Ago-RIP-Seq identifies Polycomb repressive complex I member CBX7 as a major target of miR-375 in prostate cancer progression

Abstract

Prostate cancer is a heterogeneous disease. MiR-375 is a marker for prostate cancer progression, but its cellular function is not characterized. Here, we provide the first comprehensive investigation of miR-375 in prostate cancer. We show that miR-375 is enriched in prostate cancer compared to normal cells. Furthermore, miR-375 enhanced proliferation, migration and invasion in vitro and induced tumor growth and reduced survival in vivo showing that miR-375 has oncogenic properties in prostate cancer. On the molecular level, we provide the targetome and genome-wide transcriptional changes of miR-375 expression by applying a generalized linear model for Ago-RIP-Seq and RNA-Seq, and show that miR-375 is involved in tumorigenic networks and Polycomb regulation. Integration of tissue and gene ontology data prioritized miR-375 targets and identified the tumor suppressor gene CBX7, a member of Polycomb repressive complex 1, as a major miR-375 target. MiR-375-mediated repression of CBX7 was accompanied by increased expression of its homolog CBX8 and activated transcriptional programs linked to malignant progression in prostate cancer cells. Tissue analysis showed association of CBX7 loss with advanced prostate cancer. Our study indicates that miR-375 exerts its tumor-promoting role in prostate cancer by influencing the epigenetic regulation of transcriptional programs through its ability to directly target the Polycomb complex member CBX7.

Identification of a Novel MicroRNA Panel Associated with Metastasis Following Radical Prostatectomy for Prostate Cancer

“…Each of the miRNAs identified for inclusion in the panel has previously been associated with carcinogenesis, though not all have been associated with prostate carcinogenesis. MiR-375 is well-described in the carcinogenesis and progression pathways of prostate cancer (22,23) as well as pancreatic ductal adenocarcinomas (24) and has been proposed as both a diagnostic (25) and a prognostic (26) biomarker for prostate cancer. Increased expression of miR-375 has been found in prostate cancer cells, as compared to normal cells (22,23), indicating a pro-oncogenic role despite it's anti-invasive and anti-epithelial-mesenchymal transition properties (27).…”

Circulating microRNAs and treatment response in the Phase II SWOG S0925 study for patients with new metastatic hormone‐sensitive prostate cancer

“…Recent work suggests that miR‐375 is involved in the epithelial‐mesenchymal‐transition (EMT) signature, and that disruption of this regulatory network may result in altered expression of miR‐375. Another recent report suggests miR‐375 mediated repression of the tumor suppressor CBX7, a member of the Polycomb complex involved in epigenetic regulation, which may be associated with prostate tumorigenesis …”

Current experimental strategies for intracellular target identification of microRNA

“…For example, Hannon et al used AGO2 antibody to capture RISC and isolated bound mRNAs for further analysis with microarray, followed by identifying targets for miR-124 [32]. Similarly, target genes in RISC were isolated with AGO antibody and further analyzed by RNA-seq for identifying targets for miR-375 and miR-155 [33,34]. Using antibodies targeting GW182 family proteins AIN-1 and AIN-2, Han et al isolated and identified miRNA targets in RISC of C. elegans [35].…”