1996 Volume 45 Issue 1 Pages 1-12
The combination of β-glycerol phosphate and ascorbic acid increased alkaline phosphatase (ALP) activity in clonal osteoblast-like cell line MC3T3-E1. The increase was detectable at 24 hours after the addition of these agents to growth medium and reached almost maximum at 5 days of culture, suggesting that differentiation into osteoblasts was induced. Treatment of β-glycerol phosphate and ascorbic acid suppressed phosphoinositide-specific phospholipase C (PI-PLC) and phospholipase D (PLD) activations in response to PGF2α by 20-30% and 15%, respectively. No significant increase of the intracellular cyclic-AMP levels was observed in treatment with differentiation inducers. Western blotting with antibodies of PI-PLC isozymes revealed that the levels of expr-essions of PLC-β1 and PLC-β3 were decreased to 37% and 67%, respectively, in the cells treated for 5 days with the inducers compared to those of control cells, whereas PLC-γ1 was notaltered. These results indicate that differentiation in osteoblast MC3T3-E1 induced by the combination of β-glycerol phosphate and ascorbic acid supressed signal transduction via PI-PLC and PLD activation mediated by PGF2α due to the decreases of the levels of PLC-β1 and PLC-β3.
