Parathyroid hormone activates phosphoinositide 3-kinase-Akt-Bad cascade in osteoblast-like cells.
To understand the molecular basis underlying the anabolic action of parathyroid hormone (PTH) on bone, the anti-apoptotic action of PTH on osteoblast-like cells was investigated. Since Akt is a key protein kinase for cell survival, we focused on a possible involvement of Akt in the anti-apoptotic action of PTH. Human osteoblast-like MG-63 cells cultured without serum were treated with PTH. Western blot analysis revealed that PTH rapidly phosphorylated Akt and induced its nuclear translocation. The phosphorylation of pro-apoptotic protein Bad was also increased by PTH, leading to its inactivation. The PTH-dependent activation of Akt was also detected in other osteoblastic cell lines, SaOS-2 and ROS 17/2.8. The pretreatment of MG-63 cells with either one of inhibitors for phosphoinositide 3-kinase (PI3K), wortmannin or LY294002 prevented Akt and Bad phosphorylation. Furthermore, co-immunoprecipitation analysis revealed that PTH receptor (PTH-1R) directly interacted with p85, a regulatory subunit of PI3K, in a PTH-dependent manner. Serum withdrawal induced the apoptosis of MG-63 cells, and PTH prevented the apoptosis, which was inhibited by PI3K inhibitors. These results demonstrate the presence of a novel PTH/PTH receptor signaling cascade consisting of PTH-1R, PI3K, Akt and Bad and that this cascade can work as an anti-apoptotic signaling pathway in osteoblast-like cells.
Yamamoto
Takuya
T
Department of Endocrinology and Metabolism, Division of Molecular and Cellular Adaptation, Research Institute of Environmental Medicine, Nagoya University, Nagoya 464-8601, Japan.
Kambe
Fukushi
F
Cao
Xia
X
Lu
Xiuli
X
Ishiguro
Naoki
N
Seo
Hisao
H
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D002470:Cell Survival; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D010006:Osteoblasts / Q000502:physiology*; D010281:Parathyroid Hormone / Q000494:pharmacology / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000378:metabolism; D015398:Signal Transduction; D000077191:Wortmannin; D051025:bcl-Associated Death Protein / Q000378:metabolism*
D000730:Androstadienes; D002867:Chromones; D009025:Morpholines; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D044168:Receptor, Parathyroid Hormone, Type 1; D000077191:Wortmannin; D051025:bcl-Associated Death Protein; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one