Supraphysiological androgen levels induce cellular senescence in human prostate cancer cells through the Src-Akt pathway

Background: Prostate cancer (PCa) is the second leading cause of cancer mortality of men in Western countries. The androgen receptor (AR) and AR-agonists (androgens) are required for the development and progression of the normal prostate as well as PCa. However, it is discussed that in addition to their tumor promoting activity, androgens may also exhibit tumor suppressive effects. A biphasic growth response to androgens a growth-promoting and -inhibition has been observed that suggests that administration of supraphysiological androgen levels mediates growth reduction in AR expressing PCa cells. Methods: Detection of senescence markers, three dimensional interphase fluorescence in situ hybridization (3D-iFISH), qRT-PCR, Western blotting, detection of GFP fusions, prostatectomy, ex vivo culturing. Results: Here, we describe that supraphysiological levels of androgens induce cell cycle arrest and markers of cellular senescence in human PCa cells, which may in part explain the growth inhibitory role of androgens. The expression of the senescence associated beta galactosidase is observed by treatment with the natural androgen DHT or the less metabolized synthetic androgen R1881. The induction of senescence marker was detected in human PCa cell lines as well as in human primary PCa tissue derived from prostatectomy treated ex vivo. Using interphase FISH (iFISH) suggests that the androgen-induced cellular senescence is associated with localizing the genomic E2F1 locus to senescence associated heterochromatic foci. Analysis of different signaling pathways in LNCaP cells suggest that the p16-Rb-E2F1 pathway is essential for the induction of cellular senescence since treatment with siRNA directed against p16 reduces the level of androgen-induced cellular senescence. Based on the rapid induction of androgen-mediated cellular senescence we identified the Src-PI3K-Akt-signaling pathway and autophagy being in part involved in androgen regulation. Conclusions: Taken together, our data suggest that AR-agonists at supraphysiological levels mediate induction of cellular senescence in human PCa cells, which may have a protective anti-cancer role. These results provide also new insights for understanding androgen-mediated regulation of PCa growth.