SHIP-2 is a phosphoinositidylinositol 3,4,5 trisphosphate (PtdIns[3,4,5]P3) 5-phosphatase that contains an NH2-terminal SH2 domain, a central 5-phosphatase domain, and a COOH-terminal proline-rich domain. SHIP-2 negatively regulates insulin signaling. In unstimulated cells, SHIP-2 localized in a perinuclear cytosolic distribution and at the leading edge of the cell. Endogenous and recombinant SHIP-2 localized to membrane ruffles, which were mediated by the COOH-terminal proline–rich domain. To identify proteins that bind to the SHIP-2 proline–rich domain, yeast two-hybrid screening was performed, which isolated actin-binding protein filamin C. In addition, both filamin A and B specifically interacted with SHIP-2 in this assay. SHIP-2 coimmunoprecipitated with filamin from COS-7 cells, and association between these species did not change after epidermal growth factor stimulation. SHIP-2 colocalized with filamin at Z-lines and the sarcolemma in striated muscle sections and at membrane ruffles in COS-7 cells, although the membrane ruffling response was reduced in cells overexpressing SHIP-2. SHIP-2 membrane ruffle localization was dependent on filamin binding, as SHIP-2 was expressed exclusively in the cytosol of filamin-deficient cells. Recombinant SHIP-2 regulated PtdIns(3,4,5)P3 levels and submembraneous actin at membrane ruffles after growth factor stimulation, dependent on SHIP-2 catalytic activity. Collectively these studies demonstrate that filamin-dependent SHIP-2 localization critically regulates phosphatidylinositol 3 kinase signaling to the actin cytoskeleton.

The inositol-polyphosphate 5-phosphatase enzyme family removes the 5-position phosphate from both inositol phosphate and phosphoinositide signaling molecules. We have cloned and characterized a novel 5-phosphatase, which demonstrates a restricted substrate specificity and tissue expression. The 3.9-kb cDNA predicts for a 72-kDa protein with an N-terminal proline rich domain, a central 5-phosphatase domain, and a Cterminal CAAX motif. The 3.9-kilobase mRNA showed a restricted expression but was abundant in testis and brain. Antibodies against the sequence detected a 72-kDa protein in the testis in the detergent-insoluble fraction. Indirect immunofluorescence of the Tera-1 cell line using anti-peptide antibodies to the 72-kDa 5-phosphatase demonstrated that the enzyme is predominantly located to the Golgi. Expression of green fluorescent protein-tagged 72-kDa 5-phosphatase in COS-7 cells revealed that the enzyme localized predominantly to the Golgi, mediated by the N-terminal proline-rich domain, but not the C-terminal CAAX motif. In vitro, the protein inserted into microsomal membranes on the cytoplasmic face of the membrane. Immunoprecipitated recombinant 72-kDa 5-phosphatase hydrolyzed phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3,5-bisphosphate, forming phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3-phosphate, respectively. We propose that the novel 5-phosphatase hydrolyzes phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3,5-bisphosphate on the cytoplasmic Golgi membrane and thereby may regulate Golgi-vesicular trafficking.The inositol-polyphosphate 5-phosphatases (5-phosphatases) 1 are a large family of enzymes that remove the 5-position phosphate from the inositol ring of phosphatidylinositols including phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P 2 ), phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P 3 ), and the inositol phosphates, inositol 1,4,5-trisphosphate (Ins(1,4,5)-P 3 ) and inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P 4 ). Nine distinct mammalian 5-phosphatases have been identified and characterized, while four 5-phosphatases have been described in Saccharomyces cerevisiae. All 5-phosphatases are defined by the presence of a conserved 300-amino acid domain, which contains two signature motifs, proposed to mediate substrate binding and catalysis (1, 2). Although all 5-phosphatase enzymes contain these signature motifs, there is considerable diversity in the substrate specificity of 5-phosphatase isoforms. The enzyme family has been subclassified on this basis into four types, I-IV. The type I enzymes, characterized by the 43-kDa 5-phosphatase (also called 5-phosphatase I), hydrolyze Ins(1,4,5)P 3 and Ins(1,3,4,5)P 4 but not any of the 5-position phosphoinositide substrates; the type II 5-phosphatases, including synaptojanin, 5-phosphatase II (originally designated the 75-kDa 5-phosphatase), and the protein product of the oculocerebrorenal syndrome (OCRL) gene, hydrolyze PtdIns-(4,5)P 2 , PtdIns(3,4,5)P 3 , Ins(1,3,4,5)P 4 ...

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• CEACAM2 is a novel platelet immunoreceptor.• CEACAM2 negatively regulates platelet-collagen interactions and thrombus growth and stability in vitro, in vivo and CLEC-2 pathways.Carcinoembryonic antigen-related cell adhesion molecule-2 (CEACAM2) is a cell-surface glycoprotein expressed on blood, epithelial, and vascular cells. CEACAM2 possesses adhesive and signaling properties mediated by immunoreceptor tyrosine-based inhibitory motifs. In this study, we demonstrate that CEACAM2 is expressed on the surface and in intracellular pools of platelets. Functional studies of platelets from Ceacam2) revealed that CEACAM2 serves to negatively regulate collagen glycoprotein VI (platelet) (GPVI)-FcRg-chain and the C-type lectinlike receptor 2 (CLEC-2) signaling. Cc2 2/2 platelets displayed enhanced GPVI and CLEC-2-selective ligands, collagen-related peptide (CRP), collagen, and rhodocytin (Rhod)-mediated platelet aggregation. They also exhibited increased adhesion on type I collagen, and hyperresponsive CRP and CLEC-2-induced a and dense granule release compared with wild-type platelets. Furthermore, using intravital microscopy to ferric chloride (FeCl 3 )-injured mesenteric arterioles and laser-induced injury of cremaster muscle arterioles, we herein show that thrombi formed in Cc2 2/2 mice were larger and more stable than wild-type controls in vivo. Thus, CEACAM2 is a novel platelet immunoreceptor that acts as a negative regulator of platelet GPVI-collagen interactions and of ITAM receptor CLEC-2 pathways. (Blood. 2014;124(15):2431-2441