PD08-06: ERK2 Promotes Stem Cell-Like Characteristics in Triple-Negative Breast Cancer.

Abstract Background: Triple-negative breast cancer (TNBC) is resistant to targeted therapies such as hormonal therapy and HER2−targeted therapies. Thus, no specific targeted therapy is currently available for TNBC. ERK2, a component of the MAPK pathway, plays an important role in epithelial-mesenchymal transition (EMT) in MCF-7-10A, a nontransformed human mammary epithelial cell line and is required for full acquisition of stem cell-like characteristics. Inhibition of ERK2 dramatically reduces cell growth, whereas inhibition of ERK1 significantly facilitates proliferation. ERK1 mutant mice have a strikingly milder phenotype than ERK2 mutant mice, which die early in development. In addition, we have shown that the upstream target of ERK, MEK, may be a target for treating TNBC with the MEK inhibitor selumetinib. Our reverse-phase protein array analysis showed that of patients with TNBC, those with ERK2-overexpressing tumors were at higher risk of death than those with low-ERK2-expressing tumors. Therefore, we hypothesized that ERK2 promotes the tumorigenesis and metastasis of TNBC. We sought to determine the role of ERK2 in the tumorigenic and metastatic activities in TNBC and whether ERK2 is required for acquisition of stem cell-like characteristics in TNBC. Methods: We studied the role of ERK1 and ERK2 in the TNBC cell line SUM-149. We used shRNA to specifically knockdown ERK1 and ERK2 (shERK1 and shERK2) and examined whether knocking down ERK1 and ERK2 correlated with EMT regulation, migration, and tumorigenicity in TNBC cells. Results: Compared with parental SUM-149 cells, stable clones that constitutively expressed shERK1 or shERK2 showed no difference in growth rate. However, knocking down ERK2 significantly inhibited migration and the acquisition of stem cell-like characteristics (CD44+/CD24-) in SUM-149 cells in vitro. In addition, knockdown of ERK2 also inhibited anchorage-independent growth, an indicator of in vivo tumorigenicity, whereas knockdown of ERK1 did not inhibit anchorage-independent growth. However, inhibition of ERK1 or ERK2 in 2D or 3D cell culture did not correlate with changes in epithelial and mesenchymal markers by western blot analysis. Conclusion: Our data demonstrate that ERK2 may promote the tumorigenesis of TNBC via enriching cancer stem cells. Our long-term goal is to develop ERK-targeted therapy for TNBC. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr PD08-06.