Increased TGF-β1-mediated suppression of growth and motility in castrate-resistant prostate cancer cells is consistent with Smad2/3 signaling.
BACKGROUND
Elevated TGF-β levels are associated with prostate cancer progression. Although TGF-β is a tumor suppressor for normal epithelial and early-stage cancer cells, it may act paradoxically as a tumor promoter in more advanced cancers, although its effects are largely cell and context dependent. This study analyzed prostate cancer responses to TGF-β signaling in an isogenic model of androgen-sensitive and castration-resistant prostate cancer cells.


METHODS
Phosphorylation and nuclear translocation of Smad2 and Smad3 were analyzed using immunoblotting. Proliferation and cell cycle responses to TGF-β1 (5 ng/ml) were assessed using growth assays and flow cytometry for DNA content, as well as Western blot and immunoprecipitation of cell cycle proteins.


RESULTS
Both androgen-sensitive (LNCaP) and castration-resistant (C4-2 and C4-2B) prostate cancer cell lines demonstrated TGF-β1-induced phosphorylation and nuclear translocation of Smad2/3 that was robust in metastatic lines. Smad phosphorylation was completely abrogated with inhibition of ALK-5 kinase activity using the kinase inhibitor, SB-431542. Increased sensitivity to TGF-β1-mediated growth inhibition was observed in C4-2 and C4-2B cells, as compared to LNCaP cells. This was paralleled with downregulation of Cyclin D and increased association of p15(Ink4b) or p27(Kip) with CDK's. Additionally, TGF-β1 inhibited motility and invasion of metastatic cell lines.


CONCLUSIONS
TGF-β-mediated suppression of growth and motility is enhanced in metastatic, castration-resistant prostate cancer cells. Enhanced TGF-β1-induced Smad2 and -3 signaling in prostate cancer cells may correlate with tumor suppressive activity. Therefore, the direct effects of TGF-β1 on prostate cancer cells post-castration may be anti-tumorigenic and growth-suppressive.
Laboratory for Cancer Ontogeny and Therapeutics, Department of Biological Sciences, University of Delaware, Newark, Delaware, USA.
Fayth L
FL
Miles
Navpreet S
NS
Tung
Adam A
AA
Aguiar
Senem
S
Kurtoglu
Robert A
RA
Sikes
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology*; D049109:Cell Proliferation; D006131:Growth Inhibitors / Q000502:physiology*; D006801:Humans; D008297:Male; D009919:Orchiectomy; D010766:Phosphorylation / Q000502:physiology; D011471:Prostatic Neoplasms / Q000473:pathology* / Q000628:therapy; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein / Q000502:physiology*; D051900:Smad3 Protein / Q000502:physiology*; D053773:Transforming Growth Factor beta1 / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology
D006131:Growth Inhibitors; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D053773:Transforming Growth Factor beta1