Abstract 4170: MicroRNA-135b influences androgen and estrogen receptor protein levels and regulates proliferation of hormone-receptor positive prostate and breast cancer cells.
Authors: Aakula Anna , Leivonen Suvi-Katri , Kohonen Pekka , Hintsanen Petteri , Aittokallio Tero , Ceder Yvonne , Børresen-Dale Anne-Lise , Perälä Merja , Östling Päivi , Kallioniemi Olli 
Published: August 2014

MicroRNAs (miRNAs) regulate genes and impact on a wide range of cellular signaling pathways and biological processes in both physiological and pathological states. To understand their role in prostate and breast cancer, we have carried out systematic functional high-throughput miRNA-overexpression studies in cell lines, and assessed the effect of miRNAs on androgen receptor (AR) and estrogen receptor (ER) protein levels and on cell proliferation.

We have observed that overexpression of miR-135b affected the growth of cells where the endogenous expression of miR-135b was low. Furthermore, the cells with low miR-135b expression mostly had a higher expression of AR and ER in prostate respective breast cancer cells. We identified that miR-135b is able to target AR and regulate the AR protein level in prostate cancer cells.

Our aim was thus to further explore the function and significance of miR-135b in prostate and breast cancer. We found that miR-135b inhibited the growth of AR-positive prostate cancer (LNCaP, 22Rv1 and VCaP) and ER-positive breast cancer (MCF-7 and BT-474) cells, whereas it did not have any effect on the AR- and ER-negative cells. Here, we demonstrate that miR-135b decreases the ER protein level in breast cancer cells and that miR-135b expression inversely correlates with ER protein and mRNA as well as AR mRNA levels in 101 clinical breast cancer samples and with AR protein level in 47 clinical prostate cancer samples.

In order to characterize novel target genes and to understand the mechanisms for the observed effect, we conducted gene expression analyses and identified 65 genes that were deregulated by miR-135b at three different time points (12 h, 24 h and 36 h). We discovered that for almost 50% of the genes, the expression significantly (p≤0.05) positively or negatively correlated with the expression of miR-135b in clinical breast cancer samples, suggesting that they may be relevant. For 14 genes we observed a significant inverse correlation with miR-135b in the clinical material. Hypoxia-inducible factor 1-alpha inhibitor (HIF1AN) showed an inverse correlation and is predicted to be targeted by miR-135b by TargetScan 6.2. Our results indicate that miR-135b influences the protein level of HIF1AN. This could imply that miR-135b is involved in the regulation of oxygen homeostasis, and subsequently angiogenesis and glycolytic metabolism, in breast and prostate cancer tumors by negatively regulating the inhibitor of HIF1α that plays an important role in cancer.

Citation Format: Anna Aakula, Suvi-Katri Leivonen, Pekka Kohonen, Petteri Hintsanen, Tero Aittokallio, Yvonne Ceder, Anne-Lise Børresen-Dale, Merja Perälä, Päivi Östling, Olli Kallioniemi. MicroRNA-135b influences androgen and estrogen receptor protein levels and regulates proliferation of hormone-receptor positive prostate and breast cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4170. doi:10.1158/1538-7445.AM2013-4170