CHARACTERIZATION OF CEMENTUM DERIVED GROWTH-FACTOR AS AN INSULIN-LIKEGROWTH-FACTOR-I LIKE MOLECULE

Cementum is the thin calcified outer layer through which tooth-root su rfaces are anchored to soft periodontal connective tissues. A variety of growth factors and adhesion molecules are sequestered in the extrac ellular matrix of cementum, and we have purified and characterized one of the growth factors. This growth factor, the cementum derived growt h factor (CGF), was purified from bovine cementum by acetic acid extra ction followed by heparin affinity chromatography and HPLC using catio n exchange, molecular sieve, and reverse-phase columns. NaDodSO(4)-pol yacrylamide gel electrophoresis of purified CGF preparation revealed t he presence of two major protein bands migrating with M-r, 18,000-22,0 00 and 14,000-16,000. The latter was associated with the major part of the mitogenic activity. The activity of CGF was inhibited by antibodi es to insulin-like growth factor-I (IGF-I) and IGF-I receptor. Both CG F and IGF-I were mitogenic to human gingival fibroblasts and alveolar bone cells, but the bone cells responded better to CGF than to IGF-I. The IGF-I did not bind to heparin-sepharose, while CGF bound to it and was eluted with 0.6M NaCl from heparin-sepharose columns. Heparin-sep harose 0.2M NaCl fractions of cementum extracts contained IGF-I migrat ing with M-r 7,500, but its mobility was not affected by N-glycosidase treatment. Western analysis using anti-IGF-I antibodies shelved that CGF preparations contained cross-reacting species migrating with M-r 1 8,000-22,000, 14,000-16,000 and 11,000-12,000, however after treatment with N-glycosidase the M-r 18,000-22,000 component was absent. Intern al amino acid sequences of six tryptic peptides of CGF were determined by microsequencing. The sequence of one 15-amino acid long peptide wa s the same as the receptor binding domain of IGF-I, and another 9-amin o acid peptide had 78% homology to a sequence derived from an untransl ated region of sheep IGF-I exon 1. Four other peptides had no apparent homology with IGF-I. From these results we conclude that the CGF is a n IGF-I like molecule.