Molecular regulation of matrix extracellular phosphoglycoprotein expression by bone morphogenetic protein-2.
Matrix extracellular phosphoglycoprotein (MEPE) is mainly expressed in mineralizing tissues, and its C-terminal proteolytic cleavage product is an acidic-serine-asparate-rich-MEPE-associated motif (ASARM) that is a strong regulator of body phosphate metabolism and mineralization. There is sufficient data supporting a role for MEPE protein function in mineralization, however, little is known about the regulation of MEPE gene expression. As bone morphogenetic protein-2 (BMP-2) is one of the most important signals for calvarial mineralization and MEPE expression is higher in mineralized tissues, we attempted to uncover a regulatory circuit between BMP-2 and MEPE expression. Mepe expression is very low in proliferating MC3T3-E1 cells, but is dramatically increased in the mineralization stage and is strongly stimulated by treatment with BMP-2, even in proliferating cells. Overexpression and knock-down experiments of Smads, Dlx5, and Runx2 indicated that they are indispensable mediators of BMP-2-induced Mepe expression. In contrast, Msx2 showed strong inhibition of Mepe transcription. PHEX is an enzyme that prevents the release of the ASARM motif, a mineralization inhibitor, from the MEPE molecule. Thus, the MEPE/PHEX ratio may be a good indicator of mineralization progression because we found that the mRNA ratio and protein levels were low when osteoblasts were actively differentiating to the mineralization stage and the ratio was high when the cells reached the mineralization stage when it is assumed that osteocytes may protect themselves and make a space to survive from the mineralized matrix by releasing the ASARM motif. Collectively, MEPE expression is bone cell-specific and induced by the BMP-2 signaling pathway. In addition, the MEPE/PHEX ratio of the cell could be a very important barometer indicating the progression of tissue mineralization.
Cho
Young-Dan
YD
Department of Cell and Developmental Biology, School of Dentistry and Dental Research Institute, BK21 Program, Seoul National University, Seoul 110-749, Korea.
Yoon
Won-Joon
WJ
Woo
Kyung-Mi
KM
Baek
Jeong-Hwa
JH
Lee
Gene
G
Cho
Je-Yoel
JY
Ryoo
Hyun-Mo
HM
D016475:3T3 Cells; D020816:Amino Acid Motifs; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism*; D006023:Glycoproteins / Q000096:biosynthesis / Q000737:chemistry*; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D053402:PHEX Phosphate Regulating Neutral Endopeptidase / Q000378:metabolism*; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction
D055396:Bone Morphogenetic Protein 2; D006023:Glycoproteins; D018398:Homeodomain Proteins; C084119:MSX2 protein; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506232:Phex protein, mouse; C506229:Phex protein, rat