title: Human immunodeficiency virus type 1 enhancer-binding protein 3 is essential for the expression of asparagine-linked glycosylation 2 in the regulation of osteoblast and chondrocyte differentiation.
abstract: Human immunodeficiency virus type 1 enhancer-binding protein 3 (Hivep3) suppresses osteoblast differentiation by inducing proteasomal degradation of the osteogenesis master regulator Runx2. In this study, we tested the possibility of cooperation of Hivep1, Hivep2, and Hivep3 in osteoblast and/or chondrocyte differentiation. Microarray analyses with ST-2 bone stroma cells demonstrated that expression of any known osteochondrogenesis-related genes was not commonly affected by the three Hivep siRNAs. Only Hivep3 siRNA promoted osteoblast differentiation in ST-2 cells, whereas all three siRNAs cooperatively suppressed differentiation in ATDC5 chondrocytes. We further used microarray analysis to identify genes commonly down-regulated in both MC3T3-E1 osteoblasts and ST-2 cells upon knockdown of Hivep3 and identified asparagine-linked glycosylation 2 (Alg2), which encodes a mannosyltransferase residing on the endoplasmic reticulum. The Hivep3 siRNA-mediated promotion of osteoblast differentiation was negated by forced Alg2 expression. Alg2 suppressed osteoblast differentiation and bone formation in cultured calvarial bone. Alg2 was immunoprecipitated with Runx2, whereas the combined transfection of Runx2 and Alg2 interfered with Runx2 nuclear localization, which resulted in suppression of Runx2 activity. Chondrocyte differentiation was promoted by Hivep3 overexpression, in concert with increased expression of Creb3l2, whose gene product is the endoplasmic reticulum stress transducer crucial for chondrogenesis. Alg2 silencing suppressed Creb3l2 expression and chondrogenesis of ATDC5 cells, whereas infection of Alg2-expressing virus promoted chondrocyte maturation in cultured cartilage rudiments. Thus, Alg2, as a downstream mediator of Hivep3, suppresses osteogenesis, whereas it promotes chondrogenesis. To our knowledge, this study is the first to link a mannosyltransferase gene to osteochondrogenesis.
authors.affiliation: From the Departments of Medical Joint Materials and.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Imamura
authors.forename: Shingo
authors.initials: S
authors.lastname: Maeda
authors.forename: Ichiro
authors.initials: I
authors.lastname: Kawamura
authors.forename: Kanehiro
authors.initials: K
authors.lastname: Matsuyama
authors.forename: Naohiro
authors.initials: N
authors.lastname: Shinohara
authors.forename: Yuhei
authors.initials: Y
authors.lastname: Yahiro
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nagano
authors.forename: Takao
authors.initials: T
authors.lastname: Setoguchi
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yokouchi
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Ishidou
authors.forename: Setsuro
authors.initials: S
authors.lastname: Komiya
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism*; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D059865:Endoplasmic Reticulum Stress / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D055785:Gene Knockdown Techniques; D008364:Mannosyltransferases / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis / Q000502:physiology*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins; C084779:Hivep3 protein, mouse; C493716:Runx2 protein, mouse; D008364:Mannosyltransferases
keywords: Alg2; Bone Morphogenetic Protein (BMP); Chondrogenesis; Endoplasmic Reticulum (ER); Endoplasmic Reticulum Stress; Hivep3; Osteoblasts; runx2