We used a xenograft model to investigate whether the aryl hydrocarbon receptor deletion construct CDelta553 suppresses tumor growth. HeLa cells that were infected with CDelta553 expressing adenovirus (Ad553) formed very small tumors whereas the control adenovirus-infected cells formed large tumors at day 15. CDelta553 inhibited the formation of the HIF-1 DNA complex and suppressed the induction of the HIF-1alpha target proteins CAIX and GLUT1. The Ad553 tumors had less HIF-1 function since they showed reduced microvessel formation and lesser amounts of HIF-1alpha, Arnt, phospho-Akt, CAIX, and GLUT1. Proteasome-mediated Arnt degradation was enhanced in Ad553-infected HeLa cells and tumors.