Platelet-derived growth factor induces collagenase 3 transcription in osteoblasts through the activator protein 1 complex

Platelet-derived growth factor (PDCF) BE is a mitogen that stimulates bone resorption and increases collagenase 3 transcription in osteoblasts, althou gh the mechanisms involved are as yet unknown. We examined the effect of PD GF BE on collagenase 3 transcription in cultures of osteoblasts from fetal rat calvariae (Ob cells). PDCF BE increased the activity of collagenase 3 p romoter fragments transiently transfected into Ob cells. Deletion analysis of the collagenase promoter revealed three regions that impaired the induct ion of collagenase 3 by PDGF BE. A construct spanning base pair -53 to +28 collagenase 3 sequences, in relation to the start site of transcription fl, was fully responsive to PDGF BE and was studied in detail. Targeted mutati ons of an AP-1 site in this fragment decreased basal collagenase promoter a ctivity and the responsiveness to PDGF BE, whereas mutations of Stat3 and E ts binding sites did not alter the response to PDGF. Electrophoretic mobili ty shift assay, using nuclear extracts from control and treated cells, reve aled AP-1 nuclear protein complexes that were enhanced in extracts from PDG F BE-treated Ob cells. Supershift assays revealed that antibodies to c-Fos, Fos B, Fra-2, c-Jun, Jun B, and Jun D shifted the binding of nuclear extra cts from cells treated With PDGF: BE to AP-1 sequences. In conclusion, PDGF BE induces collagenase 3 transcription in osteoblasts by regulating nuclea r proteins interacting with AP-1 sequences. J. Cell. Physiol. 184:326-333, 2000. (C) 2000 Wiley-Liss Inc.