Shin Ichi Harashima

Transmembrane TNF-α: structure, function and interaction with anti-TNF agents

Transmembrane TNF-α, a precursor of the soluble form of TNF-α, is expressed on activated macrophages and lymphocytes as well as other cell types. After processing by TNF-α-converting enzyme (TACE), the soluble form of TNF-α is cleaved from transmembrane TNF-α and mediates its biological activities through binding to Types 1 and 2 TNF receptors (TNF-R1 and -R2) of remote tissues. Accumulating evidence suggests that not only soluble TNF-α, but also transmembrane TNF-α is involved in the inflammatory response. Transmembrane TNF-α acts as a bipolar molecule that transmits signals both as a ligand and as a receptor in a cell-to-cell contact fashion. Transmembrane TNF-α on TNF-α-producing cells binds to TNF-R1 and -R2, and transmits signals to the target cells as a ligand, whereas transmembrane TNF-α also acts as a receptor that transmits outside-to-inside (reverse) signals back to the cells after binding to its native receptors. Anti-TNF agents infliximab, adalimumab and etanercept bind to and neutralize soluble TNF-α, but exert different effects on transmembrane TNF-α-expressing cells (TNF-α-producing cells). In the clinical settings, these three anti-TNF agents are equally effective for RA, but etanercept is not effective for granulomatous diseases. Moreover, infliximab induces granulomatous infections more frequently than etanercept. Considering the important role of transmembrane TNF-α in granulomatous inflammation, reviewing the biology of transmembrane TNF-α and its interaction with anti-TNF agents will contribute to understanding the bases of differential clinical efficacy of these promising treatment modalities.

Mechanisms for cytotoxic effects of anti–tumor necrosis factor agents on transmembrane tumor necrosis factor α–expressing cells: Comparison among infliximab, etanercept, and adalimumab

OBJECTIVEnThree anti-tumor necrosis factor alpha (anti-TNFalpha) agents have been proved to be effective for rheumatoid arthritis (RA) and other inflammatory disorders. Infliximab and adalimumab have been generated as anti-TNFalpha monoclonal antibodies, while etanercept is engineered from human type II TNF receptors. In spite of all 3 agents equal efficacy for RA, both infliximab and adalimumab are effective for other diseases such as Crohns disease and Wegeners granulomatosis, while etanercept is not. We undertook this study to understand the different clinical effects of these anti-TNFalpha agents by analyzing their biologic activities on transmembrane TNFalpha.nnnMETHODSnJurkat T cells stably expressing an uncleavable form of transmembrane TNFalpha were used for the following studies: 1) flow cytometric analysis of binding activities of anti-TNF agents to cell surface transmembrane TNFalpha, 2) complement-dependent cytotoxicity (CDC), 3) antibody-dependent cell-mediated cytotoxicity (ADCC) by using peripheral blood mononuclear cells, and 4) outside-to-inside (reverse) signal transduction through transmembrane TNFalpha estimated by apoptosis and cell cycle analysis using flow cytometry.nnnRESULTSnAll of the anti-TNFalpha agents bound to transmembrane TNFalpha. Infliximab and adalimumab exerted almost equal CDC activities, while etanercept showed considerably lower activity. ADCC activities were almost equal among these 3 agents. Adalimumab and infliximab induced apoptosis and cell cycle arrest in transmembrane TNFalpha-expressing Jurkat T cells, reflecting an outside-to-inside signal transduction through transmembrane TNFalpha.nnnCONCLUSIONnThree different anti-TNF agents showed different biologic effects on transmembrane TNFalpha. This finding suggests that CDC and outside-to-inside signals by anti-TNFalpha antibodies may explain the successful clinical efficacy of adalimumab and infliximab in Crohns disease and Wegeners granulomatosis.

Association of tumor necrosis factor receptor type II polymorphism 196R with systemic lupus erythematosus in the Japanese: Molecular and functional analysis

OBJECTIVEnTo investigate whether a polymorphism(s) or mutation(s) in the tumor necrosis factor receptor II (TNFRII) gene is involved in the pathogenesis of systemic lupus erythematosus (SLE).nnnMETHODSnAll 10 exons of the TNFRII gene were analyzed by exon-specific polymerase chain reaction-single-strand conformation polymorphism, followed by nucleotide sequencing of exons that displayed aberrant bands. To analyze the function of the TNFRII polymorphisms, the full-length TNFRII complementary DNA of each allele was transfected in HeLa cells and then studied for specific binding of 125I-TNFalpha, as well as interleukin-6 (IL-6) production and cytotoxic activity after treatment with recombinant human TNFalpha.nnnRESULTSnWe identified 4 polymorphisms, at codons 56, 181, 196, and 232. The latter 2 had amino acid substitutions M196R and E232K, respectively. Only the 196R allele was significantly associated with SLE in our 105 Japanese SLE patients, with an allele frequency of 20.5%, compared with 12.6% in 99 healthy controls (P = 0.0335). More importantly, using TNFRII-transfected HeLa cells, we demonstrated significantly increased IL-6 production by 196R TNFRII compared with 196M TNFRII. The cytotoxic activity induced by 196R TNFRII was also increased compared with that of 196M TNFRII. This increase was achieved without affecting the binding affinity of TNFalpha to TNF-RII, as demonstrated by the finding that specific TNFalpha binding to the HeLa transfectants of 196R and 196M TNFRII was similar, with Kd values of 3.12 x 10(-10)M and 4.34 x 10(-10)M, respectively.nnnCONCLUSIONnThese results suggest that 196R TNFRII, which transduces the signals of TNFalpha more effectively than does 196M TNFRII, is involved in the pathogenesis of SLE.

MANNOSE BINDING LECTIN (MBL) GENE MUTATION IS NOT A RISK FACTOR FOR SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) AND RHEUMATOID ARTHRITIS (RA) IN JAPANESE

Mannose binding lectin (MBL) deficiency may be associated with increased susceptibility to infection and autoimmune disorders, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). In the present study, we performed for the first systematic search for mutations in all the four exons of the MBL gene using polymerase chain reaction (PCR)/single-strand conformation polymorphism (SSCP) analysis. Of 49 healthy Japanese individuals studied, only the previously reported mutation at the codon 54 (substitution from Gly to Asp; G54D) was identified. The allele frequencies of G54D in 105 healthy Japanese individuals, 95 SLE patients and 59 RA patients, were 0.233, 0.226 and 0.178, respectively, which were not significantly different. In addition, two polymorhisms at positions of −550 and −221 in the promoter region were not associated with SLE and RA. It is unlikely that MBL deficiency plays a major role in the pathogenesis of SLE and RA in Japanese.

Hereditary angioedema in Japan: Genetic analysis of 13 unrelated cases

Introduction:The molecular bases and clinical features of hereditary angioedema (HAE) have not been systematically documented in Japan or in other Asian countries. Thus, the authors researched the genetic and clinical characteristics of Japanese patients with HAE. Methods:The authors analyzed the CIINH gene for mutations in 13 unrelated Japanese patients with HAE by means of the polymerase chain reaction and nucleotide sequencing. In addition, the authors searched the literature from January 1969 to October 2010 on Japanese patients with HAE. Results:Seven of the mutations found were novel, including 4 missense mutations (8728T>G, 8831C>A, 16661T>G and 16885C>A), 2 frameshift mutations (2281_2350del70, 14158delT) and 1 large deletion (at least 1 kb-length deletion including exon 4), whereas 6 mutations had previously been reported in European populations. Conclusions:The genetic and clinical characteristics in Japanese patients with HAE may be similar to those in Western patients although our sample size is small and the authors identified 7 novel mutations.

Aberrant HS1 molecule in a patient with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the activation of autoreactive B lymphocytes, which are supposed to carry aberrant signal transduction after the stimulation of B-cell receptor (BCR). To investigate abnormalities in BCR-mediated signaling pathway in lupus B lymphocytes, we analyzed HS1, a molecule downstream of BCR, in 80 Japanese SLE patients. We identified 37 amino acid deletion of HS1 in a 25-year-old female patient, and the aberrant HS1 lacked a part of a functional motif. Analysis of genomic DNA revealed that the aberrant HS1 was caused by exon skipping. Family study showed that the patient as well as her father and sister are heterozygous for the abnormality. WEHI-231 cell, a mouse B cell line, transfected with the aberrant HS1 displayed a significantly increased cell death upon cross-linking of BCR. Additionally, peripheral B lymphocytes from the patient exerted increased apoptosis after BCR stimulation compared to those from control SLE patients. These data suggest that the aberrant HS1 molecule may transmit an accelerated signal after BCR stimulation and may play a role in the activation of autoreactive B lymphocytes.

An NcoI polymorphism in the human complement component 7 (C7) gene.

AbstractA novel polymorphic site has been found in the 3′ untranslated region (UTR) of the human complement component 7 (C7) gene. The polymorphic site at 14-bp downstream from the TAG stop codon was either C or A (NcoI-digested), with allele frequencies of 0.660 and 0.340. This NcoI polymorphism would be useful to perform a DNA marker haplotype study in patients with deficiencies of the complement genes, such as C6, C7, C9, which are located closely on chromosome 5p13.