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Articles by Y Kamiya
Total Records ( 5 ) for Y Kamiya
  P. M Kearney , H Cronin , C O'Regan , Y Kamiya , B. J Whelan and R. A. Kenny

Background: some cohort studies of ageing and health supplement questionnaire-based surveys with in-home measurements of biological parameters and others have required respondents to attend assessment centres. Centre-based assessments facilitate detailed measurements and novel technologies, but may differentially influence participation. The aim of this paper is to compare the characteristics of participants who attended a centre with those who chose a home assessment and those who did not have a health assessment.

Methods: trained field workers administered a computer-assisted personal interview (CAPI) to a random sample of community-dwelling people aged 50 and over in the participants' homes. All questionnaire respondents were invited to attend an assessment centre for a comprehensive physical assessment. Participants who refused or were unable to attend a centre were offered a home assessment.

Results: of the 291 participants who completed the CAPI, 176 had a health assessment: 138 in an assessment centre and 38 in their own home. The centre, home and no visit respondents differed in demographic characteristics, behavioural factors, physical functioning and health. Lower socio-economic status, physical inactivity and current smoking were the most robust predictors of non-participation in the health assessment. Home respondents had the highest levels of physical disability and were much weaker (grip strength) and slower (walking speed) than centre respondents.

Conclusion: home and centre physical assessments are required to avoid systematically over-representing healthier and wealthier respondents.

  D Hu , Y Kamiya , K Totani , D Kamiya , N Kawasaki , D Yamaguchi , I Matsuo , N Matsumoto , Y Ito , K Kato and K. Yamamoto

Glucosidase II (GII) is a glycan-processing enzyme that trims two 1,3-linked glucose residues from N-glycan on newly synthesized glycoproteins. Trimming of the first 1,3-linked glucose from Glc2Man9GlcNAc2 (G2M9) is important for a glycoprotein to interact with calnexin/calreticulin (CNX/CRT), and cleavage of the innermost glucose from Glc1Man9GlcNAc2 (G1M9) sets glycoproteins free from the CNX/CRT cycle and allows them to proceed to the Golgi apparatus. GII is a heterodimeric complex consisting of a catalytic subunit (GII) and a tightly associated β subunit (GIIβ) that contains a mannose 6-phosphate receptor homology (MRH) domain. A recent study has suggested a possible involvement of the MRH domain of GIIβ (GIIβ-MRH) in the glucose trimming process via its putative sugar-binding activity. However, it remains unknown whether GIIβ-MRH possesses sugar-binding activity and, if so, what role this activity plays in the function of GII. Here, we demonstrate that human GIIβ-MRH binds to high-mannose-type glycans. Frontal affinity chromatography revealed that GIIβ-MRH binds most strongly to the glycans with the 1,2-linked mannobiose structure. GII with the mutant GIIβ that lost the sugar-binding activity of GIIβ-MRH hydrolyzes p-nitrophenyl--glucopyranoside, but the capacity to remove glucose residues from G1M9 and G2M9 is significantly decreased. Our results clearly demonstrate the capacity of the GIIβ-MRH to bind high-mannose-type glycans and its importance in efficient glucose trimming of N-glycans.

  N Hosokawa , L. O Tremblay , B Sleno , Y Kamiya , I Wada , K Nagata , K Kato and A. Herscovics

Glycoprotein folding and degradation in the endoplasmic reticulum (ER) is mediated by the ER quality control system. Mannose trimming plays an important role by forming specific N-glycans that permit the recognition and sorting of terminally misfolded conformers for ERAD (ER-associated degradation). The EDEM (ER degradation enhancing -mannosidase-like protein) subgroup of proteins belonging to the Class I 1,2-mannosidase family (glycosylhydrolase family 47) has been shown to enhance ERAD. We recently reported that overexpression of EDEM3 enhances glycoprotein ERAD with a concomitant increase in mannose-trimming activity in vivo. Herein, we report that overexpression of EDEM1 produces Glc1Man8GlcNAc2 isomer C on terminally misfolded null Hong Kong 1-antitrypsin (NHK) in vivo. Levels of this isomer increased throughout the chase period and comprised approximately 10% of the [3H]mannose-labeled N-glycans on NHK after a 3-h chase. Furthermore, overexpression of EDEM1 E220Q containing a mutation in a conserved catalytic residue essential for 1,2-mannosidase activity did not yield detectable levels of Glc1Man8GlcNAc2 isomer C. Yet, the same extent of NHK ERAD-enhancement was observed in both EDEM1 and EDEM1 E220Q overexpressing cells. This can be attributed to both wild-type and mutant EDEM1 inhibiting aberrant NHK dimer formation. We further analyzed the N-glycan profile of total cellular glycoproteins from HepG2 cells stably overexpressing EDEM1 and found that the relative amount of Man7GlcNAc2 isomer A, which lacks the terminal B and C branch mannoses, was increased compared to parental HepG2 cells. Based on this observation, we conclude that EDEM1 activity trims mannose from the C branch of N-glycans in vivo.

  N Hosokawa , Y Kamiya and K. Kato

The endoplasmic reticulum (ER) quality control system ensures that newly synthesized proteins in the early secretory pathway are in the correct conformation. Polypeptides that have failed to fold into native conformers are subsequently retrotranslocated and degraded by the cytosolic ubiquitin–proteasome system, a process known as endoplasmic reticulum-associated degradation (ERAD). Most of the polypeptides that enter the ER are modified by the addition of N-linked oligosaccharides, and quality control of these glycoproteins is assisted by lectins that recognize specific sugar moieties and molecular chaperones that recognize unfolded proteins, resulting in proper protein folding and ERAD substrate selection. In Saccharomyces cerevisiae, Yos9p, a lectin that contains a mannose 6-phosphate receptor homology (MRH) domain, was identified as an important component of ERAD. Yos9p was shown to associate with the membrane-embedded ubiquitin ligase complex, Hrd1p–Hrd3p, and provide a proofreading mechanism for ERAD. Meanwhile, the function of the mammalian homologues of Yos9p, OS-9 and XTP3-B remained elusive until recently. Recent studies have determined that both OS-9 and XTP3-B are ER resident proteins that associate with the HRD1–SEL1L ubiquitin ligase complex and are important for the regulation of ERAD. Moreover, recent studies have identified the N-glycan species with which both yeast Yos9p and mammalian OS-9 associate as M7A, a Man7GlcNAc2 isomer that lacks the 1,2-linked terminal mannose from both the B and C branches. M7A has since been demonstrated to be a degradation signal in both yeast and mammals.

  K Miyazono , Y Kamiya and M. Morikawa

Bone morphogenetic proteins (BMPs) exhibit broad spectra of biological activities in various tissues, including bone, cartilage, blood vessels, heart, kidney, neurons, liver and lung. BMPs are members of the transforming growth factor-β (TGF-β) family that bind to type II and type I serine-threonine kinase receptors, and transduce signals through Smad and non-Smad signalling pathways. Recent findings have revealed that BMP signalling is finely tuned by various mechanisms in both positive and negative fashions. Perturbations of BMP signalling pathways are linked to a wide variety of clinical disorders, including vascular diseases, skeletal diseases and cancer. Administration of recombinant BMP ligands and increasing endogenous expression of BMPs provide therapeutic effects on some diseases. The recent development of BMP receptor inhibitors may also prove useful for some clinical diseases induced by hyperactivation of the BMP signalling pathways.

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