Androgen Regulation of the Cyclin-Dependent Kinase Inhibitor p21 Gene through an Androgen Response Element in the Proximal Promoter

Abstract

Androgen is essential for the physiological maintenance of the integrity of prostatic epithelial cells, and castration causes the cells to undergo apoptosis. To study the molecular mechanism of androgen-dependent cell growth, we showed that androgen up-regulates the expression of the cyclin-dependent kinase inhibitor p21 (WAF1, CIP1, SDI1, CAP20) gene at both the mRNA and protein levels. Nuclear run-on assays demonstrated that androgen stimulates endogenous p21 gene expression at the transcriptional level. Transient transfection 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 functional 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 ARE, but not mutant ARE, confers androgen responsiveness to a heterologous promoter. The up-regulation of p21 gene expression by androgen suggests that p21 may have an antiapoptotic function in prostatic epithelial cells. However, this hypothesis will need to be tested in future experiments.

Androgen signaling is required for the vitamin D-mediated growth inhibition in human prostate cancer cells

“…However, at higher concentrations of androgen, the remarkable dephosphorylation of Rb is accompanied by lower E2F activity and lower expression of E2F target genes. The mechanisms by which androgen signaling affects the phosphorylation status of Rb and cell proliferation are still poorly understood, but may be due to increased expression of some cdk inhibitors, such as p21 (Lu et al, 1999;Lu et al, 2000) and p27 (Knudsen et al, 1998;Tsihlias et al, 2000). While examining the changes in cell cycle regulators after 1,25-VD treatment, we found decreasing cdk2 activity and increasing hypophosphorylated Rb in LNCaP cells, yet no change in the expression of total p21 and p27 (Figure 3).…”

The Complex Role of AR Signaling After Cytotoxic Insult: Implications for Cell Cycle Based Chemotherapeutics

“…23 In addition, active AR induces p21 Cip1 mRNA expression, which likely assists in formation of active CDK4/cyclin D1 complexes. 16,24 These events promote activation of CDK4 and resultant phosphorylation of RB. 25,26 Downstream, CDK2/cyclin E activity is induced by AR through post-translational mechanisms.…”

Impact of differential cyclin D1 expression and localisation in prostate cancer

“…Additional factors are also suspected to control this event, such as p21 Cip1 , which is an essential accessory factor for the assembly, stabilisation, and translocation of active cyclin D1/CDK4 complexes to the nucleus (Cheng et al, 1999;Parry et al, 1999). Furthermore, p21 Cip1 protein levels are induced by androgen stimulation (Knudsen et al, 1998) and p21 Cip1 has been shown to be a direct AR target gene (Lu et al, 1999). Displacement of p21 Cip1 from active cyclin D1/CDK4 complexes allows p21 Cip1 to bind and inhibit CDK2 activity, thereby inhibiting progression through G 1 and into S phase (Sherr and Roberts, 2004).…”