Singh A T K, Gilchrist A, Voyno-Yasenetskaya T, Radeff-Huang J M, Stern P H
Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA.
Endocrinology. 2005 May;146(5):2171-5. doi: 10.1210/en.2004-1283. Epub 2005 Feb 10.
PTH, a major regulator of bone remodeling and a therapeutically effective bone anabolic agent, stimulates several signaling pathways in osteoblastic cells. Our recent studies have revealed that PTH activates phospholipase D (PLD) -mediated phospholipid hydrolysis through a RhoA-dependent mechanism in osteoblastic cells, raising the question of the upstream link to the PTH receptor. In the current study, we investigated the role of heterotrimeric G proteins in mediating PTH-stimulated PLD activity in UMR-106 osteoblastic cells. Transfection with antagonist minigenes coding for small peptide antagonists to G alpha 12 and G alpha13 subunits of heterotrimeric G proteins prevented PTH-stimulated activation of PLD, whereas an antagonist minigene to G alphas failed to produce this effect. Effects of pharmacological inhibitors (protein kinase inhibitor, Clostridium botulinum exoenzyme C3) were consistent with a role of Rho small G proteins, but not of cAMP, in the effect of PTH on PLD. Expression of constitutively active G alpha12 and G alpha13 activated PLD, an effect that was inhibited by dominant-negative RhoA. The results identify G alpha12 and G alpha13 as upstream transducers of PTH effects on PLD, mediated through RhoA in osteoblastic cells.
甲状旁腺激素（PTH）是骨重塑的主要调节因子，也是一种具有治疗效果的骨合成代谢药物，可刺激成骨细胞中的多种信号通路。我们最近的研究表明，PTH通过成骨细胞中一种依赖RhoA的机制激活磷脂酶D（PLD）介导的磷脂水解，这就引出了与PTH受体上游联系的问题。在本研究中，我们研究了异源三聚体G蛋白在介导UMR - 106成骨细胞中PTH刺激的PLD活性中的作用。用编码异源三聚体G蛋白Gα12和Gα13亚基小肽拮抗剂的拮抗剂微型基因转染，可阻止PTH刺激的PLD激活，而针对Gαs的拮抗剂微型基因则未能产生这种效果。药理学抑制剂（蛋白激酶抑制剂、肉毒杆菌外毒素C3）的作用与Rho小G蛋白而非cAMP在PTH对PLD的作用中的作用一致。组成型活性Gα12和Gα13的表达激活了PLD，这一作用被显性负性RhoA抑制。结果表明，Gα12和Gα13是PTH对PLD作用的上游转导因子，在成骨细胞中通过RhoA介导。
