Mycoplasma fermentans binds to and invades HeLa cells: involvement of plasminogen and urokinase

Adherence of Mycoplasma fermentans to HeLa cells followed saturation kinetics, required a divalent cation, and was enhanced by preincubation of the organism at 37 degrees C for 1 h in a low-osmolarity solution. Proteolytic digestion, choline phosphate, or anti-choline phosphate antibodies partially inhibited the adherence, supporting the notion that M. fermentans utilizes at least two surface components for adhesion, a protease-sensitive surface protein and a phosphocholine-containing glycolipid. Plasminogen binding to M. fermentans greatly increased the maximal adherence of the organism to HeLa cells. Anti-plasminogen antibodies and free plasminogen inhibited this increase. These observations suggest that in the presence of plasminogen the organism adheres to novel sites on the HeLa cell surface, which are apparently plasminogen receptors. Plasminogen-bound M. fermentans was detected exclusively on the cell surface of the infected HeLa cells. Nevertheless, plasminogen binding in the presence of the urokinase-type plasminogen activator (uPA) promoted the invasion of HeLa cells by M. fermentans. The latter finding indicates that the invasiveness of M. fermentans does not result from binding plasminogen but from activation of the bound plasminogen to plasmin. Cholesterol depletion and sequestration with beta-cyclodextrin and filipin, respectively, did not affect the capacity of M. fermentans to adhere, but invasion of HeLa cells by uPA-activated plasminogen-bound M. fermentans was impaired, suggesting that lipid rafts are implicated in M. fermentans entry.