Parathyroid hormone stimulates fra-2 expression in osteoblastic cells in vitro and in vivo.
PTH and PTH-related protein (PTHrP) are key mediators of skeletal development and homeostasis through their activation of the PTH-1 receptor. Previous studies have found that several AP-1 family members are regulated by PTH, such as c-fos, fra-1, and c-jun. There are numerous genes in the bone microenvironment that contain AP-1 sites, and different Fos family members are reported to have opposing transcriptional activities at AP-1 sites. The purpose of this study was to identify the effects of PTH on expression of the AP-1 protein complex member, fra-2, to extend our understanding of transcriptional regulators of PTH action. PTH induction of fra-2 messenger RNA (mRNA) levels in MC3T3-E1 preosteoblastic cells was maximal with 0.1 microM PTH (1-34). The expression in vitro was greatest 1 h after treatment and was present with N-terminal PTH but not PTH (7-34) or (53-84). Cycloheximide treatment induced fra-2 expression, and actinomycin D inhibited basal and PTHrP-induced expression. AP-1 protein in nuclear extracts of MC3T3-E1 cells was increased with PTH treatment at 3 h and consisted of high levels of Fra-2 protein, as evidenced by a supershift in an electrophoretic mobility shift assay and Western blot analysis. Up-regulation of steady-state fra-2 mRNA was also noted in vivo, where injection of PTH (1-34) (20 microgram) resulted in a more-than-7-fold maximal increase in fra-2 mRNA expression in the calvaria of mice, after 1 h of treatment. These data add to the transcriptional mediators induced by PTH and suggest that the interplay of AP-1 family members will provide insight into regulatory pathways of PTH and PTHrP for their anabolic and catabolic actions in bone.
McCauley
L K
LK
Department of Periodontics/Prevention/Geriatrics, University of Michigan, Ann Arbor, Michigan 48109-1078, USA.
Koh-Paige
A J
AJ
Chen
H
H
Chen
C
C
Ontiveros
C
C
Irwin
R
R
McCabe
L R
LR
D000818:Animals; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics*; D051921:Fos-Related Antigen-2; D005786:Gene Expression Regulation / Q000187:drug effects*; D016762:Genes, fos; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*
D004268:DNA-Binding Proteins; D051921:Fos-Related Antigen-2; C497873:Fosl2 protein, mouse; D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D004247:DNA; D003513:Cycloheximide