Androgen regulation of the cyclin-dependent kinase inhibitor p21 gene through an androgen response element in the proximal promoter

Androgen is essential for the physiological maintenance of the integrity of prostatic epithelial cells, and castration causes the cells to undergo apo ptosis. To study the molecular mechanism of androgen-dependent cell growth, we showed that androgen upregulates the expression of the cyclin-dependent kinase inhibitor p21 (WAF1, CIP1, SDI1, CAP20) gene at both the mRNA and p rotein levels. Nuclear run-on assays demonstrated that androgen stimulates endogenous p21 gene expression at the transcriptional level. Transient tran sfection experiments showed that androgen can enhance the activity of a 2.4 -kb promoter of the p21 gene linked to a luciferase reporter. These results suggested that a putative androgen response element (ARE), which mediates androgen response to enhance the p21 transcription, is included in the 2.4- kb promoter fragment. Deletion analysis of the promoter revealed a function al ARE (AGCACGCGAGGTTCC) located at -200 bp of the p21 gene proximal to the promoter region. Electrophoretic mobility shift assay further demonstrated that the androgen receptor specifically binds to this element. Wild-type A RE, but not mutant ARE, confers androgen responsiveness to a heterologous p romoter. The upregulation of p21 gene expression by androgen suggests that p21 may have an antiapoptotic function in prostatic epithelial cells. Howev er, this hypothesis will need to be tested in future experiments.