Activation of the human aldehyde oxidase (hAOX(1)) promoter by tandem cooperative Sp1/Sp3 binding sites: Identification of complex architecture in the hAOX upstream DNA that includes a proximal promoter, distal activation sites, and a silencer element

Aldehyde oxidase (AOX) is a member of the molybdenum iron-sulfur flavoprote ins and is of interest for its role in clinical drug metabolism and as a so urce of reactive oxygen species (ROS) potentially involved in human patholo gy. The ROS derived from AOX contribute significantly to alcohol-induced he patotoxicity, Therefore, expression of AOX could determine both the suscept ibility of certain cells and tissues to clinically important pharmacologic agents and the levels of ROS produced under certain pathophysiological cond itions. Although some pharmacologic agents regulate AOX enzyme activity, ve ry little is known about the activation or regulation of the human AOX gene (hAOX). In the present study, we sought to identify features in the upstre am DNA of hAOX that could confer regulation of the gene, to locate and char acterize tbe basal promoter apparatus activating hAOX, and to identify tran scription factors that could mediate activation or regulation. We transfect ed promoter fusion constructs into epithelial cells from the lung and the m ammary gland that express AOX in cell culture. The hAOX gene was found to p ossess a structurally complex region in the upstream DNA that contained seq uences for a proximal promoter, enhancer sites, and silencer elements. In a ddition, we identified an essential role for the transcription factors Sp1 and Sp3 in the proximal promoter. Unexpectedly, hAOX was activated in lung and mammary epithelial cells by indistinguishable mechanisms. These observa tions reveal a potentially complex mode of hAOX gene expression in epitheli al cells that is dependent on Sp1 and Sp3 transcription factors.