Abstract 4049: Transcriptional regulation of FOXA1 by GATA2/3 attenuates the antitumor effects of histone deacetylase (HDAC) inhibitors in basal-like breast cancer

Abstract Introduction: Basal-like breast cancer (BLBC), an aggressive subtype of triple-negative breast cancer (TNBC), exhibits a high risk of recurrence and resistance to conventional treatments. Histone deacetylase inhibitors (HDACis), such as panobinostat and romidepsin, are approved for hematopoietic malignancies and have shown effectiveness against TNBC cells. Our study demonstrated that HDACis inhibited BLBC cell growth and induced apoptosis by suppressing HER3 expression via transcriptional downregulation of forkhead box protein A1 (FOXA1). However, the mechanisms by which HDACis regulate the expression of FOXA1 remain unclear. Methods: Cell viability was evaluated using colony formation, MTS, and LIVE/DEAD cell staining assays. Apoptosis was assessed by flow cytometry. Gene and protein expression levels were analyzed via qRT-PCR, Western blotting, and immunohistochemistry (IHC). Co-immunoprecipitation was used to evaluate protein interactions. Lentiviral vectors carrying cDNA or shRNAs enabled overexpression or knockdown of target genes. Chromatin immunoprecipitation-quantitative PCR elucidated transcriptional regulatory mechanisms. In vivo experiments were conducted to examine therapeutic effects. Kaplan-Meier analysis evaluated clinical outcomes. Results: FOXA1 was highly co-expressed with HER3 in BLBC specimens and cell lines, and FOXA1 induced HER3 expression. Panobinostat and romidepsin inhibited BLBC cell growth and induced apoptosis by suppressing FOXA1 expression and HER3 signaling. Gene expression profiling revealed a significant positive correlation between FOXA1 and transcription factors GATA2/3. High GATA2/3-FOXA1 expression correlated with poorer relapse-free survival (RFS) in BLBC patients. Mechanistic studies confirmed that GATA2/3 transcriptionally regulated FOXA1 by directly binding to its promoter. Overexpression of GATA2 in BLBC cells restored FOXA1 expression downregulated by HDACis and reduced their antitumor effects. Importantly, in vivo experiments showed that HCC1806 xenografts overexpressing GATA2 were less sensitive to panobinostat treatment. Consistent with these findings, IHC analyses revealed higher FOXA1 and HER3 expression in GATA2-overexpressing tumors. Conclusion: HDACis exhibit potent antitumor effects in BLBC by suppressing the GATA2/3-FOXA1-HER3 axis. Our study highlights the critical role of GATA2/3 in transcriptionally regulating FOXA1 and mediating resistance to HDACis. These findings suggest that targeting the GATA2/3-FOXA1-HER3 axis may represent a promising therapeutic strategy for BLBC. Citation Format: Congcong Tan, Hui Lyu, Yakun Wu, Margaret E. Larsen, Shou-Ching Tang, Bolin Liu. Transcriptional regulation of FOXA1 by GATA2/3 attenuates the antitumor effects of histone deacetylase (HDAC) inhibitors in basal-like breast cancer [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 4049.