Proto-oncogene c-fos is transcriptionally regulated by parathyroid hormone (PTH) and PTH-related protein in a cyclic adenosine monophosphate-dependent manner in osteoblastic cells.
PTH and PTH-related protein (PTHrP) bind to the PTH-1 (PTH/PTHrP) receptor and produce anabolic and catabolic effects in bone. To investigate postreceptor mechanisms of action, MC3T3-E1 cells were induced to differentiate to optimize PTH-1 receptor expression, and differentiated MC3T3-E1 cells were treated with varying doses of PTH (1-34) for 1 h. Northern blot analysis revealed a dose-dependent stimulation of steady state c-fos messenger RNA (mRNA), with measurable expression at doses as low as 1 pM PTH. The time course of c-fos mRNA induction was rapid, with peak levels detected at 30-45 min. Increased steady state c-fos mRNA was due to increased transcription of the c-fos gene as demonstrated by nuclear run-on assays and was dependent on the temporal differentiation state of the MC3T3-E1 cells. Stimulation of c-fos mRNA was induced exclusively by N-terminal PTH and PTHrP (which is also responsible for cAMP activation), and did not occur with PTH (7-34), (53-84), or PTHrP (107-139). The effects of PTH (1-34) on c-fos stimulation were dependent on intracellular cAMP. Forskolin [a guanine-nucleotide-binding protein (G(alpha)) agonist] stimulated c-fos mRNA, whereas 9-(tetrahydro-2-furyl) adenine (THFA) (a cAMP antagonist), 1,9 dideoxyforskolin (a cAMP independent analog of forskolin), and phorbol 12-myristate 13-acetate (a protein kinase C activator) did not. Furthermore, THFA inhibited the ability of PTH (1-34) to stimulate c-fos mRNA in a time-dependent manner. These findings indicate that c-fos is transcriptionally regulated by PTH (1-34) in osteoblastic cells, and that cAMP is a mediator of PTH-stimulated c-fos induction. Several known bone-associated proteins contain DNA binding sites in their promoter regions that recognize c-fos in conjunction with c-jun (AP-1 sites). Consequently, the induction of c-fos by PTH (1-34) in osteoblastic cells may be a sensitive indicator of PTH effects in vitro and in vivo, and provide valuable information regarding mechanisms of PTH action in bone.
McCauley
L K
LK
Department of Periodontics/Prevention/Geriatrics, University of Michigan, Ann Arbor 48109-1078, USA. mccauley@umich.edu
Koh
A J
AJ
Beecher
C A
CA
Rosol
T J
TJ
D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology*; D016762:Genes, fos; D010006:Osteoblasts / Q000187:drug effects / Q000502:physiology*; D010281:Parathyroid Hormone / Q000502:physiology*; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D019379:Teriparatide / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic / Q000502:physiology*
D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D019379:Teriparatide; C017759:9-(tetrahydro-2-furyl)-adenine; D000242:Cyclic AMP; D000225:Adenine