Activator protein 2α (AP-2α) is a sequence-specific DNA-binding transcription factor implicated in differentiation and transformation. In this study, we have made a replication-deficient recombinant adenovirus that expresses functional AP-2α (Ad-AP2). Cells infected with Ad-AP2 expressed induced levels of AP-2α protein, which bound to DNA in a sequence-specific manner and activated the AP-2-specific reporter 3X-AP2. Expression of AP-2α from Ad-AP2 inhibited cellular DNA synthesis and induced apoptosis. Ad-AP2 infection resulted in efficient inhibition of growth of cancer cells of six different types. In addition, prior expression of AP-2α increased the chemosensitivity of H460, a lung carcinoma cell line, to adriamycin (2.5-fold) and cisplatin (5-fold). Furthermore, the growth inhibition by AP-2α was found to be less efficient in the absence of p53 or p21, which correlated with reduced apoptosis in p53 null cells and lack of DNA synthesis inhibition in p21WAF1/CIP1 null cells by AP-2α, respectively. These results suggest that AP-2α inhibits the growth of cells by inducing cell cycle arrest and apoptosis and that the use of AP-2α should be explored as a therapeutic strategy either alone or in combination with chemotherapy.