P2-01-11: Fish Oil Targets miR-21 To Increase PTEN Expression for Inhibition of Bone Metastatic CSF-1 in Breast Cancer Cells.

Abstract

Abstract Current therapy for the breast cancer patients is aimed at treating the cancer mainly at the primary site with limited ability to block metastasis. We have recently shown that fish oil (FO) diet significantly prevents MDA MB-231 breast cancer cell (MDA) metastasis to bone in a mouse model. Colony stimulating factor-1 (CSF-1) is one of major osteoclastogenic cytokines responsible for osteolytic metastasis of breast cancer. Quantitative RT-PCR (qRT-PCR) analysis showed significant inhibition of CSF-1 mRNA expression in fish oil fed mice xenograft tumor samples and docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), two ω-3 fatty acids in fish oil, inhibited CSF-1 mRNA and protein expression in MDA cells. A positive correlation was observed between expression of CSF-1 and the bone metastatic potential of different breast cancer cells. We have demonstrated recently upregulation in PTEN expression by FO diet as a mechanism of breast tumor growth arrest in mice. Over expression of PTEN inhibited migration of MDA cells. PTEN is a negative regulator of PI 3 kinase/Akt signaling. We investigated the mechanism of CSF-1 expression by breast cancer cells. Cotransfection of the CSF-1 promoter-driven luciferase plasmid (CSF-1-Luc) in MDA with PTEN or dominant negative (DN) PI 3 kinase or DN Akt, inhibited the transcription of CSF-1, indicating requirement of PI 3 kinase/Akt signaling. Several oncogenic microRNAs including miR-21 have been shown to induce metastasis of cancer cells. Fish oil fed mice tumors and DHA- and EPA-treated MDA cells significantly blocked miR-21 expression in MDA. PTEN mRNA 3'UTR contains miR-21 recognition element. Over expression of miR-21 inhibited PTEN 3'UTR-Luc reporter activity but it was increased by downregulation of miR-21, indicating functional targeting of PTEN mRNA by miR-21 in MDA. Similarly, expression of either miR-21 or miR-21 Sponge (plasmid-coded anti-miR-21 sequences) in MDA significantly suppressed or increased PTEN protein, respectively. Moreover, DHA-increased PTEN expression is reversed by over expression of miR-21 indicating a critical regulation of PTEN by miR-21. miR-21 over expression increased migration of MDA cells and partially reversed DHA- or EPA-mediated inhibition of migration. Since PTEN regulates expression of CSF-1, we examined the involvement of miR-21. Expression of miR-21 enhanced while miR-21 Sponge reduced expression of CSF-1 mRNA and its transcription. Furthermore, DHA-inhibited CSF-1 mRNA expression is reversed by over expression of miR-21. Together these results uncover a novel function of fish oil, which beheads miR-21 signaling to dampen expression of CSF-1 thus preventing osteoclastogenesis and osteolytic lesions in breast cancer. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-01-11.