Hypoxia-inducible factor-1-dependent regulation of the multidrug resistance (MDR1) gene.

The microenvironment of rapidly growing tumors is associated with increased energy demand and diminished vascular supply, resulting in focal areas of prominent hypoxia. A number of hypoxia-responsive genes have been associated with growing tumors, and here we demonstrate that the multidrug resistance (MDR1) gene product P-glycoprotein, a Mr approximately 170,000 transmembrane protein associated with tumor resistance to chemotherapeutics, is induced by ambient hypoxia. Initial studies using quantitative microarray analysis of RNA revealed an approximately 7-fold increase in MDR in epithelial cells exposed to hypoxia (pO(2) 20 torr, 18 h). These findings were further confirmed at the mRNA and protein level.…