University of Western Ontario - Electronic Thesis and Dissertation Repository

Location of Thesis Examination

Room 447 Medical Science Building


Master of Science


Anatomy and Cell Biology


Dr. Peeyush Lala

Delay of Publication



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