The action of transforming growth factor β (TGF-β) is mediated through type 1 (TβRI) and type 2 (TβRII) receptors. Prostate cancer cells are often resistant to TGF-β signaling due to loss of TβRII expression. The authors of the current study hypothesized that CpG methylation of the TβRII promoter at the Sp1 binding site −140 mediates this loss of TβRII expression in prostate cancer.
Sixty-seven prostate cancer (PC) samples, 8 benign prostatic hyperplasia (BPH) samples, and 4 prostate cancer cell lines (DUPro, LNCaP, ND-1 and PC-3) were analyzed for 1) TβRII mRNA expression by semiquantitative RT-PCR, 2) TβRII protein expression by immunohistochemistry, and 3) TGFβRII promoter methylation at CpG site −140 by methylation specific PCR and bisulfite DNA sequencing. Prostate cancer cell lines were treated with the demethylating agent 5aza2′deoxycytidine to determine if TβRII gene expression could be increased by blocking promoter methylation.
mRNA and protein expression of TβRII was lower in the PC samples than in the BPH samples. CpG methylation at site −140 was higher in PC than in BPH (P < 0.01). Promoter methylation was inversely correlated with TβRII mRNA expression in the PC and BPH samples (P < 0.0001). PC3, ND1, and DUPro TβRII mRNA expression increased following treatment of cells with 5-aza-2′-deoxycytidine.
CpG methylation of the TβRII promoter at CPG site −140 leads to functional loss of the TβRII gene in prostate cancer. Treatment with 5-aza-2′ deoxycytidine can restore gene expression. The current study results report the first association between prostate cancer and loss of the TGF- β signaling pathway by TβRII DNA promoter methylation. Cancer 2005;. © 2005 American Cancer Society.