Endogenous parathyroid hormone-related peptide enhances proliferation and inhibits differentiation in the osteoblast-like cell line ROS 17/2.8

To investigate potential effects of endogenous parathyroid hormone-related peptide (PTHrP) on osteoblast function, ROS 17/2.8 cells were transfected w ith full-length PTHrP cDNA in a sense or antisense orientation to alter PTH rP production. Compared with vector-transfected control cells, PTHrP-overpr oducing (sense-transfected) cells showed increased DNA synthesis ([H-3]-thy midine incorporation) and increased growth (cell number). The extent of apo ptosis was compared for the different clones using the terminal deoxynucleo tide-mediated dUTP nick-end-labeling assay (TUNEL) and Hoechst staining. No differences in percentages of apoptotic cells were found under basal cultu re conditions or after 3 days of serum deprivation, which, itself, markedly increased numbers of apoptotic cells, The effect of PTHrP on osteoblast di fferentiation was assessed by examining two protein markers of differentiat ion, alkalife phosphatase, and bone morphogenetic protein (BMP)-2. Alkaline phosphatase activity was decreased in sense-transfected cells and increase d in antisense-transfected cells, compared with cells transfected with empt y vector. PTHrP-overproducing cells also showed decreased numbers of BMP-2- positive cells, whereas antisense-transfected cells showed no difference co mpared with vector control. The results indicate that: (a) endogenously pro duced PTHrP can increase growth of these osteoblastic cells by stimulating proliferation while not affecting apoptosis; and (b) the increased cell pro liferation produced by PTHrP was accompanied by a reduction in activity or amount of two proteins normally expressed by differentiated osteoblasts. (C ) 2000 by Elsevier Science Inc. All rights reserved.