Hisanori Horiuchi

The blood glycoprotein von Willebrand factor (VWF) plays an important role in hemostasis and thrombosis.VWF is produced and secreted as large multimers by endothelial cells and megakaryocytes. It is then cleaved in a sheer-stress dependent manner by a specific protease, ADAMTS13, into multimers consisting of 2-80 subunits. Among VWF multimers, high molecular weight (HMW) multimers play important roles in platelet aggregation. Therefore, their loss induces a hemostatic disorder known as von Wille

Metformin is the first-line drug in the treatment of type 2 diabetes. In addition to its hypoglycemic effect, metformin has an anti-inflammatory function, but the precise mechanism promoting this activity remains unclear. High mobility group box 1 (HMGB1) is an alarmin that is released from necrotic cells and induces inflammatory responses by its cytokine-like activity and is, therefore, a target of anti-inflammatory therapies. Here we identified HMGB1 as a novel metformin-binding protein by aff

Upon activation, platelets release many active substances stored in alpha- and dense-core granules. However, the molecular mechanisms governing regulated exocytosis are not yet fully understood. Here, we have established an assay system using permeabilized platelets to analyze the Ca(2+)-induced exocytosis of both types of granules, focusing on RabGTPases. Incubation with Rab GDP dissociation inhibitor, an inhibitory regulator of RabGTPases, reduced membrane-bound RabGTPases extensively, and cau

PGE2 inhibits NET formation through the production of cAMP. These findings will contribute to the development of novel treatments for NETosis-related diseases.

The small GTPases RalA and RalB are multifunctional proteins regulating a variety of cellular processes. Like other GTPases, the activity of Ral is regulated by the opposing effects of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Although several RalGEFs have been identified and characterized, the molecular identity of RalGAP remains unknown. Here, we report the first molecular identification of RalGAPs, which we have named RalGAP1 and RalGAP2. They are large

smg p25A/rab3A p25 is a member of the small GTP-binding protein superfamily which is implicated in intracellular vesicle transport. smg p25A has a cDNA-predicted C-terminal structure of Cys-Ala-Cys. The protein purified from bovine brain membranes is geranylgeranylated at both the two cysteine residues and carboxyl-methylated at the C-terminal cysteine residue. Two types of prenyltransferase for small GTP-binding proteins have thus far been reported: ras p21 farnesyltransferase (ras p21 FT) and

The diaphanous-related formins are actin nucleating and elongating factors. They are kept in an inactive state by an intramolecular interaction between the diaphanous inhibitory domain (DID) and the diaphanous-autoregulatory domain (DAD). It is considered that the dissociation of this autoinhibitory interaction upon binding of GTP-bound Rho to the GTPase binding domain next to DID induces exposure of the FH1-FH2 domains, which assemble actin filaments. Here, we isolated two diaphanous-related fo

Small GTPases of the Rab family are key regulators of intracellular transport. They are associated with the cytoplasmic surface of distinct exocytic and endocytic organelles and with transport vesicles connecting these compartments. Rab proteins are also present in the cytosol in the GDP-bound conformation complexed to Rab GDP dissociation inhibitor (RabGDI). Upon membrane association, RabGDI is released, and the Rab protein is converted into the GTP-bound form. In this paper we have investigate

We have previously demonstrated that Rab27 regulates dense granule secretion in platelets. Here, we analyzed the activation status of Rab27 using the thin layer chromatography method analyzing nucleotides bound to immunoprecipitated Rab27 and the pull-down method quantifying Rab27 bound to the GTP-Rab27-binding domain (synaptotagmin-like protein (Slp)-homology domain) of its specific effector, Slac2-b. We found that Rab27 was predominantly present in the GTP-bound form in unstimulated platelets

A questionnaire on COVID-19-related thrombosis in patients hospitalized before Aug 31, 2020, was sent to 399 hospitals throughout Japan. Responses were received from 111 (27.8%) with information on 6,202 COVID-19 patients. Of these, 333 and 56 required ventilation or extracorporeal membrane oxygenation (ECMO), respectively, and 212 died (3.4%). D-dimer levels were measured in 75.0% of the patients, revealing that 9.2% and 7.6% exhibited D-dimer increases of 3-8-fold and ≥8-fold the reference val

Platelets play critical roles in hemostasis and thrombosis through their aggregation following activation of integrin alphaIIbbeta3. However, the molecular mechanism of the integrin activation inside platelets remains largely unknown. Pharmacological experiments have demonstrated that protein kinase C (PKC) plays an important role in platelet aggregation. Because PKC inhibitors can have multiple substrates and given that non-PKC-phorbol ester-binding signaling molecules have been demonstrated to

Lysophosphatidylcholine (LPC) accumulates in inflammatory tissues, where neutrophils are recruited to generate superoxide anions (O2.-). Here, we show that LPC stimulates O2.- generation in human neutrophils and that the activity is inhibited with phosphatidylinositol 3-kinase (PI3 kinase) inhibitors, but not with protein kinase C (PKC) inhibitors. Furthermore, we demonstrate that LPC activates PI3 kinase in neutrophils. Thus, LPC might contribute to host defense by generating O2.- in neutrophil