Okadaic acid reverses the inhibitory effect of protein kinase C on alkaline phosphatase activity in osteoblast-like cells.
We previously reported that fetal calf serum-induced alkaline phosphatase activity is suppressed due to the activation of protein kinase C in osteoblast-like MC3T3-E1 cells (Miwa et al. (1991) Bone Miner. 14, 15-25; Kotoyori et al. (1994) Horm. Metab. Res. 26, 116-118). In the present study, we examined the effect of okadaic acid, a potent and specific inhibitor of protein phosphatase type 1 and 2A, on fetal calf serum-induced alkaline phosphatase activity in MC3T3-E1 cells. The pretreatment with okadaic acid enhanced the fetal calf serum-induced alkaline phosphatase activity in a dose-dependent manner in the range between 0.1 and 5 nM. 1-Norokadaone, a less potent analogue of okadaic acid, had little effect on the fetal calf serum-induced alkaline phosphatase activity. Okadaic acid partially reversed the suppression of fetal calf serum-induced alkaline phosphatase activity by 12-O-tetradecanoylphorbol-13-acetate, a protein kinase C activator. The effect of okadaic acid was dose-dependent in the range between 0.1 and 5 nM. The patterns of the dose-dependency of both okadaic acid effects on fetal calf serum-induced alkaline phosphatase activity and on the suppression by 12-O-tetradecanoylphorbol-13-acetate were similar. These results strongly suggest that protein phosphatase type 1 and/or 2A act as a regulator of alkaline phosphatase activity at a point downstream from protein kinase C in osteoblast-like cells.
First Department of Internal Medicine, Nagoya University School of Medicine, Japan.
Y
Y
Watanabe
O
O
Kozawa
A
A
Suzuki
J
J
Kotoyori
Y
Y
Ito
Y
Y
Oiso
D000469:Alkaline Phosphatase / Q000378:metabolism*; D002460:Cell Line; D003470:Culture Media; D004988:Ethers, Cyclic / Q000494:pharmacology*; D005312:Fetal Blood; D019319:Okadaic Acid; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology*; D011493:Protein Kinase C / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D003470:Culture Media; D004988:Ethers, Cyclic; D019319:Okadaic Acid; D011493:Protein Kinase C; D000469:Alkaline Phosphatase; D013755:Tetradecanoylphorbol Acetate