Androgen receptor and TGFbeta1/Smad signaling are mutually inhibitory in prostate cancer.
OBJECTIVE
The androgen receptor (AR) has been reported to modulate TGFbeta1/Smad signaling and is, like transforming growth factor beta 1 (TGFbeta1) often overexpressed in hormone refractory prostate cancer (HRPC). In human prostate cancer cell lines the role of AR in the response to TGFbeta1 is evaluated.


METHODS
PC3 cells grow hormone independently, lack AR expression, and have a functioning TGFbeta1/Smad signaling cascade whereas LNCaP cells express (a mutated) AR, and lack TGFbeta receptor (TGFbetaR2) expression. Luciferase reporter assays for AR signaling, TGFbeta1/Smad signaling, and E2F transcriptional activity were performed. PC3 cells and TGFbetaR2 stably-transfected LNCaP cells (LNCaP-R2) were incubated with dihydrotestosterone (DHT), or TGFbeta1. Wst-1 assay and flowcytometric evaluation of annexin-V staining were applied to quantify cell growth and apoptosis. Immunoblot analysis was performed to evaluate c-Myc expression.


RESULTS
Luciferase reporter assays showed mutual transcriptional inhibition of AR and TGFbeta/Smad signaling in AR transfected PC3 and LNCaP-R2 cells. AR expression reduced the TGFbeta1/Smad transcriptional activity and the growth inhibitory effects of TGFbeta1 also in the absence of DHT in PC3 cells. TGFbeta1 reduced the E2F transcriptional activity of AR activation by DHT. This was associated with a reduced c-Myc expression in PC3 cells. AR expression in PC3 cells prevented TGFbeta1 induced growth inhibition and apoptosis.


CONCLUSIONS
AR overexpression is an effective way of hormone refractory prostate cancer cells to overcome the growth inhibitory effects of elevated serum TGFbeta1 levels even in the absence of DHT. These findings provide an explanation for how AR overexpression favors growth in HRPC.
van der Poel
H G
HG
Department Urology, Netherlands Cancer Institute, Amsterdam. h.vd.poel@nki.nl
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D013196:Dihydrotestosterone / Q000494:pharmacology*; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015151:Immunoblotting; D008297:Male; D009376:Neoplasms, Hormone-Dependent; D011471:Prostatic Neoplasms / Q000235:genetics / Q000473:pathology*; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051785:Smad Proteins / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
D011944:Receptors, Androgen; D051785:Smad Proteins; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D013196:Dihydrotestosterone