SH2-containing inositol 5'-phosphatase SHIP2 associates with the p130(Cas) adapter protein and regulates cellular adhesion and spreading

Structural Insights into the Binding Propensity of Human SHIP2 SH2 to Oncogenic CagA Isoforms from Helicobacter pylori

SHIP2 is a multi-domain inositol 5-phosphatase binding to a variety of phosphotyrosine (pY)-containing proteins through its SH2 domain, so as to regulate various cell signaling pathways by modulating the phosphatidylinositol level in the plasma membrane. Unfavorably, Helicobacter pylori can hijack SHIP2 through the CagA protein to induce gastric cell carcinogenesis. To date, the interaction between SHIP2 and CagA was not analyzed from a structural point of view. Here, the binding of SHIP2-SH2 with Tyr-phosphorylated peptides from four EPIYA motifs (A/B/C/D) in CagA was studied using NMR spectroscopy. The results showed that EPIYA-C and -D bind to a similar interface of SHIP2-SH2, including a pY-binding pocket and a hydrophobic pocket, to achieve high affinity, while EPIYA-A and -B bind to a smaller interface of SHIP2-SH2 with weak affinity. By summarizing the interface and affinity of SHIP2-SH2 for CagA EPIYA-A/B/C/D, c-MET and FcgR2B ITIM, it was proposed that, potentially, SHIP2-SH2 has a selective preference for L > I > V for the aliphatic residues at the pY+3 position in its ligand. This study reveals the rule of the ligand sequence bound by SHIP2-SH2 and the mechanism by which CagA protein hijacks SHIP2, which will help design a peptide inhibitor against SHIP2-SH2.

PIP3 abundance overcomes PI3K signaling selectivity in invadopodia

PI3Kβ is required for invadopodia-mediated matrix degradation by breast cancer cells. Invadopodia maturation requires GPCR activation of PI3Kβ and its coupling to SHIP2 to produce PI(3,4)P2 . We now test whether selectivity for PI3Kβ is preserved under conditions of mutational increases in PI3K activity. In breast cancer cells where PI3Kβ is inhibited, short-chain diC8-PIP3  rescues gelatin degradation in a SHIP2-dependent manner; rescue by diC8-PI(3,4)P2  is SHIP2-independent. Surprisingly, the expression of either activated PI3Kβ or PI3Kα mutants rescued the effects of PI3Kβ inhibition. In both cases, gelatin degradation was SHIP2-dependent. These data confirm the requirement for PIP3 conversion to PI(3,4)P2 for invadopodia function and suggest that selectivity for distinct PI3K isotypes may be obviated by mutational activation of the PI3K pathway.

Interaction Network Provides Clues on the Role of BCAR1 in Cellular Response to Changes in Gravity

When culturing cells in space or under altered gravity conditions on Earth to investigate the impact of gravity, their adhesion and organoid formation capabilities change. In search of a target where the alteration of gravity force could have this impact, we investigated p130cas/BCAR1 and its interactions more thoroughly, particularly as its activity is sensitive to applied forces. This protein is well characterized regarding its role in growth stimulation and adhesion processes. To better understand BCAR1′s force-dependent scaffolding of other proteins, we studied its interactions with proteins we had detected by proteome analyses of MCF-7 breast cancer and FTC-133 thyroid cancer cells, which are both sensitive to exposure to microgravity and express BCAR1. Using linked open data resources and our experiments, we collected comprehensive information to establish a semantic knowledgebase and analyzed identified proteins belonging to signaling pathways and their networks. The results show that the force-dependent phosphorylation and scaffolding of BCAR1 influence the structure, function, and degradation of intracellular proteins as well as the growth, adhesion and apoptosis of cells similarly to exposure of whole cells to altered gravity. As BCAR1 evidently plays a significant role in cell responses to gravity changes, this study reveals a clear path to future research performing phosphorylation experiments on BCAR1.

An auxiliary binding interface of SHIP2-SH2 for Y292-phosphorylated FcγRIIB reveals diverse recognition mechanisms for tyrosine-phosphorylated receptors involved in different cell signaling pathways

SH2 domain-containing inositol 5-phosphatase 2 (SHIP2) plays an essential role in regulating phosphatidylinositol level in human cell, and is recruited to many phosphotyrosine (pY)-dependent signal transduction pathways by the SH2 domain. In immunity signaling, immunoreceptor FcγRIIB binds to SHIP2-SH2 via its Y292-phosphorylated immunoreceptor tyrosine-based inhibitory motif (ITIM) and transmits inhibitory signal, which regulates B cell and neuronal cell activity and is associated with immune diseases and Alzheimer's disease. To date, the interaction between SHIP2 and FcγRIIB has not been analyzed from a structural point of view. Here, the binding of SHIP2-SH2 with Y292-phosphorylated FcγRIIB-ITIM was analyzed using NMR spectroscopy. The results demonstrated that SHIP2-SH2 mainly utilizes two regions including a pY-binding pocket and a specificity pocket formed by βD, βE, and EF-loop, to bind with FcγRIIB-ITIM in high affinity. In addition to the two regions, the BG-loop of SHIP2-SH2 functions as an auxiliary interface enhancing affinity. By comparing the binding of SHIP2-SH2 with ligands from FcγRIIB and c-MET, a hepatocyte growth factor receptor associated with tumorigenesis, significant differences in interface and affinity were found, suggesting that SHIP2-SH2 applies diverse patterns for binding to different ligand proteins. Moreover, S49, S51, and R70 of SHIP2 were identified to mediate the binding of both FcγRIIB and c-MET, while R28 and Q107 were found to only participate in the binding of c-MET and FcγRIIB respectively. Taken together, this study reveals the diverse mechanisms of SHIP2-SH2 for recognizing different ligands, and provides important clues for selectively manipulating various signaling pathways and specific drug design.

Expression, purification and characterization of the RhoA-binding domain of human SHIP2 in E.coli

Human SH2-containing inositol 5-phosphatase 2 (SHIP2) is a multi-domain protein playing essential roles in various physiological and pathological processes. In cell polarization and migration, SHIP2 serves as a RhoA effector for manipulating the level of phosphatidylinositol 3,4,5-trisphosphate. The domain between SH2 and a potential PH-R domain of SHIP2 was suggested to bind with GTP-bound form of RhoA. However, the structure of this RhoA-binding domain (RBD) of SHIP2 and the mechanism for its binding with RhoA remain unknown. In this study, SHIP2^118-298 and SHIP2^176-298, two truncated proteins harboring the RBD were designed, expressed, and purified successfully in E. coli. Unexpectedly, both SHIP2^118-298 and SHIP2^176-298 were determined to exist as homo-dimers in solution by multi-angle light scattering. Circular dichroism spectra indicated that both proteins predominantly consisted of α-helix structure. Moreover, in pull-down experiments, both proteins could bind with GTP-bound RhoA and RhoA^Q63L, a mutant mimicing the state of GTP-bound RhoA. Importantly, in silico analysis showed that the shorter truncation, SHIP2^176-298, contained all ordered residues between the SH2 and the PH-R domain, and matched the RhoA effector motif 1 of PKN1 well in sequence alignment, suggesting that SHIP2^176-298 is sufficient for further studies on the structure and RhoA binding of SHIP2. This work shortens and confirms the main region of SHIP2 interacting with RhoA, provides the method for sample preparation, and presents preliminary information for SHIP2-RBD structure, which will facilitate the comprehensive understanding of the structure and function of SHIP2.

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.

Scaffold dependent role of the inositol 5'-phosphatase SHIP2, in regulation of oxidative stress induced apoptosis

Cell apoptosis is an important process that occurs during development or in response to stress stimuli such as oxidative stress. The serine-threonine kinase Akt enhances survival and suppress apoptosis. SHIP2 is known as a negative regulator of Akt. In addition to its lipid 5'-phosphatase activity, SHIP2 interacts and signals as a scaffolding complex with several proteins. Several findings have pointed out a possible role of SHIP2 in apoptosis regulation. However, the molecular mechanisms behind remain unknown. Using embryonic fibroblast lacking the lipid 5'-phosphatase domain as a genetic model system and human liver cancer cells treated with SHIP2 inhibitor (AS1949490), as a pharmacological model system. We provide the first evidence that SHIP2 regulates apoptosis independently of its 5'-phosphates activity. Indeed, absence of the 5'-phosphatase domain of SHIP2 did not prevent H2O2-induced apoptosis in fibroblasts. Whereas chemical inactivation or RNAi knockdown of SHIP2 blocked H2O2-induced apoptosis in HepG2 cells. We found that suppression of apoptosis upon SHIP2 inhibition is PI3K/Akt independent but rather MAP kinase dependent. In addition, we found that AS1949490 altered both 5'-phosphatase and scaffolding function of SHIP2. Indeed, AS1949490 mediated SHIP2 inhibition promotes protein complex formation of SHIP2 together with non-receptor tyrosine kinase SRC and ABL which in turn enhances PI3K/Akt and MAP kinase pathways activation. Dual inhibition of SRC/ABL blocked activation of both pathways upon SHIP2 inhibition and H2O2 treatment. Altogether, these findings indicate that SHIP2 protein play a determinant role in H2O2-induced apoptosis.

Intersection of TKS5 and FGD1/CDC42 signaling cascades directs the formation of invadopodia

Tumor cells exposed to a physiological matrix of type I collagen fibers form elongated collagenolytic invadopodia, which differ from dotty-like invadopodia forming on the gelatin substratum model. The related scaffold proteins, TKS5 and TKS4, are key components of the mechanism of invadopodia assembly. The molecular events through which TKS proteins direct collagenolytic invadopodia formation are poorly defined. Using coimmunoprecipitation experiments, identification of bound proteins by mass spectrometry, and in vitro pull-down experiments, we found an interaction between TKS5 and FGD1, a guanine nucleotide exchange factor for the Rho-GTPase CDC42, which is known for its role in the assembly of invadopodial actin core structure. A novel cell polarity network is uncovered comprising TKS5, FGD1, and CDC42, directing invadopodia formation and the polarization of MT1-MMP recycling compartments, required for invadopodia activity and invasion in a 3D collagen matrix. Additionally, our data unveil distinct signaling pathways involved in collagenolytic invadopodia formation downstream of TKS4 or TKS5 in breast cancer cells.

IRSp53 is a novel interactor of SHIP2: A role of the actin binding protein Mena in their cellular localization in breast cancer cells

A tight control of the machineries regulating membrane bending and actin dynamics is very important for the generation of membrane protrusions, which are crucial for cell migration and invasion. Protein/protein and protein/phosphoinositides complexes assemble and disassemble to coordinate these mechanisms, the scaffold properties of the involved proteins playing a prominent role in this organization. The PI 5-phosphatase SHIP2 is a critical enzyme modulating PI(3,4,5)P₃, PI(4,5)P₂ and PI(3,4)P₂ content in the cell. The scaffold properties of SHIP2 contribute to the specific targeting or retention of the protein in particular subcellular domains. Here, we identified IRSp53 as a new binding interactor of SHIP2 proline-rich domain. Both proteins are costained in HEK293T cells protrusions, upon transfection. We showed that the SH3-binding polyproline motif recognized by IRSp53 in SHIP2 is different from the regions targeted by other PRR binding partners i.e., CIN85, ITSN or even Mena a common interactor of both SHIP2 and IRSp53. We presented evidence that IRSp53 phosphorylation on S366 did not influence its interaction with SHIP2 and that Mena is not necessary for the association of SHIP2 with IRSp53 in MDA-MB-231 cells. The absence of Mena in MDA-MB-231 cells decreased the intracellular content in F-actin and modified the subcellular localization of SHIP2 and IRSp53 by increasing their relative content at the plasma membrane. Together our data suggest that SHIP2, through interaction with the cell protrusion regulators IRSp53 and Mena, participate to the formation of multi-protein complexes. This ensures the appropriate modulations of PIs which is important for regulation of membrane dynamics.

Helicobacter pylori CagA oncoprotein interacts with SHIP2 to increase its delivery into gastric epithelial cells

Chronic infection with Helicobacter pylori cagA‐positive strains is causally associated with the development of gastric diseases, most notably gastric cancer. The cagA‐encoded CagA protein, which is injected into gastric epithelial cells by bacterial type IV secretion, undergoes tyrosine phosphorylation at the Glu‐Pro‐Ile‐Tyr‐Ala (EPIYA) segments (EPIYA‐A, EPIYA‐B, EPIYA‐C, and EPIYA‐D), which are present in various numbers and combinations in its C‐terminal polymorphic region, thereby enabling CagA to promiscuously interact with SH2 domain‐containing host cell proteins, including the prooncogenic SH2 domain‐containing protein tyrosine phosphatase 2 (SHP2). Perturbation of host protein functions by aberrant complex formation with CagA has been considered to contribute to the development of gastric cancer. Here we show that SHIP2, an SH2 domain‐containing phosphatidylinositol 5′‐phosphatase, is a hitherto undiscovered CagA‐binding host protein. Similar to SHP2, SHIP2 binds to the Western CagA‐specific EPIYA‐C segment or East Asian CagA‐specific EPIYA‐D segment through the SH2 domain in a tyrosine phosphorylation‐dependent manner. In contrast to the case of SHP2, however, SHIP2 binds more strongly to EPIYA‐C than to EPIYA‐D. Interaction with CagA tethers SHIP2 to the plasma membrane, where it mediates production of phosphatidylinositol 3,4‐diphosphate [PI(3,4)P₂]. The CagA‐SHIP2 interaction also potentiates the morphogenetic activity of CagA, which is caused by CagA‐deregulated SHP2. This study indicates that initially delivered CagA interacts with SHIP2 and thereby strengthens H. pylori‐host cell attachment by altering membrane phosphatidylinositol compositions, which potentiates subsequent delivery of CagA that binds to and thereby deregulates the prooncogenic phosphatase SHP2.

Transcriptomic identification of miR-205 target genes potentially involved in metastasis and survival of cutaneous malignant melanoma

Cutaneous melanoma is an aggressive neoplasm and is responsible for the majority of skin cancer deaths. Several miRNAs are involved in melanoma tumor progression. One of them is miR-205, the loss of which contributes to the development of melanoma metastasis. We evaluated whole-genome mRNA expression profiling associated with different miR-205 expression levels in melanoma cells. Differential expression analysis identified 243 differentially expressed transcripts including inositol polyphosphate 5′-phosphatase-like protein-1 (INPPL1) and BTB/POZ Domain-Containing Protein 3 (BTBD3). INPPL1 and BTBD3 were downregulated when melanoma cells expressed miR-205, indicating that these genes are potential miR-205 targets. Additionally, the target prediction algorithm TargetScan revealed that INPPL1 and BTBD3 genes had predicted target sites of miR-205 in their 3′UTRs and functional analysis demonstrated that these genes were directly linked to miR-205. Interestingly, our clinical data showed that INPPL1 was significantly associated with lymph node metastasis-free survival (LNMFS), distant metastasis-free survival (DMFS) and melanoma specific survival (MSS). This study supports INPPL1 as a miR-205 target gene and, therefore, that the involvement of miR-205 in the metastatic dissemination of malignant melanoma is, at least in part, via INPPL1.

IQGAP2 Inhibits Migration and Invasion of Gastric Cancer Cells via Elevating SHIP2 Phosphatase Activity

Previous studies have shown reduced expression of Src homology 2-containing inositol 5-phosphatase 2 (SHIP2) and its tumor-suppressive role in gastric cancer (GC). However, the precise role of SHIP2 in the migration and invasion of GC cells remains unclear. Here, an IQ motif containing the GTPase-activating protein 2 (IQGAP2) as a SHIP2 binding partner, was screened and identified by co-immunoprecipitation and mass spectrometry studies. While IQGAP2 ubiquitously expressed in GC cells, IQGAP2 and SHIP2 co-localized in the cytoplasm of GC cells, and this physical association was confirmed by the binding of IQGAP2 to PRD and SAM domains of SHIP2. The knockdown of either SHIP2 or IQGAP2 promoted cell migration and invasion by inhibiting SHIP2 phosphatase activity, activating Akt and subsequently increasing epithelial–mesenchymal transition (EMT). Furthermore, knockdown of IQGAP2 in SHIP2-overexpressing GC cells reversed the inhibition of cell migration and invasion by SHIP2 induction, which was associated with the suppression of elevated SHIP2 phosphatase activity. Moreover, the deletion of PRD and SAM domains of SHIP2 abrogated the interaction and restored cell migration and invasion. Collectively, these results indicate that IQGAP2 interacts with SHIP2, leading to the increment of SHIP2 phosphatase activity, and thereby inhibiting the migration and invasion of GC cells via the inactivation of Akt and reduction in EMT.

FAK-Dependent Cell Motility and Cell Elongation

Fibroblastic cells show specific substrate selectivity for typical cell–substrate adhesion. However, focal adhesion kinase (FAK) contributes to controlling the regulation of orientation and polarity. When fibroblasts attach to micropatterns, tyrosine-phosphorylated proteins and FAK are both detected along the inner border between the adhesive micropatterns and the nonadhesive glass surface. FAK likely plays important roles in regulation of cell adhesion to the substrate, as FAK is a tyrosine-phosphorylated protein that acts as a signal transduction molecule at sites of cell–substrate attachment, called focal adhesions. FAK has been suggested to play a role in the attachment of cells at adhesive micropatterns by affecting cell polarity. Therefore, the localization of FAK might play a key role in recognition of the border of the cell with the adhesive micropattern, thus regulating cell polarity and the cell axis. This review discusses the regulation and molecular mechanism of cell proliferation and cell elongation by FAK and its associated signal transduction proteins.

Phosphoinositide 5-phosphatases SKIP and SHIP2 in ruffles, the endoplasmic reticulum and the nucleus: An update

Phosphoinositides (PIs) are phosphorylated derivatives of phosphatidylinositol. They act as signaling molecules linked to essential cellular mechanisms in eukaryotic cells, such as cytoskeleton organization, mitosis, polarity, migration or invasion. PIs are phosphorylated and dephosphorylated by a large number of PI kinases and PI phosphatases acting at the 5-, 4- and 3- position of the inositol ring. PI 5-phosphatases i.e. OCRL, INPP5B, SHIP1/2, Synaptojanin 1/2, INPP5E, INPP5J, SKIP (INPP5K) are enzymes that dephosphorylate the 5-phosphate position of PIs. Several human genetic diseases such as the Lowe syndrome, some congenital muscular dystrophy and opsismodysplasia are due to mutations in PI phosphatases, resulting in loss-of-function. The PI phosphatases are also up or down regulated in several human cancers such as glioblastoma or breast cancer. Their cellular localization, that is dynamic and varies in response to stimuli, is an important issue to understand function. This is the case for two members of the PI 5-phosphatase SKIP and SHIP2. Both enzymes are in ruffles, plasma membranes, the endoplasmic reticulum, a situation that is unique for SKIP, and the nucleus. Following localization, PI 5-phosphatases act on specific cellular pools of PIs, which in turn interact with target proteins. Nuclear PIs have emerged as regulators of genome functions in different area of cell signaling. They often localize to nuclear speckles, as do several PI metabolizing kinases and phosphatases. We asked whether SKIP and SHIP2 could have an impact on nuclear PI(4,5)P2. In two glioblastoma cell models, lowering SKIP expression had an impact on nuclear PI(4,5)P2. In a model of SHIP2 deletion in MCF-7 cells, no change in nuclear PI(4,5)P2 was observed. Finally, we present evidence of an anti-tumoral role of SKIP in vivo, in xenografts using as model U87shSKIP cells.

PI3Kβ links integrin activation and PI(3,4)P2 production during invadopodial maturation

The invasion of tumor cells from the primary tumor is mediated by invadopodia, actin-rich protrusive organelles that secrete matrix metalloproteases and degrade the extracellular matrix. This coupling between protrusive activity and matrix degradation facilitates tumor invasion. We previously reported that the PI3Kβ isoform of PI 3-kinase, which is regulated by both receptor tyrosine kinases and G protein-coupled receptors, is required for invasion and gelatin degradation in breast cancer cells. We have now defined the mechanism by which PI3Kβ regulates invadopodia. We find that PI3Kβ is specifically activated downstream from integrins, and is required for integrin-stimulated spreading and haptotaxis as well as integrin-stimulated invadopodia formation. Surprisingly, these integrin-stimulated and PI3Kβ-dependent responses require the production of PI(3,4)P2 by the phosphoinositide 5'-phosphatase SHIP2. Thus, integrin activation of PI3Kβ is coupled to the SHIP2-dependent production of PI(3,4)P2, which regulates the recruitment of PH domain-containing scaffolds such as lamellipodin to invadopodia. These findings provide novel mechanistic insight into the role of PI3Kβ in the regulation of invadopodia in breast cancer cells.

miRNAs, target genes expression and morphological analysis on the heart in gestational protein-restricted offspring

Gestational protein restriction was associated with low birth weight, hypertension and higher prevalence of cardiac disorders in adults. Several mechanisms, including epigenetics, could be related with the cardiovascular phenotype on protein-restricted offspring. Thus, we investigated the morphological cardiac effects of gestational protein restriction and left ventricle miRNAs and target genes expression pattern in both 12-day and 16-week old gestational protein-restricted male offspring. Pregnant Wistar rats were allocated into two groups, according to protein supply during pregnancy: NP (normal protein diet- 17%) or LP (low protein diet-6%). Dams on the gestational protein-restricted diet had lower body weight gain and higher food intake. Gestational protein-restricted offspring had low birth weight, followed by rapidly body weight recovery, hypertension, and increased myocytes cross-sectional area and collagen fraction at 16-week old age. At 12-days old, miR-184, miR-192, miR-376c, miR-380-3p, miR-380-5p, miR-451, and miR-582-3p had increased expression, and miR-547 and miR-743a had decreased expression in the gestational protein-restricted left ventricle. At 16-week old, let-7b, miR-125a-3p, miR-142-3p, miR-182 and miR-188-5p had increased expression and let-7g, miR-107, miR-127, miR-181a, miR-181c, miR-184, miR-324-5p, miR-383, miR-423-5p and miR-484 had decreased expression in gestational protein-restricted left ventricle. Target predicted gene expression analysis showed higher expression of Dnmt3a, Oxct1, Rictor and Trps1 and lower expression of Bbs1 and Calml3 in 12-day old protein-restricted offspring. 16-week old protein-restricted offspring had higher expression of Adrbk1, Bbs1, Dnmt3a, Gpr22, Inppl1, and Oxct1 genes. In conclusion, gestational protein restriction was related to offspring low birth weight, increased systolic blood pressure and morphological heart alterations that could be related to early heart miRNA expression changes that perpetuate into adulthood and which are associated with the regulation of essential genes involved in cardiovascular development, heart morphology, function, and metabolism.

The inositol phosphatase SHIP2 enables sustained ERK activation downstream of FGF receptors by recruiting Src kinases

Sustained activation of extracellular signal-regulated kinase (ERK) drives pathologies caused by mutations in fibroblast growth factor receptors (FGFRs). We previously identified the inositol phosphatase SHIP2 (also known as INPPL1) as an FGFR-interacting protein and a target of the tyrosine kinase activities of FGFR1, FGFR3, and FGFR4. We report that loss of SHIP2 converted FGF-mediated sustained ERK activation into a transient signal and rescued cell phenotypes triggered by pathologic FGFR-ERK signaling. Mutant forms of SHIP2 lacking phosphoinositide phosphatase activity still associated with FGFRs and did not prevent FGF-induced sustained ERK activation, demonstrating that the adaptor rather than the catalytic activity of SHIP2 was required. SHIP2 recruited Src family kinases to the FGFRs, which promoted FGFR-mediated phosphorylation and assembly of protein complexes that relayed signaling to ERK. SHIP2 interacted with FGFRs, was phosphorylated by active FGFRs, and promoted FGFR-ERK signaling at the level of phosphorylation of the adaptor FRS2 and recruitment of the tyrosine phosphatase PTPN11. Thus, SHIP2 is an essential component of canonical FGF-FGFR signal transduction and a potential therapeutic target in FGFR-related disorders.

Solution structure of SHIP2 SH2 domain and its interaction with a phosphotyrosine peptide from c-MET

SH2 domain-containing inositol 5-phosphatase 2 (SHIP2) binds with the Y1356-phosphorylated hepatocyte growth factor (HGF) receptor, c-MET, through its SH2 domain, which is essential for the role of SHIP2 in HGF-induced cell scattering and cell spreading. Previously, the experimental structure of the SH2 domain from SHIP2 (SHIP2-SH2) had not been reported, and its interaction with the Y1356-phosphorylated c-MET had not been investigated from a structural point of view. In this study, the solution structure of SHIP2-SH2 was determined by NMR spectroscopy, where it was found to adopt a typical SH2-domain fold that contains a positively-charged pocket for binding to phosphotyrosine (pY). The interaction between SHIP2-SH2 and a pY-containing peptide from c-MET (Y1356 phosphorylated) was investigated through NMR titrations. The results showed that the binding affinity of SHIP2-SH2 with the phosphopeptide is at low micromolar level, and the binding interface consists of the positively-charged pocket and its surrounding regions. Furthermore, R28, S49 and R70 were identified as key residues for the binding and may directly interact with the pY. Taken together, these findings provide structural insights into the binding of SHIP2-SH2 with the Y1356-phosphorylated c-MET, and lay a foundation for further studies of the interactions between SHIP2-SH2 and its various binding partners.

Lipid phosphatase SHIP2 functions as oncogene in colorectal cancer by regulating PKB activation

Colorectal cancer (CRC) is the second most common cause of cancer-related death, encouraging the search for novel therapeutic targets affecting tumor cell proliferation and migration. These cellular processes are under tight control of two opposing groups of enzymes; kinases and phosphatases. Aberrant activity of kinases is observed in many forms of cancer and as phosphatases counteract such "oncogenic" kinases, it is generally assumed that phosphatases function as tumor suppressors. However, emerging evidence suggests that the lipid phosphatase SH2-domain-containing 5 inositol phosphatase (SHIP2), encoded by the INPPL1 gene, may act as an oncogene. Just like the well-known tumor suppressor gene Phosphatase and Tensin Homolog (PTEN) it hydrolyses phosphatidylinositol (3,4,5) triphosphate (PI(3,4,5)P3). However, unlike PTEN, the reaction product is PI(3,4)P2, which is required for full activation of the downstream protein kinase B (PKB/Akt), suggesting that SHIP2, in contrast to PTEN, could have a tumor initiating role through PKB activation. In this work, we investigated the role of SHIP2 in colorectal cancer. We found that SHIP2 and INPPL1 expression is increased in colorectal cancer tissue in comparison to adjacent normal tissue, and this is correlated with decreased patient survival. Moreover, SHIP2 is more active in colorectal cancer tissue, suggesting that SHIP2 can induce oncogenesis in colonic epithelial cells. Furthermore, in vitro experiments performed on colorectal cancer cell lines shows an oncogenic role for SHIP2, by enhancing chemoresistance, cell migration, and cell invasion. Together, these data indicate that SHIP2 expression contributes to the malignant potential of colorectal cancer, providing a possible target in the fight against this devastating disease.

Phosphoinositide 5-phosphatase activities control cell motility in glioblastoma: Two phosphoinositides PI(4,5)P2 and PI(3,4)P2 are involved

Inositol polyphosphate 5-phosphatases or phosphoinositide 5-phosphatases (PI 5-phosphatases) are enzymes that can act on soluble inositol phosphates and/or phosphoinositides (PIs). Several PI 5-phosphatases have been linked to human genetic diseases, in particular the Lowe protein or OCRL which is mutated in the Lowe syndrome. There are 10 different members of this family and 9 of them can use PIs as substrate. One of these substrates, PI(3,4,5)P3 binds to specific PH domains and recruits as effectors specific proteins to signaling complexes. Protein kinase B is one target protein and activation of the kinase will have a major impact on cell proliferation, survival and cell metabolism. Two other PIs, PI(4,5)P2 and PI(3,4)P2, are produced or used as substrates of PI 5-phosphatases (OCRL, INPP5B, SHIP1/2, SYNJ1/2, INPP5K, INPP5J, INPP5E). The inositol lipids may influence many aspects of cytoskeletal organization, lamellipodia formation and F-actin polymerization. PI 5-phosphatases have been reported to control cell migration, adhesion, polarity and cell invasion particularly in cancer cells. In glioblastoma, reducing SHIP2 expression can positively or negatively affect the speed of cell migration depending on the glioblastoma cell type. The two PI 5-phosphatases SHIP2 or SKIP could be localized at the plasma membrane and can reduce either PI(3,4,5)P3 or PI(4,5)P2 abundance. In the glioblastoma 1321 N1 cells, SHIP2 controls plasma membrane PI(4,5)P2 thereby participating in the control of cell migration.

SHIP2 Regulates Lumen Generation, Cell Division, and Ciliogenesis through the Control of Basolateral to Apical Lumen Localization of Aurora A and HEF 1

Lumen formation during epithelial morphogenesis requires the creation of a luminal space at cell interfaces named apical membrane-initiation sites (AMISs). This is dependent upon integrated signaling from mechanical and biochemical cues, vesicle trafficking, cell division, and processes tightly coupled to ciliogenesis. Deciphering relationships between polarity determinants and lumen or cilia generation remains a fundamental issue. Here, we report that Src homology 2 domain-containing inositol 5-phosphatase 2 (SHIP2), a basolateral determinant of polarity, regulates RhoA-dependent actin contractility and cell division to form AMISs. SHIP2 regulates mitotic spindle alignment. SHIP2 is expressed in G1 phase, whereas Aurora A kinase is enriched in mitosis. SHIP2 binds Aurora A kinase and the scaffolding protein HEF1 and promotes their basolateral localization at the expense of their luminal expression connected with cilia resorption. Furthermore, SHIP2 expression increases cilia length. Thus, our findings offer new insight into the relationships among basolateral proteins, lumen generation, and ciliogenesis.

Expression and Production of SH2 Domain Proteins

The Src Homology 2 (SH2) domain lies at the heart of phosphotyrosine signaling, coordinating signaling events downstream of receptor tyrosine kinases (RTKs), adaptors, and scaffolds. Over a hundred SH2 domains are present in mammals, each having a unique specificity which determines its interactions with multiple binding partners. One of the essential tools necessary for studying and determining the role of SH2 domains in phosphotyrosine signaling is a set of soluble recombinant SH2 proteins. Here we describe methods, based on a broad experience with purification of all SH2 domains, for the production of SH2 domain proteins needed for proteomic and biochemical-based studies such as peptide arrays, mass-spectrometry, protein microarrays, reverse-phase microarrays, and high-throughput fluorescence polarization (HTP-FP). We describe stepwise protocols for expression and purification of SH2 domains using GST or poly His-tags, two widely adopted affinity tags. In addition, we address alternative approaches, challenges, and validation studies for assessing protein quality and provide general characteristics of purified human SH2 domains.

Transcriptomic evaluation of bovine blastocysts obtained from peri-pubertal oocyte donors

Assisted reproduction technologies (ART) and high selection pressure in the dairy industry are leading towards the use of younger females for reproduction, thereby reducing the interval between generations. This situation may have a negative impact on embryo quality, thus reducing the success rate of the procedures. This study aimed to document the effects of oocyte donor age on embryo quality, at the transcriptomic level, in order to characterize the effects of using young females for reproduction purpose. Young Holstein heifers (n = 10) were used at three different ages for ovarian stimulation protocols and oocyte collections (at 8, 11 and 14 months). All of the oocytes were fertilized in vitro with the semen of one adult bull, generating three lots of embryos per animal. Each animal was its own control for the evaluation of the effects of age. The EmbryoGENE platform was used for the assessment of gene expression patterns at the blastocyst stage. Embryos from animals at 8 vs 14 months and at 11 vs 14 months were used for microarray hybridization. Validation was done by performing RT-qPCR on seven candidate genes. Age-related contrast analysis (8 vs 14 mo and 11 vs 14 mo) identified 242 differentially expressed genes (DEGs) for the first contrast, and 296 for the second. The analysis of the molecular and biological functions of the DEGs suggests a metabolic cause to explain the differences that are observed between embryos from immature and adult subjects. The mTOR and PPAR signaling pathways, as well as the NRF2-mediated oxidative stress response pathways were among the gene expression pathways affected by donor age. In conclusion, the main differences between embryos produced at peri-pubertal ages are related to metabolic conditions resulting in a higher impact of in vitro conditions on blastocyts from younger heifers.

5'-Inositol phosphatase SHIP2 recruits Mena to stabilize invadopodia for cancer cell invasion

Invadopodia are membrane protrusions used by cancer cells to remodel and invade the extracellular matrix. Here, Rajadurai et al. show that the lipid phosphatase SHIP2 recruits the Ena/VASP-family actin regulatory protein Mena to stabilize invadopodia membrane protrusions and promote cell invasion.

Invadopodia are specialized membrane protrusions that support degradation of extracellular matrix (ECM) by cancer cells, allowing invasion and metastatic spread. Although early stages of invadopodia assembly have been elucidated, little is known about maturation of invadopodia into structures competent for ECM proteolysis. The localized conversion of phosphatidylinositol(3,4,5)-triphosphate and accumulation of phosphatidylinositol(3,4)-bisphosphate at invadopodia is a key determinant for invadopodia maturation. Here we investigate the role of the 5′-inositol phosphatase, SHIP2, and reveal an unexpected scaffold function of SHIP2 as a prerequisite for invadopodia-mediated ECM degradation. Through biochemical and structure-function analyses, we identify specific interactions between SHIP2 and Mena, an Ena/VASP-family actin regulatory protein. We demonstrate that SHIP2 recruits Mena, but not VASP, to invadopodia and that disruption of SHIP2–Mena interaction in cancer cells leads to attenuated capacity for ECM degradation and invasion in vitro, as well as reduced metastasis in vivo. Together, these findings identify SHIP2 as a key modulator of carcinoma invasiveness and a target for metastatic disease.

Suppression of SHIP2 contributes to tumorigenesis and proliferation of gastric cancer cells via activation of Akt

BACKGROUND

The Src homology 2-containing inositol 5-phosphatase 2 (SHIP2) is implicated in diabetes, arthrosclerosis, and cancer. However, the role of SHIP2 in human gastric cancer remains unclear.

METHODS

The expression levels of SHIP2 in gastric cancer tissues, a panel of gastric cancer cell lines, and normal gastric epithelial cells were analyzed by immunohistochemistry (IHC), Western blot, and real-time quantitative RT-PCR (qRT-PCR). Gastric cancer cells with either overexpressed SHIP2 or co-overexpressed SHIP2 and Akt were analyzed to determine cell proliferation, colony formation, apoptosis, cell migration, and invasion assays. Normal gastric epithelial cells with knockdown SHIP2 or co-knockdown SHIP2 and Akt were subjected by anchorage-independent growth assays. The effect of SHIP2 on tumor growth in vivo was detected by xenograft tumorigenesis assays.

RESULTS

SHIP2 was commonly downregulated in gastric cancer compared with normal gastric mucosa, and overexpression of SHIP2 inhibited cell proliferation, induced apoptosis, suppressed cell motility and invasion in gastric cancer cells in vitro, and retarded the growth of xenograft gastric tumors in vivo, while knockdown of SHIP2 in normal gastric epithelial cells promoted anchorage-independent growth. Moreover, overexpression of SHIP2 inactivated Akt, and upregulated p21, p27, and the pro-apoptotic protein Bim. Restoring Akt activation in gastric cancer cells largely blocked the inhibition of PI3K/Akt signaling by SHIP2 and reversed the inhibitory effect of SHIP2 on tumorigenesis and proliferation.

CONCLUSIONS

This study demonstrates, for the first time, that SHIP2 is frequently downregulated in gastric cancer, and reduced SHIP2 expression promotes tumorigenesis and proliferation of gastric cancer via activation of the PI3K/Akt signaling.

JAM-A regulates cortical dynein localization through Cdc42 to control planar spindle orientation during mitosis

Planar spindle orientation in polarized epithelial cells depends on the precise localization of the dynein–dynactin motor protein complex at the lateral cortex. The contribution of cell adhesion molecules to the cortical localization of the dynein–dynactin complex is poorly understood. Here we find that junctional adhesion molecule-A (JAM-A) regulates the planar orientation of the mitotic spindle during epithelial morphogenesis. During mitosis, JAM-A triggers a transient activation of Cdc42 and PI(3)K, generates a gradient of PtdIns(3,4,5)P3 at the cortex and regulates the formation of the cortical actin cytoskeleton. In the absence of functional JAM-A, dynactin localization at the cortex is reduced, the mitotic spindle apparatus is misaligned and epithelial morphogenesis in three-dimensional culture is compromised. Our findings indicate that a PI(3)K- and cortical F-actin-dependent pathway of planar spindle orientation operates in polarized epithelial cells to regulate epithelial morphogenesis, and we identify JAM-A as a junctional regulator of this pathway.

Polarized epithelial cells orient their mitotic spindles in the plane of the sheet but the role of cell adhesion molecules in this process is poorly understood. Here Tuncay et al. show that JAM-A regulates spindle orientation by creating a gradient of PtdIns(3,4,5)P₃, regulating cortical actin assembly and localizing dynactin to the cell cortex.

Inositol lipid phosphatases in membrane trafficking and human disease

The specific interaction of phosphoinositides with proteins is critical for a plethora of cellular processes, including cytoskeleton remodelling, mitogenic signalling, ion channel regulation and membrane traffic. The spatiotemporal restriction of different phosphoinositide species helps to define compartments within the cell, and this is particularly important for membrane trafficking within both the secretory and endocytic pathways. Phosphoinositide homoeostasis is tightly regulated by a large number of inositol kinases and phosphatases, which respectively phosphorylate and dephosphorylate distinct phosphoinositide species. Many of these enzymes have been implicated in regulating membrane trafficking and, accordingly, their dysregulation has been linked to a number of human diseases. In the present review, we focus on the inositol phosphatases, concentrating on their roles in membrane trafficking and the human diseases with which they have been associated.

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.

SHIP2 signaling in normal and pathological situations: Its impact on cell proliferation

Phosphoinositide 5-phosphatases are critical enzymes in modulating the concentrations of PI(3,4,5)P3, PI(4,5)P2 and PI(3,5)P2. The SH2 domain containing inositol 5-phosphatases SHIP1 and SHIP2 belong to this family of enzymes that dephosphorylate the 5 position of PI(3,4,5)P3 to produce PI(3,4)P2. Data obtained in zebrafish and in mice have shown that SHIP2 is critical in development and growth. Exome sequencing identifies mutations in the coding region of SHIP2 as a cause of opsismodysplasia, a severe but rare chondrodysplasia in human. SHIP2 has been reported to have both protumorigenic and tumor suppressor function in human cancer very much depending on the cell model. This could be linked to the relative importance of PI(3,4)P2 (a product of SHIP2 phosphatase activity) which is also controlled by the PI 4-phosphatase and tumor suppressor INPP4B. In the glioblastoma cell line 1321 N1, that do not express PTEN, lowering SHIP2 expression has an impact on the levels of PI(3,4,5)P3, cell morphology and cell proliferation. It positively stimulates cell proliferation by decreasing the expression of key regulatory proteins of the cell cycle such as p27. Together the data point out to a role of SHIP2 in development in normal cells and at least in cell proliferation in some cancer derived cells.

Tks5 and SHIP2 regulate invadopodium maturation, but not initiation, in breast carcinoma cells

BACKGROUND

Tks5 regulates invadopodium formation, but the precise timing during invadopodium lifetime (initiation, stabilization, maturation) when Tks5 plays a role is not known.

RESULTS

We report new findings based on high-resolution spatiotemporal live-cell imaging of invadopodium precursor assembly. Cortactin, N-WASP, cofilin, and actin arrive together to form the invadopodium precursor, followed by Tks5 recruitment. Tks5 is not required for precursor initiation but is needed for precursor stabilization, which requires the interaction of the phox homology (PX) domain of Tks5 with PI(3,4)P2. During precursor formation, PI(3,4)P2 is uniformly distributed but subsequently starts accumulating at the precursor core 3-4 min after core initiation, and conversely, PI(3,4,5)P3 gets enriched in a ring around the precursor core. SHIP2, a 5'-inositol phosphatase, localizes at the invadopodium core and regulates PI(3,4)P2 levels locally at the invadopodium. The timing of SHIP2 arrival at the invadopodium precursor coincides with the onset of PI(3,4)P2 accumulation. Consistent with its late arrival, we found that SHIP2 inhibition does not affect precursor formation but does cause decreases in mature invadopodia and matrix degradation, whereas SHIP2 overexpression increases matrix degradation.

CONCLUSIONS

Together, these findings lead us to propose a new sequential model that provides novel insights into molecular mechanisms underlying invadopodium precursor initiation, stabilization, and maturation into a functional invadopodium.

Mechanoregulation of stem cell fate via micro-/nano-scale manipulation for regenerative medicine

Recent developments in the field of mechanobiology have renewed the call for a better understanding of the role of mechanical forces as potent regulators and indicators of stem cell fate. Although it is well established that mechanical forces play a crucial role in guiding tissue development, little is known about how submicroscopic biomechanical forces can influence key stem cell behaviors. This review will detail the use of micro-/nano-technologies that are advancing our current understanding of stem cell mechanobiology, and mechanoregulation of stem cell fate using engineered surface topographies and small-scale patterning techniques. The involvement of focal adhesions and the cytoskeleton systems as a common biophysical impetus through which these mechanical signals are transduced via distinct signaling pathways will also be discussed. These insights are envisioned to provide the basis for the rational design of future biocompatible materials and may inspire alternative drug-free therapeutic strategies to manage diseased sites via biomechanical management.

Elevated expression of SHIP2 correlates with poor prognosis in non-small cell lung cancer

SH2-containing inositol 5'-phosphatase 2 (SHIP2) is a vital regulator of phosphoinositide pools in metabolic pathways and is considered to downregulate phosphatidylinositol 3'-kinase signaling, which underlies the development of several kinds of human cancers. However, SHIP2 expression in non-small cell lung cancer (NSCLC) and its relationship with the clinical characteristics of NSCLC remain poorly understood. In this study, one-step quantitative reverse transcription-polymerase chain reaction and immunohistochemistry analysis with tissue microarray was used to evaluate SHIP2 expression in NSCLC and to investigate the relationship of this expression to NSCLC prognosis. Results showed that the expression of SHIP2 messenger RNA and protein was significantly higher in NSCLC than in corresponding non-cancerous tissues (both p < 0.05). SHIP2 protein expression in NSCLC was related to lymph node metastasis (p = 0.042), TNM stage (p = 0.036), and 5-year survival rate (p = 0.046). The Kaplan-Meier method and log-rank test suggested that high SHIP2 expression, tobacco consumption, and advanced tumor stage were significantly associated with low survival of NSCLC patients. The results of this research suggested that SHIP2 expression was correlated with malignant phenotypes of NSCLC and may thus serve as a poor prognostic factor and valuable oncogene for NSCLC.

SHIP2 regulates epithelial cell polarity through its lipid product, which binds to Dlg1, a pathway subverted by hepatitis C virus core protein

The main targets of hepatitis C virus (HCV) are hepatocytes, the highly polarized cells of the liver, and all the steps of its life cycle are tightly dependent on host lipid metabolism. The interplay between polarity and lipid metabolism in HCV infection has been poorly investigated. Signaling lipids, such as phosphoinositides (PIs), play a vital role in polarity, which depends on the distribution and expression of PI kinases and PI phosphatases. In this study, we report that HCV core protein, expressed in Huh7 and Madin-Darby canine kidney (MDCK) cells, disrupts apicobasal polarity. This is associated with decreased expression of the polarity protein Dlg1 and the PI phosphatase SHIP2, which converts phosphatidylinositol 3,4,5-trisphosphate into phosphatidylinositol 4,5-bisphosphate (PtdIns(3,4)P2). SHIP2 is mainly localized at the basolateral membrane of polarized MDCK cells. In addition, PtdIns(3,4)P2 is able to bind to Dlg1. SHIP2 small interfering RNA or its catalytically dead mutant disrupts apicobasal polarity, similar to HCV core. In core-expressing cells, RhoA activity is inhibited, whereas Rac1 is activated. Of interest, SHIP2 expression rescues polarity, RhoA activation, and restricted core level in MDCK cells. We conclude that SHIP2 is an important regulator of polarity, which is subverted by HCV in epithelial cells. It is suggested that SHIP2 could be a promising target for anti-HCV treatment.

How does SHIP1/2 balance PtdIns(3,4)P2 and does it signal independently of its phosphatase activity?

The number of cellular events identified as being directly or indirectly modulated by phosphoinositides dramatically increased in the recent years. Part of the complexity results from the fact that the seven phosphoinositides play second messenger functions in many different areas of growth factors and insulin signaling, cytoskeletal organization, membrane dynamics, trafficking, or nuclear signaling. PtdIns(3,4)P2 is commonly reported as a product of the SH2 domain-containing inositol 5-phosphatases 1/2 (SHIP1 and SHIP2) that dephosphorylate PtdIns(3,4,5)P3 at the 5-position. Here we discuss recent interest in PtdIns(3,4)P2 signaling highlighting its involvement in key cellular mechanisms such as cell adhesion, migration, and cytoskeletal regulation. We question and discuss the involvement of SHIP2 either as a PI 5-phosphatase or as a scaffold protein in insulin signaling, cytoskeletal dynamics, and endocytosis of growth factor receptors.

Inositol polyphosphate phosphatases in human disease

Phosphoinositide signalling molecules interact with a plethora of effector proteins to regulate cell proliferation and survival, vesicular trafficking, metabolism, actin dynamics and many other cellular functions. The generation of specific phosphoinositide species is achieved by the activity of phosphoinositide kinases and phosphatases, which phosphorylate and dephosphorylate, respectively, the inositol headgroup of phosphoinositide molecules. The phosphoinositide phosphatases can be classified as 3-, 4- and 5-phosphatases based on their specificity for dephosphorylating phosphates from specific positions on the inositol head group. The SAC phosphatases show less specificity for the position of the phosphate on the inositol ring. The phosphoinositide phosphatases regulate PI3K/Akt signalling, insulin signalling, endocytosis, vesicle trafficking, cell migration, proliferation and apoptosis. Mouse knockout models of several of the phosphoinositide phosphatases have revealed significant physiological roles for these enzymes, including the regulation of embryonic development, fertility, neurological function, the immune system and insulin sensitivity. Importantly, several phosphoinositide phosphatases have been directly associated with a range of human diseases. Genetic mutations in the 5-phosphatase INPP5E are causative of the ciliopathy syndromes Joubert and MORM, and mutations in the 5-phosphatase OCRL result in Lowe's syndrome and Dent 2 disease. Additionally, polymorphisms in the 5-phosphatase SHIP2 confer diabetes susceptibility in specific populations, whereas reduced protein expression of SHIP1 is reported in several human leukaemias. The 4-phosphatase, INPP4B, has recently been identified as a tumour suppressor in human breast and prostate cancer. Mutations in one SAC phosphatase, SAC3/FIG4, results in the degenerative neuropathy, Charcot-Marie-Tooth disease. Indeed, an understanding of the precise functions of phosphoinositide phosphatases is not only important in the context of normal human physiology, but to reveal the mechanisms by which these enzyme families are implicated in an increasing repertoire of human diseases.

SHIP2 signalling at the plasma membrane, in the nucleus and at focal contacts

Phosphoinositide 5-phosphatases are critical enzymes in modulating the concentrations of PI(3,4,5)P(3), PI(4,5)P(2) and PI(3,5)P(2). The SH2 domain containing inositol 5-phosphatases SHIP1 and SHIP2 belong to this family of enzymes very much involved in physiopathology and development. Therefore activity and localization of the enzymes are particularly important taking into account both catalytic and non-catalytic mechanisms of the SHIP phosphatases. Several different mechanisms have been reported for SHIP2 targeting that often result from specific protein:protein interactions. In unstimulated astrocytoma cells, SHIP2 has a perinuclear and cytoplasmic localization. In serum-stimulated cells, SHIP2 can be localized at the plasma membrane and at focal contacts in polarized cells. A phosphorylated form of SHIP2 on S132 can be found in the nucleus and nuclear speckles. When present at the plasma membrane, SHIP2 may control the intracellular level of PI(3,4,5)P(3) thereby producing PI(3,4)P(2). When present in the nucleus, SHIP2 probably associates to other nuclear proteins such as lamin A/C and could potentially control nuclear PI(4,5)P(2). Finally, its presence at focal adhesions and lamellipodia could suggest a role in cell adhesion and migration. It is proposed that the complex phenotype observed in SHIP2 mutant mice in tissue development and growth could result from the addition of plasma membrane and nuclear effects consecutive to SHIP2 alteration.

A phosphatidylinositol lipids system, lamellipodin, and Ena/VASP regulate dynamic morphology of multipolar migrating cells in the developing cerebral cortex

In the developing mammalian cerebral cortex, excitatory neurons are generated in the ventricular zone (VZ) and subventricular zone; these neurons migrate toward the pial surface. The neurons generated in the VZ assume a multipolar morphology and remain in a narrow region called the multipolar cell accumulation zone (MAZ) for ∼24 h, in which they extend and retract multiple processes dynamically. They eventually extend an axon tangentially and begin radial migration using a migratory mode called locomotion. Despite the potential biological importance of the process movement of multipolar cells, the molecular mechanisms remain to be elucidated. Here, we observed that the processes of mouse multipolar cells were actin rich and morphologically resembled the filopodia and lamellipodia in growth cones; thus, we focused on the actin-remodeling proteins Lamellipodin (Lpd) and Ena/vasodilator-stimulated phosphoprotein (VASP). Lpd binds to phosphatidylinositol (3,4)-bisphosphate [PI(3,4)P₂] and recruits Ena/VASP, which promotes the assembly of actin filaments, to the plasma membranes. In situ hybridization and immunohistochemistry revealed that Lpd is expressed in multipolar cells in the MAZ. The functional silencing of either Lpd or Ena/VASP decreased the number of primary processes. Immunostaining and a Förster resonance energy transfer analysis revealed the subcellular localization of PI(3,4)P₂ at the tips of the processes. A knockdown experiment and treatment with an inhibitor for Src homology 2-containing inositol phosphatase-2, a 5-phosphatase that produces PI(3,4)P₂ from phosphatidylinositol (3,4,5)-triphosphate, decreased the number of primary processes. Our observations suggest that PI(3,4)P₂, Lpd, and Ena/VASP are involved in the process movement of multipolar migrating cells.

Network analysis of the focal adhesion to invadopodia transition identifies a PI3K-PKCα invasive signaling axis

In cancer, deregulated signaling can produce an invasive cellular phenotype. We modeled the invasive transition as a theoretical switch between two cytoskeletal structures: focal adhesions and extracellular matrix-degrading invadopodia. We constructed molecular interaction networks of each structure and identified upstream regulatory hubs through computational analyses. We compared these regulatory hubs to the status of signaling components from head and neck carcinomas, which led us to analyze phosphatidylinositol 3-kinase (PI3K) and protein kinase C α (PKCα). Consistent with previous studies, PI3K activity promoted both the formation and the activity of invadopodia. We found that PI3K induction of invadopodia was increased by overexpression of SH2 (Src homology 2) domain-containing inositol 5'-phosphatase 2 (SHIP2), which converts the phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P(3)] that is produced by PI3K activity to phosphatidylinositol 3,4-bisphosphate [PI(3,4)P(2)], which is believed to promote invadopodia formation. Knockdown of PKCα had divergent effects on invadopodia formation, depending on the status of PI3K. Loss of PKCα inhibited invadopodia formation in cells with wild-type PI3K pathway status. Conversely, in cells with constitutively active PI3K (through activating PI3K mutants or lacking the endogenous opposing enzyme PTEN), PKCα knockdown increased invadopodia formation. Mechanistic studies revealed a negative feedback loop from PKCα that dampened PI3K activity and invasive behavior in cells with genetic hyperactivation of the PI3K pathway. These studies demonstrated the potential of network modeling as a discovery tool and identified PI3K and PKCα as interacting regulators of invasive behavior.

Pharmacological targeting of phosphoinositide lipid kinases and phosphatases in the immune system: success, disappointment, and new opportunities

The predominant expression of the γ and δ isoforms of PI3K in cells of hematopoietic lineage prompted speculation that inhibitors of these isoforms could offer opportunities for selective targeting of PI3K in the immune system in a range of immune-related pathologies. While there has been some success in developing PI3Kδ inhibitors, progress in developing selective inhibitors of PI3Kγ has been rather disappointing. This has prompted the search for alternative targets with which to modulate PI3K signaling specifically in the immune system. One such target is the SH2 domain-containing inositol-5-phosphatase-1 (SHIP-1) which de-phosphorylates PI(3,4,5)P₃ at the D5 position of the inositol ring to create PI(3,4)P₂. In this article, we first describe the current state of PI3K isoform-selective inhibitor development. We then focus on the structure of SHIP-1 and its function in the immune system. Finally, we consider the current state of development of small molecule compounds that potently and selectively modulate SHIP activity and which offer novel opportunities to manipulate PI3K mediated signaling in the immune system.

Reversible Ser/Thr SHIP phosphorylation: a new paradigm in phosphoinositide signalling?: Targeting of SHIP1/2 phosphatases may be controlled by phosphorylation on Ser and Thr residues

Phosphoinositide (PI) phosphatases such as the SH2 domain-containing inositol 5-phosphatases 1/2 (SHIP1 and 2) are important signalling enzymes in human physiopathology. SHIP1/2 interact with a large number of immune and growth factor receptors. Tyrosine phosphorylation of SHIP1/2 has been considered to be the determining regulatory modification. However, here we present a hypothesis, based on recent key publications, highlighting the determining role of Ser/Thr phosphorylation in regulating several key properties of SHIP1/2. Since a subunit of the Ser/Thr phosphatase PP2A has been shown to interact with SHIP2, a putative mechanism for reversing SHIP2 Ser/Thr phosphorylation can be anticipated. PI phosphatases are potential target molecules in human diseases, particularly, but not exclusively, in cancer and diabetes. Therefore, this novel regulatory mechanism deserves further attention in the hunt for discovering novel or complementary therapeutic strategies. This mechanism may be more broadly involved in regulating PI signalling in the case of synaptojanin1 or the phosphatase, tensin homolog, deleted on chromosome TEN.

Phosphoinositide phosphatases: just as important as the kinases

Phosphoinositide phosphatases comprise several large enzyme families with over 35 mammalian enzymes identified to date that degrade many phosphoinositide signals. Growth factor or insulin stimulation activates the phosphoinositide 3-kinase that phosphorylates phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P(2)] to form phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P(3)], which is rapidly dephosphorylated either by PTEN (phosphatase and tensin homologue deleted on chromosome 10) to PtdIns(4,5)P(2), or by the 5-phosphatases (inositol polyphosphate 5-phosphatases), generating PtdIns(3,4)P(2). 5-phosphatases also hydrolyze PtdIns(4,5)P(2) forming PtdIns(4)P. Ten mammalian 5-phosphatases have been identified, which regulate hematopoietic cell proliferation, synaptic vesicle recycling, insulin signaling, and embryonic development. Two 5-phosphatase genes, OCRL and INPP5E are mutated in Lowe and Joubert syndrome respectively. SHIP [SH2 (Src homology 2)-domain inositol phosphatase] 2, and SKIP (skeletal muscle- and kidney-enriched inositol phosphatase) negatively regulate insulin signaling and glucose homeostasis. SHIP2 polymorphisms are associated with a predisposition to insulin resistance. SHIP1 controls hematopoietic cell proliferation and is mutated in some leukemias. The inositol polyphosphate 4-phosphatases, INPP4A and INPP4B degrade PtdIns(3,4)P(2) to PtdIns(3)P and regulate neuroexcitatory cell death, or act as a tumor suppressor in breast cancer respectively. The Sac phosphatases degrade multiple phosphoinositides, such as PtdIns(3)P, PtdIns(4)P, PtdIns(5)P and PtdIns(3,5)P(2) to form PtdIns. Mutation in the Sac phosphatase gene, FIG4, leads to a degenerative neuropathy. Therefore the phosphatases, like the lipid kinases, play major roles in regulating cellular functions and their mutation or altered expression leads to many human diseases.

Nephrin regulates lamellipodia formation by assembling a protein complex that includes Ship2, filamin and lamellipodin

Actin dynamics has emerged at the forefront of podocyte biology. Slit diaphragm junctional adhesion protein Nephrin is necessary for development of the podocyte morphology and transduces phosphorylation-dependent signals that regulate cytoskeletal dynamics. The present study extends our understanding of Nephrin function by showing in cultured podocytes that Nephrin activation induced actin dynamics is necessary for lamellipodia formation. Upon activation Nephrin recruits and regulates a protein complex that includes Ship2 (SH2 domain containing 5′ inositol phosphatase), Filamin and Lamellipodin, proteins important in regulation of actin and focal adhesion dynamics, as well as lamellipodia formation. Using the previously described CD16-Nephrin clustering system, Nephrin ligation or activation resulted in phosphorylation of the actin crosslinking protein Filamin in a p21 activated kinase dependent manner. Nephrin activation in cell culture results in formation of lamellipodia, a process that requires specialized actin dynamics at the leading edge of the cell along with focal adhesion turnover. In the CD16-Nephrin clustering model, Nephrin ligation resulted in abnormal morphology of actin tails in human podocytes when Ship2, Filamin or Lamellipodin were individually knocked down. We also observed decreased lamellipodia formation and cell migration in these knock down cells. These data provide evidence that Nephrin not only initiates actin polymerization but also assembles a protein complex that is necessary to regulate the architecture of the generated actin filament network and focal adhesion dynamics.

SHIP2 multiple functions: a balance between a negative control of PtdIns(3,4,5)P₃ level, a positive control of PtdIns(3,4)P₂ production, and intrinsic docking properties

The SH2 domain containing inositol 5-phosphatase 2 (SHIP2) belongs to the family of the mammalian inositol polyphosphate 5-phosphatases. The two closely related isoenzymes SHIP1 (or SHIP) and SHIP2 contain a N-terminal SH2 domain, a catalytic domain, potential PTB domain-binding sites (NPXY), and C-terminal proline-rich regions with consensus sites for SH3 domain interactions. In addition, SHIP2 contains a unique sterile alpha motif (SAM) domain that could be involved in SAM-SAM domain interactions with other proteins or receptors. SHIP2 also shows the presence of an ubiquitin interacting motif at the C-terminal end. SHIP2 is essentially a PI(3,4,5)P(3) 5-phosphatase that negatively controls PI(3,4,5)P(3) levels in intact cells and produce PI(3,4)P(2) . Depending on the cells and stimuli, PI(3,4)P(2) could accumulate at important levels and be a "second messenger" by its own. It could interact with a very large number of target proteins such as PKB or TAPP1 and 2 that control insulin sensitivity. In addition to its catalytic activity, SHIP2 is also a docking protein for a large number of proteins: Cytoskeletal, focal adhesion proteins, scaffold proteins, adaptors, protein phosphatases, and tyrosine kinase associated receptors. These interactions could play a role in the control of cell adhesion, migration, or endocytosis of some receptors. SHIP2 could be acting independently of its phosphatase activity being part of a protein network of some receptors, e.g., the EGF receptor or BCR/ABL. These non-catalytic properties associated to a PI phosphatase have also been reported for other enzymes of the metabolism of myo-inositol such as Ins(1,4,5)P(3) 3-kinases, inositol phosphate multikinase (IPMK), or PTEN.

Abnormal elevated PTEN expression in the mouse antrum of a model of GIST Kit(K641E/K641E)

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. Approximately 85% of GISTs harbor activating mutations of the KIT or PDGFRA receptor tyrosine kinases. PTEN and SHIP2 are major phosphatases that dephosphorylate PI(3,4,5)P(3), one of the intracellular signal pathways downstream of KIT. PTEN is an important tumor suppressor, whereas the involvement of SHIP2 in cancer has been proposed based essentially on cell line studies. We have used a mouse model of GIST, i.e. Kit(K641E) knock-in mice, resulting in the substitution of a Lys by Glu at position 641 of Kit. In homozygous Kit(K641E) mice, PTEN-immunoreactivity (ir) in antrum was found in the hyperplastic Kit-ir layer. The same localization was found for SHIP2. Western blot analysis in antrum showed a large increase in PTEN expression in Kit(K641E) homozygous mice as compared to wild type. In contrast, SHIP2 expression was not affected between the two genotypes. Erk1, but not PKB, phosphorylation appears to be upregulated in Kit(K641E) homozygous mice. In the human GIST882 imatinib sensitive cell line, both PTEN and SHIP2 were expressed and showed, in part, a nuclear localization. The upregulation of PTEN in antrum in Kit(K641E) mice might serve as a feedback mechanism to limit PI 3-kinase activation downstream of Kit in a context of oncogenic mutation.