SHIP1 substrates, PtdIns(3,4,5)P₃ and Ins(1,3,4,5)P₄ have been identified to date. Additional substrates were found for the homologue SHIP2. In this study, we identified new inositol phosphate (InsP) substrates of SHIP1 by metal dye detection high-performance liquid chromatography and compared the substrate profiles of SHIP1 and SHIP2. We were able to verify Ins(1,3,4,5)P₄ as a substrate of SHIP1 and interestingly found Ins(1,2,3,4,5)P₅ and Ins(2,3,4,5)P₄ to be preferably used as substrates and Ins(1,4,5,6)P₄ and Ins(2,4,5,6)P₄ to be weak substrates. All of those except Ins(2,3,4,5)P₄ are also known substrates of SHIP2 indicating a possible exclusive role of Ins(2,3,4,5)P₄ hydrolysis for SHIP1 but not SHIP2 function.

Pan-SHIP1/2 inhibitors promote microglia effector functions essential for CNS homeostasis

We show here that both SHIP1 (Inpp5d) and its paralog SHIP2 (Inppl1) are expressed at protein level in microglia. To examine whether targeting of SHIP paralogs might influence microglial physiology and function, we tested the capacity of SHIP1-selective, SHIP2-selective and pan-SHIP1/2 inhibitors for their ability to impact on microglia proliferation, lysosomal compartment size and phagocytic function. We find that highly potent pan-SHIP1/2 inhibitors can significantly increase lysosomal compartment size, and phagocytosis of dead neurons and amyloid beta (Aβ)1-42 by microglia in vitro We show that one of the more-potent and water-soluble pan-SHIP1/2 inhibitors, K161, can penetrate the blood-brain barrier. Consistent with this, K161 increases the capacity of CNS-resident microglia to phagocytose Aβ and apoptotic neurons following systemic administration. These findings provide the first demonstration that small molecule modulation of microglia function in vivo is feasible, and suggest that dual inhibition of the SHIP1 and 2 paralogs can provide a novel means to enhance basal microglial homeostatic functions for therapeutic purposes in Alzheimer's disease and, possibly, other types of dementia where increased microglial function could be beneficial.

Overexpression of SH2-Containing Inositol Phosphatase Contributes to Chronic Lymphocytic Leukemia Survival

Balanced activity of kinases and phosphatases downstream of the BCR is essential for B cell differentiation and function and is disturbed in chronic lymphocytic leukemia (CLL). In this study, we employed IgH.TEμ mice, which spontaneously develop CLL, and stable EMC CLL cell lines derived from these mice to explore the role of phosphatases in CLL. Genome-wide expression profiling comparing IgH.TEμ CLL cells with wild-type splenic B cells identified 96 differentially expressed phosphatase genes, including SH2-containing inositol phosphatase (Ship2). We found that B cell-specific deletion of Ship2, but not of its close homolog Ship1, significantly reduced CLL formation in IgH.TEμ mice. Treatment of EMC cell lines with Ship1/2 small molecule inhibitors resulted in the induction of caspase-dependent apoptosis. Using flow cytometry and Western blot analysis, we observed that blocking Ship1/2 abrogated EMC cell survival by exerting dual effects on the BCR signaling cascade. On one hand, specific Ship1 inhibition enhanced calcium signaling and thereby abrogated an anergic response to BCR stimulation in CLL cells. On the other hand, concomitant Ship1/Ship2 inhibition or specific Ship2 inhibition reduced constitutive activation of the mTORC1/ribosomal protein S6 pathway and downregulated constitutive expression of the antiapoptotic protein Mcl-1, in both EMC cell lines and primary IgH.TEμ CLL cells. Importantly, also in human CLL, we found overexpression of many phosphatases including SHIP2. Inhibition of SHIP1/SHIP2 reduced cellular survival and S6 phosphorylation and enhanced basal calcium levels in human CLL cells. Taken together, we provide evidence that SHIP2 contributes to CLL pathogenesis in mouse and human CLL.

The Msp Protein of Treponema denticola Interrupts Activity of Phosphoinositide Processing in Neutrophils

Periodontal disease is a significant health burden, causing tooth loss and poor oral and overall systemic health. Dysbiosis of the oral biofilm and a dysfunctional immune response drive chronic inflammation, causing destruction of soft tissue and alveolar bone supporting the teeth. Treponema denticola, a spirochete abundant in the plaque biofilm of patients with severe periodontal disease, perturbs neutrophil function by modulating appropriate phosphoinositide (PIP) signaling. Through a series of immunoblotting and quantitative PCR (qPCR) experiments, we show that Msp does not alter the gene transcription or protein content of key enzymes responsible for PIP3 signaling: 3' phosphatase and tensin homolog (PTEN), phosphatidylinositol 3-kinase (PI3K), or 5' Src homology 2 domain-containing inositol phosphatase 1 (SHIP1). Instead, using immunoblotting and enzyme-linked immunosorbent assays (ELISAs), we found that Msp activates PTEN through dephosphorylation specifically at the S380 site. Msp in intact organisms or outer membrane vesicles also restricts PIP signaling. SHIP1 phosphatase release was assessed using chemical inhibition and immunoprecipitation to show that Msp moderately decreases SHIP1 activity. Msp also prevents secondary activation of the PTEN/PI3K response. We speculate that this result is due to the redirection of the PIP3 substrate away from SHIP1 to PTEN. Immunofluorescence microscopy revealed a redistribution of PTEN from the cytoplasm to the plasma membrane following exposure to Msp, which may contribute to PTEN activation. Mechanisms of how T. denticola modulates and evades the host immune response are still poorly described, and here we provide further mechanistic evidence of how spirochetes modify PIP signaling to dampen neutrophil function. Understanding how oral bacteria evade the immune response to perpetuate the cycle of inflammation and infection is critical for combating periodontal disease to improve overall health outcomes.

Acute Lymphoblastic Leukemia With INPP5D-ABL1 Fusion Responds to Imatinib Treatment

We describe a patient with Down syndrome whose precursor B-cell acute lymphoblastic leukemia cells expressed INPP5D-ABL1 fusion gene that resulted in a reciprocal chromosome translocation t(2;9)(q27;q34). The fusion gene was present as a small subclone in the primary disease but was first identified at relapse when the subclone had expanded into a major clone. At relapse, the patient responded poorly to conventional induction chemotherapy but a transient morphologic remission was achieved after administration of imatinib monotherapy. This case demonstrates a pathway to relapse in a Down syndrome patients with acute lymphoblastic leukemia through a rare fusion event. It highlights the significance of minor subclonal events in therapy resistance and the opportunity provided for targeted therapy.

Analysis of the FLVR motif of SHIP1 and its importance for the protein stability of SH2 containing signaling proteins

Binding of proteins with SH2 domains to tyrosine-phosphorylated signaling proteins is a key mechanism for transmission of biological signals within the cell. Characterization of dysregulated proteins in cell signaling pathways is important for the development of therapeutic approaches. The AKT pathway is a frequently upregulated pathway in most cancer cells and the SH2-containing inositol 5-phosphatase SHIP1 is a negative regulator of the AKT pathway. In this study we investigated different mutations of the conserved FLVR motif of the SH2 domain and putative phosphorylation sites of SHIP1 which are located in close proximity to its FLVR motif. We demonstrate that patient-derived SHIP1-FLVR motif mutations e.g. F28L, and L29F possess reduced protein expression and increased phospho-AKT-S473 levels in comparison to SHIP1 wildtype. The estimated half-life of SHIP1-F28L protein was reduced from 23.2 h to 0.89 h in TF-1 cells and from 4.7 h to 0.6 h in Jurkat cells. These data indicate that the phenylalanine residue at position 28 of SHIP1 is important for its stability. Replacement of F28 with other aromatic residues like tyrosine and tryptophan preserves protein stability while replacement with non-aromatic amino acids like leucine, isoleucine, valine or alanine severely affects the stability of SHIP1. In consequence, a SHIP1-mutant with an aromatic amino acid at position 28 i.e. F28W can rescue the inhibitory function of wild type SHIP1, whereas SHIP1-mutants with non-aromatic amino acids i.e. F28V do not inhibit cell growth anymore. A detailed structural analysis revealed that F28 forms hydrophobic surface contacts in particular with W5, I83, L97 and P100 which can be maintained by tyrosine and tryptophan residues, but not by non-aromatic residues at position 28. In line with this model of mutation-induced instability of SHIP1-F28L, treatment of cells with proteasomal inhibitor MG132 was able to rescue expression of SHIP1-F28L. In addition, mutation of putative phosphorylation sites S27 and S33 adjacent to the FLVR motif of SHIP1 have an influence on its protein stability. These results further support a functional role of SHIP1 as tumor suppressor protein and indicate a regulation of protein expression of SH2 domain containing proteins via the FLVR motif.

Nuclear Phosphoinositides-Versatile Regulators of Genome Functions

The many functions of phosphoinositides in cytosolic signaling were extensively studied; however, their activities in the cell nucleus are much less clear. In this review, we summarize data about their nuclear localization and metabolism, and review the available literature on their involvements in chromatin remodeling, gene transcription, and RNA processing. We discuss the molecular mechanisms via which nuclear phosphoinositides, in particular phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2), modulate nuclear processes. We focus on PI(4,5)P2’s role in the modulation of RNA polymerase I activity, and functions of the nuclear lipid islets—recently described nucleoplasmic PI(4,5)P2-rich compartment involved in RNA polymerase II transcription. In conclusion, the high impact of the phosphoinositide–protein complexes on nuclear organization and genome functions is only now emerging and deserves further thorough studies.

A high-avidity biosensor reveals plasma membrane PI(3,4)P2 is predominantly a class I PI3K signaling product

Class I phosphoinositide 3-OH kinase (PI3K) signaling is central to animal growth and metabolism, and pathological disruption of this pathway affects cancer and diabetes. However, the specific spatial/temporal dynamics and signaling roles of its minor lipid messenger, phosphatidylinositol (3,4)-bisphosphate (PI(3,4)P₂), are not well understood. This owes principally to a lack of tools to study this scarce lipid. Here we developed a high-sensitivity genetically encoded biosensor for PI(3,4)P₂, demonstrating high selectivity and specificity of the sensor for the lipid. We show that despite clear evidence for class II PI3K in PI(3,4)P₂-driven function, the overwhelming majority of the lipid accumulates through degradation of class I PI3K-produced PIP₃ However, we show that PI(3,4)P₂ is also subject to hydrolysis by the tumor suppressor lipid phosphatase PTEN. Collectively, our results show that PI(3,4)P₂ is potentially an important driver of class I PI3K-driven signaling and provides powerful new tools to begin to resolve the biological functions of this lipid downstream of class I and II PI3K.

Class I Phosphoinositide 3-Kinase PIK3CA/p110α and PIK3CB/p110β Isoforms in Endometrial Cancer

The phosphoinositide 3-kinase (PI3K) signalling pathway is highly dysregulated in cancer, leading to elevated PI3K signalling and altered cellular processes that contribute to tumour development. The pathway is normally orchestrated by class I PI3K enzymes and negatively regulated by the phosphatase and tensin homologue, PTEN. Endometrial carcinomas harbour frequent alterations in components of the pathway, including changes in gene copy number and mutations, in particular in the oncogene PIK3CA, the gene encoding the PI3K catalytic subunit p110α, and the tumour suppressor PTEN. PIK3CB, encoding the other ubiquitously expressed class I isoform p110β, is less frequently altered but the few mutations identified to date are oncogenic. This isoform has received more research interest in recent years, particularly since PTEN-deficient tumours were found to be reliant on p110β activity to sustain transformation. In this review, we describe the current understanding of the common and distinct biochemical properties of the p110α and p110β isoforms, summarise their mutations and highlight how they are targeted in clinical trials in endometrial cancer.

Regulation of hematopoietic cell signaling by SHIP-1 inositol phosphatase: growth factors and beyond

SHIP-1 is a hematopoietic-specific inositol phosphatase activated downstream of a multitude of receptors including those for growth factors, cytokines, antigen, immunoglobulin and toll-like receptor agonists where it exerts inhibitory control. While it is constitutively expressed in all immune cells, SHIP-1 expression is negatively regulated by the inflammatory and oncogenic micro-RNA miR-155. Knockout mouse studies have shown the importance of SHIP-1 in various immune cell subsets and have revealed a range of immune-mediated pathologies that are engendered due to loss of SHIP-1's regulatory activity, impelling investigations into the role of SHIP-1 in human disease. In this review, we provide an overview of the literature relating to the role of SHIP-1 in hematopoietic cell signaling and function, we summarize recent reports that highlight the dysregulation of the SHIP-1 pathway in cancers, autoimmune disorders and inflammatory diseases, and lastly we discuss the importance of SHIP-1 in restraining myeloid growth factor signaling.

Loss of lipid phosphatase SHIP1 promotes macrophage differentiation through suppression of dendritic cell differentiation

SH2-containing inositol 5'-phosphatase-1 (SHIP1) deficiency in mice results in abnormal myeloid expansion, and proinflammatory conditions in the lung. However, the mechanisms involved in SHIP1-mediated regulation of myeloid differentiation remain unclear. Here we show that SHIP1 is a key regulator of early differentiation for dendritic cells (DCs). We also provide critical evidence to modify the function of SHIP1 in in vitro development of BMDCs using the recent framework of defining DCs. We found that loss of SHIP1 suppresses GM-CSF-induced formation of bone marrow-derived DC (BMDC) colonies, leading to reduced BMDC number in BM cell culture. The number of maturated BMDCs decreased in SHIP1-KO culture, due to reduction of immature BMDCs, suggesting SHIP1 is critical for lineage commitment rather than for maturation from myeloid precursors to DCs. We further showed that F4/80⁺/MHCII^low BM macrophage-like cells (BMMs) were the main population of SHIP1-KO BM culture. Treatment of wild-type BM culture with 3 α-aminocholestane (3AC), a specific inhibitor for functional activity of SHIP1, caused a similar developmental defect in BMDCs as seen in SHIP1-KO cells, resulting in the absence of BMDC colony, and increased number of BMMs in BM culture. In conclusion, our results suggest that differentiation of BMDCs are markedly impaired under SHIP1 deficient condition, which causes skewed development of myeloid lineage cells manifested as pathological conditions associated with an excess of macrophage population.

The impact of phosphoinositide 5-phosphatases on phosphoinositides in cell function and human disease

Phosphoinositides (PIs) are recognized as major signaling molecules in many different functions of eukaryotic cells. PIs can be dephosphorylated by multiple phosphatase activities at the 5-, 4-, and 3- positions. Human PI 5-phosphatases belong to a family of 10 members. Except for inositol polyphosphate 5-phosphatase A, they all catalyze the dephosphorylation of PI(4,5)P₂ and/or PI(3,4,5)P₃ at the 5- position. PI 5-phosphatases thus directly control the levels of PI(3,4,5)P₃ and participate in the fine-tuning regulatory mechanisms of PI(3,4)P₂ and PI(4,5)P₂ Second messenger functions have been demonstrated for PI(3,4)P₂ in invadopodium maturation and lamellipodia formation. PI 5-phosphatases can use several substrates on isolated enzymes, and it has been challenging to establish their real substrate in vivo. PI(4,5)P₂ has multiple functions in signaling, including interacting with scaffold proteins, ion channels, and cytoskeleton proteins. PI 5-phosphatase isoenzymes have been individually implicated in human diseases, such as the oculocerebrorenal syndrome of Lowe, through mechanisms that include lipid control. Oncogenic and tumor-suppressive functions of PI 5-phosphatases have also been reported in different cell contexts. The mechanisms responsible for genetic diseases and for oncogenic or tumor-suppressive functions are not fully understood. The regulation of PI 5-phosphatases is thus crucial in understanding cell functions.

Nuclear accumulation of SHIP1 mutants derived from AML patients leads to increased proliferation of leukemic cells

The inositol 5-phosphatase SHIP1 acts as negative regulator of intracellular signaling in myeloid cells and is a tumor suppressor in myeloid leukemogenesis. After relocalization from the cytoplasm to the plasma membrane SHIP1 terminates PI3-kinase mediated signaling processes. Furthermore, SHIP1 is also found in distinct puncta in the cell nucleus and nuclear SHIP1 has a pro-proliferative function. Here we report the identification of five nuclear export signals (NESs) which regulate together with the two known nuclear localization signals (NLSs) the nucleocytoplasmic shuttling of SHIP1. Mutation of NLSs reduced the nuclear import and mutation of NESs decreased the nuclear export of SHIP1 in the acute myeloid leukemia (AML) cell line UKE-1. Interestingly, four SHIP1 mutants (K210R, N508D, V684E, Q1153L) derived from AML patients showed a nuclear accumulation after expression in UKE-1 cells. In addition, overexpression of the AML patient-derived mutation N508D caused an increased proliferation rate of UKE-1 cells in comparison to wild type SHIP1. Furthermore, we identified serine and tyrosine phosphorylation as a molecular mechanism for the regulation of nucleocytoplasmic shuttling of SHIP1 where tyrosine phosphorylation of distinct residues i.e. Y864, Y914, Y1021 reduces nuclear localization, whereas serine phosphorylation at S933 enhances nuclear localization of SHIP1. In summary, our data further implicate nuclear SHIP1 in cellular signaling and suggest that enhanced accumulation of SHIP1 mutants in the nucleus may be a contributory factor of abnormally high proliferation of AML cells.

Integration of Distinct ShcA Signaling Complexes Promotes Breast Tumor Growth and Tyrosine Kinase Inhibitor Resistance

The commonality between most phospho-tyrosine signaling networks is their shared use of adaptor proteins to transduce mitogenic signals. ShcA (SHC1) is one such adaptor protein that employs two phospho-tyrosine binding domains (PTB and SH2) and key phospho-tyrosine residues to promote mammary tumorigenesis. Receptor tyrosine kinases (RTK), such as ErbB2, bind the ShcA PTB domain to promote breast tumorigenesis by engaging Grb2 downstream of the ShcA tyrosine phosphorylation sites to activate AKT/mTOR signaling. However, breast tumors also rely on the ShcA PTB domain to bind numerous negative regulators that limit activation of secondary mitogenic signaling networks. This study examines the role of PTB-independent ShcA pools in controlling breast tumor growth and resistance to tyrosine kinase inhibitors. We demonstrate that PTB-independent ShcA complexes predominately rely on the ShcA SH2 domain to activate multiple Src family kinases (SFK), including Src and Fyn, in ErbB2-positive breast cancers. Using genetic and pharmacologic approaches, we show that PTB-independent ShcA complexes augment mammary tumorigenesis by increasing the activity of the Src and Fyn tyrosine kinases in an SH2-dependent manner. This bifurcation of signaling complexes from distinct ShcA pools transduces non-redundant signals that integrate the AKT/mTOR and SFK pathways to cooperatively increase breast tumor growth and resistance to tyrosine kinase inhibitors, including lapatinib and PP2. This study mechanistically dissects how the interplay between diverse intracellular ShcA complexes impacts the tyrosine kinome to affect breast tumorigenesis.Implications: The ShcA adaptor, within distinct signaling complexes, impacts tyrosine kinase signaling, breast tumor growth, and resistance to tyrosine kinase inhibitors. Mol Cancer Res; 16(5); 894-908. ©2018 AACR.

New revelations from an old receptor: Immunoregulatory functions of the inhibitory Fc gamma receptor, FcγRIIB (CD32B)

The Fc gamma receptor IIB (FcγRIIB/CD32B) was generated million years ago during evolution. It is the sole inhibitory receptor for IgG, and has long been associated with the regulation of humoral immunity and innate immune homeostasis. However, new and surprising functions of FcγRIIB are emerging. In particular, FcγRIIB has been shown to perform unexpected activatory roles in both immune-signaling and monoclonal antibody (mAb) immunotherapy. Furthermore, although ITIM signaling is an integral part of FcγRIIB regulatory activity, it is now clear that inhibition/activation of immune responses can occur independently of the ITIM. In light of these new findings, we present an overview of the established and noncanonical functions of FcγRIIB and discuss how this knowledge might be exploited therapeutically.

SHIP negatively regulates type II immune responses in mast cells and macrophages

SHIP is a hematopoietic-specific lipid phosphatase that dephosphorylates PI3K-generated PI(3,4,5)-trisphosphate. SHIP removes this second messenger from the cell membrane blunting PI3K activity in immune cells. Thus, SHIP negatively regulates mast cell activation downstream of multiple receptors. SHIP has been referred to as the "gatekeeper" of mast cell degranulation as loss of SHIP dramatically increases degranulation or permits degranulation in response to normally inert stimuli. SHIP also negatively regulates Mϕ activation, including both pro-inflammatory cytokine production downstream of pattern recognition receptors, and alternative Mϕ activation by the type II cytokines, IL-4, and IL-13. In the SHIP-deficient (SHIP-/- ) mouse, increased mast cell and Mϕ activation leads to spontaneous inflammatory pathology at mucosal sites, which is characterized by high levels of type II inflammatory cytokines. SHIP-/- mast cells and Mϕs have both been implicated in driving inflammation in the SHIP-/- mouse lung. SHIP-/- Mϕs drive Crohn's disease-like intestinal inflammation and fibrosis, which is dependent on heightened responses to innate immune stimuli generating IL-1, and IL-4 inducing abundant arginase I. Both lung and gut pathology translate to human disease as low SHIP levels and activity have been associated with allergy and with Crohn's disease in people. In this review, we summarize seminal literature and recent advances that provide insight into SHIP's role in mast cells and Mϕs, the contribution of these cell types to pathology in the SHIP-/- mouse, and describe how these findings translate to human disease and potential therapies.

Effects of cell-cell crosstalk on gene expression patterns in a cell model of renal cell carcinoma lung metastasis

The median survival rate of patients with metastatic renal carcinoma is approximately 10 to 12 months, with up to 50% of patients developing metastases in the lung parenchyma. The molecular basis for metastatic development remains unclear. In the present study, we used renal cell carcinoma (RCC) cells and bronchial epithelial cells, representing metastasis target organ cells, conditioned medium and co-culture models to identify specific gene expression changes responsible for cancer cell viability in a metastatic microenvironment. RCC cell proliferation and migration increased when the culture was supplemented with conditioned medium from lung fibroblasts or pleural epithelial cells. Healthy epithelial cells were, in turn, also stimulated with conditioned medium from RCC cell lines. The mitogen-activated protein kinase (MAPK), interleukin (IL)-6, and phosphatidylinositol 4,5-bisphosphate (PIP2) signaling pathways were identified as deregulated upon cell‑cell interaction. Thus, cell-cell communication may contribute to the development of the metastatic niche. The identified deregulated signaling pathways may be considered as potential therapeutic targets in metastatic renal carcinoma.

Timescale Separation of Positive and Negative Signaling Creates History-Dependent Responses to IgE Receptor Stimulation

The high-affinity receptor for IgE expressed on the surface of mast cells and basophils interacts with antigens, via bound IgE antibody, and triggers secretion of inflammatory mediators that contribute to allergic reactions. To understand how past inputs (memory) influence future inflammatory responses in mast cells, a microfluidic device was used to precisely control exposure of cells to alternating stimulatory and non-stimulatory inputs. We determined that the response to subsequent stimulation depends on the interval of signaling quiescence. For shorter intervals of signaling quiescence, the second response is blunted relative to the first response, whereas longer intervals of quiescence induce an enhanced second response. Through an iterative process of computational modeling and experimental tests, we found that these memory-like phenomena arise from a confluence of rapid, short-lived positive signals driven by the protein tyrosine kinase Syk; slow, long-lived negative signals driven by the lipid phosphatase Ship1; and slower degradation of Ship1 co-factors. This work advances our understanding of mast cell signaling and represents a generalizable approach for investigating the dynamics of signaling systems.

An NF-κB-microRNA regulatory network tunes macrophage inflammatory responses

The innate inflammatory response must be tightly regulated to ensure effective immune protection. NF-κB is a key mediator of the inflammatory response, and its dysregulation has been associated with immune-related malignancies. Here, we describe a miRNA-based regulatory network that enables precise NF-κB activity in mouse macrophages. Elevated miR-155 expression potentiates NF-κB activity in miR-146a-deficient mice, leading to both an overactive acute inflammatory response and chronic inflammation. Enforced miR-155 expression overrides miR-146a-mediated repression of NF-κB activation, thus emphasizing the dominant function of miR-155 in promoting inflammation. Moreover, miR-155-deficient macrophages exhibit a suboptimal inflammatory response when exposed to low levels of inflammatory stimuli. Importantly, we demonstrate a temporal asymmetry between miR-155 and miR-146a expression during macrophage activation, which creates a combined positive and negative feedback network controlling NF-κB activity. This miRNA-based regulatory network enables a robust yet time-limited inflammatory response essential for functional immunity.

MicroRNAs (miR) are important regulators of gene transcription, with miR-155 and miR-146a both implicated in macrophage activation. Here the authors show that NF-κB signalling, miR-155 and miR-146a form a complex network of cross-regulations to control gene transcription in macrophages for modulating inflammatory responses.

Dual enhancement of T and NK cell function by pulsatile inhibition of SHIP1 improves antitumor immunity and survival

The success of immunotherapy in some cancer patients has revealed the profound capacity for cytotoxic lymphocytes to eradicate malignancies. Various immunotherapies work by blocking key checkpoint proteins that suppress immune cell activity. The phosphatase SHIP1 (SH2-containing inositol polyphosphate 5-phosphatase) limits signaling from receptors that activate natural killer (NK) cells and T cells. However, unexpectedly, genetic ablation studies have shown that the effector functions of SHIP1-deficient NK and T cells are compromised in vivo. Because chronic activation of immune cells renders them less responsive to activating signals (a host mechanism to avoid autoimmunity), we hypothesized that the failure of SHIP1 inhibition to induce antitumor immunity in those studies was caused by the permanence of genetic ablation. Accordingly, we found that reversible and pulsatile inhibition of SHIP1 with 3-α-aminocholestane (3AC; "SHIPi") increased the antitumor response of NK and CD8⁺ T cells in vitro and in vivo. Transient SHIP1 inhibition in mouse models of lymphoma and colon cancer improved the median and long-term tumor-free survival rates. Adoptive transfer assays showed evidence of immunological memory to the tumor in hematolymphoid cells from SHIPi-treated, long-term surviving mice. The findings suggest that a pulsatile regimen of SHIP1 inhibition might be an effective immunotherapy in some cancer patients.

The C-terminal region of the major outer sheath protein of Treponema denticola inhibits neutrophil chemotaxis

Treponema denticola is an oral spirochete strongly associated with severe periodontal disease. A prominent virulence factor, the major outer sheath protein (Msp), disorients neutrophil chemotaxis by altering the cellular phosphoinositide balance, leading to impairment of downstream chemotactic events including actin rearrangement, Rac1 activation, and Akt activation in response to chemoattractant stimulation. The specific regions of Msp responsible for interactions with neutrophils remain unknown. In this study, we investigated the inhibitory effect of truncated Msp regions on neutrophil chemotaxis and associated signaling pathways. Murine neutrophils were treated with recombinant protein truncations followed by assessment of chemotaxis and associated signal pathway activation. Chemotaxis assays indicate sequences within the C-terminal region; particularly the first 130 amino acids, have the strongest inhibitory effect on neutrophil chemotaxis. Neutrophils incubated with the C-terminal region protein also demonstrated the greatest inhibition of Rac1 activation, increased phosphoinositide phosphatase activity, and decreased Akt activation; orchestrating impairment of chemotaxis. Furthermore, incubation with antibodies specific to only the C-terminal region blocked the Msp-induced inhibition of chemotaxis and denaturing the protein restored Rac1 activation. Msp from the strain OTK, with numerous amino acid substitutions throughout the polypeptide, including the C-terminal region compared with strain 35405, showed increased ability to impair neutrophil chemotaxis. Collectively, these results indicate that the C-terminal region of Msp is the most potent region to modulate neutrophil chemotactic signaling and that specific sequences and structures are likely to be required. Knowledge of how spirochetes dampen the neutrophil response is limited and Msp may represent a novel therapeutic target for periodontal disease.

What goes up must come down: A tripartite Dok-3/Grb2/SHIP1 inhibitory module limits BCR signaling

Properly regulated immunity requires precise integration of activating and inhibitory signals. As for other lymphocytes, B cells express an antigen-specific activating receptor, the B-cell antigen receptor (BCR), and inhibitory receptors (e.g. FcγRIIb) that exercise checkpoint control on B-cell activation. Moreover, following BCR engagement, CD19 recruits proteins that amplify BCR signaling, while CD22 initiates a negative feedback loop by recruiting proteins that inhibit BCR signaling. Initial BCR signaling is mediated by protein tyrosine kinases and lipid kinases; inhibitory receptors directly antagonize the actions of these enzymes by recruiting protein tyrosine phosphatases and lipid phosphatases and positioning them close to actively signaling BCRs. Previously it was thought that inhibitory receptors such as FcγRIIb and CD22 were essential for bringing these phosphatases near the BCR. In this issue of the European Journal of Immunology, Manno et al. show that a tripartite inhibitory module consisting of the adaptor proteins Dok-3 and Grb2 and the lipid phosphatase SHIP1 binds directly to activated BCRs and limits the Ca²⁺ mobilization that is required for B lymphocyte activation. This reveals that the BCR can be both an activating and inhibitory receptor, one that activates signaling enzymes while initiating a negative feedback loop that prevents excessive signaling.

Regulation of immune cell signaling by SHIP1: A phosphatase, scaffold protein, and potential therapeutic target

The phosphoinositide phosphatase SHIP is a critical regulator of immune cell activation. Despite considerable study, the mechanisms controlling SHIP activity to ensure balanced cell activation remain incompletely understood. SHIP dampens BCR signaling in part through its association with the inhibitory coreceptor Fc gamma receptor IIB, and serves as an effector for other inhibitory receptors in various immune cell types. The established paradigm emphasizes SHIP's inhibitory receptor-dependent function in regulating phosphoinositide 3-kinase signaling by dephosphorylating the phosphoinositide PI(3,4,5)P₃ ; however, substantial evidence indicates that SHIP can be activated independently of inhibitory receptors and can function as an intrinsic brake on activation signaling. Here, we integrate historical and recent reports addressing the regulation and function of SHIP in immune cells, which together indicate that SHIP acts as a multifunctional protein controlled by multiple regulatory inputs, and influences downstream signaling via both phosphatase-dependent and -independent means. We further summarize accumulated evidence regarding the functions of SHIP in B cells, T cells, NK cells, dendritic cells, mast cells, and macrophages, and data suggesting defective expression or activity of SHIP in autoimmune and malignant disorders. Lastly, we discuss the biological activities, therapeutic promise, and limitations of small molecule modulators of SHIP enzymatic activity.