Abstract 3918: PEA3 is a novel transcriptional activator of Notch-1 and Notch-4 in breast cancer: Opportunity for a new combination strategy

Abstract

Abstract Women diagnosed with triple-negative breast cancer have the worst overall prognosis and frequently present with metastatic tumors. To date, there are no targeted therapies available to combat this aggressive form of breast cancer due to the lack of expression of well-known targets such as ERα, PR, or HER2/neu. Therefore, there is an immediate need to identify novel targets that are responsible for the proliferation, survival, and invasive phenotype. Notch-1 and Notch-4, both potent breast oncogenes, are overexpressed in triple-negative breast cancers-associated with the poorest overall survival. PEA3 (polyomavirus enhancer activator 3), a member of the Ets family of transcription factors, is overexpressed in triple-negative breast cancer and also correlates with aggressive behavior and poor overall survival. Here, we provide new evidence for transcriptional regulation of Notch in triple negative breast cancer and other subtypes of breast cancer. With focus on triple-negative breast cancer cells (MDA-MB-231), our results show that PEA3 is a transcriptional activator of both Notch-1 and Notch-4 as determined by using a PEA3 siRNA and measuring both transcripts and proteins. Chromatin immunoprecipitation confirmed enrichment of PEA3 within the promoter regions of both Notch-1 and Notch-4. Notch-1 recruitment appears to be AP-1 independent, whereas PEA3 recruitment on the Notch-4 promoter is dependent upon c-JUN. Furthermore, results showed that either c-Jun or Fra-1 were required for Notch-4 transcription while c-FOS was a repressor. Importantly, the combined inhibition of Notch signaling (via a gamma-secretase inhibitor, GSI) and PEA3 (via siRNA) arrested the cells in G1, decreased cell viability, reduced tumorgenicity in vitro, and increased apoptosis. Taken together, our results indicate that PEA3 is a novel transcriptional activator of both Notch-1 and Notch-4. PEA3-mediated Notch-1 transcription is AP-1 independent while Notch-4 transcription requires both PEA3 and AP-1 most probably composed of the c-Jun: Fra-1 complex. Moreover, both PEA3 and Notch signaling are essential for proliferation and survival of MDA-MB-231 breast cancer cells. Thus, dual targeting of both PEA3 and Notch pathways might provide a new therapeutic strategy for triple-negative breast cancer as well as additional therapeutic targeting in other breast cancer subtypes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3918.