Inhibition of mitosis and induction of apoptosis in MG63 human osteosarcoma-derived cells in vitro by surface proteins from Actinobacillus actinomycetemcomintans

Gentle saline extraction releases a heterogeneous mixture of proteins assoc iated with the cell surface of Actinobacillus actinomycetemcomintans, terme d the surface protein fraction (SF). Some SF components are biologically ac tive and may modulate cell behaviour in a manner of putative importance in the aetiology of periodontitis. To further characterize this activity, the ability of the SF to induce mitosis and apoptosis in MG63 cells was investi gated. Cells were plated at 10(3)-10(4) cells/cm(2) and allowed to attach b efore culture in the serum-free medium in the presence of 25 mu g/ml SF for 2-24 h. The apoptotic and mitotic figures present were counted and the res ults expressed as an apoptotic or mitotic index. The apoptotic and mitotic compartments were very small, but there was an inverse correlation between mitosis and apoptosis. In control experiments the mitotic was higher than t he apoptotic index, whilst in the presence of SF this was reversed. These r esults were confirmed using in situ end-labelling. SF, therefore, may stimu late apoptotic, but inhibit mitotic, activity in MG63 cells. This raises th e possibility that components of SF might induce subtle changes in the bala nce between apoptosis and mitosis, which, in turn, could contribute to the progression of periodontitis. (C) 2000 Elsevier Science Ltd. All rights res erved.