Hypoxa-actived XBP1s recruits HDAC2-EZH2 to engage epigenetic suppression of DNp63 expression and promotes breast cacner metastasis independent HIF1a

Hypoxia is a hallmark of cancer development. However, the molecular mechanisms by which hypoxia promotes tumor metastasis are not fully understood. In this study, we demonstrate that hypoxia promotes breast cancer metastasis through suppression of ?Np63a-dependent in a HIF1a-independent manner. We show that hypoxia activates unfolded protein response (UPR) to elevate XBP1s, which in turn forms stable repressor protein complexes with HDAC2 and EZH2 in suppression of ?Np63a. Notably, while H3K27ac is predominantly presented in the ?Np63 promoter under normoxia, it is switched to H3K27me3 under hypoxia. We show that XBP1s binds to the ?Np63 promoter to recruit HDAC2 and EZH2 in facilitating the H3K27ac-H3K27me3 switch. Knockdown or pharmacological inhibition of either HDAC2 or EZH2 leads to increased H3K27ac concomitant with reduced H3K27me3, which effectively restores ?Np63a expression suppressed by hypoxia, resulting in inhibition of cell migration. Clinical analyses reveal that reduced p63 expression is correlated with the elevated expression of XBP1, HDAC2, or EZH2, and is associated with poor overall survival in human breast cancer patients. Together, these results indicate that hypoxia-activated XBP1s modulates the epigenetic program in suppression of ?Np63a to promote breast cancer metastasis independent of HIF1a and provides a molecule basis for targeting the XBP1s/HDAC2/EZH2-?Np63a axis as a putative strategy in the treatment of breast cancer metastasis. Overall design: HCC1806 cells, which were cultured under normoxic or hypoxic conditions, with ChIP-IT Kit (53009, Active Motif, USA) using antibodies specific for H3K27me3 (9733, CST, 1:50), H3K27ac (ab4729, abcam, 1: 50) or normal rabbit IgG (2927, CST, 1:50), as described previously18. Immunoprecipitated DNA was used to construct sequencing libraries according to the protocol provided by the TruePrep DNA library Prep kit (Vazyme #TD501) and sequenced on Illumina Nova Seq6000 (Gene Denovo CO., Ltd., Guangzhou, China)