title: Mortalin inhibitors sensitize K562 leukemia cells to complement-dependent cytotoxicity.
abstract: Mortalin, the mitochondrial hsp70, is a vital constitutively expressed heat shock protein. Its elevated expression has been correlated with malignant transformation and poor cancer prognosis. Cancer cells exhibit increased resistance to complement-dependent cytotoxicity, partly due to their capacity to eliminate the complement membrane attack complex (MAC) from their cell surface. As we have previously reported, mortalin and the complement membrane attack complexes are released in membrane vesicles from complement attacked cells. As shown here, knock down of mortalin with specific siRNA reduces MAC elimination and enhances cell sensitivity to MAC-induced cell death. Similar results were obtained with MKT-077, a cationic rhodacyanine dye that inhibits mortalin. Treatment of human erythroleukemia K562 and colorectal carcinoma HCT116 cells with MKT-077 sensitizes them to cell death mediated by MAC but not by streptolysin O. Pre-treatment of cells with MKT-077 also reduces the extent of MAC-mortalin vesiculation following a sublytic complement attack. In the presence of MKT-077, the direct binding of mortalin to complement C9, the major MAC component, is inhibited. The tumor suppressor protein p53 is a known mortalin client protein. The effect of MKT-077 on complement-mediated lysis of HCT116 p53(+/+) and p53(-/-) cells was found to be independent on the presence of p53. Our results also demonstrate that recombinant human mortain inhibits complement-mediated hemolysis of rabbit erythrocytes as well as zinc-induced C9 polymerization. We conclude that mortalin supports cancer cell resistance to complement-dependent cytotoxicity and propose consideration of mortalin as a novel target for cancer adjuvant immunotherapy.
authors.affiliation: Department of Cell and Developmental Biology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Pilzer
authors.forename: Moran
authors.initials: M
authors.lastname: Saar
authors.forename: Keizo
authors.initials: K
authors.lastname: Koya
authors.forename: Zvi
authors.initials: Z
authors.lastname: Fishelson
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000494:pharmacology; D015153:Blotting, Western; D000001:Calcimycin / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D003186:Complement C9 / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D045325:HCT116 Cells; D018840:HSP70 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D020014:K562 Cells; D004915:Leukemia, Erythroblastic, Acute / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011725:Pyridines / Q000494:pharmacology; D034622:RNA Interference; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D013301:Streptolysins / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D003186:Complement C9; D018840:HSP70 Heat-Shock Proteins; D007476:Ionophores; D011725:Pyridines; D011994:Recombinant Proteins; D013301:Streptolysins; D013844:Thiazoles; C080352:mortalin; C025964:streptolysin O; D000001:Calcimycin; C097880:MKT 077