Expression of Matrix Metalloproteinases During Ascorbate-Induced Differentiation of Osteoblastic MC3T3-E1 Cells

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Abstract
The mouse calvarial osteoblast MC3T3-E1 cells released 92 kDa and 68 kDa of gelatinase activities into the conditioned media (CMs) from undifferentiated cells. When differentiation was induced by cultivating cells with ascorbate-2-phosphate (AscP), 68-kDa activity increased significantly in parallel with production of 60-kDa activity. These enzymes required Ca2+ and Zn2+ ions for their proteolytic activities. The 68-kDa activity was immunologically identified as latent matrix metalloproteinase 2 (MMP-2). The 92-kDa activity was deduced to be latent MMP-9 based on its molecular mass. The 60-kDa activity band was found to possess both gelatin and beta-casein hydrolyzing activities, indicating that this activity band might comprise the active form of MMP-2 and latent MMP-13. MC3T3-E1 cells were found to express MMP-2, MMP-13, and membrane type (MT)1-MMP genes by Northern blotting. MMP-2 was expressed constitutively. MMP-13 was up-regulated during the growth with AscP. MT1-MMP expression also was modulated by AscP; at the early stage of differentiation, its messenger RNA (mRNA) level increased and then decreased gradually to the control level. These changes in the profiles of MMPs observed here could be attributed to the maturation of collagenous extracellular matrix (ECM) induced by AscP.

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