Platelet-derived growth factor induces interleukin-6 transcription in osteoblasts through the activator protein-1 complex and activating transcription factor-2.
Platelet-derived growth factor (PDGF) BB, a mitogen that stimulates bone resorption, increases the expression of interleukin-6 (IL-6), a cytokine that induces osteoclast recruitment. The mechanisms involved in IL-6 induction by PDGF BB are poorly understood. We examined the effect of PDGF BB on IL-6 expression in cultures of osteoblasts from fetal rat calvariae (Ob cells). PDGF BB increased IL-6 mRNA and heterogeneous nuclear RNA levels, the rate of transcription, and the activity of base pairs (bp) -2906 to +20 IL-6 promoter fragments transiently transfected into Ob cells. Deletion analysis revealed two responsive regions, one containing an activator protein-1 (AP-1) site located between bp -276 and -257, and a second, less well defined, downstream of -257. Targeted mutations of a cyclic AMP-responsive element (CRE), and nuclear factor-IL-6 and nuclear factor-kappaB binding sites in a bp -257 to +20 IL-6 construct that was transfected into Ob cells, revealed that the CRE also contributed to IL-6 promoter induction by PDGF BB. Electrophoretic mobility shift assay revealed AP-1 and CRE nuclear protein complexes that were enhanced by PDGF BB. Supershift assays revealed binding of Jun and Fos to AP-1 and CRE sequences and binding of activating transcription factor-2 to CRE. In conclusion, PDGF BB induces IL-6 transcription in osteoblasts by regulating nuclear proteins of the AP-1 complex and activating transcription factor-2.
Departments of Research and Medicine, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105, USA.
N
N
Franchimont
D
D
Durant
S
S
Rydziel
E
E
Canalis
D051698:Activating Transcription Factor 2; D000818:Animals; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism*; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics; D010006:Osteoblasts / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects*
D051698:Activating Transcription Factor 2; C497107:Atf2 protein, rat; D017362:Cyclic AMP Response Element-Binding Protein; D015850:Interleukin-6; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D014157:Transcription Factors