Parathyroid hormone induces sequential c-fos expression in bone cells in vivo: in situ localization of its receptor and c-fos messenger ribonucleic acids.

Localization of PTH/PTH-related peptide (PTH/PTHrP) receptor mRNA and PTH induction of c-fos expression were examined in bones of 4-week-old rats by in situ hybridization. Receptor transcripts were most highly expressed by growth plate chondrocytes from lower proliferating to upper hypertrophic cell layers. PTH/PTHrP receptor mRNA also was expressed in osteoblasts as well as in some bone marrow stromal cells. Subcutaneous administration of human PTH-(1-84) (225 micrograms/kg) induced rapid, transient, and sequential expression of the protooncogene c-fos mRNA in cells in bone. Osteoblasts and chondrocytes expressing PTH/PTHrP receptor transcripts as well as some stromal cells expressed c-fos mRNA first (15-60 min), followed by transient expression in the majority of stromal cells and in osteoclasts (1-2 h). Delayed and transient induction of c-fos in cells with few or no detectable receptor transcripts suggests that PTH acts indirectly on stromal cells and osteoclasts by either stimulating osteoblasts to secrete a substance(s) that acts locally and/or inducing changes in cell-cell contacts between osteoblasts and adjacent cells.