Abstract 2017: The CEBPD transcription factor, a marker of good prognosis in breast cancer, becomes a signaling hub for promotion of cancer cell stemness by hypoxia and interleukin-6

Abstract

Abstract The transcription factor C/EBPdelta (CEBPD) is expressed in normal mammary epithelial cells and high expression in breast cancer correlates with hormone receptors and good prognosis (Mendoza-Villanueva et al., submitted). In the MMTV-Neu mouse model, deletion of CEBPD increases tumor multiplicity, but “paradoxically” reduces metastatic progression, suggesting that CEBPD has dual tumor suppressing and metastasis promoting functions (Balamurugan et al., 2010). Here, we identify a molecular mechanism for the tumor promoting function of CEBPD that may reach beyond breast cancer. We show that CEBPD serves as a signaling hub that integrates and amplifies pathways that promote stemness in breast cancer, glioblastoma and embryonic cancer cells. This work identifies a mechanism by which hypoxia and inflammation promote cancer stem-like cells (CSCs), which are implicated in tumor progression and resistance. Our earlier studies showed that CEBPD promotes inflammatory signaling and hypoxia adaptation by inhibiting the expression of FBXW7 (Balamurugan et al., 2010 and 2013), which can target several oncoproteins for degradation. Using a variety of established breast and glioblastoma tumor cell lines/xenografts, primary mouse mammary tumor cells and tissues, recent patient-derived glioblastoma cell lines, as well as embryonic stem/cancer cell lines, we find that deletion or depletion of CEBPD reduced the number of stem cells as determined by surface markers, sphere formation, limiting dilution xenografts, and by expression of stemness genes. Mechanistic studies in culture models show that CEBPD is expressed in CSCs and connects and amplifies both hypoxia (HIF-1) and inflammation (IL-6/STAT3) pathways to increase Notch1/NICD expression and cell stemness. CEBPD induces NICD expression transcriptionally through HIF-1 and at the level of the protein by inhibition of FBXW7-mediated degradation. In addition to its known role as a target of STAT3 and activator of IL-6 gene expression, we identified an additional role for CEBPD in promoting expression of the IL-6 receptor. Furthermore, we found that CEBPD also directly activates the expression of stemness-promoting genes such as OCT4, Sox2, KLF4, Myc, Nanog, CD44 and CD133. Taken together, this study provides novel insights into the molecular mechanisms that promote cancer cell stemness. Because CEBPD integrates and amplifies multiple stemness promoting pathways, CEBPD may represent a unique point of vulnerability in cancer stem cells, strongly suggesting that pharmacological inhibition of CEBPD signaling may effectively target CSCs. Results from current efforts to pharmacologically downregulate CEBPD in cancer stem cells will also be presented. Citation Format: Kuppusamy Balamurugan, Daniel Mendoza-Villanueva, Barbara Rath, Philip Tofilon, Shikha Sharan, Esta Sterneck. The CEBPD transcription factor, a marker of good prognosis in breast cancer, becomes a signaling hub for promotion of cancer cell stemness by hypoxia and interleukin-6. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2017.