Abstract 2587: Transcription factor ZEB1 controls lineage specificity of African ancestry-enriched breast stromal multilineage cells

Abstract Although disparity in breast cancer outcomes in women of African Ancestry (AA) as compared to European Ancestry (EA) has been thought to derive from socioeconomic factors, emerging evidence demonstrating genetic ancestry-dependent differences in normal and cancer genome, cancer-associated mutation patterns and immunosuppressed tumor microenvironment suggests the involvement of biological factors. To investigate breast cancer outcome-associated biologic factors, we analyzed breast tissues of healthy donors of distinct genetic ancestry and found that PROCR+/ ZEB1+/ PDGFRα+ stromal cells (hence, called PZP) are more abundant in normal breast tissues of women of AA as compared to EA. PZP cells display the properties of multi-lineage fibroadipogenic mesenchymal stromal cells and can differentiate into adipogenic and osteogenic lineages. Whether and how PZP cells contribute to breast cancer progression is unknown. Using a combination of gene knockout, RNA-sequencing, co-culture and immunophenotyping studies, we investigated the role of PZP cell-enriched Zinc finger E-box-binding homeobox 1 (ZEB1) transcription factor in PZP cell function. ZEB1 knockout in PZP cells resulted in altered lineage specificity. The expression of epithelial markers KRT 7, 8, 18 and adipogenic markers PPARG and PPARGC1B were upregulated upon ZEB1 knockout suggesting that ZEB1 maintains PZP cells in an undifferentiated state. ZEB1 also controlled the expression of several genes that encode extracellular matrix (ECM) associated proteins including Tenascin-C (TNC), an ECM factor linked to aggressive tumors and immunosuppressive microenvironment. Furthermore, the expression of matrix metallopeptidase 1 (MMP1) and a Leucine-rich repeat-containing protein 15 (LRRC15), both of which are markers of myofibroblasts, was downregulated in ZEB1 knockout cells suggesting the role of ZEB1 in trans-differentiation of PZP cells into cancer-promoting myofibroblast lineage. In addition, ZEB1 controlled the expression of prostaglandin-endoperoxide synthase 1 (PTGS1), which synthesizes immunosuppressive prostaglandin E2 (PGE2), in PZP cells. In support of immunosuppressive role of PZP cells, PZP cell secreted factors decreased the expression of Interferon γ and Granzyme B in CD8+ T cells, which are critical for effector function of T cells. Ongoing studies are investigating the potential contributions of ZEB1, PGE2, and TNC in PZP cell-mediated decrease in effector function of CD8+ T cells. Collectively, our results suggest that PZP cells are enriched in breast tissues of AA women and contribute to breast cancer progression through the breast stroma-enriched therapeutic target ZEB1. Citation Format: Madhura Shirish Shukla, Maya Shraddha Krishnan, Michelle Niese, Jia Ji, Hongyu Gao, Yunlong Liu, Mark H. Kaplan, Harikrishna Nakshatri. Transcription factor ZEB1 controls lineage specificity of African ancestry-enriched breast stromal multilineage cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2587.