Stimulating Effect of Manumycin A on Suicidal Erythrocyte Death

Abstract

Background/Aims: The streptomycete derived farnesyltransferase inhibitor Manumycin A triggers apoptosis of tumor cells and is thus considered for the treatment of malignancy. The present study explored whether Manumycin A could similarly stimulate eryptosis, the suicidal death of erythrocytes characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Stimulators of eryptosis include Ca²⁺ entry as well as activation of staurosporine sensitive protein kinase C and SB203580 sensitive p38 kinase. The present study explored, whether Manumycin A induces eryptosis and, if so, to shed some light on the mechanisms involved. Methods: Phosphatidylserine abundance at the human erythrocyte surface was estimated from annexin-V-binding, cell volume from forward scatter, and hemolysis from hemoglobin concentration in the supernatant. Results: A 48 hours exposure of human erythrocytes to Manumycin A (≥ 5 µg/ml) significantly increased the percentage of annexin-V-binding cells, significantly decreased forward scatter and significantly incrased hemolysis. The effect of Manumycin A on annexin-V-binding was significantly blunted by removal of extracellular Ca²⁺, by addition of staurosporine (1 µM) and by addition of SB203580 (2 µM). Conclusions: Manumycin A triggers hemolysis, cell shrinkage and phospholipid scrambling of the human erythrocyte cell membrane. The effect on cell membrane scrambling was in part but not fully dependent on entry of extracellular Ca²⁺, as well as activity of staurosporine and SB203580 sensitive kinases.