<i>TMPRSS2:ERG</i>gene fusion variants induce TGF-β signaling and epithelial to mesenchymal transition in human prostate cancer cells

Abstract

// Leonie Ratz 1 , Mark Laible 1, 5 , Lukasz A. Kacprzyk 1, 6 , Stephanie M. Wittig-Blaich 1, 7 , Yanis Tolstov 2 , Stefan Duensing 2 , Peter Altevogt 3, 4 , Sabine M. Klauck 1 , Holger S&uuml;ltmann 1 1 Cancer Genome Research Group, German Cancer Research Center (DKFZ), German Cancer Consortium (DKTK), and National Center for Tumor Diseases (NCT), 69120 Heidelberg, Germany 2 Department of Urology, Section of Molecular Urooncology, University Hospital Heidelberg, 69120 Heidelberg, Germany 3 Skin Cancer Unit, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany 4 Department of Dermatology, Venereology and Allergology, University Medical Center Mannheim, Ruprecht-Karls University of Heidelberg, 68135 Mannheim, Germany 5 Present address: BioNTech Diagnostics GmbH, 55131 Mainz, Germany 6 Present address: UGA Biopharma GmbH, 16761 Hennigsdorf, Germany 7 Present address: Institute of Comparative Molecular Endocrinology (CME), University of Ulm, 89081 Ulm, Germany Correspondence to: Holger S&uuml;ltmann, email: [e-mail] Keywords: TMPRSS2:ERG fusion variants, TGF-&beta; signaling, ALK1, EMT, prostate cancer Received: November 25, 2016&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Accepted: February 15, 2017&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Published: March 06, 2017 ABSTRACT TMPRSS2:ERG (T/E) gene fusions are present in approximately 50% of all prostate cancer (PCa) cases. The expression of fusion mRNAs from distinct T/E variants is associated with clinicopathological parameters, while the underlying molecular processes remain unclear. We characterized the molecular mechanisms and functional implications caused by doxycycline (Dox)-inducible overexpression of the frequent T/E III and VI fusion variants in LNCaP cells. Induction of T/E expression resulted in increased cellular migratory and invasive potential, and reduced proliferation and accumulation in G1 phase. T/E overexpressing cells showed epithelial-to-mesenchymal transition (EMT), as demonstrated by upregulation of TGF-&beta; and WNT pathway genes, mesenchymal markers, and increased phosphorylation of the p38 MAPK. Augmented secretion of TGF-&beta;1 and &ndash;&beta;2, and T/E-mediated regulation of ALK1, a member of the TGF-&beta; receptor family, was detected. ALK1 inhibition in T/E overexpressing cells blocked p38 phosphorylation and reduced the expression of the TGF-&beta; target genes VIM, MMP1 , CDH2, and SNAI2. We found a T/E variant VI-specific induction of miR-503 associated with reduced expression of SMAD7 and CDH1. Overexpression of miR-503 led to increased levels of VIM and MMP1 . Our findings indicate that TGF-&beta; signaling is a major determinant of EMT in T/E overexpressing LNCaP cells. We provide evidence that T/E VI-specific transcriptional modulation by miR-503 accounts for differences in the activation of EMT pathway genes, promoting the aggressive phenotype of tumors expressing T/E variant VI. We suggest that ALK1-mediated TGF-&beta; signaling is a novel oncogenic mechanism in T/E positive PCa.