epidermal-growth-factor and beta-glycerophosphoric-acid

The role of epidermal growth factor receptors (EGF-R) in osteogenic cell differentiation was investigated using preosteoblastic MC3T3-E1 (MC3T3) cells and osteoblast-like ROS 17/2.8 (ROS) cells. When cultured in the presence of beta-glycerophosphate (GP) and ascorbic acid (AA), MC3T3 cells underwent spontaneous differentiation into osteoblasts which was confirmed as they expressed osteoblast markers such as alkaline phosphatase (ALP), bone sialoprotein (BSP) and osteocalcin (OC). Interestingly, the number of EGF-binding sites decreased during their differentiation into osteoblasts, and the osteogenic protein-1 (OP-1) treatment, which accelerated their differentiation, lowered the number of EGF-binding sites even further. On the other hand, ROS cells with high expression levels of osteoblast markers and no EGF-R, after being transfected with human EGF-R cDNA (EROS cells), expressed numerous EGF-binding sites as well as EGF-R mRNA and protein; in the process, they ceased to express osteoblast markers, indicating their dedifferentiation into osteoprogenitor cells. Both MC3T3 and EROS cells showed increased cell growth in response to EGF, whereas ROS cells did not. These results imply that the EGF/EGF-R system in osteogenic cells has a crucial function in osteoblast phenotype suppression and osteogenic cell proliferation.

Topics: Alkaline Phosphatase; Ascorbic Acid; Blotting, Northern; Bone Morphogenetic Protein 7; Bone Morphogenetic Proteins; Cell Differentiation; Cell Line; DNA, Complementary; Down-Regulation; Epidermal Growth Factor; ErbB Receptors; Flow Cytometry; Glycerophosphates; Humans; Integrin-Binding Sialoprotein; Osteoblasts; Osteocalcin; RNA, Messenger; Sialoglycoproteins; Transformation, Genetic; Transforming Growth Factor beta

Significant amounts of inorganic polyphosphates and of polyphosphate-degrading exopolyphosphatase activity were detected in human mandibular-derived osteoblast-like cells. The amount of both soluble and insoluble long-chain polyphosphate in unstimulated osteoblast-like cells was higher than in human gingival cells, erythrocytes, peripheral blood mononuclear cells, and human blood plasma. The cellular content of polyphosphate in osteoblast-like cells strongly decreased after a combined treatment of the cells with the stimulators of osteoblast proliferation and differentiation, dexamethasone, beta-glycerophosphate, epidermal growth factor, and ascorbic acid. The amount of soluble long-chain polyphosphate, but not the amount of insoluble long-chain polyphosphate, further decreased after an additional treatment with 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3). The decrease in polyphosphate content during treatment with dexamethasone, beta-glycerophosphate, epidermal growth factor, and ascorbic acid was accompanied by a decrease in exopolyphosphatase, pyrophosphatase, and alkaline phosphatase activity. However, additional treatment with 1,25(OH)2D3 resulted in an increase in these enzyme activities. Osteoblast-like cell exopolyphosphatase activity and exopolyphosphatase activity in yeast, rat tissues, and human leukemia cell line HL60 were inhibited by the bisphosphonates etidronate and, to a lesser extent, clodronate and pamidronate. From our results, we assume that inorganic polyphosphate may be involved in modulation of the mineralization process in bone tissue.

Topics: Acid Anhydride Hydrolases; Alkaline Phosphatase; Animals; Calcitriol; Cell Differentiation; Cell Division; Cells, Cultured; Dexamethasone; Diphosphonates; Epidermal Growth Factor; Etidronic Acid; Glycerophosphates; HL-60 Cells; Humans; Inorganic Pyrophosphatase; Mandible; Osteoblasts; Polyphosphates; Pyrophosphatases; Rats; Solubility

Treatment of PC12 cells with either nerve growth factor, a differentiating agent, or epidermal growth factor, a mitogen, leads to an increase in the phosphorylation of the ribosomal protein S6. The soluble fraction of PC12 cells contains two S6 kinases, separable on heparin-Sepharose. Treatment of the cells with nerve growth factor results in an increase in the activity of one of these kinases; treatment of the cells with epidermal growth factor results in an increase in the activity of the other one. The data suggest that the patterns of phosphorylation and, in turn, the functional properties of S6 are different in cells instructed to differentiate from those in cells instructed to divide.

Topics: Adrenal Gland Neoplasms; Animals; Cell Differentiation; Cell Line; Chromatography, Affinity; Egtazic Acid; Enzyme Activation; Epidermal Growth Factor; Glycerophosphates; Kinetics; Mitogens; Nerve Growth Factors; Pheochromocytoma; Phosphorylation; Protein Kinases; Ribosomal Protein S6 Kinases