title: BIG-3, a novel WD-40 repeat protein, is expressed in the developing growth plate and accelerates chondrocyte differentiation in vitro.
abstract: Among the local signaling pathways that regulate the sequential steps of chondrocyte differentiation is the bone morphogenetic protein (BMP) signaling pathway. We have identified a novel gene, named BIG-3 (BMP-2-induced gene 3 kb) that is expressed in a BMP-regulated fashion in the prechondroblastic cell line MLB13MYC clone 17. BIG-3 is also expressed in proliferating and hypertrophic chondrocytes in the developing growth plate in vivo. We undertook studies to address whether BIG-3 played a functional role in chondrocyte differentiation, using mouse clonal chondrogenic ATDC5 cells. BIG-3 protein levels increased during ITS (insulin, transferrin, sodium selenite)-induced ATDC5 differentiation and in response to BMP-2 treatment. To determine whether stable expression of BIG-3 could alter the program of chondrocytic differentiation, ATDC5 cells were stably transfected with the full-length coding region of BIG-3 (ATDC5-BIG-3) or with the empty vector (ATDC5-EV). Accelerated matrix proteoglycan synthesis was observed in the pooled ATDC5-BIG-3 clones. Alkaline phosphatase and osteopontin mRNA levels were also increased in ATDC5-BIG-3 clones compared with ATDC5-EV clones. Stable expression of BIG-3 also accelerated mineralized matrix formation in both the presence and absence of ITS. These findings, which demonstrate that BIG-3 accelerates chondrocyte differentiation in vitro, combined with the observation that BIG-3 is expressed in the growth plate during embryonic development, suggest that this novel protein is likely to play an in vivo regulatory role in the developing growth plate.
authors.affiliation: Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA. gori@helix.mgh.harvard.edu
authors.forename: Francesca
authors.initials: F
authors.lastname: Gori
authors.forename: Marie B
authors.initials: MB
authors.lastname: Demay
mesh_terms: D000818:Animals; D002113:Calcification, Physiologic / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D019902:Chondrocytes / Q000166:cytology* / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D006132:Growth Plate / Q000166:cytology* / Q000196:embryology / Q000502:physiology*; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D053495:Osteopontin; D011506:Proteins / Q000235:genetics*; D011509:Proteoglycans / Q000096:biosynthesis; D012795:Sialoglycoproteins / Q000096:biosynthesis
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D011509:Proteoglycans; D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; C443118:Wdr5 protein, mouse; D053495:Osteopontin