Stimulation of matrix vesicle enzyme activity in osteoblast-like cells by 1,25(OH) 2D 3 and transforming growth factor β (TGFβ)

• Published in: Bone and mineral Vol. 17; no. 2; pp. 139 - 144
• Main Authors: Bonewald, L.F., Schwartz, Z., Swain, L.D., Boyan, B.D.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1992
• ISSN: 0169-6009
• DOI: 10.1016/0169-6009(92)90725-S

After demonstrating the presence of matrix vesicles in three osteosarcoma cell lines, MG-63, ROS 17/2.8 and MC-3T3-E1, we sought to determine whether two major enzymes localized to matrix vesicles, alkaline phosphatase and phospholipase A 2, could be regulated by 1,25(OH) 2D 3 and/or TGFβ. Intravesicular calcification is probably dependent on these two enzymes. Alkaline phosphatase is essential for hydrolysis of phosphate-containing substrates and phospholipase A 2 hydrolyzes diacylphosphatides in a calcium-mediated manner at lipid-aqueous interfaces leading to changes in membrane fluidity and possibly breakdown of the matrix vesicle. The 1,25(OH) 2D 3 induced increase of alkaline phosphatase in bone cells is localized to the matrix vesicle. TGFβ also increased alkaline phosphatase activity in two of the cell lines, MG-63 and ROS 17/2.8 but to a greater degree than 1,25(OH) 2D 3. Matrix vesicle alkaline phosphatase activity exhibited a greater response than that in the plasma membrane. TGFβ increased phospholipase A 2 activity in both matrix vesicles and plasma membranes, therefore, no targeting was observed with respect to this enzyme. When TGFβ was combined with 1,25(OH) 2D 3, 1,25(OH) 2D 3 had no effect on phospholipase A 2 and did not interfere with TGFβ stimulation of phospholipase A 2 activity. When 1,25(OH) 2D 3 and TGFβ were combined, a tremendous synergy was observed in alkaline phosphatase specific activity in both plasma membranes and matrix vesicles with targeting to matrix vesicles. Therefore, TGFβ not only plays an important role in matrix formation and differentiation, but works in conjunction with 1,25(OH) 2D 3 to greatly potentiate the effects seen with 1,25(OH) 2D 3 alone.