Abstract 2857: Induced expression of DUSP4 and PPM1A in ER-negative breast cancer cells suppresses proliferation and invasion

Abstract

Abstract Background: ER-negative breast cancers are poor prognosis tumors that occur more commonly in young women. Current treatments for ER-negative tumors include cytotoxic chemotherapy, or for those ER-negative breast cancers that overexpress HER2, the anti-HER2 antibody herceptin. Targeted therapy for ER-negative tumors, particularly those that do not express HER2 (“triple-negative breast cancer”) is urgently needed. We previously identified kinases that are critical for the growth of “triple-negative” breast cancer. In this project, we investigated whether phosphatases are differentially expressed in ER-negative as compared to ER-positive breast cancers. We hypothesized that: (1) the specific phosphatases that govern the growth of ER-negative cancers are different from those of ER-positive cancers, (2) Induced expression of those phosphatases that are lowly expressed in ER-negative breast cancers will suppress the growth and invasion of ER-negative breast cancers. Methods: Using 277 human breast tumors (56 ER-positive and 221 ER-negative) from the Baylor Breast Center tumor bank, we isolated RNA and performed Affymetrix microarray studies. cDNA was synthesized and Biotin-labeled and was then hybridized onto an Affymetrix HGU133A GeneChipTM, comprised of 22,000 genes. Statistical analysis of phosphatases was done with dChip software, and phosphatases more highly (>1.5 fold; FDR=0.05) or lowly (<0.66-fold; FDR=0.05) expressed in ER-negative breast cancers as compared to ER-positive breast cancers were selected for further study. Over expression of DUSP4 and PPM1A in breast cancer cells was achieved using a Tet-regulated pUHD vector (Tet Off System). Cell growth was measured by MTS assay. Soft agar and invasion assays were performed using previously published protocols. Results: We identified 20 highly-expressed (>1.5 fold; FDR=0.05), and 29 lowly-expressed (<0.66-fold; FDR=0.05) phosphatases in ER-negative human breast cancers. We selected two lowly expressed phosphatases (DUSP4 and PPM1A) for further study. Induced expression of DUSP4 and PPM1A in ER-negative MDA-MB-468 cells inhibited anchorage-dependent and -independent growth. Induced expression of DUSP4 and PPM1A also suppressed the invasion of MDA-MB-468 cells. We are currently investigating the cellular and molecular consequences of induced DUSP4 and PPM1A expression in other ER-negative and ER-positive breast cancer cell lines. Conclusion: We identified a set of highly expressed and lowly expressed phosphatases in ER-negative breast cancers as compared to ER-positive cancers. Two phosphatases (DUSP4 and PPM1A) when expressed in an ER-negative breast cancer cells inhibit growth and invasion of these cells. By identifying the molecules that regulate breast cancer cell growth we will identify potential new targets for the treatment of these aggressive ER-negative breast cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2857. doi:1538-7445.AM2012-2857