The clinical use of gene therapy requires tight regulation of the gene of interest and functional expression only when it is needed. Thus, it is necessary to develop ways of regulating functional gene expression with exogenous stimuli. Many regulatable systems are currently under development. For example, the tetracycline-dependent transcriptional switch has been successfully employed for in vivo preclinical applications. However, there are no examples of regulatable systems that have been employed in human clinical trials. In the present study, we established an adenovirus-delivered functional gene expression system that is regulated by estrogen. This system uses p16INK4A fused at its C-terminus to the ligand-binding domain of the estrogen receptor (DeltaERalpha). We were able to establish cell lines expressing this gene wherein the functional expression of p16INK4A is estrogen-dependent and causes the arrest of several ovarian cancer cell lines. This inducible and adenovirus-mediated gene transfer system may allow gene therapy using nuclear functioning genes in postmenopausal or ovariectomized women.