COMPLEMENT MEMBRANE ATTACK COMPLEX, PERFORIN, AND BACTERIAL EXOTOXINSINDUCE IN K562 CELLS CALCIUM-DEPENDENT CROSS-PROTECTION FROM LYSIS

The complement membrane attack complex (MAC), the cytolytic granule pr otein of cytotoxic lymphocytes perforin, the streptococcal exotoxin st reptolysin O (SLO), and the bee venom polypeptide melittin utilize a s imilar mechanism to incorporate into cell membranes, induce a Ca2+ inf lux and a rise in intracellular Ca2+ concentration, and produce cell l ysis. At sublytic concentrations, these proteins trigger several cellu lar activities, including protein phosphorylation and synthesis. We ha ve recently demonstrated that human leukemic cells treated with sublyt ic doses of human complement become more resistant to lytic complement doses. The study has now been extended to include three other pore-fo rmers: murine perforin, SLO and melittin. As shown here, sublytic MAC induces in the K562 human erythroleukemic cells protection from lytic perforin, and vice versa, sublytic perforin induces protection from co mplement. Also, sublytic SLO and melittin increase resistance of K562 cells to lytic complement and perforin doses. The capacity of Ca2+ ion ophores to induce resistance to the lytic proteins has been examined. Exposure of K562 cells to sublytic concentrations of ionomycin or A231 87 for 1 h at 37 degrees C confers on them resistance to complement- a nd perforin-mediated lysis. The protective effects of the ionophores c an be abrogated by chelation of extracellular Ca2+ and by inhibition o f RNA or protein synthesis in the cells. These results indicate the fo llowing: 1) nucleated cells exposed to sublytic complement MAC, perfor in, SLO, or melittin may become resistant to the four pore-formers. Ph ysiologically, this may be regarded as an immunologic tachyphylaxis. 2 ) Ca2+ influx induced by these pore-formers is an essential and suffic ient factor to produce this tachyphylaxis.