OSTEOGENIC PROTEIN-1 (BMP-7) INHIBITS CELL-PROLIFERATION AND STIMULATES THE EXPRESSION OF MARKERS CHARACTERISTIC OF OSTEOBLAST PHENOTYPE INRAT OSTEOSARCOMA-(17 2.8) CELLS/

We recently showed that osteogenic protein-1(OP-1), a bone morphogenet ic protein member of TGF-beta superfamily, induces endochondral bone f ormation in vivo, and stimulates growth and differentiation of osteobl asts in rat calvarial-derived cell cultures. In the present study, we examined the effect of OP-1 on cell growth and expression of markers t hat are characteristic of osteoblast phenotype using the clonal rat os teosarcoma cells (ROS 17/2.8). A comparison of OP-1 and TGF-beta 1 eff ects on cell growth showed that, both OF-I and TGF-beta 1 inhibited DN A synthesis up to 90 percent and 60 percent of the controls at concent rations of 10 ng/ml and 1 ng/ml, respectively, in serum-free medium. I n the presence of 5% serum, TGF-beta 1 did not have any significant in hibitory effects while 40 ng OP-1/ml inhibited the DNA synthesis up to 80% of the controls. Examination of collagen synthesis showed that 40 ng OP-1/ml increased the expression of type I collagen mRNA, and thus increased collagen synthesis (4-fold), as examined by collagenase-dig estible protein. Evaluation of markers that are characteristic of the osteoblast phenotype demonstrated that OP-1 stimulated cAMP production in response to PTH (10-fold at 200 ng/ml), alkaline phosphatase speci fic activity (ALPase) (4-fold at 80 ng/ml), and osteocalcin (OC) synth esis (4.5-fold at 40 ng/ml). Northern blot analysis revealed that OP-1 increased mRNA expression for both ALPase and OC in a dose-dependent manner. These data collectively demonstrate that OP-1 suppresses cell proliferation and stimulates the expression of markers characteristic of osteoblast phenotype in rat clonal osteoblastic osteosarcoma cells (ROS 17/2.8).