PGC-1alpha is induced by parathyroid hormone and coactivates Nurr1-mediated promoter activity in osteoblasts.
Parathyroid hormone (PTH) potently activates cAMP-protein kinase A (PKA)-driven molecular cascades in osteoblasts. The NR4A/NGFI-B orphan nuclear receptor (NR) Nurr1 is a PTH-induced, cAMP-responsive primary response gene (PRG) that transactivates osteocalcin (Ocn) expression through a putative NGFI-B response element (NBRE) in the proximal promoter. As a true orphan NR, Nurr1's expression level and coactivator recruitment regulate its transactivation capacity. We postulated that Nurr1's induction through cAMP-PKA signaling might favor a coactivator that is likewise cAMP-dependent. A possible candidate is the cAMP-inducible coactivator PPARgamma coactivator-1alpha (PGC-1alpha). We hypothesize that PGC-1alpha is a PTH-induced PRG that synergizes with Nurr1 to induce target gene transcription in osteoblasts. We show that 10 nM PTH for 2 h maximally induced PGC-1alpha mRNA in primary mouse osteoblasts (MOBs) and calvariae. Selective signaling agonists and antagonists demonstrated that PTH induced PGC-1alpha mRNA primarily through the cAMP-PKA pathway. Protein synthesis inhibition sustained PTH-induced PGC-1alpha expression. PGC-1alpha enhanced Nurr1-induced transactivation of a consensus 3xNBRE-luciferase construct and the rat (-1050)Ocn promoter-luciferase construct from 3.7- to 9.6- and 10.1-fold, respectively. This synergy required Nurr1-DNA binding, since a mutation of the Ocn promoter NBRE abolished both Nurr1- and Nurr1-PGC-1alpha-induced transactivation. Using GST pull-down assays, PGC-1alpha directly interacted with in vitro-generated and nuclear Nurr1. We conclude that PGC-1alpha is a PTH-induced, cAMP-dependent PRG that directly synergizes with Nurr1 to transactivate target genes in osteoblasts. Taken together with published data, our findings suggest that Nurr1 and PGC-1alpha may be pivotal mediators of cAMP-induced osteoblast gene expression and osteoblast function.
Nervina
Jeanne M
JM
Section of Orthodontics, UCLA School of Dentistry, Los Angeles, CA 90095, USA.
Magyar
Clara E
CE
Division of Diagnostic and Surgical Sciences, UCLA School of Dentistry, Los Angeles, CA 90095, USA.
Pirih
Flavia Q
FQ
Division of Diagnostic and Surgical Sciences, UCLA School of Dentistry, Los Angeles, CA 90095, USA.
Tetradis
Sotirios
S
Division of Diagnostic and Surgical Sciences, UCLA School of Dentistry, Los Angeles, CA 90095, USA; UCLA Molecular Biology Institute, Los Angeles, CA 90095, USA. Electronic address: sotirist@dent.ucla.edu.
D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015675:Osteocalcin / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D004268:DNA-Binding Proteins; C539882:NR4A2 protein, human; C539883:Nr4a2 protein, mouse; C539884:Nr4a2 protein, rat; D057126:Nuclear Receptor Subfamily 4, Group A, Member 2; C470125:PTH protein, human; D010281:Parathyroid Hormone; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; C485290:Ppargc1a protein, mouse; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D015675:Osteocalcin; D000242:Cyclic AMP; D008156:Luciferases; D017868:Cyclic AMP-Dependent Protein Kinases