Abstract 2748: The role of TMPRSS2_ERG fusions in modulating tumor microenvironment in prostate cancer

The control region of TMPRSS2 fuses with ETS transcription factor family members, particularly ERG. This occurs in ~20-50% of human prostate cancers depending on the ethnicity. TMPRSS2-ERG (T2E) fusions, however, do not display a notable phenotype in genetically engineered mouse models (GEMM) recapitulating the fusion expression and T2E also has no prognostic significance in humans, despite its high incidence. Wnt signaling has been implicated in prostate cancer. Here, we report a discovery of a role for T2E fusion that impacts the prostate stroma in pre-clinical models. The composition of stromal cells within the microenvironment in T2E mice was studied by single cell RNAseq analysis. We identified stromal cell clusters in T2E mice that differed from wild type mice in the expression of Pdgfrβ, Pdgfrα and Col1a1. Interestingly, these clusters showed an increase of expression of Wnt receptors such as Lgr5 and Fzd7 as well as Wnt ligands such as Sfrp2, Wnt2 and Wnt6. T2E GEMMs also exhibited upregulation of the Wnt-secretion regulator porcupine (PORCN-Protein-serine O-palmitoleoyltransferase) in the stroma adjacent to the T2E-expression prostate epithelial cells. Furthermore, lineage-tracing with the Wnt reporter and epithelial stem cell marker Lgr5 showed that Wnt-active cells were increased in prostatic intraepithelial neoplasia (PIN) lesions in T2E;Pten+/- mice. Strikingly, Lgr5+ cells were also found in the prostate stroma surrounding these PINs. Since, TMPRSS2/ERG fusions represent an early event in prostate tumorigenesis, here we provide a mechanism whereby induction of Wnt signaling in the stroma by T2E-expressing prostate epithelial cells increases the stem cell compartments in both epithelial and stromal cells. These data suggest that aberrant ERG-expressing prostate epithelial cells activate upregulation of Wnt signaling in stromal cells, which provides a possible route for enhancing prostate carcinogenesis. Citation Format: Hubert Pakula, Caroline F. Ribeiro, Giuseppe N. Fanelli, Rory Kirchner, Sudeepa Syamala, Basudev Chowdhury, Giorgia Zadra, Paolo Chetta, Zhe Li, Massimo Loda. The role of TMPRSS2_ERG fusions in modulating tumor microenvironment in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2748.