The effects of BIG-3 on osteoblast differentiation are not dependent upon endogenously produced BMPs.
BMPs play an important role in both intramembranous and endochondral ossification. BIG-3, BMP-2-induced gene 3 kb, encodes a WD-40 repeat protein that accelerates the program of osteoblastic differentiation in vitro. To examine the potential interactions between BIG-3 and the BMP-2 pathway during osteoblastic differentiation, MC3T3-E1 cells stably transfected with BIG-3 (MC3T3E1-BIG-3), or with the empty vector (MC3T3E1-EV), were treated with noggin. Noggin treatment of pooled MC3T3E1-EV clones inhibited the differentiation-dependent increase in AP activity observed in the untreated MC3T3E1-EV clones but did not affect the increase in AP activity in the MC3T3E1-BIG-3 clones. Noggin treatment decreased the expression of Runx2 and type I collagen mRNAs and impaired mineralized matrix formation in MC3T3E1-EV clones but not in MC3T3E1-BIG-3 clones. To determine whether the actions of BIG-3 on osteoblast differentiation converged upon the BMP pathway or involved an alternate signaling pathway, Smad1 phosphorylation was examined. Basal phosphorylation of Smad1 was not altered in the MC3T3E1-BIG-3 clones. However, these clones did not exhibit the noggin-dependent decrease in phosphoSmad1 observed in the MC3T3E1-EV clones, nor did it decrease nuclear localization of phosphoSmad1. These observations suggest that BIG-3 accelerates osteoblast differentiation in MC3T3-E1 cells by inducing phosphorylation and nuclear translocation of Smad1 independently of endogenously produced BMPs.
Gori
Francesca
F
Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
Demay
Marie B
MB
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis*; D002352:Carrier Proteins; D002454:Cell Differentiation; D002460:Cell Line; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D010006:Osteoblasts / Q000166:cytology*; D011506:Proteins / Q000378:metabolism / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000096:biosynthesis; D000099176:Noggin Protein
D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D016212:Transforming Growth Factor beta; D000099176:Noggin Protein; C525719:Bmp2 protein, mouse; C443118:Wdr5 protein, mouse