Abstract 270: Modulation of EGFR localization and transcriptional activity

Abstract The triple negative (ER-, PR-, Her2-) or basal-like breast cancers are the most difficult forms of breast cancer to treat, because the cancer is often chemoresistant and highly metastatic. As these cancers progress from early to late stage the 5-year survival rate drops dramatically. Many proteins are responsible for this progression, including MUC1 and the Epidermal Growth Factor Receptor (EGFR). MUC1 is a heavily O-glycosylated transmembrane protein that is over expressed in 90% of all breast and ovarian cancers. In normal cells, MUC1 is only found on the apical surface of epithelium, but in cancer, MUC1 is found to be mislocalized. As a result, MUC1 plays a role in promoting tumorigenesis and metastases, by interacting with other oncogenes such as EGFR. EGFR is overexpressed in about 60% of the most aggressive form of breast cancer (triple negative). In an EGFR-dependent mouse model of breast cancer, the loss of Muc1 directly correlates to the loss of cyclin D1. Additionally, blocking MUC1 and EGFR interactions significantly inhibited tumor progression in a xenograft and s spontaneous mouse model of breast cancer. Recently, a novel trafficking pathway of EGFR has been discovered, which was described as EGFR trafficking to the nuclear compartment. Following entry into the nucleus EGFR can act in an oncogenic manner by aberrantly activating transcription of genes such as, cyclin D1 and v-myb. In this study we discovered a novel regulator function of MUC1 in EGFR trafficking and transcriptional activity. We found that MUC1 expression in basal-like breast cancer promotes the accumulation of nuclear EGFR and mediates EGFR's interaction with chromatin. Additionally, we determined that EGFR's interaction with the cyclin D1 promoter and upregulation of the cyclin D1 protein was MUC1-dependent. The main focus of anti-EGFR therapeutics have been its tyrosine kinase activity, however this study reveals that EGFR's subcellular localization should also be considered in the development of future cancer therapeutics. 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 270.