COUP-TFII inhibits TGF-β-induced growth barrier to promote prostate tumorigenesis

A cell-autonomous role for the COUP-TFII transcription factor in prostate cancer cells is identified, in which COUP-TFII inhibits TGF-β signalling by binding to SMAD4; COUP-TFII promotes prostate tumorigenesis and metastasis in a mouse model, and is associated with more aggressive disease in human prostate cancers. The transcription factor COUP-TFII has been implicated in cancer, where it promotes the growth of blood vessels in tumours. Sophia Tsai and colleagues now show that COUP-TFII promotes growth in prostate cancer cells by inhibiting transforming growth factor-β signalling by binding to SMAD4. In a mouse prostate cancer model, COUP-TFII promotes prostate tumorigenesis and metastasis. In human prostate cancers, COUP-TFII expression is associated with more aggressive disease. This work identifies COUP-TFII as a potential drug target in metastatic human prostate cancer. Mutations in phosphatase and tensin homologue (PTEN) or genomic alterations in the phosphatidylinositol-3-OH kinase-signalling pathway are the most common genetic alterations reported in human prostate cancer1,2,3,4. However, the precise mechanism underlying how indolent tumours with PTEN alterations acquire metastatic potential remains poorly understood. Recent studies suggest that upregulation of transforming growth factor (TGF)-β signalling triggered by PTEN loss will form a growth barrier as a defence mechanism to constrain prostate cancer progression5, underscoring that TGF-β signalling might represent a pre-invasive checkpoint to prevent PTEN-mediated prostate tumorigenesis. Here we show that COUP transcription factor II (COUP-TFII, also known as NR2F2)6,7,8,9, a member of the nuclear receptor superfamily, serves as a key regulator to inhibit SMAD4-dependent transcription, and consequently overrides the TGF-β-dependent checkpoint for PTEN-null indolent tumours. Overexpression of COUP-TFII in the mouse prostate epithelium cooperates with PTEN deletion to augment malignant progression and produce an aggressive metastasis-prone tumour. The functional counteraction between COUP-TFII and SMAD4 is reinforced by genetically engineered mouse models in which conditional loss of SMAD4 diminishes the inhibitory effects elicited by COUP-TFII ablation. The biological significance of COUP-TFII in prostate carcinogenesis is substantiated by patient sample analysis, in which COUP-TFII expression or activity is tightly correlated with tumour recurrence and disease progression, whereas it is inversely associated with TGF-β signalling. These findings reveal that the destruction of the TGF-β-dependent barrier by COUP-TFII is crucial for the progression of PTEN-mutant prostate cancer into a life-threatening disease, and supports COUP-TFII as a potential drug target for the intervention of metastatic human prostate cancer.