Loss of Let-7 Up-Regulates EZH2 in Prostate Cancer Consistent with the Acquisition of Cancer Stem Cell Signatures That Are Attenuated by BR-DIM

Abstract

The emergence of castrate-resistant prostate cancer (CRPC) contributes to the high mortality of patients diagnosed with prostate cancer (PCa), which in part could be attributed to the existence and the emergence of cancer stem cells (CSCs). Recent studies have shown that deregulated expression of microRNAs (miRNAs) contributes to the initiation and progression of PCa. Among several known miRNAs, let-7 family appears to play a key role in the recurrence and progression of PCa by regulating CSCs; however, the mechanism by which let-7 family contributes to PCa aggressiveness is unclear. Enhancer of Zeste homolog 2 (EZH2), a putative target of let-7 family, was demonstrated to control stem cell function. In this study, we found loss of let-7 family with corresponding over-expression of EZH2 in human PCa tissue specimens, especially in higher Gleason grade tumors. Overexpression of let-7 by transfection of let-7 precursors decreased EZH2 expression and repressed clonogenic ability and sphere-forming capacity of PCa cells, which was consistent with inhibition of EZH2 3′UTR luciferase activity. We also found that the treatment of PCa cells with BR-DIM (formulated DIM: 3,3′-diindolylmethane by Bio Response, Boulder, CO, abbreviated as BR-DIM) up-regulated let-7 and down-regulated EZH2 expression, consistent with inhibition of self-renewal and clonogenic capacity. Moreover, BR-DIM intervention in our on-going phase II clinical trial in patients prior to radical prostatectomy showed upregulation of let-7 consistent with down-regulation of EZH2 expression in PCa tissue specimens after BR-DIM intervention. These results suggest that the loss of let-7 mediated increased expression of EZH2 contributes to PCa aggressiveness, which could be attenuated by BR-DIM treatment, and thus BR-DIM is likely to have clinical impact.

Molecular Pathways: Epigenetic Modulation of Wnt–Glycogen Synthase Kinase-3 Signaling to Target Human Cancer Stem Cells

“…Lineage-mapping studies have identified epigenetic dysregulation as a critical early event in human tumorigenesis (24), supporting the concept of an epigenetic progenitor origin of cancer (22). Furthermore, cells with CSC features appear molecularly dissociable from non-CSCs (25)(26)(27)(28)(29), and animal models have demonstrated that epigenetic interventions can reduce CSC frequencies and attenuate tumorigenesis (30,31). For instance, microRNAs suppressing the expression of members of the polycomb repressive complex-2 (PRC2), including Let-7 and the miR200 family, are downregulated in CSC-containing fractions of breast and prostate cancer whereas increased levels were observed in non-stem cancer cells (25,28,29).…”

“…Furthermore, cells with CSC features appear molecularly dissociable from non-CSCs (25)(26)(27)(28)(29), and animal models have demonstrated that epigenetic interventions can reduce CSC frequencies and attenuate tumorigenesis (30,31). For instance, microRNAs suppressing the expression of members of the polycomb repressive complex-2 (PRC2), including Let-7 and the miR200 family, are downregulated in CSC-containing fractions of breast and prostate cancer whereas increased levels were observed in non-stem cancer cells (25,28,29). Accordingly, the expression of PRC2 members SUZ12 and EZH2 was shown to be upregulated in CSC-enriched fractions of breast and prostate tumors (25,29).…”

miRNAs as novel biomarkers in the management of prostate cancer

“…Aberrantly expressed miRNAs can cause deregulation of specific signaling pathways that are associated with the functions of CSCs. Particularly, miR-34 family or let-7 family [50,51] have been involved in the regulation of PCa CSC properties.…”

Roles of enhancer of zeste homolog 2: From skeletal muscle differentiation to rhabdomyosarcoma carcinogenesis

“…Several miRNA negatively regulate EZH2 expression, for example, miRNA-101, miRNA-26a, miR-29, and miR-214 negatively regulate EZH2 during various differentiation processes. 56 Furthermore, downregulation of miRNA is frequently associated with abnormally elevated levels of EZH2 in cancer; for instance, the downregulation of miR-25 and miR30d is involved in thyroid carcinoma 57 , let-7 in prostate cancer, 58 miR-98 and miR-214 in esophageal squamous cell carcinoma, miR26a and miR-29 in rhabdomyosarcoma. 59,60 Post-translational modifications of EZH2 PRC2 activity can be regulated by post-translational modifications that are able to control the recruitment of target genes and/or its catalytic activity.…”