Abstract A34: Critical and reciprocal regulation of SLUG-KLF4 and SLUG-miR-1/miR-200b in TGFβ-initiated prostate cancer EMT

Epithelial-mesenchymal transition (EMT) is implicated in various pathological processes within the prostate, including benign prostate hyperplasia (BPH) and prostate cancer progression. However, an ordered sequence of signaling events initiating carcinoma-associated EMT has not been established. We have used a mouse model of Pten and TP53 null prostate adenocarcinoma, which undergoes progressive TGFβ-dependent EMT leading eventually to sarcomtoid carcinoma formation. Sarcomatoid carcinomas are characterized by various mesenchymal lineages and bone formation. In this model, SLUG is the dominant regulator of EMT initiation in vitro and in vivo. Depletion of Slug inhibited EMT. We determined that TGFβ-stimulated KLF4 degradation is the mechanism of SLUG induction, and the introduction of a degradation-resistant mutant of KLF4 inhibited EMT. We show that KLF4 and another epithelial determinant, FOXA1, are direct transcriptional inhibitors of SLUG expression in mouse and human prostate cancer cells. In addition, SLUG-dependent binding of polycomb repressive complexes to the Klf4 and Foxa1 promoters was demonstrated to inhibit transcription of these epithelial transcription factors, suggesting that SLUG expression helps to consolidate mesenchymal commitment. Analysis of tissue arrays demonstrated decreased KLF4 and increased SLUG expression in advanced stage primary prostate cancer, substantiating the involvement of the EMT signaling events described in model systems. As microRNAs are pleiotropic regulators of differentiation and tumorigenesis, we evaluated miR expression associated with tumorigenesis and EMT. Mir-1 and mir-200 were reduced with progression of prostate adenocarcinoma, and we identified Slug as one of the phylogenetically-conserved targets of these miRs. We established that SLUG is a direct repressor of miR-1 and miR-200 transcription. Thus, SLUG and miR-1/miR-200 act in a self-reinforcing regulatory loop leading to amplification of EMT. Depletion of Slug inhibited EMT during tumorigenesis, while forced expression of miR-1 or miR-200 inhibited both EMT and tumorigenesis in human and mouse model systems. Various miR targets were analyzed, and our findings suggest that miR-1 has roles in regulating EMT and mesenchymal differentiation through Slug and functions in tumor-suppressive programs by regulating additional targets. Citation Format: Yen-Nien Liu, Philip Martin, Kathleen Kelly, Juan Juan Yin, Wassim Abou-Kheir, Paul Hynes, Lei Fang, Orla Casey, Ming Yi, Victoria Seng, Heather Tillman. Critical and reciprocal regulation of SLUG-KLF4 and SLUG-miR-1/miR-200b in TGFβ-initiated prostate cancer EMT [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A34.