FIGURE 1.

NQO1 regulates C/EBPα and PU.1. A, lack of induction of C/EBPα and PU.1 in the bone marrow of NQO1^−/− mice exposed to γ -radiation. Mice were irradiated with 3 Grays γ-radiation, bone marrow cells were collected and analyzed by immunoblotting. The bar graph shows relative protein levels after densitometry analysis, * indicates significant changes of protein levels between control and treatment throughout all the figures. B, MG132 and epoxomycin rescues C/EBPα and PU.1 from γ-radiation induced degradation in NQO1^−/− cells. Bone marrow cells were exposed to 3 Grays γ-radiation, then left alone or treated with 20 μm MG132 or 50 nm epoxomycin for 10 h. The cells were lysed and immunoblotted. p53 was analyzed as control for MG132 treatment (left panel). C, HL-60 cells express relatively low level of NQO1 compared with U937 cells. D, overexpression of NQO1 up-regulates C/EBPα and PU.1. HL-60 cells were transfected with increasing amount of V5-tagged random control peptide (upper panel) or same amounts of NQO1-V5 (lower panel), transfected cells were lysed and immunoblotted. E, siRNA inhibition of NQO1 leads to down-regulation of C/EBPα and PU.1. U937 cells were transfected with control or NQO1 siRNA and cell lysates were immunoblotted. F, NQO1 protects C/EBPα against 20S proteasomal degradation. In vitro translated C/EBPα and NQO1, purified 20S proteasome and NADH were mixed in combinations as shown for 1 h at 37 °C. 5 μl mixtures from different treatment were immunoblotted. G, γ-radiation destructs C/EBPα and PU.1 in KG-1 cells with NQO1 knock-down. KG-1 cells were transfected with control or NQO1 siRNA, and 60 μg cell lysates were immunoblotted (left panel). KG-1 cells with NQO1 knock-down were irradiated with 3 Grays γ-radiation, then analyzed by immunoblotting (middle panel and bar graph). Molecular weight markers are shown on the right side of panels in A.