Abstract 2403: A novel mechanism for regulation of breast cancer metastasis

Abstract

Abstract Our major goal is to determine the role of Chromodomain-helicase-DNA-binding protein 7 during breast cancer (BC) metastasis. This protein is an ATP-dependent nucleosome remodeling factor and is critical for embryonic development in both animal models and human patients. Our most recent studies provide direct evidence suggesting its novel role in repressing BC metastasis. We found that this protein, but not the mRNA, is highly expressed in a low-metastatic breast cancer cell line (Mcf-7), while its expression is much reduced in metastatic cell lines (MDA-MB-468 and MDA-MB-231). Furthermore, this protein is predominantly localized in the cytoplasm of 468 and 231 cells, in contrast to its nuclear localization in Mcf-7 cells. In the cytoplasm of 468 and 231 cells, this protein is colocalized with a lysosome marker, suggesting that in high metastatic BC cells, this protein is exported to the cytoplasm to be degraded in lysosomes. Blocking the activity of lysosomes increased expression of this protein in high metastatic BC cell lines. This result suggests a mechanism accounting for the reduced expression of this protein in high metastatic BC cell lines. To further support the potential clinic relevance of our results, this protein is localized in the nucleus of almost all duct epithelial cells in normal breast tissues; however, in a large portion of epithelial cells of breast tumors, this protein is localized in the cytoplasm. Through reporter and mutagenesis analysis, we identified the nuclear exporting signal (NES) sequence responsible for exporting this protein into cytoplasm. In the next set of experiments, we attempted to determine the function of this gene in BC metastasis. We found that knocking down expression of this gene in 468 cell significantly increased their migration and invasion. We next applied the CRISPR genome editing technique to mutate the critical amino acids within the NES region in the endogenous gene locus and found that the amount of protein in the nucleus is significantly increased compared to wild type cells. Migration/invasion of these cells was also dramatically decreased. At the molecular level, we found that forced expression of this protein in nucleus reduced expression of epithelial markers and increased expression of epithelial-mesenchymal-transition markers. We are now applying ChIP-Seq and RNA-Seq approaches to determine direct regulatory network of this protein in 231 cells. We will further test whether this protein acts through modulating the epigenetic status of the enhancers/promoters to regulate expression of its target genes to repress BC metastasis. In summary, our data collectively suggest that Chromodomain-helicase-DNA-binding protein 7 is a novel epigenetic regulator to repress BC metastasis. To the best of our knowledge, our study represents the first to address the activity of this protein in BC. Note: This abstract was not presented at the meeting. Citation Format: Kenneth Jiao, Yin Peng, Lizhong Wang, Runhua Liu. A novel mechanism for regulation of breast cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2403. doi:10.1158/1538-7445.AM2017-2403