Abstract 1259: Stem cell property-suppressing microRNAs are stimulated and their target proteins inhibited by vitamin D and progesterone in ovarian cancer cells
Authors: Rosales Rebecca , Turbov Jane , Yoo Jennifer , Rodriguez Gustavo C. , Thaete Larry G. 
Published: July 2017

Vitamin D (1,25(OH)2D3) and progesterone (P4) have both been shown to reduce the incidence of ovarian cancer. Mechanisms involved in their actions are not fully known but each one can enhance the effect of the other. Six microRNAs (miRNAs), associated with suppression of cancer stem cell properties, were investigated first in a screening array and then with a more definitive RT-PCR investigation of the response of these miRNAs to 100 nM 1,25(OH)2D3 and 100 nM P4. These experiments were conducted in cells that do (OVCAR-3-PGR) and do not (SKOV3) express nuclear progesterone receptors (PGR).

Let-7a and Let-7b are known to decrease expression of Ras and c-Myc and reduce stem cell self-renewal. Let-7b expression was increased (p&lt;0.001) at 48 h in response to combined 1,25(OH)2D3 and P4 when PGR were present, and in response to individual and combined treatments at 72 h (p&lt;0.01). Correspondingly, c-Myc expression was decreased (p&lt;0.001) by both P4 and combined P4 and 1,25(OH)2D3. Let-7a expression was not affected by these treatments. No treatment-related change in the production of ras protein was observed compared to controls. In the absence of PGR (SKOV3 cells), c-Myc was suppressed by combined P4 and 1,25(OH)2D3 treatment at 24 h and 48 h.

miR-26a and miR-101 are known to downregulate EpCAM and EZH2, leading to decreased invasion and metastasis and to reduced proliferation. miR-101 increased (p&lt;0.001) at 48 h in response to combined 1,25(OH)2D3 and P4 in cells expressing PGR. It was increased (p&lt;0.05) at 36 h and showed synergy in the screening array in the absence of PGR. Target proteins EZH2 and EpCAM decreased moderately (p&lt;0.05) at 72 h combined treatment, both with and without PGR present. miR-26a expression was not affected by these treatments.

miR-200b and miR-200c are known to suppress expression of ZEB1 which in turn decreases Bmi1 and Sox2 to increase E-cadherin (epithelial marker) and decrease vimentin (mesenchymal marker), thus inhibiting the epithelial-to-mesenchymal transition. Expression of miR-200b was increased (p&lt;0.05) at 24 h and 72 h in response to P4 when PGR were present. miR-200c expression was not responsive to these treatments. ZEB1 was decreased (p&lt;0.01) at 48 h in response to combined 1,25(OH)2D3 and P4.

These results point not only to differences among cancer cell lines but they also emphasize a possible mechanism by which P4 and 1,25(OH)2D3 may work together to prevent the occurrence of ovarian cancer, namely by suppressing stem cell renewal and the formation of neoplastic lesions. The results also reveal that P4 may act via other signaling pathways than its primary nuclear receptors to effect suppression of stem cell properties. Increased expression of cancer stem cell-suppressing miRNAs may be an important mechanism mediating the efficacy of a progestin-based ovarian cancer prevention strategy.

Citation Format: Rebecca Rosales, Jane Turbov, Jennifer Yoo, Gustavo C. Rodriguez, Larry G. Thaete. Stem cell property-suppressing microRNAs are stimulated and their target proteins inhibited by vitamin D and progesterone in ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1259. doi:10.1158/1538-7445.AM2017-1259