👤 Hiroki Namba

Apolipoprotein A-IV (apoA-IV), the largest member of the exchangeable apolipoprotein family, is a common constituent of amyloid deposits in renal and cardiac amyloidosis. In this study, we characterized the aggregation propensity of the apoA-IV N-terminal fragment to form amyloid fibrils using a variety of biophysical techniques. Thioflavin T fluorescence assay, circular dichroism measurement, and microscopic observations revealed that the N-terminal 1-70 amino acid fragment of apoA-IV readily forms amyloid fibrils by a transition from a random coil to a β-sheet-rich structure. Sequence-based analysis indicated that residues 7-16 and 38-42 are the major aggregation-prone segments within the N-terminal 1-70 residues of apoA-IV. Consistent with this, deletion of these residues strongly inhibited the β-transition and fibril formation of apoA-IV 1-70. Kinetic and thermodynamic analyses of fibril formation by the apoA-IV 1-70 fragment demonstrated that primary nucleation is the dominant step in fibril formation, for which the activation energy barrier is entirely entropic. In addition, we found that the presence of heparin, a representative glycosaminoglycan, accelerated fibril formation kinetics and enhanced the yield of apoA-IV 1-70 fibrils, and the positively charged residues K58-K59 play a critical role in heparin interaction. Overall, our results suggest that the strong amyloid-forming propensity of the N-terminal fragment of apoA-IV may play a key role in amyloid deposition associated with apoA-IV amyloidosis. Show less

Germline mutation and functional loss of EXT1 or EXT2 are commonly found in multiple osteochondromas and predispose to the development of chondrosarcoma. Mutations of EXT1 and EXT2 have rarely been detected in sporadic secondary chondrosarcomas from osteochondroma; these frequently display loss of heterozygosity at the EXT1 and EXT2 loci, but primary chondrosarcomas typically do not. To evaluate promoter methylation (which is an epigenetic gene silencing mechanism) of EXT1 and EXT2, we performed methylation-specific polymerase chain reaction (PCR) for 20 chondrosarcoma cases (12 primary, 3 secondary to osteochondroma, 2 secondary to enchondromatosis, 2 extraskeletal ordinary, and 1 clear cell) and in five cell lines. In addition, mutation analysis of the EXT1 and EXT2 coding regions was performed using PCR-single-strand conformation polymorphism and sequencing analysis for 12 of the 20 chondrosarcoma cases (8 primary, 1 secondary to enchondromatosis, 1 secondary to osteochondroma, and 2 extraskeletal ordinary) and five cell lines. Promoter methylation of EXT1 and EXT2 was not detected in any of the cases, and both EXT1 and EXT2 were expressed in all cell lines. Two missense mutations in EXT2 (D227E and R299H) were detected among the chondrosarcoma cases. When considering tumor development in primary chondrosarcoma, we should include mutations in EXT2, along with the status of other members of the EXT gene family. Show less

To clarify the roles of Wnt pathway in medulloblastoma oncogenesis, immunohistochemical staining of beta-catenin and Wnt-1 and genomic analyses of CTNNB1 (beta-catenin) and AXIN1 (axin 1) were examined in 23 sporadic cases. Accumulation of beta-catenin in tumor cells was immunohistochemically proven in 5 cases; 2 cases showed positive immunoreactivity for Wnt-1 and another 2 showed mutation of either CTNNB1 or AXIN1. AXIN1 mutation was in exon 3, corresponding to GSK-3beta binding site and CTNNB1 mutation was in exon 3, corresponding to its phosphorylation site. Disruption of these proteins could result in upregulation of the Wnt signaling and accumulation of beta-catenin, followed by cell proliferation and medulloblastoma oncogenesis. Show less