Abstract 118: BACH1 is an oxygen-sensitive mediator of the hypoxia response in triple-negative breast cancer

Abstract

Abstract Triple-negative breast cancer (TNBC) is an aggressive solid tumor characterized by a hypoxic phenotype that promotes metastatic progression and resistance to therapy. The canonical cellular response to hypoxia is largely driven by hypoxia inducible factors (HIFs) that stimulate transcription of genes related to angiogenesis, cancer stem cells, cell survival, and glucose and iron metabolism. There is growing evidence that several factors, in addition to HIFs, contribute to the tumor hypoxia response. Thus, identifying novel mechanisms that regulate this cellular response in addition to the HIFs is key to our understanding of hypoxia and could have direct clinical impact. High expression of BTB and CNC homology 1 (BACH1), a heme-regulated bZIP transcription factor, drives metastatic progression in various cancers including TNBC. While BACH1 has been shown to be induced under hypoxia in some cell lines, its regulation and role in hypoxia signaling, specifically with regards to cancer cells, is poorly understood. Here we report a novel regulatory pathway of the tumor hypoxia response in TNBC. We show that BACH1 is post-translationally prolyl-hydroxylated by the HIF prolyl-hydroxylases (PHDs) in an oxygen-dependent and NRF2/HMOX1-independent manner. Hypoxic exposure thus stabilizes BACH1 protein and enhances its DNA binding activity at loci of both canonical and hypoxia-specific downstream targets. We further show that BACH1 regulates the hypoxia response by promoting expression of both HIF-dependent and HIF-independent hypoxia-induced genes in TNBC cells. Our findings describe BACH1 as a novel oxygen-sensitive effector of the hypoxia response in TNBC that represents an alternative target for attenuating hypoxia-induced, pro-metastatic signaling and therapeutic resistance. Citation Format: Christopher M. Dann, Long C. Nguyen, Dongbo Yang, Joseph P. Wynne, Andrea Valdespino, Letícia Stock, Marsha R. Rosner. BACH1 is an oxygen-sensitive mediator of the hypoxia response in triple-negative 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 118.