PARATHYROID-HORMONE RESPONSES OF CYCLIC-AMP-RESPONSIVE, SERUM-RESPONSIVE AND PHORBOL-ESTER-RESPONSIVE REPORTER GENES IN OSTEOBLAST-LIKE UMR-106 CELLS

Parathyroid hormone (PTH) and PTH-related protein interact with a G pr otein-coupled. receptor linked to the activation of adenylyl cyclase a nd phospholipase C signaling pathways. Regulation by PTH of the expres sion of three distinct, stably transfected luciferase reporter genes r esponsive to cAMP (CRE-luc), serum (SRE-luc) and phorbol ester (TRE-lu c) has been studied in rat osteoblast-like UMR-106 cells. Maximal 43-f old induction of CRE-luc expression occurred in response to 100 nM rat (r)PTH(1-34) (EC50 = 0.44 nM), but SRE-luc and TRE-luc remained unaff ected. Maximal 2.8- and 3.4-fold inductions of SRE-luc by 10 ng/ml EGF and 100 nM phorbol ester (PMA) were suppressed with 100 nM rPTH(1-34) (IC50 = 0.04 and 0.15 nM, respectively). Similarly, 7.3-fold inductio n of TRE-luc by 100 nM PMA was inhibited to 50% with 100 nM rPTH(1-34) (IC50 = 0.5 nM). Activation of mitogen-activated protein kinase by EG F and PMA was also suppressed by rPTH(1-34). 1 mM 8-Br-cAMP and 0.1 mM forskolin mimicked all the effects of rPTH(1-34). In conclusion, the regulation of target genes by PTH in osteoblast-like UMR-106 cells is mediated by the activation of the cAMP/protein kinase. A signaling pat hway. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.