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NAD(P)H:quinone oxidoreductase 1 (NQO1) is a quinone reductase expressed in epithelial and endothelial cells. Homozygous expression of the NQO1*2 polymorphism results in an essentially null phenotype due to rapid proteasomal degradation of the mutant NQO1*2 protein. Increased risk of benzene induced myeloid toxicity and increased risks of a variety of de-novo and therapy induced leukemias have been associated with the NQO1*2 polymorphism but the mechanisms involved remain unclear. NQO1 is present in bone marrow stroma, specifically, endothelial cells and adipocytes so we have employed an immortalized human bone marrow endothelial cell (HBMEC) line to study the potential impact of the lack of NQO1 activity on gene expression. We have utilized a mechanism based inhibitor of NQO1 (ES936) to inhibit NQO1 in HBMEC. After inhibition of NQO1 in HBMEC by ES936, Affymetrix gene array analysis identified a number of genes whose expression was altered. One of these genes was VCAM-1 (Vascular Cell Adhesion Molecule 1) and its decreased expression was confirmed by RT-PCR. Immunoblot analysis demonstrated downregulation of VCAM-1 at the protein level after inhibition of NQO1 by ES936. To confirm a link between NQO1 inhibition and VCAM-1 downregulation, HBMEC were treated with NQO1 siRNA which efficiently knocked down NQO1 protein levels as indicated by immunoblot analysis. HBMEC treated with NQO1 siRNA also demonstrated decreased VCAM-1 protein levels relative to mock transfected cells. Pretreatment with ES936 also significantly decreased the ability of TNF-α to induce expression of VCAM-1 in HBMEC. The downregulation of critical cellular adhesion molecules such as VCAM-1 after inhibition of NQO1 activity in human bone marrow endothelium may play a role in bone marrow pathologies which have been associated with the NQO1*2 polymorphism (supported by NIH grant ES09554).

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA