MicroRNA let-7c suppresses androgen receptor expression and activity via regulation of Myc expression in prostate cancer cells

How does Lin28 let-7 control development and disease?

One of the most ancient and highly conserved microRNAs (miRNAs), the let-7 family, has gained notoriety owing to its regulation of stem cell differentiation and essential role in normal development, as well as its tumor suppressor function. Mechanisms controlling let-7 expression have recently been uncovered, specifically the role of the RNA-binding protein Lin28 - a key developmental regulator - in blocking let-7 biogenesis. This review focuses on our current understanding of the Lin28-mediated control of let-7 maturation and highlights the central role of Lin28 in stem cell biology, development, control of glucose metabolism, and dysregulation in human disease. Manipulating the Lin28 pathway for the precise control of let-7 expression may provide novel therapeutic opportunities for cancer and other diseases.

MicroRNA let-7c is downregulated in prostate cancer and suppresses prostate cancer growth

Purpose

Prostate cancer (PCa) is characterized by deregulated expression of several tumor suppressor or oncogenic miRNAs. The objective of this study was the identification and characterization of miR-let-7c as a potential tumor suppressor in PCa.

Experimental Design

Levels of expression of miR-let-7c were examined in human PCa cell lines and tissues using qRT-PCR and in situ hybridization. Let-7c was overexpressed or suppressed to assess the effects on the growth of human PCa cell lines. Lentiviral-mediated re-expression of let-7c was utilized to assess the effects on human PCa xenografts.

Results

We identified miR-let-7c as a potential tumor suppressor in PCa. Expression of let-7c is downregulated in castration-resistant prostate cancer (CRPC) cells. Overexpression of let-7c decreased while downregulation of let-7c increased cell proliferation, clonogenicity and anchorage-independent growth of PCa cells in vitro. Suppression of let-7c expression enhanced the ability of androgen-sensitive PCa cells to grow in androgen-deprived conditions in vitro. Reconstitution of Let-7c by lentiviral-mediated intratumoral delivery significantly reduced tumor burden in xenografts of human PCa cells. Furthermore, let-7c expression is downregulated in clinical PCa specimens compared to their matched benign tissues, while the expression of Lin28, a master regulator of let-7 miRNA processing, is upregulated in clinical PCa specimens.

Conclusions

These results demonstrate that microRNA let-7c is downregulated in PCa and functions as a tumor suppressor, and is a potential therapeutic target for PCa.