In the prostate,
androgens negatively regulate the expression of
transforming growth factor-beta (
TGF-beta)
ligands and receptors and Smad activation through unknown mechanisms. We show that
androgens (
dihydrotestosterone and
R1881) down-regulate TGF-beta1-induced expression of
TGF-beta1, c-Fos, and Egr-1 in the human prostate
adenocarcinoma cell line, LNCaP. Moreover, 5alpha-dihydrotestosterone (DHT) inhibits
TGF-beta1 activation of three TGF-beta1-responsive promoter constructs, 3TP-luciferase, AP-1-luciferase, and SBE4(BV)-luciferase, in LNCaP cells either with or without enforced expression of
TGF-beta receptors (TbetaRI and TbetaRII). Similarly, DHT inhibits the activation of Smad-binding
element (SBE)4(BV)-luciferase by either constitutively activated TbetaRI (T204D) or constitutively activated Smad3 (S3*). Activation of SBE4(BV)-luciferase by S3* in the NRP-154 prostatic cell line, which is
androgen receptor (AR)-negative but highly responsive to
TGF-beta1, is blocked by co-transfection with either full-length AR or AR missing the
DNA binding domain. Immunoprecipitation and GST pull-down assays show that AR directly associates with Smad3 but not Smad2 or Smad4. Electrophoretic mobility shift assays indicate that the AR
ligand binding domain directly inhibits the association of Smad3 to the Smad-binding
element. In conclusion, our data demonstrate for the first time that
ligand-bound AR inhibits
TGF-beta transcriptional responses through selectively repressing the binding of Smad3 to SBE.