University of Western Ontario - Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Anatomy and Cell Biology

Supervisor

Dr. Peeyush Lala

Delay of Publication

1

Abstract

We had shown that overexpression of cyclooxygenase (COX)-2 in human, as well as murine breast cancer cells promotes tumor progression and metastasis by multiple mechanisms: host immune cell inactivation and stimulation of cancer cell migration, invasion, tumor-associated angiogenesis and lymphangiogenesis, which support blood- borne and lymph-borne metastasis. Most of these events resulted from the activation of the prostanoid receptor EP4 by endogenous PGE2. Recently, by stable transfection of COX-2 cDNA into a non-metastatic COX-2 negative human breast cancer cell line, MCF-7, we showed that COX-2 induces all the phenotypic properties of stem-like or “tumor initiating cells” (TICs) in MCF-7-COX-2 cells, as defined by in vitro studies and validated in vivo. Through combined gene expression and microRNA (miRNA) micro array analysis, we identified two miRNAs (miR-526b and miR-655) that are up-regulated in MCF-7-COX-2 cells that are associated with a down-regulation of 14 target genes linked with tumor-suppressor functions. We hypothesize that these miRNAs are important for COX-2 mediated TIC associated functions in human breast cancer. As a first step, we validated their expression in several COX-2 disparate human breast cancer cell lines: MCF-7, MCF-7-COX-2, SKBR-3 (HER-2 over-expressing but COX-2 negative) and SKBR-3-COX-2. The expression levels of miR-655 were strongly correlated with COX-2 mRNA expression in these cell lines. Furthermore, the migratory and invasive capacities of the cell lines went hand in hand with miR-655 expression. Expression of miR-655 was markedly inhibited by treating MCF-7-COX-2 cells with a COX-2 inhibitor (NS398) or an EP4 antagonist (ONO-AE3-208), indicating that the expression depended on both COX-2 and EP4 activity. derived from tumorspheres exhibited a dramatic increase in COX-2 expression in comparison to the cells grown as monolayer. We also found that the tumorspheres derived from MCF-7, MCF-7-COX-2 and SKBR-3 overexpressed miR-655. These findings, taken together, fortify the notion that COX-2, EP4 and COX-2 induced miR- 655 expression play important roles in promoting and maintaining the TIC phenotype in breast cancer cells.

Available for download on Monday, May 18, 2015

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