Kakita Ayako, Suzuki Atsushi, Ono Yasunaga, Miura Yoshitaka, Itoh Mitsuyasu, Oiso Yutaka
First Department of Internal Medicine, Nagoya University School of Medicine, Nagoya 466-8550, Japan.
Prostaglandins Leukot Essent Fatty Acids. 2004 May;70(5):469-74. doi: 10.1016/j.plefa.2003.09.003.
Prostaglandins are now recognized to be important regulators for both bone formation and resorption. Among them, prostaglandin E(1) (PGE(1)) has been reported to stimulate cAMP accumulation and to induce alkaline phosphatase (ALP) activity, a marker of differentiation, in osteoblast-like cells. Recently, we have shown that p38 mitogen-activated protein (MAP) kinase pathway regulates ALP activity in response to activation of Gi protein-coupled receptors in mouse osteoblast-like MC3T3-E1 cells (Suzuki et al., Endocrinology 140 (1999) 3177). In the present study, we investigated whether p38 MAP kinase is involved in ALP activation by PGE(1) in MC3T3-E1 osteoblast-like cells. PGE(1) dose-dependently enhanced ALP activities in the concentration range between 1 nM and 1 microM in MC3T3-E1 cells. SB203580, a specific inhibitor of p38 MAP kinase, blocked the increase in ALP activity induced by PGE(1). Further analysis with western blotting suggested that PGE(1) induced an increase in tyrosine (Tyr) phosphorylation of p38 MAP kinase. Both Bt(2)cAMP, a permeable analogue of cAMP, and forskolin, which directly activates adenylate cyclase, also induced an increase in Tyr phosphorylation of p38 MAP kinase. H-89, a potent inhibitor of protein kinase A (PKA), significantly suppressed PGE(1)-induced Tyr phosphorylation of p38 MAP kinase. The results of this study suggest that PGE(1) stimulates p38 MAP kinase through the activation of PKA, resulting in the enhancement of ALP activity.
前列腺素现已被公认为是骨形成和骨吸收的重要调节因子。其中，前列腺素E(1)（PGE(1)）已被报道可刺激环磷酸腺苷（cAMP）积累，并在成骨样细胞中诱导碱性磷酸酶（ALP）活性，这是分化的一个标志物。最近，我们已经表明，p38丝裂原活化蛋白（MAP）激酶途径可调节小鼠成骨样MC3T3-E1细胞中Gi蛋白偶联受体激活后的ALP活性（Suzuki等人，《内分泌学》140（1999）3177）。在本研究中，我们调查了p38 MAP激酶是否参与PGE(1)对MC3T3-E1成骨样细胞中ALP的激活作用。在MC3T3-E1细胞中，PGE(1)在1 nM至1 microM的浓度范围内剂量依赖性地增强了ALP活性。p38 MAP激酶的特异性抑制剂SB203580可阻断PGE(1)诱导的ALP活性增加。蛋白质印迹法的进一步分析表明，PGE(1)诱导了p38 MAP激酶酪氨酸（Tyr）磷酸化增加。cAMP的可渗透类似物Bt(2)cAMP和直接激活腺苷酸环化酶的福司可林也诱导了p38 MAP激酶Tyr磷酸化增加。蛋白激酶A（PKA）的强效抑制剂H-89显著抑制了PGE(1)诱导的p38 MAP激酶Tyr磷酸化。本研究结果表明，PGE(1)通过激活PKA刺激p38 MAP激酶，从而导致ALP活性增强。
