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Articles by H Iwasaki
Total Records ( 4 ) for H Iwasaki
  H Iwasaki , J. C Kovacic , M Olive , J. K Beers , T Yoshimoto , M. F Crook , L. H Tonelli and E. G. Nabel
  Rationale:

Arginine methylation by protein N-arginine methyltransferases (PRMTs) is an important posttranslational modification in the regulation of protein signaling. PRMT2 contains a highly conserved catalytic Ado-Met binding domain, but the enzymatic function of PRMT2 with respect to methylation is unknown. The JAK-STAT pathway is proposed to be regulated through direct arginine methylation of STAT transcription factors, and STAT3 signaling is known to be required for leptin regulation of energy balance.

Objective:

To identify the potential role of STAT3 arginine methylation by PRMT2 in the regulation of leptin signaling and energy homeostasis.

Methods and Results:

We identified that PRMT2–/– mice are hypophagic, lean, and have significantly reduced serum leptin levels. This lean phenotype is accompanied by resistance to food-dependent obesity and an increased sensitivity to exogenous leptin administration. PRMT2 colocalizes with STAT3 in hypothalamic nuclei, where it binds and methylates STAT3 through its Ado-Met binding domain. In vitro studies further clarified that the Ado-Met binding domain of PRMT2 induces STAT3 methylation at the Arg31 residue. Absence of PRMT2 results in decreased methylation and prolonged tyrosine phosphorylation of hypothalamic STAT3, which was associated with increased expression of hypothalamic proopiomelanocortin following leptin stimulation.

Conclusions:

These data elucidate a molecular pathway that directly links arginine methylation of STAT3 by PRMT2 to the regulation of leptin signaling, suggesting a potential role for PRMT2 antagonism in the treatment of obesity and obesity-related syndromes.

  T Taira , H Hayashi , Y Tajiri , S Onaga , G. i Uechi , H Iwasaki , T Ohnuma and T. Fukamizo
 

Chitinase-A (CrChi-A) was purified from leaf rachises of Cycas revoluta by several steps of column chromatography. It was found to be a glycoprotein with a molecular mass of 40 kDa and an isoelectric point of 5.6. CrChi-A produced mainly (GlcNAc)3 from the substrate (GlcNAc)6 through a retaining mechanism. More interestingly, CrChi-A exhibited transglycosylation activity, which has not been observed in plant chitinases investigated so far. A cDNA encoding CrChi-A was cloned by rapid amplification of cDNA ends and polymerase chain reaction procedures. It consisted of 1399 nucleotides and encoded an open reading frame of 387-amino-acid residues. Sequence analysis indicated that CrChi-A belongs to the group of plant class V chitinases. From peptide mapping and mass spectrometry of the native and recombinant enzyme, we found that an N-terminal signal peptide and a C-terminal extension were removed from the precursor (M1-A387) to produce a mature N-glycosylated protein (Q24-G370). This is the first report on a plant chitinase with transglycosylation activity and posttranslational modification of a plant class V chitinase.

  T Kodama , N Tomita , S Horie , N Sax , H Iwasaki , R Suzuki , K Maruyama , S Mori and F. Manabu
 

Sonoporation is achieved by ultrasound-mediated destruction of ultrasound contrast agents (UCA) microbubbles. For this, UCAs must be tissue specific and have good echogenicity and also function as drug carriers. Previous studies have developed acoustic liposomes (ALs), liposomes that encapsulate phosphate buffer solution and perfluoropropane (C3F8) gas and function as both UCAs and drug carriers. Few studies have examined the co-existence of gas and liquid in ALs. This study aims to elucidate AL structure using TEM. The size, zeta potential and structure of ALs were compared with those of two other UCAs, human albumin shell bubbles (ABs; Optison) and lipid bubbles (LBs). ABs and LBs encapsulate the C3F8 gas. Particle size was measured by dynamic light scattering. The zeta potential was determined by the Smoluchowski equation. UCA structure was investigated by TEM. ALs were ~200 nm in size, smaller than LBs and ABs. ALs and LBs had almost neutral zeta potentials whereas AB values were strongly negative. The negative or double staining TEM images revealed that ~20% of ALs contained both liquid and gas, while ~80% contained liquid alone (i.e. nonacoustic). Negative staining AB images indicated electron beam scattering near the shell surface, and albumin was detected in filament form. These findings suggest that AL is capable of carrying drugs and high-molecular-weight, low-solubility gases.

  T Matsumoto , M Ii , H Nishimura , T Shoji , Y Mifune , A Kawamoto , R Kuroda , T Fukui , Y Kawakami , T Kuroda , S. M Kwon , H Iwasaki , M Horii , A Yokoyama , A Oyamada , S. Y Lee , S Hayashi , M Kurosaka , S Takaki and T. Asahara
 

The therapeutic potential of hematopoietic stem cells/endothelial progenitor cells (HSCs/EPCs) for fracture healing has been demonstrated with evidence for enhanced vasculogenesis/angiogenesis and osteogenesis at the site of fracture. The adaptor protein Lnk has recently been identified as an essential inhibitor of stem cell factor (SCF)–cKit signaling during stem cell self-renewal, and Lnk-deficient mice demonstrate enhanced hematopoietic reconstitution. In this study, we investigated whether the loss of Lnk signaling enhances the regenerative response during fracture healing. Radiological and histological examination showed accelerated fracture healing and remodeling in Lnk-deficient mice compared with wild-type mice. Molecular, physiological, and morphological approaches showed that vasculogenesis/angiogenesis and osteogenesis were promoted in Lnk-deficient mice by the mobilization and recruitment of HSCs/EPCs via activation of the SCF–cKit signaling pathway in the perifracture zone, which established a favorable environment for bone healing and remodeling. In addition, osteoblasts (OBs) from Lnk-deficient mice had a greater potential for terminal differentiation in response to SCF–cKit signaling in vitro. These findings suggest that inhibition of Lnk may have therapeutic potential by promoting an environment conducive to vasculogenesis/angiogenesis and osteogenesis and by facilitating OB terminal differentiation, leading to enhanced fracture healing.

 
 
 
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