Inhibitory effect of bortezomib on MDS and AML cell viability and progenitor function. (A) THP1 cells were treated with 10nM bortezomib or DMSO for the indicated times. Protein lysates were immunoblotted for ubiquitin-conjugated proteins and GAPDH (left panel). BM cells from MDS (MDS-01) and AML (AML-03) patients were treated with 10nM bortezomib or DMSO for 24 hours and evaluated by immunoblotting for ubiquitin and GAPDH (right panels). (B) The indicated cell lines and primary patient samples were treated with bor-tezomib for 24 hours and analyzed for cell survival by staining for annexin V⁺ cells. (C) Hematopoietic stem/progenitor cell colony-forming potential of THP1 and MDSL cell lines treated with bortezomib (10nM) was determined in methylcellulose. (D) Hematopoietic stem/progenitor cell colony-forming potential of control CD34⁺ cells and BM cells from MDS (MDS-01 and MDS-02) and AML (AML-03) patients treated with bortezomib (10nM) was determined in methylcellulose. Colonies were evaluated after 10 days. *P < .05; #P < .1.