Platelet interaction with exposed adhesive ligands at sites of vascular injury is required to initiate a normal hemostatic response and may become a pathogenic factor in arterial diseases leading to thrombosis. We report a targeted disruption in a key receptor for collageninduced platelet activation, glycoprotein (GP) VI. The breeding of mice with heterozygous GP VI alleles produced the expected frequency of wild-type, heterozygous, and homozygous genotypes, indicating that these animals had no reproductive problems and normal viability. GP VI null platelets failed to aggregate in response to type I fibrillar collagen or convulxin, a snake venom protein and known platelet agonist of GP VI. Nevertheless, tail bleeding time measurements revealed no severe bleeding tendency as a consequence of GP VI deficiency. Ex vivo platelet thrombus formation on type I collagen fibrils was abolished using blood from either GP VI null or FcR-␥ null animals. Reflection interference contrast microscopy revealed that the lack of thrombus formation by GP VI null platelets could be linked to a defective platelet activation following normal initial tethering to the surface, visualized as lack of spreading and less stable adhesion. These results illustrate the role of GP VI in postadhesion events leading to the development of platelet thrombi on collagen fibrils. IntroductionPlatelet membrane receptors interact with surface-bound adhesive ligands and, as such, become essential for hemostasis and thrombosis. 1 There are numerous unique receptors interacting with different adhesive ligands suggesting that a large opportunity exists for functional redundancy in platelet adhesion. However, an emerging theme of platelet biology is the relevance of different membrane receptors in different areas of the vasculature. 2,3 A specific example is the exclusive role for the platelet glycoprotein (GP) Ib-IX-V complex and von Willebrand factor in areas of the vascular system where flow rates and high shear occur, such as in small arteries and arterioles. 4 Thus, defining the physiologic relevance of an individual receptor and its ligand is an important aspect for understanding participation of the platelet in hemostasis and thrombosis.Among adhesive ligands of the extravascular matrix, collagen is a significant component with a number of known collagen receptors on the platelet surface. 5,6 One of the more recently characterized collagen receptors is GP VI. 7 The molecular cloning of GP VI revealed it to be a member of the immunoglobulin superfamily of type I transmembrane proteins. [8][9][10] The surface expression of GP VI requires the concomitant expression of the ␥-subunit of the FcR receptor (FcR-␥) and their association is functionally relevant as collagen binding to GP VI results in platelet signaling via the immunoreceptor tyrosine-based activation motif (ITAM) located in the FcR-␥ subunit. 8,[11][12][13][14] As with many of the platelet receptors, the in vivo relevance of GP VI was established prior to its description and recognition as a p...

NK cell transcript 4 (NK4), now denoted as IL-32, was originally identified as a transcript whose expression was increased in activated NK cells. It has been very recently demonstrated that NK4 is secreted from several cells upon the stimulation of some inflammatory cytokines such as IL-18, IL-1beta, IFN-gamma and IL-12. Furthermore, NK4 induces production of tumor necrosis factor, macrophage inflammatory protein (MIP)-2 and IL-8 in monocytic cell lines, indicating that this factor would be involved in the inflammatory responses. Based on these findings, NK4 was renamed IL-32. However, the biological activities of IL-32 on other cell types remained undetermined. Furthermore, it was still argued whether IL-32 acts on cells from outside or inside the cells. In this article, we first report that expression of IL-32 was up-regulated in activated T cells and NK cells, and that IL-32beta was the predominantly expressed isoform in activated T cells. IL-32 was specifically expressed in T cells undergoing apoptosis and enforced expression of IL-32-induced apoptosis, whereas its down-regulation rescued the cells from apoptosis in HeLa cells. IL-32 existing in the supernatant would be derived from the cytoplasm of apoptotic cells. These results strongly indicated that IL-32 would be involved in activation-induced cell death in T cells, probably via its intracellular actions. Our present findings expand our understanding of the biological function of IL-32 and argue that IL-32 may act on cells, not only from the outside but also from the inside.

Tom20 is a major receptor of the mitochondrial preprotein translocation system and is bound to the outer membrane through the NH2-terminal transmembrane domain (TMD) in an Nin-Ccyt orientation. We analyzed the mitochondria-targeting signal of rat Tom20 (rTom20) in COS-7 cells, using green fluorescent protein (GFP) as the reporter by systematically introducing deletions or mutations into the TMD or the flanking regions. Moderate TMD hydrophobicity and a net positive charge within five residues of the COOH-terminal flanking region were both critical for mitochondria targeting. Constructs without net positive charges within the flanking region, as well as those with high TMD hydrophobicity, were targeted to the ER-Golgi compartments. Intracellular localization of rTom20-GFP fusions, determined by fluorescence microscopy, was further verified by cell fractionation. The signal recognition particle (SRP)–induced translation arrest and photo–cross-linking demonstrated that SRP recognized the TMD of rTom20-GFP, but with reduced affinity, while the positive charge at the COOH-terminal flanking segment inhibited the translation arrest. The mitochondria-targeting signal identified in vivo also functioned in the in vitro system. We conclude that NH2-terminal TMD with a moderate hydrophobicity and a net positive charge in the COOH-terminal flanking region function as the mitochondria-targeting signal of the outer membrane proteins, evading SRP-dependent ER targeting.

Excessive production of airway mucus is a cardinal feature of bronchial asthma and chronic obstructive pulmonary disease (COPD) and contributes to morbidity and mortality in these diseases. IL-13, a Th2-type cytokine, is a central mediator in the pathogenesis of bronchial asthma, including mucus overproduction. Using a genome-wide search for genes induced in airway epithelial cells in response to IL-13, we identified pendrin encoded by the SLC26A4 (PDS) gene as a molecule responsible for airway mucus production. In both asthma and COPD mouse models, pendrin was up-regulated at the apical side of airway epithelial cells in association with mucus overproduction. Pendrin induced expression of MUC5AC, a major product of mucus in asthma and COPD, in airway epithelial cells. Finally, the enforced expression of pendrin in airway epithelial cells in vivo, using a Sendai virus vector, rapidly induced mucus overproduction in the lumens of the lungs together with neutrophilic infiltration in mice. These findings collectively suggest that pendrin can induce mucus production in airway epithelial cells and may be a therapeutic target candidate for bronchial asthma and COPD.

Summary Background von Willebrand Factor (VWF) is a glycoprotein that plays an important role in primary hemostasis. VWF is synthesized and stored in endothelial cells (ECs) and megakaryocytes/platelets. Plasma VWF is primarily derived from ECs and is generally believed to be essential for hemostasis. VWF synthesized in megakaryocytes is stored in platelet α-granules from which it is released following platelet activation. The relative contribution of VWF stored in ECs or megakaryocytes/platelets, or present in plasma to hemostasis is not clear. Objectives We investigated whether EC-derived VWF plays the major role in hemostasis while the contribution of platelet-derived VWF is negligible, or if platelet-derived VWF also significantly contributes to hemostasis. Methods and Results Mice expressing VWF only in ECs (EC-VWF) or platelets (Plt-VWF) were created by reciprocal bone marrow transplantation between C57BL/6J (WT) and VWF knockout mice (VWF−/−). Plasma VWF levels in EC-VWF were similar to WT. Plt-VWF mice had a trace amount of VWF in their plasma while VWF levels in platelet lysate were comparable to WT. Tail bleeding time was normal in EC-VWF. Interestingly, Plt-VWF showed partially corrected bleeding time and significantly decreased blood loss volume compared to VWF−/−. Adhesion of platelets perfused over immobilized collagen under shear stress was significantly higher in both EC-VWF and Plt-VWF compared to VWF−/−. Conclusion VWF synthesized in ECs is sufficient to support hemostasis in VWF−/− mice, and VWF produced in megakaryocytes/platelets can also contribute to hemostasis in the absence of EC-derived VWF.