ZHX2 Promotes HIF1a Oncogenic Signaling in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive and highly lethal disease. Due to its heterogeneity and lack of hormone receptors or HER2 expression, it is critical to identify novel therapeutic targets in TNBC. Analysis of copy number and gene expression in tumors from The Cancer Genome Atlas suggested that ZHX2 was amplified and overexpressed in breast cancer patients. Correspondingly, we found that ZHX2 was highly expressed in TNBC cell lines and TNBC patient tissues. Functionally, depletion of ZHX2 inhibited TNBC cell growth and invasion in vitro, orthotopic tumor growth and spontaneous lung metastasis in vivo. Mechanistically, ZHX2 bound with Hypoxia inducible factor (HIF) family members and positively regulated HIF1 activity in TNBC by using loss-of-function or gain-of-function studies. Our integrated ChIP-Seq and gene expression profiling demonstrated that ZHX2 co-occupied with HIF1 on transcriptionally active promoters marked by H3K4me3 and H3K27Ac, therefore promoting gene expression. Furthermore, structural simulation and functional studies revealed that multiple residues (R491, R581 and R674) are important in regulating the phenotype of ZHX2 on TNBC tumorigenic potential, which correspond with their roles on controlling HIF1 activity in TNBC cells. These studies establish that ZHX2 activates oncogenic HIF1 signaling, therefore serving as a potential therapeutic target for TNBC. ChIP-seq of ZHX2 and input control, and RNA-seq of ZHX2-knockdown vs control shRNAs in MDA-MB-231 breast cancer cells