the effect of knockout Brd7 on 4T07-TGL cells under in vitro condition [scRNA-Seq]
Metastasis is a major cause of mortality in cancer and is likely influenced by epigenetic and gene regulatory factors. Using an in vivo screen, we demonstrated that several subunits of the polybromo-associated BAF (PBAF) complex, particularly BRD7, were required for breast cancer metastatic dormancy in lung. BRD7 loss induced metastatic outgrowth, along with modifications in epigenomic landscapes and upregulated oncogenic signaling. Breast cancer cells harboring BRD7 loss also reprogrammed the surrounding immune microenvironment, downregulating MHC-1 expression and promoting a pro-metastatic cytokine profile. Flow cytometric and single-cell analyses revealed increased levels of pro-tumorigenic neutrophils, CD8+ exhausted T cells, and CD4+ stress response T cells in lungs harboring BRD7-deficient metastases. Finally, attenuating this immunosuppressive milieu by neutrophil depletion, neutrophil extracellular trap (NET) inhibition, or immune checkpoint therapy abrogated metastatic outgrowth. These findings, for the first time, implicate BRD7 and PBAF in metastasis, pointing to targetable underlying mechanisms involving specific immune cell compartments. Overall design: To interrogate the effects of BRD7 loss on specific immune microenvironmental constituents,we performed single cell RNAseq on Cd45+ cells sorted from dissociated lungs removed from naïve 6 week-old mice or similarly aged littermates 14 days after injection with either control or BRD7-KO 4T07 cells.