Abstract P1-07-29: The role of cytoplasmic polyadenylation element binding protein-2 in breast cancer

Abstract

Abstract Background: We had shown that over-expression of the inflammation-associated enzyme cyclo-oxygenase (COX)-2 promotes breast cancer progression and metastasis and sustains stem-like cells (SLC), believed to evade traditional therapy and promote tumor reoccurrence. Stable transfection of the COX-2 gene into COX-2–, HER-2–, non-metastatic human MCF-7 breast cancer cell line (named MCF-7-COX-2) led to a highly aggressive phenotype in vitro, where we observed epithelial-mesenchymal transition, increased migration, invasion, clonogenic tumorsphere forming ability (surrogate of SLC) and expression of SLC marker ALDH. Furthermore, we observed an increase in the tumorigenic and metastatic capacity of the cells in immuno-compromised mice in vivo. Combined gene expression and microRNA (miRNA) micro-array analysis of MCF-7 and MCF-7-COX-2 cells revealed COX-2 induced up-regulation of two miRNAs, miR-526b and miR-655, and down-regulation of their common gene target, cytoplasmic polyadenylation element binding protein (CPEB)-2. While both miRNAs were found to be oncogenic in functional assays, the function of CPEB-2 in breast cancer remains untested. Hypothesis: miR-526b and miR-655 down-regulate CPEB-2 to promote breast cancer cell aggressiveness and the SLC phenotype. Approaches & Results: (1) To test if expression levels of COX-2 and CPEB-2 are inversely related, we measured both gene and protein expression in multiple COX-2 disparate breast cancer cell lines. (2) We also tested if there is an inverse relationship between miRNA expression and the expression levels of their target gene CPEB-2. We found that high COX-2/miRNA expressing cell lines such as MDA-MB-231 and MCF-7-COX-2 had significantly lower expression of CPEB-2 than MCF-7 cells (low COX-2/low miRNA). (3) To test the functional effects of CPEB-2 gene manipulation in vitro and in vivo, we knocked down CPEB-2 in CPEB-2-high MCF-7 cell line. MCF-7-CPEB-2-KD cells were found to be more migratory and invasive than control cells in transwell assays. Ongoing studies are to test (a) whether there is a cause and effect relationship between the expression of the miRNAs and CPEB-2 expression, that is, whether knocking down or knocking in the miRNAs respectively up-regulates and down-regulates CPEB-2 expression; and (b) whether CPEB-2 expression is lower in breast cancer tissues than in adjacent non-tumor tissues, and inversely correlated with the miRNAs in breast cancer tissues. Conclusion and Significance: If CPEB-2 is proven to be tumor suppressor, these oncogenic miRNAs and putatively anti-oncogenic CPEB-2 may serve as potential biomarkers in personalizing breast cancer therapy with COX-2 inhibitors as adjuvant. (Supported by funds of the OICR to PKL. AH and MM are CaRTT/TBCRU scholars). Citation Format: Asma Hasan, Mousumi Majumder, Peeyush K Lala. The role of cytoplasmic polyadenylation element binding protein-2 in breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-07-29.