Abstract 3122: HMGA1 reprograms breast cancer cells by inducing transcriptional networks involved in an epithelial-mesenchymal transition, stemness, and metastatic progression.
Authors: Shah Sandeep N. , Cope Leslie , Belton Amy , Poh Weijie , Sukumar Saraswati , Huso David , Resar Linda 
Published: August 2014

Abstract
Despite advances in our ability to detect and treat breast cancer, it remains a leading cause of death in women with cancer worldwide, and the incidence is rising. Approximately 15-20% of all cases are classified as triple negative breast cancer (TNBC), a subtype that is frequently associated with rapid progression and poor outcome. TNBC refers to the lack of detectable markers for the estrogen receptor (ER), progesterone receptor (PR), and Her2/neu amplification. These tumors do not respond to our most effective and least toxic therapies, including hormonal therapy (tamoxifen) or trastuzumab. We are studying molecular pathways that lead to tumor progression in TNBC and can be targeted with novel therapies. Our focus is the high mobility group A1 (HMGA1) oncogene. HMGA1 is highly expressed during embryogenesis, with low or undetectable levels in differentiated, adult tissues. HMGA1 is enriched in virtually all high-grade (poorly differentiated) cancers studied to date, including TNBCs, and high expression portends a poor prognosis in breast and other cancers. To investigate the role of HMGA1 in tumor progression in breast cancer, we silenced HMGA1 expression in TNBC cell lines (MDA-MB-231, Hs578T) using lentiviral-mediated delivery of short hairpin RNA. Strikingly, proliferation was markedly impaired, and many cells underwent apoptotic cell death within 5 days following HMGA1 knock-down. Surprisingly, cell morphology also changed dramatically, whereby the fibroblast-like, spindle-shaped cells became cuboidal and epithelial-like, consistent with a mesenchymal-epithelial transition, or MET. E-CADHERIN mRNA was induced, while both SNAIL and VIMENTIN were repressed in the knock-down cells, also consistent with MET. In addition, silencing HMGA1 blocked migration, invasion, and the formation of tumor foci in the lungs following tail vein injection of MDA-MB-231 cells. Moreover, both primary tumorigenesis and metastatic progression to the lungs were markedly inhibited in MDA-MB-231 cells with knock-down of HMGA1 following implantation in mammary fat pads. Furthermore, silencing HMGA1 blocked primary and secondary mammosphere formation, indicating that HMGA1 is required for this stem cell property. Tumorigenesis experiments at limiting dilutions showed that silencing HMGA1 depletes the tumor initiator/cancer stem cell pool. Using global gene expression analysis, we identified an HMGA1 signature of differentially-regulated genes in the control cells compared to knock-down cells. We also found that the HMGA1 signature is highly enriched in embryonic stem cells. Together, these findings indicate that silencing HMGA1 reprograms invasive, mesenchymal TNBCs into non-invasive, epithelial-like cells with slower growth and an altered gene expression signature. Studies are now needed to determine how to target HMGA1 in therapy.
Citation Format: Sandeep N. Shah, Leslie Cope, Amy Belton, Weijie Poh, Saraswati Sukumar, David Huso, Linda Resar. HMGA1 reprograms breast cancer cells by inducing transcriptional networks involved in an epithelial-mesenchymal transition, stemness, and metastatic progression. [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 3122. doi:10.1158/1538-7445.AM2013-3122