Abstract 858: ERK2 rather than ERK1 contributes to EMT and metastatic potential in triple-negative breast cancer.
Authors: Bartholomeusz Chandra , Saso Hitomi , Dadbin Ali , Masuda Hiroko , Kogawa Takahiro , Van Laere Steven , Bertucci François , Hortobagyi Gabriel N. , Ueno Naoto T. 
Published: August 2014

Background: Patients with triple-negative breast cancer (TNBC), which lacks estrogen receptor and progesterone receptor and has low HER2 expression, have a very poor prognosis because the disease often metastasizes. Preventing metastasis, as well as inhibiting tumor growth, is crucial to improving the prognosis of patients with TNBC. We previously showed using reverse-phase protein array analysis that patients with ERK2-overexpressing TNBC had a higher risk of death than those with low-ERK2-expressing TNBC. TNBC is characterized by an epithelial-to-mesenchymal transition (EMT) phenotype, which has features in common with those of cancer stem cells. Cells undergoing EMT may contribute to the metastatic process and have increased ability to form mammospheres in vitro. The roles of the 2 ERK isoforms, ERK1 and ERK2, in TNBC are not well defined. We hypothesized that ERK2, but not ERK1promotes EMT and metastasis in TNBC.

Methods & Results: We compared parental SUM-149 TNBC cells and stable clones that constitutively expressed shERK1 or shERK2 and observed no differences in cell proliferation. However, reducing the expression of ERK2, but not reducing the expression of ERK1, changed the mesenchymal phenotype of TNBC to an epithelial phenotype, reduced formation of mammospheres in a dose-dependent manner, and reduced the stem cell subpopulation (CD44+/CD24-), which correlated with a reduction in migration and invasion. In addition, ERK2 knockdown inhibited anchorage-independent growth, an indicator of in vivo tumorigenicity. To determine which genes are involved in ERK2-induced EMT and metastasis, we performed transcriptional profiling using real-time PCR-based EMT and metastasis arrays. After normalization, we observed that mRNA levels of the epithelial markers KRT7 and KRT14 were increased by 4 and 1.8 fold, respectively, in ERK2-silenced cells as in control cells; mRNA levels of the mesenchymal markers Twist1, vimentin, and ZEB1 were reduced by 0.6, 0.1 and 0.2 fold respectively, in ERK2-silenced cells as in control cells; and mRNA levels of the metastasis-related genes MMP-2, MMP-7, MMP-13, IL1B, and COL4A2 were reduced by 0.3, 0.3, 0.6, 0.6 and 0.3 fold respectively, in ERK2-silenced cells as in control cells. Further, using an Affymetrix gene chip and the Inflammatory Breast Cancer World Consortium patient data set (n=389), we did a class comparison test in which the P value was calculated by Wilcoxon test. We observed significantly lower ERK1 mRNA expression in the TNBC group than the non-TNBC group (P &lt; 0.0001) but significantly higher ERK2 mRNA expression in the TNBC group than in the non-TNBC group (P &lt; 0.005).

Conclusions: ERK2 but not ERK1 may promote tumorigenesis of the TNBC subgroup by enriching the cancer stem cell population and inducing EMT and metastasis. Our long-term goal is to confirm these findings in xenograft studies and develop ERK2-targeted therapy for TNBC.

Citation Format: Chandra Bartholomeusz, Hitomi Saso, Ali Dadbin, Hiroko Masuda, Takahiro Kogawa, Steven Van Laere, François Bertucci, Gabriel N. Hortobagyi, Naoto T. Ueno. ERK2 rather than ERK1 contributes to EMT and metastatic potential in triple-negative breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 858. doi:10.1158/1538-7445.AM2013-858