Androgen receptor phosphorylation and stabilization in prostate cancer by cyclin-dependent kinase 1

Abstract

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 (Cdk1) mediates AR phosphorylation at Ser-81 and increases AR protein expression, and that Cdk1 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 Cdk1 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 Cdk1-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 Cdk1 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 Cdk1 as a Ser-81 kinase and indicate that Cdk1 stabilizes AR protein by phosphorylation at a site(s) distinct from Ser-81. Moreover, these results indicate that increased Cdk1 activity is a mechanism for increasing AR expression and stability in response to low androgen levels in androgen-independent PCas, and that Cdk1 antagonists may enhance responses to androgen-deprivation therapy.

TET2 repression by androgen hormone regulates global hydroxymethylation status and prostate cancer progression

“…Furthermore, Cyclin-dependent kinase 1 (CDK1), a 5-hmCregulated gene, is involved in AR phosphorylation (Ser81) in response to DHT stimulation 35 . The CDK1 is upregulated in BicR cells and repressed by the inhibition of miR-29a/b ( Supplementary Fig.…”

“…We also noted that phosphorylation of AR at serine 81 is promoted by miR-29 induction in HRPC cells. Phosphorylation of AR at serine 81 by CDK1 has been reported to increase AR sensitivity by promoting AR binding to specific ARBSs 35 . Thus, on the basis of the results of our clinical and biological experiments, we demonstrate the significance of TET regulation for the progression to HRPC by activating AR sensitivity.…”

ZIP kinase plays a crucial role in androgen receptor-mediated transcription

“…In the case of STAT3, ZIP kinase seems to phosphorylate STAT3 directly (Sato et al, 2005). The AR is subject to multiple phosphorylations by different kinases such as PKA, PKC, MAP kinases, Akt kinase, and so on (for review, see Gioeli et al, 2002) and Cdk1/Cyclin B (Chen et al, 2006). However, although the AR has four potential phosphorylation sites for ZIPK, we did not observe a direct phosphorylation in vitro under conditions that revealed efficient phosphorylation by Cdk1/Cyclin B.…”

“…Flag-AR was isolated from transfected cells by immunoprecipitation and subjected to in vitro phosphorylation by ZIPK purified from the baculovirus expression system. As a positive control, we employed recombinant Cdk1/Cyclin B, which was shown to phosphorylate AR (Chen et al, 2006). As control substrate we included histones in the assay.…”

Isosilybin B causes androgen receptor degradation in human prostate carcinoma cells via PI3K-Akt-Mdm2-mediated pathway

“…Various studies have shown the role of glycogen synthase kinase 3b (GSK3b), stress kinase, mammalian target of rapamycin (mTOR) kinase and cyclin-dependent kinase 1 in regulating phosphorylation, stability and localization of AR (Wang et al, 2004;Cinar et al, 2005;Chen et al, 2006;Gioeli et al, 2006). Further, there are numerous studies suggesting the importance of Akt/PKB (a serine/threonine kinase) activation in AR degradation (Lin et al, 2001(Lin et al, , 2002Liao et al, 2005) as well as AR activation (Miyamoto et al, 2005;Reddy et al, 2006); though the interaction of Akt with AR largely remains unclear.…”