MAPK pathways activate and phosphorylate the osteoblast-specific transcription factor, Cbfa1.
The bone-specific transcription factor, Cbfa1, regulates expression of the osteocalcin (OCN) gene and is essential for bone formation. However, little is known about the mechanisms regulating Cbfa1 activity. This work examines the role of the MAPK pathway in regulating Cbfa1-dependent transcription. Stimulation of MAPK by transfecting a constitutively active form of MEK1, MEK(SP), into MC3T3-E1 preosteoblast cells increased endogenous OCN mRNA, while a dominant negative mutant, MEK(DN), was inhibitory. MEK(SP) also stimulated activity of a 147-base pair minimal OCN promoter, and this stimulation required an intact copy of OSE2, the DNA binding site for Cbfa1. Effects of MEK(SP) were specific to Cbfa1-positive osteoblast-like cells. A purified His-tagged Cbfa1 fusion protein was directly phosphorylated by activated recombinant MAPK in vitro. Furthermore, (32)P metabolic labeling studies demonstrated that MEK(SP) clearly enhanced phosphorylation of Cbfa1 in intact cells, while MEK(DN) decreased phosphorylation. The specific MEK1/MEK2 inhibitor, PD98059, inhibited extracellular matrix-dependent up-regulation of the OCN promoter, indicating that the MAPK pathway and, presumably, Cbfa1 phosphorylation are also required for responsiveness of osteoblasts to extracellular matrix signals. This study is the first demonstration that Cbfa1 is controlled by MAPKs and suggests that this pathway has an important role in the control of osteoblast-specific gene expression.
Xiao
G
G
Department of Periodontics, Prevention, and Geriatrics, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48109-1078, USA.
Jiang
D
D
Thomas
P
P
Benson
M D
MD
Guan
K
K
Karsenty
G
G
Franceschi
R T
RT
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009363:Neoplasm Proteins; D010006:Osteoblasts / Q000378:metabolism; D015675:Osteocalcin / Q000235:genetics; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000494:pharmacology*; D015533:Transcriptional Activation / Q000187:drug effects*; D014162:Transfection
D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins; D005419:Flavonoids; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D014157:Transcription Factors; D015675:Osteocalcin; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one