研究者総覧

氣駕 恒太朗 (キガ コウタロウ)

  • 感染・免疫学講座(細菌学部門) 准教授
メールアドレス: kotarokiga
Last Updated :2021/12/08

研究者情報

学位

  • 医学(東京大学)

ホームページURL

J-Global ID

研究キーワード

  • 薬剤耐性菌   ファージセラピー   バクテリオファージ   遺伝子工学   細菌学   

研究分野

  • ライフサイエンス / 細菌学

経歴

  • 2021年06月 - 現在  自治医科大学 医学部 感染・免疫学講座 細菌学部門 准教授
  • 2016年09月 - 2021年05月  自治医科大学医学部 感染・免疫学講座 細菌学部門講師
  • 2014年11月 - 2016年08月  東京大学医科学研究所感染症国際研究センター 細菌学分野特任助教
  • 2014年03月 - 2014年10月  東京大学医科学研究所感染症国際研究センター 細菌学分野特任研究員
  • 2011年04月 - 2014年02月  Max-Planck-Institute of Immunobiology and Epigenetics博士研究員
  • 2008年04月 - 2011年03月  日本学術振興会特別研究員(DC1)

学歴

  • 2007年04月 - 2011年03月   東京大学   医学系研究科   病因・病理学専攻
  • 2005年04月 - 2007年03月   東京大学   工学系研究科   化学生命工学専攻
  • 2001年04月 - 2005年03月   東京大学   工学部   化学生命工学科

所属学協会

  • 日本感染症学会   日本ファージセラピー研究会 (https://sites.google.com/view/jp-phage-therapy)   日本ブドウ球菌研究会   日本化学療法学会   ファージ研究会   日本細菌学会   

研究活動情報

論文

  • Aa Haeruman Azam, Xin-Ee Tan, Srivani Veeranarayanan, Kotaro Kiga, Longzhu Cui
    Antibiotics 10 8 999 - 999 2021年08月 
    The bacteriophage (or phage for short) has been used as an antibacterial agent for over a century but was abandoned in most countries after the discovery and broad use of antibiotics. The worldwide emergence and high prevalence of antimicrobial-resistant (AMR) bacteria have led to a revival of interest in the long-forgotten antibacterial therapy with phages (phage therapy) as an alternative approach to combatting AMR bacteria. The rapid progress recently made in molecular biology and genetic engineering has accelerated the generation of phage-related products with superior therapeutic potentials against bacterial infection. Nowadays, phage-based technology has been developed for many purposes, including those beyond the framework of antibacterial treatment, such as to suppress viruses by phages, gene therapy, vaccine development, etc. Here, we highlighted the current progress in phage engineering technology and its application in modern medicine.
  • Ryo Kinoshita-Daitoku, Kotaro Kiga, Masatoshi Miyakoshi, Ryota Otsubo, Yoshitoshi Ogura, Takahito Sanada, Zhu Bo, Tuan Vo Phuoc, Tokuju Okano, Tamako Iida, Rui Yokomori, Eisuke Kuroda, Sayaka Hirukawa, Mototsugu Tanaka, Arpana Sood, Phawinee Subsomwong, Hiroshi Ashida, Tran Thanh Binh, Lam Tung Nguyen, Khien Vu Van, Dang Quy Dung Ho, Kenta Nakai, Toshihiko Suzuki, Yoshio Yamaoka, Tetsuya Hayashi, Hitomi Mimuro
    Nature Communications 12 1 2085 - 2085 2021年04月 [査読有り]
     
    AbstractLong-term infection of the stomach with Helicobacter pylori can cause gastric cancer. However, the mechanisms by which the bacteria adapt to the stomach environment are poorly understood. Here, we show that a small non-coding RNA of H. pylori (HPnc4160, also known as IsoB or NikS) regulates the pathogen’s adaptation to the host environment as well as bacterial oncoprotein production. In a rodent model of H. pylori infection, the genomes of bacteria isolated from the stomach possess an increased number of T-repeats upstream of the HPnc4160-coding region, and this leads to reduced HPnc4160 expression. We use RNA-seq and iTRAQ analyses to identify eight targets of HPnc4160, including genes encoding outer membrane proteins and oncoprotein CagA. Mutant strains with HPnc4160 deficiency display increased colonization ability of the mouse stomach, in comparison with the wild-type strain. Furthermore, HPnc4160 expression is lower in clinical isolates from gastric cancer patients than in isolates derived from non-cancer patients, while the expression of HPnc4160’s targets is higher in the isolates from gastric cancer patients. Therefore, the small RNA HPnc4160 regulates H. pylori adaptation to the host environment and, potentially, gastric carcinogenesis.
  • Tanit Boonsiri, Shinya Watanabe, Xin-Ee Tan, Kanate Thitiananpakorn, Ryu Narimatsu, Kosuke Sasaki, Remi Takenouchi, Yusuke Sato'o, Yoshifumi Aiba, Kotaro Kiga, Teppei Sasahara, Yusuke Taki, Feng-Yu Li, Yuancheng Zhang, Aa Haeruman Azam, Tomofumi Kawaguchi, Longzhu Cui
    Scientific reports 10 1 16907 - 16907 2020年10月 [査読有り]
     
    Staphylococcus aureus strains that are susceptible to the β-lactam antibiotic oxacillin despite carrying mecA (OS-MRSA) cause serious clinical problems globally because of their ability to easily acquire β-lactam resistance. Understanding the genetic mechanism(s) of acquisition of the resistance is therefore crucial for infection control management. For this purpose, a whole-genome sequencing-based analysis was performed using 43 clinical OS-MRSA strains and 100 mutants with reduced susceptibility to oxacillin (MICs 1.0-256 µg/mL) generated from 26 representative OS-MRSA strains. Genome comparison between the mutants and their respective parent strains identified a total of 141 mutations in 46 genes and 8 intergenic regions. Among them, the mutations are frequently found in genes related to RNA polymerase (rpoBC), purine biosynthesis (guaA, prs, hprT), (p)ppGpp synthesis (relSau), glycolysis (pykA, fbaA, fruB), protein quality control (clpXP, ftsH), and tRNA synthase (lysS, gltX), whereas no mutations existed in mec and bla operons. Whole-genome transcriptional profile of the resistant mutants demonstrated that expression of genes associated with purine biosynthesis, protein quality control, and tRNA synthesis were significantly inhibited similar to the massive transcription downregulation seen in S. aureus during the stringent response, while the levels of mecA expression and PBP2a production were varied. We conclude that a combination effect of mecA upregulation and stringent-like response may play an important role in acquisition of β-lactam resistance in OS-MRSA.
  • Kanate Thitiananpakorn, Yoshifumi Aiba, Xin-Ee Tan, Shinya Watanabe, Kotaro Kiga, Yusuke Sato'o, Tanit Boonsiri, Feng-Yu Li, Teppei Sasahara, Yusuke Taki, Aa Haeruman Azam, Yuancheng Zhang, Longzhu Cui
    Scientific reports 10 1 16107 - 16107 2020年09月 [査読有り]
     
    We first reported a phenomenon of cross-resistance to vancomycin (VCM) and daptomycin (DAP) in methicillin-resistant Staphylococcus aureus (MRSA) in 2006, but mechanisms underlying the cross-resistance remain incompletely understood. Here, we present a follow-up study aimed to investigate genetic determinants associated with the cross-resistance. Using 12 sets of paired DAP susceptible (DAPS) and DAP non-susceptible (DAPR) MRSA isolates from 12 patients who had DAP therapy, we (i) assessed susceptibility to DAP and VCM, (ii) compared whole-genome sequences, (iii) identified mutations associated with cross-resistance to DAP and VCM, and (iv) investigated the impact of altered gene expression and metabolic pathway relevant to the cross-resistance. We found that all 12 DAPR strains exhibiting cross-resistance to DAP and VCM carried mutations in mprF, while one DAPR strain with reduced susceptibility to only DAP carried a lacF mutation. On the other hand, among the 32 vancomycin-intermediate S. aureus (VISA) strains isolated from patients treated with VCM, five out of the 18 strains showing cross-resistance to DAP and VCM carried a mprF mutation, while 14 strains resistant to only VCM had no mprF mutation. Moreover, substitution of mprF in a DAPS strain with mutated mprF resulted in cross-resistance and vice versa. The elevated lysyl-phosphatidylglycerol (L-PG) production, increased positive bacterial surface charges and activated cell wall (CW) synthetic pathways were commonly found in both clinical isolates and laboratory-developed mutants that carry mprF mutations. We conclude that mprF mutation is responsible for the cross-resistance of MRSA to DAP and VCM, and treatment with DAP is more likely to select for mprF-mediated cross-resistance than is with VCM.
  • Kotaro Kiga, Xin-Ee Tan, Rodrigo Ibarra-Chávez, Shinya Watanabe, Yoshifumi Aiba, Yusuke Sato'o, Feng-Yu Li, Teppei Sasahara, Bintao Cui, Moriyuki Kawauchi, Tanit Boonsiri, Kanate Thitiananpakorn, Yusuke Taki, Aa Haeruman Azam, Masato Suzuki, José R Penadés, Longzhu Cui
    Nature communications 11 1 2934 - 2934 2020年06月 [査読有り][通常論文]
     
    The emergence of antimicrobial-resistant bacteria is an increasingly serious threat to global health, necessitating the development of innovative antimicrobials. Here we report the development of a series of CRISPR-Cas13a-based antibacterial nucleocapsids, termed CapsidCas13a(s), capable of sequence-specific killing of carbapenem-resistant Escherichia coli and methicillin-resistant Staphylococcus aureus by recognizing corresponding antimicrobial resistance genes. CapsidCas13a constructs are generated by packaging programmed CRISPR-Cas13a into a bacteriophage capsid to target antimicrobial resistance genes. Contrary to Cas9-based antimicrobials that lack bacterial killing capacity when the target genes are located on a plasmid, the CapsidCas13a(s) exhibit strong bacterial killing activities upon recognizing target genes regardless of their location. Moreover, we also demonstrate that the CapsidCas13a(s) can be applied to detect bacterial genes through gene-specific depletion of bacteria without employing nucleic acid manipulation and optical visualization devices. Our data underscore the potential of CapsidCas13a(s) as both therapeutic agents against antimicrobial-resistant bacteria and nonchemical agents for detection of bacterial genes.
  • Yoshifumi Aiba, Shinya Watanabe, Rieko Tsukahara, Naoka Umemoto, Kanate Thitiananpakorn, Tanit Boonsiri, Feng-Yu Li, Kotaro Kiga, Yusuke Sato'o, Xin-Ee Tan, Yusuke Taki, Aa Haeruman Azam, Yuancheng Zhang, Teppei Sasahara, Toshio Demitsu, Longzhu Cui
    Microbiology resource announcements 9 23 2020年06月 [査読有り][通常論文]
     
    The association of Panton-Valentine leukocidin (PVL) toxin with necrotizing soft tissue infection (NSTI) caused by Staphylococcus aureus remains controversial. Here, we report the complete genome sequence of the PVL-negative S. aureus strain JMUB1273, isolated from a patient with pervasive NSTI.
  • Ryo Kinoshita-Daitoku, Kotaro Kiga, Takahito Sanada, Yoshitoshi Ogura, Zhu Bo, Tamako Iida, Rui Yokomori, Eisuke Kuroda, Mototsugu Tanaka, Arpana Sood, Toshihiko Suzuki, Kenta Nakai, Tetsuya Hayashi, Hitomi Mimuro
    Biochemical and biophysical research communications 525 3 806 - 811 2020年05月 [査読有り][通常論文]
     
    Helicobacter pylori, a pathogenic bacterium that colonizes in the human stomach, harbors DNA repair genes to counter the gastric environment during chronic infection. In addition, H. pylori adapts to the host environment by undergoing antigenic phase variation caused by genomic mutations. The emergence of mutations in nucleotide sequences is one of the major factors underlying drug resistance and genetic diversity in bacteria. However, it is not clear how DNA repair genes contribute to driving the genetic change of H. pylori during chronic infection. To elucidate the physiological roles of DNA repair genes, we generated DNA repair-deficient strains of H. pylori (ΔuvrA, ΔuvrB, ΔruvA, Δnth, ΔmutY, ΔmutS, and Δung). We performed susceptibility testing to rifampicin in vitro and found that ΔmutY exhibited the highest mutation frequency among the mutants. The number of bacteria colonizing the stomach was significantly lower with ΔmutY strain compared with wild-type strains in a Mongolian gerbil model of H. pylori infection. Furthermore, we performed a genomic sequence analysis of the strains isolated from the Mongolian gerbil stomachs eight weeks after infection. We found that the isolated ΔmutY strains exhibited a high frequency of spontaneous G:C to T:A mutations. However, the frequency of phase variations in the ΔmutY strain was almost similar to the wild-type strain. These results suggest that MutY may play a role in modes of gastric environmental adaptation distinct from phase variation.
  • Ryo Kinoshita-Daitoku, Yoshitoshi Ogura, Kotaro Kiga, Fumito Maruyama, Tomoyo Kondo, Ichiro Nakagawa, Tetsuya Hayashi, Hitomi Mimuro
    Microbiology resource announcements 9 18 2020年04月 [査読有り][通常論文]
     
    Helicobacter pylori ATCC 43504 is a type strain isolated from a gastric cancer patient in Australia and is commonly used for pathogenicity studies. In this study, we report the complete genome sequence of a strain that can infect gerbils. The data provide a basis for future H. pylori research.
  • Mototsugu Tanaka, Ryo Kinoshita-Daitoku, Kotaro Kiga, Takahito Sanada, Bo Zhu, Tokuju Okano, Chihiro Aikawa, Tamako Iida, Yoshitoshi Ogura, Tetsuya Hayashi, Koshu Okubo, Miho Kurosawa, Junichi Hirahashi, Toshihiko Suzuki, Ichiro Nakagawa, Masaomi Nangaku, Hitomi Mimuro
    Scientific reports 10 1 3251 - 3251 2020年02月 [査読有り][通常論文]
     
    Group A Streptococcus (GAS) secretes deoxyribonucleases and evades neutrophil extracellular killing by degrading neutrophil extracellular traps (NETs). However, limited information is currently available on the interaction between GAS and NETs in the pathogenicity of GAS pharyngitis. In this study, we modified a mouse model of GAS pharyngitis and revealed an essential role for DNase in this model. After intranasal infection, the nasal mucosa was markedly damaged near the nasal cavity, at which GAS was surrounded by neutrophils. When neutrophils were depleted from mice, GAS colonization and damage to the nasal mucosa were significantly decreased. Furthermore, mice infected with deoxyribonuclease knockout GAS mutants (∆spd, ∆endA, and ∆sdaD2) survived significantly better than those infected with wild-type GAS. In addition, the supernatants of digested NETs enhanced GAS-induced cell death in vitro. Collectively, these results indicate that NET degradation products may contribute to the establishment of pharyngeal infection caused by GAS.
  • Shinya Watanabe, Bintao Cui, Kotaro Kiga, Yoshifumi Aiba, Xin Ee Tan, Yusuke Sato'o, Moriyuki Kawauchi, Tanit Boonsiri, Kanate Thitiananpakorn, Yusuke Taki, Fen Yu Li, Aa Haeruman Azam, Yumi Nakada, Teppei Sasahara, Longzhu Cui
    Frontiers in Microbiology 11 2020年02月 
    In the original article, there was a mistake in Table 1 as published. “GC% of L. wadei JMUB3933, JMUB3934, JCM16777, Leptotrichia sp.-1 JMUB3936, L. shahii JCM16776, L. hofstadii JCM16775, L. trevisanii JMUB3870, JMUB4039, JMUB3935 and L. buccalis C-1013-b, Leptotrchia sp.-3 F0260, Leptotrichia sp. F0590, L. goodfellowi JCM16774 and Leptotrichia sp.-6W10393, and chromosome length of L. wadei JCM16777” were incorrect. The corrected Table 1 appears below. In the original article, there was an error. GC% of genome-sequenced strains was incorrect. A correction has been made to Results and Discussion, Comparative Analysis of Leptotrichia Genome, line 373-375: As shown in Table 1, the chromosome size of the genus Leptotrichia varies from 2,142,946 to 2,829,322 bp with GC contents of 29.5% to 31.7%. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.
  • Helicobacter small RNA regulates host adaptation and carcinogenesis
    Ryo Kinoshita-Daitoku, Kotaro Kiga, Ryota Otsubo,, Yoshitoshi Ogura, Takahito Sanada, Zhu Bo,, Tuan Vo Phuoc, Tokuju Okano, Tamako Iida, Rui Yokomori, Eisuke Kuroda, Sayaka Hirukawa, Mototsugu Tanaka, Arpana Sood, Phawinee Subsomwong, Hiroshi Ashida, Tran Thanh Binh, Lam Tung Nguyen, Khien Vu Van, Dang Quy Dung Ho, Kenta Nakai, Toshihiko Suzuki, Yoshio Yamaoka, Tetsuya Hayashi, Hitomi Mimuro
    Biorxiv 2020年02月 [査読無し][通常論文]
  • RNAで細菌を制御する ヘリコバクターの難治性の感染状況下においてsRNAは病原性を調節する(Regulating with RNA in Bacteria sRNA regulates pathogenicity during persistent infection of Helicobacter)
    木下 遼, 氣駕 恒太朗, 大坪 亮太, 小椋 義俊, 眞田 貴人, 岡野 徳壽, 鈴木 敏彦, 山岡 吉生, 林 哲也, 三室 仁美
    日本細菌学雑誌 75 1 33 - 33 日本細菌学会 2020年01月
  • RNAで細菌を制御する(Regulating with RNA in Bacteria sRNA regulates pathogenicity during persistent infection of Helicobacter)
    木下 遼, 氣駕 恒太朗, 大坪 亮太, 小椋 義俊, 眞田 貴人, 岡野 徳壽, 鈴木 敏彦, 山岡 吉生, 林 哲也, 三室 仁美
    日本細菌学雑誌 75 1 33 - 33 日本細菌学会 2020年01月 [査読有り][通常論文]
  • ヘリコバクター・ピロリのsmall RNAによる持続感染機構の解析
    木下 遼, 氣駕 恒太朗, 大坪 亮太, 小椋 義俊, 真田 貴人, 岡野 徳壽, 鈴木 敏彦, 林 哲也, 三室 仁美
    日本細菌学雑誌 74 1 95 - 95 日本細菌学会 2019年03月 [査読有り][通常論文]
  • Shinya Watanabe, Bintao Cui, Kotaro Kiga, Yoshifumi Aiba, Xin-Ee Tan, Yusuke Sato'o, Moriyuki Kawauchi, Tanit Boonsiri, Kanate Thitiananpakorn, Yusuke Taki, Fen-Yu Li, Aa Haeruman Azam, Yumi Nakada, Teppei Sasahara, Longzhu Cui
    Frontiers in microbiology 10 2838 2838 - 2838 2019年 [査読有り][通常論文]
     
    Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas13a, previously known as CRISPR-C2c2, is the most recently identified RNA-guided RNA-targeting CRISPR-Cas system that has the unique characteristics of both targeted and collateral single-stranded RNA (ssRNA) cleavage activities. This system was first identified in Leptotrichia shahii. Here, the complete whole genome sequences of 11 Leptotrichia strains were determined and compared with 18 publicly available Leptotrichia genomes in regard to the composition, occurrence and diversity of the CRISPR-Cas13a, and other CRISPR-Cas systems. Various types of CRISPR-Cas systems were found to be unevenly distributed among the Leptotrichia genomes, including types I-B (10/29, 34.4%), II-C (1/29, 2.6%), III-A (6/29, 15.4%), III-D (6/29, 15.4%), III-like (3/29, 7.7%), and VI-A (11/29, 37.9%), while 8 strains (20.5%) had no CRISPR-Cas system at all. The Cas13a effectors were found to be highly divergent with amino acid sequence similarities ranging from 61% to 90% to that of L. shahii, but their collateral ssRNA cleavage activities leading to impediment of bacterial growth were conserved. CRISPR-Cas spacers represent a sequential achievement of former intruder encounters, and the retained spacers reflect the evolutionary phylogeny or relatedness of strains. Analysis of spacer contents and numbers among Leptotrichia species showed considerable diversity with only 4.4% of spacers (40/889) were shared by two strains. The organization and distribution of CRISPR-Cas systems (type I-VI) encoded by all registered Leptotrichia species revealed that effector or spacer sequences of the CRISPR-Cas systems were very divergent, and the prevalence of types I, III, and VI was almost equal. There was only one strain carrying type II, while none carried type IV or V. These results provide new insights into the characteristics and divergences of CRISPR-Cas systems among Leptotrichia species.
  • Bintao Cui, Shinya Watanabe, Yusuke Sato'o, Fumiya Nihashi, Yoshifumi Aiba, Kotaro Kiga, Teppei Sasahara, Xin-Ee Tan, Moriyuki Kawauchi, Tanit Boonsiri, Kanate Thitiananpakorn, Yusuke Taki, Feng-Yu Li, Shiro Imokawa, Longzhu Cui
    Microbiology resource announcements 8 4 pii: e01652-18.  2019年01月 [査読有り][通常論文]
     
    Severe community-acquired pneumonia (CAP) caused by methicillin-resistant Staphylococcus aureus (MRSA) is relatively rare and is usually associated with rapid progression to death. Here, we report the complete genome sequence of the MRSA strain JMUB3031, which was isolated from a patient with fatal CAP.
  • Shinya Watanabe, Yoshifumi Aiba, Xin-Ee Tan, Feng-Yu Li, Tanit Boonsiri, Kanate Thitiananpakorn, Bintao Cui, Yusuke Sato'o, Kotaro Kiga, Teppei Sasahara, Longzhu Cui
    BMC genomics 19 1 810 - 810 2018年11月 [査読有り][通常論文]
     
    BACKGROUND: Staphylococcus caprae is an animal-associated bacterium regarded as part of goats' microflora. Recently, S. caprae has been reported to cause human nosocomial infections such as bacteremia and bone and joint infections. However, the mechanisms responsible for the development of nosocomial infections remain largely unknown. Moreover, the complete genome sequence of S. caprae has not been determined. RESULTS: We determined the complete genome sequences of three methicillin-resistant S. caprae strains isolated from humans and compared these sequences with the genomes of S. epidermidis and S. capitis, both of which are closely related to S. caprae and are inhabitants of human skin capable of causing opportunistic infections. The genomes showed that S. caprae JMUB145, JMUB590, and JMUB898 strains contained circular chromosomes of 2,618,380, 2,629,173, and 2,598,513 bp, respectively. JMUB145 carried type V SCCmec, while JMUB590 and JMUB898 had type IVa SCCmec. A genome-wide phylogenetic SNP tree constructed using 83 complete genome sequences of 24 Staphylococcus species and 2 S. caprae draft genome sequences confirmed that S. caprae is most closely related to S. epidermidis and S. capitis. Comparative complete genome analysis of eight S. epidermidis, three S. capitis and three S. caprae strains revealed that they shared similar virulence factors represented by biofilm formation genes. These factors include wall teichoic acid synthesis genes, poly-gamma-DL-glutamic acid capsule synthesis genes, and other genes encoding nonproteinaceous adhesins. The 17 proteinases/adhesins and extracellular proteins known to be associated with biofilm formation in S. epidermidis were also conserved in these three species, and their biofilm formation could be detected in vitro. Moreover, two virulence-associated gene clusters, the type VII secretion system and capsular polysaccharide biosynthesis gene clusters, identified in S. aureus were present in S. caprae but not in S. epidermidis and S. capitis genomes. CONCLUSION: The complete genome sequences of three methicillin-resistant S. caprae isolates from humans were determined for the first time. Comparative genome analysis revealed that S. caprae is closely related to S. epidermidis and S. capitis at the species level, especially in the ability to form biofilms, which may lead to increased virulence during the development of S. caprae infections.
  • Sayaka Hirukawa, Hiroshi Sagara, Satoshi Kaneto, Tomoyo Kondo, Kotaro Kiga, Takahito Sanada, Hiroshi Kiyono, Hitomi Mimuro
    Microbiology and immunology 62 4 221 - 228 2018年04月 [査読有り][通常論文]
     
    Helicobacter pylori (H. pylori), a gram-negative microaerophilic bacterial pathogen that colonizes the stomachs of more than half of all humans, is linked to chronic gastritis, peptic ulcers and gastric cancer. Spiral-shaped H. pylori undergo morphologic conversion to a viable but not culturable coccoid form when they transit from the microaerobic stomach into the anaerobic intestinal tract. However, little is known about the morphological and pathogenic characteristics of H. pylori under prolonged anaerobic conditions. In this study, scanning electron microscopy was used to document anaerobiosis-induced morphological changes of H. pylori, from helical to coccoid to a newly defined fragmented form. Western blot analysis indicated that all three forms express certain pathogenic proteins, including the bacterial cytotoxin-associated gene A (CagA), components of the cag-Type IV secretion system (TFSS), the blood group antigen-binding adhesin BabA, and UreA (an apoenzyme of urease), almost equally. Similar urease activities were also detected in all three forms of H. pylori. However, in contrast to the helical form, bacterial motility and TFSS activity were found to have been abrogated in the anaerobiosis-induced coccoid and fragmented forms of H. pylori. Notably, it was demonstrated that some of the anaerobiosis-induced fragmented state cells could be converted to proliferation-competent helical bacteria in vitro. These results indicate that prolonged exposure to the anaerobic intestine may not eliminate the potential for H. pylori to revert to the helical pathogenic state.
  • Yusuke Sato'o, Yoshifumi Aiba, Kotaro Kiga, Shinya Watanabe, Teppei Sasahara, Yasuhiko Hayakawa, Longzhu Cui
    Journal of microbiological methods 146 25 - 32 2018年03月 [査読有り][通常論文]
     
    Electroporation is a common technique necessary for genomic manipulation of Staphylococci. However, because this technique has too low efficiency to be applied to some Staphylococcal species and strains, especially to coagulase-negative Staphylococcus (CNS) isolates, basic researches on these clinically important Staphylococci are limited. Here we report on the optimization of electroporation parameters and conditions as well as on the generation of a universal protocol that can be efficiently applicable to both CNS and Coagulase-positive Staphylococci (CPS). This protocol could generate transformants of clinical Staphylococcus epidermidis isolate, with an efficiency of up to 1400 CFU/μg of plasmid DNA. Transformants of 12 other clinically important Staphylococcal species, including CNS and CPS, were also generated with this protocol. To our knowledge, this is the first report on successful electroporation in nine these Staphylococcal species.
  • Hiroki Iwai, Keiji Funatogawa, Kazunori Matsumura, Masako Kato-Miyazawa, Fumiko Kirikae, Kotaro Kiga, Chihiro Sasakawa, Tohru Miyoshi-Akiyama, Teruo Kirikae
    Tuberculosis (Edinburgh, Scotland) 95 3 246 - 50 2015年05月 [査読有り][通常論文]
     
    MicroRNAs (miRNAs) are short, conserved, non-coding RNA molecules that repress translation, followed by the decay of miRNA-targeted mRNAs that encode molecules involved in cell differentiation, development, immunity and apoptosis. At least six miRNAs, including microRNA-155 (miR-155), were up-regulated when born marrow-derived macrophages from C57BL/6 mice were infected with Mycobacterium tuberculosis Erdman. C57BL/6 mice intravenously infected with Erdman showed up-regulation of miR-155 in livers and lungs. Following infection, miR-155-deficient C57BL/6 mice died significantly earlier and had significantly higher numbers of CFU in lungs than wild-type mice. Moreover, fewer CD4(+) T cells, but higher numbers of monocytes and neutrophils, were present in the lungs of Erdman-infected miR-155 knockout (miR-155(-/-)) than of wild-type mice. These findings indicated that miR-155 plays a critical role in immune responses to M. tuberculosis.
  • Kotaro Kiga, Hitomi Mimuro, Masato Suzuki, Aya Shinozaki-Ushiku, Taira Kobayashi, Takahito Sanada, Minsoo Kim, Michinaga Ogawa, Yuka W Iwasaki, Hiroyuki Kayo, Yoko Fukuda-Yuzawa, Masakazu Yashiro, Masashi Fukayama, Taro Fukao, Chihiro Sasakawa
    Nature communications 5 4497 - 4497 2014年09月 [査読有り][通常論文]
     
    Persistent colonization of the gastric mucosa by Helicobacter pylori (Hp) elicits chronic inflammation and aberrant epithelial cell proliferation, which increases the risk of gastric cancer. Here we examine the ability of microRNAs to modulate gastric cell proliferation in response to persistent Hp infection and find that epigenetic silencing of miR-210 plays a key role in gastric disease progression. Importantly, DNA methylation of the miR-210 gene is increased in Hp-positive human gastric biopsies as compared with Hp-negative controls. Moreover, silencing of miR-210 in gastric epithelial cells promotes proliferation. We identify STMN1 and DIMT1 as miR-210 target genes and demonstrate that inhibition of miR-210 expression augments cell proliferation by activating STMN1 and DIMT1. Together, our results highlight inflammation-induced epigenetic silencing of miR-210 as a mechanism of induction of chronic gastric diseases, including cancer, during Hp infection.
  • Hiroyuki Kayo, Kotaro Kiga, Yoko Fukuda-Yuzawa, Sebastian Hedlund, Kazuyoshi Murakami, Inti A De La Rosa-Velazquez, Tokuhiro Kimura, Kouji Shimoda, Masanobu Tanabe, Taro Fukao
    Nature genetics 46 8 802 - 4 2014年08月 [査読有り][通常論文]
  • Kotaro Kiga, Yoko Fukuda-Yuzawa, Masanobu Tanabe, Shoji Tsuji, Chihiro Sasakawa, Taro Fukao
    RNA biology 11 11 1347 - 54 2014年 [査読有り][通常論文]
     
    Overexpression of SIRT1 is frequently observed in various types of cancers, suggesting its potential role in malignancies. However, the molecular basis of how SIRT1 is elevated in cancer is less understood. Here we show that cancer-related SIRT1 overexpression is due to evasion of Sirt1 mRNA from repression by a group of Sirt1-targeting microRNAs (miRNAs) that might be robustly silenced in cancer. Our comprehensive library-based screening and subsequent miRNA gene profiling revealed a housekeeping gene-like broad expression pattern and strong CpG island-association of the Sirt1-targeting miRNA genes. This suggests aberrant CpG DNA methylation as the mechanistic background for malignant SIRT1 elevation. Our work also provides an example where epigenetic mechanisms cause the group-wide regulation of miRNAs sharing a common key target.
  • Yuka W Iwasaki, Kotaro Kiga, Hiroyuki Kayo, Yoko Fukuda-Yuzawa, Jasmin Weise, Toshifumi Inada, Masaru Tomita, Yasushi Ishihama, Taro Fukao
    RNA (New York, N.Y.) 19 4 490 - 7 2013年04月 [査読有り][通常論文]
     
    Proper regulation of gene expression during cell cycle entry ensures the successful completion of proliferation, avoiding risks such as carcinogenesis. The microRNA (miRNA) network is an emerging molecular system regulating multiple genetic pathways. We demonstrate here that the global elevation of miRNAs is critical for proper control of gene expression program during cell cycle entry. Strikingly, Exportin 5 (XPO5) is promptly induced during cell cycle entry by a PI3K-dependent post-transcriptional mechanism. Inhibition of XPO5 induction interfered with global miRNA elevation and resulted in a proliferation defect associated with delayed G1/S transition. During cell cycle entry, XPO5 therefore plays a paramount role as a critical molecular hub controlling the gene expression program through global regulation of miRNAs. Our data suggest that XPO5-mediated global miRNA elevation might be involved in a broad range of cellular events associated with cell cycle control.
  • Masato Suzuki, Kotaro Kiga, Dangeruta Kersulyte, Jaime Cok, Catherine C Hooper, Hitomi Mimuro, Takahito Sanada, Shiho Suzuki, Masaaki Oyama, Hiroko Kozuka-Hata, Shigeru Kamiya, Quan-Ming Zou, Robert H Gilman, Douglas E Berg, Chihiro Sasakawa
    The Journal of biological chemistry 286 34 29964 - 72 2011年08月 [査読有り][通常論文]
     
    Population genetic analyses of bacterial genes whose products interact with host tissues can give new understanding of infection and disease processes. Here we show that strains of the genetically diverse gastric pathogen Helicobacter pylori from Amerindians from the remote Peruvian Amazon contain novel alleles of cagA, a major virulence gene, and reveal distinctive properties of their encoded CagA proteins. CagA is injected into the gastric epithelium where it hijacks pleiotropic signaling pathways, helps Hp exploit its special gastric mucosal niche, and affects the risk that infection will result in overt gastroduodenal diseases including gastric cancer. The Amerindian CagA proteins contain unusual but functional tyrosine phosphorylation motifs and attenuated CRPIA motifs, which affect gastric epithelial proliferation, inflammation, and bacterial pathogenesis. Amerindian CagA proteins induced less production of IL-8 and cancer-associated Mucin 2 than did those of prototype Western or East Asian strains and behaved as dominant negative inhibitors of action of prototype CagA during mixed infection of Mongolian gerbils. We suggest that Amerindian cagA is of relatively low virulence, that this may have been selected in ancestral strains during infection of the people who migrated from Asia into the Americas many thousands of years ago, and that such attenuated CagA proteins could be useful therapeutically.
  • Michinaga Ogawa, Yuko Yoshikawa, Taira Kobayashi, Hitomi Mimuro, Makoto Fukumatsu, Kotaro Kiga, Zhenzi Piao, Hiroshi Ashida, Mitsutaka Yoshida, Shigeru Kakuta, Tomohiro Koyama, Yoshiyuki Goto, Takahiro Nagatake, Shinya Nagai, Hiroshi Kiyono, Magdalena Kawalec, Jean-Marc Reichhart, Chihiro Sasakawa
    Cell host & microbe 9 5 376 - 89 2011年05月 [査読有り][通常論文]
     
    Selective autophagy of bacterial pathogens represents a host innate immune mechanism. Selective autophagy has been characterized on the basis of distinct cargo receptors but the mechanisms by which different cargo receptors are targeted for autophagic degradation remain unclear. In this study we identified a highly conserved Tectonin domain-containing protein, Tecpr1, as an Atg5 binding partner that colocalized with Atg5 at Shigella-containing phagophores. Tecpr1 activity is necessary for efficient autophagic targeting of bacteria, but has no effect on rapamycin- or starvation-induced canonical autophagy. Tecpr1 interacts with WIPI-2, a yeast Atg18 homolog and PI(3)P-interacting protein required for phagophore formation, and they colocalize to phagophores. Although Tecpr1-deficient mice appear normal, Tecpr1-deficient MEFs were defective for selective autophagy and supported increased intracellular multiplication of Shigella. Further, depolarized mitochondria and misfolded protein aggregates accumulated in the Tecpr1-knockout MEFs. Thus, we identify a Tecpr1-dependent pathway as important in targeting bacterial pathogens for selective autophagy.
  • Masato Suzuki, Hitomi Mimuro, Kotaro Kiga, Makoto Fukumatsu, Nozomi Ishijima, Hanako Morikawa, Shigenori Nagai, Shigeo Koyasu, Robert H Gilman, Dangeruta Kersulyte, Douglas E Berg, Chihiro Sasakawa
    Cell host & microbe 5 1 23 - 34 2009年01月 [査読有り][通常論文]
     
    CagA, a major virulence factor of Helicobacter pylori (Hp), is delivered into gastric epithelial cells and exists in phosphorylated and nonphosphorylated forms. The biological activity of the phosphorylated form is well established; however, function(s) of the nonphosphorylated form remain elusive. Here, we report that a conserved motif in the C-terminal region of CagA, which is distinct from the EPIYA motifs used for phosphorylation and which we designate CRPIA (conserved repeat responsible for phosphorylation-independent activity), plays pivotal roles in Hp pathogenesis. The CRPIA motif in nonphosphorylated CagA was involved in interacting with activated Met, the hepatocyte growth factor receptor, leading to the sustained activation of phosphatidylinositol 3-kinase/Akt signaling in response to Hp infection. This in turn led to the activation of beta-catenin and NF-kappaB signaling, which promote proliferation and inflammation, respectively. Thus, nonphosphorylated CagA activity contributes to the epithelial proliferative and proinflammatory responses associated with development of chronic gastritis and gastric cancer.
  • Kimihiro Hino, Kiichiro Tsuchiya, Taro Fukao, Kotaro Kiga, Ryuichi Okamoto, Takanori Kanai, Mamoru Watanabe
    RNA (New York, N.Y.) 14 7 1433 - 42 2008年07月 [査読有り][通常論文]
     
    Maintenance of the intestinal epithelium is based on well-balanced molecular mechanisms that confer the stable and continuous supply of specialized epithelial cell lineages from multipotent progenitors. Lineage commitment decisions in the intestinal epithelium system involve multiple regulatory systems that interplay with each other to establish the cellular identities. Here, we demonstrate that the microRNA system could be involved in intestinal epithelial cell differentiation, and that microRNA-194 (miR-194) is highly induced during this process. To investigate this inducible expression mechanism, we identified the genomic structure of the miR-194-2, -192 gene, one of the inducible class of miR-194 parental genes. Furthermore, we identified its transcriptional regulatory region that contains a consensus-binding motif for hepatocyte nuclear factor-1alpha (HNF-1alpha), which is well known as a transcription factor to regulate gene expression in intestinal epithelial cells. By chromatin immunoprecipitation assay and luciferase reporter analysis, we revealed that pri-miR-194-2 expression is controlled by HNF-1alpha, and its consensus binding region is required for the transcription of pri-miR-194-2 in vivo in an intestinal epithelial cell line, Caco-2. Our observations indicate that microRNA genes could be targets of lineage-specific transcription factors and that microRNAs are regulated by a tissue-specific manner in the intestinal epithelium. Therefore, our work suggests that induced expression of these microRNAs have important roles in intestinal epithelium maturation.
  • Taro Fukao, Yoko Fukuda, Kotaro Kiga, Jafar Sharif, Kimihiro Hino, Yutaka Enomoto, Aya Kawamura, Kaito Nakamura, Tsutomu Takeuchi, Masanobu Tanabe
    Cell 129 3 617 - 31 2007年05月 [査読有り][通常論文]
     
    Many microRNAs (miRNAs) are evolutionarily conserved and have intriguing expression patterns. Tissue and/or time-specific expressions of some miRNAs are presumably controlled by unique cis-acting regulatory elements that coevolved with the miRNA sequences. Exploiting bioinformatics, we identified several miRNAs whose primary transcripts could be regulated by conserved genomic elements proximal to their transcription start sites. Such miRNAs include microRNA-223 (miR-223), which is reportedly controlled by a unique regulatory mechanism during granulopoiesis. Here, we define a mechanism distinct from that previously proposed to regulate miR-223 expression. We find that the mir-223 gene resembles a "myeloid gene" and might be driven by the myeloid transcription factors, PU.1 and C/EBPs. This mechanism is specified by the conserved proximal cis-regulatory element and might be common among different species. Hence, it needs to be considered that two distinct mechanisms that would play critical roles in myeloid functions and differentiation are actually concerned with the regulation of miR-223.

書籍

  • 古くて新しい医術:ファージ療法
    氣駕 恒太朗 ()
    バイオミディア・生物工学会誌 2021年04月
  • 耐性菌に対する抗菌ファージ技術
    氣駕 恒太朗, 崔 龍洙 ()
    Medical Science Digest・ニューサイエンス社 2021年03月
  • ファージテクノロジーと現代医療
    氣駕 恒太朗, 崔 龍洙 ()
    実験医学・羊土社 2020年11月
  • ファージと現代医学
    氣駕 恒太朗, 崔 龍洙 ()
    Precision Medicine・北隆館 2019年04月
  • H. pylori慢性感染におけるmiR-210のエピジェネティックな抑制が、胃上皮細胞の増殖を亢進させる
    氣駕恒太朗, 三室仁美, 笹川千尋 ()
    分子消化器病・先端医学社 2015年
  • 免疫系統合におけるmicroRNAシステムの役割
    氣駕恒太朗, 深尾太郎 ()
    感染・炎症・免疫・医薬の門社 2013年

講演・口頭発表等

  • バクテリオファージを利用した次世代創薬研究 https://iseminar.weebly.com  [招待講演]
    氣駕 恒太朗
    iSeminar 2021年06月
  • 氣駕 恒太朗
    千里ライフサイエンスセミナー 2021年05月
  • ファージを創る:次世代抗菌治療法の開発  [招待講演]
    氣駕 恒太朗
    早稲田大学 学術講演 2021年04月
  • シンポジウム「あなたの知らないファージの世界」(オーガナイザー)  [通常講演]
    第94回 日本細菌学会総会 2021年03月
  • SaPIを用いたファージ様パーティクルの合成方法  [通常講演]
    氣駕 恒太朗
    第65回 日本ブドウ球菌研究会 ワークショップ「ファージを利用してブドウ球菌感染症を克服する」(発表・オーガナイザー) 2020年10月 口頭発表(一般)
  • 遺伝子標的型ファージ製剤の開発
    氣駕 恒太朗, 崔 龍洙
    第93回 日本細菌学会総会 2020年02月 シンポジウム・ワークショップパネル(公募)
  • ファージを利用した遺伝子標的型殺菌剤の開発  [招待講演]
    氣駕 恒太朗
    日本細菌学会関東支部インターラボセミナー 2019年11月
  • 薬剤耐性菌を選択的に殺菌するファージ製剤の開発  [招待講演]
    氣駕 恒太朗
    第102回 日本細菌学会関東支部総会 2019年10月
  • Developing bacteriophage-based antimicrobials for killing antimicrobial-resistant bacteria.  [通常講演]
    Kotaro Kiga, XinEe Tan, Rodrigo Ibarra-Chávez, José R Penadés, Longzhu Cui
    Oxford phage 2019 2019年09月 ポスター発表
  • 狙った細菌を選択的に殺菌する殺菌技術の開発  [通常講演]
    氣駕 恒太朗, 李 峰宇, XinEe Tan, 佐藤 祐介, 渡邊 真弥, 相羽 由詞, Rodrigo Ibarra-Chávez, José R Penadés, 鈴木 仁人, 崔 龍洙
    第92回 日本細菌学会総会 2019年04月 ポスター発表
  • ピロリ菌の小さなRNAを介した酸化ストレス耐性機構  [通常講演]
    氣駕 恒太朗, Zhu Bo, 三室 仁美
    第11回 細菌学若手コロッセウム 2017年08月
  • Identification of sRNAs regulating oxidative stress in Helicobacter pylori.  [通常講演]
    Kotaro Kiga, Zhu Bo, Hitomi Mimuro
    第16回 東京大学 生命科学シンポジウム 2016年04月 ポスター発表
  • Identification of sRNAs controlling respiratory chain in Helicobacter pylori.  [通常講演]
    Kotaro Kiga, Zhu Bo, Hitomi Mimuro
    第89回 日本細菌学会総会 2016年03月 ポスター発表
  • Downregulation of miR-210 increases gastric cell proliferation during Helicobacter pylori infection.  [招待講演]
    Kotaro Kiga, Hitomi Mimuro
    第88回 日本細菌学会総会 2015年03月 口頭発表(一般)
  • Epigenetic silencing of miR-210 increases the proliferation of gastric epithelium during chronic Helicobacter pylori infection.  [通常講演]
    Kotaro Kiga, Hitomi Mimuro, Chihiro Sasakawa
    The 13th Awaji International Forum on Infection and Immunity 2014年09月 口頭発表(一般)
  • Epigenetic silencing of miR-210 increases the proliferation of gastric epithelium during chronic Helicobacter pylori infection.  [通常講演]
    Kotaro Kiga, Hitomi Mimuro, Chihiro Sasakawa
    The 21st East Asia Joint Symposium on Biomedical Research 2014年07月 口頭発表(一般)
  • Epigenetic silencing of miR-210 increases the proliferation of gastric epithelium during chronic Helicobacter pylori infection.  [通常講演]
    Kotaro Kiga, Hitomi Mimuro, Chihiro Sasakawa
    平成26年度 医科学研究所研究成果発表会 2014年05月 ポスター発表
  • Cluster-Wide microRNA Silencing is a Mechanism for SIRT1 Overexpression in Cancer.  [通常講演]
    Kotaro Kiga, Taro Fukao
    第36回 日本分子生物学会年会 2013年12月 ポスター発表
  • Simultaneous control of miR-212/132 and HIC1 on chromosome 17p13.3.  [通常講演]
    Kotaro Kiga, Yoko Fukuda, Hiroyuki Kayo, Taro Fukao
    MPI retreat 2011 2011年11月 ポスター発表
  • ヒト染色体17p13.3上に存在するマイクロRNAによる発癌制御  [通常講演]
    氣駕恒太朗, 深尾太郎
    RNAフロンティアミーティング2010 2010年09月 口頭発表(一般)
  • ヒト染色体17p13.3上に存在するマイクロRNAによる発癌制御  [通常講演]
    氣駕恒太朗, 深尾太郎
    第一回microRNA研究会本会 2010年08月 口頭発表(一般)
  • Transcription factors regulating myeloid lineage-specific miRNA.  [通常講演]
    氣駕恒太朗, 川村綾, 深尾太郎
    第35回 日本免疫学会総会・学術集会 2005年12月 口頭発表(一般)

MISC

  • 国内外ファージ研究の状況と推進すべき研究開発戦略に関する提言
    崔 龍洙, 氣駕 恒太朗, 渡邊真弥 JST-CRDS(研究開発の俯瞰報告書) 2021年03月 [査読無し]
  • 英国の情報サイトBioTechScopeにて、論文(Kiga et al. 2020 Nat Commun)の記事が2020の合成生物学分野で第2位。
    https, biotechscope.com/our-top-synthetic-biology-articles-of BioTechScope 2020年12月
  • 国内外ファージ研究の状況と推進すべき研究開発戦略に関する提言
    崔 龍洙, 氣駕 恒太朗, 渡邊真弥 JST-CRDS(研究開発の俯瞰報告書) 2019年03月 [査読無し][通常論文]

共同研究・競争的資金等の研究課題

  • クラスター型ナノバイオロジクスによる革新的抗菌療法の開発
    日本学術振興会 科学研究費助成事業 基盤研究(B):
    研究期間 : 2021年04月 -2026年03月 
    代表者 : 氣駕 恒太朗
  • 薬剤耐性菌を殺菌する広宿主域バイオロジクスの開発
    日本医療研究開発機構(AMED):新興・再興感染症研究基盤創生事業(多分野融合研究領域)
    研究期間 : 2020年12月 -2023年03月 
    代表者 : 氣駕 恒太朗, 鈴木 仁人, 新谷 正己, 末次 正幸
  • 薬剤耐性菌対策に資する新規遺伝子検査法・抗菌治療法の開発研究
    日本医療研究開発機構(AMED):新興・再興感染症に対する革新的医薬品等開発推進研究事業
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 崔 龍洙, 氣駕 恒太朗, 渡邊 真弥, 相羽 由詞, 佐藤 祐介, 笹原 鉄平, 永沢 善三
  • 高い殺菌活性能を有するCRISPR-Cas13aを利用した細菌感染制御法の開発
    公共財団法人MSD生命科学財団:感染症領域
    研究期間 : 2020年12月 -2022年12月 
    代表者 : 氣駕 恒太朗
  • バクテリオファージの疾患治療への応用
    自治医科大学:自治医科大学医学部研究奨励金
    研究期間 : 2020年04月 -2021年03月 
    代表者 : 氣駕 恒太朗
  • バクテリオファージを用いた新規殺菌技術の開発
    公益財団法人 興和生命科学振興財団:研究助成金
    研究期間 : 2020年04月 -2021年03月 
    代表者 : 氣駕 恒太朗
  • バクテリオファージを用いた追撃型抗菌治療法の開発
    日本学術振興会:科学研究費助成事業 若手研究
    研究期間 : 2018年04月 -2020年03月 
    代表者 : 氣駕 恒太朗
  • 日本学術振興会:科学研究費助成事業 挑戦的研究(萌芽)
    研究期間 : 2017年06月 -2019年03月 
    代表者 : 崔 龍洙, 氣駕 恒太朗
     
    黄色ブドウ球菌のメチシリン耐性遺伝子mecAを標的とするCRISPR-Cas13aを設計し、ブドウ球菌ファージに搭載した。それをMRSA、MSSA株を撒いた重層寒天培地上に添加して殺菌斑を確認したところ、合成ファージはMRSA株のみを殺菌するものの、MSSA株は殺菌しないことが確認された。また、mecAを欠損させたMRSA(ΔmecA)を作製し、同様の実験を行なったが、mecAを欠損させた黄色ブドウ球菌への殺菌力は失われていた。以上の結果は、mecAを保有する菌を遺伝子特異的に殺菌する殺菌キメラファージの合成に成功したことを意味する。
  • 重点助成
    大和日英基金:Daiwa-foundation Awards
    研究期間 : 2018年04月 -2019年03月 
    代表者 : Jose R Penades
  • バイオ技術を基盤とする先端医療に関する研究
    公益財団法人 持田記念医学薬学振興財団:研究助成金
    研究期間 : 2018年04月 -2019年03月 
    代表者 : 氣駕 恒太朗
  • 薬剤耐性菌に対する新規追尾型抗菌治療法の開発
    日本医療研究開発機構(AMED):J-PRIDE
    研究期間 : 2017年04月 -2019年03月 
    代表者 : 崔 龍洙, 氣駕 恒太朗, 渡邊 真弥, 相羽 由詞, 佐藤 祐介, 笹原 鉄平
  • 日本学術振興会:科学研究費助成事業 若手研究(B)
    研究期間 : 2016年04月 -2018年03月 
    代表者 : 氣駕 恒太朗
     
    ピロリ菌の慢性感染は、胃炎、胃潰瘍、胃癌そしてMALTリンパ腫の発症に密接に関わっている。本研究を進めていくと、ピロリ菌は自身が保有するある小さなRNA(sRNA)を用いることで、酸化ストレスによる細胞障害を免れていることが明らかとなった。さらに本研究では、sRNA-X遺伝子の欠損ピロリ菌株を作製し、解析することで、sRNA-Xが酸化ストレス応答に重要な遺伝子であるチオレドキシン関連遺伝子の発現を安定化するという新規メカニズムを見つけた。sRNA-Xを欠損したピロリ菌は胃への定着能も著しく減少したことから、このような小さなRNAがピロリ菌感染による胃の疾患に関与していることも示唆された。
  • 日本学術振興会:科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2015年04月 -2017年03月 
    代表者 : 三室 仁美, 氣駕 恒太朗
     
    本研究では、Helicobacter pyloriの新規RNAエフェクター分子を明らかにする目的で、H. pyloriがコードするBacterial small RNA (sRNA)を同定し、宿主細胞へ注入される可能性のあるRNAを精査した。次世代シークエンサー解析により、H. pyloriのsRNAを同定し、菌体内発現量を定量的PCRにより精査した。さらに、同定したsRNAのいくつかは、菌体細胞外分泌外膜小胞 (OMV)に特異的に濃縮され、宿主細胞へ移行する可能性が示唆された。
  • ピロリ菌の外膜小胞に含まれるRNAの同定とその機能解明
    花王芸術・科学財団:研究助成
    研究期間 : 2016年04月 -2017年03月 
    代表者 : 氣駕 恒太朗
  • 日本学術振興会:科学研究費助成事業 研究活動スタート支援
    研究期間 : 2014年08月 -2016年03月 
    代表者 : 氣駕 恒太朗
     
    胃がん発症の原因の一つとして、ピロリ菌がCagAと呼ばれる病原タンパク質を胃の細胞に打ち込むことが知られている。そこで、ピロリ菌がCagA以外にも機能性RNAを宿主細胞に打ち込み、病態の促進に寄与しているのではないかと考えた。本研究では、菌由来のRNAが、ピロリ菌が持つ針状の分泌装置を介してではなく、菌体表面から多数分泌されている小胞に含まれる形で、宿主細胞に到達していることを確認した。
  • 赤痢菌感染におけるmicroRNAの機能解明
    日本学術振興会:科学研究費助成事業 特別研究員奨励費
    研究期間 : 2008年 -2010年 
    代表者 : 氣駕 恒太朗
     
    microRNAはさまざまな条件・状況下で発現変化し、標的遺伝子を配列特異的に調節することで、多様な生命現象を引き起こすが知られている。しかしながら、細菌の感染現象におけるmicroRNAの役割はほとんど解明されていない。菌の感染にmicroRNAが関与していることを知るためには、菌の感染で発現変化するmicroRNAを見出す必要がある。昨年度までの研究では、赤痢菌を始め、ピロリ菌、結核菌、リステリア菌、サルモネラ菌、黄色ブドウ球菌等のさまざまな細菌の感染で共通して発現上昇するmicroRNAを同定することに成功した。中でも、胃癌発症の主要因の一つとして知られるピロリ菌の感染で制御されるmicroRNAの誘導率が非常に高かったため、ピロリ菌に対して集中的に研究を行った。興味深いことに、本microRNAは、胃上皮細胞の増殖を抑制することが分かった。microRNAがどのようにして胃上皮細胞の抑制を行っているかを調べるために、バイオインフォマティクス、マイクロアレイのそれぞれからのアプローチを用い、システマティックな標的遺伝子探索を行った。その結果、本microRNAが直接的に標的としている遺伝子が新たに13個見つかり、そのうち3つの遺伝子が胃上皮細胞の増殖に関与していることが示唆された。これらの結果から、細菌感染による細胞増殖抑制メカニズムの一端に本microRNAが関与していることが強く示唆された。本研究成果は、細菌の感染という免疫反応のメカニズムにおいてもmicroRNAという小さなRNAが重要な役割を果たしており、microRNAが感染症の治療や創薬の標的となり得ることを示している。


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