OSTEOGENIC ACTION OF PARATHYROID HORMONE-RELATED PEPTIDE-(1-141) IN RAT ROS CELLS

To examine the autocrine/paracrine effect of parathyroid hormone-relat ed peptide (PTHrP) on osteoblast function, the entire coding region of rat PTHrP (1-141) cDNA inserted into the expression vector was stably transfected into the rat clonal strain of the osteoblast-like cell, R OS 17/2.8, and established stable transfectants. Using the PTHrP-overe xpressing ROS cells (ROS/PLP/6), we analyzed in vitro cell characteriz ation and in vivo osteogenic properties. As expected, overexpression o f endogenous PTHrP in vitro induced PTH/PTHrP receptor down-regulation confirmed by Northern blots, receptor binding assays, and functional analysis. The established transfectants indicated a decreased growth r ate compared with the original non-transfected ROS 17/2.8. Although cA MP production induced by exogenous PTH was suppressed in ROS/PLP/6, th e stimulatory effects of forskolin and chorela toxin showed no signifi cant difference between the original ROS 17/2.8 and transfected cells, but the in vivo osteogenic properties were histologically potentiated in transfectants with increased bone matrix and acceleration of miner alization within tumors. The levels of osteocalcin and osteopontin mRN As were also increased in transfectants. The down-regulated in vitro P TH/PTHrP receptor mRNA was restored in in vivo tumor tissues. Our stud y provides clear evidence that the in vivo osteogenic function in ROS cells is potentiated by PTHrP, through an autocrine/paracrine mode of action.