Lk. Mccauley et al., Parathyroid hormone stimulates fra-2 expression in osteoblastic cells in vitro and in vivo, ENDOCRINOL, 142(5), 2001, pp. 1975-1981
PTH and PTH-related protein (PTHrP) are key mediators of skeletal developme
nt 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 micro
environment that contain AP-1 sites, and different Fos family members are r
eported to have opposing transcriptional activities at AP-1 sites. The purp
ose of this study was to identify the effects of PTH on expression of the A
P-1 protein complex member, fra-2, to extend our understanding of transcrip
tional regulators of PTH action. PTH induction of fra-2 messenger RNA (mRNA
) levels in MC3T3-E1 preosteoblastic cells was maximal with 0.1 muM PTH (1-
34). The expression in vitro was greatest Ih after treatment and was presen
t with N-terminal PTH but not PTH (7-34) or (53-84). Cycloheximide treatmen
t induced fra-2 expression, and actinomycin D inhibited basal and PTHrP-ind
uced expression. AP-1 protein in nuclear extracts of MC3T3-E1 cells was inc
reased with PTH treatment at 3 h and consisted of high levels of Fra-a prot
ein, as evidenced by a supershift in an electrophoretic mobility shift assa
y and Western blot analysis. Up-regulation of steady-state fra-2 mRNA was a
lso noted in vivo, where injection of PTH (1-34) (20 mug) resulted in a mor
e-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 mediato
rs induced by PTH and suggest that the interplay of AP-1 family members wil
l provide insight into regulatory pathways of PTH and PTHrP for their anabo
lic and catabolic actions in bone.