Civitelli R, Hruska K A, Shen V, Avioli L V
Division of Endocrinology and Bone Metabolism, Jewish Hospital of St. Louis, Washington University Medical Center, Missouri 63110.
Exp Gerontol. 1990;25(3-4):223-31. doi: 10.1016/0531-5565(90)90056-8.
Previous work demonstrated that parathyroid hormone (PTH) activates the Ca2+/protein kinase C (PKC) system in addition to cAMP production. Therefore, the authors explored the role of cAMP-dependent and Ca2(+)-dependent signals in the regulation of osteoblastic growth and bone resorption. In exponentially growing UMR 106-01 osteogenic sarcoma cells, PTH (10(-7) M) inhibited [3H] thymidine incorporation by 80%. This effect was reproduced by maximal doses of both dibutyryl-cAMP (dbcAMP) and forskolin. The Ca2+ ionophore ionomycin (10(-7) M) had no effect, whereas phorbol 12-myristate 13-acetate (PMA) was slightly mitogenic. The antimitogenic action of dbcAMP was dose-dependent, with ED0.5 at about 3 X 10(-5) M. Ionomycin enhanced this dbcAMP effect at submaximal doses of the cAMP analog. PMA used in combination with both dbcAMP and ionomycin induced further depression of cell proliferation, indicating synergism with cAMP. Both dbcAMP (10(-4) M) and ionomycin (10(-7) M) stimulated 45Ca release from fetal rat limb bones after five days in culture, although the Ca2+ ionophore was less potent. 1-Oleoyl 2-acetyl-glycerol (2 X 10(-6) M) was ineffective alone, and slightly inhibited the 45Ca release produced by the other second messenger analogs in all combinations. The combination of dbcAMP and ionomycin showed a synergistic effect, and fully reproduced PTH effect. In conclusion, PTH signal transduction for control of cell proliferation and bone resorption is mediated mainly by cAMP. Activation of the Ca2+/PKC message system is nevertheless necessary to express a full hormonal response in both cell and organ culture systems.
先前的研究表明，甲状旁腺激素（PTH）除了能产生环磷酸腺苷（cAMP）外，还能激活Ca2+/蛋白激酶C（PKC）系统。因此，作者探讨了cAMP依赖性信号和Ca2+依赖性信号在调节成骨细胞生长和骨吸收中的作用。在呈指数生长的UMR 106-01骨肉瘤细胞中，PTH（10-7M）使[3H]胸苷掺入量降低了80%。最大剂量的二丁酰环磷腺苷（dbcAMP）和福斯可林均可重现这一效应。Ca2+离子载体离子霉素（10-7M）无此作用，而佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）有轻微的促有丝分裂作用。dbcAMP的抗有丝分裂作用呈剂量依赖性，半数有效剂量（ED0.5）约为3×10-5M。在低于最大剂量的cAMP类似物作用下，离子霉素可增强dbcAMP的这一效应。PMA与dbcAMP和离子霉素联合使用可进一步抑制细胞增殖，表明其与cAMP具有协同作用。培养5天后，dbcAMP（10-4M）和离子霉素（10-7M）均可刺激胎鼠四肢骨释放45Ca，尽管Ca2+离子载体的作用较弱。1-油酰基2-乙酰甘油（2×10-6M）单独使用无效，且在所有组合中均轻微抑制其他第二信使类似物诱导的45Ca释放。dbcAMP和离子霉素联合使用显示出协同效应，并完全重现了PTH的作用。总之，PTH控制细胞增殖和骨吸收的信号转导主要由cAMP介导。然而，在细胞和器官培养系统中，激活Ca2+/PKC信号系统对于表达完整的激素反应是必要的。
