Abstract 5701: HDAC inhibition decreases YAP1 expression but parodoxically activates TEAD transcription by the AP-1 pathway in breast cancer

Abstract

Abstract The Hippo pathway is an evolutionally conserved pathway that is crucial in numerous aspects of cell biology, including contact inhibition, cell density, and others. Hippo pathway is well reported to be dysregulated in multiple cancer types and plays important oncogenic roles in human cancers. In mammalian cells, YAP is regulated by a phosphorylated cascade mediated by the kinases MST1/2 and LATS1/2, known as the canonical Hippo pathway. These upstream kinases phosphorylate YAP/TAZ and leads to its cytosolic degradation. Perturbation of the Hippo pathway leads to YAP intranuclear translocation and downstream activation of target genes, inducing proliferative signals and thus initiating oncogenesis. Novel mechanism linking the hippo pathway to various oncogenic mechanisms are rapidly discovered and reported, further establishing the significance of this pathway and its role in cancer biology. Breast cancer is the top leading cause of cancer in women and poses a significant morbidity and economic burden on society. Hormone positive (defined as positivity of the estrogen receptor ER and/or the progesterone receptor PR) breast cancer composes 70% of breast cancer. Endocrine therapy, chemotherapy, and more recently, CDK4/6 inhibitors and PI3K inhibitors are currently approved strategies towards breast cancer. Histone deacetylase (HDAC) inhibitors have been FDA approved for several hematological cancers, and recently have shown inconsistent results in clinical trials for breast cancer. In our study, we demonstrate and characterize a link between HDAC inhibition and the Hippo pathway. We discover that HDAC inhibitors suppress YAP expression both transcriptionally and translationally. Paradoxically, we demonstrate that although YAP is downregulated, TEAD mediated transcription of downstream Hippo targets is activated. Mechanistically, HDAC inhibition leads to upregulation of the AP-1 transcriptional machinery that cooperates with TEAD to facilitate transcription. By RNA-seq, chromatin studies and CRISPR knockout studies, we confirm that HDAC inhibition have the ability to activate downstream of Hippo pathway, suggesting a possible mechanism for breast cancer resistance towards HDAC inhibitor. Co-targeting HDAC inhibition and AP-1 results in enhanced efficacy of HDAC inhibitors and may be a promising approach for development towards breast cancer. Citation Format: Ting-Yi Lin, Yi-Ru Tseng, Naikuan Wang, Ta-Chung Chao, Chun-Yu Liu, Ling-Ming Tseng, Jiun-I Lai. HDAC inhibition decreases YAP1 expression but parodoxically activates TEAD transcription by the AP-1 pathway in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5701.