Contribution of synergism between PHF8 and HER2 signalling to breast cancer development and drug resistance

HER2 plays a critical role in tumorigenesis and is associated with poor prognosis of patients with HER2-positive breast cancers. Although anti-HER2 drugs are beneficial benefits for treating breast cancer, de novo, or acquired resistance often develops. Epigenetic factors are increasingly targeted for therapy; however, such mechanisms that interact with HER2 signaling are poorly understood. RNA sequencing was performed to identify PHF8 targets downstream of HER2 signaling. CHIP-qPCR were used to investigate how PHF8 regulates HER2 transcription. ELISA determined cytokine secretion. Cell-based assay revealed a feed forward loop in HER2 signaling and then evaluated in vivo. We report the synergistic interplay between histone demethylase PHF8 and HER2 signaling. Specifically, PHF8 levels were elevated in HER2-positive breast cancers and upregulated by HER2. PHF8 functioned as a coactivator that regulated the expression of HER2, markers of the HER2-driven epithelial-to-mesenchymal transition and cytokines. The HER2-PHF8-IL-6 regulatory axis was active in cell lines and in newly established MMTV-Her2/MMTV-Cre/Phf8-floxed mouse models, which revealed the oncogenic function of Phf8 in breast cancer for the first time. Further, the PHF8-IL-6 axis contributed to the resistance to trastuzumab in vitro and may play a critical role in the infiltration of T cells in HER2-driven breast cancers. These findings provided informative mechanistic insight into the potential application of PHF8 inhibitors to overcome resistance to anti-HER2 therapies. mRNA profiles of MCF10A cells stably expressing a scramble shRNA, PHF8 shRNA, and HER2 overexpression were generated by RNA-seq, in duplicate, using HiSeq2500 instrument.