Parathyroid hormone (PTH), a powerful bone-resorbing agent, is capable of stimulating interstitial collagenase (MMP-13) mRNA production in osteoblastic cells. In this study, a PEA3 consensus binding sequence (-80; AGGAAGT) in addition to a 'TRE-like' sequence (-89; CGACTCA) in the 5' upstream regulatory region of the rat MMP-13 gene were examined. In response to PTH, there was a time-dependent increase in binding of nuclear factors to an oligonucleotide containing the PEA3 region (-95 to -71). This increase in binding was first observed at 0.5 h, peaked at 4 h (7. 6-fold) then returned to basal levels by 24 h. Mutagenesis of the PEA3 site in a chloramphenicol acetyl transferase (CAT) construct containing 5' upstream regulatory sequence of the rat MMP-13 gene significantly decreased activation by PTH. PTH-mediated binding of nuclear factors to an oligonucleotide containing the mutant PEA3 sequence was decreased as compared with the wild type. Mutation or deletion of the TRE-like sequence affected basal as well as PTH-mediated induction of corresponding CAT constructs. Treatment with KN93, a Ca(2+)/calmodulin-dependent protein kinase II specific inhibitor, greatly reduced the amount of protein binding to the PEA3 region in response to PTH which correlated to a notable decrease in the amount of MMP-13 mRNA produced in response to PTH. Antibodies against Ets-1, cyclic AMP response element (CREB)-binding protein (CBP) and CREB were capable of supershifting proteins binding to the oligonucleotide containing the PEA3 region. These data suggest a possible co-operative interaction of factors binding to the PEA3 and TRE-like sequences and provide the first indication of a role for a calcium-mediated pathway in the PTH induction of MMP-13 mRNA in osteoblastic cells.
Effect of cyclic AMP on collagen synthesis in osteoblastic cells derived from newborn mouse calvaría