Androgen Receptor Phosphorylation and Stabilization in Prostate Cancer by Cyclin-Dependent Kinase 1

• Published in: Proceedings of the National Academy of Sciences - PNAS 2006-10, Vol.103 (43), p.15969-15974
• Main Authors: Chen, Shaoyong, Xu, Youyuan, Yuan, Xin, Bubley, Glenn J., Balk, Steven P.
• Format: Article
• Language: English
• Subjects: Androgens; Androgens - metabolism; Binding sites; Biological Sciences; CDC2 Protein Kinase - antagonists & inhibitors; CDC2 Protein Kinase - metabolism; Cell Line, Tumor; Cell lines; Cells; Cellular immunity; Cyclin-dependent kinases; Cyclins; Genes; HeLa cells; Humans; Male; Phosphorylation; Phosphorylation - drug effects; Phosphoserine - metabolism; Plasmids; Prostatic Neoplasms - genetics; Prostatic Neoplasms - metabolism; Protein Kinase Inhibitors - pharmacology; Protein synthesis; Proteins; Purines - pharmacology; Receptors, Androgen - genetics; Receptors, Androgen - metabolism; Transcription, Genetic - genetics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0604193103

Androgen receptors (ARs) are phosphorylated at multiple sites in response to ligand binding, but the kinases mediating AR phosphorylation and the importance of these kinases in AR function have not been established. Here we show that cyclin-dependent kinase 1 (Cdkl) mediates AR phosphorylation at Ser-81 and increases AR protein expression, and that Cdkl inhibitors decrease AR Ser-81 phosphorylation, protein expression, and transcriptional activity in prostate cancer (PCa) cells. The decline in AR protein expression mediated by the Cdk inhibitor roscovitine was prevented by proteosome inhibitors, indicating that Cdkl stabilizes AR protein, although roscovitine also decreased AR message levels. Analysis of an S81A AR mutant demonstrated that this site is not required for transcriptional activity or Cdkl-mediated AR stabilization in transfected cells. The AR is active and seems to be stabilized by low levels of androgen in "androgen-independent" PCas that relapse subsequent to androgen-deprivation therapy. Significantly, the expression of cyclin B and Cdkl was increased in these tumors, and treatment with roscovitine abrogated responses to low levels of androgen in the androgen-independent C4-2 PCa cell line. Taken together, these findings identify Cdkl as a Ser-81 kinase and indicate that Cdkl stabilizes AR protein by phosphorylation at a site(s) distinct from Ser-81. Moreover, these results indicate that increased Cdkl activity is a mechanism for increasing AR expression and stability in response to low androgen levels in androgen-independent PCas, and that Cdkl antagonists may enhance responses to androgen-deprivation therapy.