MITOGENIC SIGNALING MECHANISMS OF HUMAN CEMENTUM-DERIVED GROWTH-FACTOR

Cementum-derived growth factor (CGF) is a M(r) 23,000 protein, which i s sequestered in the mineralized matrix of tooth cementum. We have inv estigated the mitogenic signaling reactions induced by CGF using quies cent human gingival fibroblasts as target cells. Cells activated with CGF were compared with those treated with CGF plus epidermal growth fa ctor (EGF) and other growth factors. CGF caused a transient increase i n cytoplasmic Ca2+ concentration, and this was accompanied by enhancem ent of membrane protein kinase C activity, myelin basic protein and S6 kinase activities, inositol phosphate levels, and activation of c-fos and jun-B gene expression. Membranes obtained from cells activated wi th CGF contained several protein bands, which cross-reacted with antip hosphotyrosine antibody; however, proteins corresponding to a putative phosphorylated CGF receptor were not detected. DNA synthesis induced by CGF was inhibited by 65% in cells treated with pertussis toxin but only 25-29% in cultures exposed to H7 or 12-O-tetradecanoylphorbol-13- acetate; these values were different from those obtained when EGF, PDG F, or fetal bovine serum were used as mitogens. CGF and TGF-beta, but not EGF, caused an increase of PDGF-A chain mRNA expression 4 h after mitogen addition. However, while CGF was mitogenic for gingival fibrob lasts, TGF-beta was not. Kinetics of DNA stimulation and experiments w ith anti-PDGF antibodies indicated that PDGF-A expression does not con tribute significantly to CGF-induced DNA synthesis. When the stimulati on of various signaling pathways induced by CGF and other growth facto rs was compared, the pattern of stimulation by CGF was different from other growth factors. The characteristic signaling reactions of CGF ar e likely to be important components of the mechanisms that regulate th e formation and regeneration of cementum and adjacent connective tissu es.