title: Vitamin D receptor-dependent 1 alpha,25(OH)2 vitamin D3-induced anti-apoptotic PI3K/AKT signaling in osteoblasts.
abstract: Osteoblast apoptosis plays a crucial role in bone remodeling. Physiological doses of 1 alpha,25(OH)(2)-vitamin D(3) (1,25D) protect osteoblasts against apoptosis by means of mechanisms only partially understood. We studied activation of an Akt survival cascade downstream of 1,25D nongenomic stimulation of phosphatidylinositide-3'-kinase (PI3K) in osteoblastic cells. We measured a dose- and time-dependent 1,25D induction of Akt phosphorylation (p-Akt) in cultured osteoblastic cells. Maximal response was achieved with 10 nM 1,25D after 5 min. We found that staurosporine (STSP)-induced apoptosis was significantly reduced in 1,25D-pretreated osteoblasts. 1,25D prosurvival effects were abolished when cells were preincubated with inhibitors of PI3K activation. By means of siRNA silencing, we proved that 1,25D induction of p-Akt requires a classic vitamin D receptor (VDR) in osteoblasts. Furthermore, non-osteoblastic CV-1 cells transfected with an enhanced green fluorescent protein (EGFP)-VDR construct responded to 1,25D treatment with a rapid p-Akt response associated with increased cell survival not detected in native, nontransfected cells. We measured increased levels of p-Akt substrates p-Bad and p-FKHR and significantly reduced activity of caspases 8 and 3/7 after 1,25D treatment. In addition, 1,25D-induced protection against apoptosis was abolished when osteoblasts were preincubated with pertussis toxin. We conclude that anti-apoptotic effects of 1,25D in osteoblasts occur through nongenomic activation of a VDR/PI3K/Akt survival pathway that includes phosphorylation of multiple p-Akt substrates and reduction of caspase activities.
authors.affiliation: Department of Biochemistry, University of California, Riverside, California 92521, USA.
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Zhang
authors.forename: Laura P
authors.initials: LP
authors.lastname: Zanello
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002117:Calcitriol / Q000494:pharmacology*; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D051858:Forkhead Transcription Factors / Q000378:metabolism; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D037342:Pertussis Toxin / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D018167:Receptors, Calcitriol / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D019311:Staurosporine / Q000494:pharmacology; D013997:Time Factors; D051025:bcl-Associated Death Protein / Q000378:metabolism; D000071161:Forkhead Box Protein O1
chemical_list: D002117:Calcitriol; D061945:Caspase Inhibitors; D051858:Forkhead Transcription Factors; D009419:Nerve Tissue Proteins; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D018167:Receptors, Calcitriol; D019311:Staurosporine; D051025:bcl-Associated Death Protein; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1