Parathyroid hormone increases activating transcription factor 4 expression and activity in osteoblasts: requirement for osteocalcin gene expression.
PTH is an important peptide hormone regulator of calcium homeostasis and osteoblast function. However, its mechanism of action in osteoblasts is poorly understood. Our previous study demonstrated that PTH activates mouse osteocalcin (Ocn) gene 2 promoter through the osteoblast-specific element 1 site, a recently identified activating transcription factor-4 (ATF4) -binding element. In the present study, we examined effects of PTH on ATF4 expression and activity as well as the requirement for ATF4 in the regulation of Ocn by PTH. Results show that PTH elevated levels of ATF4 mRNA and protein in a dose- and time-dependent manner. This PTH regulation requires transcriptional activity but not de novo protein synthesis. PTH also increased binding of nuclear extracts to osteoblast-specific element 1 DNA. PTH stimulated ATF4-dependent transcriptional activity mainly through protein kinase A with a lesser requirement for protein kinase C and MAPK/ERK pathways. Lastly, PTH stimulation of Ocn expression was lost by small interfering RNA down-regulation of ATF4 in MC-4 cells and Atf4(-/-) bone marrow stromal cells. Collectively, these studies for the first time demonstrate that PTH increases ATF4 expression and activity and that ATF4 is required for PTH induction of Ocn expression in osteoblasts.
Yu
Shibing
S
Division of Hematology/Oncology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15240, USA.
Franceschi
Renny T
RT
Luo
Min
M
Zhang
Xiaoyan
X
Jiang
Di
D
Lai
Yumei
Y
Jiang
Yu
Y
Zhang
Jian
J
Xiao
Guozhi
G
D016475:3T3 Cells; D051701:Activating Transcription Factor 4 / Q000235:genetics*; D000818:Animals; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D004247:DNA / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D015675:Osteocalcin / Q000235:genetics*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D015398:Signal Transduction; D014158:Transcription, Genetic
D017362:Cyclic AMP Response Element-Binding Protein; D010281:Parathyroid Hormone; D015675:Osteocalcin; D051701:Activating Transcription Factor 4; D004247:DNA; D017868:Cyclic AMP-Dependent Protein Kinases