Abstract P2-04-08: Functions of KLF5 in the cell cycle and breast cancer cell proliferation

Abstract As a transcription factor associated with the regulation of growth, development, and maintenance of stemness, the expression and transcriptional activity of the KLF5 protein are influenced by the Hippo signaling pathway. This study aims to investigate the spatiotemporal expression characteristics of KLF5 during the development of breast cancer and further explore the molecular mechanisms by which KLF5, in coordination with the TAZ factor in the Hippo signaling pathway, controls cell growth and proliferation, potentially elucidating mechanisms underlying breast cancer initiation and progression. Results showed that the KLF5/AP1/TAZ/TEAD4 (KATT complex) is highly expressed in triple-negative breast cancer (TNBC), particularly in the basal subtype, regulating the transcription of downstream genes associated with stem cells and lipid metabolism, thus promoting lipid synthesis. Gel filtration chromatography and immunofluorescence staining confirmed the presence of the KATT complex in TNBC. Using knockdown experiments of the KATT complex and transcriptome sequencing analysis, we found that the KATT complex can collectively regulate the expression of lipid metabolism and stem cell-related genes. ChIP-seq analysis revealed mutual regulation among KATT complex members through super-enhancers, forming a core regulatory loop in TNBC. Furthermore, we found that the KATT complex promotes the synthesis of lipid metabolism products (lipidomics), significantly enhancing the synthesis of medium- and long-chain fatty acids (GC-MS). Knockdown of the KATT complex inhibited lipid droplet formation (Nile red staining) and suppressed cholesterol formation and distribution (cholesterol staining). Under cell culture conditions of human breast cells during the metaphase of mitosis, eGFP-KLF5 and endogenous TAZ form phase-separated granules with excellent co-localization characteristics. Similar to reported TAZ behavior, purified KLF5 protein exhibited phase separation capability in vitro. Upon formation of complexes with related transcription factors such as AP1 and TEAD4, it can collectively regulate the transcriptional expression of downstream target genes. Furthermore, we discovered that KLF5 protein undergoes liquid-liquid phase separation during the G2/M phase of the cell cycle and preliminarily found that the transcription factor KLF5 forms phase-separated granules with TAZ and participates in cell proliferation regulation. These data collectively demonstrate that KLF5 protein plays a crucial role in promoting cell cycle progression during the cell cycle process, thereby exerting significant effects on the rapid proliferation of triple-negative breast cancer cells. Citation Format: Xiaoyun Mao, Jian Sun, Ceshi Chen. Functions of KLF5 in the cell cycle and breast cancer cell proliferation [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P2-04-08.