[show abstract][hide abstract] ABSTRACT: Stalled replication forks undergo DNA double-strand breaks (DSBs) under certain conditions. However, the precise mechanism underlying DSB induction and the cellular response to persistent replication fork stalling are not fully understood. Here we show that in response to hydroxyurea (HU) exposure DSBs are generated in an Artemis nuclease-dependent manner following prolonged stalling with subsequent activation of the ataxia-telangiectasia mutated (ATM) signaling pathway. The kinase activity of the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), a prerequisite for stimulation of the endonuclease activity of Artemis, is also required for DSB generation and subsequent ATM activation. Our findings indicate a novel function of Artemis as a molecular switch that converts stalled replication forks harboring single-stranded gap DNA lesions into DSBs, thereby activating the ATM signaling pathway following prolonged replication fork stalling.
[show abstract][hide abstract] ABSTRACT: The function of the kinase Btk in neutrophil activation is largely unexplored. Here we found that Btk-deficient neutrophils had more production of reactive oxygen species (ROS) after engagement of Toll-like receptors (TLRs) or receptors for tumor-necrosis factor (TNF), which was associated with more apoptosis and was reversed by transduction of recombinant Btk. Btk-deficient neutrophils in the resting state showed hyperphosphorylation and activation of phosphatidylinositol-3-OH kinase (PI(3)K) and protein tyrosine kinases (PTKs) and were in a 'primed' state with plasma membrane-associated GTPase Rac2. In the absence of Btk, the adaptor Mal was associated with PI(3)K and PTKs at the plasma membrane, whereas in control resting neutrophils, Btk interacted with and confined Mal in the cytoplasm. Our data identify Btk as a critical gatekeeper of neutrophil responses.
[show abstract][hide abstract] ABSTRACT: Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency disease affecting cell morphology and signal transduction in hematopoietic cells. The function of Wiskott-Aldrich syndrome protein (WASp) and its partners in protein interaction have been studied intensively in mice; however, detailed biochemical characterization of its signal transduction and assessment of its functional consequence in human WASp-deficient lymphocytes remain difficult. In this study, we generated Nalm-6 cells in which the WAS protein gene (WASP) was disrupted by homologous recombination-based gene targeting and a cell-permeable form of recombinant WASp for functional study. The WASP⁻/⁻ cells showed impaired adhesive capacity and polarization to plate-bound anti-CD47 mAb, anti-CD9 mAb, or to fibronectin. The defective morphological changes were accompanied by impaired intracellular signaling. In addition, the WASp-deficient cells displayed augmented apoptosis induced by CD24 cross-linking. A recombinant fusion protein composed of Hph-1 cell-permeable peptide and WASp prepared in Escherichia coli. Hph-1-WASp was efficiently transduced and expressed in WASP⁻/⁻ Nalm-6 cells in a dose-dependent manner. The wild-type WASp, but not the mutant restored adhesion capacity, spreading morphology, and cytoskeletal reorganization. Additionally, the recombinant protein was successfully transduced into normal lymphocytes. These findings suggest that gene-disrupted model cell lines and cell-permeable recombinant proteins may serve as important tools for the detailed analysis of intracellular molecules involved in PID.
International journal of hematology 02/2012; 95(3):299-310. · 1.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: Protein delivery to primary cells by protein transduction domain (PTD) serves as a novel measure for manipulation of the cells for biological study and for the treatment of various human conditions. Although the method has been employed to modulate cellular function in vitro, only limited reports are available on its application in the replacement of deficient signaling molecules into primary cells. We examined the potential of recombinant proteins to compensate for defective cytosolic components of the NADPH oxidase complex in chronic granulomatous disease (CGD) neutrophils in both p47(phox) and p67(phox) deficiency. The p47(phox) or p67(phox) protein linked to Hph-1 PTD was effectively expressed in soluble form and transduced into human neutrophils efficiently without eliciting unwanted signal transduction or apoptosis. The delivered protein was stable for more than 24h, expressed in the cytoplasm, translocated to the membrane fraction upon activation, and, most importantly able to restored reactive oxygen species (ROS) production. Although research on human primary neutrophils using the protein delivery system is still limited, our data show that the protein transduction approach for neutrophils may be applicable to the control of local infections in CGD patients by direct delivery of the protein product.
Biochemical and Biophysical Research Communications 11/2011; 417(1):162-8. · 2.41 Impact Factor
[show abstract][hide abstract] ABSTRACT: A nationwide survey was conducted for identifying ataxia-telangiectasia (AT) patients in Japan. Eighty-nine patients were diagnosed between 1971 and 2006. Detailed clinical and laboratory data of 64 patients including affected siblings were collected. Analyses focused on malignancy, therapy-related toxicity, infection, and hematological/immunological parameters. The phenotypic variability of AT was assessed by comparing 26 affected siblings from 13 families. Malignancy developed in 22% of the cases and was associated with a high rate of severe therapy-related complications: chemotherapy-related cardiac toxicity in 2 children, and severe hemorrhagic cystitis requiring surgery in 2 patients. The frequency of serious viral infections correlated with the T cell count. Hypogammaglobulinemia with hyper-IgM (HIGM) was recorded in 5 patients, and 3 patients developed panhypogammaglobulinemia. Differences in immunological parameters were noted in siblings. Four patients showed an HIGM phenotype, in contrast to their siblings with normal IgG and IgM levels. The patients with HIGM phenotype showed reduced levels of TRECs and CD27+CD20+ memory B cells. The findings suggest that hitherto unidentified modifier genes or exogenous environmental factors can influence the overall immune responses. Our data along with future prospective study will lead to better understanding of the hematological/immunological phenotypes and to better care of the patients.
International journal of hematology 09/2009; 90(4):455-62. · 1.17 Impact Factor