Wen-Li et al. Journal of Experimental & Clinical Cancer Research 2012, 31:92 http://www.jeccr.com/content/31/1/92 Page 6 of 9 Figure 3 McAb7E10 inhibits cell surface ATP generation and proliferation in AML cell. To examine the inhibitory effect of the antibody on ATP synthesis, a cell surface ATP generation assay was performed. Results showed that McAb7E10 antibody significantly inhibited ATP synthesis in AML cells. The effect of McAb7E10 on the proliferation of the AML cell lines MV4-11 and HL-60 was evaluated using the MTT assay. (A, B) ATP generation on the surface of MV4-11 (A) and HL-60 (B) cells is inhibited dose-dependently in the presence of McAb7E10 and oligomycin. Oligomycin, a known inhibitor of ATP synthase F1, was used as positive control and mouse IgG as negative control. Data represent means ± SD. (C) Proliferation analysis of MV4-11 cells treated with mouse IgG and McAb7E10. At 120 h, the relative inhibitory rates for 5, 10 and 50 μg/mL McAb7E10 treated MV4-11 cells were 24.5%, 44% and 69.6% respectively, compared to control mouse IgG treated cells. (D) Proliferation analysis of HL-60 cells treated with mouse IgG and McAb7E10. At 120 h, the relative inhibitory rates for 5, 10 and 50 μg/mL McAb7E10 treated HL-60 cells were 39.4%, 62.1% and 81.9% respectively, compared to control mouse IgG treated cells. induce apoptosis of leukemia cells, we test the apoptosis of cells with Annexin V test Kit. The data showed that the relative apotosis rate of 50ug/ml McAb7E10 treated MV4-11 cells was 50.5% ± 7.04% vs mouse IgG treated cells was 21.9% ± 3.11% P < 0.01 (Figure 5 A-C). The relative apotosis rate of 50ug/ml McAb7E10 on HL-60 cells was 32.9% ± 4.52% vs mouse IgG treated cells was15.3% ± 3.95% P < 0.01 (Figure 5D). ATPase β subunit inhibition provides a target for immuotherapy in hematologic malignancies The cell surface ATPase β subunit acts as a high-density lipoprotein (HDL) receptor, through binding of apolipo- protein A-I in hepatocytes, and also regulates lipoprotein internalization in endothelial cells [21]; however the effects downstream of the cell surface ATPase β subunit remain to be determined. ATPase β subunits have been detected on the membrane of tumor cells, raising the possibility that the structure of the β subunit protein on the cell surface may perform a different function to the inner mitochondrial protein structure. Our findings indi- cate that ectopic expression of the ATPase β subunit is a tumor-associated antigen in hematological malignancies. Although the function of the cell surface ATPase β sub- unit requires further study, this study implies that the ATPase β subunit plays an important role in cancer cell proliferation and apoptosis. Our findings are in agree- ment with previous studies which have indicated that angiostatin, plasminogen kringle 1–5 (K1–5), McAb against the ATPase β subunit [3,35] and small molecular inhibitors [1,36] can bind to ATP synthase on the cell surface and inhibit endothelial cell proliferation, migra- tion, trigger apoptosis [3-6,10,14,19]. Cell surface ATP synthase is more active at a low extracellular pH [21]; therefore, ectopic expression of the ATPase β subunit may play an important role in the survival of cells suffering an energy shortage or during treatment with chemotherapy drugs, indicating cell sur- face ATP synthase may play important role in the devel- opment and treatment resistance of hematological malignancies. Our study suggests that abnormal cell sur- face expression of ecto-F1F0-ATPase β subunit may pro- vide a potential target for cancer immunotherapy in hematological malignancies. F1F0 ATP synthase was recently reported to be a co- chaperone of heat shock protein Hsp90, as F1F0 ATP