THE FUNCTIONAL INTERACTION OF EGF AND PDGF WITH BRADYKININ IN THE PROLIFERATION OF HUMAN GINGIVAL FIBROBLASTS

EPIDERMAL GROWTH FACTOR (EGF) and platelet-derived growth factor (PDGF )-BB are both involved in periodontal wound healing. Each of these gro wth factors exerts a positive proliferative effect on cells of the per iodontium in vitro. However, in vivo the peptide bradykinin is one of a complex array of mediators present in addition to these growth facto rs. The purposes of this investigation were to: 1) evaluate bradykinin interactions with EGF and PDGF-BB altering cell proliferation in cult ured human gingival fibroblasts (HGF), periodontal ligament cells (HPD L), and cells derived from alveolar bone (HOB); and 2) determine at th e signal transduction level the mechanism of interaction between EGF a nd bradykinin in HGF. EGF and PDGF-BB stimulated DNA synthesis in a co ncentration-dependent manner, as measured by [H-3] thymidine incorpora tion. Bradykinin alone did not alter significantly basal DNA synthesis values; however, bradykinin in combination with EGF reduced DNA synth esis to nearly basal levels and bradykinin in combination with PDGF re duced the DNA synthesis over 50%. Examination of the interactions betw een bradykinin and EGF signal transduction pathways revealed that PGE( 2) release was increased in the presence of bradykinin and EGF (167 +/ - 33% to 317 +/- 29%). The bradykinin-stimulated PGE(2) release was co mpletely abolished by indomethacin. Indomethacin also was found to blo ck the bradykinin inhibition of EGF-induced DNA synthesis. Additional evidence supporting a mechanism involving PGE(2) in the bradykinin inh ibition of growth factor-stimulated DNA synthesis was that EGF-induced DNA synthesis was inhibited by exogenously added PGE(2) but not by en dothelin, vasopressin, or des-Arg(9) bradykinin. Forskolin and dibutyr yl cAMP also were found to inhibit EGF-induced DNA synthesis, suggesti ng that cAMP was involved in the mechanism of inhibition. In conclusio n, the present study demonstrates that both EGF- and PDGF-BB-induced p roliferative responses are inhibited by bradykinin in cells of the per iodontium. The signaling mechanism of the bradykinin inhibition of EGF appears to be mediated by PGE(2) through a cAMP-dependent pathway in HGFs.