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Dive into the research topics where Junichi Koga is active.

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Featured researches published by Junichi Koga.


Journal of Clinical Investigation | 1997

Biologically inactive growth hormone caused by an amino acid substitution.

Yutaka Takahashi; Hiroyuki Shirono; Osamu Arisaka; Kenichi Takahashi; Toshihiro Yagi; Junichi Koga; Hidesuke Kaji; Yasuhiko Okimura; Hiromi Abe; Toshiaki Tanaka; Kazuo Chihara

Short stature caused by biologically inactive growth hormone (GH) is characterized by lack of GH action despite high immunoassayable GH levels in serum and marked catch-up growth to exogenous GH administration. We found a heterozygous single-base substitution (A-->G) in exon 4 of the GH-1 gene of a girl with short stature, clinically suspected to indicate the presence of bioinactive GH and resulting in the substitution of glycine for aspartic acid at codon 112. We confirmed the presence of mutant GH in the serum using isoelectric focusing analysis. The locus of mutation D112G was found within site 2 of the GH molecule in binding with GH receptor (GHR)/GH binding protein (GHBP). The expressed recombinant mutant GH tended to form a 1:1 instead of the 1:2 GH-GHBP complex normally produced by wild-type GH. The formation of a 1:2 GH-GHBP complex is compatible with the dimerization of GHRs by GH, a crucial step in GH signal transduction. Mutant GH was less potent than wild-type GH not only in phosphorylation of tyrosine residues in GHR, janus kinase 2 (JAK2), and signal transducers and activators of transcription 5 (STAT5) in IM-9 cells, but also in metabolic responses of BaF/GM cells, a stable clone transfected with cDNA of the chimera of the extracellular domain of human GHR, the transmembrane and the cytoplasmic domain of the human thrombopoietin receptor. These results indicate that the D112G mutation in the GH-1 gene causes production of bioinactive GH, which prevents dimerization of GHR and is therefore responsible for the patients short stature.


Thrombosis Research | 2002

Role of each Asn-linked glycan in the anticoagulant activity of human protein C inhibitor.

Mitsugu Fujita; Wakako Izutani; Kenichi Takahashi; Koji Nishizawa; Hiroyuki Shirono; Junichi Koga

The N-glycosylation site mutants of human protein C inhibitor (PCI; N230S, N243Q, N319Q, N230S/N243Q, and N230S/N319Q) were prepared by amino acid replacement of the asparagine residue with a serine or glutamine residue using site-directed mutagenesis and expressed in the baculovirus/insect cell expression system. To examine the importance of each Asn-linked glycan in the activity of PCI, we compared wtPCI with the mutants of N-glycosylation site(s) in terms of the procoagulant protease-inhibitory and anticoagulant activities. The inhibitory activities of N230S, N319Q, and N230S/N319Q toward human thrombin and plasma kallikrein were significantly increased compared with wtPCI, but those of N243Q and N230S/N243Q were reduced. The inhibitory activity of N230S toward human plasma coagulation was significantly increased compared with wtPCI, and that of N230S/N319Q was also significantly increased compared with N319Q. Furthermore, the procoagulant protease-inhibitory and anticoagulant activities of N230S/N319Q (glycosylated on Asn243 only) compared favorably with those of N230S, and both of the mutants possessed highest activities in the purified mutants. These results suggest that the Asn243-linked glycan in PCI molecule possesses critical roles for its anticoagulant activity in the circulation, and the Asn230-linked glycan down-regulates the activity of PCI.


Biochemical and Biophysical Research Communications | 1990

Existence and unique N-terminal sequence of alpha II (omega) interferon in natural leukocyte interferon preparation

Hiroyuki Shirono; Keiko Kono; Junichi Koga; Saburo Hayashi; Akio Matsuo; Hajime Hiratani

Human alpha interferon produced in Sendai virus-stimulated leukocytes was purified by immunosorbent affinity chromatography and subjected to subtype analysis. All subtypes in leukocyte culture supernatant were confirmed in purified preparation. One of these subtypes was reactive in Western blotting with antibody specific to alpha II (omega). N-terminal amino acid sequence analysis of this particular subtype showed addition of two amino acids to the N-terminus of alpha II predicted through cDNA studies. The apparent cleavage site for leader sequence of alpha II was different from the site common to all other alpha subtypes. This is the first report on the isolation of natural alpha II and its unique N-terminal amino acid sequence.


Journal of Virological Methods | 1990

Studies on subtype composition in natural leukocyte interferon preparations

Hiroyuki Shirono; Chitose Ito; Junichi Koga

Antisera raised against partially purified human leukocyte interferon in goat and horse were exhaustively adsorbed and purified. Affinity chromatography using these antibodies gave 10,000-fold purification in one step without losing interferon activity. Then enzyme immunoassay was established with these antibodies and utilized for subtype analysis. Crude and affinity purified leukocyte interferons showed identical profiles of antiviral activity and immunoreactivity when fractionated by means of reversed phase high performance liquid chromatography. These results suggested the possibility of providing mixture of subtypes of leukocyte interferon occurring in natural host response, with comparable purity of recombinant ones.


Journal of Clinical Investigation | 1991

Exon skipping during splicing of dystrophin mRNA precursor due to an intraexon deletion in the dystrophin gene of Duchenne muscular dystrophy kobe.

Masafumi Matsuo; T Masumura; Hisahide Nishio; T Nakajima; Y Kitoh; T Takumi; Junichi Koga; Hajime Nakamura


Biochemical and Biophysical Research Communications | 1990

A very small frame-shifting deletion within exon 19 of the Duchenne muscular dystrophy gene

Masafumi Matsuo; Takehiro Masumura; Toshihiro Nakajima; Yoshihiko Kitoh; Toru Takumi; Hisahide Nishio; Junichi Koga; Hajime Nakamura


Biochemical and Biophysical Research Communications | 2001

Amino-terminal fragment of urokinase-type plasminogen activator inhibits HIV-1 replication.

Manabu Wada; Naoko Wada; Hiroyuki Shirono; Katsumi Taniguchi; Hideaki Tsuchie; Junichi Koga


Human Molecular Genetics | 1993

A new mutation causing inherited growth hormone deficiency: a compound heterozygote of a 6.7 kb deletion and a two base deletion in the third exon of the GH-1 gene

Yutaka Igarashi; Masamichi Ogawa; Takashi Kamijo; Noritaka Iwatani; Yoshikazu Nishi; Hitoshi Kohno; Takehiro Masumura; Junichi Koga


American Journal of Medical Genetics | 1992

Amplification of ten deletion-rich exons of the dystrophin gene by polymerase chain reaction shows deletions in 36 of 90 Japanese families with Duchenne muscular dystrophy

Yoshihiko Kitoh; Masafumi Matsuo; Hisahide Nishio; Toru Takumi; Toshihiro Nakajima; Takehiro Masumura; Junichi Koga; Hajime Nakamura


Plant Biotechnology | 2006

Production of biologically active human interferon-α in transgenic rice

Takehiro Masumura; Satoshi Morita; Yoshiyuki Miki; Akihiro Kurita; Shigeto Morita; Hiroyuki Shirono; Junichi Koga; Kunisuke Tanaka

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Hiroyuki Shirono

Kyoto Prefectural University

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Takehiro Masumura

Kyoto Prefectural University

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Kunisuke Tanaka

Kyoto Prefectural University

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Akio Matsuo

Kyoto Prefectural University of Medicine

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Akihiro Kurita

Kyoto Prefectural University

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Satoshi Morita

Kyoto Prefectural University

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