okadaic-acid and beta-glycerophosphoric-acid

Although basic fibroblast growth factor (FGF-2) had been shown to inhibit type I collagen gene expression in osteoblast, its inhibitory mechanism is unknown. In the present study, we investigated the underlying mechanisms by which growth factors downregulate type I collagen gene expression. Treatment of mouse osteoblastic MC3T3-E1 cells with okadaic acid (40 ng/ml), an inhibitor of phosphoserine/threonine-specific protein phosphatase and activator of ERK1/2, for 24 h and 48 h completely inhibited steady-state mRNA levels of type I collagen. FGF-2 (30 ng/ml), platelet-derived growth factor-BB (PDGF-BB), 30 ng/ml, and serum, which activate ERK mitogen-activated protein kinase (MAPK) pathway also inhibited collagen type I gene expression, suggesting that the activation of ERK pathway mediates inhibition of type I collagen mRNA. This observation was further confirmed by experiments using inhibitors of the ERK pathway (i.e., PD and U0126), which increased type I collagen mRNA in MC3T3-E1 cells, indicating that the inhibition of ERK pathway upregulates type I collagen gene expression. Low serum (0.3%) markedly increased type I collagen mRNA. MEK inhibitor PD inhibited c-fos induction by FGF-2 and PDGF-BB, suggesting that c-fos is the downstream target of ERK pathway. Our data have clearly demonstrated for the first time that the ERK MAPK pathway play an important role in the regulation of type I collagen gene expression in osteoblastic cells. Results also showed that one of the mechanisms by which FGF-2 and PDGF-BB downregulate type I collagen gene expression in the osteoblast is through the activation of ERK signaling pathway.

Topics: 3T3 Cells; Animals; Ascorbic Acid; Becaplermin; Butadienes; Down-Regulation; Enzyme Inhibitors; Fibroblast Growth Factor 2; Flavonoids; Genes, fos; Glycerophosphates; Humans; Mice; Mitogen-Activated Protein Kinases; Nitriles; Okadaic Acid; Osteoblasts; Platelet-Derived Growth Factor; Procollagen; Proto-Oncogene Proteins c-sis; Recombinant Proteins; RNA, Messenger; Signal Transduction

PC12 pheochromocytoma cells contain at least two different and separable kinases that phosphorylate the S6 protein of the ribosomes. The activity of one of these S6 kinases is increased by treatment of the cells with nerve growth factor and of the other by treatment with epidermal growth factor. Okadaic acid increases the activity of the nerve growth factor-sensitive S6 kinase. The data suggest that the nerve growth factor-sensitive S6 kinase is activated by phosphorylation on serine or threonine residues and is inactivated by either phosphatase 1 or phosphatase 2A, probably the latter.

Topics: Animals; Dose-Response Relationship, Drug; Egtazic Acid; Enzyme Activation; Ethers, Cyclic; Glycerophosphates; Nerve Growth Factors; Okadaic Acid; Phosphoprotein Phosphatases; Phosphorylation; Protein Kinases; Protein Phosphatase 1; Protein Phosphatase 2; Ribosomal Protein S6; Ribosomal Proteins; Tumor Cells, Cultured