PREFERENTIAL DOWN-REGULATION OF PHOSPHOLIPASE C-BETA-1 (PLC-BETA-1) DURING THE EARLY-STAGE OF DIFFERENTIATION IN MC3T3-E1 OSTEOBLAST CELLS

The healing of bone fracture and remodeling are associated with differ entiation of osteoblasts. Previous investigations in our laboratory in dicated that the differentiation in osteoblast-like cell line MC3T3-E1 induced by the combination of beta-glycerol phosphate and ascorbic ac id suppressed the signal transduction via phosphoinositide-specific ph ospholipase C (PLC) and phospholipase D (PLD) activation mediated by P GF(2 alpha) (9). The present investigation was designed to examine qua ntitative changes in the levels of PLC and GTP-binding protein (G-prot ein) by Western-blotting analysis. Alkaline phosphatase activity, a di fferentiation marker, was measured using p-nitrophenylphosphate. The r esults revealed that the levels of PLC-beta 1 and G-protein (G(q alpha )) were remarkably down-regulated with an increase of alkaline phospha tase activity. In contrast, PLC-gamma 1 and PLC-beta 3 were not affect ed. The levels of p42 mitogen-activated protein kinase (p42 MAPK) and protein kinase C (PKC) were also unchanged. The results suggest that p referential down-regulation of PLC-beta 1 is associated with the diffe rentiation of osteoblast-like cell line MC3T3-E1.